A frequency domain controller design method

With the advent of the relay feedback auto-tuning technique, a number of PI/PID auto-tuning rules based on the results of the relay test are reported. Many of them employ only one or two points of the process frequency response. The designed controllers are limited to certain simple structured processes. In this paper, a multiple-point of frequency response fitting controller design method is proposed. First, multiple points on the process frequency response are estimated from a relay feedback test. The objective closed-loop response is then properly chosen with respect to the process frequency response. The controller is determined by minimizing the error between the actual and desired closed-loop response in a certain frequency region. Both over-damped and oscillatory processes are covered in the discussion. Simulation examples are included to demonstrate the proposed method.