Two-degree-of-freedom Design Between Intersample and Sample Responses: Closed-loop State-space Approach Based on Steady-state Characteristics

Abstract A dual-rate sampled-data control system is designed in which the sampling interval of measured signals is twice as long as the holding interval of a control input. In the proposed method, a control law is extended based on the null space and intersample ripples are eliminated without changing the sampled output trajectory in the steady state. Polynomial and state-space approaches are conventional open-loop design methods based on the null space. However, conventional methods are ineffective for unstable systems and are unavailable when the null space of the plant model is only the zero vector because the controlled plant is not arbitrarily selectable. On the other hand, the proposed method is effective for unstable systems, as well as stable systems, even when the null space of the plant model is only the zero vector, because the proposed controller is designed based on a closed-loop system.