Disturbance rejection using sliding mode control of adjustable speed drives

We propose a sliding mode controller (SMC) for a nonlinear voltage-controlled DC motor and consider its use for disturbance rejection. The nonlinearity includes the effect of magnetisation saturation and a nonlinear fan load. The performance of the controller under the effects of various torque disturbances and under measurement errors is studied. The SMC is shown to be very effective in suppressing the disturbance when perfect information about the states and disturbance are fed back to the controller. The effect of time delay on the sliding mode controller system is also studied. Using a disturbance observer, an estimate of the disturbance is obtained and fed to the SMC for effective speed control. We are currently tuning this observer and extending it to provide prediction as to reduce the effect of delay.