pev motor and inverter diagnosis and repair

PEV Motor and Inverter

Diagnosis and Repair

Technical Resource Guide

PEV Motor and Inverter Diagnosis and RepairRevision 1October 1, 2014

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

1PEV Motor and Inverter Diagnosis and Repair

COURSE INTRODUCTIONCourse Title PEV Motor and Inverter Diagnosis and Repair

Course Length 16 hours

Description: This course is designed to provide professional automotive technicians with the general skills needed to safely diagnose, repair, and service motor-generators and inverters in plug-in vehicles (PEVs), including plug-in hybrid and electric vehicles. Discussion topics, many of which will be reinforced by hands-on exercises, include:

▪ Safely discharging inverter capacitors, and con-firming capacitor discharge

▪ Conversion of DC to AC, and AC to DC, by inverter

▪ Diagnosing, repairing, and servicing inverter cooling systems

▪ Measuring motor winding phase resistances

▪ -Measuring motor winding insulation resistance

▪ Understanding series-parallel hybrid transaxle operation

▪ Understanding series-parallel hybrid transaxle scan data

▪ Diagnosing, repairing, and servicing motor-gen-erators NOTE: This course is only intended to supple-ment manufacturer-specific (OEM) safety, ser-vice, and diagnostic information. This course cannot serve as a substitute for such information, which changes often. In all cases, manufactur-er-specific information for a particular plug-in vehicle supersedes any information presented in this course.

Course Benefits The benefit of this course is designed to help the fleet technician become familiar with all aspects of motorgenerators and inverters as they relate to plug-in vehicles, including vehicle diagnosis, repair, and service.

Prerequisites Students should have a basic experience in in automotive diagnosis, repair, and maintenance, including the use of scan tools and online service information databases. Solid understanding of basic automotive electrical systems. Ability to correctly follow safety procedures.

Objectives By the end of this course participants will be able to:

List safety issues related to motor-generators and inverters

▪ Describe basic components of a typical motor-gen-erator

▪ Explain the purpose of a milliohmmeter

▪ Demonstrate correct measurement of phase-to-phase resistances

▪ Explain the purpose of an insulation resistance meter

▪ Describe safety issues related to insulation resis-tance measurements

▪ Demonstrate correct measurement of insulation resistance

▪ Explain the potential diagnostic value of mo-tor-generator torque scan data

Competence Competence will be measured by both lab demonstration and pre and post tests.

2 PEV Motor and Inverter Diagnosis and Repair

Pretest

PretestPEV 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 ohm to prevent a voltage 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


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


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

Table of Contents


7. Diagnosing, repairing, and servicing motor-generators

8. Comparing commanded motor torque to actual motor torque

Post-Test


Module One1


Motor-Generators & Inverters in ContextAn 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 direct current (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 voltages whenever their rotors are physically rotated, the inverter must change

Motor-generators & Inverters in Context

(rectify) motor-generator AC into DC, at the proper voltage, to charge the battery pack.

Module Two2



Capacitors in InvertersInverters have many high-voltage circuits, including circuits that incorporate capacitors to stabilize voltages and act as filters. As high-voltage capacitors can store electrical charge, charged capacitors in inverters can create a safety issue for a technician, even after a plug-in vehicle has been powered OFF.

During operation, a plug-in vehicle’s inverter capacitors typically remain charged with high voltage. When the vehicle is powered OFF, high-voltage (HV) relays open, electrically isolating the vehicle’s battery pack from the inverter. Two redundant circuits are employed to discharge a typical inverter after the vehicle has been powered OFF:

▪ Active discharge circuit

▪ Passive discharge circuit

OEM service information will typically direct a technician to allow a specific amount of time to elapse after a vehicle has been powered OFF, to allow the vehicle’s inverter capacitors to discharge. The technician must still measure voltage at the appropriate test points to confirm that the capacitors have been discharged, if he or she is required to access high-voltage inverter circuits when working on the vehicle. These test points can also be identified by referring to OEM service information.

Active Discharge Circuit

A plug-in vehicle’s inverter incorporates active discharge circuits that typically discharge the inverter’s capacitors in less than one second. As indicated by the name, these are active circuits that

Capacitors in Inverters

must be activated to discharge the capacitors.

