Concept of EV Motors
Special considerations for EV motors
1. offer the maxium torque that 4 to 5 times of rated torque for acceleration
2. Achieve 4 to 5 times the base speed for cruising
3.Designedd according to the vehicle driving profiles and drivers' habits
4. High power density and good efficiency map
5. High controllability, high steady-state accuracy and good dynamic performance
6. Harsh operating conditions
compared with industrial motor
1. twice rated torque for overload operation
2. twice the base speed for constant-power operation
3. based on a typical working mode
4. Need a compromise ammong power density, efficiency and cost with the efficiency optimized at a rated operating point
5. only special purpose industrial motor need
6. generally located in fixed places
Key issues on system technology
Single or multiple motor technology
Fixed or multiple gear transmission
Gear or Gearless
System voltage
Integration
Classification of EV motors
Commutator
Self-excited
Series
Shunt
Separately-excited
Field-excited
PM excited
Cons
Not reliable
Need to change brush
Cannot pass high current
EMI
Limited power output(field weaking)
Commutatorless
Induction
Wound-rotor
Squirrel cage
Pros
No magnet, Low cost
High power
No brush
Cons
Non-peak torque at low speed
complicated control
Synchronous
Wound-rotor
PM rotor
Reluctance
PM burshless DC
PROS
Coil outside, easy cooling
No commutator, reliable
High power density
CONS
Dteact rotor angle
Complicated control
Magnet is expensive
Switched reluctancce
Pros
No magnet, cheap
No temperature problem
Reliable
Cons
Difficult to control
PM hybrid
PV power electronics
Switching Devices
Criteria
Ratings
Voltage rating is based on battery nominal V, max Vcharging, and max Vregeneration
Irate depends on motor peak power and number of power devices
Switching frequency, e.g. 20kHz
EMI limiation
Filter size
Power losses
Base/gate driverability
Dynamic characteristics
Ruggedness
Maturity and cost
Power Convertors
4-quadrant DC chopper
3-phase full-bridge voltage-fed inverter
Soft switching(compared with hard switching)
Switching loss almost ZERO
Overall efficiency possibly HIGHER
Heat-sinking requirement possibly LOWER
Hardware count MORE
Overall power density possibly HIGHER
EMI problem LOW
dv/dt Problem LOW
modulation scheme LIMITED
maturity DEVELOPING
Cost HIGHER
