Energy-saving control for electro-hydraulic systems under time-varying negative loads

In a hydraulic system, employment of counterbalance valve introduces sizable energy consumption. In addition, a pressure-feedback control architecture with inflexible parameters causes instability under time-varying negative loads. As an alternative, an adjustable meter-out orifice was adopted, and a stable controller was proposed in this study. By combining inlet pressure and velocity, the concept of a flow rate follower was developed. Mathematical analysis of dynamic model illustrated that both the inlet pressure and velocity converged to a range related to the flow rate follower bounds. Feedback linearization with robust control was utilized such that flow rate follower converged in the presence of parametric uncertainties; meanwhile, a high-gain load observer was constructed for disturbance compensation. The effectiveness of the controller was verified by experiments and its performance discussed. As a result, the inlet pressure was held near a specified low value, thus significantly reducing energy consumption. Also, the velocity matched the supply flow rate, and the oscillations were acceptable in applications.