1
Inverters &
DC/DC
Converters
High Voltage Safety
Danger
High Voltage
• Contact with voltage of less than
50 volts is unlikely to cause injury.
• Voltages above 50 volts are
potentially deadly.
• Anytime you work on and around
electrical systems that have
voltages above 50 volts proper
safety procedures must be
observed to avoid injury.
2
PPE – Personal Protective Equipment
• High Voltage gloves with leather
covers
• Test gloves for tears and punctures
before use
• Gloves need to be tested annually
by an approved glove testing facility
Test Date
• Safety Glasses
• Leather work shoes
3
CAT III DVOM
CAT III
rating
• A CAT III DVOM with
CAT III test leads is
required when testing
components of the high
voltage system
4
Remove the service plug
HV rubber gloves must
be worn when removing
the service plug..!
• The service plug disconnects
the HV battery from the rest of
the electrical system
• The service plug is mounted
on the HV battery assembly
cover
• Make sure that the vehicle is
turned off and the ‘ready’ light
is off before removing the
service plug
5
6
Check voltage after removing service
plug
• Before doing any work
on the HV system check
the voltage at the HV
battery cable connections
• It should be no more than
a few 10ths of a volt
HV Safety
• High voltage cables connect the inverter to the battery
and motor generator.
• High voltage electrical cables are identified by the
orange harness cover.
• Never touch these cables without first removing the
battery service plug…!
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8
Inverter function
• The inverter converts high
voltage DC current from the
high voltage battery array into
AC current that is synchronized
to the operating speed of the
traction motor[s]
• During regenerative braking the
inverter converts the AC current
from the stator coils into DC
current that is stored in the high
voltage batteries
Image courtesy of General Motors Corp.
9
Inverter Voltage regulation
• The inverter can step
down voltage level
applied to the HV batteries
without using a
transformer.
• The inverter can also
adjust the HV [high
voltage] charging voltage
so that the battery array is
not overcharged or
undercharged
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DC-DC converter
• The DC-DC converter converts high voltage DC current
from the HV battery array into 14 Volt DC current that is
used by the vehicles conventional electrical system
Connector for
high voltage
battery cables
14 Volt DC
output
The DC-DC Converter is normally located
inside the inverter case or underneath it
11
IGBTs
Electrical
symbol for an
IGBT
• Integrated Gate Bi-Polar Transistor
• Function as high speed, solid state
switches to convert DC voltage into
AC to power the traction motor
• Since power can flow through the
IGBT in either direction the IGBT
also can converted AC voltage
generated in the stator coils into DC
current to recharge the battery
How IGBTs convert DC current to AC
+ 300 V
- 300 V
+ 150 V
- 150 V
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• The inverter electronic
controls turn the IGBTs
on and off to vary the
DC voltage pulse width
• The effective current is
similar to an AC sine
wave
• The IGBT also limits
voltage by reducing the
pulse width
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Inverter construction
• An inverter is made up
of 6 IGBTs and is
similar in operation to
the rectifier in an
alternator
• 6 high current diodes
are connected in
parallel with the IGBT
• 3 of the IGBTs are connected to the HV battery
positive terminal and 3 are connected to the
negative terminal
+B
Stator
-B
Inverter operation –
forward
Motor / Generator
control module
1st
phase – drive
Battery current flows
through IGBT Q1 to
stator terminal U,
through the stator
windings, then back to
the battery through
terminal W and IGBTQ4
14
High voltage
battery array
+B -B
Q1
U
Q4
Stator
Windings
W
V
Inverter operation –
forward
Motor / Generator
control module
2nd
phase – drive
Battery current flows
through IGBT Q3 to
stator terminal W,
through the stator
windings, then back to
the battery through
terminal V and IGBT Q6
High voltage
battery array
+B -B
Q3
U
Q6
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Stator
Windings
W
V
Inverter operation –
forward
Motor / Generator
control module
3rd
phase – drive
Battery current flows
through IGBT Q5 to
stator terminal V,
through the stator
windings, then back to
the battery through
terminal U and IGBT Q2
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High voltage
battery array
+B -B
Q5
U
Q2
Stator
Windings
