Discrete sliding mode control for processes with long dead-time

A new, input-output based discrete sliding mode control (DSMC) method is proposed for the control of processes with dead-time. However, it is necessary to combine DSMC with the Smith predictor for the dead-time compensation of processes with long dead-time. Because DSMC is sensitive to apparent dead-time in the process to be controlled, two Smith predictors were used in the control schema. One with high order is used to cancel out actual process output signal as good as possible. Another one with low order is used in the identification of the controlled process and in the design of DSMC. When this new DSMC is compared to the optimally tuned PID controller, it shows much better overall characteristics. Simulation experiments are made to illustrate the effectiveness of the new DSMC both for plants with short and with long dead-times.