Modeling and torque control implementtion for an 8/6 switched reluctance motor.

Abstract

This thesis begins with a brief introduction of the basic principles of operation of SRMs, and explains how flux characteristics are derived from voltage and current measurements, and presents results obtained from an 8/6 SRM. Torque characteristics are derived from these flux characteristics using both the inductance and co-energy methods. Comparison of these results with direct torque measurements shows that the co-energy method is significantly more accurate than the inductance method. Electrical and mechanical simulation models are derived from inductance and torque characteristics, and implemented in Matlab/Simulink. Simulated results are shown to agree with measurements obtained from physical locked and free rotor alignment experiments. These models are also used to illustrate the need for sophisticated commutation strategies and high performance current control loops to achieve low ripple torque control. The Matlab/Simulink models are transferred to PSCAD to compare the current control abilities, cost, complexity and robustness of the Asymmetrical Half Bridge (AHB), n+ 1 switch, and C-dump SRM converter topologies. The relatively high cost of the AHB converter is justified in terms of its robustness, simplicity and superior capabilities for current and torque control. The torque sharing function commutation strategy for low ripple torque control is presented and simulated with hysteresis current control for the 8/6 SRM fed from a four phase AHB converter. A DSP implementation of the current and torque control loops is also presented and tested under various dynamic speed and load conditions and recommendations are made for future work.