Optimal dual-rate digital redesign with closed-loop order reduction

Abstract

An optimal dual-rate digital redesign method is proposed that can be applied to continuous-time and fast-rate discrete-time control systems. The paper presents a technique, which relies on the solution of a dual-rate H2 discrete-time control problem, to convert such systems to either a slow-rate or a dual-rate sampled-data control system while guaranteeing closed-loop stability and performance in the discrete-time H2 sense. The proposed technique results in sampled-data control systems providing satisfactory closed-loop performances over an extended range of sampling rates, as compared with other widely used methods of digital redesign. Furthermore, the proposed digital redesign technique is useful in practice since it allows the designer to constrain the complexity of the digital controllers, thus resulting in low-order digital controllers easily implementable in software code and free of causality and real-time problems. Numerical examples provide a comparison of the proposed digital redesign technique with well-known approaches.