How two-degree-of-freedom controllers optimize setpoint response, minimize the effect of load disturbances

Feb. 22, 2022

Greg: I am truly excited and appreciative of the involvement and achievement of leaders in process control who are coming together to create the ISA 5.9 Technical Report—a potential game changer. The PID algorithm is the most powerful tool for achieving individual loop performance as seen in the legacy of Greg Shinskey highlighted in last month’s tribute column. PID capabilities are underutilized mostly due to a lack of understanding.

Here Sigifredo Nino and I share our knowledge of PID structure and external-reset feedback (e.g., dynamic reset limit). Both of these features enable one to tune a PID to maximize load disturbance rejection as advocated by Shinskey, and still address the many other objectives and limitations. Presently, the PID is frequently detuned to deal with these situations, posing a severe, confusing burden on users, and resulting in a serious degradation in load response. The features presented here are simple to use and robust, enabling us to move on, which is greatly appreciated.