Variable speed control of single and two phase induction motors using a three phase voltage source inverter

The authors propose a method for using a standard three-phase voltage source inverter to achieve wide-range variable-speed control of a single-phase induction motor, by connecting the main and auxiliary windings of the motor across the bridge as an unbalanced three-phase load. The motor is analyzed as an unbalanced two-phase system to determine the torque that can be expected under variable frequency control. A modulation strategy is described which achieves the maximum possible converter utilization for a two-phase output voltage (balanced or unbalanced). With the proposed modulation strategy, rated torque can be achieved from the motor at any speed with the motor operating at a small slip. The theoretical basis for the control strategy, simulation and full experimental results are presented