A high-frequency alternating current plasma ignition power supply system and control method for a pulverized coal boiler

Abstract

The present application belongs to the field of plasma ignition power supply, and discloses a coal powder boiler high-frequency alternating current plasma ignition power supply system and a control method. The three-phase alternating current is converted into a direct current bus voltage through a rectifying module, and the direct current bus voltage is inverter processed according to an inverter frequency and a phase shift angle through a high-frequency inverter module, so that high-frequency alternating current with adjustable frequency and output state is formed to provide stable power input for subsequent arc striking and arc maintaining. The high-frequency alternating current is resonant converted through a resonant arc striking and maintaining module, high-voltage alternating current arc striking power is output in the arc striking stage, and high-frequency alternating current arc maintaining power is output in the arc maintaining stage, so that the arc striking process and the arc maintaining process are connected with each other, arc maintaining power can be continuously provided to the plasma torch after the alternating current arc is formed, and the continuity of the arc striking and arc maintaining processes is improved.

Description

Technical Field

[0001] This invention belongs to the field of plasma ignition power supply, specifically relating to a high-frequency AC plasma ignition power supply system and control method for pulverized coal boilers. Background Technology

[0002] Pulverized coal power plant boilers typically require ignition devices during startup and low-load stable combustion. To reduce fuel consumption and unit startup costs, 300MW, 600MW, and 1000MW pulverized coal boilers have gradually adopted plasma oil-free ignition devices. These devices supply power to a plasma torch via a power supply unit to generate an electric arc, producing high-temperature plasma for igniting pulverized coal.

[0003] Existing plasma ignition power supplies for pulverized coal boilers mainly employ a three-phase power frequency step-down, thyristor phase-controlled rectification, and DC filtering power supply method, with some equipment using low-frequency DC inverters below 20kHz. These power supplies typically output a unidirectional DC arc and separate the high-voltage pulse arc ignition circuit from the main arc-maintaining circuit. Existing DC power supplies can achieve a constant DC output through power frequency transformer step-down, thyristor rectification, and filter inductors, with an external high-voltage pulse module then igniting the arc; low-frequency inverter power supplies regulate the DC output through IGBT inverter topology.

[0004] In the above methods, the unidirectional DC arc subjectes the cathode to prolonged electron emission and high-temperature particle bombardment, easily leading to uneven losses between the cathode and anode and shortening electrode life. For low-volatile coal types such as anthracite and lean coal, insufficient arc stability and coal powder activation capacity can easily result in arc ignition failure, arc breakage, or arc extinction. Power frequency transformers and large-capacity filter inductors are bulky and heavy, resulting in low equipment power density. Thyristor phase-controlled rectification generates significant harmonics, and increased magnetic component losses increase overall energy consumption. Separating the arc ignition circuit from the arc maintenance circuit can also generate high-voltage pulse crosstalk, affecting electrical parameter sampling and fault response.

[0005] Furthermore, low-frequency DC inverters have limited frequency and voltage regulation ranges, making them difficult to adapt to plasma torches of different power levels, as well as different coal types and boiler operating conditions. Measuring only unidirectional current also makes it difficult to promptly identify arc bias, asymmetrical discharge, and precursors to arc extinction. The power and continuous operation capabilities of existing small-scale AC plasma equipment are also insufficient to meet the high-power, long-duration ignition and deep peak-shaving and stable combustion requirements of power plant boilers. Summary of the Invention

[0006] The purpose of this invention is to overcome the problems of existing plasma ignition power supplies for pulverized coal boilers, such as poor adaptability to low-volatile coal types, uneven electrode wear, large equipment size, significant harmonic interference, limited output adjustment range, and insufficient fault prediction capability. This invention provides a high-frequency AC plasma ignition power supply system and control method for pulverized coal boilers.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a high-frequency AC plasma ignition power supply system for pulverized coal boilers, comprising: The rectifier module is used to receive three-phase AC power, rectify the three-phase AC power, and output DC bus voltage; The high-frequency inverter module is used to receive the DC bus voltage and the inverter control parameters output by the control module, and to perform inverter processing on the DC bus voltage according to the inverter control parameters to output high-frequency AC power. The resonant arc ignition and arc maintenance module is used to receive high-frequency AC power for resonant conversion. During the arc ignition stage, it outputs high-voltage AC arc ignition power to the plasma torch to form an AC arc, and during the arc maintenance stage, it outputs high-frequency AC arc maintenance power to the plasma torch to maintain the AC arc. The arc parameter acquisition module is used to acquire the positive and negative half-cycle electrical parameters of the AC arc and output arc parameter data based on the acquisition results. The control module receives arc parameter data, determines the operating state of the AC arc based on the positive and negative half-cycle electrical parameters, generates inverter control parameters including inverter frequency and phase shift angle based on the operating state, and outputs the inverter control parameters to the high-frequency inverter module to adjust the electrical energy output from the resonant arc ignition and arc maintenance module to the plasma torch.

[0008] A further improvement of the present invention is that the rectifier module includes: A three-phase common-mode electromagnetic interference filter array is used to filter three-phase alternating current. An active power factor correction unit is used to correct the current waveform of the filtered three-phase AC power. A three-phase rectifier bridge is used to rectify three-phase alternating current after the current waveform has been corrected. The bus energy storage capacitor bank is used to store and smooth the rectified DC power to form the DC bus voltage. A spike buffer circuit is used to suppress voltage spikes during the rectification process.

