Performance analysis and tuning of variable-structure PID controllers for level process

A methodology of analysis of stability and performance of variable structure (VS) PID controllers is proposed. It is proposed that stability of the VS system can be approximately assessed via the describing function method. The describing function of the VS PID controller is derived. It is shown that the system with the VS PID controller is quasilinear. Tuning rules for VS PI controller for the level process are given. It is shown that the VS PI controller has higher performance than the conventional PI controller for the process considered.