An induction motor position control system based on the sliding mode control is presented. In the sliding mode control, the control function is discontinuous on the hyperplane, which causes harmful effects such as current harmonics and acoustic noise in the motor drive application. A low-pass filter is introduced between the sliding mode controller output and the motor controller input to reduce these effects. Although the filter smooths the motor input current and alleviates the vibration at the final reference position, it may cause sluggish response in transient condition. To overcome the problem, a variable-bandwidth filter is proposed. In steady state, the bandwidth of the filter is made to be narrow to mitigate the ripple components while it is widened during the transient to improve the response. To achieve such an operation, the bandwidth of the filter is adjusted according to the error function. The proposed method shows good performance, which is confirmed through computer simulation and experiments.
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