Control and performance analysis of variable speed pump-controlled asymmetric cylinder systems under four-quadrant operation

Since the energy crisis, the further development of a variable speed pump-controlled hydraulic system driven by an electric machine has attracted increasing attention during the past few years. As a response to this, an innovative double pump-controlled asymmetric cylinder system (DPC) and its control method are proposed in this study. The purpose of this study is to investigate the performance of two variable speed pump-controlled systems for asymmetric cylinders under a four-quadrant operating condition, in comparison with single pump control (SPC). The four-quadrant operating principles of the two systems are analyzed by simulation. Simulation models for both systems are introduced, and a position control method is proposed, with a tracking differentiator and speed feedforward, plus proportional-integral-derivative (PID) for four-quadrant operation. The DPC model was validated with the measurement of a crane. The simulations using the validated model were performed with a position reference and a varying load (four-quadrant operating arm of an excavator). The results demonstrated that the velocity fluctuation is eliminated by using the DPC instead of the SPC, and the position control performance of the DPC is better compared to the SPC, although the energy efficiency decreases slightly. Hence, the proposed DPC and its position control method are feasible for the four-quadrant operation of asymmetric cylinders.