Abstract: An adjustable speed drive for single-phase induction motors has a low-cost structure including a rectifier and a two-switch inverter. During full-speed operation, power is supplied directly from the AC power system to the main winding of the motor and from the inverter at line frequency but phase-shifted from the line voltage to an auxiliary winding of the motor to develop start up torque for the motor. In one or more lower speed operating modes, power is supplied from the inverter at a lower frequency directly to the main winding and through a phase-shifting capacitor to the auxiliary winding of the motor. Low cost switching devices may be used in the inverter since they are not required to switch the full-speed power of the motor.

Abstract: An adjustable speed drive for single-phase induction motors has a low-cost structure including a rectifier and a two-switch inverter. During full-speed operation, power is supplied directly from the AC power system to the main winding of the motor and from the inverter at line frequency but phase-shifted from the line voltage to an auxiliary winding of the motor to develop start up torque for the motor. In one or more lower speed operating modes, power is supplied from the inverter at a lower frequency directly to the main winding and through a phase-shifting capacitor to the auxiliary winding of the motor. Low cost switching devices may be used in the inverter since they are not required to switch the full-speed power of the motor.