Two degrees of freedom PID auto-tuning controller based on frequency region methods

Recently two degrees of freedom PID control systems have attracted attention, because of their better process control quality for both set point variable tracking and disturbance resistivity than that of conventional PID control systems. This paper describes a practical auto-tuning method for the two degrees of freedom PID control system based on frequency region methods; the well known recursive least square parameter estimation method, a frequency characteristics conversion method and a model matching method in frequency region. By combining frequency region method, the auto-tuning method can use for both minimum phase process and non-minimum phase process. This method was introduced into the two degrees of freedom PID auto-tuning controller. The superior features of the controller and the results of field tests are presented.