For many electro-hydraulic pump-controlled systems, supply pressure control of the hydraulic pump is of great importance. However, the control performance is significantly affected by unknown time-varying load flow requirements. To improve the supply pressure tracking performance in the presence of unknown time-varying load flow disturbances, a nonlinear controller is designed based on the control-oriented mathematical model presented in this article. First, a disturbance observer is used to estimate the unknown time-varying load flow; a nonlinear feedforward controller is then derived using the differential flatness property of the system based on the estimated load flow; in addition, a feedback controller is implemented to stabilize the system. Sliding mode control is also used to compensate for load flow estimation error. The stability of the whole system is proved using Lyapunov theory. Experimental results demonstrate that the proposed control strategy has good supply pressure tracking performance.
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