IFP School
PWT MASTER MODULE 1-2020
Fundamentals of Hybrid/Electric Vehicles
Vittorio Ravello
Rueil-Malmaison (Paris) 26-30 October 2020
Fundamentals of Hybrid/Electric Vehicles
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1
ICE based Propulsion Systems
The existing Propulsion Systems (ICE + mechanical transmission):
Trasmission
Internal
Combustion
Engine
Tank
have reached a high development and maturity level and give a satisfactorily
answer to the main part of the end user needs
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2
Environmental Needs
Noxious Emissions
(local level)
Green House Gases Emissions
(global level)
Fundamentals of Hybrid/Electric Vehicles
Energy Efficiency
(conversion chain)
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3
Compliancy
Noxious Emissions
(local level)
new pollutant emissions
standards (Euro 6 for LD
vehicles with RDE…)
new EC regulation on
CO2 emissions
(443/2009)
EMEA 2020
possible future
green credits on
efficiency
Green House Gases Emissions
(global level)
Fundamentals of Hybrid/Electric Vehicles
Energy Efficiency
(conversion chain)
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4
ICE based Propulsion Systems
The existing Propulsion Systems (ICE + mechanical transmission):
Trasmission
Internal
Combustion
Engine
Tank
•
have reached a high development and maturity level and give a
satisfactorily answer to the main part of the end user needs
•
but, due to the stronger and stronger regulations (noxious emissions, CO2
emissions…), will have higher difficulties in satisfy also the social and
environmental needs:
 local emissions: CO, NOx, HC…  pollution
 global emissions: CO2  global warming and climate modifications
 effective energy usage  resources shortage
Fundamentals of Hybrid/Electric Vehicles
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5
Energy Conversion Efficiency
8.7%
Idle losses
100%
ICE
18%
Transmission
Transmission
losses
ICE losses
1.3%
16.7%
Aerodynamic
friction
5.2%
Rolling friction
5.5%
Acceleration
6%
73.3%
ICE based mid size vehicle (reference NEDC - New European Driving Cycle)
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6
Internal Combustion Engine
to satisfy the desired
performance
(acceleration, max
speed, gradeability…)
urban mode
working area
ICE 1,2 liter 16 valves MPI gasoline
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7
Pure Electric based Powertrain
Battery
Pack
Fundamentals of Hybrid/Electric Vehicles
Inverter
Electric
machine
Mrechanical
Trasmission
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8
Energy Conversion Efficiency
A pure electric powertrain based vehicle on the same reference cycle has the following
typical average efficiencies:
 electric drive (electric machine and power electronics):
80-85%
 mechanical transmission:
90-95%
to be multiplied with the efficiency of the electrical energy source:
 if electrochemical batteries:
(depending on the type and technology)
 if direct H2 PEMFC:
(PEMFC: Proton Exchange Membrane Fuel Cell)
80-90%
50-60%
Moreover:
 possible recovery of a part of the kinetic braking energy (regenerative braking)
 no idle losses
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9
Battery Electric Vehicles: Reasons Why (1/2)
Complete environmental solution (at least at local level (TtW - Tank to Wheels)):
 zero noxious emissions
 zero carbon dioxide emissions
(WtT - Well to Tank emissions depending on the energy production pathway
extra WtW emissions (including the recycling phase) to be evaluated)
 very high energy efficiency
(also thanks to the regenerative braking and the zero idle consumptions)
 from an OEM perspective, solution for/answer to:
 tailpipe noxious emissions homologation
 CO2 fleet based fines (being TtW based)
 green credit based “bonus-malus” policies
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10
Battery Electric Vehicles: Reasons Why (2/2)
Moreover:
 acceleration (high torque available at zero-low speed and high dynamics)
 climbability (high torque available at zero-low speed)
 elasticity and smoothness (with proper transmission)
 limited noise (in some cases considered too low)
 easy acceleration-braking integration (one pedal)
 performance configurability (at driver level)
 low operational costs (if the batteries have not to be replaced during the vehicle
life or the costs of their replacement is not in charge of the customer)
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11
Consumption reduction impact
Passenger Cars
Average values
Traveled distance:
Fuel cost:
Fuel consumption:
20’000 km/year
1,5 €/l
8 l/100 km
1% Fuel saving  16 l/year  24 €/year
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12
Battery Electric Vehicles: Roadblocks/Challenges
From the end user point of view, the weak points in respect of the traditional engine
based vehicles are:
 Vehicle Range: limited and highly dependant on the ambient conditions, driving
style, auxiliaries connected…
 Battery Charging:
 Charging Time
Vehicle Range
 Charging Infrastructure diffusion
 Purchasing price
Charging
time
Fundamentals of Hybrid/Electric Vehicles
Infrastructure
availability
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13
Car of Tomorrow
from:
to:
Social &
Environment
needs
Customer
demands
•
•
•
•
•
Fun to drive
Comfort & driveability
Style
Acceptable purchasing
and operation costs
(perceived value)
Fuel consumption
reduction
•
•
•
Regulated noxious, particle
and acoustic emission
reduction (near Zero
Emission Vehicle)
CO2 reduction
Energy preservation and
sources diversification
Social &
Environ.
needs
Customer
demands
Manufacturer
targets
starting from the nowadays propulsion systems which have all the pros coming from a more
than one century effective development plus low costs due to the high volume production,
the challenge is to find better solutions from an environmental point of view but also of
interest for the final end user and sustainable for the vehicle manufacturers
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14
Electrification of the ICE based Propulsion Systems
The conventional powertrain electrification can guarantee at the same time:
 flexibility: it is a degree of freedom applicable in different ways depending on
the needs/weakness of the ICE type
 impact: it is a way to counteract different problems with important effects
(some tens of % consumption reduction, one order of magnitude noxious
emission reduction…)
 wideness: it’s an effective way to impact at the same time on the
environmental-social and end-user directly and/or as enabling technology (for
instance for the introduction on-board of high power electric auxiliaries)
Moreover the hybridisation enables new degrees of freedom in the ICE design and
management-usage and helps the vehicle functional integration and the
introduction of new functions
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15
Definitions
Hybrid Vehicle:
•
A hybrid vehicle is a vehicle able to use also together (at least) two different
propulsion systems (based on two different typologies of energy) for its motion
•
A Hybrid Electric Vehicle (HEV) is a type of hybrid vehicle that combines a
conventional Internal Combustion Engine (ICE) based traction system with at
least one electric propulsion based one
to be classified as hybrid, the traction systems combined operation has to be
possible (otherwise the system is called multimodal)
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16
Pure Thermal Traction System
Fuel
Tank
Fundamentals of Hybrid/Electric Vehicles
ICE
Engine
Control
Unit
Mechanical
transmission
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17
Thermal-Electric Hybrid Traction System
Fuel
Tank
ICE
Engine
Control
Unit
Inverter
Battery Pack
Fundamentals of Hybrid/Electric Vehicles
Mechanical
transmission
Electric
machine
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18
Pure Electric Traction System
Mechanical
transmission
Inverter
Battery Pack
Fundamentals of Hybrid/Electric Vehicles
Electric
machine
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19
Traction System Method (Joseph Beretta - PSA)
This method is suitable:
 for all types of hybrids (not only thermal-electric)
 both for single and multi-source propulsion systems
 both for simple and complex hybrids
 to correctly compare from an energy perspective different traction systems
Traction system: sum of all the devices actively involved in the energy pathway for the
vehicle motion
Each elementary traction system is the sum of two main parts:
 powertrain
 on-board energy source
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20
Traction System Method (Joseph Beretta - PSA)
Elementary Traction System (building blocks):
On Board Energy/Power Source
S
Energy
/power source
Powertrain
A
M
T
adaptation/
conversion system
Engine or
Motor
Transmission
wheels
An hybrid traction system is realised properly connecting two or more elementary traction
systems
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21
Traction System Method (Joseph Beretta - PSA)
Traction System: Powertrain plus On Board Energy Source
Powertrain:
 mechanical actuator (engine or motor)
 mechanical transmission:
 fixed speed
 variable speed:
 Manual Transmission (MT)
 Automated Manual Transmission (AMT)
 Dual Clutch Transmission (DCT)
 Continuous Variable Transmission (CVT)
 differential unit and wheels
On Board Energy Source:
 energy/power source
 energy adaptation/conversion system (if needed)
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22
Traction System Method (Joseph Beretta - PSA)
Simple Thermal-Electric Traction Systems
The simple thermal-electric traction systems are realised connecting one ICE
elementary traction system with one electric elementary traction system
ICE elementary traction system
FT
ICE
MT
FT: Fuel Tank
ICE: Internal Combustion Engine
MT: Mechanical transmission
DW: Differential unit and wheels
DW
Electric elementary traction system
ES
PE
Fundamentals of Hybrid/Electric Vehicles
EM
MT
DW
ES: Electric Energy/Power Source
PE: Power Electronics
EM: Electric Machine
MT: Mechanical Transmission
DW: Differential unit and wheels
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23
Traction System Method (Joseph Beretta - PSA)
Simple Thermal-Electric Traction Systems
The simple thermal-electric traction systems are realised connecting one elementary
traction system with an Internal Combustion Engine (ICE) with one elementary traction
system with an electric machine (E-motor).
The elementary traction systems are connected through linking components:
 mechanical linking components when the connection is done at powertrain level
 Parallel Simple Thermal Electric Hybrids (two mechanical actuators: one ICE
and one e-motor)
 electrical linking components when the connection is done at on board energy
source level  Series Simple Thermal Electric Hybrids (one mechanical
actuator: one e-motor)
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24
Traction System Method (Joseph Beretta - PSA)
Simple Thermal-Electric
Traction Systems
Parallel
W
Double drive
system
T
M1
Series
A
W
T
M2
S2
W
T
M1
A
T
M2
S2
S1
Double energy
source
S1
Double shaft
W
T
M1
A
M2
S2
Single shaft
Fundamentals of Hybrid/Electric Vehicles
Double energy
storage
W
W
T
T
M1
M1
A
S1
A
S3
A
S1
S3
S1
W: differential + wheels
T: transmission
M1: electric motor
S1: electric energy/power
source
: linking components
A: energy conversion
/adaptation system
M2: ICE
S2: fuel tank
S3: ICE based generator
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25
Traction System Method (Joseph Beretta - PSA)
Simple Thermal-Electric Traction Systems
Hybridisation Ratios Rh (F. Badin 1997):
 Parallel simple thermal-electric traction systems: ratio between the ICE power and
the sum of the ICE and electric motor powers
Rh paral. = PICE / (PICE + Pelt)
 Series simple thermal-electric traction systems: ratio between the electric generator
and electric motor powers
Rh series = Pg_elt / Pm_elt
Hybrids Indicators
Hybrids can be described through the following indicators:
 order: number of different elementary traction systems of the traction system
 index: number of linking components of the traction system
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26
Traction System Method (Joseph Beretta - PSA)
Simple Thermal-Electric Traction Systems: hybridisation levels
Powertrain
On board energy source
Pure ICE Vehicle
Parallel Hybrid
1
Minimal Hybrid (FAS, BAS)
ICE
Mild Hybrid
Rh paral.
Full Hybrid
Pure Battery Electric Vehicle
Battery
Electric
Motor
Series Hybrid
Range Extender
Load Follower
Electric
Generator
ICE
0
0
Rh series
Full Performance
Vehicle with electric transmission
1
On board installed power
3
2
1
0
Red: single traction system solutions; Blue: simple thermal-electric parallel hybrids; Green: simple thermal-electric series hybrids
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27
Traction System Method (Joseph Beretta - PSA)
Energy performance Indicator:
summation of the efficiencies of the different possible energy pathways multiplied for the
percentages of the energy flowing in the pathway in the related working mode. The single
pathway efficiency can be evaluated multiplying the efficiencies of all the devices of the
pathway
Energy route (Er):
number of the possible energy pathways in the traction system. This number is the
number of degrees of freedom of the traction systems. It can be calculated as:
Er = (order)2
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28
Traction System Method (Joseph Beretta - PSA)
Energy route examples
Single shaft simple thermal-electric parallel hybrid 4 energy pathways
pure ICE traction
Ta
Tr
EM
I
pure electric
traction
BS
regenerative
braking
Fundamentals of Hybrid/Electric Vehicles
generation
& battery
charging
Tr:
EM:
I:
BS:
Ta:
Transmission
E-Machine
Inverter
Battery System
Tank
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29
Traction System Method (Joseph Beretta - PSA)
Energy route examples
simple thermal-electric series hybrid 4 energy pathways
pure electric traction
regenerative braking
Tr
Tr:
EM:
I:
Transmission
E-Machine
Inverter
Fundamentals of Hybrid/Electric Vehicles
BS
I
EM
pure ICE traction
C
Ta
EG
EG:
C:
BS:
generation
& battery
charging
E-Generator
AC/DC converter
Battery System
Ta:
tank
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30
Traction System Method (Joseph Beretta - PSA)
Complex Thermal-Electric Hybrids
The simple hybrid traction systems have:
 order = 2
 index = 1
The complex hybrid traction systems can be realised increasing the elementary traction
systems and the linking components numbers.
The traction systems of practical interest have in general order and index not higher than 4
Complex Thermal-Electric Hybridisation Ratio (Rch):
Rch = ( Rh paral) • ( Rh serie)
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31
Complex Hybrids: Series-Parallel
Large relevance have the complex series-parallel hybrid solutions realising a double
power-energy pathway: one parallel (mechanical) and one series (electrical). They can
be classified as:
• Compound hybrid: able to operate in series hybrid OR in parallel hybrid mode (i.e.
Mitsubishi Outlander hybrid)
• Split hybrid: able to operate at the same time in series hybrid AND in parallel hybrid
mode with capability to regulate the two energy path flows (i.e. Toyota Prius hybrid)
In many split hybrid solutions, two electric machines with one ore more planetary gear
set, a differential and other mechanical devices replace the conventional mechanical
transmission (manual, automatic, CVT (Continuous Variable Transmission…)
The typical complex series-parallel hybrid architecture has:
 only one ICE (as it is for the simple parallel and series hybrid ones)
 2 e-machines (as the simple series one) but with more flexible connection and use
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32
Complex Hybrids: Series-Parallel
Compound Hybrid principle scheme
Mechanical chain
Transm.
Wheels
Wheels
E-motor
E-motor
Transm.
DC/AC
DC/AC
Series
mode
Parallel
mode
ICE
Batteries
AC/DC
Generator
ICE
Batteries
Electrical chain
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33
Complex Hybrids: Series-Parallel
Split Hybrid principle scheme
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Wheels
Transmission
E-motor
Electrical chain
DC/AC
AC/DC
Generator
ICE
Batteries
Mechanical chain
34
Traction System Method (Joseph Beretta - PSA)
Complex Split Hybrid example: order 3 and index 3
W1
T1
Fundamentals of Hybrid/Electric Vehicles
ICE
S1
M1
A1
M2
A2
where:
S2
W1: front wheels
T1: transmission
ICE: Internal Combustion Engine
S1: fuel tank
M1: AC e-machine 1
A1: DC/AC inverter 1
S2: Battery Pack
M2: AC e-machine 1
A2: DC/AC inverter 1
: links
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35
Traction System Method (Joseph Beretta - PSA)
General remarks:
 two traction systems with the same order and index have the same potentialities
(if realised with equivalent devices)