W
V
Inverter operation – Regenerative braking –
Phase During regenerative braking current generated in the stator
winding U-V passes through Q5 to the HV battery +B terminal
High voltage
battery array
Current from the battery
negative terminal passes
through Q2 to re-enter
the stator windings at
terminal U
Motor /
Generator
control
module
+B -B
Q5
U
Q2
1st
Stator
Windings
W
V
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Inverter operation – Regenerative braking – 2nd
Phase As the rotor turns the next winding that has current induced is
W-U. Current flows from terminal U through Q1 back to +B
High voltage
battery array
Current from the battery
negative terminal passes
through Q4 to re-enter
the stator windings at
terminal W
Motor /
Generator
control
module
+B -B
Q1
U
Q4
Stator
Windings
W
V
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Inverter operation – Regenerative braking –
Phase
As the rotor turns the next winding that has current induced is
V-W. Current flows from terminal W through Q3 back to +B
High voltage
battery array
Current from the battery
negative terminal passes
through Q6 to re-enter
the stator windings at
terminal V
Motor /
Generator
control
module
+B -B
Q3
U
Q6
2nd
Stator
Windings
W
V
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Inverter IGBT assembly
• Inverters for electric vehicles use IGBT [Integrated BiPolar Transistors] as high speed, solid state switches
• An inverter consists of 6 IGBTs mounted on a heat sink
Connectors for high
voltage battery
array
Control module
connector
Control module
connector
Connectors for
stator leads
•
Inverter heat
The IGBTs are bondeddissipation
to a flat steel heat sink
plate that transfers heat
from the IGBT to the
inverter case
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Inverter for
MG2
Inverter for MG1
Inverter case
• Silicone heat transfer grease
improves the transfer of heat
from the inverters to the case
• The inverter assemblies are bolted to the bottom of the
inverter case
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Inverter case
Coolant
Out
Coolant
In
• A serpentine coolant passage is cast into the bottom of the
inverter case
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Inverter cooling
The DC-DC
Converter
• The bottom cover plate for the serpentine coolant passage
contains the DC-DC converter electronics
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Bus Bars
• Large steel or copper strips called ‘Buss Bars” carry electrical
current from the IGBTs to the stator cable assemblies
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Inverters for two motor hybrids
+B
• Each high voltage
motor/generator
needs it’s own
inverter
• A two motor system
[Prius] has one
inverter for MG1
and another inverter
for MG2
-B
Stator for
MG1
Control
module
Stator for
MG2
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Resolver circuit
Electronic control
unit
+B
-B
Stator
Resolver
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Resolver function
• The resolver is a rotor position sensor
• The inverter control module needs to know to position of
the rotor so that it can turn on the correct set of IGBTs
A/C compressor inverter
MG1
Electronic
control
module
MG2
Inverter for A/C
compressor
A/C
compressor
motor
• The A/C compressor
for BEVs and most
hybrids is driven by a
High Voltage three
phase electric motor
• The inverter is
normally on top of the
compressor housing
where it is cooled by
refrigerant
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A/C Compressor inverter
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The electrical
connection to the HV
battery is made inside
the inverter assembly
case
The inverter for most electric A/C compressors
is located on top of the compressor housing
Image courtesy of General Motors Corp.
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Electric A/C Compressor
Oscillator
Assembly
3 Phase AC
Motor
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Inverter for A/C Compressor
The inverter circuit
board for this
compressor has been
pried away from the
case to reveal it’s
circuitry.
Inverter IGBTs are cooled
by contact with the
compressor housing.
Refrigerant vapor passing
through the compressor
carries inverter heat to the
A/C condenser.
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A/C compressor with external inverter
• Some older hybrids
located the inverter
for the A/C
compressor inside
the traction motor
inverter housing
• The electrical
connector shown
here is for 3 phase
AC current
Image courtesy of Denso Corp.
