PEV Motor and Inverter Diagnosis and Repair

Technical Resource Guide Doing what matters for jobs and the economy with funding provided by the California Energy Commission (senate bill AB118) through a partnership with the California Community Colleges, Office of Workforce Development, Advanced Transportation and Renewable Energy sector.

This material is based upon work supported by the California Energy Commission under Grant No. 12-041-008

Revision 1 PEV Motor and Inverter Diagnosis and Repair October 1, 2014 COURSE INTRODUCTION

Course Title Course Benefits PEV Motor and Inverter Diagnosis and Repair The benefit of this course is designed to help the fleet technician become familiar with all aspects of

Course Length motorgenerators and inverters as they relate to plug- 16 hours in vehicles, including vehicle diagnosis, repair, and Description: This course is designed to provide service. professional automotive technicians with the general Prerequisites skills needed to safely diagnose, repair, and service Students should have a basic experience in in motor-generators and inverters in plug-in vehicles automotive diagnosis, repair, and maintenance, (PEVs), including plug-in hybrid and electric vehicles. including the use of scan tools and online service Discussion topics, many of which will be reinforced information databases. Solid understanding of basic by hands-on exercises, include: automotive electrical systems. Ability to correctly ▪▪ Safely discharging inverter capacitors, and con- follow safety procedures. firming capacitor discharge Objectives ▪▪ Conversion of DC to AC, and AC to DC, by By the end of this course participants will be able inverter to: ▪▪ Diagnosing, repairing, and servicing inverter List safety issues related to motor-generators and cooling systems inverters ▪▪ Measuring motor winding phase resistances ▪▪ Describe basic components of a typical motor-gen- ▪▪ -Measuring motor winding insulation resistance erator ▪▪ Understanding series-parallel hybrid transaxle ▪▪ Explain the purpose of a milliohmmeter operation ▪▪ Demonstrate correct measurement of phase-to- ▪▪ Understanding series-parallel hybrid transaxle phase resistances scan data ▪▪ Explain the purpose of an insulation resistance ▪▪ Diagnosing, repairing, and servicing motor-gen- meter erators ▪▪ Describe safety issues related to insulation resis- NOTE: This course is only intended to supple- tance measurements ment manufacturer-specific (OEM) safety, ser- ▪▪ Demonstrate correct measurement of insulation vice, and diagnostic information. This course resistance cannot serve as a substitute for such information, ▪▪ Explain the potential diagnostic value of mo- which changes often. In all cases, manufactur- tor-generator torque scan data er-specific information for a particular plug-in vehicle supersedes any information presented in this course. Competence Competence will be measured by both lab demonstration and pre and post tests.

PEV Motor and Inverter Diagnosis and Repair 1 Pretest

Pretest PEV Motor and Inverter Diagnosis and Repair

1. What part of an alternating current (AC) motor normally spins? a. Stator b. Rotor c. Resolver d. Neither

2. What part of an alternating current (AC) motor contains the motor winding? a. Stator b. Rotor c. Resolver d. Neither

3. One cycle of alternating current equals: a. 1000 degrees b. 360 degrees c. 180 degrees d. 90 degrees

4. Resistance in a negative coefficient temperature sensor: a. Is constant; varying current through the sensor is measured b. Should be less than one to prevent a drop c. Increases as temperature falls d. Decreases as temperature falls

5. Before applying torque according to manufacturer’s specification: a. The technician should always apply a light oil to fastener threads b. The technician should ensure that the correct units are referenced (Nm, Ft. Lb.) c. The technician should chill the fastener to prevent an interference fit d. The technician should attach a one-foot extension between wrench and socket

2 PEV Motor and Inverter Diagnosis and Repair Pretest

6. During hard acceleration, a hybrid or electric vehicle will typically: a. Use regenerative braking to charge the vehicle’s battery pack b. Use friction braking to charge the vehicle’s battery pack c. Discharge the battery pack into the inverter d. Shift into neutral to improve fuel economy

7. High-voltage cables in hybrid and electric vehicles are typically: a. Colored orange b. Colored yellow c. Enclosed in metal housings d. Found only at the rear of the vehicle, near the battery pack

