A Novel 4-Level Converter for High Speed SR Drive

This paper proposes a novel 4-level converter and instantaneous switching angle detector for a high speed SRM (Switched Reluctance Motor) drive. When the excitation time is shorter than a general speed range SRM, the excitation current can not be sufficiently built-up. And the demagnetization current can be easily extended to the negative torque region. In order to obtain the fast excitation and current build-up and suitable demagnetization, a novel 4-level converter is proposed. The proposed 4-level converter has additional charge capacitor and an active power switch compare than a conventional asymmetric converter. For the fast current built-up, the high charged voltage of additional capacitor is supplied to the phase winding in the fast excitation mode. And the demagnetization phase current is decreased fast during the recharging of capacitor in demagnetization mode. In addition, an instantaneous switching angle detector separated by main digital controller is designed for the precise switching angle control. In the high speed, rotor position error is increased by the sampling period of digital controller. The proposed instantaneous switching angle detector operates with optical encoder pulse and pre-set switching position regardless of sampling time. So, it determines the precise switching pattern without time delay from the sampling time. The proposed high speed control system for SRM is verified by computer simulations and experimental results.