The high-voltage electrostatic precipitator controller with single-chip microcomputer as the core has the characteristics of low cost and powerful functions, but the human-machine interaction is poor, the system maintenance is difficult, the industrial site interference is obvious, and the dust removal efficiency, operation, maintenance and operating costs cannot be taken into account. Aiming at this problem, this paper builds a controller with PLC as the core. Its modular structure is easy to expand and replace, the system reliability is high, the network communication between the controller and the host computer is simple, and there is no emission standard for reducing dust.
1 Principle of electrostatic dust control system
The principle block diagram of the high-voltage power supply control system is shown in Figure 1. The primary voltage, current, secondary voltage, current, and turbidity analog signals collected by the acquisition circuit are sent to the CPU through the PLC analog input module; the transformer oil temperature and oil level , Switching signals such as partial excitation enter the CPU through the digital input signal processing circuit of PLC. The PLC reads all input states and data in sequence by scanning, and generates two trigger pulses according to the results of data processing. The two anti-parallel thyristor control electrodes sent to the main loop trigger the thyristor. The conduction angle of, controls the input voltage of the primary side of the booster transformer, thereby controlling the voltage of the input electric field. On the one hand, it is necessary to automatically adjust the voltage of the dust collector according to the change of working conditions, so that the electric field strength between the collector and the dust collecting electrode is as large as possible, and the ion is as much as possible. Also consider that the voltage between the plates of the dust collector should not be too high, avoid the breakdown of the dust collector, to prevent damage to the body and electrical equipment, and save unnecessary power consumption, but also to restore normal power supply quickly when the medium is restored .
Figure 1 Functional block diagram of high-voltage power supply control system
2 Design and implementation of control system
2.1 Hardware design
The hardware structure block diagram of the high-voltage electrostatic dust removal control system is shown in Figure 2, which is mainly composed of PLC and its peripheral circuits, touch screen, and host computer.
Figure 2 Block diagram of the hardware structure of the control system
2.1.1 PLC selection
PLC has the advantages of simple and intuitive logic, good electrical performance, convenient function combination, high reliability, easy maintenance, and can directly control and drive digital and analog quantities. It is widely used in the field of industrial control. This system uses PLC as the control core , Choose Siemens' new generation of modular small PLC S7-1200, S7-1200 PLC is mainly composed of CPU module, signal board, signal module, communication module and programming software, various modules are installed on the standard rails, microprocessor selection CPU 1214C, 14 digital input points, 10 output points, 2 analog input points, up to 8 signal modules can be expanded, the biggest feature of S7-1200 is the configuration of Ethernet interface RJ45, the system has a total of 8 analog Quantity input, 12 digital input, 2 analog output, 19 digital output PLC hardware configuration shown in Figure 3.
Figure 3 PLC hardware composition
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Dongguan City Leya Electronic Technology Co. Ltd , https://www.dgleya.com