Sampled-data controller reduction procedure

The problem of controller order reduction aimed at preserving the closed-loop performance of a sampled-data closed-loop system is investigated. Past sampling of the system at a multiple of the sampling frequency followed by lifting allows capturing of the system´s intersample behavior and yields a time-invariant single-rate system; this then permits standard order-reduction ideas to be applied. Special weighting functions aimed at preserving the closed-loop transfer function are obtained, and weighted balanced truncation is used to reduce the controller, An example shows that without the use of fast-sampling, an unstable closed loop can result from the reduction