Research On Power Assembly Control Strategy Of Pure Electric-driven Construction Machinery

Pure electric drive is the ultimate way for construction machinery to achieve zero emission and pollution-free.Currently,most pure electric-driven construction machines use electric motors instead of engines.It has achieved a degree of energysaving and emission-reducing purpose by simply simulates the functions of the engine,but doesn't exert the excellent speed regulation performance and strong overload capability of the motor.In this scenario,the control strategy of the power assembly is not combined with the working characteristics of the hydraulic system,the energy saving,handling,power and safety of the whole machine need to be improved.In order to make full use of the advantages of high-efficiency,energy-saving and environmental protection of pure electric-driven construction machinery,it is of great significance to the promotion of pure electric-driven construction machinery to explore the power assembly structure scheme and control strategy which are applicable to the complex working conditions of construction machinery.Taking a 8-ton hydraulic excavator as the research object,this paper proposes a power assembly structure using a lithium battery as the energy storage unit and a PMSM to drive the internal gear pump by analyzing its load characteristics and working conditions.In order to achieve the integration of power assembly and hydraulic system,a quantitative pump load-sensing system based on variable speed control is designed.The mathematical model of the quantitative pump load-sensing system based on variable speed control is established,and the stability of system is analyzed.Based on the endurance and dynamic performance of the machine,a power assembly parameter matching method is proposed.A variable differential pressure control strategy is proposed.In the low speed and small flow occasion,the system energy saving is improved by reducing the system differential pressure.In the high speed and large flow occasion,the system handing is improved by increasing the system differential pressure.A piecewise constant power control strategy is proposed.A piecewise constant power control strategy is proposed.According to the discharge characteristics of the power battery pack and the operating state of the motor drive system,different maximum power points are set to improve the dynamic performance of the power system under the premise of ensuring safety.The feasibility of variable differential pressure control and piecewise constant power control is verified by building AMESim model.According to the principle of the system and the setting of component parameters,a new pure electric-driven excavator power assembly and hydraulic system test platform was built.Combined with the pressure and flow characteristics of the excavator under different working conditions,the energy saving,handling,dynamics and safety of the quantitative pump load system based on variable speed control were studied,the test verifies the feasibility of variable differential pressure control and piecewise constant power control.Compared with the traditional pure electric excavator load-sensing system,the new pure electric excavator's load-sensing system based on variable speed control is more energy-efficient and maneuverable.