Quantitative Feedback Theory (QFT) for Chattering Reduction and Improved Tracking in Sliding Mode Control (SMC)

Sliding mode control (SMC) is a robust control technique with chattering as a major drawback. Chattering is undesirable because it can excite unmodeled high-frequency dynamics of the system. One way to reduce chattering is to introduce a boundary layer around the sliding surface while keeping the boundary layer attractive. Introduction of the boundary layer, however, causes the system response to oscillate around the sliding manifold. These oscillations, in turn, may lead to undesirable tracking errors. In this paper, we propose a quantitative feedback theory (QFT) controller (a low pass filter) to minimize the oscillations within the boundary layer and considerably improve the tracking response. We also provide an example to demonstrate the key features of the proposed method.