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A novel Lyapunov function-based direct torque controller for minimization of torque ripples in a switched reluctance motor (SRM) drive system is reported in this paper. SRM magnetization characteristics are highly nonlinear, where torque is a complex and coupled function of the phase currents and rotor position. The direct torque control (DTC) scheme avoids the complex process of torque-to-current conversion as required in indirect torque control scheme. The traditional DTC scheme uses a hysteresis-type torque controller and it leads to large amount of torque ripples when implemented digitally. The proposed controller is intended to take care of the nonlinear system dynamics of magnetic characteristics associated with accurate torque control using DTC scheme for the SRM drive system. In the Lyapunov function-based controller, the feedback gain is varied using a heuristic technique. The stability of the proposed controller is ensured by the direct method of Lyapunov. Experimental results for a 1-hp, 4-phase SRM are provided to demonstrate the efficacy of the proposed torque control scheme.
Date of Publication: Feb. 2012