8. Before attempting a dangerous service procedure, a technician should first: a. Ask a co-worker for advice on the procedure b. Review OEM service information, including TSBs c. Put on high-voltage insulating gloves d. Drain the vehicle of fuel and discharge the battery pack

9. A motor-generator produces current (acts as a generator): a. When its rotor is electrically rotated by the inverter b. Any time the vehicle is operating at highway speed c. During moderate acceleration d. When its rotor is physically rotated by an external force

10. A plug-in hybrid vehicle: a. Generally has a larger battery pack that that of a non-plug-in hybrid b. Generally has a smaller battery pack that that of a non-plug-in hybrid c. Does not have an internal-combustion engine d. Does not require a charging port

PEV Motor and Inverter Diagnosis and Repair 3 Table of Contents

A. Introduction ▪▪ PreTest

1. Motor-Generators and Inverters ▪▪ Basic Inverter Functions

2. Capacitors in Inverters ▪▪ Active Discharge Circuit ▪▪ Passive Discharge Circuit

3. Conversion of DC to AC, and AC to DC, by the Inverter ▪▪ Inverter Function When a Motor-Generator is Functioning as a Motor ▪▪ Inverter Function When a Motor-Generator is Functioning as a Generator ▪▪ Inverter Cooling System ▪▪ Diagnosing Inverter Cooling Systems

4. Motor-Generator Operation ▪▪ Rotor Construction ▪▪ Stator Construction ▪▪ Resolver and Motor Control

5. Measuring Stator Winding Phase-to-Phase Resistances

6. Measuring Stator Winding Insulation Resistance

4 PEV Motor and Inverter Diagnosis and Repair 7. Diagnosing, repairing, and servicing motor-generators

8. Comparing commanded motor torque to actual motor torque

Post-Test

PEV Motor and Inverter Diagnosis and Repair 5 Module One 1

6 PEV Motor and Inverter Diagnosis and Repair Motor-generators & Inverters in Context

Motor-Generators & Inverters in (rectify) motor-generator AC into DC, at the proper Context voltage, to charge the battery pack. An inverter uses current from a plug-in vehicle’s battery pack to drive one or more motor-generators, which in turn propel, or help propel, a plug-in vehicle. The inverter also controls the speed and torque output of the vehicle’s motor-generator(s). NOTE: The terms motor, generator, and motor- generator are often used, sometimes interchangeably, by manufacturers of hybrid and electric vehicles. All motors in a hybrid or electric vehicle’s powertrain are actually motor-generators: during certain operating modes, they function as motors, and as generators during other operating modes. However, some motor-generators are referred to as either motors or generators by vehicle manufacturers, depending on their primary purpose.

Basic Inverter Functions As the battery pack can only supply (DC) to the inverter, and motor-generators in hybrid and electric vehicles are powered by alternating current (AC), the inverter must change (invert) DC into AC whenever the battery pack is supplying current to the inverter. The inverter then supplies AC to the motor-generator(s). For example, the battery pack can be expected to supply current to the inverter to power the vehicle’s motor-generator(s) during heavy acceleration and/or all-electric mode.

The vehicle’s motor-generator(s) can also charge the battery pack during certain operating modes, such as deceleration. Since the motor-generators produce alternating current of varying whenever their rotors are physically rotated, the inverter must change

PEV Motor and Inverter Diagnosis and Repair 7 Module Two 2

8 PEV Motor and Inverter Diagnosis and Repair Capacitors in Inverters

Capacitors in Inverters must be activated to discharge the capacitors. Inverters have many high-voltage circuits, including When the vehicle is powered OFF and the battery circuits that incorporate capacitors to stabilize pack’s HV relays open, a typical active discharge voltages and act as filters. As high-voltage capacitors circuit will turn on the appropriate power transistors can store electrical charge, charged capacitors in within the inverter, electrically connecting the inverters can create a safety issue for a technician, inverter to a motor-generator. The inverter’s even after a plug-in vehicle has been powered OFF. capacitors then discharge into the motor-generator’s stator winding. The inverter’s control system must During operation, a plug-in vehicle’s inverter select transistors that will allow the capacitors to capacitors typically remain charged with high discharge into the motor-generator without causing voltage. When the vehicle is powered OFF, high- the rotor to turn. voltage (HV) relays open, electrically isolating the vehicle’s battery pack from the inverter. Two Active discharge can be observed in an instructor- redundant circuits are employed to discharge a led lab, but is more accurately observed with a typical inverter after the vehicle has been powered scope than with a , as a voltmeter’s display OFF: often refreshed too slowly to allow the observer to accurately see the speed at which the inverter’s ▪▪ Active discharge circuit capacitors are discharged.

