2 High Voltage SafetyContact 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.DangerHigh Voltage
3 PPE – Personal Protective Equipment High Voltage gloves with leather coversTest gloves for tears and punctures before useGloves need to be tested annually by an approved glove testing facilitySafety GlassesLeather work shoesTest Date
4 CAT III DVOMA CAT III DVOM with CAT III test leads is required when testing components of the high voltage systemCAT IIIrating
5 Remove the service plug The service plug disconnects the HV battery from the rest of the electrical systemThe service plug is mounted on the HV battery assembly coverMake sure that the vehicle is turned off and the ‘ready’ light is off before removing the service plugHV rubber gloves must be worn when removing the service plug..!
6 Check voltage after removing service plug Before doing any work on the HV system check the voltage at the HV battery cable connectionsIt should be no more than a few 10ths of a volt
7 HV SafetyHigh 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…!
8 Inverter functionThe 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 batteriesImage 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
10 Connector for high voltage battery cables 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 systemDC-DC converterConnector for high voltage battery cablesThe DC-DC Converter is normally located inside the inverter case or underneath it14 Volt DC output
11 Electrical symbol for an IGBT IGBTsIntegrated Gate Bi-Polar TransistorFunction as high speed, solid state switches to convert DC voltage into AC to power the traction motorSince 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 batteryElectrical symbol for an IGBT
12 How IGBTs convert DC current to AC The inverter electronic controls turn the IGBTs on and off to vary the DC voltage pulse widthThe effective current is similar to an AC sine waveThe IGBT also limits voltage by reducing the pulse width- 300 V+ 150 V- 150 V
13 Inverter construction An inverter is made up of 6 IGBTs and is similar in operation to the rectifier in an alternator6 high current diodes are connected in parallel with the IGBT+B-BStator3 of the IGBTs are connected to the HV battery positive terminal and 3 are connected to the negative terminal
14 Inverter operation – 1st phase – drive forward Motor / Generator control moduleBattery current flows through IGBT Q1 to stator terminal U, through the stator windings, then back to the battery through terminal W and IGBTQ4High voltage battery array+B-BQ1Stator WindingsUQ4WV
15 Inverter operation – 2nd phase – drive forward Motor / Generator control moduleBattery current flows through IGBT Q3 to stator terminal W, through the stator windings, then back to the battery through terminal V and IGBT Q6High voltage battery array+B-BQ3Stator WindingsUQ6WV
16 Inverter operation – 3rd phase – drive forward Motor / Generator control moduleBattery current flows through IGBT Q5 to stator terminal V, through the stator windings, then back to the battery through terminal U and IGBT Q2High voltage battery array+B-BQ5Stator WindingsUQ2WV
17 Inverter operation – Regenerative braking – 1st Phase During regenerative braking current generated in the stator winding U-V passes through Q5 to the HV battery +B terminalHigh voltage battery arrayCurrent from the battery negative terminal passes through Q2 to re-enter the stator windings at terminal U+B-BMotor / Generator control moduleQ5Stator WindingsUQ2WV
18 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 +BHigh voltage battery arrayCurrent from the battery negative terminal passes through Q4 to re-enter the stator windings at terminal W+B-BMotor / Generator control moduleQ1Stator WindingsUQ4WV
19 Inverter operation – Regenerative braking – 2nd Phase As the rotor turns the next winding that has current induced is V-W. Current flows from terminal W through Q3 back to +BHigh voltage battery arrayCurrent from the battery negative terminal passes through Q6 to re-enter the stator windings at terminal V+B-BMotor / Generator control moduleQ3Stator WindingsUQ6WV
20 Inverter IGBT assembly Inverters for electric vehicles use IGBT [Integrated Bi-Polar Transistors] as high speed, solid state switchesAn inverter consists of 6 IGBTs mounted on a heat sinkConnectors for high voltage battery arrayControl module connectorControl module connectorConnectors for stator leads
21 Inverter heat dissipation The IGBTs are bonded to a flat steel heat sink plate that transfers heat from the IGBT to the inverter caseInverter for MG2Inverter for MG1
22 Inverter caseSilicone heat transfer grease improves the transfer of heat from the inverters to the caseThe inverter assemblies are bolted to the bottom of the inverter case
23 Inverter caseCoolant OutCoolant InA serpentine coolant passage is cast into the bottom of the inverter case
24 Inverter coolingThe DC-DC ConverterThe bottom cover plate for the serpentine coolant passage contains the DC-DC converter electronics
25 Buss BarsLarge steel or copper strips called ‘Buss Bars” carry electrical current from the IGBTs to the stator cable assemblies
26 Inverters for two motor hybrids Each high voltage motor/generator needs it’s own inverterA two motor system [Prius] has one inverter for MG1 and another inverter for MG2Stator for MG1Control moduleStator for MG2
27 Electronic control unit Resolver circuitElectronic control unit+B-BStatorResolver
28 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
29 A/C compressor inverter The A/C compressor for BEVs and most hybrids is driven by a High Voltage three phase electric motorThe inverter is normally on top of the compressor housing where it is cooled by refrigerantMG1Electronic control moduleMG2Inverter for A/C compressorA/C compressor motor
30 A/C Compressor inverter The electrical connection to the HV battery is made inside the inverter assembly caseThe inverter for most electric A/C compressors is located on top of the compressor housingImage courtesy of General Motors Corp.
