Approximating sampled-data systems with applications to digital redesign

Despite the existence of methods for a direct optimal design of sampled-data control systems, it is often desired to approximate sampled-data systems with discrete-time ones. This occurs frequently in the context of digital redesign, in which one retains intuition in the continuous-time context. This paper investigates and gives conditions under which such a method works. Under some conditions, we guarantee that fast-sampling approximation works well for H^∞ sampled-data design, and give an estimate for such an upsampling factor. As an application, we propose a new method for obtaining an FIR controller (possibly with first-order approximation). A comparison is made with an existing method.