Harmonic control of multiple-stator induction machines for voltage regulation

Abstract

Small, one to a few horsepower, three-phase induction machines with three sets of electrically-isolated, magnetically-coupled stator winding circuits are described. A voltage inverter is developed and used to drive one set of the machine stator winding circuits. The second set of machine stator winding circuits is connected to a three-phase rectifier in which a path for zero-sequence current is provided from the winding circuits to the rectifier. The last set of stator winding circuits is connected to another three-phase rectifier, however, the stator circuit star point is floating, not providing a zero-sequence current path. By controlling the phase of the third harmonic on the machine drive stator circuits, and thus the waveforms present on the secondary and tertiary stator winding circuits, the output voltage of the rectifier with a zero-sequence current path can be tune above or below the rectifier output without third harmonic injection. The rectifier connected without a zero-sequence current path does not display this tunability with respect to third harmonic phase.