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 f requency response. The designed controllers are limited to certain sim ple structured processes. In this paper, a multiple-point of frequency response fitting controller design method is proposed. First, multipl e points on the process frequency response are estimated from a relay feedback test. The objective closed-loop response is then properly cho sen with respect to the process frequency response. The controller is determined by minimizing the error between the actual and desired clos ed-loop response in a certain frequency region. Both over-damped and o scillatory processes are covered in the discussion. Simulation example s are included to demonstrate the proposed method.