1/10/2014
Power Electronic Circuits
Prof. Daniel Costinett
ECE 482 Lecture 2
January 10, 2014
Power Electronics in EVs

12V
battery
High voltage
storage system
(~300V)
Conventional low
power loads
DC/DC converter
LV
Battery
HV Battery
Battery
charge/
discharge
unit
Propulsion
system
Electric
machine
PE converter
Battery
charge/
discharge
unit
14V DC bus
DC/AC inverter
Air‐conditioning system
PE converter
Power steering
PE converter
Electric motors
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PHEV/EV Drivetrain
Battery Management System
SOCmax
SOCmin
+
Vpack
–
• BMS monitors batteries to ensure operation within safe limits of
• Charge/discharge current
• State‐of‐Charge (SOC)
• (Temperature, SOH, … )
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Battery Mismatch
SOCmax
SOCmin
+
Vpack
–
• EV battery consists of many (100’s) series battery cells (LFP, Li‐ion, NiMH)
• Cells share a charging and discharging current, but may have mismatches in series
resistance, capacity, operating temperature, health, or dynamics
• Cells binned by manufacturer to limit mismatch at beginning‐of‐life
Battery Management System
SOCmax
SOCmin
+
Vpack
–
• Discharge is limited by the first cell to reach the minimum allowable State‐of‐
Charge (SOC).
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Battery Management System
SOCmax
Inaccessible
Capacity
SOCmin
+
Vpack
–
• Discharge is limited by the first cell to reach the minimum allowable State‐of‐
Charge (SOC).
• Effective pack capacity limited to the capacity of the lowest cell (in Amp‐hours)
Battery Management System
SOCmax
Uncharged
Capacity
SOCmin
+
Vpack
–
• When recharged, charging is stopped when the first cell reaches maximum
capacity, leading to incomplete charging of some cells and lower total pack
capacity
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Battery Management System
SOCmax
SOCmin
+
Vpack
–
• Option 1: Dissipate, then recharge
• Repeat a number of cycles to balance all cells at full charge
Battery Management System
SOCmax
SOCmin
+
Vpack
–
• Option 2: Redistribute
• Requires more advanced circuits
• Can be run continuously, during runtime
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(Optional) Bidirectional DC‐DC
Converter
• A DC‐DC converter to boost
battery voltage is included in
many EVs
• Allows higher η operation
of ED
• Wider operating range
• Lower pack voltage
Reference: Oak Ridge National Lab, “Benchmarking of Competitive Technologies”
DC‐AC Motor Drive
• Motor drive generates three, 120° out of phase
signals to drive motor windings
• Individually operate as three individual electronic
power converters
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Growing Popularity of E‐bikes
Electric Bicycles Worldwide
• E‐bikes accounted for $6.9 billion in revenue in 2012
• By utilizing sealed lead‐acid (SLA) batteries, the cost of e‐
bicycles in China averages about $167 (compared to $815 in
North America and $1,546 in Western Europe)
• China accounts for 90% of world market
• Western Europe accounts for majority of remaining 10%
despite $1,546 average cost
• North America: 89,000 bicycles sold in 2012
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Electric Bicycle Platform
Power Conversion
and Control
Battery
Electric Motor
Electric Bicycle System
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System Structure
Battery
BMS
3‐φ
Inverter /
Driver
Boost
DC‐DC
Converter
D
Vout
g1‐6
Throttle
Brake
Filtering
and
Control
Iabc
3‐φ PWM
Controller
PWM
Controller
Motor
θabc
Vref
fref
Experiment 1
Battery
Motor
BMS
θabc
•
•
•
•
Identification and characterization of motor
Modeling of system using simulink
Derivation of model parameters from experimental data
Specification of performance for power electronics
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Experiment 2
Battery
BMS
Boost
DC‐DC
Converter
D
Motor
Vout
θabc
•
•
•
•
Open‐loop operation of Boost converter
Inductor design
Converter construction and efficiency analysis
Bidirectional operation using voltage source / resistive load
Experiment 3
Battery
BMS
Boost
DC‐DC
Converter
D
Motor
Vout
PWM
Controller
θabc
Vref
• Closed loop operation of boost converter
• Feedback loop design and stability analysis
• Analog control of PWM converters
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Experiment 4/5
Battery
BMS
3‐φ
Inverter /
Driver
Boost
DC‐DC
Converter
D
Vout
Motor
g1‐6
3‐φ PWM
Controller
PWM
Controller
θabc
Vref
• Circuit layout and PCB design
• Device selection and implementation according to loss analysis
• Basic control of BLDC motors
Experiment 6
Battery
BMS
3‐φ
Inverter /
Driver
Boost
DC‐DC
Converter
D
Vout
g1‐6
Throttle
Brake
Filtering
and
Control
Iabc
3‐φ PWM
Controller
PWM
Controller
Motor
θabc
Vref
fref
• System‐level control techniques
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Example System Implementation
Experiment 7
Battery
Charger
and BMS
ZVS
Conv.
Battery
BMS
D
Solar Cell
3‐φ
Inverter /
Driver
LED
Driver
Throttle
Brake
Pedal
Torque
Filtering
and
Control
Vout
g1‐6
Iabc
Vector
Controller
PWM
Controller
Motor
θabc
Vref
fref
• System improvements
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Characterize
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Test
Design Expo
• No final exam
• Demo operational electric bicycles with
system improvements
• Competition to determine the most efficient
and well‐controlled system
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Electric Bicycle Safety and Law
• Traffic Law:
• Electric motor with power output not more than
1000 W
• Not capable of propelling or assisting at greater
than 20 mph
• No helmet laws for riders over age 16; you
may request one at any time
• Read Tennessee bicycle safety laws on website
General Safety
• Lab will work with high voltages (Up to 100 V)
• Will use various machinery with high power
moving parts
• Use caution at all times
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Introduction to Vehicle Dynamics
Vehicle as a Feedback Sytem
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Basic Vehicle Dynamics
Angle of inclination
H 
  tan 1  
L
Slope or “grade”
H
Z  
L
g  9.81 m/s2
Air density
  1.204 kg/m3
Rolling resistance
coefficient Cr
Aerodynamic drag
coefficient Cd
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Rolling resistance coefficient Cr
Aerodynamic drag coefficient
Cd
Reference: Mehrdad Ehsani, Yimin Gao, Sebastien E .Gay, and Ali
Emadi, Modern Electric, Hybrid Electric, and Fuel Cell Vehicles, CRC
Press 2004.
Chapter 2
Typical Performance Specifications
•Cruising (v = const) specs
–Top cruising speed on a flat road: vmax
–Gradeability: ability to ascend a road of grade Z (in %) at a cruising speed vzmax
•Acceleration specs
–Time ta it takes to accelerate from vs to vf Typical: vs = 0 mph to vf = 60 mph
(100 km/h) in ta seconds
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Cruising on a flat road
Pv  Fv v 
1
dv
Cd Av v 3  Cr M v gv  M v v
2
dt
Engine Traction Characteristics
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Acceleration Spec
Mv
dv
1
 Fv  Cd Av v 2  Cr M v g
2
dt
Engine Power Rating
Pv 


1 Mv 2
1
2
3
vb  v f  Cd Av v f  Cr M v gv f
2 ta
2
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