Robust analysis and PID tuning of cascade control systems

The robustness and performance of the cascade control system are analyzed in this article. A robustness measure is defined, and it is shown that it can reflect the interaction between the inner loop and the outer loop and has a clear indication of the robustness of each loop. The measure can serve as a graphic aid for tuning the cascade controller. Moreover, it is observed that the cascade controller can be tuned individually for each loop instead of sequentially.