[0009] A further improvement of the present invention is that the high-frequency inverter module includes: The isolation drive unit is used to receive the drive signal generated by the control module according to the inverter frequency and phase shift angle, and control the silicon carbide switching devices in the phase-shifted full bridge to turn on or off according to the drive signal, so that the phase-shifted full bridge converts the DC bus voltage into high-frequency AC. Soft-switching resonant inductors are used in conjunction with phase-shifted full-bridge circuits to achieve zero-voltage turn-on and zero-current turn-off of silicon carbide switching devices.

[0010] A further improvement of the present invention is that the resonant arc-initiating and arc-maintaining module includes: A high-frequency step-up transformer is used to receive high-frequency alternating current and step it up. The LC resonant branch is used to resonate and boost the high-frequency AC power after the arc ignition stage, so that the pulse energy storage capacitor outputs high-voltage AC arc ignition power through the discharger. It is also used to output high-frequency AC arc maintenance power through the same LC resonant branch during the arc maintenance stage. High-voltage DC blocking capacitors are used to block the DC component in the output power, causing the AC arc to form a bipolar alternating discharge.

[0011] A further improvement of the present invention is that the arc parameter acquisition module is used to simultaneously acquire the positive half-cycle current, negative half-cycle current, positive half-cycle voltage and negative half-cycle voltage of the AC arc, and send the acquisition results to the control module. The control module is used to determine the operating status of the AC arc based on the acquisition results as open circuit waiting to be ignited, pulse ignition, stable arc maintenance, or asymmetric arc extinction precursor state. When the bidirectional arc current stabilizes within the preset range, the control module determines that the AC arc is in a stable arc-maintaining state; When the difference between the positive half-cycle current and the negative half-cycle current exceeds the preset range, the control module adjusts the phase shift angle to reduce the difference between the positive half-cycle current and the negative half-cycle current. When a sudden drop in arc current or a deviation in arc waveform is detected, the control module adjusts the inverter frequency to increase the resonant voltage output by the resonant arc initiation and maintenance module.

[0012] A further improvement of the present invention is that it also includes a multi-parameter protection cooling module for acquiring DC bus overvoltage signal, high-frequency inverter module short-circuit signal, transformer magnetic saturation signal, arc positive and negative half-cycle asymmetry signal, plasma torch insulation status signal, cooling water temperature signal, air duct status signal and cabinet condensation signal. When a DC bus overvoltage signal, a high-frequency inverter module short-circuit signal, or a transformer magnetic saturation signal is received, the drive signal of the high-frequency inverter module is latched and cut off. When receiving signals of arc asymmetry in positive and negative half-cycles, plasma torch insulation status, cooling water temperature, air duct status, or cabinet condensation, output a warning or shutdown signal. It is also used to send fault signals to the boiler distributed control system, so that the boiler distributed control system can interlock the coal mill, primary air fan and plasma cooling water pump according to the fault signals.

[0013] Secondly, this invention provides a method for controlling a high-frequency AC plasma ignition power supply for a pulverized coal boiler, comprising the following steps: It receives three-phase AC power, rectifies the three-phase AC power, and obtains DC bus voltage; The inverter control parameters, including the inverter frequency and phase shift angle, are obtained. The DC bus voltage is then inverted based on the inverter control parameters to obtain high-frequency AC power. During the arc ignition stage, the high-frequency AC current is resonantly transformed to obtain high-voltage AC arc ignition energy, which is then output to the plasma torch to form an AC arc. During the arc maintenance stage, the high-frequency AC current is resonantly transformed to obtain high-frequency AC arc maintenance energy, which is then output to the plasma torch to maintain the AC arc. Collect the positive and negative half-cycle electrical parameters of the AC arc, and generate arc parameter data based on the collection results; The operating status of the AC arc is determined based on the arc parameter data. The inverter frequency and phase shift angle are updated based on the operating status. The DC bus voltage is then inverted based on the updated inverter frequency and phase shift angle to regulate the electrical energy output to the plasma torch.

[0014] A further improvement of this invention lies in the following method for receiving three-phase alternating current, rectifying the three-phase alternating current, and obtaining the DC bus voltage: The three-phase AC power is sequentially subjected to electromagnetic interference filtering, power factor correction, and rectification. The rectified DC power is then subjected to energy storage and smoothing to obtain the DC bus voltage.

[0015] A further improvement of this invention lies in obtaining inverter control parameters, including inverter frequency and phase shift angle, and then performing inverter processing on the DC bus voltage according to the inverter control parameters to obtain high-frequency AC power. The specific method is as follows: The phase-shifted full-bridge drive signal is generated based on the inverter frequency and phase shift angle. The phase-shifted full-bridge drive signal is used to control the silicon carbide switching device to perform inverter processing on the DC bus voltage, so as to obtain high-frequency AC power with a frequency of 50kHz to 120kHz.

[0016] A further improvement of this invention lies in the method for determining the operating state of the AC arc based on arc parameter data, and updating the inverter frequency and phase shift angle based on the operating state as follows: Based on the positive and negative half-cycle electrical parameters, the operating state of the AC arc is determined as open-circuit waiting-to-ignite state, pulse ignition state, stable arc maintenance state, or asymmetric arc extinction precursor state. When the bidirectional arc current stabilizes within a preset range, the AC arc is determined to be in a stable arc-maintaining state. When the difference between the positive half-cycle current and the negative half-cycle current is greater than the preset range, the phase shift angle is adjusted to balance the discharge energy of the positive and negative half-cycles of the AC arc. When a sudden drop in arc current or a deviation in arc waveform is detected, it is determined that the AC arc is in an asymmetrical arc extinction precursor state. After detecting the asymmetrical arc extinction precursor state, the inverter frequency is increased, the resonant voltage output to the plasma torch is increased, and the AC arc is re-established.