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Capacitors
• Capacitors store high voltage
electrical charges
• Unlike a battery, capacitors cannot
deliver continuous electrical
power over a long period of time
• Capacitors act like a ‘shock
absorber’ for electricity –
smoothing out the surge of
electrical voltage as the IGBTs
turn on and off
Capacitor
boost function
Capacitor
assembly
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• When the vehicle is
suddenly accelerated there
may be a slight lag in the
delivery of electric power
because the chemical
reactions that produce
electricity in the battery
take a few seconds to build
up full power
• The electrical energy
stored in the capacitors
provides a momentary
surge of electrical power
to improve initial
acceleration – but only for
a couple seconds
Capacitors
Buss bar
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• Three large capacitors are connected
via buss bars between each of the stator
windings and HV negative
Capacitor Pack
Gen 2 Prius
• Capacitors can be packaged in metal cylinders or in brick shaped
packs
• Since there is very little heat produced in the capacitor they are
normally located at the top of the inverter assembly
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Drain resistor
• The capacitors can hold lethal voltage potential so a
drain resistor is wired in parallel with the capacitors
• When the system is shut down the voltage in the
capacitors leaks out through the resistor
• It can take up to 5 minutes for the capacitors to drain
completely
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Current sensor
• The Motor Control Module needs to know how much current
[amps] each motor/generator is using or generating
• A current sensor measures the strength of the magnetic field
surrounding the wires connecting the HV battery to the inverter
and sends this information to the MCU
40
HV Battery Current Sensor
• The leads for the HV battery connectors pass through
the current sensor
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DC / DC
Converter
42
DC to DC converter
• All BEV and Hybrid vehicles have two separate
electrical systems
– The high voltage electrical system provides current for the
traction motor
– The low voltage electrical system provides current for all
other vehicle functions
• The A/C compressor on BEV and two motor hybrids normally runs
off of the high voltage system
• BEV vehicles have a PTC heater that runs off of the high voltage
electrical system to provide cabin heat
• The DC to DC converter is the bridge between the high
voltage and low voltage systems
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Motor
Generator
Low and High Voltage Systems
The DC to DC converter uses
high voltage current from the HV
battery array to produce low
voltage current for the vehicles
normal electrical system
Inverter
High
Voltage
High voltage battery array
DC/DC
converter
to ignition switch
12 Volt
battery
Power
distribution
center
Low
Voltage
to computers
to lighting system
DC-DC converter functions
• The DC-DC converter does the same thing for a hybrid
or BEV as an alternator does for a conventional vehicle
– It provides electrical power at 14 volts DC for all of the lights
and electrical accessories when the vehicle is being driven
– Instead of being powered mechanically by a belt the DC-DC
converter is powered electrically by the high voltage
electrical system
– When the system is turned on but the ICE engine is not
running the DC-DC converter converts takes electrical power
from the HV battery and converts it to 14 volts to run the
lights, heater fan and accessories
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DC-DC Converter Operation
Step down
transformer
Rectifier
High
voltage
battery
current
Oscillator
14 Volts DC
Chassis
ground
• The DC-DC converter is made up of three components:
– Oscillator
– Step down transformer
– Rectifier
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Oscillator
Feedback loop
Square wave output current
• The Oscillator employs a
feedback loop to switch a
circuit on and off several
hundred or thousand times
each second
• The oscillator effectively
turns DC current into AC
• The current output of an
oscillator will be a square
wave
Transformers
Transformer
schematic symbol
• Transformers are used to change the
voltage level of an AC current
• Transformers only work with AC
current
• A step up transformer increases
voltage – a step down transformer
decreases voltage
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Transformers
• The input of a transformer is called the primary coil
• The output of a transformer is called the secondary coil
Primary coil
winding
Secondary
coil winding
• Since the power flowing through the transformer primary coil is
constantly reversing, the magnetic field surrounding the core is
constantly expanding and contracting
• The moving lines of magnetic force induce an electric current into
the secondary coil
Turns ratio
100
turns
120 volts
1 amp
input
10
turns
• If the primarily coil has 100 turns
[loops] and the secondary coil has
10 turns the voltage induced into the
secondary coil will be reduced by a
12 volts
10 amps
factor of 10
output
• When voltage is increased by a transformer the
current [amps] is decreased in inverse proportion –
when voltage is decreased current is increased in
inverse proportion
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Transformers
• The transformer output is AC current
with a sine waveform
+
_
51
Rectifier
Rectifier
Capacitor
• The rectifier uses 4 diodes to
convert AC current into DC
• Diodes are one way valves
for electrical current
• The diodes are arranged into
a rectifier bridge
• Current from each end of the
secondary winding is
connected to two diodes
52
Rectifier
+
D1
D3
-
D2
D4
• When the secondary coil
shown here is positive at the
top and negative at the
bottom diodes D2 and D3
allow current to flow through
them [forward biased]
• Diodes D1 and D4 are
blocking the flow of current
[reverse biased]
53
Rectifier
D1
D3
+
D2
D4
• When the polarity of the coil
is reversed so positive is at
the bottom and negative is at
the top diodes D4 and D1 are
turned on [forward biased]
