Digital Redesign of Continuous Time Controller by Multirate Sampling and High Order Holds

This paper presents the digital redesign of continuous time controller when the measurement sampling period is relatively large and standard discretization methods are most likely not able to provide a suitable digital controller from either stability or performance point of view. An analysis tool is provided to improve the performance of digital control systems by the following two measures: 1) update the controller output N times faster than the measurement sampling frequency, and 2) utilize past sampled outputs to predict the evolution of the output error between two consecutive sampling instances. The analysis tool is developed by regarding the overall system as a multirate sampled data system. An illustrative example is given to show the utilization of the developed analysis tool.