[0017] Compared with the prior art, the present invention has the following beneficial effects: This invention converts three-phase AC power into DC bus voltage using a rectifier module, and then inverts the DC bus voltage using a high-frequency inverter module based on the inverter frequency and phase shift angle. This generates high-frequency AC power with adjustable frequency and output state, providing a stable power input for subsequent arc ignition and arc maintenance. The invention uses a resonant arc ignition and arc maintenance module to resonate and transform the high-frequency AC power, outputting high-voltage AC arc ignition energy during the arc ignition stage and high-frequency AC arc maintenance energy during the arc maintenance stage. This allows for seamless connection between the arc ignition and arc maintenance processes, continuously supplying arc maintenance energy to the plasma torch after the AC arc is formed, improving the continuity of the ignition and arc maintenance processes. Finally, the invention uses an arc parameter acquisition module to collect the positive and negative half-cycle electrical parameters of the AC arc, obtaining arc parameter data that reflects the bidirectional discharge state of the AC arc. The control module determines the operating state of the AC arc based on the arc parameter data, and generates inverter control parameters including inverter frequency and phase shift angle accordingly. It then performs feedback adjustment on the high-frequency inverter module, thereby dynamically adjusting the electrical energy output to the plasma torch according to the actual state of the AC arc. Attached Figure Description

[0018] Figure 1 This is the electrical connection diagram of the system of the present invention; Figure 2 This is a schematic diagram of the resonant arc-initiating and arc-maintaining module circuit topology in this invention; Figure 3 This is a schematic diagram of the silicon carbide phase-shifted full-bridge high-frequency inverter main circuit in this invention. Figure 4 This is a flowchart of the bidirectional arc adaptive control logic in this invention; Figure 5 This is a schematic diagram of the 50kW to 200kW modular inverter parallel output architecture in this invention. Detailed Implementation

[0019] To further understand the content of this invention, the invention will be described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the embodiments are merely illustrative and not limiting of the invention.

[0020] Example 1: like Figure 1 As shown, the high-frequency AC plasma ignition power supply system for pulverized coal boilers in this embodiment includes a rectifier module, a high-frequency inverter module, a resonant arc ignition and arc maintenance module, an arc parameter acquisition module, a control module, and a multi-parameter protection and cooling module.

[0021] The rectifier module, high-frequency inverter module, resonant arc ignition and maintenance module, and plasma torch are connected in sequence to form a power transmission link; the arc parameter acquisition module is connected to the output side of the plasma torch, and the control module is connected to the arc parameter acquisition module and the high-frequency inverter module to form an arc status feedback control link; the multi-parameter protection and cooling module acquires the status signals of the DC bus, high-frequency inverter module, resonant arc ignition and maintenance module, plasma torch, cooling water circuit, cabinet air duct and cabinet environment, and communicates with the boiler distributed control system.

[0022] In a preferred configuration, a three-phase 380V industrial power grid is rectified by a rectifier module to form a 780V DC bus voltage; a high-frequency inverter module converts the DC bus voltage into high-frequency AC power with adjustable frequency and voltage; a resonant arc ignition and arc maintenance module resonates and boosts the high-frequency AC power during the arc ignition stage, outputting high-voltage AC arc ignition energy to the plasma torch; after the electrode gap is broken down and an AC arc is formed, the module switches to the arc maintenance stage, outputting high-frequency AC arc maintenance energy.

[0023] The arc parameter acquisition module synchronously acquires the voltage and current of the positive and negative half-cycles of the AC arc. Based on this, the control module identifies the operating status of the AC arc, generates inverter control parameters including inverter frequency and phase shift angle, and feeds the inverter control parameters back to the high-frequency inverter module.

[0024] All modules are integrated into a single IP54 standard cabinet. Power harnesses, sampling harnesses, and communication harnesses are arranged in isolated zones to reduce interference from high-voltage pulses and high-frequency power circuits on arc parameter acquisition and control communication. This system can be used for oil-free ignition and low-load stable combustion of pulverized coal boilers from 300MW to 1000MW, and can be modularly configured according to the plasma torch power.

[0025] The rectifier module is used to receive three-phase AC power and sequentially perform electromagnetic interference filtering, current waveform correction, rectification, energy storage and smoothing, and output DC bus voltage.

[0026] In one specific structure, the rectifier module includes a three-phase common-mode electromagnetic interference filter array, a three-level silicon carbide active power factor correction unit, a silicon carbide three-phase rectifier bridge, a bus energy storage capacitor bank, and an RC spike buffer circuit.

[0027] The three-phase common-mode electromagnetic interference filter array is connected to a three-phase 380V industrial power grid to filter out common-mode and differential-mode noise on the input side; the active power factor correction unit is connected to the output of the three-phase common-mode electromagnetic interference filter array to correct the input current waveform in real time; the three-phase rectifier bridge rectifies the three-phase AC power after the current waveform correction; the bus energy storage capacitor bank stores energy and smooths the DC power obtained by rectification; and the RC spike buffer circuit is used to suppress the spike voltage generated during rectification.

[0028] Specifically, the active power factor correction unit can use the UCC28056 control chip, the three-phase rectifier bridge can use the C4D40120D rectifier device, and the bus energy storage capacitor bank can use three 680μF / 1200V film capacitors connected in series. After the above processing, the rectifier module outputs a DC bus voltage of approximately 780V, the input power factor can be stabilized above 0.995, and the total harmonic distortion rate can be controlled below 3.8%, thus eliminating the need for a separate independent filter cabinet.

