Two-degree-of-freedom design for integral compensation in a multirate control system

This paper proposes a new design method for a multirate control system, in which a continuous-time plant is controlled by using a discrete-time controller, in which the sampling interval of the plant output is restricted to an integer multiple of the hold interval of the control input. In such a multirate system, the intersample response might be deteriorated even if ideal sample response is obtained. In a conventional method, the steady-state intersample response can be improved independently of the sample response. However, this method can be useful only when neither a modeling error nor a disturbance exists. In this study, using an integral compensation, this problem is resolved. In a control system designed using an integral compensation, because the stability margin is degraded because of the integral compensation, a two-degree-of-freedom system is designed in this study. In the two-degree-of-freedom system, the integral compensation is revealed only when there is a modeling error or a disturbance. Therefore, the stability margin is not deteriorated by the integral compensation if neither a modeling error nor a disturbance exists. Finally, numerical examples demonstrate the effectiveness of the proposed method.