Application of the hottest PLC in domestic high vo

2022-08-24
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The application of PLC in domestic high-voltage high-power inverter

1. Introduction

in the design of domestic high-voltage inverter, in order to improve the flexibility of internal control of high-voltage inverter and the scalability of field application, PLC is usually built in high-voltage inverter. Since the birth of the first PLC in the 1970s, PLC has been more and more widely used and its functions have become more and more perfect. In addition to its powerful logic control function, it also has other extended functions: a/d and d/a conversion, PID closed-loop control, high-speed counting, communication connection, interrupt control and special function calculation. It can display, alarm, record and man-machine dialogue through the upper computer, so that its control level is greatly improved

taking the domestic high-voltage inverter zinvert-h800/b10 designed and produced by Guangzhou Zhiguang Motor Co., Ltd. for the sewage treatment plant of Chengdu Iron and Steel Co., Ltd. of Pangang Group as an example, this paper introduces the application of Mitsubishi PLC in the control system of high-voltage inverter

2. Introduction to Guangzhou Zhiguang motor high voltage inverter

the new generation of high-performance zinvert series intelligent high-voltage variable frequency speed regulation system launched by Guangzhou Zhiguang Motor Co., Ltd. is a direct high-high variable frequency speed regulation system, which realizes the regulation of motor speed by directly adjusting the power frequency and voltage connected to the stator winding of high-voltage motor, so as to achieve the purpose of energy saving. It is a high-tech product integrating high-power power electronic control technology, microelectronics technology, high-speed optical fiber communication technology, automation control technology, high-voltage technology and other disciplines. The product adopts the mainstream high-performance special dual DSP control system and large-scale integrated circuit design, and realizes the flexible adjustment and energy consumption control of high-voltage motor through accurate digital phase-shifting technology and waveform control technology

3. The design and use of PLC in domestic high-voltage inverter

3.1 the main logic control of PLC

(1) the user requires that the high-voltage inverter can quickly and automatically switch to the power frequency bypass operation in case of fault shutdown. The author specially configures the bypass cabinet that can realize the automatic bypass function for the high-voltage inverter, as shown in Figure 1. K1 ~ K4 are manually operated knife switches, J1 ~ J3 are high-voltage vacuum contactors. When the frequency converter fails, the bypass cabinet can complete the conversion from frequency conversion to power frequency within a few seconds; When the frequency converter is operating at power frequency, the conversion from power frequency to frequency conversion can be realized through one button. Such control requirements increase the complexity of the inverter control logic

Figure 1 automatic bypass cabinet

the control logic of automatic bypass cabinet is briefly introduced as follows:

there are two ways for the variable frequency speed regulation system to exit the operation from variable frequency to power frequency, one is automatic mode, the other is manual mode. When the automatic mode is selected, when the frequency converter stops, the frequency converter will automatically switch from variable frequency to power frequency; Manual operation is required when manual mode is selected

there are also two ways for the frequency conversion speed regulation system to exit the operation of power frequency conversion, one is automatic mode, the other is manual mode. When selecting the automatic mode, just press a button on the control cabinet, and the frequency converter will automatically complete the conversion from power frequency to frequency; Manual operation is required when selecting manual mode

(2) schematic diagram of PLC control system

48 input and output points are selected for PLC host. The model is FX2N, which breaks through the key technical equipment constraints in industrial structure adjustment and the development of key industries -48mr. PLC, as the control core of system logic quantity control, plays a vital role in the logic relationship control of automatic bypass cabinet. The schematic diagram of PLC control system is shown in Figure 2

Figure 2 Schematic diagram of PLC control system

the logic control requirements of bypass cabinet are relatively complex. PLC control is adopted, and the wiring is simple, which improves the reliability; The logic change of bypass cabinet has also become very simple. It only needs to modify the PLC ladder program, which is convenient to meet the control requirements of users on site

