A Novel Four-Level Converter and Instantaneous Switching Angle Detector for High Speed SRM Drive

Abstract

A novel four-level converter and instantaneous switching angle detector for a high speed switched reluctance motor are proposed. Since the excitation time is very short compared to the general speed range of a high speed drive, the excitation current can not be built-up sufficiently. Also, the demagnetization current can be easily extended to the negative torque region. To obtain a fast current buildup and suitable demagnetization, a novel four-level converter is proposed. The proposed converter has an additional charge capacitor and an active power switch compared to a conventional asymmetric converter. The high voltage of the additional capacitor is applied to the phase winding in the fast excitation mode and the phase current is rapidly decreased during the recharging of capacitor in demagnetization mode. In addition, an instantaneous switching angle detector separated by main digital controller is designed for precise switching angle control. During high speed operation, rotor position error increases due to the constant sampling period of digital controller. The proposed instantaneous switching angle detector operates with optical encoders pulse and pre-set switching position regardless of sampling time. So, it determines the precise switching pattern without time delay from sampling time. The proposed high speed control system is verified by computer simulation and experimental results.