[0029] In other implementations, the three-level silicon carbide active power factor correction unit can be replaced with a two-level silicon carbide active power factor correction unit to simplify the circuit structure of small and medium power devices. As long as the three-phase AC power can be converted to a DC bus voltage that meets the input requirements of the high-frequency inverter module, the rectifier topology and device model can be adjusted according to the rated power.

[0030] like Figure 3 As shown, the high-frequency inverter module is used to receive the DC bus voltage and the inverter control parameters output by the control module, and convert the DC bus voltage into high-frequency AC power according to the inverter frequency and phase shift angle.

[0031] In one specific structure, the high-frequency inverter module includes a phase-shifted full bridge composed of four sets of SCT3040KL silicon carbide MOSFETs, a UCC21520 isolated drive unit, and a 25μH soft-switching resonant inductor.

[0032] The isolated drive unit receives the drive signal generated by the control module based on the inverter frequency and phase shift angle, and controls the turn-on and turn-off of the silicon carbide switching devices in each arm of the phase-shifted full-bridge. The control module continuously adjusts the inverter AC frequency within the range of 50kHz to 120kHz by adjusting the frequency of the drive signal; and adjusts the output AC voltage within the range of 0 to 3800V by linearly adjusting the phase shift angle within the range of 0° to 180°.

[0033] The soft-switching resonant inductor, in conjunction with the phase-shifted full-bridge, enables the silicon carbide switching devices to achieve zero-voltage turn-on and zero-current turn-off across the entire load range. Using this structure, the inverter conversion efficiency of the high-frequency inverter module can reach over 98.7%, and the switching losses are reduced by approximately 62% compared to the low-frequency IGBT inverter structure.

[0034] The high-frequency AC power output from the high-frequency inverter module serves as the input to the resonant arc ignition and arc maintenance module. During the arc ignition phase, the control module sets the inverter frequency to the arc ignition frequency, enabling the resonant arc ignition and arc maintenance module to generate high-voltage AC arc ignition power. During the arc maintenance phase, the control module adjusts the inverter frequency and phase shift angle based on the arc parameter data, ensuring that the high-frequency inverter module outputs high-frequency AC power suitable for stably maintaining the AC arc.

[0035] In low-cost, low-power configurations, a hybrid switching module composed of IGBTs and silicon carbide devices can be used to replace the all-silicon carbide MOSFET phase-shifted full-bridge, while still retaining the power transfer relationship between the phase-shifted full-bridge and the resonant arc-starting and arc-maintaining module.

[0036] like Figure 2 As shown, the resonant arc ignition and arc maintenance module is connected between the high-frequency inverter module and the plasma torch, and is used to complete high-voltage AC arc ignition and high-frequency AC arc maintenance through the same resonant circuit.

[0037] In one specific structure, the resonant arc-initiating and arc-maintaining module includes a nanocrystalline high-frequency step-up transformer T1, a series LC resonant branch, a parallel pulse energy storage capacitor, a spark gap discharger, and two high-voltage DC blocking ceramic capacitors.

[0038] The high-frequency step-up transformer T1 has 42 turns on the primary side and 1360 turns on the secondary side, with a turns ratio of approximately 32.4:1. The resonant inductance Lr in the series LC resonant branch is 12mH, and the resonant capacitance Cr is 0.022μF. The parallel pulse energy storage capacitor Cp is 0.1μF / 20kV. The withstand voltages of the two high-voltage DC blocking ceramic capacitors are 15kV each. The spark gap discharger is denoted as FC.

[0039] During the arc ignition stage, the control module controls the high-frequency inverter module to output 110kHz high-frequency AC power. The high-frequency AC power is stepped up by the high-frequency step-up transformer T1 and further stepped up by the series LC resonant branch, so that the parallel pulse energy storage capacitor stores electrical energy. When the spark gap discharger is activated, it outputs a high-voltage AC arc ignition pulse with a peak value of about 28kV to the plasma torch, which breaks down the gap between the two electrodes of the plasma torch and forms an AC arc.

[0040] If no AC arc is detected, the control module initiates the arc ignition process cyclically, with each attempt lasting 3 seconds and a maximum of 5 times. If no AC arc is detected after reaching the maximum number of arc ignition attempts, the control module stops the high-frequency inverter output and outputs an ignition failure signal.

[0041] During the arc-maintaining phase, when the arc parameter acquisition module detects the AC arc conduction and the control module determines that ignition is successful, the control module lowers the inverter frequency from the arc-ignition frequency to 60kHz to 90kHz, so that the same LC resonant branch outputs symmetrical low-voltage high-frequency AC arc-maintaining power.

[0042] Two high-voltage DC blocking ceramic capacitors are respectively set in the output circuit to block the DC component in the high-frequency AC arc energy, so that the two electrodes of the plasma torch alternately undertake the discharge function in the positive and negative half-cycles, forming bipolar alternating discharge, thereby reducing the unbalanced loss between the two electrodes.

[0043] Since the arc ignition and arc maintenance stages share the same high-frequency step-up transformer and LC resonant branch, there is no need to set up an independent high-voltage arc ignition power supply, which can reduce crosstalk caused by multi-circuit high-voltage wiring.

[0044] In another embodiment, the series LC resonant branch can be replaced with a parallel LC resonant branch, and the inductance and capacitance parameters can be adjusted according to the plasma torch lead length and the required arc ignition voltage to adapt to ultra-high voltage or long-distance wiring conditions. The spark gap discharger can also be replaced with a solid-state thyristor pulse generator to reduce the maintenance frequency of the pulse circuit.

