FPGA based sliding mode control of PMSM for torque ripple reduction

Abstract

This work illustrates a simple and efficient torque ripple reduction method for Permanent Magnet Synchronous Motors. In this technique, the Sliding Mode controller will be used as a tracking controller. The control objective is to track a reference speed with the actual speed of rotor. In order to achieve the desired speed, the phase voltage must be varied as a function of rotor angular displacement. The angular speed of the synchronous motor depends on the frequency of the voltage applied to the stator windings. This neccesitates the measurement of angular displacement of the motor. The error signal between the reference and actual speeds represents the sliding surface s. The sliding mode controller is derived from the d-q variables and is based on Lyapunov's stability concept. Moreover with the addition of an observer to estimate the applied load torque, it can compensate for load torque disturbances. Hence the torque ripples get reduced in Permanent Magnet Synchronous Motor. The results obtained in Sliding Mode Control is compared with the conventional Direct Torque Control. The Direct Torque Control and Sliding Mode Control are simulated in Matlab/Simulink environment. The simulation results validate the effectiveness of Sliding Mode Control over Direct Torque Control. Hardware implementation of Sliding Mode Control is done on a prototype motor of 5V using Xilinx FPGA Spartan 3AN and ISE Design Suite 14.5.