Research On Variable Speed Electro-Hydraulic Control System Based On Energy Regulating Strategy

The vairable speed electro-hydraulic technology can control hydraulic systems via changing pump speed. As this technology functions in the source of power, it has high energy-saving potential. But the disadvantages in practical application, such as low dynamic response characteristic, bad performance in low speed and so on have limited the popularization of this technology.In this dissertation, a new type of variable speed electro-hydraulic system, variable speed electro-hydraulic control system based on energy regulating strategy is schemed out. This system is realized by setting an energy regulation device in traditional variable speed electro-hydraulic control systems, recurring to valve resistance techonique and adopting the uniform controller with the idea of energy regulation to control each part of the system according to the actual energy request. With the idea of energy regulation, energy regulation device can store energy in system decceleration phase to reduce the energy loss and release energy in system acceleration phase to overcome the disadvantage of scarcity of enough flux in the acceleration phase because of large inertia of motor and pump, so as to improve the dynamic response and efficiency of the system.This dissertation has studied the operation principle, control strategy and design principle of the system. Digital simulation and experiment results show that this system has high energy-saving efficiency similar with traditional variable speed electro-hydraulic congrol system, excellent dynamic response characteristics and good low-speed performance which even better than valve resistance control systems.The first chapter of this dissertation generally discusses the control characteristics of valve resistance technique and pump displacement control technique and each strongpoints and flaws of the two techniques on the basis of study on lots of domestic and foreign literature and reference, and then the development of variable speed electro-hydraulic control systems is generally introduced. The advantage and disadvantage of variable speed electro-hydraulic control systems is especially introduced in this chapter compared with traditional hydraulic systems. The variable speed electro-hydraulic control system based on energy regulating strategy is put forward to solve the flaws of variable speed hydraulic control system. At the same time the application of accumulator in hydraulic systems and the development of control theory are introduced. At the end of this chapter, the project background, significance of the research and main research content of the subject is illustrated. In the second chapter, the disadvantages and causes of the problems of variable speed electro-hydraulic system are analyzed, and based on this analysis, the variable speed electro-hydraulic control system based on energy regulating strategy is put forward. Then, the construction of energy regulation device is selected through comparison and analysis, and the holistic structure design of hydraulic cylinder displacement control system is made as an example. The working process of the variable speed electro-hydraulic cylinder displacement control system based on energy regulating strategy is schemed out.The third chapter has analyzed the work performance of accumulator is and made mathematical model of the accumulator. The mathematical model is linearized to get the system transfer function, upon which the influence upon the performance of accumulator of pre-charge pressure and volume of the accumulator is analyzed. The energy regulation effect is proved by digital simulation on the nonlinear mathematical model of the energy regulation device, meawhile the key parameters which influence the function performance of the energy regulation device is got.The fourth chapter has made mathematical model of the main hydraulic loop in variable speed electro-hydraulic control system based on energy regulating strategy to get the nonlinear differential equation of main hydraulic loop, and recurring to mathematical model of the accumulator, the simulation block diagram of the whole system is established. With the method of fixupping certain parameter, the simulation of valve resistance system and valve resistance - variable speed compound control system is carried out according to simulation block diagram. The simulation results have confirmed the validity of the mathematical model, as well as the analysis of dynamic response performance and energy cost performance of the two types of speed regulation techniques mentioned in the first chapter and the second chapter. The mathematical model of the system is linearized, so as to verify the controllability and observability of the system. The effect of key parameters on system dynamic performance has been got by root locus method.In the fifth chapter, the overall control scheme and energy regulation oriented control strategy are put forward, and on the basis of which, the system controller is developed. To verify control performance of this system, a serial of simulations on the performance were made to make comparison with other three types of hydraulic system. The simulation result shows the advantages of this system in dynamic characteristic and energy cost characteristics. The lectotype of accumulator and the influence of inverter-motor parameters on the system are got through the digital simulation.In the sixth chapter, the experimental bench for the variable speed electro-hydraulic control system based on energy regulating strategy is established. The hydraulic loops, electric systems and control software are all introduced in detail. The response of rectangle signal input and bode diagram are got. According to the experimental curve, the system is thoroughly analyzed. The comparison among the experiments of valve resistance system, valve resistance - variable speed compound control system and this sy stem have been made, and the result shows the validity of the theory and design in this project.In the seventh chapter, the cylinder velocity control application of variable speed electro-hydraulic control technology based on energy regulating strategy is studied. The difference between displacement control systems and velocity control systems is analyzed; the control strategy of velocity control system is put forward and the digital simulation experiment is schemed out. The simulation and experiment result shows that the variable speed electro-hydraulic control technology based on energy regulation also has advantages of energy-saving and speediness in the field of velocity control.