When the vehicle is powered OFF and the battery pack’s HV relays open, a typical active discharge circuit will turn on the appropriate power transistors within the inverter, electrically connecting the inverter to a motor-generator. The inverter’s capacitors then discharge into the motor-generator’s stator winding. The inverter’s control system must select transistors that will allow the capacitors to discharge into the motor-generator without causing the rotor to turn.

Active discharge can be observed in an instructor-led lab, but is more accurately observed with a scope than with a voltmeter, as a voltmeter’s display often refreshed too slowly to allow the observer to accurately see the speed at which the inverter’s capacitors are discharged.

Passive discharge circuit

A plug-in vehicle’s inverter typically incorporates a passive discharge circuit, which serves as a back-up discharge circuit in the event that the active discharge circuit is not activated when the vehicle is powered OFF. This may occur when:

▪ The active discharge circuit is disabled due to a motor or inverter fault

▪ The active discharge circuit has a fault

A passive discharge circuit is usually made up of a resistor, or group of resistors, which connect the inverter’s HV positive DC circuit to the inverter’s HV negative DC circuit. The resistor circuit has enough resistance to prevent it from interfering with the inverter’s other high-voltage circuits, and


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.


Capacitors in Inverters

Module Three3



Conversion of DC to AC, and AC to DC, by the Inverter

Inverter function when a motor-generator is functioning as a motorA motor-generator can produce torque from current that is supplied by:

▪ The vehicle’s battery pack

▪ Another motor-generator, functioning as a generator

Hybrid and electric vehicle motor-generators are three-phase, and are powered by alternating current. When a motor-generator is powered by current from the battery pack, the inverter must change that current from direct current to alternating current, and switch current between all three phases in the proper sequence to rotate the motor. The inverter must also control motor-generator speed and torque:

▪ Motor speed is controlled by controlling AC frequency

▪ Motor torque is controlled by controlling current amplitude

An inverter uses power transistors to switch direct current back and forth through each of a motor-generator’s three phases, effectively creating an alternating current. By controlling transistor “on-time” through pulse-width modulation (PWM), the inverter can control effective voltage, and create a voltage pattern that drives a sine wave current.

Most inverters employ several voltage patterns to drive a motor-generator, depending on motor speed,

Conversion of DC to AC, & AC to DC, by the Inverter

motor load, and required torque.

Inverter function when a motor-generator is functioning as a generator

When a motor-generator’s rotor is physically rotated, such as during deceleration, the motor-generator produces an alternating current. The voltage level of the alternating current increases with rotor speed. The inverter must rectify this uncontrolled AC into DC, and supply direct current to the battery pack at the correct voltage level to charge the battery pack. Diodes are mounted in the power transistor block, in parallel to each transistor, to rectify alternating current into direct current. The method for adjusting the voltage level of the rectified current varies from manufacturer to manufacturer.

Inverter Cooling SystemPower transistors can get very hot during operation, and must be rapidly cooled to avoid damage from overheating. Although a few hybrid vehicles use air-cooled inverters, most use liquid-cooled inverters. Plug-in vehicles also typically use liquid-cooled inverters due to the amount of power that they generate. The inverter’s power transistors are typically bolted to a heat sink, with thermal grease to aid in heat transfer. The heat sink is connected in some way to a cooling system.

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 the components. Some inverter cooling systems


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 SystemsInverter 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.


Conversion of DC to AC, and AC to DC, by the Inverter


Module Four4


Motor-Generator Operation

Motor-Generator OperationMost electric vehicles have one motor-generator, housed in a transaxle assembly with fixed gearing. As mentioned previously, hybrid and electric vehicle motor-generators are three-phase, alternating current machines. All motor-generators used in hybrid and electric vehicles are brushless.

As motor-generators typically have excellent torque at almost all speeds, variable gear ratios are not normally employed in electric vehicles. Rather, the vehicle will typically have a single-speed transaxle. Some motor-generators used in plug-in hybrids have variable gearing, because the action of the motor-generator affects the gearing of the vehicle’s internal-combustion engine.

