Displacement control of hydraulic actuators using a passivity based nonlinear controller

To increase the efficiency of hydraulic systems by eliminating valve throttling losses, a direct displacement open circuit is proposed to control a single rod hydraulic actuator. The circuit provides three control inputs, including the displacement of a variable displacement pump, the opening area of a proportional valve, and the position of a directional valve. Pump control has a low bandwidth, but the efficiency is high due to the lack of throttling losses. Valve control has a high bandwidth, but the throttling loss is high. A novel approach has been proposed to distribute the control efforts between the pump and the proportional valve considering both control bandwidth balancing and throttling loss reduction. The proportional valve will follow a high frequency opening profile, while the nominal valve opening is large, and the pump output flow will follow a low frequency demand. Experimental results validate the effectiveness of the proposed approach.