How does AC and DC motor control differ?
AC MOTOR The speed of an AC motor is given by the formula Speed = 120 f / P, where ‘f’ is the applied frequency and ‘P’ is the number of poles. Since we cannot change the poles of a motor, the only way to change the speed is to vary the frequency, Hence variable frequency drives are used which generate V/F (Voltage / Frequency) output to control speed. DC MOTOR A DC Motor has a stator (field) winding and a rotor (armature) winding. Generally the stator winding voltage is kept constant and the armature winding voltage is varied by means of phase angle firing using Silicon Controlled Rectifier (SCR) bridges.
