Rejection of periodic disturbances with adaptation to unknown systems

The rejection of periodic disturbances is a problem frequently encountered in control engineering, and in active noise and vibration control in particular. The paper considers situations where the plant is stable but unknown and possibly time-varying. The approach consists in obtaining on-line estimates of the plant frequency response parameters and of the disturbance parameters. A least-squares identifier with forgettting and stabilization factors is used. The estimates are used to continuously update control parameters and cancel the effect of the disturbance. Experiments on an active noise control testbed demonstrate the ability of the algorithm to recover from abrupt system changes as well as to track slowly-varying plant parameters.