Improvement of boom control performance for hybrid hydraulic excavator with potential energy recovery

Potential energy recovery (ER) is an effective way to reduce energy consumption of hybrid hydraulic excavators; however, the ER system with a direct speed-control strategy is prone to oscillation of actuators due to the reduction of damping in comparison to the conventional throttle governing system. This paper aims to improve the boom control performance of a hybrid hydraulic excavator by properly designing the ER controller. Based on the dynamics of the system, mathematical modeling including hydraulic components and electrical components is carried out. A staged composite control strategy is proposed to achieve acceptable performance in the whole velocity range. Load torque observation is employed to increase the speed stiffness of the permanent magnet generator applied in the system as well as the stiffness of the boom motion. The leakage flow which affects the anti-disturbance capability and accuracy of the control system is compensated. Finally, the effectiveness of the proposed control scheme is verified by simulation and experimental results.