Robust controller for a servo positioning system of an automobile

The authors present a controller for an electric motor-driven servosystem intended for use in automobiles. The controller features a low-sensitivity design to provide robustness against external disturbances and the nonlinearity of the positioning mechanism. To eliminate the effects of gradual but significant change in the plant characteristics with use, the addition of the identifier to the controller was examined, along with the retuning of the controller gain. The plant, denoted as a discrete system, has a zero near the unit circle in the z plane that can cause the controller output to oscillate when the controller is designed to contain the inverse system of the plant, producing a sound or electric noise. To avoid this problem, a delta operator is used to represent the discrete system, making it possible to ignore this zero. The effect of ignoring the zero on stability and response was examined by using the Nyquist stability criterion and computer simulation, respectively. The validity of the proposed identification method was confirmed through computer simulation. An experiment confirmed the low sensitivity of the controller