• Diodes D2 and D3 are
turned off [reverse biased] so
no current can flow through
them
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Capacitor
14 V DC
0 V DC
• After AC current has been rectified to DC there is
normally a little bit of voltage fluctuation
• The voltage fluctuation is called an eddy current and is
minimized by placing a small capacitor between the
positive and negative DC output terminals of the
rectifier
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Eddy current with capacitor
14 V DC
0 V DC
• Excess eddy current can interfere with the operation of
some electronic circuits and can also effect the
operation of AM and FM radios
• Adding a capacitor to the DC output flattens out the
eddy current
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Battery charger
Step down
transformer
Rectifier
bridge
120 Volt AC
input
• The DC-DC converter is very
similar to a battery charger
• Since the DC-DC converter
works off of high voltage DC
current it needs an oscillator
circuit to convert DC to AC
before the transformer steps
down the voltage
Capacitor
14.6 Volt DC
output
DC-DC Converter operation – Key Off
Low voltage
Battery
Lights
Horn, clock etc
Computer KAM
Ignition
switch
A/C
compressor
HV Battery
Injectors
Fuel pump
Accessories
12 .8 volts
Hybrid
control
module
Control signal
for master
relay is off
DC-DC
converter
DC-DC
converter is
turned off
HV power is
turned off
MG1
HV
Master
relay
MG2
Inverter
• When the vehicle is turned off the HV master relay is open
• The HV battery array is disconnected from the inverter/DC-DC
converter assembly
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DC-DC operation – Key On / ICE off
Low voltage
Battery
Lights
Horn, clock etc
Computer KAM
Ignition
switch - on
A/C
compressor
58
HV Battery
Injectors
Fuel pump
Accessories
14 .4 volts
Hybrid
control
module
Control signal
for master
relay is on
DC-DC
converter
DC-DC
converter is
turned on
HV power is
turned on
MG1
HV
Master
relay
MG2
Inverter
• When ignition switch is on, but the ICE engine is not running
HV power is converted into 14.4 volts to operate the electrical
system and keep the LV battery fully charged
DC-DC operation – Key On / ICE
running
Low voltage
Battery
Lights
Horn, clock etc
Computer KAM
Ignition
switch - on
A/C
compressor
59
HV Battery
Injectors
Fuel pump
Accessories
14 .4 volts
Hybrid
control
module
Control signal
for master
relay is on
DC-DC
converter
DC-DC
converter is
turned on
HV power is
turned on
MG1
HV
Master
relay
MG2
Inverter
• When the vehicle running current generated by the traction motor/generators
provides power for the DC-DC converter and the HV Batteries
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DC-DC Converter location
• The DC-DC converter is normally located at the bottom of
the inverter housing
High voltage
battery input
Low voltage
output
• The coolant flowing through the passages in the inverter
housing removes excess heat from the DC-DC converter
DC-DC Converter
Step down
transformer
Low Voltage
+B output
High Voltage
+B input
High Voltage B input
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DC / DC Converter
• This Toyota
Highlander has its
own DC-DC
converter that is
provides low
voltage electric
current to the
power steering
system
2006 Highlander Hybrid
Low Voltage Battery
AGM
Battery
Chassis
ground
connection
Backup power 63
supply for
power brake
booster
• The low voltage battery is usually a 12 volt AGM type battery
• Conventional [flooded cell] batteries may also be used
Jump starting
• If the headlights or interior lights are left on overnight
the 12 volt battery will be depleted and the vehicle will
not start
• Current from the 12 volt battery is needed to turn on the
master relays for the HV batteries
• A jump box or jumper cables to another vehicle’s
battery will provide the electric power needed to for the
computer system and HV system relays to bring the HV
battery system online so the vehicle can be driven
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Jump starting another vehicle
• Never use a hybrid or BEV vehicle as a donor power
source when trying to jump start a conventional vehicle
..!
• Thousands of dollars in damage to the DC-DC
converter and inverter could occur if a hybrid or BEV
system is used to power a conventional starter
• The DC-DC converter is designed for relatively low
amperage [less than 40 Amps]. Operating a
conventional starter normally requires 150 amps or
more
If the LV battery
is located in the
rear hatch the
hybrid electrical
system may need
to be energized
from the underhood fuse box to
activate the hatch
release solenoid
Jump Starting
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Once the hatch is
open connect the
jump box directly
to the LV battery
terminals
Jump Starting
Terminal for
activating the
hatch release
solenoid
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Inverter
cooling
69
Inverter Cooling
• The IGBTs and other electronic
components require cooling
• Mild hybrids that have single
motor/generator that has a
relatively low power output can
use a fan driven air cooling system
• Full hybrids with 2
motor/generators will require
liquid cooling
• The in liquid type cooling systems
the inverter and the transmission
share a common cooling system
that has its own radiator and
electrically driven coolant pump
Coolant inlet and
outlet tubes
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Inverter Cooling
• The Inverter is often
mounted directly above the
transaxle so coolant can flow
from the transaxle upward
into the inverter
• Coolant passages are cast
into the inverter and
transmission to cook the
IGBTs and stator coils
Coolant Inlet and Outlet Tubes
Air cooled inverters
144 Volt Battery
pack
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Inverter + DC-DC
converter
• Light hybrids [Honda IMA] don’t generate as much heat as a 2 motor
hybrids so they can be air cooled
• The Inverter and DC-DC converter are mounted next to the battery
array – behind the rear seat
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Inverter
Cooling
System
Reservoir and
Pressure Cap
Electric
Water
Pump
Dedicated Radiator
for Inverter
and Motor / Generator
Image courtesy of Toyota U.S.A.