 between two traction systems with the same order and index, the comparison can
be done using the energy performance indicator
 physical limits in the design of some devices of the traction systems can make
equivalent systems with different order
 typically the considered efficiency for the devices is the average value referred to
the considered usage profile
 this method can give first general level indications for sizing and energy
considerations. Obviously it is not able to completely substitute a deeper
evaluation that needs the knowledge and use of other parameters as for instance
weights, volumes, costs, ICE idle and auxiliaries consumption…)
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36
Hybrid Classification based on E-machine Position
P1: e-machine always connected to the engine (f = front and r = rear considering a
longitudinal engine layout) [P1f is also called P0]
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Hybrid Classification based on E-machine Position
P1: e-machine always connected to the engine (f = front and r = rear considering a
longitudinal engine layout) [P1f is also called P0]
P2: e-machine between engine and transmission with decoupling capability also from the
engine through an added clutch
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38
Hybrid Classification based on E-machine Position
P1: e-machine always connected to the engine (f = front and r = rear considering a
longitudinal engine layout) [P1f is also called P0]
P2: e-machine between engine and transmission with decoupling capability also from the
engine through an added clutch
P3: e-machine between transmission and differential unit (sometimes, mainly in
transversal engine layout, with a devoted ratio from e-machine shaft and transmission
secondary shaft) [if the e-machine is coupled (for instance) on one of the two
secondary shafts of a DCT, it is called P2,5]
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Hybrid Classification based on E-machine Position
P1: e-machine always connected to the engine (f = front and r = rear considering a
longitudinal engine layout) [P1f is also called P0]
P2: e-machine between engine and transmission with decoupling capability also from the
engine through an added clutch
P3: e-machine between transmission and differential unit (sometimes, mainly in
transversal engine layout, with a devoted ratio from e-machine shaft and transmission
secondary shaft) [if the e-machine is coupled (for instance) on one of the two
secondary shafts of a DCT, it is called P2,5]
P4: e-machine on the secondary axle (engine on the primary axle). It is typically linked to
the differential through a devoted transmission (with or w/o clutch)
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Definitions
Hybrid Electric Vehicle (HEV):
•
Micro or Mini HEV: 12 V solution in general with a BSG (Belt driven Starter
Generator) plus passive belt tensioner and two 12 V batteries (lead and lithium)
directly or indirectly connected.
Max e-Power levels: few kW
•
Mild HEV: typically 48 V solution in general with one e-machine (in the alternator
position or between transmission and engine) with a 48 V Lithium based battery
and a 48-12V DC/DC converter.
Max e-Power levels: some kW (typically up to around 15 kW)
•
Full HEV: HV solution (in general hundreds of volt) with one (or two)
emachines (with different possible positions) with a HV Lithium based battery and a
galvanically insulated HV-12V DC/DC converter.
Max e-Power levels: from lot of tens up to few hundreds of kW
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Definitions
Hybrid Electric Vehicle with charging capability from the electric grid:
•
P-HEV (Plug-in HEV): it is typically a HV full HEV with a HV Battery System
having an available energy for a pure EV range of at least some tens of km (today
up to around 50-60 km)
•
EREV (Extended Range Electric Vehicle)1: it is a HV full HEV with a HV Battery
System with an available energy enabling a large pure EV range (in general more
than 50-60 km), In these architectures the engine operated only/near always as
“battery charger” and the vehicle motion is only coming from an e-motor (series
HEV configuration)
1
also called REEV (Range Extended Electric Vehicle)
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42
Powertrain electrification roadmap
for future mass production high volumes
Pure Electric Vehicle:
• Battery (BEV) urban use
• Fuel Cells (FCEV) extended use
100
Pelet / Ptot [%]
Extender Range
Electric Vehicle
Hybrid
Electric
Vehicle
50
Plug-in Hybrid
Electric Vehicle
PHEVs
EVs
EV range
(hundreds of km)
EREVs
Limited urban EV range
(tens of km)
HEVs
ICE – aux
improvements
ICEVs
EV range
(from 0 to few km)
time
0
Today
Fundamentals of Hybrid/Electric Vehicles
Short term
Mid term
Long term
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43
Hybrids Enabled Functions
Hybridization focused on engine
assistance. Typically there is no or
few additional contents offer to the
customer other than fuel economy
mini/micro
HEV
MILD HEV
Hybridization targeted to electric
propulsion. Typically it could offer
additional contents to the customers
(E-FEATURES)
Full HEV
P-HEV
BEV
CONVENTIONAL ENGINE POWER
“EXTENDED START-STOP SYSTEM“
ENERGY RECOVERY (REGENERATIVE BRAKING)
E-MOTOR ASSIST ENGINE (EG. BOOSTING)
E-LAUNCH: VEHICLE STARTS MOVING IN ELECTRIC
ELECTRIC DRIVE: VEHICLE COULD MOVE IN ELECTRIC
VEHICLE CHARGEABLE FROM GRID
(I.E. IT HAS A SOCKET and a CHARGER)
Zero Emission
Vehicle (ZEV)
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Voltage Levels & Electric Shock Protection: Voltage Classes
AC
DC
Voltage Classes
VRMS
Vpeak
VDC
Class 1
≤ 30 V
≤ 42 V
≤ 60 V
Class 2
≤ 600 V
≤ 849 V
≤ 900 V
Class 3
≤ 1000 V
≤ 1414 V
≤ 1500 V
ISO 6469-3 groups voltage class 2 and 3 in Class B
AC
DC
Voltage Classes
VRMS
Vpeak
VDC
Class A
≤ 30 V
≤ 42 V
≤ 60 V
Class B
≤ 1000 V
≤ 1414 V
≤ 1500 V
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A Voltage Class
A and Class B systems present different technical solutions being only the second
ones to have to face the electric shock risks.
A Class Electric Systems (Vdc ≤ 60 Vdc)
[mini/micro hybrids and Mild HEV]
There is no risk of electric shock. As a consequence no need of:
• electrical isolation. As a consequence the electric DC circuit negative pathway is
managed through the vehicle chassis. Positive effect: highly reduction in the
cabling length/volume, weight and cost
• mechanical protections/shielding to avoid contact to the living voltage parts.
Positive impact on installation and maintenance operations. Simpler approach for
fire brigades in case of crash with rescue actions.
This is the standard approach applied in the today cars with internal combustion
engine (12 V electric grid).
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46
B Voltage Classes
B Class Electric Systems (60 Vdc < Vdc ≤ 1500 Vdc)
[Full HEV, P-HEV, EREV and EVs]
With voltages higher than 60 Vdc, there is a risk of electric shock in case of
direct/indirect electric contact with both the positive and negative voltage terminals.
As a consequence:
• mechanical protections/shielding are introduced to avoid direct contact to the
living voltage parts (i.e. HV battery terminals)
• complete electrical isolation of the HV circuits is requested (also the electric
circuit negative pathway is insulated from the vehicle chassis) in order to increase
the safety level (two faults on both positive and negative pathways are requested
to have an electric shock (one free touch approach)
The vehicle LV 12V (Class A) system has to be completely separate from the HV
(Class B) system. The HV system does NOT use the chassis ground as the 12V
does. Instead, the HV components have their own dedicated HV+ and HV- insulated
cables (orange color cables and connectors).
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47
B Class System Isolation: One Free Touch Approach
Load
Battery Pack
housing
connected to
the chassis
+
_
Vehicle chassis
In HV Systems (B Class), the goal of complete HV isolation is that:
• there is no return path other than the opposite battery terminal
• the ground/chassis is electrically separated from any potential circuit
 in case of undesired contact with one energized conductor, there is no return
path and no risk of electric shock
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48
B Class System Loss of Isolation: no Free Touch
Loss of isolation
(Battery Pack
positive terminal
vs. housing short
circuit)
Battery Pack
housing
connected to
the chassis
Load
+
_
_
Vehicle chassis
If there were a non detected loss of isolation on the Class B system (for instance a HV
battery pack internal wiring damaged/shorted to the battery pack housing), the battery
would become a hazard during the usage and a further isolation fault on the other
battery terminal would cause an electric shock:
 Loss of high voltage isolation takes away the “one free touch”
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49
HV Electrified Vehicles: A & B classes components link
High Power HV
Electric Loads
B-Class
(HV side)
DC
AC
EM
DC
DC
14 V
Electric Loads
A-Class
(12V side)
HV
Battery
Galvanical isulation
12 V
Battery
A-Class (12V side)
B-Class (HV side)
EM: AC Electric Machine
AC/DC: Inverter
HV: High Voltage (B Class)
DC/DC: HV-14 V (in general step down) converter.
Creating a link between a B Class voltage (HV side) and an A Class voltage (the on-board 12 VDC
grid), it has to be galvanically insulated
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50
Protection System against Electric Shock
High Voltage (Class B) involves:
• HV Battery System
• HV wiring (orange colour)
• HV components (e-machines, power inverter module…)
• HV connectors (orange colour)
• any HV coming into contact with the vehicle chassis or non HV components
On the vehicle, there is a multi layered system designed to protect users and service
personnel from gaining access to HV avoiding electric shock (Direct Access Protection
- DAP).
The DAP system uses multiple protective layers to deter, detect, and isolate any
potential high voltage contact. Layers and protective devices include also:
• Access cover protection with proper labels
• High-voltage interlock loop (HVIL) system to identify any accidental HV connector
unlock and in this case protect the users
• Continuous isolation integrity monitoring
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51
few kW
Power level
tens of kW
Enabled Functions vs. HEV Typologies
V ≤ 60 V Class A
V > 60 V Class B with
higher safety requirements
Full-hybrids
EV
Drive
Mild-hybrids
E-motor
assist
E-motor
assist
Regenerative
braking
Regenerative
braking
Regenerative
braking
Engine
Start&stop
Engine
Start&stop
Engine
Start&stop
Micro-mini
hybrids
Engine
Start&stop
Min voltage level
14 V
14 V - <60 V
<60 V - Hundreds of V
Hundreds of V
increasing the installed and available electric power, the functions intensity is higher and the
customer evaluation could be better
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52
Electrical and Thermal-Electrical Propulsion systems:
non conventional devices
 Storage systems (energy sources and/or power buffers)
 batteries (Lead, Nickel, Lithium based…) and Battery Systems
 supercapacitors
 pure mechanical and electromechanical flywheels
 Fuel Cell Stack and Fuel Cell System
 Electric machines (traction motors and generators)
 DC
 AC induction
 AC synchronous (wounded or Permanent Magnet)
 Reluctance (Switched or Synchronous Reluctance)
 Mixed solutions
 Power electronics
 DC/DC converters (step-up, step-down….)
 DC/AC and AC/DC converters (passive, active bridges…)
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53
IFP School
PWT MASTER MODULE 1-2020
E-based Storage Systems
Vittorio Ravello
Rueil-Malmaison (Paris) 26-30 October 2020
E-based Storage Systems
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1
Chemical and Alternative Energy Storage Systems
Differently by the vehicles connected to an external energy source during the usage (as
for instance trains, trolleybuses, trams, underground…), typically the road vehicles have a
storage system on board and the related tanks are sized for an amount of energy to
have the desired range.
The energy is typically stored in chemical form in a liquid fuel (gasoline, diesel…), but
can be also stored in a pressurised gaseous fuel (for instance natural gas).
Other possible storage forms are:
 electrochemical energy
 elastic energy
 kinetic energy
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2
Liquid Fuels
Liquid fuels advantages:
 easy refuelling procedures
 very high specific energy:
 for gasoline:
 for diesel:
 for an 85% methanol and 15% gasoline blend:
11,8
kWh/kg
13,3÷13,7
kWh/kg
6,7
kWh/kg
9,4
kWh/l
11,1÷11,4
kWh/l
 very high energy density:
 for gasoline:
 for diesel:
 maturity of the usage technology
 existing highly distributed refuelling infrastructure
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3
Gaseous Fuels
to have an energy density similar to the liquid fuels one, the gaseous fuels have to be
stored on board at high pressure (hundreds of bars)
Being the compression a process from the energy point of view highly consumptive, the
pressure level has to be chosen, under the regulation limits, as a compromise (energy
consumption vs. vehicle range) considering also safety issues related to:
 the refuelling phase
 the on board storage and usage
 the management in crash condition
All of them are more and more complex with the increase of the pressure level
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4
Alternative Energy Systems
All these solutions have a poor specific energy:
 electrochemical storage: from 30 to something more than 200 Wh/kg (cell level)
 elastic storage:
from 2 to 10 Wh/kg
 kinetic storage:
from 6 to 20 Wh/kg
On the other hand, from the energy point of view all these methods have a reversible
behaviour that enables the recovery of the kinetic energy during the braking
phases
Moreover, while the fossil fuels locally produce noxious emissions in the vehicle usage
(TtW - Tank to Wheels) place, the alternative storage solutions have only emissions
(if any) in the energy production phase (WtT - Well to Thank)
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5
Classification of cells and batteries
Electrochemical cells
Batteries
Primary
(non-rechargeable)
-
Zn-C
Alkaline
Zn-air
Zn/Ag2O
Li-metal
E-based Storage Systems
Fuel cells
Secondary
(rechargeable)
- Pb based
- Ni based
- Li based
Capacitors
-
Electrolytic
Supercapacitors
-
PEMFC
AFC
PAFC
SOFC
MCFC
DMFC
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6
Electrochemical Batteries
Batteries are electrochemical energy storage devices able to convert the chemical
energy contained in their active materials directly into electric energy: they are
energy and power sources
The conversion process occurs through an electrochemical oxidation-reduction
(redox) reaction, which can be one-directional (primary batteries) or reversible
(secondary batteries):
• Primary batteries: batteries good for one use (non-rechargeable)
• Secondary batteries: make possible multiple charge/discharge cycles
(rechargeable)
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7
Electrochemical Secondary (rechargeable) Batteries
The electrochemical (secondary) battery modules are obtained connecting in series
and/or parallel elementary electrochemical cells made of:
 anode and cathode electrodes: negative and positive poles and plates with
coated catalyser substrates
 separator between the positive and negative electrodes
 electrolyte (liquid, gel or solid) acting or as a carrier for ion flow between the
electrodes (as for instance in lithium-ion cells) or as an active participant in the
electrochemical reaction (as for instance in lead-acid cells)
 current collectors (one positive connected to the cathode and one negative
connected to the anode)
 packaging
The current moves out from the positive pole of the battery in discharge mode and
moves in the positive pole in charging mode
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8
Batteries
12 V lead battery module (automotive auxiliary battery)
flooded typology
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9
Electrochemical reactions
The electrochemical reactions taking place in the batteries are REDOX reactions.
The passage of electrons from the oxidising species to the reducing one takes place
through a metallic conductor (the electrolyte)
The chemical species loosing electrons is OXIDISING
The chemical species acquiring electrons is REDUCING
The charge collector (electrode) where the oxidation reaction takes place is called anode
The charge collector (electrode) where the reduction reaction takes place is called
cathode
The battery electrochemical process is the sum of one reduction reaction (at the
cathode) and one oxidation reaction (at the anode)
Anode reaction (oxidation): Red1  Ox1n+ + n eCathode reaction (reduction): Ox2n+ + n e-  Red2
Red1 + Ox2  Ox1 + Red2