31 Electric A/C Compressor 3 Phase AC MotorOscillator Assembly
32 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.
33 A/C compressor with external inverter Some older hybrids located the inverter for the A/C compressor inside the traction motor inverter housingThe electrical connector shown here is for 3 phase AC currentImage courtesy of Denso Corp.
34 Capacitors Capacitors store high voltage electrical charges Unlike a battery, capacitors cannot deliver continuous electrical power over a long period of timeCapacitors act like a ‘shock absorber’ for electricity – smoothing out the surge of electrical voltage as the IGBTs turn on and off
35 Capacitor boost function 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 powerThe electrical energy stored in the capacitors provides a momentary surge of electrical power to improve initial acceleration – but only for a couple secondsCapacitor boost functionCapacitorassembly
36 CapacitorsThree large capacitors are connected via buss bars between each of the stator windings and HV negativeBuss bar
37 Gen 2 PriusCapacitor PackCapacitors can be packaged in metal cylinders or in brick shaped packsSince there is very little heat produced in the capacitor they are normally located at the top of the inverter assembly
38 Drain resistorThe capacitors can hold lethal voltage potential so a drain resistor is wired in parallel with the capacitorsWhen the system is shut down the voltage in the capacitors leaks out through the resistorIt can take up to 5 minutes for the capacitors to drain completely
39 Current sensorThe Motor Control Module needs to know how much current [amps] each motor/generator is using or generatingA 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
42 DC to DC converterAll BEV and Hybrid vehicles have two separate electrical systemsThe high voltage electrical system provides current for the traction motorThe low voltage electrical system provides current for all other vehicle functionsThe A/C compressor on BEV and two motor hybrids normally runs off of the high voltage systemBEV vehicles have a PTC heater that runs off of the high voltage electrical system to provide cabin heatThe DC to DC converter is the bridge between the high voltage and low voltage systems
43 Low and High Voltage Systems Motor GeneratorLow and High Voltage SystemsThe DC to DC converter uses high voltage current from the HV battery array to produce low voltage current for the vehicles normal electrical systemInverterHigh VoltageHigh voltage battery array12 Volt batteryDC/DC converterPower distribution centerLow Voltageto ignition switchto computersto lighting system
44 DC-DC converter functions The DC-DC converter does the same thing for a hybrid or BEV as an alternator does for a conventional vehicleIt provides electrical power at 14 volts DC for all of the lights and electrical accessories when the vehicle is being drivenInstead of being powered mechanically by a belt the DC-DC converter is powered electrically by the high voltage electrical systemWhen 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
45 DC-DC Converter Operation Step down transformerRectifierHigh voltage battery currentOscillator14 Volts DCChassis groundThe DC-DC converter is made up of three components:OscillatorStep down transformerRectifier
46 Square wave output current OscillatorThe Oscillator employs a feedback loop to switch a circuit on and off several hundred or thousand times each secondThe oscillator effectively turns DC current into ACThe current output of an oscillator will be a square waveFeedback loopSquare wave output current
47 Transformer schematic symbol Transformers are used to change the voltage level of an AC currentTransformers only work with AC currentA step up transformer increases voltage – a step down transformer decreases voltageTransformer schematic symbol
48 Secondary coil winding TransformersThe input of a transformer is called the primary coilThe output of a transformer is called the secondary coilPrimary coil windingSecondary coil windingSince the power flowing through the transformer primary coil is constantly reversing, the magnetic field surrounding the core is constantly expanding and contractingThe moving lines of magnetic force induce an electric current into the secondary coil
49 Turns ratioIf 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 factor of 10100 turns10 turns120 volts 1 amp input12 volts 10 amps outputWhen voltage is increased by a transformer the current [amps] is decreased in inverse proportion – when voltage is decreased current is increased in inverse proportion
50 TransformersThe transformer output is AC current with a sine waveform+_
51 Rectifier The rectifier uses 4 diodes to convert AC current into DC Diodes are one way valves for electrical currentThe diodes are arranged into a rectifier bridgeCurrent from each end of the secondary winding is connected to two diodesCapacitor
