Sliding mode control using time-varying switching gain and boundary layer for electrohydraulic position and differential pressure control

It is well known that: the sliding mode control possesses the following advantages: fast response, less sensitive to uncertainties, and easy implementation. However, traditional sliding mode control often results in a chattering control input because of its discontinuous switching control. The chattering control input has some drawbacks: easy damage of mechanism and excitation of unmodelled dynamics. Although the boundary layer method can attenuate the degree of high-frequency control input, its stability is guaranteed only outside the boundary layer, and its asymptotic tracking often cannot be achieved if the boundary layer is insufficiently small. Furthermore, a fixed switching gain often gives too much energy for the purpose of trajectory tracking. Owing to these disadvantages of traditional sliding mode control (i.e. fixed switching gain and fixed boundary layer), one sufficient condition for a time-varying switching gain and a time-varying boundary layer, which is the memoryless function of the tracking error, is achieved to reduce the control effort in magnitude and frequency, and to ensure asymptotic tracking. To verify the effectiveness of the proposed control, computer simulations for the combination of weighted electrohydraulic position and differential pressure control are demonstrated.