▪▪ Passive discharge circuit Passive discharge circuit OEM service information will typically direct a A plug-in vehicle’s inverter typically incorporates a technician to allow a specific amount of time to passive discharge circuit, which serves as a back-up elapse after a vehicle has been powered OFF, to discharge circuit in the event that the active discharge allow the vehicle’s inverter capacitors to discharge. circuit is not activated when the vehicle is powered The technician must still measure voltage at the OFF. This may occur when: appropriate test points to confirm that the capacitors ▪▪ The active discharge circuit is disabled due have been discharged, if he or she is required to to a motor or inverter fault access high-voltage inverter circuits when working on the vehicle. These test points can also be identified ▪▪ The active discharge circuit has a fault by referring to OEM service information.

A passive discharge circuit is usually made up of Active Discharge Circuit a , or group of , which connect the A plug-in vehicle’s inverter incorporates active inverter’s HV positive DC circuit to the inverter’s discharge circuits that typically discharge the HV negative DC circuit. The resistor circuit has inverter’s capacitors in less than one second. As enough resistance to prevent it from interfering indicated by the name, these are active circuits that with the inverter’s other high-voltage circuits, and

PEV Motor and Inverter Diagnosis and Repair 9 Module Two

has a sufficient power rating to be able to withstand capacitor discharge. However, the resistance of the passive discharge circuit increases the time that it takes for the capacitors to discharge, as compared to capacitor discharge through an active discharge circuit.

OEM service information typically publishes a specification for an amount of time that must elapse after a plug-in vehicle is powered down, before the inverter’s capacitors can be considered to have been discharged under normal circumstances. This specification reflects the time required for the inverter’s capacitors to discharge through the inverter’s passive discharge circuit. The time varies from vehicle to vehicle. Many plug-in vehicles have time intervals of at least ten minutes, depending on the vehicle.

NOTE: Before working on an inverter’s high-voltage circuits, a technician must use a properly rated voltmeter to confirm that the inverter’s capacitors have discharged. This procedure varies from vehicle to vehicle, and can be found in OEM service information.

10 PEV Motor and Inverter Diagnosis and Repair Capacitors in Inverters

PEV Motor and Inverter Diagnosis and Repair 11 Module Three 3

12 PEV Motor and Inverter Diagnosis and Repair Conversion of DC to AC, & AC to DC, by the Inverter

Conversion of DC to AC, and AC motor load, and required torque. to DC, by the Inverter Inverter function when a motor-generator Inverter function when a motor-generator is functioning as a generator is functioning as a motor A motor-generator can produce torque from current When a motor-generator’s rotor is physically that is supplied by: rotated, such as during deceleration, the motor- ▪▪ The vehicle’s battery pack generator produces an alternating current. The voltage level of the alternating current increases ▪▪ Another motor-generator, functioning as a with rotor speed. The inverter must rectify this generator uncontrolled AC into DC, and supply direct current to the battery pack at the correct voltage level Hybrid and electric vehicle motor-generators are to charge the battery pack. Diodes are mounted three-phase, and are powered by alternating current. in the power transistor block, in parallel to each When a motor-generator is powered by current transistor, to rectify alternating current into direct from the battery pack, the inverter must change that current. The method for adjusting the voltage level current from direct current to alternating current, of the rectified current varies from manufacturer to and switch current between all three phases in the manufacturer. proper sequence to rotate the motor. The inverter must also control motor-generator speed and torque: Inverter Cooling System ▪▪ Motor speed is controlled by controlling AC Power transistors can get very hot during operation, frequency and must be rapidly cooled to avoid damage from overheating. Although a few hybrid vehicles ▪▪ Motor torque is controlled by controlling use air-cooled inverters, most use liquid-cooled current amplitude inverters. Plug-in vehicles also typically use liquid- cooled inverters due to the amount of power that An inverter uses power transistors to switch direct they generate. The inverter’s power transistors are current back and forth through each of a motor- typically bolted to a heat sink, with thermal grease generator’s three phases, effectively creating an to aid in heat transfer. The heat sink is connected in alternating current. By controlling transistor “on- some way to a cooling system. time” through pulse-width modulation (PWM), the inverter can control effective voltage, and create a voltage pattern that drives a sine wave current. In general, an inverter cooling system consists of a radiator, a coolant pump, coolant passages within the inverter, and coolant hoses to connect all of Most inverters employ several voltage patterns to the components. Some inverter cooling systems drive a motor-generator, depending on motor speed,

