Microcontroller based multi-mode operation of a three-phase induction generator with the Smith connection

The Smith connection is a special winding connection that enables a three-phase motor or generator to operate with high efficiency on a single-phase supply system. This paper describes the multi-mode operation of a single-phase induction generator with the Smith connection. This operation involves the selection of appropriate phase-balancing capacitances that give minimum voltage and current imbalance in the generator as the rotor speed changes. A simple switching strategy is adopted by using one of the stator phase voltages as the control signal that determines the mode selection. A prototype multi-mode system (namely L-mode, M-mode and H-mode) is implemented by using a microcontroller as a voltage comparator and mode selector. Experiments performed on a small induction machine confirm the feasibility of the proposed controller. The features of the proposed controller are simplicity in circuit design, low cost, and no need for a speed sensor.