[0045] The arc parameter acquisition module is used to synchronously acquire the positive half-cycle current, negative half-cycle current, positive half-cycle voltage, and negative half-cycle voltage of the AC arc, and generate arc parameter data based on the acquisition results, and send the arc parameter data to the control module.

[0046] In one specific structure, the arc parameter acquisition module includes a high-precision Hall current sensor with a bidirectional range of 0 to 60A, a multi-channel high-voltage synchronous sampling circuit, and a DC bus voltage synchronous sampling circuit.

[0047] Hall current sensors are used to collect the positive and negative half-cycle currents of the AC arc, multi-channel high-voltage synchronous sampling circuits are used to collect the positive and negative half-cycle voltages of the AC arc, and DC bus voltage synchronous sampling circuits are used to collect the DC bus voltage.

[0048] Each sampling channel samples synchronously according to a unified time base to form arc parameter data that can characterize the polarity, amplitude, positive and negative half-cycle differences, waveform offset, and instantaneous changes of the AC arc. The arc parameter acquisition module transmits the arc parameter data to the control module as input data for arc state judgment and inverter frequency and phase shift angle adjustment.

[0049] The control module can use a TMS320F280049C digital signal processor and be configured with an RS-485 interface, a Modbus TCP communication interface and a 7-inch touch screen human-machine interface.

[0050] The RS-485 interface and Modbus TCP communication interface are used to transmit operating parameters, status data, and fault data with the boiler distributed control system or upper-level monitoring equipment. The touch screen human-machine interface is used to display DC bus voltage, positive half-cycle voltage, negative half-cycle voltage, positive half-cycle current, negative half-cycle current, inverter frequency, phase shift angle, operating status, protection status, and historical fault information, and is used to input start commands and parameter settings.

[0051] like Figure 4 As shown, the control module divides the operating state of the AC arc into open-circuit waiting-to-ignite state, pulse ignition state, stable arc maintenance state, and asymmetric arc extinction precursor state based on the arc parameter data.

[0052] In the open-circuit waiting-to-ignite state, the control module outputs a 110kHz arc-ignition drive signal, which causes the resonant arc-ignition and arc-maintaining module to generate a high-voltage AC arc-ignition pulse, while continuously reading the voltage and current of the positive and negative half cycles of the AC arc.

[0053] In pulsed arc ignition mode, the control module determines whether the electrode gap of the plasma torch has been broken down based on the decrease in arc voltage, the generation of arc current, and the continuous occurrence of positive and negative half-cycle currents. When the bidirectional arc current stabilizes within the range of 12A to 45A and lasts for 300ms, the control module determines that ignition is successful and switches the operating state to stable arc maintenance mode.

[0054] In a stable arc-maintaining state, the control module adjusts the inverter frequency to 60kHz to 90kHz and adjusts the phase shift angle according to the target arc current and the actual arc current.

[0055] When the difference between the positive half-cycle current and the negative half-cycle current is greater than 3A, the control module corrects the phase shift angle, changes the output voltage of the high-frequency inverter module and the discharge energy of the positive and negative half-cycles of the AC arc, so that the positive and negative half-cycle currents tend to be balanced, thereby reducing the unbalanced loss of the two electrodes of the plasma torch.

[0056] When a sudden drop in arc current or a deviation in arc waveform is detected, the control module determines that there is an asymmetrical arc extinction precursor in the AC arc. Within 10μs after detecting this state, the inverter frequency is increased to change the resonant operating state of the resonant arc initiation and arc maintenance module and increase the output resonant voltage, so as to re-break down or maintain the conductive channel between the electrodes and realize the reconstruction of the AC arc.

[0057] After the AC arc is restored, the control module readjusts the inverter frequency and phase shift angle according to the positive and negative half-cycle electrical parameters, and returns to stable arc-maintaining control.

[0058] In an optional implementation, the control module also reads the boiler primary air temperature and pulverized coal volatiles, and matches the steady-state inverter frequency within the range of 60kHz to 90kHz. For pulverized coal operating conditions with lower volatiles or lower primary air temperature, an operating frequency that can improve the stability of the AC arc can be selected; when the coal type or boiler operating conditions change, the control module regenerates the inverter control parameters to adapt the same power supply to plasma torches of different power levels and different coal types.

[0059] The control module can also use a high-performance STM32 industrial microcontroller to replace the TMS320F280049C digital signal processor, as long as it can perform functions such as positive and negative half-cycle synchronous sampling, operating status identification, inverter frequency adjustment, phase angle adjustment, arc extinction precursor processing, and communication.

[0060] The multi-parameter protection cooling module is used to acquire DC bus overvoltage signals, high-frequency inverter module short-circuit signals, transformer magnetic saturation signals, arc positive and negative half-cycle asymmetry signals, plasma torch insulation status signals, cooling water temperature signals, air duct status signals, and cabinet condensation signals, and performs protection in a three-level hierarchical manner.

[0061] The first level is microsecond-level hardware latching protection. When DC bus overvoltage, high-frequency inverter module short circuit, or high-frequency step-up transformer magnetic saturation is detected, the hardware protection circuit latches the fault state and instantly cuts off the drive signal of the high-frequency inverter module to prevent silicon carbide switching devices, high-frequency step-up transformer, and DC bus devices from continuing to be subjected to abnormal voltage or current.