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10
Red Cat and An Ox
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11
Electrochemical reactions: discharge and charge phases
Traction system in motor mode
cathode
Traction system in regenerative braking mode
anode
current flow in the circuit
E-based Storage Systems
cathode
anode
current flow in the circuit
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12
Battery Cell Main Requirements
• highest possible emf (electro motive force)
• discharge should be free (as much as possible) from kinetic limitations in
order to have a limited over-potential
• internal resistance as low as possible
• limited self-discharge reactions
• low cost materials (cheap)
• eco-friendly materials
• easy recyclability
• no/less as possible CRMs (Critical Raw Materials)
• wide temperature operating (and storage) range
• fast charge able
• long life (cycling and calendar)
• safe (as much as possible)
• high specific energy/power [Wh/kg and W/kg]
• high energy/power density [Wh/l and W/l]
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13
Battery Cycling and Calendar Life
Cycling life is the number of complete charge-discharge cycles a battery can
perform before its capacity reach a given percentage of its initial capacity.
Temperature, discharging and charging rates, max SoC (in charging) and
min SoC (in discharging) are the most important parameters impacting on the
cycling life.
Calendar life depends also on the
duration of the periods in which the
battery is neither discharged nor
charged.
Storage SoC and temperature are
the most important parameters
impacting on the calendar life
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14
On board electrochemical batteries
One of the main issue of the batteries is the practical impossibility to design the
cells to have at the same time:
 the highest specific power (to satisfy limited time requests - tens of seconds)
 the highest specific energy (to satisfy long duration requests - weight, volume
and cost of the storage system mainly depend on the installed (and usable)
energy)
From the design point of view, power and energy sizing criteria’s ask for conflicting
choices. As a consequence, usually the battery sizing is the outcome of a
compromise.
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15
Batteries
12 V Batteries for ICE based vehicles
Battery main functions and sizing criteria:
 with ICE (and alternator) off:
 supply the starter motor during the cranking phase (power sizing)  high
specific power for transient needs (seconds)
 supply the vehicle loads during the car parking phases (energy sizing) 
high specific energy for small currents (mA) and long duration (weeks)
 with ICE (and alternator) on:
 transiently supply the delta power to the vehicle loads
 Power vs. Energy sizing criteria compromise
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16
Conventional vehicles: 12 V electric net
Diodes bridge
AC
12 V Battery
A
DC
Vehicle
e-loads
SM
SM: Starter Motor
A: Alternator
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17
Batteries
Dual Battery and Electric Architectures
Architectures with two batteries: one sized/specialised for energy and one for
power purposes.
It can be conveniently applied to vehicle architectures with two voltages (at
battery level):
 Dual voltage architectures (12-48 V) [Class A Electric Systems]
 High Voltage (hundreds of volts) Hybrids [Class B Electric Systems]
In both cases, the higher voltage battery can be mainly sized for power
needs and the lower voltage one (12 V battery) for energy purposes
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18
Dual voltage architectures (12-48 V)
High Power >48 V
Electric Loads
SM
DC
AC
A
DC
DC
48 V Battery
14 V
Electric Loads
12 V Battery
SM: Starter Motor
A: Alternator
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19
Hybrid Architectures
High Power HV
Electric Loads
DC
AC
EM
DC
DC
HV Battery
14 V
Electric Loads
12 V Battery
EM: AC Electric Machine
AC/DC: Inverter
HV: High Voltage B Class (typically > 100 V)
DC/DC: HV-14 V galvanically insulated step down converter (it connects a B Class
voltage (HV side) and an A Class voltage (the on-board 12 VDC grid))
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20
Ragone Plot (power vs. energy)
PbA: Lead Acid
NiMH: Nickel Metal Hydride
Li-Ion: Lithium Ion
Source: ERTRAC
for a given cell technology, higher is the specific energy design request lower will be the
available specific power and, the other way around, higher is the specific power design
request lower will be the available specific energy
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21
Batteries Limits
Summing-up:
 the design choices to maximise the battery specific energy are opposite to the
ones to maximise the specific power
 it is not possible to have at the same time the max power and the max energy
 lower is the SoC, lower is the output power
 lower is the temperature, lower is the output power
Moreover:
 performance are affected by the ageing phenomena
 recharge times are long (the complete recharge time asks for hours)
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22
Batteries Main Typologies
Lots of solutions have been, are and will be investigated in future. Up to now the
main part of the one already investigated has not been able to reach the industrial
applicability (Sodium-Sulphur (Na-S), Nickel-Iron, Nickel-Zinc, Zinc-Brome…)
Today the used batteries can be classified in three main families:
 Lead: VRLA (Valve Regulated Lead Acid), gel, AGM (Absorbed Glass Mat)
 Nickel: Nickel-Cadmium (Ni-Cd) in the past and Nickel Metal Hydrides (Ni-MeH)
nowadays
 Lithium: Lithium-Ion (Li-ion) and Lithium-Polymer (Li-pol)
For BEVs (Battery Electric Vehicles) applications also the Sodium-Nickel Chloride
(Na-NiCl2) are used for fleets (Zebra high temperature batteries) niche volumes.
Coming new technologies:
•
Short-Term: titanate solutions (LTO…), Solid State Batteries (SSB)
•
Mid-Term: Li-S
•
Longer-term: Li-air, (other) Metal-air solutions
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23
Batteries: cylindrical, prismatic, pouch
Prismatic cell
Cylindrical cell
Pouch cell
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24
Operating Principles of a Li-ion Cell
Lithium-ion (Li-ion) batteries employ lithium storage compounds as the positive
and negative electrode materials. As a battery is cycled, lithium ions (Li+) exchange
between the positive and negative electrodes. Li-ion batteries have been referred to
as rocking chair batteries because the lithium ions “rock” back and forth between
the positive and negative electrodes as the cell is charged and discharged.
rocking chair
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25
Operating Principles of a Li-ion Cell
When the cell is charged, lithium is combined in the anode as LiC6
During discharging, the Lithium
ions are extracted from the anode
(deintercalation
mechanism).enter the liquid
phase migrate, through the
separator, and are inserted into
the cathode with the metal oxide
(intercalation mechanism)
electrolyte
During charging, the opposite
process takes place).
electrolyte
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26
Lithium-Ion Cathode Materials
LCO first generation cells
Expensive, limited safety.
NMC safer and less
expensive than LCO (LG,
Samsung - BMW i3, VW
e-Golf, Renault Zoe)
LMO: less expensive and safer than Co
based materials. Doping with Ni 5V for
applications (AESC: Leaf, LEJ: Mitsubishi
iMieV, Citroen Czero e Peugeot iOn)
E-based Storage Systems
LFP stable and safe, low
energy density (Wh/l)
(stationary applications
and traction BYD)
NCA high energy density, safety
as LCO (Panasonic/Tesla)
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27
Cell Components
Cathode
E-based Storage Systems
Separator
Anode
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28
Lithium Battery Cell Safety issues (1/2)
Overcharge
• charge above defined charge end voltage
• leads to irreversible damage and loss of capacity
• lithium-plating (formation of metallic lithium around the anode during charging)
• safety critical as cathode active material starts to break down (> 4.4 V):
exothermic process with generation of heat (self-triggering) and oxygen
(oxidizing)
• thermal runaway
Overdischarge
• discharge below defined discharge end voltage
• leads to irreversible damage (dissolution of electrolyte) and loss of capacity
• safety critical if overdischarged batteries (< 1 V) are charged again
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29
Lithium Battery Cell Safety issues (2/2)
Short-circuit
• means a direct connection between positive and negative terminal of a cell or
battery that provides a virtual zero resistance path for current flow
• high short-circuit current
• heating of the cell/battery
• decomposition and evaporation of the electrolyte fluid
• decomposition of the active material of cathode
• additional heat production and release of oxygen
• gas formation
• emitted gas may get ignited at hot connectors
• fire
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30
Li Cells Roadmap
Post
Li-ion
(2025-2030)
500 Wh/kg, 1000 Wh/l
350 Wh/kg, 700 Wh/l
Advanced
Li-ion
(2020-2025)
235 Wh/kg
630 Wh/l
Li-ion
(2010-2020)
90 Wh/kg
200 Wh/l
Sources:
- Nationale Plattform Elektromobilität: “Roadmap integrierte Zell-und Batterieproduktion Deutschland“, Jan. 2016
- M. Meeus, “Overview of Battery Cell Technologies”, European Battery Cell R&I Workshop (European Commission), Brussels, Jan. 2018
- JRC (Joint Research Committee) - European Union
- “Battery requirements for future automotive applications”, EUCAR, Jul. 2019
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31
Battery Trends
Gasoline:
• 12.000 Wh/kg
• 10.000 Wh/l
today best cells
E-based Storage Systems
Battery System
values can be
reduced by as
much as half
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32
Batteries: Modelling
The batteries behaviour strongly depends on the temperature, State of Charge (SoC),
requested dynamic and ageing.
In order to predict the battery behaviour, there are lots of models often based on
electric equivalent lamped parameters circuits with parameters function of SoC,
temperature and ageing. These parameters are different considering discharge and
charge modes.
The circuits are typically including:
 an ideal DC voltage generator (whose voltage is equal to the OCV of the
battery)
 a series connected impedance with different combinations of passive
components (R, L e C) depending on the phenomena to be modelled (for
instance: fast discharge, recharge or regenerative braking...)
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33
Battery modelling
Example of equivalent circuit for discharge/charge with variable current
(dynamic behaviour)
R2
R1
L
I
+
+
E
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C1
V
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34
Battery: Efficiency and Power
From the energy point of view, the battery can be modelled as an ideal voltage
generator with a resistor series connected:
R
+ I
+
E
U
According to the model the max discharge power would be obtained with a
voltage (U) equal to one half of the OCV (E). Being the efficiency (UI/EI) in
that condition it would be equal to 50%, a trade-off solution has to be reached
limiting the max discharging power but obtaining an higher efficiency.
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35
Battery: voltage and power vs. current
Usage Area
14,0
12,0
10,0
8,0
Battery voltage [V]
6,0
Power [kW]
4,0
2,0
0,0
0
200
400
600
800
1000
1200
Current [I]
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36
Battery efficiency
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37
High power battery modelling
All the batteries, in particular the power sized ones, for short transients (seconds tens of seconds) can deliver high current levels with good efficiency:
R1
R2
+
I
+
E
C
U
At the beginning of the transient, only R1 (modelling the electric behaviour) is active: C
is initially a short circuit an accordingly the current (I) doesn’t flow through R2
(modelling the chemical behaviour).
For a prismatic cells Ni-MeH battery, R1 ~ 1/2 • R2 and the deliverable power for 10 s
is still 90% of the 2 s one (pulse discharge)
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38
State of Charge (SoC) and State of Health (SoH)
SoC = 1 – DoD
where DoD (Depth of Discharge)
DoD is defined as the integration of the delivered current (Is) in the time (delivered
capacity) divided for the effectively deliverable capacity (Crated):
I

