Simplified output control via parallel compensation

Because controller complexity tends to increase with the relative degree of the plant, output control of plants with high relative degree may be difficult to implement successfully. To alleviate the problem, a filter is placed in parallel with the minimum phase plant such that the combination of plant and filter is relative degree one and minimum phase. Very little knowledge of the uncertain plant is required for the design. With the filter in place, a controller designed for relative degree one plants may be used to control the high relative degree plant; designs for stabilization via gain feedback and robust output tracking using model reference robust control and variable structure control are detailed