[0062] The second level is millisecond-level software predictive protection. The control module and the multi-parameter protection cooling module output early warning, power reduction, or shutdown signals based on the degree of asymmetry of the positive and negative half-cycles of the AC arc, the changing trend of the plasma torch insulation parameters, the cooling water temperature, the air duct pressure difference or air volume, and the condensation status of the cabinet.

[0063] Among them, the asymmetry of the positive and negative half-cycles of the AC arc is used to identify abnormal electrode conditions or arc bias; the gradient change of the insulation parameters of the plasma torch is used to identify insulation aging; and the overheating of cooling water, blockage of air ducts, and condensation of the cabinet are used to determine whether the heat dissipation and environmental conditions meet the conditions for continuous operation.

[0064] The third level is boiler interlock protection. The multi-parameter protection cooling module uploads fault signals to the boiler distributed control system, which then synchronously interlocks the coal mill, primary air fan, and plasma cooling water pump according to the fault level. If the ignition power supply cannot continue operating, the supply of pulverized coal and primary air is stopped or adjusted to reduce the risk of pulverized coal accumulation and deflagration.

[0065] In terms of heat dissipation structure, silicon carbide power devices are mounted on an embedded water-cooled substrate with a rated cooling water flow rate of 8L / min; the cabinet is equipped with upper and lower layered air ducts to thermally isolate the power area from the control area.

[0066] When using a combination of water cooling and air cooling, the overall cabinet dimensions can be 850mm×600mm×420mm, and the weight can be 245kg. For high-temperature enclosed boiler rooms, a fully water-cooled immersion cooling structure can also replace the water-cooling and air-cooling combined cooling structure.

[0067] Example 2: The control method for high-frequency AC plasma ignition power supply of pulverized coal boiler includes the following steps: Step S1: The control module reads the boiler operating status, primary air temperature, pulverized coal volatiles, plasma torch rated parameters, protection settings, and cooling status. After confirming that the cooling water circuit, cabinet air duct, plasma torch insulation, and boiler interlock conditions meet the startup requirements, three-phase AC power is connected.

[0068] Step S2 involves sequentially performing electromagnetic interference filtering, power factor correction, and rectification on the three-phase AC power, and then storing and smoothing the rectified DC power to obtain the DC bus voltage. The control module reads the DC bus voltage and confirms that it is within the allowable range.

[0069] In step S3, the control module generates inverter control parameters, including an inverter frequency of 110kHz and a corresponding phase shift angle, based on the arc ignition status, and generates a phase-shifted full-bridge drive signal based on the inverter frequency and phase shift angle. The high-frequency inverter module converts the DC bus voltage into high-frequency AC power based on the phase-shifted full-bridge drive signal.

[0070] In step S4, the resonant arc-initiating and arc-maintaining module boosts and resonates the high-frequency AC power to generate high-voltage AC arc-initiating power with a peak value of approximately 28kV, and outputs the high-voltage AC arc-initiating power to the plasma torch.

[0071] While outputting high-voltage AC arc-ignition power, the arc parameter acquisition module simultaneously acquires the positive half-cycle voltage, negative half-cycle voltage, positive half-cycle current, and negative half-cycle current, and generates arc parameter data based on the acquisition results.

[0072] In step S5, the control module determines whether the AC arc is conducting based on the arc parameter data. If no AC arc is detected, the arc is repeatedly ignited in a manner of 3 seconds per attempt, up to a maximum of 5 times. If no AC arc is detected after reaching the maximum number of ignition attempts, the high-frequency inverter output is stopped and an ignition failure signal is generated.

[0073] When the bidirectional arc current stabilizes within the range of 12A to 45A and lasts for 300ms, the control module determines that ignition is successful.

[0074] Step S6: After successful ignition, the control module adjusts the inverter frequency to 60kHz to 90kHz, so that the resonant arc ignition and arc maintenance module outputs high-frequency AC arc maintenance power through the same LC resonant branch as the arc ignition stage.

[0075] High-voltage DC blocking capacitors block the DC component in the high-frequency AC arc-generating power, enabling the plasma torch to output a bipolar alternating high-frequency AC arc.

[0076] In step S7, during the arc maintenance process, the control module continuously calculates the difference between the positive half-cycle current and the negative half-cycle current. When the difference exceeds 3A, the phase shift angle is adjusted to change the output voltage of the high-frequency inverter module and the discharge energy of the AC arc until the difference between the positive and negative half-cycle currents returns to the preset range.

[0077] The control module can also adjust the steady-state inverter frequency in the range of 60kHz to 90kHz according to the primary air temperature and volatile matter content of pulverized coal.

[0078] In step S8, the control module continuously monitors for sudden drops in arc current and arc waveform deviation. When an asymmetric arc extinction precursor is detected, the inverter frequency is increased within 10μs to enhance the resonant voltage output to the plasma torch and re-establish the AC arc.

[0079] After the AC arc is restored, the inverter frequency and phase shift angle are readjusted based on the updated positive and negative half-cycle electrical parameters.

[0080] Step S9: During the above process, the three-level hierarchical protection is continuously executed. When DC bus overvoltage, high-frequency inverter module short circuit, or high-frequency step-up transformer magnetic saturation occurs, the drive signal is latched and cut off; when arc asymmetry, insulation aging, water cooling overheating, air duct blockage, or cabinet condensation occurs, a warning, power reduction, or shutdown signal is output; when boiler-side interlocking is required, the fault signal is sent to the boiler distributed control system.

