Active-Phase Converter for Operation of Three-Phase Induction Motors on Single-Phase Grid

The operation of a three-phase induction machine on single-phase supply has been an approach used for electromechanical energy conversion in rural communities with limited or no access to the three-phase grid. Such single-phase to three-phase conversion can be achieved by passive and active means. In passive methods, fixed capacitors are used for starting and running the motor. Single-phase to three-phase conversion with reduced switch count is desirable, as this leads to a lower cost. However, it is a challenge to start an induction motor using such a power converter and to maintain balanced three-phase voltage under all loading conditions. It is shown in this work that balanced excitation cannot be achieved under all conditions with variable capacitor emulation method. An active phase-converter configuration and its control that ensures balanced three-phase power supply at the motor terminals under all operating conditions is proposed. Also, this approach has the ability to soft-start the motor. It is shown that this can be done without drawing excessive currents from the power converter or from the single-phase grid. A design methodology is presented for the selection of the autotransformer taps to limit startup transient currents to the desired level, based on the analytical results. Simulation and experimental results are presented that validate the proposed topology and control.