Aliasing effects in direct digital adaptive control of plants with High-Frequency Dynamics and Disturbances

In this paper we consider sampled-data adaptive control in the presence of aliasing, due to either the high-frequency free response of the plant, or the high-frequency content in the disturbances. In particular, we present a numerical investigation of retrospective cost adaptive control (RCAC) applied to sampled-data command-following and disturbance-rejection problems, and investigate the performance of RCAC in the presence of aliasing. It is shown that RCAC is able to stabilize the plant despite the high-frequency dynamics, unless the controllability of unstable modes is not lost due to sampling. However, the intersample command-following performance may be nonzero due to aliasing of disturbances.