[0081] Example 3: This embodiment applies to a 120kW anthracite ignition host for a 600MW tangential pulverized coal boiler. The boiler burns anthracite with a volatile matter content of 14.2%, the installation site is at an altitude of 1100m and the ambient humidity is 82%, and no oil ignition system is configured.

[0082] The system adopts a three-phase 380V input, and the rectifier module outputs a 780V DC bus voltage; the high-frequency inverter module adopts a full silicon carbide phase-shifting full bridge; the arc ignition frequency is set to 110kHz, and the resonant arc ignition and arc maintenance module outputs a high-voltage AC arc ignition pulse with a peak value of about 28kV.

[0083] After successful ignition, set the steady-state inverter frequency to 75kHz, the working AC voltage to 2600V, and the symmetrical arc current to 22A.

[0084] After operation, the anthracite ignition success rate reached 99.7%, the average electrode life reached 4200 hours, the overall efficiency reached 98.8%, and the total harmonic distortion rate was 3.5%. This configuration can maintain a high-frequency AC arc under conditions of high altitude, high humidity, and low volatile coal powder.

[0085] Example 4: This embodiment is applied to a 50kW lean coal stable combustion device for a 300MW circulating fluidized bed boiler.

[0086] Compared to the 120kW configuration, the number of silicon carbide inverter power units in the high-frequency inverter module is halved, and the turns ratio of the high-frequency step-up transformer is reduced. The remaining rectifier topology, resonant arc-initiating and arc-maintaining topology, arc parameter acquisition method, and control logic remain unchanged.

[0087] The steady-state inverter frequency is set to 65kHz, the arc current is set to 15A, and the peak arc voltage is set to 25kV.

[0088] After operation, the boiler can remain unextinguished under 40% low load conditions, and the electrode life reaches 3900 hours.

[0089] Example 5: like Figure 5 As shown, this embodiment is applied to a 200kW modular parallel ignition device for a 1000MW supercritical pulverized coal boiler.

[0090] The system is equipped with two 120kW high-frequency inverter modules, which share a DC bus and are connected in parallel in a master-slave configuration for current sharing. The outputs of the two high-frequency inverter modules are connected to a common resonant arc-starting and arc-maintaining module after parallel coupling, and the common LC resonant output circuit supplies power to multiple plasma torch loads.

[0091] The control module sends collaborative drive parameters to both the master and slave high-frequency inverter modules, and adjusts the phase shift angle according to the output current of each module to achieve current sharing between the master and slave modules. The parallel current sharing error is no greater than 0.8A.

[0092] When one of the high-frequency inverter modules fails, the faulty module shuts down, while the other high-frequency inverter module continues to supply power to the common LC resonant output circuit at reduced power, thus achieving reduced-power operation without interrupting ignition. This configuration is compatible with synchronous ignition of four-layer burners.

[0093] The modular parallel configuration allows for the number of high-frequency inverter modules to be configured according to the load power within the range of 50kW to 200kW, and enables multiple high-frequency inverter modules to share a resonant output circuit to adapt to boilers of different capacities and multi-burner ignition scenarios.

[0094] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A high-frequency AC plasma ignition power supply system for a pulverized coal boiler, characterized in that, include: The rectifier module is used to receive three-phase AC power, rectify the three-phase AC power, and output DC bus voltage; The high-frequency inverter module is used to receive the DC bus voltage and the inverter control parameters output by the control module, and to perform inverter processing on the DC bus voltage according to the inverter control parameters to output high-frequency AC power. The resonant arc ignition and arc maintenance module is used to receive high-frequency AC power for resonant conversion. During the arc ignition stage, it outputs high-voltage AC arc ignition power to the plasma torch to form an AC arc, and during the arc maintenance stage, it outputs high-frequency AC arc maintenance power to the plasma torch to maintain the AC arc. The arc parameter acquisition module is used to acquire the positive and negative half-cycle electrical parameters of the AC arc and output arc parameter data based on the acquisition results. The control module receives arc parameter data, determines the operating state of the AC arc based on the positive and negative half-cycle electrical parameters, generates inverter control parameters including inverter frequency and phase shift angle based on the operating state, and outputs the inverter control parameters to the high-frequency inverter module to adjust the electrical energy output from the resonant arc ignition and arc maintenance module to the plasma torch.

2. The high-frequency AC plasma ignition power supply system for a pulverized coal boiler according to claim 1, characterized in that, The rectifier module includes: A three-phase common-mode electromagnetic interference filter array is used to filter three-phase alternating current. An active power factor correction unit is used to correct the current waveform of the filtered three-phase AC power. A three-phase rectifier bridge is used to rectify three-phase alternating current after the current waveform has been corrected. The bus energy storage capacitor bank is used to store and smooth the rectified DC power to form the DC bus voltage. A spike buffer circuit is used to suppress voltage spikes during the rectification process.

3. The high-frequency AC plasma ignition power supply system for a pulverized coal boiler according to claim 1, characterized in that, The high-frequency inverter module includes: The isolation drive unit is used to receive the drive signal generated by the control module according to the inverter frequency and phase shift angle, and control the silicon carbide switching devices in the phase-shifted full bridge to turn on or off according to the drive signal, so that the phase-shifted full bridge converts the DC bus voltage into high-frequency AC. Soft-switching resonant inductors are used in conjunction with phase-shifted full-bridge circuits to achieve zero-voltage turn-on and zero-current turn-off of silicon carbide switching devices.

