Single-phase induction motor adjustable speed drive: direct phase angle control of the auxiliary winding supply

An adjustable-speed drive acting on the auxiliary winding of single-phase induction motors is described. Speed variations are obtained by adjusting the electromagnetic torque by controlling the auxiliary winding voltage magnitude and phase angle while the motor's main winding is directly connected to the local utility outlet. A variable auxiliary winding voltage phase angle is shown to yield significant torque control, providing starting and motoring torque as well as reversability and some braking torque. The analysis includes the determination of the relationship between the auxiliary winding voltage phase angle and the phase angle difference between the auxiliary winding currents. A control methodology for selecting an auxiliary winding voltage magnitude and phase angle is examined. Simulation results of the motor's torque-speed characteristics using the controlled auxiliary winding supply are shown and discussed. The drive is tested using a dynamometer to experimentally verify the results of the theory and simulations, and to explore the practicality of a simple, low-cost single-phase induction-motor drive using auxiliary winding voltage control.<>