Study Of A High Power Frequency Voltage Switch Supply And Monitor System For Electrostatic Precipitator (esp) Use

Energy-saving, benefit-increasing and emission-reducing have become the theme of development of the times. In controlling the flue gas emissions of particulate matter pollution, electrostatic precipitator (ESP) in accordance with its unique advantages is widely used. At present, the almost 100% ESP power supply of thermal power plant is the power-frequency power supply in China. Compared with the high-frequency ESP power supply, the power-frequency power supply has many faults, for example, low removal dust efficiency (four electric fields in turn need to remove dust), large energy consumption (the ESP power consumption is about 5% of the total thermal power plant power consumption). And that the high-frequency ESP power supply may supply almost no-fluctuations corona voltage and fast response time. According to test, the smoke particles emission requirements of the standard are met when the high-frequency ESP power supply is adopted as long as only one removal dust electric field is used. Furthermore, the 20% energy-saving is reached in high-frequency ESP power supply compared with power-frequency power supply. Thus, the high-frequency ESP power supply has broadly application prospects, and is concerned by the researchers generally.This paper is focus on developing the energy-saving, benefit-increasing, high-frequency ESP power supply system. A complete high-frequency ESP power supply system consists of high power (60kW) high-frequency (20kHz) high-voltage (52kV) transformer, high power inverter, ESP controller and ESP monitor system.The high-power high-frequency transformer is different from the conventional low-voltage switching power transformers, high-voltage pulse transformers and power frequency high-voltage transformer. Firstly, this paper analyzed the characteristics of high-frequency transformer and the model of high-frequency transformer equivalent circuit is established. The classification method of high-frequency transformer equivalent circuit is obtained according to power electronic circuits for the different points of emphasis, namely, the time response characteristics of the equivalent circuit and energy transfer characteristics of the equivalent circuit. Secondly, since that the product parameters of the magnetic material given by manufacturers were measured under the sinusoidal excitation and specific shape of the sample, the test platform was built. The test of the pre-adopted super-crystalline (nano-crystalline) core in the square-wave voltage excitation was carried out. The result shows that the core characteristics was subject to external environmental factors of production, and also influenced by the excitation voltage waveform, the core shape, size. Thirdly, considering the characteristics of high-power high-frequency high-voltage transformer, the optimization design method of high-frequency high-voltage transformer based on transformer insulation structure was proposed. The high-frequency characteristics (skin effect and proximity effect), high-voltage characteristics (insulation), core shape and size, thermal characteristics and optimum efficiency of transformer were optimized completely in this design method. Finally, an ESP transformer used in this paper is built, the basic data as follows: 510 V input voltage, 52 kV output voltage, 60 kW output power, 20 kHz operating frequency, 96% efficiency, super-crystalline core.Commonly, improving the operating frequency of the transformer can increase the power density of it. However, the volume of high-frequency high-voltage transformer with conventional structure is not expected to be scaled down by frequency in the production practice. By analyzing the reason that the conventional high-frequency high-voltage transformer power density is low, based on plane core and cascade transformer technology a new kind of transformer are proposed. The contradiction between "high-frequency led to transformer volume decreasing" and "high-voltage led to transformer volume increasing" has been solved effectively by the new kind of transformer. According to the principles of the new proposed transformer, firstly, a transformer based on planar core and wound winding is designed, which improved the potential distribution inside the transformer conductor and increased the power density of the transformer. Secondly, a transformer based on planar core and the ML-PCB (multi-layer printed circuit board) winding is designed, so that wiring of the transformer windings is more flexible, accurate, and improved the conformance of the distributed (parasitic) parameters of the transformer mass. Finally, a variety of structural topologies of the transformers and the variation law were given. For reasons of time limit, the prototype of the new kind of transformer has been built and tested only.Because conventional structure high-frequency high-voltage transformer has large turns ratio (>100), there is a serious issue of the distribution parameters. By calculation and experimental verification, the entrance characteristic of the transformer is capacitive. Based on this discovery, this paper proposes a new method of designing the ESP power supply: serially adding an inductor to the primary side of the high-voltage, high-frequency transformer to compensate for the intrinsic stray capacitance. And the corresponding DC-AC-DC converter was developed. Firstly, the operating principle and The design considerations of the proposed converter are presented. Secondly, the ESP operating characteristics curves and different operating areas are derived by analyzing the ESP load operation rules, and the criterion among different operating areas is given. According to criterion and to take rapping cycle as control interval, self-learning control strategy based on data retrieval is proposed. To take DSP control chip as the core, hardware and software part of the ESP controller has developed. Thirdly, considering the high-power high-frequency high-voltage and other characteristics of working conditions, the voltage sharing method between combination capacitance is proposed, the electric strength of the PCB board structure is enhanced and the design of the spatial arrangement of silicon ions is optimized. Base on above factors, the high-voltage high-frequency rectifier bridge is designed. Finally, according to the characteristics of the ESP load, a simulated load is set up. By running the tests confirmed that the converter is not only compensate for and take advantage of the inherent distributed capacitance of the transformer, but also has soft-switching characteristics, a good full-power output capability, ESP spark flashover limit current capability and pulse power characteristics, these characteristics show that the converter of based on transformer distributed capacitance compensation method is particularly suitable for ESP applications and has excellent performance.The work mechanism of ESP power supply is high-power high-voltage power flow high-frequency switch, the output voltage is 50kV, sampling and signal voltage is 3 ~ 5V, and the spark and arc are frequent occurrence in working process, so the power supply of electromagnetic interference is serious. For this situation, the electromagnetic compatibility is designed from the interference source, propagation path and interfered bodies, experiment results show that those measures effective suppressed the mutual electromagnetic interference.In the monitor system for ESP, the substation communication protocol IEC 60870-5-103 is adopted. A description method of substation communication protocol conformance test model based on EFSE (Extended Finite State Machine) is defined and proposed. The software module of this monitor system is developed based on EFSM consistency test model and the conformance is ensured. The physical interface for future monitoring of the plant and substation is provided.The ESP power supply system of this paper has accumulated more than 300 hours of operation, continuous heavy load operation more than 24 hours, the output voltage, current and power were 51kV, 1200mA and 61.2kW respectively, the temperature of IGBT and the inductor is below 63℃, the maximum temperature of transformer is 79℃. It met the design objectives. The product-oriented is complete successfully, and the first batch of four ESP power supplies is pass customer's acceptance.