Adaptive Notch Filter Using Real-Time Parameter Estimation

Abstract

The control of flexible systems is often difficult due to the exact frequencies of the elastic modes being hard to identify. These flexible modes may change over time, or vary between units of the same system. The variation in the modal dynamics may cause a degradation in performance or even instabilities unless compensated for by the control scheme. Controllers designed for these types of systems use notch filters for suppression, however variation in the parameters of the flexible modes cause the need for wide notch filters. An adaptive scheme is proposed which uses an online estimator based on plant parameterization. Since the estimator is able to identify the modal dynamics, an adaptive notch filter is able to track an incorrectly modeled or varying flexible mode. The adaptive notch filter can be designed narrower, adding less phase lag at lower frequencies, thereby allowing an increase in bandwidth and disturbance rejection capability. Simulation and experimental verification of the adaptive mode suppression scheme is given through the use of a laser beam pointing system. The adaptive scheme is compared to a nonadaptive scheme, and is able to decrease the standard deviation of the experimentally measured tracking error by 14% even when the flexible dynamics are unknown.