Plasma intelligent ignition control cabinet

Abstract

The application relates to the field of food technology, in particular to a plasma intelligent ignition control cabinet, which comprises at least one AC / DC rectifying module for converting alternating current into high-voltage direct current, the AC / DC rectifying module comprises an active power factor correction circuit and a resonant isolation type DC / DC conversion circuit connected in sequence, the active power factor correction circuit is used for performing power factor correction on input alternating current and generating intermediate direct current, and the resonant isolation type DC / DC conversion circuit is used for converting the intermediate direct current into stable high-voltage direct current; by adopting a two-stage high-frequency conversion architecture of 'active power factor correction + resonant isolation type DC / DC conversion', the traditional power frequency phase control rectification is replaced, and the output direct current ripple is fundamentally reduced. In particular, the application of the resonant conversion circuit realizes soft switching of a power switch tube, and greatly reduces switching noise and output ripple.

Description

Technical Field

[0001] This invention relates to the field of food technology, and more specifically, to a plasma intelligent ignition control cabinet. Background Technology

[0002] In the operation of coal-fired boilers in power plants, the start-up and low-load stable combustion processes traditionally rely on fuel oil (such as diesel or heavy oil) burners. This not only consumes a large amount of fuel oil resources and increases operating costs, but also involves a series of issues such as fuel oil procurement, transportation, and storage. Therefore, the technology of directly igniting pulverized coal with plasma, namely plasma oil-free ignition technology, has become an important energy-saving and consumption-reducing development direction in the industry.

[0003] The basic principle of plasma ignition is that a high-temperature DC arc plasma jet is generated by a plasma generator and sent into the boiler burner, causing the pulverized coal gas flow carried by the primary air to be rapidly heated, cracked, and ignited in a very short time. To achieve this process, a stable, controllable, and sufficiently powerful DC power supply must be provided to the plasma generator. The arc characteristics inside the generator are extremely sensitive to the power quality of the power supply; any large current ripple, voltage fluctuation, or response lag can cause arc instability, flickering, or even extinction (i.e., "arc interruption"), leading to ignition failure.

[0004] Early plasma ignition systems mostly used thyristor-based power frequency phase-controlled rectifiers. This approach controls the output voltage and current by adjusting the thyristor's firing angle. However, this technology has inherent drawbacks: its output DC power contains a large number of low-order harmonics, resulting in a high ripple factor and unstable plasma arc combustion; it has a low power factor, causing harmonic pollution and reactive power surges to the plant power grid; the equipment is bulky and heavy, and its dynamic response is slow, making it impossible to accurately and promptly adjust the arc energy according to rapid changes in coal quality and operating conditions. Furthermore, some solutions lack effective electrical isolation and robust protection mechanisms. If a short circuit or arcing fault occurs on the generator side, it can easily backfire to the power grid, affecting the plant's overall power supply safety and even causing equipment damage. These problems collectively limit the adaptability of plasma ignition technology to complex coal types (such as lean coal and anthracite) and its long-term operational reliability. Summary of the Invention

[0005] The purpose of this invention is to provide a plasma intelligent ignition control cabinet to solve the technical problems mentioned in the background art.

[0006] This invention provides a plasma intelligent ignition control cabinet, comprising:

[0007] At least one AC / DC rectifier module is used to convert alternating current into high-voltage direct current. The AC / DC rectifier module includes an active power factor correction circuit and a resonant isolated DC / DC converter circuit connected in sequence. The active power factor correction circuit is used to correct the power factor of the input AC power and generate intermediate DC power. The resonant isolated DC / DC converter circuit is used to convert the intermediate DC power into stable high-voltage direct current.

[0008] At least one DC / DC step-down module, the input of which is connected in parallel with the output of the AC / DC rectifier module, is used to step down the high voltage DC power and convert it into low voltage high current DC power suitable for driving the plasma generator.

[0009] The control unit is communicatively connected to the AC / DC rectifier module and the DC / DC buck module, respectively, and is used to coordinate and control the operating status of each module according to the preset plasma ignition process parameters.

[0010] As a preferred embodiment of the present invention, the resonant isolated DC / DC converter circuit is an LLC resonant full-bridge converter circuit.

