Design And Application Research On Variable Frequency And Close Circuit Hydraulic Power System

The variable speed control hydraulic technology is a new kind of energy saving transmission technique,and it has extensive potential application in many kinds of equipments such as machine tool, hydraulic elevating mechanism and injection machine. In this paper, a new variable speed control hydraulic power unit is developed; it concludes a main oil circuit and a supplementary oil circuit; it has many virtues such as compact construction, energy-saving and reducing noise, long use life, wide applied area. The math and simulation model of the system are built. The algorithm methods are selected and the models of the system are simulated.Using Matlab , the simulation was studied with PID, fuzzy PID, fuzzytune PID controlled method. According to thesimulation results, the control characteristic of fuzzy tune PID control is best. Some relevant invent patents of using this system in hydraulic elevating mechanism are applied for. Some detailed engineering application examples are presented.The main reseach contents are as follows.In chapter 1, the development course, research actuality and application field of variable frequency hydraulic technology and variable frequency hydraulic power unit home and abroad are summarized. The main research subjects are summarized in the paper.In chapter 2, the types and performance of electro motors and hydraulic pumps that can be suitable for variable frequency hydraulic system are compared. The select conditions of electro motors and hydraulic pumps are pointed out. The principle project of hydraulic system in this paper is detailed introduced. The hydraulic components are selected. The structure of variable frequency hydraulic power unit is designed.In chapter 3, according to the different control methods of converter-electromotor, mathematic models of the variable frequency hydraulic power unit are built in the VVVF control method and the vector control method, simulation models are also set up using Simulink tool. The values of model's parameters are selected and determined.In chapter 4, the speed and pressure control characteristic of open and close loop control simulation for the frequency conversion hydraulic system is carried out. According to the characteristic of the system, some control methods are selected. These control methods include conventional PID control, fuzzy PID control and fuzzy tune PID control. The simulation results of speed and pressure response of different control methods are compared. From these results, both fuzzy PID control and fuzzy tune PID control have good control characteristic. The control characteristic of fuzzy tune PID control is best.In chapter 5, the application of the frequency conversion and close circuit hydraulic system in hydraulic elevating mechanism and electro-hydraulic injection moulding machine isstudied. According to design and application research, the characteristics hydraulic elevator and hydraulic oil pumping unit are improved by using the system above. The installed power and energy consumption are reduced, and the structure of the application system is simplified. The application status of the power unit in electro-hydraulic injection moulding machine is introduced, and the merits of electro-hydraulic injection moulding machine are pointed out.In chapter 6, some conclusions are reached and some new views are put forward.To sum up, the thesis showed that painstaking research has been done with the frequency conversion and close circuit hydraulic system. Some valuable results will be helpful to research next step.