The Design Of Control System Based On Variable Frequency Hydraulic Station

The variable frequency control hydraulic technology is a new kind of energy saving transmission technique. It is formed while the variable frequency variable speed applied to the hydraulic system. It changes actuating element speed through changing the power supply frequency. By this way, the motor is always in high efficiency. Energy is saved from the source. This technology improves the low energy efficiency of traditional hydraulic power transmission and low efficiency of the whole system. The application of variable frequency control hydraulic technology is widely applied in mechanical equipment, such as machine tools, hydraulic machines, and injection molding machines and so on. So its marketing will saves a lot of energy for our country. Now the technology of Variable Frequency Hydraulic System is not mature. There are some problems for further research, such as slow dynamic response, poor low speed characteristics, and low speed accuracy.A prototype of variable frequency hydraulic Station was designed and built. It uses variable speed motor and fixed displacement pump to drive actuating element instead of using traditional pattern with fixed-speed motor and variable displacement pump. It not only achieves energy conservation, but also omits the complex changing displacement organization. To meet the system requirements, PLC is adopted to control it. According to technical indicators, we built the prototype of variable frequency hydraulic Station with appropriate components. Then the mathematic model is founded and the simulation model is founded based on MATLAB7.0.To solve the problem of slow dynamic response and low speed accuracy, different control algorithms are used to improve the problem. First, conventional PID control is used in the system and the parameters are obtained by the Ziegler-Nichols empirical formula. Then simulation is carried on based on the mathematical model with MATLAB 7.0. Simulation results show that there is low steady-state error, but larger overshoot and long adjustment time in the system. In order to obtain good dynamic characteristic and the accuracy properties are not lost, fuzzy-PID control is used, which combines the advantages of fuzzy control and PID control. When the deviation is large, fuzzy control is worked. When the deviation is small PID control is worked. The two controllers switch through the switching function. Simulation result shows that the fuzzy-PID controller effectively reduces the adjustment time. But the simulation curve fluctuates before the stability output because of the rigid switch pattern. Besides quantization factors and scaling factor of fuzzy control are not adjustable, so the system cannot adapt the great changes of controlled object and has poor robustness. Thus, the self-adaptive fuzzy-PID control is designed and implemented. It is based on fuzzy switching arithmetic and the online self-tuning arithmetic with quantized and proportional factors. The simulation results show that the control system has good dynamic and static performances. It solves fluctuations generated by the switch of two control mode.