DoD 
s
 dt
Crated
Crated depends on the allowable energy at different delivered power levels (as
shown in the Ragone Plot) and temperature
SoH (State of Health) is a coefficient (< 1) keeping into account the phenomena
reducing the battery capacity due to irreversible phenomena (corrosion, wear…)
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39
Batteries Main Typologies
 moving from Lead to Lithium solutions, on one side performance (specific energy
and power), efficiency and lifetime increase but on the other one costs too
 for all the typologies, to have high power and energy levels at the same time, lots
of modules are series connected  increasing importance of the electrical,
thermal and mechanical management (from battery cells to battery modules
and battery system)
 as a direct effect, the on-board integration is a key issue and volume, weight and
costs have to be considered at battery system level (modules plus protection and
management auxiliaries and parts) and on the operational lifetime/calendar life
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40
Batteries Usage Profiles and Applications
Battery usage profiles (and related applications):
 Charge Depletion (CD) mode: the battery is fully
charged with a battery charger and progressively
depleted during driving (in general up to the lowest
possible SoC)  BEVs application  battery mainly
sized to maximise specific energy
 Charge Sustaining (CS) mode: the battery is
charged and discharged on board around
intermediate SoC values (never approaching the
fully-charged or fully-discharged conditions)  HEVs
and FCHEVs full performance  battery mainly
sized to maximise specific power
 Dual Mode: at the beginning CD mode then switch to
CS mode  PHEVs (Plug-in HEVs)  battery mainly
sized to maximise power but with acceptable energy
content for the pure EV range
E-based Storage Systems
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41
Battery System
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42
Nickel Metal Hydride (Ni-MeH) Battery System
PEVE (Toyota-Panasonic) example
Battery Pack:
28 modules series connected
Battery Module:
6 cells (6,5 Ah - 1,2 V each)
series connected (7,2 V)
Battery System:
forced air cooled
aluminium housing
BMU only (no equalization system)
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43
Sodium-Nickel Chloride (Na-NiCl2) Battery System
former MesDea now FZSoNick
High temperature (270 °C)
Energy Battery for traction
purposes
ZEBRA single cell (ML3X)
ZEBRA Battery System
Z36-371-76
(371 V - 76 Ah - 28.2 kWh
288 cells, 248 kg
114 Wh/kg, 181 Wh/l)
welding-sealed cells and heat insulation
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44
Lithium-ion (Li-ion) Battery System
LEJ (Lithium Energy Japan) example:
Battery cells
50 Ah - 3,65 V
Li-Mn Oxide
Battery Modules (LEV50-4 & LEV50-8)
(4 or 8 cells series connected)
Battery System
Forced air thermally managed
Battery Pack (88S1P)
Installed Energy: 16 kWh
OCV: 321,2 V
10 modules by 8 and 2 by 4 cells
series connected
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45
Why battery management is needed
Cells/modules management aims:
•
electric safety ( electric shock)
•
thermal safety ( flammability)
•
reliability
•
life (cycling life and calendar life)
•
performance (max discharge/charge power, available energy, min-max
allowable voltage…)
and, as an effect, contribute to the costs limitation
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46
Role of the BS auxiliary components
Electric:
• Safety: electric shock (fuses, relays, contactors…)
• Management: monitoring and balancing
Mechanical:
• Safety: crash (housing…)
• Management: life (vibrations, cell fixing…)
Thermal:
• Safety: flammability (cooling to avoid thermal runaway)
• Management: calendar life and performance (thermal management)
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47
Specific energy: from theory to practice
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48
Battery Packs and Management
The battery packs are realised connecting (in general) in series several battery modules
(realised putting some battery cells in series and/or parallel)
The battery pack electrical management (minimum discharge voltages, maximum charge
voltages in charge and/or regenerative braking conditions, maximum currents in charge
and discharge…) is done starting from the hypothesis that all the modules/cells have
the same behaviour
The manufacturing differences among the modules/cells are the reasons of degenerative
behaviours (unbalancing) causing, if not correctly counteracted:
 performance reduction (in a first phase)
 irreversible damages (in a second phase)
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49
Battery System
Example of a Battery System and its on-vehicle integration
Nissan Leaf BS
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Nissan Leaf Chassis with BS
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50
Battery Packs and Management
Lead batteries: BMUs (Battery Management Units) and active or passive balancing
systems - BMSs (Battery Management Systems) - are used due to the typically high
production parametrical scattering
Nickel batteries (for power buffer applications): BMUs (Battery Management Units) are
sufficient due to the typically low production parametrical scattering and limited
operational delta SoC (no deep discharge or full charge)
Lithium batteries: BMS (Battery Management Systems) - are used due to the thermal
weakness and the need to use near all the installed energy
To limit the performance reduction during the ageing and improve the lifetime, it is
important to keep the delta temperature among the pack modules/cells close as much
as possible putting all the modules/cells in the same housing with a forced air thermal
management system or in more than one housing using a liquid/fluid thermal
management system
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51
Battery System and Management
Battery Management Unit
Battery Management System
Battery Pack
Balancing
Set points
Delivered
power
CAN bus
Current
Voltages
Traction E-drive
Vehicle Management Unit
Example of a BMS for Lead batteries
Temperatures
Features:
SoC and SoH evaluation
Overtemperature protection
Over discharge and overcharge protection
Active balancing
Battery recharge management
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52
Lead and Lithium Batteries: Recharge Profile
I Phase
(CC - Constant Current)
U Phase
(CV - Constant Voltage)
Voltage
Current
0
1
2
3
4
5
6
7
8
time [hours]
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53
Nickel and Lithium Batteries: Recharge Profile
Nickel:
 constant voltage recharge profile (with voltage value depending on the battery
temperature)
 the recharge is completed when the voltage start to decrease and the battery
charged capacity is equal to the delivered one multiplied for a coefficient
depending on the battery efficiency (around 1,1)
Lithium:
 it is very important not to overcome the maximum voltage limit to avoid
degenerative overheating phenomena (possible burning conditions: thermal
runaway)
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54
Partial Fast Charge
 it asks for very high efficiency battery technologies (it is in general applied only
to the Lithium ones)
 it is a partial charge (up to 80-85% SoC)
 the I Phase is performed with very high currents (some times more than the
standard charge current)
 it asks in general for a battery forced cooling system (due to the high charging
losses) and an high power charger
 the charger is usually an off board (DC type) directly connected to the battery
pack
 due to the graphite negative pole possible lithium plating phenomena (higher
with high currents, low temperatures and/or higher SoC), to have the proper
battery pack lifetime, it is better to use it only when necessary and possibly
alternating it with standard charges with long U phase (to complete the secondary
chemical reactions enabling the battery long lifetime)
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55
Supercapacitor Systems
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56
Supercapacitors
Supercapacitors are an alternative to the power sized batteries for power buffer
applications.
Supercapacitors are double electrical layers capacitors with extremely high
capacity (at least thousands of farad) but with a very low voltage level (typically
between 2,2 e 2,8 V). They have typically cylindrical shape and are realised rolling
up two conductive strips (one positive and one negative) with in between a
separator and plunged into an electrolyte.
From an electrical point of view, they are described with the same laws of the
standard capacitors:
E = ½ C (Vi2 – Vf2)
E: usable energy [J]
C: capacity [F]
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Vi: beginning of discharge voltage [V]
Vf: end of discharge voltage [V]
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57
Supercapacitors key features and drawbacks
Key features:

