Transient disturbance rejection improvement by a combined variable structure-model following control approach

The attractive invariance features of variable structure control (VSC) systems are present only during the sliding motion and not in the initial phase of reaching the sliding manifold. If the transient at initial phase is not negligible, the overall system performance, e.g., the overall disturbance rejection, may not be satisfactory. In this paper, a novel combined variable structure-model following control (VS-MFC) scheme which is quite different from the general variable structure model following control (VSMFC) is proposed to improve the load disturbance rejection of a variable structure control brushless DC motor speed drive. Numerical results demonstrate that the proposed VS-MFC scheme can greatly improve the transient load rejection of the speed drive during the nonsliding recovery process resulting from the suddenly added load disturbance while maintaining the robustness of the sliding mode control to motor parameter variations