PEV Motor and Inverter Diagnosis and Repair
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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 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 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 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 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 voltmeter, as a voltmeter’s display OFF: often refreshed too slowly to allow the observer to accurately see the speed