impressive specific power (up to 2÷4 kW/kg)

very high efficiency (higher than 90%)

dynamic behaviour

very high cycling number
Drawbacks:
 poor specific energy (lower than 4 Wh/kg)
 at pack level a management system with balancing unit is mandatory
(similar to batteries)
 cost (even if no noble material is inside the supercapacitors)
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58
Supercapacitors
Single SC cells
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Honda Supercapacitors System
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59
Power batteries vs. supercapacitors
Buffer Type
Supercapacitors
Ni-MeH batteries
Layout
cylindrical
prismatic
Manufacturer
Honda
Panasonic
Specific Power
1400 W/kg
1350 W/kg
Specific Energy
3.9 Wh/kg
46 Wh/kg
Pack
80 cells
28 modules
Connection
in series
in series
Rated voltage
2.7 V (pack: 216 V)
7.2 V (pack: 201.6 V)
Min Voltage
1.35 V (pack: 108 V)
6 V (pack: 168 V)
Max voltage
9.6 V (pack: 268.8 V)
Pack weight
34.3 kg
29.1 kg
Efficiency
90÷97%
89÷96%
Cycling Life
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240.000 km
(at vehicle level)
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60
12 V BSG (Belt driven Starter&Generator) improvements
Maxwell supercaps
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61
Fuel Cell Stacks and Systems
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62
63
What is a Fuel Cell
 Fuel Cells are devices able to directly convert chemical energy into electricity,
without combustion neither moving parts, through the electrochemical combination
between hydrogen and oxygen, producing water, electricity and heat
 The earliest Fuel Cell, in which hydrogen and oxygen were combined to form water,
was realised in 1839 by the Englishman William Grove
 The fundamental difference between the Fuel Cell and the battery is that the FC are
using reactants coming from outside, that means that they continue to run as far as
they are fuelled with hydrogen and oxygen (in general from ambient air)
First Fuel Cell
(William Grove, 1843)
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63
64
Fuel Cell Features
The typical behavior of the fuel cell make them attractive for the energy production
sector:
 high electrical efficiency: from 40% up to 60% and more
 wide variety of reactants (hydrogen, methane, methanol, ethanol..) can be used
 high modularity
 wide high efficiency area
 poor dependence of the efficiency on the plant size
 limited environment impact
 co-generation able (CHP Combined Heat and Power)
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64
Fuel Cell Types Classified by "Electrolyte"
Fuel cell
Electrolyte
Operative
Temperature
Fuel
o
( C)
Polymeric
Electrolyte
(PEM)
Alkaline
(AFC)
Solid Polymer organic,
poliperfluorosulfonic acid
40 - 50
Mobile Ion H
Diluted potassium hydroxide
solution in a porous matrix
Hydrogen
50 - 200
40 - 50
Oxygen and Hydrogen must be free from CO2.
Used in Apollo and Shuttle spacecraft.
Low power : 100 W - 20 kW
Hydrogen
175 - 220
40 - 50
First commercial product with reformer from CNG
Medium power: 10 kW - 1 MW
-
Mobile Ion OH
Liquid lithium, Sodium,
Potassium carbonates
solution in a matrix
Molten
Carbonate
(MCFC)
Direct
Methanol
(DMFC)
50 - 120
Mobile Ion CO3
Mobile Ion O
--
Solid polymer electrolyte
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Hydrogen
Natural Gas
600 - 700
>60
Reactions use CO2 present in the air
Inexpensive Ni catalyst . Internal reforming - Corrosive
electrolyte
High power : 100 kW to >10 MW
Internal reforming, simple catalyst.
Uses ceramic materials
Wide span of power : 1 kW to>10 MW.
--
Zirconia doped with yttria
Notes
Requires precious metal (Pt) catalyst and pure
hydrogen.
High specific power.
Very low to medium power : <1W to >100 kW
+
Liquid phosphoric acid
Phosphoric
contained in a porous matrix
Acid
+
(PAFC)
Mobile Ion H
Solid Oxide
(SOFC)
Hydrogen
System
Efficiency
(% )
@50 % Pmax
Hydrogen
Natural Gas
600-1000
>60
Methanol
80 - 140
35 - 45
Precious metal catalyst (more than in PEMFC)
Low power: 1W to 10 kW
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65
Fuel Cell Fields of Application
Typical
applications
POWER
in Watts
Main
advantages
Portable electronics
equipment
1
10
Mobile & residential Cars,
generation
boats
100
1k
Higher energy
density than batteries.
Faster recharging
10k
Distributed power
generation
100k
Potential for zero
emissions,
higher efficiency
1M
Higher efficiency
Low pollution
AFC
Range of
application of
the different
types of
Fuel Cell
MCFC
SOFC
PEMFC
DMFC
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10M
PAFC
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66
Automotive Applications: PEM Fuel cell basic principles
Hydrogen and Oxygen recombines and an electric current is produced
M
FUEL CELL
e-
Hydrogen
+
e-
Air
ee-
H+
H+
Electrode
Electrochemical
reaction
Anode
H2  2 H+ + 2 e-
Cathode
O2 +4 H+ +4 e-  2 H2O
Cell
2 H2 +O2  2 H2O
O
H+
H
H
H
H
H
Anode
Air
Water
Heat
O
Electrolyte
Cathode
Reactions
at the anode, oxidation 2H2  4H+ + 4eat the cathode, reduction O2 + 4e- + 4H+  2H2O
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67
67
68
Why PEM FC are interesting for automotive applications?
Respect to the other FC technologies, PEM FC can satisfy the following requirements:
 cheap technology (in respect of the other FC ones)
 low operating temperature (from 70-90°C to something more than 100°C)
 fast response
 at least 3000-5000 h as functional life
 good vibration resistance
 safety
 air as oxidant
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68
The Polymeric Electrolyte Fuel Cell
MEA
(Membrane Electrode Assembly)
Bipolar Plate
Bipolar Plate
Hydrogen
Outlet
Air exhaust and
water vapours
Heat
(hot water)
Hydrogen
Inlet
ANODE
Air
Inlet
CATHODE
Applications
Advantages
Disadvantages
Portable power sources
Stationary plants
Transportation
High Power Density
Low temperatures Fast start-up
Reduced corrosion
Platinum catalyst
Poisoning effects from
fuel impurities
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69
FCS: external humidification
with water injection and cooling cells
H2 STORAGE
(high pressure)
Pressure
Regulator
AIR BOX
(FILTER)
-
+
H2
H2O + H2
H2O
Recirculation
AIR
COMPRESSOR
Air + H2O
Air
FUEL CELL
STACK
Air + H2O
+ steam
CONDENSER
SEPARATOR
H20
recovery
HUMIDIFICATION
(WATER INJECTION)
Hydrogen Line
Air Line
Cooling Circuit
WATER
FILTER
COOLING
WATER PUMP
Exhausted
Air
H2O + glycol
HEAT EXCHANGER
Humidification Circuit/
condenser
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70
The fuel cell system power module
Air compressor
Fuel Cell
stacks
Air box
Water filter
Cathode exhaust pipe
Stack heat
exchanger
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Water condenser
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71
Higher Temperature FCS: simplification and cost reduction
FILTER
mass flow
meter
AIRBOX
PI
Air flow
distribution
TI
AIR COMPRESSOR
water
injector
WATER
FILTER
air out
WATER
CONDENSER
DEMI-WATER
TANK
H2 in
high
pressure
pump
Fuel Cell
Stack
recirculating
pump
TI
WATER
FILTER
GLYCOL & WATER
TANK
H2 out
DEMI WATER PUMP
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HEAT EXCHANGER
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72
The role of high temperature membrane in the FCS layout
STANDARD
 No water recovery/recycling
 Simplified cooling
 Extended ambient operating
range
IMPROVED
Key technical targets for
innovative membrane
 Higher temperature (90 - 120 °C)
 No reactant humidification
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73
Fuel Cell Stack, System and Powertrain
ENERGY/POWER SOURCE
Fuel Cell System
Fuel Cell
Stack
Power
Converter
Electric
Machine
Transmission
Fuel Cell
Auxiliaries
ELECTRIC DRIVE
Power Buffer
Electronic
Interface
BUFFER
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FUEL CELL POWERTRAIN
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74
H2 Fuel Cell Stack, System and Powertrain Efficiency
PEM Stack
•
•
•
•
0,80
258 cells
Max stack power: 47 kW
Operating pressure: 1,2 bar
Operating temperature: 60°C
Stack efficiency
0,70
Electric motor
• Induction, 15/30 kW - 120 Nm
Efficiency
0,60
0,50
FCS Efficiency
0,40
FC Propulsion Efficiency
0,30
0,20
Power sustains constant vehicle speed
0,10
0,00
0
10
20
30
40
50
60
70
80
90
100
P/Pmax
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75
FC System Efficiency vs. diesel engine
70
Experimental data
60
EFFICIENCY (%)
50
STACK efficiency
SYSTEM Efficiency
DIESEL Efficiency
40
30
20
Stack Efficiency   f 
10
Vc
1.24
f = fuel utilisation coefficient
Vc = cell operating voltage
Power @ wheels
System Efficiency = -------------------------H2 calorific value
0
0.00
10.00
20.00
30.00
40.00
50.00
60.00
70.00
80.00
90.00
100.00
OUTPUT POWER (%)
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76
Hydrogen Production Pathways
FOSSIL FUELS
NUCLEAR
WATER THERMOLYSIS
COAL
GASSIFICATION
PARTIAL
OXIDATION
REFINING
OIL
REFORMING
NATURAL GAS
ALTERNATIVE
SOURCES
FERMENTATION
BIO GAS
METABOLISM
BIOMASS
SOLID WASTE
PURIFICATION
SYNGAS
H2
THERMOELECTRIC
RENEWABLES
GEOTHERMAL
SOLAR
ELECTRICITY
WATER
ELECTROLYSIS
HYDRO
WIND
DIVERSIFICATION OF PRIMARY ENERGY SOURCES
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77
Hydrogen today production
HYDROGEN PRODUCTION (2000): 500*109 Nm3/yr
(corresponding to 41.6 Mt/yr)
SHARE OF PRODUCTION: 2000
Reforming of hydrocarbons
78 %
18 %
Electrolysis 4%
Coal gasification
99 % OF HYDROGEN IS PRODUCED TODAY FROM FOSSIL FUELS
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78
Hydrogen on-board storage alternatives
Compressed hydrogen
Liquid hydrogen
• Cylindrical tanks
• Quasi conformable tanks
Solid state
• Cylindrical tanks
• Elliptical tanks
• Metal Hydrides
• Carbon absorption
• Glass microsphere
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79
Compressed hydrogen tank technology
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80
Liquid hydrogen tank technology
LH2 in
active cooling
GH2 out
(pulse tube
refrigerator)
inner vessel
(austenitic steel)
distance holder
(glass-fibre)
high temperature
superconductor
permanent magnet
liquid hydrogen
at 20 Kelvin
multilayer +
vacuum insulation
thermal shield
liquid level indicator
outer vessel
(austenitic steel)
Advantages
• Low pressure
• High storage density
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heater
Disadvantages
• Energy required for liquefaction
• Evaporative losses
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81
On-board hydrogen storage technologies
140
Gravimetric energy density of different fuels
Compressed hydrogen
• Reinforced carbon fibre
• Max pressure: 350 bar
Energy density (MJ/kg)
120
100
80
60
40
MANUAL
SHUT OFF
VALVE
20
0
gasoline
35
diesel
natural gas
hydrogen
Volumetric energy density of different fuels
HIGH PRESSURE
REGULATOR
350 bar --> 10 bar
Ref. Thiokol
Liquid hydrogen
Energy density (MJ/l)
30
Fuel energy density
25
System energy density
20
Super-insulation
Level probe
Filling line
Gas extraction
Liquid extraction
Filling port
Inner vessel
Outer vessel
Suspension
Liquid Hydrogen
(-253oC)
Safety valve
15
Gaseous Hydrogen
(+20oC up to +80oC)
10
5
Shut-off valve
Electrical heater
0
gasoline
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Liquid
Compressed Compressed
700 bar
350 bar
Reversing valve
(gaseous / liquid)
Cooling water
heat exchanger
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Ref. Linde
82
FC technological road blocks
Main problems to be solved for a wide FC Vehicle diffusion
 Stack: cost, efficiency, lifetime
 FCS and FC auxiliaries: efficiency, cost, integration level, lifetime, vehicle
parking at very low temperatures (-20°C)
 H2 on-board storage: capacity, weight (if solid i.e.: metal hydrides), volume (if
gaseous), cost (if liquid), safety
 H2 distribution infrastructure: which type (centralized, distributed…), availability
and diffusion times, costs (of the infrastructure and of the hydrogen)
 Standardisation: connectors for the refueling, test procedure (both at vehicle and
components level)
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83
Toyota FCHV- MIRAI (2014)
 Hybrid full power architecture (TFCS)
(PEMFC + ~20 kW Ni-MeH batteries)
 Stack Toyota: 114 kWmax (370 cells
(single line stacking) with internal
water circulation (humidifier-less))
 High pressure conformable H2 tank:
700 bar
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84
Toyota FCHV- MIRAI: main components
Ni-MeH
AC Synchronous
(Pmax: 113 kW; Tmax: 335 Nm)
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(Inverter with DC/DC converter)
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85
Toyota FCHV- MIRAI: FC stack
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86
Toyota FCHV- MIRAI: FC Stack
Electrolyte Membrane
Catalyst Layers
Gas Diffusion layers
Electrode improvements:
• membrane thinner by 2/3
• proton conductivity improved threefold
• platinum/Cobalt alloy catalyst activity increased by 180%
• density reduced (Layers thinned)
• gas diffusibility improved twofold
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87
Toyota FCHV- MIRAI: FC Stack
with the 3D field channels solution, it is possible
to avoid the water accumulation inside the FC
cells (as it happens in the classical straight
channel solution) increasing the electricity
generation efficiency and improving the behavior
at under zero ambient temperature (up to -30°C)
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88
Toyota FCHV- MIRAI: FC Boost and H2 storage system
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89
Toyota FCHV- MIRAI: Refueling and range vs. BEVs
Refueling procedure and time vs. ICEVs and BEVs
Range vs. BEVs
up to now Toyota has sold more than
10.000 Mirai samples worldwide
* JC08 test cycle
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90
Toyota FCHV- MIRAI next gen (2020)
In 2020 Toyota is putting on the market the Mirai Gen 2 (whose preview has been
presented at the Tokyo Motor Show as “Mirai Concept”)
The MIRAI Gen 2 is a premium segment sedan with:
• a 30% increase of the range through higher efficiency system and bigger
hydrogen tanks
• improved driving performance, increased roomability and comfort
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91
IFP School
PWT MASTER MODULE 1-2020
Electric Machines
Vittorio Ravello
Rueil-Malmaison (Paris) 26-30 October 2020
Electric Machines
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1
Electrical Power Conversion Typologies
from Electric to Electric:
 transformers: to modify, at constant frequency (different from 0), output
voltages/currents amplitudes
AC
AC
3 phases
single phase
 power electronics (variable frequency):
 DC/DC converters to regulate output voltages/currents amplitudes
 DC/AC converters to regulate output voltages/currents amplitudes & frequencies
DC
DC
DC
DC/DC converter
Electric Machines
AC
3 phase inverter
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2
Electrical Power Conversion Typologies
from Electric to Mechanical:
electric motors with at least one rotating or linearly shifting part. Lorentz or reluctance
forces mechanism are used to deliver mechanical power
Electric
motor
Pelectric
Pmechanical
from Mechanical to Electric:
electric generators with at least one rotating or linearly shifting part. Faraday induced
emf (electromotive force) rule to deliver electric power
Electric
generator
Pmechanical
Electric Machines
Pelectric
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3
Electric Machines
Electric
generator
Electric
motor
Pelectric
Pmechanical
Pmechanical
Pelectric
Input
Electrical
Magnetic
Mechanical
Magnetic
Output
Mechanical
Electric Machines
Electrical
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4
Electric Machines: classification based on the source type
AC
DC
PM Stator
Separately
excited
Wounded
stator
Synchronous
Induction
Series
excited
PM excited
SMPM
Synchronous
Wounded
rotor
Synchronous
reluctance
IPM
Synchronous
PM: Permanent Magnets
SMPM: Surface Mounted PM
IPM: Internal PM
Electric Machines
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5
Electric Machines: Electro-Mechanical Conversion
Forces (and torques) can be generated through two mechanisms:
 Lorentz Force
 Reluctance Forces
Lorenz Force:
 DC e-machines
 AC synchronous (PM brushless and wounded rotor) machines
 AC induction machines
Reluctance forces (co-energy minimisation):
 Reluctance machines:
 synchronous
 switched and step motors
 electromagnets
Electric Machines
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6
Electric Machines: Lorentz Force
Lorenz rule:
F = q v  B  F = i l  B  |F| = B i l sen a
(if B  i)  |F| = B i l
where:
F: Lorentz force [N]
q: elementary electric charge [As]
v: speed [m/s]
B: magnetic induction [T]
i: current [A]
l: length of the active part of the conductive winding [m]
a: angle between induction ad current direction vectors
F
I
B
a
electric conductor
In an e-machine the magnetic, induction is produced by the inductor circuit (permanent
magnets or windings with currents), while the current flows in the windings of the
induced circuit. These currents can be:
 supplied by an external circuit (DC and AC synchronous machines)
 induced with the electromagnetic induction and Faraday rule (AC induction)
Electric Machines
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7
Electric Machines: Reluctance Forces
Co-energy minimisation
mechanism: the current flowing in
the stator coil create a flux and the
magnetic attraction of the rotor
pole in order to put it in a
minimum co-energy position
The reluctance forces depend on the interacting surfaces, the square of the magnetic
induction and the difference of the inverse of the permeability of the material
constituting the parts of the system and the one of the air (airgap).
The magnetic induction depends on the reluctance of the complete magnetic circuit
Electric Machines
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8
DC Electric Machines
Electromagnetically active
stator and rotor parts
Currents are driven to (motor
mode) or taken from the rotor
(generator mode) through the
brushes-commutator unit
Electric Machines
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9
DC Electric Machines
2 magnetic poles DC machine: magnetic field
Magnetic Pole
Stator yoke
Air gap
Excitation winding
Rotor
Electric Machines
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10
DC Electric Machines
2 magnetic poles DC machine: torque production mechanism
T = i Fi rr
Fi
Fi
where:
T: torque [Nm]
i: each of the rotor conductors
Fi: elementary force generated on each
rotor conductor [N]
rr: rotor radius [m]
The electromechanical collector operates the current flow inversion
Electric Machines
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11
DC electric machine - Equivalent circuit
Rotor (armature) and stator (excitation) circuits
ia(t) +
Ra
La
•
•
•
•
ua(t)
ea(t)
iexc(t) +
• La : armature leakage inductance [H]
Rexc
Lexc
uexc(t)
ua(t): armature voltage [V]
ia(t): armature current [A]
ea(t): induced emf [V]
Ra: armature resistance [W]
•
•
•
•
•
uexc(t): excitation voltage [V]
iexc(t): excitation current [A]
Rexc: excitation resistance [W]
Lexc : excitation inductance [H]
F (magnetic flux) = Lexc iexc(t)
(in the PM excited DC machines, the magnetic flux is roughly constant)
Electric Machines
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12
DC electric machine - Steady state relations
Va = E + R a  Ia
(armature circuit relation)
E = KFw
(emf relation)
Tm = K  F  Ia
(torque relation)
 regulating the armature voltage
amplitude, it is possible to control the electric
machine speed
 regulating the armature current amplitude,
it is possible to control the electric machine
rotor shaft torque
Electric Machines
where:
• Va: armature voltage [V]
• E: induced emf [V]
• Ra: armature resistance [W]
• Ia: armature current [A]
• K: constant coefficient
• F: magnetic flux [Wb]
• w: rotor speed [rad/s]
• Tm: torque [Nm]
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13
DC electric motor - Mechanical Behaviour
Armature voltage regulation at constant excitation flux
Tm [Nm]
100% Van
50% Van
Tr
w [rad/s]
Electric Machines
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14
DC electric motor - Main Limits
 mechanical commutation:
 brushes wear  maintenance needs
 limited max rotor speed (around 6000 rpm). In comparison, an AC machine
can have a max speed also three times higher (with conventional
technologies)  higher torque (and as a consequence higher dimensions)
for same power level
 brushes-collector sparkling in commutation
 rotor complex manufacturability (collector and winding)
 axial length increase due to the commutator-brushes-brush keeper system
 distributed winding on the rotor  high Joule losses on the rotor  complex
heat dissipation and problems in realising watertight solutions
 lower efficiency
 lower transient power (poor overload capability)
Electric Machines
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15
AC electric machine - speed regulation
AC e-machines speed regulation
 synchronous types: there is a direct proportionality between the rotor shaft
angular speed and the frequency of the supply voltage/current
 induction (asynchronous) type: the proportionality is between the
frequency of the supply voltage/current and the synchronous speed (the
speed of the rotor shaft at no load and without frictions)
The synchronous speed (W) inversely depends also on the pair poles number
(pp):
W [rpm] = 60 • f [Hz] / pp
 the only way to regulate in a wide area and continuously the angular speed is
to modify the frequency (f) of the stator voltages and currents
The electronic regulation in the case of the DC e-motors (chopper) is a very
good opportunity while in the case of the AC e-motors (inverter) is in
practice mandatory
Electric Machines
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16
DC e-motors vs. AC e-motors
E-motor torque production
The mechanical torque is produced through the magnetic flux and electric current
interaction:
DC e-motors:
 scalar relation
 torque is maximised (flux  current) through:
 electromagnetic distribution
 commutator-brushes system (electromechanical way)
AC e-motors:
 vector relation
 flux-current vectors product maximisation is reached through:
 electromagnetic distribution
 field orientation control techniques (electronic way)
Electric Machines
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17
AC Electric Machines
Flux Production mechanism:
 Stator multi-phases winding space shifted with AC voltages and current time
shifted (AC Induction and Synchronous Reluctance machines)
 Rotor DC winding with brushes and slip rings (AC wounded synchronous
machines)
 Rotor Permanent Magnets (AC PM synchronous machines)
Electric Machines
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18
AC Electric Machines
Classification based on the flux production mechanism
DC (rotor)
AC (stator)
Induction
Synchronous
Reluctance
PM (rotor)
SM PM
Synchronous
DC or AC
Brushless
Switched
Reluctance
Wounded rotor
Synchronous
IPM
Synchronous
(also called buried
PM Synchronous)
Winding-less rotor
Synchronous
bold characters: solutions applied for the pure electric or hybrid propulsion
PM: Permanent Magnets; IPM: Internal Permanent Magnets; SM: Surface Mounted
Electric Machines
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19
AC Electric Machines
Classification based on flux direction:
 Radial flux: rotating machines (typically: external stator and internal rotor)
 Axial flux: rotating disc shape machines (two external rotors and one internal stator
or two external stators and one internal rotor)
 Planar flux machines: linear and tubular machines
Electric Machines
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20
Radial Flux electric machines
AC Induction Machine (cross section)
External stator
Internal rotor
Electric Machines
Magnetic induction (radial direction)
Electric current (axial direction)
Force (tangential direction)
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21
AC Brushless Synchronous Axial Flux electric machine
Internal rotor Axial Flux machine
Stator
Rotor
(2 external rotors and 1 internal stator)
Slots
N
F
I
B
S
S
N
N
S
S
Torus Axial Flux machine
Stator 1
Rotor
N
Stator 2
SN
NS
SN
NS
Electric Machines
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22
AC Electric Machines
Electric Machines for EV and HEV propulsion systems
Typically the e-machines for these application are radial flux type with internal rotor and
external stator
Geometrical main options:
 “salami” shape with high l ratio (l between 1 and 2): for EVs (battery and/or FC
supplied), series and non coaxial parallel hybrid applications
 disc or ring shape with low l ratio (l « 1) for EVs (battery and/or FC supplied)
and series hybrid wheel-motors and for coaxial parallel hybrid applications
l: rotor active length/diameter
Electric Machines
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23
Main AC E-Machines: stator and rotor structures
Stator copper winding
Rotor squirrel cage
Rotor PM
Stator copper winding
Stator iron lamina
Stator iron lamina
Rotor iron lamina
Rotor iron lamina
Induction or Asynchronous
SMPM Brushless Synchronous
Stator copper winding
Stator copper winding
Rotor PM
Stator iron lamina
Air barriers
Stator iron lamina
Rotor iron lamina
IPM Synchronous Reluctance
Electric Machines
Rotor iron lamina
Switched Reluctance
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24
AC E-Machines: stator and rotor view
IPM Synchronous
Induction
Switched Reluctance
Electric Machines
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25
Main AC E-Machines: active parts
Induction (Continental)
SMPM Synchronous (Audi)
IPM Synchronous (GM)
Electric Machines
Switched Reluctance
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26
Salami shape traction induction e-machines
Continuous Power: 20 kW
Rotor 3D
FEM Analysis
Copper rotor squirrel cage
Stator-Rotor 2D
FEM Analysis
Continuous Power: 45 kW
Electric Machines
Active parts
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27
Salami shape traction synchronous reluctance e-machines
Liquid cooled electric machine
Stator and rotor lamina
Integrated fixed speed transmission - electric machine
Electric Machines
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28
Salami shape traction wounded synchronous e-machines
Renault ZOE R240 e-motor
Salient pole rotor lamina
Electric Machines
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29
Disc-ring shape e-machines for parallel HEVs
Induction
Induction for FAS Applications
© Siemens Automotive
© Bosch
Synchronous Permanent Magnet
© Honda
Electric Machines
Switched Reluctance
© Dana
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30
Traction E-Machines Technologies Comparison
IPM
Synchronous
Electric Machines
SMPM
Synchronous
Induction
machine
Wounded rotor
Synchronous
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31
E-Machines: Induction vs. SMPM Synchronous
Torque vs. Speed map: efficiency comparison with different stator winding technologies
Induction machine
Electric Machines
SMPM Synchronous
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32
E-Machines: pole number effect
2 poles
4 poles
8 poles
Increasing the poles number:
• lower stator and rotor yoke height (the main flux is split in more pathways)
• lower stator end winding height
• higher frequencies (higher iron losses)
Electric Machines
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33
E-machine dimensions vs. poles number
(@ fixed external diameter)
Electric Machines
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34
E-machine normalised losses vs. poles number
(@ fixed external diameter)
Electric Machines
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35
E-Machines Cooling
Main methods:

natural air

forced air

liquid (stator jacket)
or combinations of these methods (for instance: stator liquid cooled and rotor forced air
cooled)
Special solutions:

liquid cooled rotor shaft

airgap nebulised oil cooling (integrated with mechanical transmission)