PEV Motor and Inverter Diagnosis and Repair 13 Module Three

have coolant temperature sensors; others rely on temperature sensors that are mounted on or near the inverter’s power transistor assembly. Some inverter cooling systems also cool other parts of the vehicle’s electric powertrain, such as a heat sink for a motor- generator.

Most manufacturers of plug-in vehicles use inverter coolant that is identical or similar to the coolant used to cool internal-combustion engines made by that manufacturer.

Diagnosing Inverter Cooling Systems Inverter cooling systems can be affected by a range of issues, including coolant leaks, pump failure, and reduced coolant flow. As inverter cooling systems are designed to cool the inverter rather than maintain a specific temperature, they do not use thermostats, and do not have thermostat-related issues.

Only coolant specified by the vehicle manufacturer should be used, and only in the mixture specified by the manufacturer. Some inverter coolant is sold pre- mixed, and some must be mixed with water to the correct dilution by the technician.

14 PEV Motor and Inverter Diagnosis and Repair Conversion of DC to AC, and AC to DC, by the Inverter

PEV Motor and Inverter Diagnosis and Repair 15 Module Four 4

16 PEV Motor and Inverter Diagnosis and Repair Motor-Generator Operation

Motor-Generator Operation produce a permanent magnetic field. The stator winding’s electromagnetic field interacts with the Most electric vehicles have one motor-generator, rotor’s magnetic field to produce rotation. Potential housed in a transaxle assembly with fixed issues with permanent-magnet motors include gearing. As mentioned previously, hybrid and magnet deterioration due to excessive temperature. electric vehicle motor-generators are three-phase, alternating current machines. All motor-generators used in hybrid and electric vehicles are brushless. Stator Construction Insulated copper wire is wound around an iron core, As motor-generators typically have excellent torque in three phases, to create a motor-generator’s stator at almost all speeds, variable gear ratios are not winding. The three phases are generally connected normally employed in electric vehicles. Rather, the at one end in a configuration called a wye winding. vehicle will typically have a single-speed transaxle. Although there are many different configurations in Some motor-generators used in plug-in hybrids which a stator winding can be constructed, the basic have variable gearing, because the action of the architecture of stator windings are similar to one motor-generator affects the gearing of the vehicle’s another. internal-combustion engine. Resolver and Motor Control Rotor Construction A plug-in hybrid vehicle’s inverter controls a motor- Depending on rotor type, a plug-in vehicle’s motor- generator by commanding currents that interact with generator(s) may be either an induction motor or a the motor-generator’s rotor to produce the desired permanent-magnet synchronous motor (PMSM). effect. To do this, the inverter must “know” the exact position of a motor-generator’s rotor at all An induction motor uses the stator winding’s times. electromagnetic field to induce a current into conductors within the rotor. The electromagnetic field produced by the rotor then interacts with the This requires an extremely accurate position sensor electromagnetic field produced by the stator, to that reads rotor position whenever the vehicle’s produce rotation. Potential issues with induction powertrain is powered up (READY), even if the rotors include cracked rotor bars. Tesla is one of rotor is not moving. Most hybrid and electric the few electric vehicle manufacturers that uses vehicles use a sensor called a resolver, although a induction motors in mass-produced vehicles. few vehicles use conventional hall effect sensors.