Rotor ConstructionDepending on rotor type, a plug-in vehicle’s motor-generator(s) may be either an induction motor or a permanent-magnet synchronous motor (PMSM).

An induction motor uses the stator winding’s electromagnetic field to induce a current into conductors within the rotor. The electromagnetic field produced by the rotor then interacts with the electromagnetic field produced by the stator, to produce rotation. Potential issues with induction rotors include cracked rotor bars. Tesla is one of the few electric vehicle manufacturers that uses induction motors in mass-produced vehicles.

Most hybrid and electric vehicles use permanent-magnet synchronous motor has powerful permanent magnets embedded in the rotor. The magnets

produce a permanent magnetic field. The stator winding’s electromagnetic field interacts with the rotor’s magnetic field to produce rotation. Potential issues with permanent-magnet motors include magnet deterioration due to excessive temperature.

Stator ConstructionInsulated copper wire is wound around an iron core, in three phases, to create a motor-generator’s stator winding. The three phases are generally connected at one end in a configuration called a wye winding. Although there are many different configurations in which a stator winding can be constructed, the basic architecture of stator windings are similar to one another.

Resolver and Motor ControlA plug-in hybrid vehicle’s inverter controls a motor-generator by commanding currents that interact with the motor-generator’s rotor to produce the desired effect. To do this, the inverter must “know” the exact position of a motor-generator’s rotor at all times.

This requires an extremely accurate position sensor that reads rotor position whenever the vehicle’s powertrain is powered up (READY), even if the rotor is not moving. Most hybrid and electric vehicles use a sensor called a resolver, although a few vehicles use conventional hall effect sensors.

A resolver consists of a ring of coils, resembling a stator winding, surrounding an elliptical steel lobe mounted on the motor-generator’s rotor shaft. The


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 SensorsMany 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.


Motor-Generator Operation


Module Five5


Measuring Stator Winding Phase-to-Phase Resistances

Measuring Stator Winding Phase-to-Phase ResistancesA healthy three-phase motor will have relatively balanced resistances across all phases of its stator winding. If the winding develops an internal short, the electrical resistance of that part of the winding will eventually change. The technician can verify this by comparing resistance measurements across all three phases, as well as to the vehicle manufacturer’s specifications.

A typical digital multimeter (DVOM) will have a resolution of 0.01 ohms, or 100 milliohms. Some higher-quality digital multimeters also have a “low ohms” feature which produces a resolution of 0.01 ohms, or 10 milliohms, and cancels out the resistance of the meter’s leads.

However, since typical windings have phase resistances of considerably less than one ohm, the technician may be required to detect phase-to-phase resistance variations as small as two milliohms (two thousandths of an ohm). This requires an extremely accurate meter, far beyond the capabilities of a conventional DVOM. By comparison, a typical milliohmmeter has a resolution of a tenth of a milliohm (0.0001 ohms) or less. This will be adequate for the needs of a technician who must measure hybrid or electric vehicle motor-generator stator windings.

We shall use the main drive motor or MG2, of a 2001 Toyota Prius as an example. As hybrid motor-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

a time. The motor cables of this vehicle are marked U, V, and W, and the technician will need to take three measurements: U-V, V-W, and W-U.

Resistance specifications for many hybrid and electric vehicle motor-generator windings, including those of this Prius, are typically given for a winding that is measured at a fixed reference temperature, usually 20ºC (68ºF). Measurements taken at any other temperature will be inaccurate, and must be corrected. Since the resistance of copper rises when its temperature rises, Toyota specifies that the vehicle must be at rest (not powered up) for at least eight hours before measurements are taken, to allow the stator winding to cool and stabilize at ambient temperature. The winding’s phase-to-phase resistances can then be measured, and the measured resistances can then be corrected to calculated resistance at 20ºC, using a standard formula that is provided in OEM service information. Some milliohmmeters incorporate an internal ambient temperature sensor that enables the meter to correct resistance measurements made at ambient temperature to resistance at the reference temperature. This feature saves time and helps prevent incorrect calculations.

The technician would then compare the final, corrected measurements to factory specifications: in this case, 31 to 36 milliohms. Some vehicle manufacturers may also list a maximum variation between phase-to-phase resistances, or between each phase resistance and an average of all phase-to-phase resistances.

