Adaptive sliding mode control of a pressure relief valve

In this contribution the control of a hydraulic pressure relief valve is discussed. Due to strong nonlinearities of the valve and the influence of a varying oil flow advanced control strategies are mandatory if advanced closed-loop performance is demanded. On the one hand, classical PI-like control structures can be applied to achieve the desired closed-loop performance. However, for this the controller has to utilize nonlinear gains for the P- and I-branch, which results in a large number of parameters to determine. In order to overcome this complexity a second order homogeneous control concept is proposed that achieves the desired control quality. Since modeling of the hydraulic valve is not intended and hence the system’s states cannot be recovered by using an observer-based approach the state recovery by differentiation of the measured system output is discussed. For this, differentiation techniques based on second-order sliding modes are briefly introduced. The performance of the presented control concept is evaluated on a typical pressure relief valve in terms of tracking of different pressure drop trajectories and disturbance rejection caused by a varying oil flow. The results show an improved control quality compared to classical approaches while the complexity of the utilized sliding mode controller is kept low.