Research On Main Drive Motor Control System Of Pure Electric-driven Construction Machinery

With the increasingly serious environmental pollution and much stricter emission standards,energy conservation and environmental protection have become the mainstream trend of construction machinery development.The pure electric-driven construction machinery with the advantages of low noise,zero emissions and efficient driving because of using electric motors instead of traditional fuel engines has become the key development direction of the construction machinery industry.However,due to the rough working environment and complex and changeable working conditions,industrial frequency converters and pure electric vehicle motor drivers can't be transplanted to construction machinery directly.Therefore,the study of motor control system according to the working characteristics of construction machinery has far-reaching significance for the development of pure electric-driven construction machinery.In this paper,the performances of four common motors are compared,and PMSM is chosen as the main motor for pure electric-driven construction machinery.By analyzing the influence of vector control and direct torque control on the control performance of PMSM,vector control as motor control strategy is determined.The mathematical model of PMSM is decoupled by vector coordinate transformation method,and the mathematical model of the motor in the corresponding coordinate system is established.The mathematical model of the hydraulic pump is analyzed and the requirements of the hydraulic system for the motor control performance are obtained according to the flow continuous equation and the torque equation of the hydraulic pump.In order to increase the robustness and anti-interference ability of the speed control,a closed-loop vector control strategy based on sliding mode speed observation is proposed.The speed SMC regulator which combines the exponential approach law with the mathematical model of the PMSM and whose current loop is controlled by PI and corrected to type I system is designed and discredited.The models of vector control system and hydraulic system are established in Simulink and AMESim respectively,and joint simulation are carried out.The vector control strategy performances based on PI speed closed loop and SMC speed closed loop are compared by simulation.The simulation results show that the sliding mode variable structure control has better robustness and anti-jamming ability in the process of hydraulic load change.In order to satisfy the requirements of motor control,the overall scheme of motor control system for pure electric-driven construction machinery is proposed.The hard ware taking TMS320F28335 as the control core,including communication,driving and acquisition circuits is designed.Based on the designed circuit system,the vector control closed-loop algorithm based on sliding mode speed observation is written,and the motor test platform is built.The performances of PI speed closed loop and SMC speed closed loop are compared under no-load,loading,unloading and variable load.The results show that the closed-loop vector control strategy based on sliding mode speed observation has stronger anti-interference ability and better robustness.To further verify the feasibility of the designed hardware and control algorithms,the motor control system is tested on the excavator prototype driven by pure electricity.The results show that the output power of the motor control system can quickly follow the load change,and the sliding mode speed control can better suppress the speed fluctuation caused by the load change,and the motor control system in this paper is effective and feasible.