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Dual radiator
ICE
motor
Inverter
&
traction
motor
• The radiator assembly is often divided into two separate
radiators
• The upper radiator services the ICE engine
• The lower radiator cools the inverter, DC-DC converter
and traction motors
Inverter Cooling
• The Inverter / transaxle has it’s own expansion tank
and pressure cap.
Inverter / Transaxle Coolant
Engine Coolant
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Inverter cooling passages
Coolant Out
Coolant In
• Passages in the base of the inverter remove heat from the IGBT modules.
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Inverter Cooling System
Coolant Hoses
Drain for Inverter
/ traction motor
coolant
Drain for Transmission Fluid
• Note how the transaxle has 2 drain plugs.
Electric water pump
Coolant out
• To circulate coolant through the radiator, inverter and
transmission case an electric water pump is used
• The pump for the inverter/traction motor system uses
14 volt DC current and is controlled by the inverter
module
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Inverter Cooling System Air Bleed
Bleeder nipple for Inverter
/ Transaxle coolant
2007 Prius
• To bleed the inverter/transmission system connect a small vacuum
hose between the bleeder nipple and reservoir.
• Open the bleeder.
• Run the inverter pump until no air bubbles are seen at the end of the
hose.
• The coolant type used
by the
inverter/traction
motor is the same as
used in the ICE
cooling system – a
50/50 solution of 5
year anti-freeze and
water
• The coolant level
should be between the
‘L’ and ‘F’ line on the
reservoir
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Inverter
coolant
‘F’ line
‘L’ line
Topping off inverter coolant
• Most manufacturers recommend that service
technicians do not top off the inverter coolant during
routine service checks
• Topping off the coolant will mask a slow leak in the
system
• A fluid level sensor in the reservoir will trigger a
warning light to alert the driver when the coolant level
is too low
• If the coolant is constantly topped off the warning light
will not turn on until the slow leak becomes a big leak
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Inverter
service
82
Inverter R&R
• Since the inverter often is located above the
transmission you may need to removed it to service the
engine, transmission, ABS controller or the steering
rack
• Removal of the inverter normally involves:
–
–
–
–
–
–
Disconnecting the HV battery service plug
Draining inverter coolant
Disconnecting the coolant hoses
Disconnecting HV DC and 3 phase electrical cables
Disconnecting low voltage electrical connectors
Disconnecting the inverter from its mounting brackets
Inverter
R&R
• To gain access to the rear of the
inverter housing the wiper motor and
wiper transmission had to be
removed on this vehicle
83
Inverter
R&R
• With the wiper transmission removed the 84
components at the rear of the engine
compartment are easily accessible
The plastic trim panel has also
been removed for access to the
front of the inverter
85
Remove service plug
• Make sure the vehicle
is turned off
• Using HV rubber
gloves remove the
service plug
• On this Prius the loop
at the top of the plug
is pulled up first –
then arm on the
service plug is rotated
90 counterclockwise
86
Safety plug
• A safety plug is incorporated
into the inverter cover
• The safety plug is in series
with the HV battery master
relay control circuit
• If the inverter cover is
removed the master relay will
turn off automatically
Safety plug
•
Test for
Allow 5 minutes for the capacitors to drain
and then check
voltage
for voltage between the two HV battery terminals
Safety plug
connector
HV battery
terminals
87
Three phase cables
• Three phase
cables for the
traction
motor[s] are
connected to
the buss bars
with 6mm
bolts
88
89
Threaded cable end terminals
• Some 3 phase cable have threaded terminal ends
90
Two wire connectors
• Two wire HV connectors for the A/C compressor normally have
a push-on type connector
• A lock tab is used to prevent the connector loosening
91
HV Battery cables
• The HV battery
cables may also use a
push-on type
connector
Inverter storage
92
After removing the
inverter the cover[s]
should be
reinstalled and any
openings for cables
should be covered
with tape to prevent
dust from
contaminating the
internal components
Image courtesy of Toyota U.S.A.
No serviceable parts
• The are no replacement parts currently available for
inverters/DC-DC converters
• Any damage to the inverter or DC-DC converter
requires replacement of the entire inverter assembly at a
cost of several thousand dollars
93