…
Electric Machines
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36
E-Machines Cooling Examples
Liquid cooling
Electric Machines
Mixed liquid - forced air cooling
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37
E-machine speed sensors
Speed Sensor
Rotor shaft bearing with integrated speed sensor
Electric Machines
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38
E-machine speed-position sensors
Reluctance resolvers
Electric Machines
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39
AC Induction Machine:
Equivalent Circuit for steady state conditions
RS
IS
+
US
s = (w0wm)/w0
w = pp w
w S = 2p fS
S
Electric Machines
0
I’R
LSl
L’Rl
R’R
ImS
Rir
1 s
R' R
s
Lm
U S stator voltage
I m S stator magnetising current
RR rotor resistance
I R rotor current
s slip
f s stator frequency
RS
LSl
RR
LRl
Rir
Lm
stator resistance
stator leakage inductance
rotor resistance
rotor leakage inductance
iron losses resistance
magnetising inductance
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40
AC Induction Machine: mechanical behaviour
Constant amplitude and frequency stator voltage supply
T [Nm]
Motor mode
Tpo
Transient operation area
(thermal limits on insulating materials)
T0
Continuous operation area
w0
0
1
Electric Machines
sT@Tpo
0
wm [rad/s]
s
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41
AC Induction Machine: mechanical behaviour
Temperature increase  Rotor resistance increase
T [Nm]
Tpo
0
RR
Motor mode
w0
wm [rad/s]
Constant amplitude and frequency stator voltage supply
Electric Machines
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42
AC Induction Machine: mechanical behaviour
Reduced amplitude of the stator voltage supply at constant frequency
T [Nm]
Motor mode
US
0
Electric Machines
w0
wm [rad/s]
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43
AC Induction Machine: mechanical behaviour
Increased frequency of the stator voltage supply at constant amplitude
f
T [Nm]
0
Electric Machines
w0
Motor mode
w0’
w0”
wm [rad/s]
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44
AC PM and IPM Synchronous Machines
SMPM: Surface Mounted PM
Electric Machines
IPM: Internal mounted PM
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45
AC PM Synchronous Machines
 inductor circuit is on rotor side (magnetic flux produced through PMs)
 induced circuit on stator side
 highest specific torque [Nm/kg and Nm/l] and peak efficiency machine
 relatively poor efficiency in partial load conditions (due to iron losses)
 potential limited maximum speed due to the PM on the rotor surface (external
rotor layouts, rotor hub…)
 depending on the stator winding layout:
 AC Brushless (lower ripple torque but need of more precise mechanical
sensors (i.e. reluctance resolvers))
 DC Brushless (higher ripple torque but very simple mechanical sensors
(Hall sensors))
Electric Machines
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46
Radial flux SMPM Synchronous
Internal Rotor vs. External Rotor Lay-out
Electric Machines
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47
AC IPM Synchronous Machines
 inductor circuit is on rotor side (magnetic flux produced through PMs)
 induced circuit on stator side
In respect of SMPS Synchronous machines:
 specific torque [Nm/kg and Nm/l] and peak efficiency lower
 higher efficiency in partial load conditions (lower iron losses)
 lower high speed limitation (PM kept by the rotor iron)
 easier flux weakening capability
SMPS
Synchronous
Electric Machines
IPM
Synchronous
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48
Switched Reluctance Machines
Radial Flux Solution
Electric Machines
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49
Switched Reluctance Machines
Key features:
 high mechanical robustness (rotor without PMs and/or windings)
 easy manufacturability in high volumes (single pole stator winding layout with really
reduced end windings length)
 low cost (thanks to the materials (no PM) and the easy manufacturability)
 high efficiency
 high torque at low speed
Drawbacks:
 poor magnetic utilisation (only one pair pole is active)
 limited specific torque
 high ripple torque and noise
 really reduced airgap (mandatory)
 high reactive power (negative effects on the power electronics sizing)
Electric Machines
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50
AC Synchronous Reluctance Machines
Radial Flux Solutions
Axial lamination
Electric Machines
Transversal lamination
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51
AC Synchronous Reluctance Machines
Key features:
 rotating MMF (MagnetoMotive Force)  vs. switched reluctance:
 lower torque ripple
 less vibrations
 lower noise
 high specific torque:
 15% higher than the induction one
 80-85% of the brushless PM synchronous one with Sm-Co PMs
 no rotor windings  high average efficiency
 possible rotor solutions:
 axial lamination: higher specific torque but high rotor losses due to local
harmonics
 transversal lamination: lower specific torque but near no rotor losses
 transversal lamination with added compensation PMs to reduce the power
electronic sizing/increase the high speed e-machine power (limit: compensation is
complete only for one load condition)
Electric Machines
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52
Lorentz Force based E-Machines Comparison
Lorentz force based where the main main flux
e-machines
flux is produced produced by
Torque
current
Current moved to/from
rotor through
DC machine
Stator
PMs or DC
winding
Rotor
Brushes and commutator
AC Induction
(asynchronous)
Stator
AC winding
Rotor
Electromagnetic induction
AC Synchronous
SMPM
Rotor
PMs
Stator
N.A.
AC Synchronous
wounded rotor
Rotor
DC winding
Stator
Brushes and slip rings
Electric Machines
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53
Traction E-Machines Basics
 nowadays in the applications with high dynamic, efficient and precise e-machine
torque-speed control requirements, AC e-machine solutions are the solution
 in the traction applications (wide speed and torque range), to maximise the
performance and the efficiency and minimise the weight and volume:
 high torque ad specific torque at low speed conditions (constant torque area)
typical of the SMPM (Surface Mounted Permanent Magnets) synchronous
machines
 wide flux weakening range and easy & efficient flux weakening (constant
power area) typical of the induction machines
 synchronous SMPM machines have the best specific torque but a poor flux
weakening capability. Vice versa induction machines are good in flux weakening
but limited in specific torque
Electric Machines
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54
Traction E-Machines Trends
 the conventional design approach aims to maximise the isotropy contribution
minimising the anisotropy one (i.e. induction or SMPM synchronous machines
(Lorentz force based)) or maximise the anisotropy contribution minimising the
isotropy one (i.e. switched or synchronous reluctance machines (Reluctance forces
based))
 to find e-machines able to overcome the opposite specific torque and flux weakening
limitations, new electromagnetic non linear solutions to manage together the
isotropy and the anisotropy torque (synchronous mixed e-machines) are
requested
 depending on the starting point and the amount of PMs, synchronous mixed emachines can be seen as:
 SMPM synchronous machines with PMs moved inside the rotor (IPM (Internal
Permanent Magnets) synchronous machines) with important anisotropy torque
contribution
 synchronous reluctance e-machine with IPM proper compensation
Electric Machines
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55
Traction E-Machines Typologies
Anisotropy Torque:
Isotropy Torque:
SMPM Synchronous
Induction
Switched Reluctance
Isotropy + Anisotropy Torque:
Synchronous Reluctance
with compensation PM
Electric Machines
IPM Synchronous
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56
Traction E-Machines Trends
 these solutions(called mixed machines) are today possible thanks to some enabling
tools and technologies:
 FEM (Finite Element Methods) for the coupled electromagnetic and thermal
design
 cheap, robust and precise position sensors (reluctance resolver)
 powerful and cheap microprocessors (dual core and more) or DSP (Digital
Signal Process) for the control
Electric Machines
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57
Costs
Traction E-Machines Road Map
Direct Current
AC SMPM
Synchronous
AC Induction
PM: Permanent Magnets
AC IPM
Synchronous
Switched
Reluctance
Mixed
Performances (efficiency and specific torque/power)
Mixed: Synchronous Machine with IPM that sums isotropic synchronous and anisotropic reluctance torques
Electric Machines
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58
IFP School
PWT MASTER MODULE 1-2020
Power Electronics
Vittorio Ravello
Rueil-Malmaison (Paris) 26-30 October 2020
Power electronics
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1
AC Electric Drive
Electric Drive
Power electronics
Electrical
Power & Energy
Source
Power Stage
Electric
Machine
Control Stage
Mechanical sensors (speed, position)
Electric sensors (DC voltage, AC voltages, DC current, AC currents)
Thermal sensors (stator windings, power electronics heatsink…)
Power electronics
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2
Electric Drive
An electric drive is the sum of:
 reversible electric machine (able to operate both as motor and
generator). In traction applications is usually AC with 3 phases
 power and di control converter to link the e-machine to the
energy/power source and regulate mechanical power, torque and speed in
motoring mode and electric power, voltage and currents in generating
mode. In traction applications is bidirectional DC/AC type (called inverter)
 electric (currents, voltages…), thermal (of the e-machine and power
converter) and mechanical sensors (e-machine rotor shaft speed and
position). In traction applications the e-machine sensors (thermal and
mechanical) are integrated In the e-machine. The converter thermal
sensor/s and all the electric ones are integrated in the power converter
Power electronics
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3
Power Electronics: power devices
 Uncontrollable devices:
 Power diodes
 Turn-on controllable devices:
 SCR (Silicon Controlled Rectifier)
 Turn-on and off controllable devices:
 GTO (Gate Turn Off) Thyristor
 Power MOSFET (Metal Oxide Semiconductor Field Effect Transistor)
 BJT (Bipolar Junction Transistor)
 IGBT (Insulated Gate Bipolar Transistor)
For automotive power electronics applications today the most diffused ones are:
 Class A applications (V ≤ 60 Vdc): power MOSFET plus power diodes
 Class B applications (60 Vdc < V < 1500 Vdc): IGBT (typically hundreds of volts)
or Power MOSFET (only for very high switching frequency DC/DC converters)
in both cases plus power diodes (but Silicon Carbides (SiC) are coming)
Power electronics
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4
Power Electronics: power devices behaviour
Diodes
if directly polarised, on mode (current conduction) up to when the
current changes its direction (no control)
SCR
if directly polarised, on mode (current conduction), only when a
control pulse is given, up to when the current changes its direction
(turn-on control)
GTO
BJT
MOSFET
IGBT
Power electronics
if directly polarised on mode (current conduction), only when a
control pulse is given, up to when the pulse is present (turn-on and
off control). They are used as high frequency power switches (on-off
mode)
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5
Power Diodes
Structure:
-
+
iA
VAC
p+
Anode
Real behaviour:
iA
I
n-
n+
Cathode
Simplified models:
iA
iF
iA
Vbd
vAC
v
V AC
Power electronics
vT vF
vAC
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6
Power Switches
Simplified models:
C
A
IA
iA
B
VAB
Real behaviour
iA
VC
vrb
Ideal switch model
vAB
iA
vfb
reverse
polarisation
vAB
vT
direct
polarisation
switching
on
off
vAB
iR
used only in on or off mode (no linear conduction usage)
Power electronics
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7
Devices: symbols and nomenclature
SCR
Silicon Controlled
Rectifier
GTO
Gate Turn-Off
Thyristor
Anode
iA
+
Gate
iG
Anode
iA
vAK
Gate
-
BJT
Bipolar Junction
Transistor
+
IGBT
Insulated Gate
Bipolar Transistor
iC
+
vCE
Gate
-
+
iB
vCE
vAK
+
vBE
-
-
Drain
MOSFET
Metal Oxide
Semiconductor
Field Effect
Gate
Transistor
iE
Emitter
Cathode
Collector
iC
Base
iG
Cathode
Collector
iD
+
vDS
+
-
vGS
Emitter
Power electronics
Source
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8
Power Electronics: power switches and voltages
Today scenario:
 Power MOSFET is the best device for the low voltage applications without
galvanic insulation (DC max voltage lower than 60 Vdc (65 Vdc in US )), as for
instance: 12 V (n.p. cars and light delivery vehicles), 24 V Medium-Heavy
Commercial Vehicles, 12-48 V (dual voltage) or pure 48 V of the possible future
electric on-board nets [A Class]
 IGBT is the best device for the high voltage (> 100 V) and high power (> 10-15
kW) applications with galvanic insulation, as for instance: BEVs, full HEVs,
P-HEVs, FCEVs, FCHEVs [B Class].
In this case, the source max DC voltage is typically selected as not higher than
2/3 of the max IGBT voltage (hard switching power electronics).
Referring to the allowable classes for industrial applications: 600 Vdc or 1200 Vdc
are typically used (lower diffusion solutions are the 200 Vdc and 800 Vdc IGBT)
Power electronics
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9
Power semiconductors qualitative comparison
Device
SCR
MOSFET
BJT
IGBT
GTO
low losses





easy
controllability





high frequency





high current





high voltage





low cost





Power electronics
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10
Power semiconductors power and switching frequency
Power [VA]
100 M
10 M
1M
SCR
100 k
GTO
10 k
IGBT
BJT
1k
100
MOSFET
10
10
Power electronics
500
1k
10 k
100 k
1M
Switching
frequency [Hz]
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11
Power module or Half Bridge
IC
T1
D1
IL
VDC
T2
D2
VC
ID
Power electronics
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12
Power converters typologies
The main power electronics conversion structures for automotive purposes can be
classified in three families according to the functions:
1. Converters to connect on-board DC e-energy/power sources & e-machines:
 DC/DC converters for DC machines (choppers) [typically bidirectional]
 DC/AC converters for AC machines (inverters) [typically bidirectional]
2. DC/DC converters for electrical adaptation (typically voltage) between:
 e-energy/power sources [one way or bidirectional]
 e-energy/power sources and inverters [bidirectional]
 e-energy/power sources and e-loads (vehicle auxiliaries) [one way, in some
cases bidirectional]
3. AC/DC converters to connect electric Grid and the on-board DC e-energy
sources for charging [today one way, in future also bidirectional - energy V2G]
 AC/DC converters (on-board battery charging)
 AC/DC converters (off-board DC fast charging)
All these converters have on the DC sides a capacitor filtering unit
Power electronics
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13
Converters to connect
on-board DC e-energy/power sources
and
e-machines
Power electronics
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14
One Quadrant Chopper
DC e-motor
T
i
(inductive load)
u
U
iB
U
D
v
iB
ton
toff
v
U
Vm
V
chopper
I
i
only forward mode with no regenerative braking
The current shape is due to the inductive behaviour of
the e-motor and the ripple amplitude from the switching
frequency combined with the inductance value
Power electronics
Vm 
t on
U  D U
t on  t of f
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15
Four Quadrants Chopper
This chopper structure (also called H Bridge) enables both directions for the current and
voltage supply on the load (the-machine)  it makes possible not only the regenerative
braking but also the reverse speed (and the regenerative braking in reverse speed)
U
T3
D2
T1
D4
Working quadrants
T
V
w
I
i
v
T2
Power electronics
D1
T4
D3
electrical
mechanical
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16
DC/AC Power Converters (Inverters)
While the chopper regulates the output voltage and current amplitudes, the inverter
is able to regulate both amplitude and frequency of the output voltages and
currents (with PWM modulation techniques)
The automotive inverter (Current Regulated VSI) chops the input DC voltage in order
to apply to the e-machine windings waveforms whose first harmonic has the desired:
 frequency (to regulate the e-machine speed)
 amplitude (amplitude/frequency is proportional to the e-machine flux from which it is
possible to regulate the e-machine torque)
PWM: Pulse Width Modulation
VSI: Voltage Source Inverter
Power electronics
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17
Single phase Voltage Source Inverter
T1 e T4 gate signal
ON
T1
T3
D1
VAB
U
iC A
D3
V AB
D2
OFF
B
T4
U for T1 e T 4 on

