The direct Nyquist array design of PID controllers

The gain and phase margins design for single-input single-output proportional-integral-derivative controllers is extended to the multivariable systemʹs Nyquist array. The design method allows the user to specify the robustness and performance of the system through gain and phase margin specifications. The unformatted design procedure given in this paper is well suited for implementing self-tuning PID control for multivariable processes. A laboratory implementation is given in the paper to demonstrate the design method.