PID CONTROLLER TUNING TO OBTAIN DESIRED CLOSED-LOOP RESPONSES FOR CASCADE CONTROL-SYSTEMS

A new method for PID controller tuning based on process models for cas caded control systems is proposed in this paper. The method consists o f first finding the ideal controller that gives the desired closed loo p response and then finding the PID approximation of the ideal control ler by Maclaurin series. This method can be applied to any open loop s table processes. Furthermore, it enables us to tune the PID controller s both for the inner loop and the outer loop simultaneously while exis ting tuning methods tune the inner loop first and the outer loop next. Closed loop responses of cascade control loops tuned by the proposed method are compared with those of existing methods such as the frequen cy response method and the ITAE method. The results show that the prop osed tuning method is superior to the existing methods.