4. The high-frequency AC plasma ignition power supply system for a pulverized coal boiler according to claim 1, characterized in that, The resonant arc-starting and arc-maintaining module includes: A high-frequency step-up transformer is used to receive high-frequency alternating current and step it up. The LC resonant branch is used to resonate and boost the high-frequency AC power after the arc ignition stage, so that the pulse energy storage capacitor outputs high-voltage AC arc ignition power through the discharger. It is also used to output high-frequency AC arc maintenance power through the same LC resonant branch during the arc maintenance stage. High-voltage DC blocking capacitors are used to block the DC component in the output power, causing the AC arc to form a bipolar alternating discharge.

5. A high-frequency AC plasma ignition power supply system for a pulverized coal boiler according to claim 1, characterized in that, The arc parameter acquisition module is used to synchronously acquire the positive half-cycle current, negative half-cycle current, positive half-cycle voltage, and negative half-cycle voltage of the AC arc, and send the acquisition results to the control module. The control module is used to determine the operating status of the AC arc based on the acquisition results as open circuit waiting to be ignited, pulse ignition, stable arc maintenance, or asymmetric arc extinction precursor state. When the bidirectional arc current stabilizes within the preset range, the control module determines that the AC arc is in a stable arc-maintaining state; When the difference between the positive half-cycle current and the negative half-cycle current exceeds the preset range, the control module adjusts the phase shift angle to reduce the difference between the positive half-cycle current and the negative half-cycle current. When a sudden drop in arc current or a deviation in arc waveform is detected, the control module adjusts the inverter frequency to increase the resonant voltage output by the resonant arc initiation and maintenance module.

6. The high-frequency AC plasma ignition power supply system for a pulverized coal boiler according to claim 1, characterized in that, It also includes a multi-parameter protection cooling module, used to acquire DC bus overvoltage signals, high-frequency inverter module short-circuit signals, transformer magnetic saturation signals, arc positive and negative half-cycle asymmetry signals, plasma torch insulation status signals, cooling water temperature signals, air duct status signals, and cabinet condensation signals; When a DC bus overvoltage signal, a high-frequency inverter module short-circuit signal, or a transformer magnetic saturation signal is received, the drive signal of the high-frequency inverter module is latched and cut off. When receiving signals of arc asymmetry in positive and negative half-cycles, plasma torch insulation status, cooling water temperature, air duct status, or cabinet condensation, output a warning or shutdown signal. It is also used to send fault signals to the boiler distributed control system, so that the boiler distributed control system can interlock the coal mill, primary air fan and plasma cooling water pump according to the fault signals.

7. A method for controlling a high-frequency AC plasma ignition power supply for a pulverized coal boiler, characterized in that, Includes the following steps: It receives three-phase AC power, rectifies the three-phase AC power, and obtains DC bus voltage; The inverter control parameters, including the inverter frequency and phase shift angle, are obtained. The DC bus voltage is then inverted based on the inverter control parameters to obtain high-frequency AC power. During the arc ignition stage, the high-frequency AC current is resonantly transformed to obtain high-voltage AC arc ignition energy, which is then output to the plasma torch to form an AC arc. During the arc maintenance stage, the high-frequency AC current is resonantly transformed to obtain high-frequency AC arc maintenance energy, which is then output to the plasma torch to maintain the AC arc. Collect the positive and negative half-cycle electrical parameters of the AC arc, and generate arc parameter data based on the collection results; The operating status of the AC arc is determined based on the arc parameter data. The inverter frequency and phase shift angle are updated based on the operating status. The DC bus voltage is then inverted based on the updated inverter frequency and phase shift angle to regulate the electrical energy output to the plasma torch.

8. The method for controlling a high-frequency AC plasma ignition power supply for a pulverized coal boiler according to claim 7, characterized in that, The specific method for receiving three-phase alternating current, rectifying it, and obtaining the DC bus voltage is as follows: The three-phase AC power is sequentially subjected to electromagnetic interference filtering, power factor correction, and rectification. The rectified DC power is then subjected to energy storage and smoothing to obtain the DC bus voltage.

9. The method for controlling a high-frequency AC plasma ignition power supply for a pulverized coal boiler according to claim 7, characterized in that, The specific method for obtaining high-frequency AC power by acquiring inverter control parameters, including inverter frequency and phase shift angle, and then inverting the DC bus voltage according to these parameters is as follows: The phase-shifted full-bridge drive signal is generated based on the inverter frequency and phase shift angle. The phase-shifted full-bridge drive signal is used to control the silicon carbide switching device to perform inverter processing on the DC bus voltage, so as to obtain high-frequency AC power with a frequency of 50kHz to 120kHz.

10. A method for controlling a high-frequency AC plasma ignition power supply for a pulverized coal boiler according to claim 7, characterized in that, The specific method for determining the operating status of the AC arc based on the arc parameter data, and updating the inverter frequency and phase shift angle based on the operating status, is as follows: Based on the positive and negative half-cycle electrical parameters, the operating state of the AC arc is determined as open-circuit waiting-to-ignite state, pulse ignition state, stable arc maintenance state, or asymmetric arc extinction precursor state. When the bidirectional arc current stabilizes within a preset range, the AC arc is determined to be in a stable arc-maintaining state. When the difference between the positive half-cycle current and the negative half-cycle current is greater than the preset range, the phase shift angle is adjusted to balance the discharge energy of the positive and negative half-cycles of the AC arc. When a sudden drop in arc current or a deviation in arc waveform is detected, it is determined that the AC arc is in an asymmetrical arc extinction precursor state. After detecting the asymmetrical arc extinction precursor state, the inverter frequency is increased, the resonant voltage output to the plasma torch is increased, and the AC arc is re-established.

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