EVT Electric Vehicle Systems & Powertrains 3

Question 1

What is 'torque vectoring' in an EV with multiple motors?

Accepted Answer

Independently varying torque output to individual wheels to improve handling

Answer

Torque vectoring precisely controls how much torque each motor (or wheel) delivers, improving cornering stability and traction without mechanical differentials.

Question 2

In an EV high-voltage system, what does 'galvanic isolation' protect against?

Accepted Answer

Electric shock to vehicle occupants and technicians by separating HV from low-voltage circuits

Answer

Galvanic isolation ensures no direct electrical path exists between the high-voltage traction system and the low-voltage (12V) chassis, protecting occupants and technicians.

Question 3

What is the purpose of the pre-charge circuit in an EV high-voltage system?

Accepted Answer

Slowly charge inverter capacitors before closing the main contactors to prevent inrush current damage

Answer

The pre-charge resistor and relay gradually charge large capacitors in the inverter to near-battery voltage before the main contactors close, preventing destructive current spikes.

Question 4

Which parameter does a variable frequency drive (VFD/inverter) primarily adjust to control motor speed?

Accepted Answer

The frequency of the AC output supplied to the motor

Answer

An inverter varies the frequency of its AC output to control motor speed, since synchronous and induction motor speeds are directly proportional to supply frequency.

Question 5

What is back-EMF in an electric motor, and when is it highest?

Accepted Answer

A counter-voltage generated by the spinning rotor; highest at maximum motor speed

Answer

Back-EMF is a voltage opposing the supply generated by the rotating rotor's magnetic field; it increases proportionally with rotor speed and limits top-end current.

(EVT) Certified Electric Vehicle Technician Practice Test

(EVT) Certified Electric Vehicle Technician Practice Test

EVT Electric Vehicle Systems & Powertrains 3