| As a multiple-actuator pressure conversion device,the Switch-mode Hydraulic Power Supply which can reduce or increase the pressure of the constant pressure oil source to the desired load pressure without changing the constant pressure nature of the oil source and provide adaptive flow to the load to achieve the best energy-saving effect,whose conversion efficiency can reach 100% under the ideal condition,is a new kind of energy-saving hydraulic system.But due to the influence of dynamic loss and transient loss caused by the hydraulic components,The system will produce a great energy loss.It is necessary to do further research on the control performance of the system in order to minimize the loss,and realize the practicality and industrialization of Switch-mode Hydraulic Power Supply.In view of the lack of domestic and foreign research on the application of speed control in large flow load,this paper designed a speed control system base on Buck Switch-mode Hydraulic Power Supply and did a research on the control method of the traditional PID by simulation.Firstly,according to the similarity principle of hydraulic and electronic components on the mathematical model,this paper established a structure model of Buck Switch-mode Hydraulic Power Supply with reference to the structure of Buck Switching Power,analyzed the principle of depressurization and flow-increasing and verified the system pressure output is proportional to the duty ratio of PWM wave in high-speed switch valve and the flow output is inversely proportional to it.In order to study the effect of various system parameters on the output characteristics of the load,this paper established a function relationship among the steady-state speed fluctuation,the working frequency of system and duty ratio,the liquid capacity and inductance,the load pressure and its structural parameters in the circumstance with and without accumulator filter.In order to apply the system to large flow load,a two-way cartridge valve in control of high-speed switch valve and a one-way cartridge valve were applied to it to increase the amount of oil through the system and maintain the high frequency switching characteristic of the system.Further,due to the small size of the selected high-speed switch valve,this paper designed a hydraulic control valve as secondary pilot valve of the cartridge valve to increase the oil through the volume of control cavity and improve the response speed of the valve.Based on the constant pressure network technology,this paper established the speed control system model of BuckSwitch-mode Hydraulic Power Supply.Its constant pressure network can provide a constant pressure and output the required flow for the system,and its oil filling and flushing system can supply the consumed oil due to leakage and cooling and cool the oil to ensure the system reliable operation.In order to analyzed the influence of every component parameter on the system parameters and energy consumption,this paper established respective mathematical model of the hydraulic components such as the liquid accumulator,hydraulic motor,the two-way and one-way cartridge valve and analyzed their selection.This paper took the hydraulic motor speed control system as the research object,did a optimized design for the system and made a device to recover the energy caused by the brake or sudden shutdown when encountering a large load.Moreover,this paper set up a joint simulation model with AMESim and Simulink software and analyzed the control performance and control method of the system by simulation.Research showed that the system has a higher efficiency which can reach more than70% under a condition with low frequency,high duty cycle,small high frequency cavity or large load pressure and flow.Reducing the throttle aperture and increasing the air volume of accumulator appropriately can well eliminate the speed fluctuation when the system is starting up,while increasing the working frequency can reduce the steady-state fluctuation of speed.The differential control of the system can enlarge steady-state fluctuation of the speed,so it is unsuitable for use in general.The system under the PI control has a good control performance for a given speed,but at a different speed system will easily cause overshoot or oscillation.It doesn't meet the needs of all operating conditions.In integral separation PI control,the system will cause a speed oscillation under a low speed operating condition.Only in the anti-integral saturation PI control,the system has a good speed regulation performance with a low overshoot and small fluctuation and run smoothly under the condition of speed mutation,impact load,abrupt load,overload,loss of load and noise.What's more,add a pressure feedback check valve between the input of load and the high pressure source can avoid the hydraulic shock and energy waste caused by the brake or sudden shutdown when encountering a large load. |
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