(3) PLC function instruction realizes the PID closed-loop control of high-voltage inverter

the requirements of the user's site for the closed-loop control of the inverter are: the inverter can automatically adjust the speed of the variable-frequency pump according to the change of the water consumption of the user's system, so as to realize the constant pressure water supply; At the same time, the pressure target value can be set on the LCD screen

according to the requirements of users, PLC is additionally configured with special analog modules fx2n-4ad and fx2n-2da. Fx2n-4ad is an analog input module, with four input channels, laboratory construction, planning and other related services. The mechanical part is guaranteed for free for two years, with a maximum resolution of 12 bits, and the input range of analog values is -10v ~ 10V or 4 ~ 20mA; Fx2n-2da is an analog output module, which has two output channels, with a maximum resolution of 12 bits. The range of analog output values is -10v to 10V or 4 to 20 mA. In this way, through reading instructions (from) and writing instructions (to), as well as PID closed-loop control function instructions with PLC (as shown in Figure 3), PID closed-loop control of pipe water pressure at the user's site can be realized

the PLC program of PID closed-loop control function command in Figure 3

the specific programming process is as follows: the PLC reading instruction (from) reads the user's water pressure feedback value, and stores the feedback value in the D12 data address in the PID instruction with the mobile instruction (MOV) in recent years; Store the user's water pressure setting value into the D10 data address in the PID command with mov; D200 ~ D222 save the operation parameters of PID; D14 is the operation value output of PID command. The PID closed-loop operation result D14 is written into the analog output module through the write command (to) of PLC, and then converted into -10v ~ 10V or 4 ~ 20mA analog signal through the analog output module, which is sent to the high-voltage converter controller for frequency setting

when setting PID operation parameters, the parameter setting of P, I and D is particularly important, and its setting is directly related to the quality of pipe water pressure control. P refers to the proportional gain. The setting range is 0 ~ 99 (%). If the proportional adjustment setting is large, the adjustment can be accelerated and the error can be reduced when the system has deviation. However, if the proportional gain is too large, the system will be unstable; I refers to the integration time, and the setting range is 0 ~ 32767 (*100ms). The smaller the integration time is, the stronger the integration effect is. On the contrary, the larger I is, the weaker the integration effect is; D refers to the differential time, and the setting range is 0 ~ 32767 (*10ms). The differential adjustment has the leading control function. The appropriate differential time can improve the dynamic performance of the system

the water supply pipe of Panzhihua Steel sewage treatment plant is relatively large, and the response of pipe water pressure to the change of pump speed is relatively slow, so the calculation speed of PID cannot be too fast, that is, the proportion adjustment cannot be too fast, otherwise if the pipe water pressure changes suddenly, the adjustment of frequency converter is easy to form a long-term oscillation. According to this situation, as shown in Figure 3, PID interval calculation time (T0) and PID calculation dead zone (M0) can be added to the PLC control program, so that the calculation speed of PID can be adjusted to be consistent with the change speed of pipe water pressure to avoid pipe water pressure oscillation

(4) PLC function instruction realizes the communication between PLC and the upper computer of frequency converter

in order to make the upper function of frequency converter display, alarm and record PLC, PLC is also configured with communication module fx2n-232bd to realize serial port communication with the upper computer of frequency converter. The communication programming instruction is shown in Figure 4

Figure 4 communication programming instructions

plc RS232 serial port communication can use no protocol (RS instruction) or special protocol to communicate with the upper computer. In this example, no protocol is used to communicate with the upper computer, as shown in Figure 4: d8120 is used to set the PLC communication format, D50 represents the starting address of sending, K60 represents the number of bytes sent, D150 represents the starting address of receiving, and K20 represents the number of bytes received

4. Conclusion

the automatic bypass cabinet of high-voltage converter adopts PLC for bypass logic control. Through the analog fault description of Zhiguang high-voltage converter running in Pangang sewage treatment plant, the automatic bypass cabinet of high-voltage converter is switching from frequency conversion to power frequency. The mutual switching of power frequency conversion is very convenient and can be completed within 10s, which greatly improves the reliability of water pump operation. The effect of on-site PID closed-loop control is very ideal. The fluctuation of water pressure is very small. When the fluctuation exceeds 0.1kg, the frequency converter can quickly adjust the speed, control the water pressure within the set range, and there will be no oscillation when adjusting the speed. At the same time, through the serial port RS-232 communication between PLC and high-voltage converter controller, the system pipe water pressure and various state quantities of PLC can be monitored on the LCD screen of high-voltage converter. (end)

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