Proportion-Integral-Derivative (PID) controllers are widely used for process control across various industries, including the chemical industry. However, the traditional one-degree-of-freedom PID controller struggles to balance a good setpoint tracking and disturbance rejection. This paper proposes two novel two-degree-of-freedom nonlinear PID (TDOF NPID) controllers. As such, this approach combines a nonlinear PID controller with its specific strengths with an independent linear compensator, which can be either a P-type or a PD-type compensator. A hybrid genetic algorithm is also employed for optimizing the parameters of the TDOF nonlinear PID controllers, considering both the setpoint tracking and disturbance rejection performance, with the goal of minimizing the integral of absolute error criterion. The performance of the proposed controllers is evaluated by benchmarking them against the traditional PID controller for three processes with varying orders and one nonlinear system.
*This paper is an extended study of a previous paper with the title "Design of a Nonlinear PID Controller and Tuning Rules for First-Order Plus Time Delay Models", published in Studies in Informatics and Control journal, vol. 28(2), 2019, pp. 157–166 (DOI: 10.24846/v28i2y201904).
Nonlinear PID controller, Two-degree-of-freedom, Feedforward compensator, Parameter tuning, Hybrid genetic algorithm.
Gun-Baek SO, Gang-Gyoo JIN, Yung-Deug SON, "Design of Novel TDOF Nonlinear PID Controllers for Linear and Nonlinear Systems*", Studies in Informatics and Control, ISSN 1220-1766, vol. 35(1), pp. 5-17, 2026. https://doi.org/10.24846/v35i1y202601
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