Sensor elimination and converter topology simplification in switched reluctance motor drives for commercial applications

Abstract

Advantages of switched reluctance motor (SRM) drives make it an attractive alternative candidate for replacing adjustable speed ac and dc drives in both industrial and consumer applications. The SRM drive system consists of a power converter and a control section. Technology simplifications are required in both of those sections in order to develop a simple, low-cost and robust SRM drive that can be efficiently operated in hostile environments, such as under the hood of an automobile. A modified converter topology for star-connected SRMs, which is also suitable for low-voltage applications, has been developed during the course of this research. The converter has a dual time-constant freewheeling circuit that enhances the efficiency and the operating range of speed as compared to the currently used single switch converters for low-cost, low-voltage applications. In the control section, shaft position sensing is essential in SRMs in order to synchronize the phase excitation pulses with the rotor position. The phase inductance variation of an SRM varies significantly between the aligned and unaligned rotor positions. This variation of phase inductance as a function of rotor position has been utilized to develop three new indirect rotor position sensing schemes. Two of these methods are based on modulation techniques commonly used in communication systems. These schemes employ an analog electronic circuit to extract the instantaneous self inductance variation of a phase in an encoded form and then process the information to obtain the rotor position. In the other method, the mutually induced voltage variation in an unenergized phase is used to detect the rotor position indirectly. The need for discrete current sensors for current feedback information has also been eliminated by the use of integrated current sensing techniques. MOS-gated power semiconductor devices in conjunction with a smart current regulation algorithm provide continuous current information in the active phase which can be appropriately processed to develop the desired torque...