  U for T 2 e T3 on
ON
OFF
vAB
iC
D4
-U
D1
D4
Power electronics
ON
T2 e T3 gate signal
U
T2
OFF
T1
T4
D2
D3
T2
T3
D1 T1
D4 T4
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18
Inverter: DC side behaviour
The inverter can operate to transfer power and energy both from DC to AC side (the
connected AC e-machine operates as motor) and from AC to DC side (the connected AC
e-machine operates as generator)
the connected AC e-machine
operated as generator
(energy flows from AC to DC)
VDC
the connected AC e-machine
operated as motor
(energy flows from DC to AC)
IDC
Power electronics
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19
Three Phases Inverters (DC/AC Converters)
IGBT based Three Phases
Current Regulated Voltage Source Inverter
Inverter leg
+
Cin
VDC
AC electric
machine
Power electronics
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20
Three phases Voltage Source Inverter
Each of the three inverter legs has one switch in ON mode and one in OFF mode.
Neglecting the commutation transientsonly seven different conditions are possible:
Phase 2
(011)
(010)
(110)
(100)
(000) = (111)
Phase 1
Phase 3
(001)
(101)
In each triplet, the first digit is related to the e-machine
phase 1, the second digit to the phase 2 and the third one
to phase 3.
When the digit is 1 the upper switch is on and the lower
one is off. When the digit is 0 the upper switch is off and
the lower one is on.
000 e 111 configurations are for the e-machine equivalent
(e-machine not externally supplied)
Power electronics
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21
Three phases Voltage Source Inverter
Vll
010
100
001
wt
110
Black line: Phase 1
Red line: Phase 2
Blue line: Phase 3
Power electronics
001
101
Vll: e-machine line to line voltage
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22
Three phases Voltage Source Inverter
Example of commutation status
(100 status)
I DC
+
I
V DC
I/2
-
Power electronics
I/2
AC
e-machine
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23
Three phases Voltage Source Inverter and Modulation
Being the inverter different statuses only 7, the desired behaviour is reached
commutating the switches status at a frequency at least 10 times higher than the AC
machine first harmonic desired one and using the filtering characteristic of the emachine.
The simultaneous regulation of input voltages frequencies and amplitudes asks for
PWM (Pulse Width Modulation) techniques.
The output ripple decreases increasing the switching frequency.
The switch commutations can be:
 previously defined to cancel some undesired higher frequency harmonics (preprogrammed PWM)
 calculated in real time through calculations on the reference output voltage (real
time PWM)
The PWM can be:
 analog PWM (sinus-triangle with or w/o superimposed harmonics)
 digital PWM (Space Vector)
Power electronics
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24
3 phases VSI: PWM sinus-triangle modulation
vS, vtri
p
2p
wt
using the PWM sinustriangle modulation
technique and e-machine
stator phase star
connected, the line to line
rms voltage can be from 0
up to 0.612 times the input
DC voltage (VDC)
Power electronics
vao
wt
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25
3 phases VSI: Space Vector modulation
In the Space Vector modulation solutions, an equivalent reference voltage vector is
positioned in the inverter hexagon.
Referring to the triangle in which the voltage vector is included, it is defined a linear function
of the inverter triplets related to the interested triangle vertexes with proper coefficients in
order to have an average value the closest as possible to the desired voltage vector:
Commutation sequence:
111
110
010
000
010
110