[0011] As a preferred embodiment of the present invention, the AC / DC rectifier module further includes a digital signal processor, which is used to execute a voltage and current dual closed-loop control algorithm to control the switching frequency and duty cycle of the active power factor correction circuit and the resonant isolated DC / DC converter circuit.

[0012] As a preferred embodiment of the present invention, the DC / DC step-down module includes two step-down chopper circuits connected in parallel at the input and output terminals. The topologies of the two step-down chopper circuits are completely symmetrical and are used to share the total current output to the plasma generator.

[0013] As a preferred embodiment of the present invention, the phase difference between the switching transistor drive signals of the two buck chopper circuits is 180 degrees.

[0014] As a preferred embodiment of the present invention, the DC / DC buck module further includes a current sensor for sampling the output current of the two buck chopper circuits respectively, and a control circuit electrically connected to the current sensor. The control circuit is configured to dynamically adjust the duty cycle of the two buck chopper circuits based on the sampled current value so as to balance the output current of the two circuits.

[0015] As a preferred embodiment of the present invention, the AC / DC rectifier modules are included in a plurality of parallel AC / DC rectifier modules. The control unit is configured to adjust the output voltage reference of each AC / DC rectifier module based on the average total output current of the plurality of AC / DC rectifier modules and the real-time output current of each AC / DC rectifier module, so as to achieve output current sharing among the plurality of AC / DC rectifier modules.

[0016] As a preferred embodiment of the present invention, the plurality of AC / DC rectifier modules connected in parallel are configured to support an N+1 redundancy mode with hot-swappable capability.

[0017] As a preferred embodiment of the present invention, it further includes an isolation transformer, the secondary side of which is connected to the input terminal of the AC / DC rectifier module, and the primary side of which is used to connect to a three-phase AC power grid.

[0018] As a preferred embodiment of the present invention, the control unit communicates with the AC / DC rectifier module and the DC / DC buck module via a CAN bus or an industrial Ethernet.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0020] This application employs a two-stage high-frequency converter architecture with active power factor correction and resonant isolated DC / DC conversion, replacing the traditional power frequency phase-controlled rectification, fundamentally reducing the ripple of the output DC power. In particular, the application of the resonant converter circuit enables soft switching of the power transistors, significantly reducing switching noise and output ripple. This results in extremely pure and stable electrical energy obtained by the plasma generator, effectively avoiding arc interruption caused by power fluctuations and significantly improving the ignition success rate.

[0021] This application utilizes a fully digital control unit and modular design to achieve high-precision, high-dynamic-response closed-loop control of the power supply's output voltage and current. Whether responding to fluctuations in grid voltage or power adjustment commands from the upper-level control system due to changes in coal quality and air volume, this system can quickly and accurately adjust the output, ensuring precise matching between the plasma arc's energy state and real-time operating conditions, thereby broadening its adaptability to different coal types. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the overall invention. Detailed Implementation

[0023] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0024] This application provides a plasma intelligent ignition control cabinet, which integrates multiple functional units such as power conversion, control, and protection into a highly integrated unit. The input end of the control cabinet is connected to the three-phase AC 380V / 480V power grid of the power plant through an isolation transformer, and the output end is directly connected to the anode and cathode of the plasma generator.

[0025] Inside the control cabinet, there are three main types of core components: one or more AC / DC rectifier modules, one or more DC / DC step-down modules, and a control unit. The inputs of multiple AC / DC rectifier modules are connected in parallel on the AC side, and their outputs are connected in parallel on the DC side, forming a high-voltage DC bus. The input of the DC / DC step-down module is connected to this high-voltage DC bus, and its output serves as the output for the entire control cabinet, supplying power to the load. The control unit establishes a communication connection with each AC / DC rectifier module and DC / DC step-down module via a communication bus (such as a CAN bus or the Profinet protocol based on industrial Ethernet) for command issuance, status monitoring, and fault diagnosis.

[0026] The core function of the AC / DC rectifier module is to convert unstable input AC power into stable, low-ripple high-voltage DC power. To this end, this module employs a two-stage high-frequency conversion topology.

