| Electro-hydraulic proportional control system has been widely used in aviation,aerospace,military,civil industry and other fields due to its reliability,energy saving,convenient maintenance and low cost.The proportional control amplifier is the core unit of the control algorithm and power drive in the electro-hydraulic proportional control system,and its performance directly affects the control quality of the electro-hydraulic proportional control system.The traditional control algorithm of analog proportional control amplifier is realized by hardware circuit composed of analog electronic components.It has fast operation speed,but it is difficult to adjust parameters,inflexible to set,and can not adjust and store parameters online.The internal control algorithm of digital proportional control amplifier with microcontroller as its core is realized by software program.Its parameters are flexible to adjust,and it has the function of memory storage.However the response speed is restricted by the speed of the hardware and software of the controller.For the systems that require fast response,the control requirements are not met.Based on the requirement of flexibility and rapidity of modern electro-hydraulic control system,this paper presents and designs an analog-digital hybrid proportional control amplifier.Its control algorithm is realized by analog PID circuit.The parameters of controller are adjusted and set by digital potentiometer instead of analog potentiometer.The value of digital potentiometer is adjusted by single chip computer and stored in memory.The single chip computer collects the state variables of the field control system and obtains the setting parameters of the PID controller according to the system model.This design scheme not only realizes online setting,adjustment and storage of controller parameters by using single chip microcomputer,but also realizes control algorithm quickly by using analog PID circuit.Specific research contents are as follows:(1)In the aspect of internal integration algorithm of analog-digital hybrid proportional control amplifier.Because of the uncertainties of model parameters of electro-hydraulic proportional valve,based on the theoretical model of proportional valve,this paper uses L-M(Levenberg-Marquardt)algorithm to identify the model of electro-hydraulic proportional valve,and obtains a mathematical model with high fitting degree with the real controlled object.The mathematical model provides a theoretical basis for the parameter tuning of the analog-digital hybrid proportional control amplifier.(2)In the aspect of hardware design,the overall scheme of hardware circuit of proportional control amplifier is designed at first.Freescale single-chip MC9S12XS128 is selected as the core chip of proportional amplifier,and the peripheral circuits such as input interface module,analog-digital hybrid controller module,PWM power driver module,measurement feedback circuit and power module are designed.Multisim is used to simulate the circuit of the PWM power drive module,and the performance of the designed power drive circuit is verified.(3)In the aspect of software design,according to the top-down design idea of each functional module of the system,the software program of each module was written in the integrated development environment CodeWarrior,and the priority of each functional module program was reasonably divided.At the same time,in order to give the control parameters in the proportional control amplifier and monitor the controlled object in real time,the upper computer interface program was developed by using Labview.(4)In order to verify the rationality of the hardware and software design,the experimental platform of the analog-digital hybrid proportional control amplifier was built with the proportional electromagnet as the control object.In the open-loop experiment of analog-digital hybrid proportional control amplifier,the input voltage and proportional solenoid coil current is measured by digital multimeter,and the measured data is linearly fitted by MATLAB.The nonlinearity of the solenoid coil current is calculated to be 0.55%.In the closed-loop experiment,the output voltage response time of the proportional control amplifier is about 0.2ms by using double tracer oscilloscope to display the voltage at both ends of the proportional solenoid coil.From the above experimental results,it can be concluded that the analog-digital hybrid proportional control amplifier designed in this paper has smaller steady-state error,higher control accuracy and faster response speed,and can achieve better control effect. |
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