Most hybrid and electric vehicles use permanent- A resolver consists of a ring of coils, resembling a magnet synchronous motor has powerful permanent stator winding, surrounding an elliptical steel lobe magnets embedded in the rotor. The magnets mounted on the motor-generator’s rotor shaft. The

PEV Motor and Inverter Diagnosis and Repair 17 Module Four

coils are made up of three separate circuits: ▪▪ an excitation winding, which is supplied with current whenever the vehicle is READY

▪▪ two sensor windings, cross-referenced, which are used to determine rotor position

The excitation winding, which is usually powered by a powertrain control module, induces current into the two sensor windings, which are wound asymmetrically. The sensor windings interact with the resolver’s elliptical lobe, mounted on the rotor shaft, to produce a signal of varying amplitude. The cross-referenced amplitudes of the sensor windings provide rotor position; the rate at which rotor position changes is used to calculate rotor speed.

Resolvers are mounted inside motor-generator housings, and are not normally serviceable, although the external wiring from motor-generator case to powertrain control module is generally serviceable in case of damage. Incorrect resolver signals can cause the inverter to incorrectly command motor- generator rotation. If resolver signals cannot be processed, the inverter will simply stop commanding the motor-generator, effectively shutting it down.

Motor-Generator Temperature Sensors Many stator windings in hybrid and electric vehicles are equipped with temperature sensors, which are typically not serviceable. These sensors are designed to detect overheating due to a short circuit within the stator winding, as well as overheating due to a motor cooling issue.

18 PEV Motor and Inverter Diagnosis and Repair Motor-Generator Operation

PEV Motor and Inverter Diagnosis and Repair 19 Module Five 5

20 PEV Motor and Inverter Diagnosis and Repair Measuring Stator Winding Phase-to-Phase Resistances

Measuring Stator Winding Phase- a time. The motor cables of this vehicle are marked to-Phase Resistances U, V, and W, and the technician will need to take three measurements: U-V, V-W, and W-U. A healthy three-phase motor will have relatively balanced resistances across all phases of its stator winding. If the winding develops an internal short, Resistance specifications for many hybrid and the electrical resistance of that part of the winding electric vehicle motor-generator windings, including will eventually change. The technician can verify those of this Prius, are typically given for a winding this by comparing resistance measurements across all that is measured at a fixed reference temperature, three phases, as well as to the vehicle manufacturer’s usually 20ºC (68ºF). Measurements taken at any specifications. other temperature will be inaccurate, and must be corrected. Since the resistance of copper rises when its temperature rises, Toyota specifies that A typical digital (DVOM) will have a the vehicle must be at rest (not powered up) for at resolution of 0.01 , or 100 milliohms. Some least eight hours before measurements are taken, higher-quality digital also have a “low to allow the stator winding to cool and stabilize ohms” feature which produces a resolution of 0.01 at ambient temperature. The winding’s phase- ohms, or 10 milliohms, and cancels out the resistance to-phase resistances can then be measured, and of the meter’s leads. the measured resistances can then be corrected to calculated resistance at 20ºC, using a standard However, since typical windings have phase formula that is provided in OEM service information. resistances of considerably less than one ohm, the Some milliohmmeters incorporate an internal technician may be required to detect phase-to-phase ambient temperature sensor that enables the resistance variations as small as two milliohms (two meter to correct resistance measurements made at thousandths of an ohm). This requires an extremely ambient temperature to resistance at the reference accurate meter, far beyond the capabilities of a temperature. This feature saves time and helps conventional DVOM. By comparison, a typical prevent incorrect calculations. milliohmmeter has a resolution of a tenth of a milliohm (0.0001 ohms) or less. This will be adequate The technician would then compare the final, for the needs of a technician who must measure corrected measurements to factory specifications: hybrid or electric vehicle motor-generator stator in this case, 31 to 36 milliohms. Some vehicle windings. manufacturers may also list a maximum variation between phase-to-phase resistances, or between each We shall use the main drive motor or MG2, of a phase resistance and an average of all phase-to-phase 2001 Toyota Prius as an example. As hybrid motor- resistances. generators typically don’t have a neutral wire, the technician will need to measure the winding at the motor-generator’s three motor cable terminal ends, phase-to-phase. This method measures two phases at

