Robust Non-Overshoot Time Responses Using Cascade Sliding Mode-PID Control

Overshoot is a serio us problem in automatic control systems. This paper presents a new method for elimination of the step response overshoot in a conventional PID-controlled system and enhancement of its robustness by cascading a sliding mode controller in the outer loop. The idea is first to use the cascade control principle to model the under-damped system under PID control with a second-order system. Then, by making use of the sliding mode control outer loop, a robust, reduced-order response can be obtained to suppress the control overshoot. The proposed approach can also deal with time delay systems. Its v alidity is verified through simulation for some dynamic systems subject to hig hly nonlinear uncertainties, where overshoot remains an issue.