22

Module Six6

PEV Motor and Inverter Diagnosis and Repair

Measuring Stator Winding Insulation Resistance


Measuring Stator Winding Insulation ResistanceA conventional, low-voltage DVOM “measures” resistance by producing a small fixed voltage across two test points, measuring the resulting current, and using Ohm’s Law to calculate the resistance. Although everything has some electrical resistance, the typical DVOM will display an “infinite” reading when measuring electrical resistance between a high-voltage conductor — for example, a properly 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 enough voltage to drive current across high-voltage insulation.

A megohmmeter, also referred to as a megger or insulation resistance tester, can produce DC voltages as high as 1000V volts although test voltages are more commonly specified at 250 or 500 volts. To accurately test the resistance of a given component, the technician must electrically isolate the component’s high-voltage circuits from the rest of the vehicle. The resulting resistance measurement can then be compared to the OEM specification for the component under test.

As this is a test of high-voltage insulation, rather than circuit resistance, the technician will NOT connect the megohmmeter to two conductors. Instead, the technician will connect one of the megohmmeter’s leads to chassis or component ground, as directed by 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 transaxle case, and the other to the terminal end of one of the motor-generator’s motor cables.

The technician would then select a test voltage according to manufacturer’s specifications (for the 2001 Prius, 500 volts), press and hold the meter’s high-voltage test button, wait for the reading to stabilize, and record the insulation resistance. Note that most megohmmeters have a spring-loaded test button, which must be held down until the displayed insulation resistance reading stabilizes. It is normal for the insulation resistance reading to rise for several seconds while the test button is pushed down, and the technician must wait until the reading stabilizes.

CAUTION: Never allow the high-voltage conductor to touch chassis or component ground. This will create a high-voltage short circuit and invalidate the test.

After the technician has taken his or her readings, he or she then releases the test button, which discharges the meter’s leads, before disconnecting the leads from the component under test.

As a hybrid’s high-voltage circuits are normally isolated from chassis ground, insufficient resistance 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 Toyota Prius has a minimum insulation resistance specification of 10 MΩ (ten million ohms, or megohms) at 500 volts. Our test winding failed at 0.1 megohms, indicating that the motor-generator’s stator winding has shorted to ground.

After replacing the motor, the insulation resistance of the new winding was measured, and easily passed the test with a resistance of more than 500 megohms at 527 volts.

Module Seven7



Diagnosing, Repairing, & Servicing Motor-Generators

Diagnosing, Repairing, and Servicing Motor-GeneratorsMotor windings for plug-in hybrids such as the 2011 Chevrolet Volt 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 ohmmeter 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.

Module Eight8



Comparing Commanded Motor Torque to Actual Motor Torque

Comparing Commanded Motor Torque to Actual Motor TorqueAlmost all hybrid and electric vehicles generate scan data that indicates motor-generator torque. However, it may not be apparent as to whether the scan data indicates commanded motor-generator torque or actual motor-generator torque. OEM service information may help the technician deter-mine what the scan tool is indicating.

Some hybrid or electric vehicles include separate motor-generator scan data for both commanded torque and actual torque. In some cases, it may be useful to compare commanded torque to actual torque as part of a diagnosis. While some variation between commanded torque and actual torque can be expected, wide variations may indicate an elec-trical or mechanical issue with a motor-generator that prevents it from producing the torque com-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

issue that is caused by either a motor-generator or the inverter that drives the motor-generator.

A careful examination of the freeze frame for the DTC — or a snapshot of motor-generator torque data — may indicate zero torque commanded to the motor-generator. This, in turn, indicates that the inverter’s control system detected an issue before applying current to the motor-generator. In this case, a motor-generator issue is not indicated: the issue probably lies with the inverter, or some-where “upstream” of the inverter.

If, on the other hand, a freeze frame or snapshot indicates that the inverter had commanded torque to the motor-generator, and that torque was ap-plied, the issue may be with the motor-generator. In both cases, further testing may be required to rule out the motor-generator, the inverter, or some other component.


Post TestPEV 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

Test


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


Notes

pev motor and inverter diagnosis and repair

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