Relay Control with Parallel Compensator for Nonminimum Phase Plants

Following the Smith compensator the parallel compensator designed for difficult, e.g. nonminimum phase plants is applied to systems with relay control. The compensator connected in parallel to the plant changes its properties so that the replacement plant model becomes simpler and may be shaped dependently upon the goal of the control. In the case of regulation on a constant level a first order lag may be chosen for the replacement plant model. In the case of tracking or disturbance rejection of signals with frequencies belonging to some working frequency band, the replacement plant model shouldhave its frequency response close to that of the plant, in the working frequency band. The proposed approach simplifies the design and improves accuracy of the control.