[0027] The first stage is an active power factor correction (PFC) circuit, preferably a three-phase Vienna structure or a three-phase six-switch PWM rectifier structure. This circuit controls the switching of the power switches through a digital signal processor (DSP), forcing the input current waveform to track the input voltage waveform, thereby achieving a power factor close to 1 and extremely low input current harmonic distortion. Simultaneously, the PFC stage generates a stable intermediate DC bus voltage at the output, for example, 800V.

[0028] The second stage is a resonant isolated DC / DC converter circuit, preferably an LLC resonant full-bridge converter circuit. This circuit receives the intermediate DC voltage provided by the PFC stage and converts it into high-frequency square wave AC through an H-bridge inverter circuit composed of four switching transistors. This high-frequency AC is applied to an LLC resonant network composed of a resonant inductor, resonant capacitor, and transformer magnetizing inductance. Then, it undergoes voltage transformation and isolation through a high-frequency transformer, and finally passes through an output rectifier and filter circuit to obtain the required high-voltage DC. Because the LLC circuit operates in a resonant state, its switching transistors can be turned on or off under zero voltage or zero current conditions, greatly reducing switching losses and electromagnetic interference. This is key to achieving high efficiency and low output ripple in the module. The DSP within the module is responsible for executing complex control algorithms, sampling the output voltage and current in real time, and precisely adjusting the switching frequency and duty cycle of the PFC and LLC stages through dual closed-loop control of the voltage outer loop and current inner loop, ensuring the accuracy and fast response of the output voltage / current.

[0029] The AC / DC rectifier module in this embodiment differs fundamentally from existing technologies in terms of topology, control method, and system architecture. Existing technologies commonly employ thyristor-based power frequency phase-controlled rectification schemes. This scheme relies on large power frequency transformers and thyristor phase-shift triggering, with output voltage regulation achieved by changing the thyristor conduction angle. This results in significant 6-pulse or 12-pulse low-order harmonics in the output DC, with a ripple factor typically exceeding 5% and a power factor below 0.7, injecting substantial harmonics and reactive power into the power grid. Another diode-based uncontrolled rectifier scheme, while simple in structure, completely lacks output voltage regulation capabilities and cannot meet the precise power parameter control requirements of plasma generators under different operating conditions.

[0030] The AC / DC rectifier module proposed in this application makes the following key improvements: First, the topology is innovated, abandoning the power frequency phase-controlled rectification and adopting a two-stage high-frequency conversion architecture of active power factor correction plus resonant isolated DC / DC conversion. The front-stage PFC circuit actively shapes the input current waveform through high-frequency switching devices and DSP control, thereby improving the power factor to above 0.99 and reducing the total harmonic distortion of the input current to below 5%, significantly reducing pollution to the power grid. The rear-stage LLC resonant converter circuit increases the switching frequency to tens of kilohertz, using the resonance principle to achieve zero-voltage or zero-current switching of the switching devices, effectively reducing switching losses and switching noise. Second, the control method is upgraded, replacing traditional analog or simple digital control with all-digital DSP control. By executing a voltage and current dual closed-loop algorithm and high-precision pulse width modulation, the output voltage / current accuracy is better than ±0.5%, the peak ripple coefficient does not exceed ±0.5%, and the dynamic response time enters the millisecond level. Third, the modular and redundant design breaks down the traditional centralized high-power power cabinet into multiple standardized, hot-swappable 20kW power modules. Each module independently completes the full function, supports N+1 redundant parallel connection and online maintenance, and significantly improves the availability and maintainability of the system.

[0031] After implementing the above improvements, this AC / DC rectifier module has achieved significant technical results in plasma ignition applications: First, the low-ripple, high-stability DC output provides a clean energy source for the plasma arc, reducing the probability of arc interruption caused by power supply disturbances to below 0.1% and increasing the ignition success rate to over 99.5%; Second, the conversion efficiency has increased from less than 85% in traditional solutions to no less than 95%, reducing operating losses and heat dissipation requirements at the same output power; Third, the modular architecture reduces the system size by approximately 60% compared to earlier power frequency transformer solutions, lowering the installation space requirement to within 1.5m × 0.8m × 2.0m; Fourth, it can maintain full-load output within a wide input voltage range of 320Vac to 490Vac, adapting to the voltage fluctuation environment of power plant grids, and has an ambient temperature adaptability range of -40℃ to 55℃ (full power) and 55℃ to 75℃ (derating operation), meeting the requirements of harsh industrial sites.