110 (third leg)
010 (first leg)
000 (second leg)
010 (second leg)
110 (first leg)
111 (third leg)
Using the Space Vector modulation technique (or the PWM sinus-triangle with a
reference done summing the desired sinus plus its third harmonic) and e-machine
stator phase star connected, the line to line rms voltage can be from 0 up to 0.707 times the
input DC voltage (VDC)
Power electronics
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26
Six Steps
In the Six Steps modulation technique, only the frequency is regulated and only the inverter
hexagon points are used with a low frequency switching frequency (the same of the first
harmonic desired one) with very positive effects on the inverter commutation losses reduction
and electromagnetic noise production.
On the other side the e-machine losses are highly increased due to the larger current
harmonic content in respect of the PWM based solutions:
Six Steps Output Waveforms
For a proper flux control, a separate DC bus voltage amplitude control is due (with a DC/DC
converter) or its usage has to be limited to the flux weakening region (single ramp).
Power electronics
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27
Inverter: protection, control and regulation
The base protection is implemented in HW mode. All the other protection functions are
implemented in SW mode. The same is for the stability control and regulation.
The SW functions are realised or in analog or digital way (using microprocessors and/or
DSP units).
Thanks to these more and more powerful units, the applied control and regulation
techniques are highly sophisticated using e-machine model based approaches (rotating
axis models) to optimise the working conditions for dynamics and/or performance and/or
efficiency targets.
Also sensorless control solutions are increasingly used or to avoid the use mechanical
sensors or improve the fault tolerance of the electric drives.
DSP: Digital Signal Processor
Power electronics
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28
Power electronics: e-machine control structure
DC Bus
Switching
Functions
Control
Set points
Set-points
adaptation
REF.
• system protection
(limitations)
• control (lops)
• regulation
Modulator
(i.e.: analog or digital
PWM or digital
Space Vector)
Feed-Back
• signal passage
• estimator
• observer
• amplifier
• reduction
DSP based Control Board
Power electronics
Power
Electronics
Data Acquisition
• transduction
• filtering
• conditioning
Electrical and
thermal
measures
Mechanical
measures
Electric
Machine
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29
Example of DC/AC VSI (Voltage Source Inverter)
CRF
Main features:
• 600V - 400A IGBT
• Hard Switching
• Switching frequency: > 10 kHz
• Current sensors:
• 2 AC (e-machine phases)
• 1 DC (electrical source)
• Liquid cooling
• Texas TMS320 F2407 DSP
• CAN bus
Power electronics
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30
Example of DC/AC VSI (Voltage Source Inverter)
DC Input (+)
DC Input (-)
Signal connector
(analog and
digital I/O)
AC three phases connectors
Liquid cooling
(inlet and outlet)
Power electronics
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31
VSI (Voltage Source Inverter): Internal Layout
Cooling Fans
Control board
AC current
sensors
Drive board
DC bus
capacitors
IGBT modules
Power electronics
Heat Sink
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32
VSI (Voltage Source Inverter): Internal Layout
Toyota Prius 2010: double inverter with integrated bidirectional step-up
Plus HV-12V galvanically insulated step-down DC/DC converter
Liquid cooling
Power electronics
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33
Power switches sizing criteria
Power switches sizing and cost directly depend on their apparent (complex)
power (max applicable voltage multiplied for max continuous current they can
sustain).
For each power switch voltage class (for IGBTs: 200 Vdc, 600 Vdc, 800 Vdc and
1200 Vdc) the cost depends on the current.
To correctly keep into account overshoots and spikes, typically the max applied
continuous voltage is 2/3 of the max switch voltage (for instance for a 600 Vdc
IGBT it means 400 Vdc. If the DC source is a battery, considering the braking
condition related to the highest possible voltage, the correct battery rated voltage
has to be around 300 Vdc. Lower battery voltages would mean, for the same
power, higher currents).
For the AC e-machines, a right sizing of the switch means to have the peak value
of the first harmonic of the max transient phase current closest as possible to the
switch size current
Power electronics
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34
Power switches: Safe Operating Area
Current
Safe Operating Area
Switch current not
fully utilised
Correct usage area
for hard switching
Inverter without snubbers
Voltage
Switch voltage not fully utilised
Power electronics
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35
Power switches: Thermal Sizing
For all the power electronic devices, the max allowable current depends on the capability
to remove the heat (due to the conduction and switching losses) from the silicon area.
This capability is related to:
 the cooling typology (natural air, forced air, liquid…)
 the thermal coupling with the heat sink (thermal resistance)
 the maximum allowable switch silicon junction temperature: today the
standard value for automotive IGBTs is around 120°C and in the next generations it
will be increased to around 200°C (as already today for the automotive power
diodes)
 the possible presence of commutation assistance circuits (snubbers, clamps…)
and/or the usage of modulation techniques to limit the commutation losses
(soft switching…)
Power electronics
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36
Power switches: Thermal Sizing
Insulating Substrate
copper
copper
ceramic
copper
Power electronics
dielectric
aluminium
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37
Traction Inverters: enhanced cooling solutions examples
New Toyota Prius double side liquid cooling
Power electronics
GM Chevy Volt oil cooling channels
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38
DC/DC converters
for
electrical adaptation
Power electronics
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39
DC/DC converters for electric adaptation
DC/DC converters for electrical adaptation (typically voltage adaptation) between:
 electric energy/power sources (for instance: FC System and power batteries
or energy batteries and supercaps) [one or bidirectional]
 electric energy/power sources and converters of the first family for EVs
and/or HEVs (in general for AC drives) [bidirectional]
 electric energy/power sources and electric loads (vehicle auxiliaries) [one, in
some cases bidirectional]
Usually these devices do not need electrical galvanic insulation between input and
output terminals. Only the ones of the third typology need it when they couple a
Class B high voltage (> 60 VDC) side with the on board 12 VDC net (Class A)
Power electronics
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40
DC/DC converters for energy/power sources adaptation
FC System and batteries example
Battery
Pack
Inverter
unidirectional
DC/DC
converter
Fuel Cell
System
Power electronics
AC
Electric
Machine
Fuel Cell
System
Inverter
AC
Electric
Machine
bidirectional
DC/DC
converter
Power Buffer
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41
DC/DC converters for energy/power sources adaptation
Toyota MIRAI FC Boost Converter
One way step-up DC/DC converter
Power electronics
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42
Bidirectional Buck-Boost DC/DC step-up converter
Boost DC/DC step-up converter
Buck DC/DC step-down converter
VDC
IDC
L
D2
Vin
C1
T1
D1
C2
Vout
VDC
IDC
Power electronics
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43
Three Phases Inverters with DC/DC step-up
Voltage Source Inverter
with integrated bidirectional DC/DC step-up converter
DC/DC Step-up
+
VDC in
AC
e-machine
-
Power electronics
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44
Three Phases Inverters with DC/DC step-up
Toyota Prius 2004 integrated double inverter
with the step-up Buck-Boost bidirectional DC/DC converter
main
capacitors
IGBT
(below)
to the e-motor
Power Control Unit (PCU)
Power electronics
Inductance
to the
generator
to the batteries
Advantages:
 higher e-drives efficiency
 lower PCU costs
 higher e-motor power
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45
DC/DC converters to adapt energy sources and vehicle loads
BEVs architecture
Inverter
Battery Pack
AC
Electric
Machine
Step-down
DC/DC
Converter
12 V
auxiliaries
12 V
battery
Power electronics
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46
Galvanically insulated bidirectional DC/DC converter
VDC
IDC
T1
Vin
T3
C2
C1
T2
Vout
T4
(planar transformer solution with intermediate plug)
Power electronics
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47
Converters to connect
electric grid
and
the on-board battery
Power electronics
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48
On board AC-DC battery charger
MAIN SWITCH
HV
BATTERY
SYSTEM
INVERTER
TRACTION
E-MOTOR
MECHANICAL
TRANSMISSION
MAIN SWITCH
Charging Port
DC/DC
CONVERTER
AC/DC On Board
Battery Charger
12 V AUX
12 V BAT.
HVBS: High Voltage Battery System
OBCM: On Board Charger Module
RCD: Residual-Current Device
LOI: Loss Of Insulation circuit
RCD
240 V - 50 Hz ELECTRIC GRID
Control and
Communication
Power electronics
Control and
Communication
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49
Off board DC fast charge station
AC and DC Combo connectors
DC-Fast Charge Station
Control and
Communication
Vehicle
Power electronics
Control and
Communication
HVBS: High Voltage Battery System
LoI: Loss of Insulation
IMD: Insulation Monitor Device
RCD: Residual-Current Device
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50
Power Electronics Trends
Power electronics
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51
Power Electronics Trends
Voltage Technology
DC/AC power converter
DC/ACpower
powerconverter
bridge
DC/AC
Energy
Source
Dead Times
Compensation
idref
> 100 V
IGBT
AC
machine
Control Unit
iqref
48 V
Power
Mosfet
vdref
vqref
Syncronous
Current
Regulator
dq  ab
~
e
id
ab  dq
iq
va ref
vb ref
Space
Vector
Modulator
m2
m3
wm
Luenberger
Flux
Observer
ia
ib
m1
ab  ab
ia
ib
VDC
Trends
Commutation time reduction
Higher operating temperature Tj 200°C
Lower conduction losses:
• lower Rdson for Mosfet
• lower VCEsat for IGBT
Compliant with harsh automotive
environment
Integrated packaging
Control Trends
Digital control techniques
Direct Torque Control (DTC) approaches
Mechanical Sensorless controls
Hybrid Modulation Techniques:
• Digital PWM (Space Vector) at low speed
• Six Step at high speed
Reduced commutation modulation approaches
Power electronics
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52
Power Electronics Trends
Power Electronics: New Materials and Processes
• Power Switches: standard solutions (silicon based PowerMosfet for Class A
applications and IGBT for Class B applications) will be progressive substitute
with SiC (Silicon Carbide) and GaN (Gallium Nitride) based switches to
improve the performance, reduce the losses…
• Switch dies to heat sink coupling improvement to reduce thermal
resistance and simplify the cooling part (enhanced gluing solutions, direct
cooling, two side cooling, inert materials usage (i.e. 3M one)…)
• wider usage of thermally conductive plastics with electric insulation
properties to make the heatsinks lighter, cheaper and simpler
• Graphene usage in the signal electronics
Power electronics
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53
Power switches: enhanced liquid cooling solutions
Power electronics
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54
Power Electronics Trends
Toyota evolution
Prius 2015
SiC impact on inverter dimensions
Power electronics
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55
IFP School
PWT MASTER MODULE 1-2020
E-Drives and Controls
Vittorio Ravello
Rueil-Malmaison (Paris) 26-30 October 2020
E-Drives and Controls
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1
Electric Drive
Electric Drive
Power electronics
Electrical
Power & Energy
Source
Power Stage
Electric
Machine
Control Stage
Mechanical sensors (speed, position)
Electric sensors (DC voltage, AC voltages, DC current, AC currents)
Thermal sensors (stator windings, power electronics heatsink…)
E-Drives and Controls
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2
Traction E-drives for EVs and HEVs:
Electrical and Mechanical Behaviour Curve
and Supply Strategies
E-Drives and Controls
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E-Drives: Control Aims and Mechanical Behaviour
The application of “modern control” techniques to the e-drives (power electronics
plus electric machine) makes possible to fully exploit the e-machine potentialities in
terms of:
 maximum continuous performance (S1)
 maximum transient performance (S2 – x minutes)
 steady state error minimisation (“zero steady state error”)
 dynamic response (fast, limited overshoot)
 conversion efficiency (full chain)
 conversion quality (ripple, noise, vibration...)
Typically an e-drive, acting as a motor, is regulated in two working regions:
 constant torque from 0 to base speed
 constant mechanical power from base to max speed
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E-drive: mechanical behaviour
base speed
120,0
Constant Mechanical Power Region
100,0
80,0
Torque
Constant
Torque
Region
60,0
Mechanical Power
40,0
20,0
0,0
0
2000
4000
6000
8000
10000
12000
speed [rpm]
E-Drives and Controls
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AC E-Drives: supply strategy
Constant Torque Region:
the supply strategy (voltage amplitude/frequency law) is a straight line: the machine
flux is (can be) kept constant.
As a consequence, torque is directly proportional to:
 the stator current for PM excited e-machines (as for instance the AC SMPM
synchronous one) or rotor wounded synchronous e-machines
 a component of the stator current (called q axis current), while the other (d axis
current) generating the machine flux is kept constant, for machines in which it is
not possible to decouple the electromagnetic excitation (as for instance the
induction one)
The output behaviour is the same of a PM excited or separately excited DC machine
with constant flux regulation.
SMPM: Surface Mounted Permanent Magnet
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AC E-Drives: supply strategy
Constant Power Region:
the voltage amplitude is kept constant while the frequency increases proportionally
to the speed. As a consequence, the e-machine flux decreases accordingly to the
torque (flux weakening).
In the case of PM excited e-machines, this behaviour can be obtained producing a
counteracting magnetic field through the stator currents.
The flux weakening option enables an inverter sizing reduction in terms of kVA (that
means also a cost reduction).
On the other hand, the maximum e-machine power is limited to the base speed one
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E-drive: e-machine supply strategies (single ramp)
Voltage
amplitude
Flux
amplitude
0
2000
4000
6000
8000
10000
12000
speed [rpm]
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E-drive: e-machine supply strategies
Voltage amplitude [V]
base speed
flux weakening
full flux
[rpm]
0
E-Drives and Controls
2000
4000
6000
8000
10000
12000
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AC E-Drives: thermal behaviour
For each speed value, it is possible to define from a thermal point of view:
 continuous performance (S1): obtainable without time limitations
 transient performance (S2 - X min): obtainable for a limited time. For instance:
5 minutes (S2-5 min), 3 minutes (S2-3 min) or 2 minutes (S2-2 min)
The transient performance can be defined starting from e-machine at ambient
temperature or at an higher temperature (defined through a percentage of the rated
torque condition. For instance: 67% or 100%).
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E-drive: continuous and transient regions
250
Transient torque
200
Continuous mechanical power
150
Continuous torque
Transient mechanical power
100
50
0
0
2000
4000
6000
8000
10000
12000
speed [rpm]
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Induction motor: continuous, transient and max performance
800,0
Pull out torque
loci (1/w²)
Torque [Nm]
600,0
400,0
200,0
0,0
0
2000
4000
6000
8000
10000
12000
speed [rpm]
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AC E-Drives: performance vs. DC voltage
The inverter input DC voltage (DC bus) value has the following impacts:
 if higher than the sizing voltage, it enlarges the constant torque region
 if lower than the sizing voltage, it reduces the constant torque and power
regions, creating a third region (called Reduced Power Region) in which the emachine output power is decreasing as 1 / speed and the torque as 1 / speed2
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E-drive: output power with increasing DC voltage
base speed
120
100
increasing VDC
80
performance @ sizing VDC
60
40
20
0
0
2000
4000
6000
8000
10000
12000
speed [rpm]
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Induction motor based E-drive: usage areas
Constant
Torque Region
350
Constant
Power Region
base speed
Reduced
Power Region
critical speed
max operational
speed
300
250
200
150
100
50
0
0
2000
4000
6000
8000
10000
12000
speed [rpm]
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Traction E-drives for EVs and HEVs:
Control Basics
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16
Open and Close Loop Controls
Open loop controls are existing and sometimes used (i.e. V/Hz (“volt on hertz”)
control) with limitations on the control quantities (i.e. currents) for protection
purposes.
Close loop controls are preferred in the main part of the application cases to make
the system more robust in respect of noises and parameter variations.
General close loop
control block diagram
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Cascades Control
The closest loop is the torque loop (typically it is a current loop). It is the fastest
loop. It is realized through a torque (current) controller and an indirect torque feedback (usually currents) from the “plant”
The speed loop is built-up on the torque one. It is a slower loop. It is realized with a
speed controller and a speed feed-back from the “plant”
The position loop is built-up on the speed one. It is the slowest loop. It is realized
with a position controller and a position feed-back (direct or not) from the “plant”
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Proportional-Integral (PI) Controller
In torque and speed loops, a pure proportional controller (no integral contribution input)
leads to steady-state errors.
With cascade schemes, the design has to be performed starting from the inner loop up to
the more external one, considering the inside loops as ideal
Further elements to be considered:
• Feed-forward techniques: to speed-up the dynamic response
• Limits effects: non linearity behaviour
• Anti wind-up integration: suspend integration when output saturates
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19
DC electric machine - Equivalent circuit
Rotor (armature) circuit
ia(t) +
Ra
La
•
•
•
•
ua(t)
ea(t)
E-Drives and Controls
ua(t): armature voltage [V]
ia(t): armature current [A]
ea(t): induced emf [V]
Ra: armature resistance [W]
• La : armature leakage inductance [H]
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DC electric machine - Steady state relations
Va = E + R a  Ia
(armature circuit relation)
E = KFw
(emf-flux-speed relation)
Tm = K  F  Ia
(torque-flux-current relation)
where:
• Va: armature voltage [V]
• E: induced emf [V]
• Ra: armature resistance [W]
• Ia: armature current [A]
• K: constant coefficient
• F: magnetic flux [Wb]
• w: rotor speed [rad/s]
• Tm: torque [Nm]
Speed control is based on the armature voltage amplitude control
Torque control is based on the armature current amplitude control
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21
DC electric machine - Speed control example
dia (t)
+ e(t)
va (t) = Ra ia (t) + La
dt
Tem(t) = kT  ia (t)
e(t) = kE  wm( t )
dwm(t)
+ TL (t)
Tem(t) = J 
dt
Modeling of DC e-machines and mechanical load combination
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DC electric machine - Torque PI control
PWM (Pulse Width Modulation) gain
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23
DC electric machine - Speed control
Chopper
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24
Direct-quadrature-zero transformation
Three phases to stationary two phases
b axis
b
a axis
a
c
The matrix transforms a three phases reference (a-b-c) in a stationary two phases
reference (a-b) with a third homopolar component whose axis is orthogonal in
respect of the a-b axes plane and with a axis overlapped with a axis. If the three
phases system is balanced, the homopolar component is equal to 0.
Using this reference, a three phases e-machine can be represented as an
equivalent two phases e-machine simplifying its analysis and control.
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Direct-quadrature-zero transformation
Stationary two phases to rotating two phases
The rotating matrix transforms a stationary two phases reference (a-b) in a
rotating two phases reference (d-q).
The q angle is the one between the stator and the rotor. w is the rotor angular speed.
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AC electric machines control
In the AC machines to try to reproduce (as much as possible) the typical DC emachines behaviour with torque equal to the scalar product of stator flux and rotor
current, the control has to operate to keep a 90 degrees angle between flux and
current vectors through the “so called” Field Oriented Control (FOC) techniques.
In particular:
• in the synchronous e-machines, the rotor flux vector speed is synchronous with
the rotor speed. Torque is proportional to the stator current and to maximise it, the
stator current vector has to be “positioned” 90 degrees in advance to the rotor flux
vector (that is rotating at the same speed)
• in the asynchronous (or induction) e-machines, the stator current vector has one
component on the rotating d axis and one on the rotating q axis. The first is
proportional to the stator flux while the second to the rotor current. The stator flux
and rotor current interaction generates the torque. To maximise the dynamic
behaviour, the d axis current contribution is kept constant at its max value and the
torque variations are managed through the q axis current contribution. This
decoupling can be completely obtained in linear region up to the saturation
conditions when the cross coupling effects take place.
For these e-machines slip and rotor temperature compensations have to be applied
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AC electric machines control: flux and torque
In general, in the AC machines neither flux nor torque are directly measured. They
can be very precisely derived from other electric and mechanical quantities.
In particular flux can be observed or estimated:
• Observation techniques are based on stator voltage integration and usually
applied for medium-high speed conditions where the stator voltage largely
depends on the induced emf (electro motive force) and the stator voltage drop
has a minor influence
• Estimation techniques are based on e-machine model (with related identified
parameters) plus current measures and usually applied for low speed conditions
where the stator voltage largely depends on the stator voltage drop and the
induced emf (electro motive force) and is very low
The two techniques are usually combined on the speed basis to effectively cover all
the range conditions.
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AC induction e-machines: example of speed control
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AC electric machines control: Field Oriented Control (FOC)
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AC e-machines control solutions
In high performance industrial applications, where the dynamic response is the
most important requirement, Direct Torque Controls (DTC) have been developed
and more and more applied.
On the contrary, in the case of traction e-drives, this extreme dynamic behaviour is
in many cases not requested and sometimes to be avoided not to have discomfort
problems.
For e-drives based on e-machines with flux produced by currents, starting from this
consideration and taking also into account the need to maximise the efficiency to
reduce consumption (hybrids - HEVs) and/or increase the EV range (electric
vehicles - EVs and plug-in hybrids - P-HEVs in EV mode), Optimal Flux Control
techniques can be effectively applied (mainly in the Constant Torque Region).
In practice, not only the q-axis current component but also the d-axis one is
dynamically regulated to have, for each torque load level, the proper flux
maximising the e-machine efficiency (accepting a torque response reduction
anyway not negatively impacting on the desired vehicle acceleration)
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31
AC e-machines control solutions
Optimal Flux Control impact on the e-machine efficiency
100
100
92 %
92 %
90 %
90 %
88 %
90
88 %
90
86 %
86 %
84 %
80
84 %
80
82 %
82 %
80 %
80 %
78 %
70
78 %
70
76 %
76 %
60
74 %
72 %
70 %
68 %
50
66 %
64 %
40
62 %
Coppia [Nm]
Coppia [Nm]
74 %
60
72 %
70 %
50
68 %
66 %
64 %
40
62 %
60 %
58 %
30
56 %
60 %
30
58 %
54 %
52 %
20
50 %
56 %
54 %
20
52 %
48 %
10
46 %
1000
2000
3000
4000
5000
6000
7000
8000
9000
velocita'[rpm]
Sizing flux efficiency map
E-Drives and Controls
10000 11000 12000
50 %
10
48 %
44 %
1000
2000
3000
4000
5000
6000
7000
8000
9000
10000 11000 12000
46 %
velocita'[rpm]
Optimal flux strategies efficiency map
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32
AC e-machines control solutions
Sensorless Controls
Also (mechanical) Sensorless Controls techniques are becoming more and more
popular to avoid the speed-position sensor or, for systems keeping it, giving an
higher reliability and fault tolerance in case of sensor faults. This solution is
particularly challenging in case the e-drive has to produce traction torque at zero
speed condition with positive applied load torque (as for instance in case of an EV
starting on a slope or with hill holder mode)
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33
Inverter: protection, control and regulation
The base protection is implemented in HW mode. All the other protection functions
are typically implemented in SW mode. The same is for the stability control and
regulation.
The SW functions are realized or in analog or digital way (using microprocessors
and/or DPS (Digital Signal Processor) units. Today the second option is the most
common.
The e-drive has not only to manage the safety of its parts (inverter, e-machine,
sensors…) but also the safety of the electric source.
E-Drives and Controls
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34
Power electronics: e-machine control structure
DC Bus
Switching
Functions
Control
Set points
Set-points
adaptation
REF.
• system protection
(limitations)
• control (lops)
• regulation
Modulator
(i.e.: analog or digital
PWM or digital
Space Vector)
Feed-Back
• signal passage
• estimator
• observer
• amplifier
• reduction
DSP based Control Board
E-Drives and Controls
Power
Electronics
Data Acquisition
• transduction
• filtering
• conditioning
Electrical and
thermal
measures
Mechanical
measures
Electric
Machine
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35
Inverter: protection, control and regulation
In case of batteries as DC source, the torque request has to be satisfied but, both in
motor and regenerative braking mode, taking into account respectively the lowest and
higher possible battery voltage level.
For instance, in braking mode, to try to guarantee the requested braking torque without
damaging the batteries, a double max voltage level is defined. If the voltage overcome
the first limit, the braking torque is progressively reduced to avoid to overcome the
second limit and an instantaneous lack of torque at the shaft (the same logic is applied
also for the traction torque with two min voltage limits to protect the battery and avoid an
instantaneous lack of traction torque with possible vehicle behavior safety problems)
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36
Traction E-drives for EVs and HEVs:
E-machine vs. Power Electronics Sizing
Compromises and Modulation Techniques
E-Drives and Controls
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37
Three Phases Inverters (DC/AC Converters)
IGBT based Three Phases
Current Regulated Voltage Source Inverter
Inverter leg
+
Cin
VDC
AC electric
machine
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38
AC E-Drives: sizing compromises
Fixed as a constraint the supply DC voltage, to have the desired flux weakening
range (max speed / base speed) it has to be identified a compromise solution
between:
 the e-machine dimensions (higher is the ratio between the maximum
electromagnetic and transient torques at base speed, higher are the emachines dimensions)
 the maximum phase current, from whose peak value the switch current size
(and cost) are directly linked
For instance, if the required current to satisfy the desired performance were lower
than the best switch one (whose possible sizes are not continuous: 50 A, 100 A, 150
A, 200 A, 300 A, 400 A, 600 A…), it is possible to use a part of the allowable voltage
between base and max speed to have the same performance with a lower size emachine (double ramp regulation)
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39
E-drive e-machine supply
Single and double ramp regulation
Single ramp
Double ramp
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40
AC E-Drives: single and double ramp regulation
For instance for a three phases induction machine:
Tpo
Vb2
s =  = r 
Tmax
Vmax2
where:
 Tpo pull-out torque at base speed
 Tmax maximum transient torque at base speed
 r desired flux weakening range (max speed / base speed)
 Vb base speed e-machine line to line voltage
 Vmax max allowable e-machine line to line voltage
If for instance the desired r = 4 and the switch current is 20% higher than the required
one:
 single ramp: Vb = Vmax  s = 4
 Double ramp: Vb ~ 0,8 Vmax  s = 2,56
as a consequence, using the double ramp, the same IGBTs, with the same e-drive
performance, enables an e-machine size reduction of 36%
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41
AC E-Drives: modulation techniques
Vll_rms = k (Vdc_min – 2 VCE_sat) AM
where:
 Vll_rms : 3 phases e-machine line to line voltage (RMS value) [V]
 for star connected e-motor:
 k = 0,612 (analog sinusoidal PWM)
 k = 0,707 (analog sinusoidal plus third harmonic PWM or digital Space Vector)
 k = 0,78 (six steps at low frequency)
 Vdc_min : minimum inverter DC input voltage [V]
 VCE_sat: IGBT saturation voltage in ON condition
 AM: coefficient < 1 keeping into account the commutation real behaviour
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42
Inverter: VDC - Vll_rms relations
Analog sinusoidal PWM (e-motor star connected): k = 0,612
Vphase_rms = VDC_min / (2 x 2)
Vphase
VDC_min
Vll_rms = VDC_min x 3 / (2 x 2)
Analog sinusoidal plus third harmonic PWM or digital Space Vector (e-motor star
connected): k = 0,707
1st harmonic
3rd harmonic
1st+3rd harmonics
Same as analog sinusoidal PWM + 15% (2/3)
Vll_rms = VDC_min / 2
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43
Inverter: VDC - Vll_rms relations
Six steps (e-motor star connected): k = 0,78
Same as analog sinusoidal PWM x (4 / )
Vll_rms = VDC_min x 6 / 
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44
Double inverter
with or without intermediate step-up
Sizing considerations
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45
Double Direct Inverter (without) intermediate step-up
AC
AC
Battery
PAC
DC
AC
AC
Pbatt
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46
Double Inverter with intermediate step-up
AC
AC
DC
DC
Battery
PAC
DC
AC
AC
Pbatt
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47
Three Phases Inverters with DC/DC step-up
Voltage Source Inverter
with integrated bidirectional DC/DC step-up converter
DC/DC Step-up
+
VDC in
AC
e-machine
-
The DC/DC converter manages the voltage amplitude. The inverter its frequency
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Comparison
Hypotheses:
 efficiencies are not considered
 Pbatt = ½ PAC
 without step-up: Vdc min = 250 V
 with step-up: Vdc min = 500 V (inverter DC side)
 comparison with same PAC
Direct System (without step-up):
 12 IGBT (6 for each inverter): 600 V and I ampere (Vdc min = 250 V)
System with step-up:
 12 IGBT (6 for each inverter): 600 V and I/2 ampere (Vdc min = 500 V)
 2 IGBT (step-up): 600 V and I/2 ampere (Vbatt = 250 V and Pbatt = ½ PAC)
 (System with step-up power / Direct System power) = 7/12
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49