A two degrees of freedom PID control system, its features and applications

PID control systems are widely used as a basic control technology for industrial control systems today, due to its well-known simple PID control structure. However, the tuning of the PID control systems is not always easy, because of its simple control structure for wide class of process characteristics. What is a widely applicable and simple process controller with an easy tuning and good control performance? This is a motivation of the paper. Prof. Hidenori Kimura of Univ. of Tokyo proposed "morel driven control (MDC) concept" at CDC2000 Sydney. He defined a model driven control as a control system architecture, which uses a model of the plant as a principal component of controller. PIDrd, PPI (predictive PI), IMC (internal model control) and DMC (dynamic matrix control) belong to a class of MDC. Features of MDC are simple structure, easy tuning approach and proven stability and robustness. Based on the MDC concept, aiming for wide applicability for even unstable processes, we developed a model driven PID control system, named MD PID control system, combining with a PD local feedback, an IMC and a set-point filter. That was one degree of freedom type. In this paper, we propose a new model driven two degrees of freedom PID control scheme, named MD TDOF PID control, in order to obtain better disturbance regulating property by extending conventional MD PID control system. Through some features and some practical field experiments, the MD TDOF PID control system shows good control performances with easy tuning.