A unified approach to design the RZN PID controller for stable and unstable processes with time delay

In this paper, the well-known RZN method is discussed. It is demonstrated that both the RZN control structure and the inner stabilizing control structure can be equivalent to the classical unity feedback loop with a set-point filter, or the two-degree-of-freedom control structure. This implies that many design and analysis techniques developed for the classical control structure can be utilized for the two special control structures. A new procedure is developed for designing the parameters of the RZN PID controller. Suboptimal formulas without the limitation are analytically derived. The load response of the proposed method can be independently optimized.