Angle-domain internal model control via a time-varying Kalman filter

Angle-domain structured disturbances refer to disturbances that satisfy a dynamic structure in a generic angle variable which is monotonically increasing with time but not uniformly. A difficulty in designing controllers to compensate for such angle-domain structured disturbances is that the system is invariably either time-varying or angle-varying. This paper uses the affine parameterization control design perspective and proposes a straight forward design procedure that utilizes a time-varying Kalman filter to estimate the disturbance state and a feedforward controller to install the disturbance cancellation. A sandwiched system is assumed where the input and output plants can be non-minimum phase. With non-minimum phase input plants, approximate feedforward controls are proposed to avoid the need for full future information on the angular rate.