Model and Conditional PID Compensation Control on Flow of Hydraulic Source Driven by Permanent Magnet Servo Motor

Abstract

In view of the existed defects of hydraulic source driven by variable frequency induction motor in practical applications, such as slow response, low control accuracy and difficult to master control parameters, a flow control strategy of permanent magnet servo motor driven constant pump hydraulic power unit is presented. This strategy mixes merits of permanent magnet servo motor, such as good dynamic characteristics, high control precision, and saving energy, and characteristics of constant pump, such as simple structure, good reliability and strong ability to fight pollution, etc. According to the relationship between speed, flow and pressure of constant pump, and oil temperature, viscosity, elastic modulus and other related parameters, model and conditional compensation proportion, integration, differentiation(PID) control on motor speed is proposed, through which the rapidity and accuracy of control on the output flow of constant pump are realized easily. The control system makes full use of the stability and timeliness of the open-loop model control to approaching target flow, overcoming the adverse effect that the measured flow signal delay brings serious hysteresis influence on system response in the traditional flow control system. In addition, the conditional PID compensation control, through the comparison with the conditional threshold value to open, can further eliminate flow deviation and improve the precision of the system. Simulation results show that the feasibility of the model control and the conditional PID compensation control. Experimental results show that the response of model control is close to motor speed open-loop control, which is better than indirect measurement flow feedback control, and significantly ahead of the turbine flowmeters measured flow feedback control. The control system has good resistance to load disturbance ability; the conditional PID compensation control can completely eliminate the steady-state error caused by the system parameter nonlinear change and simplified model, and can follow target flow at slope response without error.