52 Rectifier+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]D2D1D3D4-
53 Rectifier-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 themD2D1D3D4+
54 Capacitor14 V DC0 V DCAfter AC current has been rectified to DC there is normally a little bit of voltage fluctuationThe 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
55 Eddy current with capacitor 14 V DC0 V DCExcess eddy current can interfere with the operation of some electronic circuits and can also effect the operation of AM and FM radiosAdding a capacitor to the DC output flattens out the eddy current
56 Battery chargerStep down transformerRectifier bridge120 Volt AC inputThe DC-DC converter is very similar to a battery chargerSince 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 voltageCapacitor14.6 Volt DC output
57 DC-DC Converter operation – Key Off Low voltage BatteryLightsHV BatteryHorn, clock etcIgnition switchComputer KAMInjectorsFuel pumpAccessoriesA/C compressor12 .8 voltsHybrid control moduleControl signal for master relay is offDC-DC converterDC-DC converter is turned offHV power is turned offMG1HV Master relayMG2InverterWhen the vehicle is turned off the HV master relay is openThe HV battery array is disconnected from the inverter/DC-DC converter assembly
58 DC-DC operation – Key On / ICE off Low voltage BatteryLightsHV BatteryHorn, clock etcIgnition switch - onComputer KAMInjectorsFuel pumpAccessoriesA/C compressor14 .4 voltsHybrid control moduleControl signal for master relay is onDC-DC converterDC-DC converter is turned onHV power is turned onMG1HV Master relayMG2InverterWhen 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
59 DC-DC operation – Key On / ICE running Low voltage BatteryLightsHV BatteryHorn, clock etcIgnition switch - onComputer KAMInjectorsFuel pumpAccessoriesA/C compressor14 .4 voltsHybrid control moduleControl signal for master relay is onDC-DC converterDC-DC converter is turned onHV power is turned onMG1HV Master relayMG2InverterWhen the vehicle running current generated by the traction motor/generators provides power for the DC-DC converter and the HV Batteries
60 DC-DC Converter location The DC-DC converter is normally located at the bottom of the inverter housingHigh voltage battery inputLow voltage outputThe coolant flowing through the passages in the inverter housing removes excess heat from the DC-DC converter
61 DC-DC Converter Step down transformer Low Voltage +B output High Voltage +B inputHigh Voltage - B input
62 DC / DC ConverterThis Toyota Highlander has its own DC-DC converter that is provides low voltage electric current to the power steering system2006 Highlander Hybrid
63 Backup power supply for power brake booster Low Voltage BatteryChassis ground connectionAGM BatteryThe low voltage battery is usually a 12 volt AGM type batteryConventional [flooded cell] batteries may also be used
64 Jump startingIf the headlights or interior lights are left on overnight the 12 volt battery will be depleted and the vehicle will not startCurrent from the 12 volt battery is needed to turn on the master relays for the HV batteriesA 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
65 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 starterThe DC-DC converter is designed for relatively low amperage [less than 40 Amps]. Operating a conventional starter normally requires 150 amps or more
66 Jump StartingIf the LV battery is located in the rear hatch the hybrid electrical system may need to be energized from the under-hood fuse box to activate the hatch release solenoid
67 Terminal for activating the hatch release solenoid Jump StartingOnce the hatch is open connect the jump box directly to the LV battery terminalsTerminal for activating the hatch release solenoid
69 Inverter CoolingThe IGBTs and other electronic components require coolingMild hybrids that have single motor/generator that has a relatively low power output can use a fan driven air cooling systemFull hybrids with 2 motor/generators will require liquid coolingThe in liquid type cooling systems the inverter and the transmission share a common cooling system that has its own radiator and electrically driven coolant pumpCoolant inlet andoutlet tubes
70 Coolant Inlet and Outlet Tubes Inverter CoolingThe Inverter is often mounted directly above the transaxle so coolant can flow from the transaxle upward into the inverterCoolant passages are cast into the inverter and transmission to cook the IGBTs and stator coilsCoolant Inlet and Outlet Tubes
71 Inverter + DC-DC converter 144 Volt Battery packAir cooled invertersInverter + DC-DC converterLight hybrids [Honda IMA] don’t generate as much heat as a 2 motor hybrids so they can be air cooledThe Inverter and DC-DC converter are mounted next to the battery array – behind the rear seat
72 Inverter Cooling System Reservoir andPressure CapElectricWaterPumpDedicated Radiatorfor Inverterand Motor / GeneratorImage courtesy of Toyota U.S.A.
