| The Direct Drive Volume Control (DDVC) Electro-Hydraulic Servo System is a new mechanic-electro-hydraulic system developed in recent years. It has both the advantages of an AC servo motor control's flexibility and a hydraulic system's great force. Due to it having less bulky features, simpler construction, energy saving being prone to control with computer, etc., the system has been applied extensively in many fields such as space flight, national defense, and several other industrial fields and has helped to achieve great economic and social benefits. The system is considered to be one of the most important developing directions in the field of hydraulic-control.The bucket wheel reclaimer is a large material handling equipment, which is widely used for mining, ports, power plants, building materials and industry etc. Host machine pitching motion is one of its major functions, accompanied by problems of consuming large amounts of energy and arm vibration. In this article DQ1250.35 type bucket wheel reclaimer is taken as an example, an improved DDVC hydraulic system was proposed, and separately controls with two different modes, its static and dynamic characteristics were analyzed by simulation.In this paper we see that the force of the hydraulic cylinder was quantified and analyzed under the three conditions of no-load, take materials, stack materials of bucket wheel reclaimer's host pitch movement. When the hydraulic cylinder endured negative pressure by the impact of bob-weight, the relationship between the value of bob-weight and the size and amplitude of hydraulic cylinder force was noted, and the rule of reducing power installed the system was summed up.The value calculating method of establishing pressure was analyzed. The reason for the loud vibration is because of the false chosen of lock valves and pressure valves existing in hydraulic system. Upon this discovery improvements were suggested. When the DDVC hydraulic system of bucket wheel was upgraded, the secondary pump loop helped to reduce the adverse effects of low-speed characteristics by dead zone nonlinearity. After this upgrade the structural design of the system was complete. The system's main components were integrated in the hydraulic package, so ultimately the system volume was reduced.The two mathematical models of an AC motor were established under the two modes of U/f and Vector Control, it was discovered that the dead zone error of induction motor under U/f control mode could be eliminated by low-voltage compensation; the limitations applications of the U/f control mode were analyzed. The precise simulation of Vector Control AC motor was also analyzed. The result showed that the vector controlled AC motor has good static and dynamic characteristics, and it was appropriated to be the power source of DDVC hydraulic system.The model of a pump controlled non-asymmetric cylinder was then established, and its static and dynamic characteristics were analyzed by simulation. The models of DDVC hydraulic system under U/f control mode and Vector Control mode were then established. The feasibility of taking the two models as the power equipment of the bucket wheel reclaimer's host machine pitching motion was analyzed by simulation. Useful simulation methods were provided for further study of DDVC hydraulic system. |
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