Development of an intelligent high-voltage inverter DC power supply for electrostatic precipitator
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Abstract: This paper introduces a high voltage inverter power supply for electrostatic precipitator. The main structure of the power supply, the working principle of the main circuit, and the working principle of the control circuit are briefly discussed. At the same time, the system software is also briefly explained. Keywords: electrostatic precipitator; high-voltage inverter; intelligent 0 Introduction With the increasing amount of industrial dust and waste gas emissions, the pollution to the environment is becoming more and more serious, especially in the metallurgical, mining, building materials, chemical and other industries. It is well known that the application of electrostatic precipitators can effectively collect these dusts, but conventional high-voltage electrostatic precipitators are large and heavy, and inconvenient to use. Therefore, it is particularly important to reduce the size and weight of high-voltage electrostatic precipitators. In recent years, with the rapid development of power electronics technology, especially the application of new generation power electronic devices such as IGBT, MOSFET, etc., high-frequency inverter technology has become more and more mature, and various types and characteristics of circuits are widely used in DC/DC and DC/AC and other occasions. Under this premise, it has become possible to design a high-voltage inverter power supply to replace the conventional high-voltage power supply to achieve the purpose of reducing the volume and weight of the high-voltage power supply device. At the same time, its use effect, output characteristics and cost are also significantly superior to conventional high-voltage power supply devices, and the system efficiency has also been improved to a certain extent. 1 System Hardware Design 1.1 Power supply main structure Figure 1 shows the circuit block diagram of the high-voltage inverter power supply, which mainly includes two parts: the main circuit and the control circuit. The main circuit mainly includes the distribution switch, power frequency rectifier, chopper, filter, IGBT bridge inverter, protection circuit, high-frequency high-voltage transformer, high-frequency high-voltage silicon stack (high-frequency rectifier), etc. The control circuit mainly includes current, voltage, spark rate sampling and processing unit, PWM signal generation and drive circuit, single-chip microcomputer controller, parameter input keyboard and LCD display, communication interface, etc. 
Figure 1 Power supply structure diagram 1.2 Working mechanism of the main circuit The working principle of the main circuit is shown in Figure 2. The power switch tube in the high-frequency inverter adopts IGBT (insulated gate bipolar transistor). It is a new type of composite device that integrates the advantages of MOSFET and GTR. It has the advantages of high input impedance and available voltage drive of MOSFET and low on-state power consumption of GTR. 
Figure 2 Main circuit schematic diagram In Figure 2, the AC voltage is rectified, regulated by a chopper, and filtered to obtain a DC voltage U1 , which is then added to the full -bridge high-frequency inverter. D1 ~D4 are connected in reverse parallel with the power switch tubes S1 ~ S4 to withstand the reverse current generated by the load to protect the switch tube. The introduction of C1 ~ C4 , R3 ~ R6 , and D5 ~ D8 is to avoid the excessive voltage rise rate of the four switch tubes when they are turned off and to reduce the turn-off loss of the tubes. When the gate pulse signal drives S1 , S4 or S2 , S3 in turn , the inverter main circuit converts the DC voltage U1 into a 20kHz high-frequency rectangular wave AC voltage and sends it to the high-frequency high-voltage transformer, which is then boosted, rectified, and filtered to supply power to the load (electrostatic precipitator). By controlling the duty cycle of the two groups of IGBTs S1 , S4 and S2 , S3 , a rectangular wave AC voltage with adjustable pulse width can be obtained. 1.3 Working mechanism of control circuit 1.3.1 Microcontroller Controller In order to make the whole power supply system have self-diagnosis and human-machine exchange control functions, the power supply uses PHILIPS series single-chip microcomputer 80C552, which is mainly responsible for real-time monitoring and data communication with the host computer. When the dust collector is in working state, the single-chip microcomputer collects the current and voltage values of its feedback regularly, reads them through the A/D conversion channel, and obtains the control quantity Uk through a certain algorithm, and outputs the control quantity to the pulse width modulation controller through the single-chip microcomputer, thereby changing the modulation pulse width; on the other hand, it can realize the change of the external characteristics of the power supply according to the needs of the user, such as constant current, constant voltage, slow decline, etc. In addition, the single-chip microcomputer also regularly transmits the output current, output voltage, spark rate and other information of the power supply to the host computer, sends the fault information to the host computer through the serial port as a warning, and receives the control command from the host computer at the same time, so that it can start or exit work or change the working parameters. 1.3.2 Pulse Width Modulation Controller The pulse width modulation controller circuit is shown in Figure 3. Its main function is to provide control pulses for the drive circuit to achieve PWM control. Its core is the dedicated integrated chip SG3525A that generates PWM signals. SG3525A is a voltage-type PWM integrated controller with few external components and good performance. It has functions such as external synchronization, soft start, dead zone adjustment, undervoltage lockout, error amplification, and shutting down output drive signals. Its internal structure mainly includes five parts: reference voltage source, undervoltage lockout circuit, sawtooth oscillator, error amplifier, and pulse width modulation comparator. 
Figure 3 Pulse width modulation control circuit 2 System Software Design Each power module's single-chip microcomputer has an independent main program, a communication program with the host computer, a data acquisition subroutine, etc. Due to space limitations, this article only discusses the software structure of the main program and communication subroutine of the power module. The main program flow chart is shown in Figure 4, and the data communication subroutine flow chart is shown in Figure 5. 
Figure 4 Main program flow chart 
Figure 5 Data communication subroutine flow chart The software of the power module mainly completes the following functions: receiving data and instructions sent by the host computer; transmitting data to the host computer; completing real-time monitoring of power output; and controlling various external characteristics according to user needs. 3 Experiments and analysis 3.1 Study on the influence of main inverter bridge PWM regulation on efficiency and determination of standard regulation method As shown in Figure 6, when the input voltage of the power supply is the same, when the duty cycle is less than 50%, the efficiency increases with the increase of the duty cycle; when the duty cycle is greater than 50%, the efficiency decreases with the increase of the duty cycle. It can be seen that if the duty cycle is adjusted over a large range, the power supply will enter a very low efficiency area, and when the duty cycle is between 40% and 70%, the efficiency is higher. To this end, by adjusting the duty cycle of the chopper circuit to control the DC bus voltage, the purpose of high efficiency can be achieved. 
Figure 6 Efficiency curves at different duty cycles 3.2 Field Experimental Test Experimental conditions: electrostatic precipitator plate area 250m2, inter-electrode spacing 150mm, duty cycle 60%, frequency 18.6kHz. Experimental results: Figure 7 shows the corresponding relationship between output voltage and input voltage, and Figure 8 shows the corresponding relationship between output current and input voltage. When the output voltage reaches 58kV (current 82mA at this time), the dust collector begins to flash over, meeting the design requirements. 
Figure 7 Relationship between output voltage and input voltage 
Figure 8 Relationship between output current and input voltage 4 Conclusion 1) The study on the effect of PWM regulation of the main inverter bridge on efficiency has determined that the method of regulating the DC bus voltage by the chopper circuit is feasible; 2) The power supply has greatly reduced its volume and weight. Compared with traditional power supplies, its utilization rate of electric energy is also improved. It is more convenient to control the dust collector than traditional power supplies. At the same time, it can also communicate data with industrial computers to realize remote control of the dust collector. About the Author Zhou Haobin (1965-), male, associate professor, graduated from Xi'an Jiaotong University with a major in welding technology and equipment in 1987. He is currently working in the Department of Materials Science and Engineering at Xi'an Shiyou University, mainly engaged in the research of welding equipment and its automation technology.
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