Starting and running the induction motor with a variable capacitor

Single phase induction motors employ during the startup a capacitor that is connected to the auxiliary winding in order to create a rotating magnetic field and consequently the necessary starting torque. When the motor has acquired during the starting phase about 75% of its nominal rotational speed, fast enough just for the main winding to maintain the torque, a centrifugal switch disconnects the auxiliary winding and capacitor from the supply. This paper examines the possibility to use instead of the fixed capacitor and the centrifugal switch a variable capacitor whose impedance can be controlled by electronics and digital processing with respect to the necessary starting and adequate steady state torque with further prospects of optimal working point regulation.