Abstract
By switching control laws, a VSS (variable structure system) control method realizes a new performance that can not be achieved by an individual control law. Chattering caused by lag-time on the switching is a serious problem, if the VSS control method is applied to actual plants. Chattering factors are switching speed, needless high-gain and lag-time of dynamics in inputs and outputs. This paper considers the needless high-gain and the lag-time in the factors. To reduce the needless high-gain, an adaptive gain VSS control method has been developed. In this method, a disturbance is estimated and a controller gain is modified by the estimated disturbance. Therefore this method can always supply suitable gain for the disturbance. But the chattering becomes larger as the disturbance grows larger. To realize more reduction of the chattering, a hybrid control system has been constructed. As the adaptive gain VSS controller only reduces the needless high-gain, the hybrid control method is more effective. The hybrid control system combines the adaptive gain VSS controller with a disturbance observer which considers the dynamics in inputs and outputs. In the hybrid control method, the disturbance is quickly compensated by the adaptive gain VSS controller. The gain and the chattering decrease as an estimation error of the observer becomes smaller. Experimental results evidence that the chattering is reduced by our methods and that the disturbance is compensated quickly.
