| The quality of output signals of power amplifier is an important factor affecting the pressure control quality of proportional pressure reducing valve.After investigation and research on existing power amplifiers,proportional pressure reducing valves and their control strategies,it is found that the following problems are caused by improper parameter selection and matching in the design process of power amplifiers:(1)Improper design of PWM signal frequency: when the frequency is too low,the ripple current fluctuation amplitude on the solenoid coil is too large;When the frequency is too high,the ratio of the transition time to the switching period of the power driving circuit is too large,which results in the distortion of the voltage waveform of the electromagnetic coil pulse width modulation.Both of them lead to the decrease of pressure stability accuracy of proportional pressure reducing valve.(2)PWM signal duty ratio change rate or mutation amplitude is too large,resulting in the proportional pressure reducing valve pressure peak,resulting in pressure impact.(3)When designing the independent flutter signal,only its effect on improving the hysteresis of the proportional pressure reducing valve is considered,and its influence on the valve pressure stabilizing accuracy is not taken into account.This thesis aims at the above problems,considering the high frequency characteristics of power switching tube,a mathematical model of electromagnetic coil pulse width modulation voltage with harmonic interference is established.By analyzing the force balance of the proportional valve spool,the dynamic mathematical model of the proportional valve is established.Based on this,the circuit simulation software PSpice and the hydraulic system simulation analysis software AMESim are co-simulated to study:(1)The relationship between PWM signal frequency and voltage stability accuracy of proportional pressure reducing valve when considering pulse width modulation voltage waveform distortion;(2)The relationship between the rate and amplitude of duty cycle mutation of PWM signal and the peak pressure of proportional pressure reducing valve;(3)The relationship between the frequency and amplitude of independent flutter signal and the pressure stabilizing accuracy of proportional pressure reducing valve.The results show that when the duty ratio of PWM signal is constant,with the increase of PWM signal frequency,the influence of ripple current on the stability accuracy of proportional valve decreases,but the influence of waveform distortion on the stability accuracy increases,and the amplitude of outlet pressure fluctuation and the frequency of PWM signal show a "U" shape relationship.The peak pressure at the outlet of proportional pressure reducing valve can be effectively suppressed by properly reducing the changing rate of PWM signal duty ratio or changing the duty ratio of PWM signal in two stages.Increasing the frequency or decreasing the amplitude of independent flutter signal can effectively improve the stability accuracy,but the upper frequency and lower amplitude are limited by the improvement of hysteresis.Secondly,through the co-simulation of AMESim and MATLAB/Simulink,the influence of harmonic interference generated by high-speed on-off of power amplifier switch tube on pressure closed-loop control quality of proportional pressure reducing valve is further studied.The results show that the traditional PID control algorithm has limited compensation effect for dynamic errors caused by harmonic interference of power amplifier.In this thesis,the linear active disturbance Rejection control algorithm(LADRC)is adopted.The simulation results for an example show that compared with the traditional PID control algorithm,LADRC can improve the pressure stability accuracy by 5.31% and the response speed by 59%.Finally,a direct-acting proportional pressure reducing valve control test bench was built,and the waveform distortion of PWM coil pulse width modulation voltage was measured when PWM signal frequency is 5 k Hz.The relation between PWM signal frequency and ripple current amplitude of electromagnet coil was obtained.The relationship between PWM signal frequency and stability accuracy of proportional reducing valve,the influence of PWM signal duty ratio change rate and mutation amplitude on outlet pressure peak value of proportional reducing valve were experimentally studied,and the accuracy of theoretical and simulation results were verified. |
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