PEV Motor and Inverter Diagnosis and Repair 21 Module Six 6

22 PEV Motor and Inverter Diagnosis and Repair Measuring Stator Winding Insulation Resistance

Measuring Stator Winding The technician would then select a test voltage Insulation Resistance according to manufacturer’s specifications (for the 2001 Prius, 500 ), press and hold the meter’s A conventional, low-voltage DVOM “measures” high-voltage test button, wait for the reading to resistance by producing a small fixed voltage across stabilize, and record the insulation resistance. Note two test points, measuring the resulting current, that most megohmmeters have a spring-loaded test and using Ohm’s Law to calculate the resistance. button, which must be held down until the displayed Although everything has some electrical resistance, insulation resistance reading stabilizes. It is normal the typical DVOM will display an “infinite” reading for the insulation resistance reading to rise for several when measuring electrical resistance between a seconds while the test button is pushed down, and the high-voltage conductor — for example, a properly technician must wait until the reading stabilizes. functioning hybrid vehicle motor-generator cable — and the external surface of its high-voltage insulation. This is because the DVOM doesn’t generate a high CAUTION: Never allow the high-voltage conductor enough voltage to drive current across high-voltage to touch chassis or component ground. This will insulation. create a high-voltage short circuit and invalidate the test. A megohmmeter, also referred to as a megger or insulation resistance tester, can produce DC voltages After the technician has taken his or her readings, he as high as 1000V volts although test voltages are or she then releases the test button, which discharges more commonly specified at 250 or 500 volts. To the meter’s leads, before disconnecting the leads from accurately test the resistance of a given component, the component under test. the technician must electrically isolate the component’s high-voltage circuits from the rest of the vehicle. The resulting resistance measurement can As a hybrid’s high-voltage circuits are normally then be compared to the OEM specification for the isolated from chassis ground, insufficient resistance component under test. between (a) one of the motor winding cable terminals and (b) chassis ground indicates a short to ground in the insulation of the winding itself. The 2001 As this is a test of high-voltage insulation, rather than Toyota Prius has a minimum insulation resistance circuit resistance, the technician will NOT connect specification of 10 MΩ (ten million ohms, or the megohmmeter to two conductors. Instead, the megohms) at 500 volts. Our test winding failed at 0.1 technician will connect one of the megohmmeter’s megohms, indicating that the motor-generator’s stator leads to chassis or component ground, as directed by winding has shorted to ground. OEM service information, and the other lead to an appropriate high-voltage conductor. In the case of our example vehicle, one lead will be connected to the After replacing the motor, the insulation resistance of transaxle case, and the other to the terminal end of the new winding was measured, and easily passed the one of the motor-generator’s motor cables. test with a resistance of more than 500 megohms at 527 volts.

PEV Motor and Inverter Diagnosis and Repair 23 Module Seven 7

24 PEV Motor and Inverter Diagnosis and Repair Diagnosing, Repairing, & Servicing Motor-Generators

Diagnosing, Repairing, and Servicing Motor-Generators Motor windings for plug-in hybrids such as the 2011 Chevrolet and electric vehicles such as the Nissan LEAF are similar to convention- al hybrid motor windings. Milliohmmeters and megohmmeters are specified or recommended for service procedures by many manufacturers. How- ever, motor and inverter diagnostic procedures vary widely among vehicle manufacturers, and not all manufacturers employ both tools.

Some OEMs rely exclusively on DTCs to detect motor faults. Others recommend using a conven- tional to check for a winding short to ground. Such a procedure can only detect severe shorts to ground, and will be unable to detect in- ternal shorts within a stator winding. Some hybrid vehicles, such as Fords Escape and early Fusion hybrids (and their variants) integrate the vehicle’s inverter into its transaxle. The design of the tran- saxle prevents a technician from easily separating the inverter from the motor windings to access the motor cables. In such cases, the technician will be unable to use a milliohmmeter or megohmmeter to evaluate the motor windings.

Finally, it is important to keep in mind that a mo- tor-generator winding can develop an internal short which can’t be detected by either a milliohmmeter or a megohmmeter, or by the testing procedures specified by the OEM.

