Research On The Performance And Measurement And Control Technology Of Hydraulic Power System Driven By Permanent Magnet Servo Motor

Due to the existed defects of hydraulic source as constant speed motor driven constant pump with high energy consumption and low efficiency; constant speed motor driven variable displacement pump with complicated structure, poor ability to resist pollution and narrow range of speed; hydraulic source driven by variable frequency induction motor with big inertia, slow response, poor performance at low speed, and low motor power factor, the paper presents permanent magnet servo motor driven constant pump hydraulic source, which mixes merits of the permanent magnet servo motor,as high control precision at speed control, wide speed range, good dynamic characteristics and high motor power factor, and the characteristics of constant pump,as strong ability to fight pollution, good reliability, compact structure and low cost etc. Then, on the basis of full research on the system parameters, as voltage, current, rotate speed and torque of servo motor, flow rate, pressure, displacement and leakage rate of constant pump, and the temperature, viscosity and modulus of elasticity of the oil, a soft-sensing method for the output flow and pressure of constant pump is put forward. In addition, control strategy for flow and pressure, and constant power control system of the hydraulic power system are realized at different load types. At last, graphic analysis of efficiency status for hydraulic power system under different working conditions is put forward, which provides a new thought and method for hydraulic power system working at high efficiency and energy saving, load matching, and load adaptive control. Concretely, the dissertation’s main research and innovation are as follows:(1) According to the working principle of the permanent magnet synchronous servo motor, and constant pump with gear pump as an example, the mathematical model of permanent magnet synchronous servo motor driven constant pump hydraulic system and load model based on the relief valve are built, where analytical method was used. The model has analysis on the operating parameters, the coupling mechanism, and constraint conditions of the hydraulic power system from system level, which lays a theoretical foundation for the study on the control mode, indirect measurement for flow and pressure, load efficiency matching features of the hydraulic power system.(2) According to the coupling mechanism of the parameters for hydraulic power system, such as flow, pressure, rotational speed, torque current, leakage coefficient and moment inertia etc, the soft measurement model of flow and pressure is established, which is realized easily by measuring the speed of the motor and torque current. And the accuracy of measurement model for the flow has been improved with considering the compensation of viscosity-temperature behavior and viscosity-pressure characteristic of the oil. Results of the experiment and simulation show that the soft-sensing model is of enough accuracy and has an excellent response. This provides an innovative method for studying on the accuracy and rapidity of the flow control.(3) On the basis of analysis on the open-loop control, closed-loop PID control, feed forward compensation PID control and fuzzy PID control for flow, model control and conditional PID compensation control on flow is proposed, mixed merits of both the timeliness and stability of the open-loop model control and the ability to eliminate steady-state error of PID control. By setting the threshold of PID control, overshoot and adjustment time reduce effectively, and the quickness, accuracy and stability of the flow control has been implemented.(4)According to the technical performance index on the constant pressure variable displacement pump widely used in engineering, pressure feedback control and open-loop direct torque control on pressure for the servo hydraulic source are proposed. Experiments show that pressure feedback control can stabilize pressure and eliminate error of the system; open-loop direct torque control on pressure shows fast response and good stability; open-loop direct torque control on pressure with viscous damping compensation keeps both the advantages of original open-loop direct torque control on pressure, and enough precision at the same time, which can satisfy the demand of load on constant pressure variable flow.(5)On the analysis of the control features of constant power variable pump, constant power control model of permanent magnet motor driven constant pump is established, where weak magnetic control is used. Experiment and simulation show that the control strategy can make full use of the power of the motor, and meet the demand of changing load on constant power, realized high pressure small flow and low pressure high flow control of the pump.(6)Energy consumption, speed characteristics, power matching, and response characteristics, based on hydraulic source system driven by the asynchronous induction motor and permanent magnet synchronous motor, are contrasted and analyzed. After equivalent conversion of the working conditions, matching characteristics of load and the corresponding efficiency are studied. Two-dimensional colorful and grayscale notation for efficiency are set up, which are respectively based on the RGB and the superposition method, providing a new description method for matching load or choosing type, and the interval division about the working conditions and the corresponding efficiency.