Fig. 3 shows the system output, solid line is FSPSMC,
dashed line is PID. From this figure, it is obvious that the
control performance of FSPSMC is better than that of PID.
Note that there are no residual errors under constant external
disturbance. It shows that the feedforward control is effective.
Due to the system uncertainty, Smith predictor can not work
well, the feedback control algorithm is required to guarantee
the system performance. SMC has strong robustness and
disturbance suppression ability. Hence, it can achieve better
performance than that of PID. Fig. 4 is the control input of
FSPSMC. From this figure, one can see the chattering is
reduced greatly in light of integral switching gain technique