PEV Motor and Inverter Diagnosis and Repair 25 Module Eight 8

26 PEV Motor and Inverter Diagnosis and Repair Comparing Commanded Motor Torque to Actual Motor Torque

Comparing Commanded Motor issue that is caused by either a motor-generator or Torque to Actual Motor Torque the inverter that drives the motor-generator. Almost all hybrid and electric vehicles generate A careful examination of the freeze frame for the scan data that indicates motor-generator torque. DTC — or a snapshot of motor-generator torque However, it may not be apparent as to whether the data — may indicate zero torque commanded to scan data indicates commanded motor-generator the motor-generator. This, in turn, indicates that torque or actual motor-generator torque. OEM the inverter’s control system detected an issue service information may help the technician deter- before applying current to the motor-generator. In mine what the scan tool is indicating. this case, a motor-generator issue is not indicated: the issue probably lies with the inverter, or some- Some hybrid or electric vehicles include separate where “upstream” of the inverter. motor-generator scan data for both commanded torque and actual torque. In some cases, it may If, on the other hand, a freeze frame or snapshot be useful to compare commanded torque to actual indicates that the inverter had commanded torque torque as part of a diagnosis. While some variation to the motor-generator, and that torque was ap- between commanded torque and actual torque can plied, the issue may be with the motor-generator. be expected, wide variations may indicate an elec- In both cases, further testing may be required to trical or mechanical issue with a motor-generator rule out the motor-generator, the inverter, or some that prevents it from producing the torque com- other component. manded by the inverter.

A comparison between commanded motor-genera- tor torque and actual motor-generator torque may also, in some cases, aid the technician in the diag- nosis of an inverter fault. For example, a hybrid or electric vehicle may have a no-start issue in which the vehicle will momentarily READY up, then shut down.

Let us assume that a scan of the vehicle reveals that a diagnostic trouble code (DTC) has been set, which indicates a motor-generator performance

PEV Motor and Inverter Diagnosis and Repair 27 Test

Post Test PEV Motor and Inverter Diagnosis and Repair

1. Capacitors in inverters: a. Stabilize voltages and act as filters b. Are used to boost inverter voltage to power transistors c. Are only used in the inverter’s low voltage circuits d. Are sometimes used instead of battery packs

2. An active discharge circuit in an inverter: a. Discharges capacitor charge into a motor-generator’s stator winding b. Discharges capacitor charge into a resistor upon vehicle shutdown c. Disconnects the vehicle’s safety disconnect and discharges the inverter d. Discharges capacitor charge into the vehicle’s battery pack

3. A passive discharge circuit in an inverter: a. Discharges capacitor charge into a motor-generator’s stator winding b. Discharges capacitor charge into a resistor upon vehicle shutdown c. Disconnects the vehicle’s safety disconnect and discharges the inverter d. Discharges capacitor charge into the vehicle’s battery pack

4. Capacitors in inverters a. Are used to power up a plug-in vehicle’s battery pack at start-up b. Are used to power motor-generators during heavy acceleration c. Are used to discharge a plug-in vehicle’s battery pack d. Are normally discharged when a plug-in vehicle is powered OFF

5. A technician can confirm that an inverter’s capacitors have discharged by: a. Using a properly rated voltmeter at the appropriate test points b. Powering down the vehicle and allowing the capacitors to discharge c. Powering down the vehicle and checking whether or not it will power up d. Using a properly rated ohmmeter at the appropriate test points

28 PEV Motor and Inverter Diagnosis and Repair Post Test

6. Motor speed is controlled by controlling the: a. Amplitude of alternating current fed to the motor b. Voltage level of alternating current fed to the motor c. Number of phases which receive alternating current d. Frequency of alternating current fed to the motor

7. Motor torque is controlled by controlling the: a. Amplitude of alternating current fed to the motor b. Voltage level of alternating current fed to the motor c. Number of phases which receive alternating current d. Frequency of alternating current fed to the motor

8. An inverter uses ______to invert DC to AC: a. Capacitors b. Power transistors c. Diodes d. Passive discharge circuits

9. Most hybrid and electric vehicles use: a. Asynchronous induction motor-generator(s) b. Permanent-magnet synchronous motor-generator(s) c. Switched reluctance motor-generator(s) d. Linear motor-generators

10. To sense motor rotor position, most hybrid and electric vehicles use: a. Resolvers b. Hall-effect sensors c. Magnetoresistive sensors d. Positive temperature coefficient sensors

PEV Motor and Inverter Diagnosis and Repair 29 Notes

30 PEV Motor and Inverter Diagnosis and Repair Notes

PEV Motor and Inverter Diagnosis and Repair 31 Notes

32 PEV Motor and Inverter Diagnosis and Repair Notes

PEV Motor and Inverter Diagnosis and Repair 33