Two-degree-of-freedom multirate control system with integral compensation for improvement in steady-state intersample response

This paper deals with a multirate control system, where the sampling interval of the plant output is an integer multiple of the hold interval of the control input. In that multirate system, the intersample output may oscillate in steady state even if a sampled output converges to a set point. The oscillation is called ripple, and it causes a deterioration of the control performance. This paper proposes a new design method to suppress the ripple in the multirate system using the integral compensation. In the proposed control system, the integral compensation is revealed only when there is a modeling error or a disturbance. Therefore, the transient response is not deteriorated by the integrator if neither a modeling error nor a disturbance exists. A numerical example demonstrates the effectiveness of the proposed method.