The desired attenuation ratio of a closed loop system can be obtained through tuning the PID controller by using attenuated frequency characteristic. However, it is difficult to determine the optimum tuning parameters due to the obtained solutions of tuning parameters are uncertain. A novel tuning method of PID controller is proposed by the way of optimizing controller parameters with a constraint of attenuation ratio as a substitute for that of calculating the controller parameters with attenuated frequency characteristic. With this method, firstly curves or curved surfaces of the solutions w...
