Pneumatic control valve is one of the industrial process control instruments, widely used in chemical, electric power, metallurgy, pharmaceutical and other industries. The most central parts of valve positioner pneumatic control valve, pneumatic control valve control play a decisive role. The piezo positioner is a new type of structure in recent years, emerging locator which uses piezoelectric valve (piezoelectric transducer unit), electrical conversion function, very low power consumption when the work into steady state air intake and exhaust ports are closed, air consumption is almost zero, and is conducive to energy saving, its application will be more and more widely. The piezo positioner using mainly MCU acquisition given signal and the valve position feedback signal, based on the rate of change of the error and error information, the output control signal according to a certain control algorithm, after the drive circuit drives the piezoelectric valve control the intake port and the state of the exhaust port, so as to achieve the purpose of the control valve position, to form a complete closed-loop control. Can be divided into different piezoelectric valve, valve positioner switch mode with proportional valve positioner. The intake and exhaust ports of the switch valve locator can only fully open or fully closed, the control voltage is logic high and low control algorithms generally use the 5-way switch that is farther away from the target location when using BB control using PWM control, when close to the target position; an intake port and an exhaust port of the proportional valve positioner is presented in accordance with the control voltage different size, different sizes of openings, compared to the switch-mode control process is more gentle, close to the target position, the use of a smaller control voltage to achieve micro-air intake or the exhaust gas, can improve the control accuracy.
At present, the domestic and international switching valve positioner depth, German company Siemens production of SIPARTPS2 of piezoelectric switching valve positioner foreign domestic Chongqing Sichuan Instrument Automation Co., Ltd. produces HVP piezoelectric switching valve positioner achieved good control effect. But at home and abroad on the piezoelectric proportional valve positioner is not deep enough. Piezoelectric proportional valve positioner Korea YTC produced, as well as domestic Jingyi Group piezoelectric valve with proportional developed a fully electronic valve positioner.
This paper analyzes the characteristics of a proportional piezoelectric valve, proposed a step size divided range control algorithm for a given value, and parameter tuning method step structures as the core control based on the real-time simulation system dSPACE control experiment system, different types of valves in Chongqing Sichuan Instrument Automation Technology Center, to achieve good control effect
Proportional piezoelectric valve characteristics analysis
The piezoelectric valve of the proportional type, the terminal 4, the control signal via a drive circuit through the four terminals to control the piezoelectric valve. The terminals 2,3 control the intake port, the terminal 1,4-controlled exhaust port. Within a certain voltage range, and its intake port and exhaust port are presented with a voltage difference of 2,3 channel voltage difference and 1,4 changes the different size of the opening, i.e. the the linear feed gas and linear exhaust, As shown in Table 1, BB represents a Bang-Bang control table to the data only for the measured data for a piezoelectric valve, the measured data obtained by the different valve may not be the same.
The voltage of the control signal sent by the MCU or dSPACE is relatively low, the piezoelectric valve is supplied after amplification. To this end, the noninverting amplification circuit to amplify the signal after a 1,2-way connected to the piezoelectric valve; PWM wave transferred DA is connected to the signal processing of 3,4-way of the piezoelectric valve, i.e. by changing the PWM the duty cycle of the wave to change the size of the control voltage.
For different duty cycle corresponds to the exhaust gas characteristic curve, wherein the voltage of the first channel is fixed at low level, with the increasing of the duty cycle of the first 4-way, correspond to the first 4-way piezoelectric valve with the first channel a voltage difference between in increasing, and the exhaust velocity is more and more slowly.
For different duty ratio corresponding to the intake air characteristic curve, wherein the voltage of the second channel is fixed to a low level. Seen from the figure, with the duty ratio of the third channel is continually reduced, and the corresponding voltage difference between the 3-way with the second road to the first piezoelectric valve constantly reduced, the intake air speed is more and more slowly.
In summary, when the control voltage within a certain range (i.e., linear range), the size of the piezoelectric valve in the intake port and the exhaust port of the proportional type is variable, from the BB intake air or the exhaust gas until the micro gas or the exhaust gas, showing the proportionality characteristic. Actual control process can be measured in linear interval to complete the BB the intake or exhaust after gentle deceleration and high-precision fine-tuning.
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