Trajectory-adaptive digital tracking controllers for non-minimum phase systems without factorisation of zeros

This paper discusses the design of a zero-phase-error feedforward digital tracking algorithm. The proposed algorithm can be used for minimum or non-minimum phase systems without requiring the polynomial zeros to be factored into minimum and non-minimum phase factors. To improve tracking when the zeros are close to the unit circle, a scheme called "trajectory-adaptive zero-phase-error control" is proposed in which the controller parameters are automatically tuned online to the current reference trajectory without requiring explicit information on the function to be tracked. The performance of the trajectory-adaptive controller is further improved by using a look-ahead learning scheme that enables the controller to make advance adjustments in anticipation of the upcoming trajectory