By exploiting the particular characteristic of variable structure systems, a new approach is introduced to estimate a system perturbation signal from the dynamics of the sliding mode. Its implementation is simple and make use of the bound on perturbation estimation error. However, knowledge on the bounds of model parameter errors and external disturbances are not required. Perturbation feedforward compensation is then incorporated into the design of a control law which cancels the effects of system uncertainties and external disturbances. The robust control law ensures sliding mode reaching in finite time and with prescribed transient behaviour. This robust control technique is applied to the control of a servo system. Detailed computer simulation results are presented to demonstrate the effectiveness of this approach. Comparison is made with conventional variable structure control (VSC) method.
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