Design of optimal output disturbance cancellation controllers via loop transfer recovery

The authors have introduced optimal disturbance cancellation controllers as a class of controllers minimizing a non-standard quadratic performance index explicitly including disturbances. This paper discusses the application of the classical loop transfer recovery (LTR) technique to the optimal disturbance cancellation controller for step disturbances entering the plant output. The estimation error dynamics of the Kalman filter jointly estimating the plant states and the disturbances is chosen as a target of the LTR design. The weighting coefficient of the performance index is used to recover the target which has guaranteed stability margins as in the standard LTR design. It is shown by a numerical example that the proposed design provides flexible tuning of the disturbance rejection capability with sufficient stability margins.