Control strategies of power system in hybrid hydraulic excavator

Hybrid system, which has been successfully used in vehicles, is introduced to hydraulic excavators nowadays. The primary focus of this study is to investigate the control strategies of hybrid system used in hydraulic excavators. At first, the structure and working conditions of hybrid hydraulic excavators are analyzed. Based on the analyses, a control strategy named the engine constant-work-point is proposed and studied in a simulative experimental system. Then the control strategy named double-work-point is presented to overcome the limitations of the constant-work-point control strategy. The features and experimental results of the double-work-point control strategy show that the engine's efficiency and the capacitor's state of charge (SOC) cannot be optimized simultaneously. Thus a dynamic-work-point control strategy, which regulates the engine's working point dynamically, is developed to make the system work better. Experimental results show that the dynamic-work-point control strategy can improve the distribution of engine's working points, restrain the capacitor's SOC and has little influence on the performance of the system.