Q. How does motor speed controller works?

Answer

The battery connection to the motor is on and off rapidly in all 4QD controllers thanks to a technique called pulse width modulation [PWM] often at a rate of roughly 20000 times per second. In order to supply power to the AC motor the AC motor controller must change the incoming voltage to a frequency that can be adjusted. Through its variable output the motor's speed can be modulated with great accuracy. Since the motor can't keep up with such a rapid switching rate it simply averages out the pulses. In addition the inductance of the motor serves as an electrical flywheel to maintain a consistent flow of current in the motor despite the rapid switching.