A novel variable frequency three-phase induction motor drive system using only three controlled switches

This paper presents a novel variable frequency motor drive system for a three-phase induction machine. In this drive system, the machine is excited by unidirectional stator currents shaped and sequenced such that a rotating air gap flux is induced so that the machine can operate. Due to the unidirectional nature of the currents, an "inverter" that incorporates only three active, IGBT type switches, and three freewheeling diodes can synthesize them. The drive system requires an asymmetric induction machine that can easily be obtained by externally rewiring a motor with a dual wound stator. The inverter is supplied by a single-phase input via a voltage doubler diode rectifier; hence it can be operated with residential service. In this paper, theoretical control methods are presented and both simulation and experimental results are provided proving the validity of the proposed drive system.