https://avt.inl.gov/sites/default/files/pdf/fsev/power.pdf
Power system of electric vehicle consists of just two components:
Motor: Provides power – converts electrical energy into mechanical energy, DC and AC motor used in EVs
Controller: Controllers application of this power
In contrast the power system of a gas-powered car has lots of components including the engine, carburetor, oil pump, exhaust system etc
DC motor components:
Coils that create magnetic forces which provide torque
A rotor or armature mounted on bearings that turns inside the field
Commutating device that reverses magnetic forces and makes the rotor turn(this provides power)
AC motor components:
Same components but no commutating device because there is continuous current reversal
AC motor:
Advantages:
Lighter weight
Reliable
Only one moving part(the shaft) and therefore should last a long time
Disadvantages:
While the motor itself is cheaper than a DC motor, the cost of the electronics needed to invert the battery’s direct current to alternating current makes it overall more expensive
DC
Advantages:
Cheaper overall
Simpler controller
IN the past EVs used DC motors/controllers because they operate with the battery’s current without lots of complicated electronics. Now that these electronics are getting better and better lost of EVs use AC motors/controllers due to lighter weight and better efficiency
Controllers:
The controller is the electronics that operate between the batteries and the motor to control the speed/acceleration
Regulates energy flow from the battery
For ac motors it transforms the battery’s direct current into alternating
Controller converts the motor to generator(regenerative braking)
Reverses motor rotation so car can reverse
Modern controllers change speed and acceleration by a process called pulse width modulation
o Silicone-controlled rectifiers interrupt the electricity flow to the motor rapidly
o High power when intervals are short(when current is turned off)
o Low power when long intervals
o Older controllers for EVs with dc motors a variable resistor controller was used
Full power always draw and high resistance was used to reduce current to motor when it wasn’t necessary
Criteria for selecting battery based on motor and controller
Battery voltage should match motor rating(you can overvolt a motor usually?)
Battery AH rating = motor power rating/motor voltage rating x 1 hr
Controller current rating should be quite a bit higher than motors max current draw – eg min 20A controller for 10.4A that a hypothetical motor draws
Rated power of motor is calculated from the combination of speed, torque and duty cycle; this establishes critical voltage, current, and capacity requirements of battery
Battery discharge current rating should meet or exceed motor current input requirements
Battery discharge curve is important because output voltage directly affects output speed of motor