73 Inverter & traction motor Dual radiatorICE motorInverter & traction motorThe radiator assembly is often divided into two separate radiatorsThe upper radiator services the ICE engineThe lower radiator cools the inverter, DC-DC converter and traction motors
74 Inverter / Transaxle Coolant Inverter CoolingThe Inverter / transaxle has it’s own expansion tank and pressure cap.Inverter / Transaxle CoolantEngine Coolant
75 Inverter cooling passages Coolant OutCoolant InPassages in the base of the inverter remove heat from the IGBT modules.
76 Inverter Cooling System Coolant HosesDrain for Inverter/ traction motor coolantDrain for Transmission FluidNote how the transaxle has 2 drain plugs.
77 Electric water pumpCoolant outTo circulate coolant through the radiator, inverter and transmission case an electric water pump is usedThe pump for the inverter/traction motor system uses 14 volt DC current and is controlled by the inverter module
78 Inverter Cooling System Air Bleed Bleeder nipple for Inverter/ Transaxle coolant2007 PriusTo 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.
79 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 waterThe coolant level should be between the ‘L’ and ‘F’ line on the reservoirInverter coolant‘F’ line‘L’ line
80 Topping off inverter coolant Most manufacturers recommend that service technicians do not top off the inverter coolant during routine service checksTopping off the coolant will mask a slow leak in the systemA fluid level sensor in the reservoir will trigger a warning light to alert the driver when the coolant level is too lowIf the coolant is constantly topped off the warning light will not turn on until the slow leak becomes a big leak
82 Inverter R&RSince the inverter often is located above the transmission you may need to removed it to service the engine, transmission, ABS controller or the steering rackRemoval of the inverter normally involves:Disconnecting the HV battery service plugDraining inverter coolantDisconnecting the coolant hosesDisconnecting HV DC and 3 phase electrical cablesDisconnecting low voltage electrical connectorsDisconnecting the inverter from its mounting brackets
83 To gain access to the rear of the inverter housing the wiper motor and wiper transmission had to be removed on this vehicleInverter R&R
84 With the wiper transmission removed the components at the rear of the engine compartment are easily accessibleInverter R&RThe 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 plugOn 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 circuitIf the inverter cover is removed the master relay will turn off automaticallySafety plug
87 Allow 5 minutes for the capacitors to drain and then check for voltage between the two HV battery terminalsTest for voltageHV battery terminalsSafety plug connector
88 Three phase cablesThree phase cables for the traction motor[s] are connected to the buss bars with 6mm bolts
89 Threaded cable end terminals Some 3 phase cable have threaded terminal ends
90 Two wire connectorsTwo wire HV connectors for the A/C compressor normally have a push-on type connectorA lock tab is used to prevent the connector loosening
91 HV Battery cablesThe HV battery cables may also use a push-on type connector
92 Inverter storageAfter 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 componentsImage courtesy of Toyota U.S.A.
93 No serviceable partsThe are no replacement parts currently available for inverters/DC-DC convertersAny damage to the inverter or DC-DC converter requires replacement of the entire inverter assembly at a cost of several thousand dollars