[0032] To meet the system's high power requirements, this control cabinet uses multiple AC / DC rectifier modules in parallel. To address the issue of uneven current distribution when multiple modules are connected in parallel, each module's DSP broadcasts its own output current information via the CAN bus. Each module's DSP calculates the average current of all parallel modules and compares it with its own real-time output current. A built-in current sharing control loop then fine-tunes the output voltage setpoint of the module, thereby ensuring that the output current of all modules is consistent.

[0033] The DC / DC step-down module is located between the AC / DC rectifier module and the plasma generator load. Its function is to step down the high-voltage DC bus voltage and convert it into the low-voltage, high-current DC power required by the plasma generator, and to perform precise closed-loop control of the generator's operating current.

[0034] To address the challenges of high stress requirements and reliability issues associated with single-channel high-current chopper circuits, this embodiment employs a symmetrical dual-channel parallel buck chopper architecture. Specifically, the module contains two identical buck chopper circuits (left and right). The inputs of the two circuits are connected in parallel to the high-voltage DC bus of the preceding stage; their outputs are also connected in parallel, jointly supplying current to the load. Each circuit includes at least one power switch, a freewheeling diode, an output filter inductor, and a current sensor. By distributing the total output current across the two circuits, each circuit only bears half the current stress; for example, with a total output of 200A, each circuit outputs 100A. This significantly reduces the selection requirements for individual power devices, disperses heat sources, and improves the module's power density and long-term operational reliability.

[0035] Compared with existing single-channel high-current buck chopper solutions, the DC / DC buck module in this embodiment has made substantial improvements in both circuit architecture and control strategy. Existing technologies typically use a single IGBT or MOSFET chopper circuit to handle the entire load current, requiring a single switching device and freewheeling diode to continuously withstand current stresses up to hundreds of amperes. This leads to difficulties in device selection, concentrated heat dissipation pressure on the package, and the failure of the entire buck stage if the single power path fails. Furthermore, traditional hard-switching chopper methods have a large overlap area between voltage and current waveforms during switching, and switching losses increase sharply with increasing frequency and current, limiting further increases in power density and causing serious electromagnetic interference problems.

[0036] This application addresses the aforementioned issues with the following improvements: First, it adopts a symmetrical, dual-path parallel buck chopper architecture, decomposing the high-current load into two structurally identical but independently operating power branches. Each branch only needs to carry half of the total current, thereby halving the current stress on power devices such as IGBTs, freewheeling diodes, and output inductors, lowering the device selection threshold and cost. Simultaneously, it disperses the heat source to two physically separate heat dissipation areas, improving thermal management conditions. Second, it configures independent current closed-loop control loops and current sensors for the left and right paths. The control circuit compares the output currents of the two paths in real time and achieves active current sharing by dynamically fine-tuning their respective duty cycles. The current sharing error can be controlled within ±3%, effectively preventing current distribution imbalance caused by differences in device parameters or parasitic parameter asymmetry. Third, as a preferred control method, this module can further employ interleaved parallel control technology, that is, the phases of the PWM signals driving the two IGBTs are staggered by 180 degrees. The two current ripples cancel each other out on the output bus, which greatly reduces the amplitude of the total current ripple in the final output and doubles the ripple frequency. With the same output filter capacitor configuration, a smoother DC output can be obtained, while reducing the requirements for the capacity and size of the input filter capacitor.

[0037] The aforementioned improvements bring clear benefits to the plasma ignition system: First, through power shunting and independent current sharing control, the reliability of the DC / DC buck module under continuous high current output conditions exceeding 100A is significantly improved. Thermal stress in power devices is balanced, local hot spots are reduced, and the module's expected mean time between failures (MTBF) is correspondingly extended. Second, the application of interleaved parallel technology further reduces the ripple content of the plasma generator's input current. Combined with the low ripple characteristics of the front-end AC / DC module, this reduces the fluctuation of electrical parameters acting on both ends of the arc to an extremely low level, playing a decisive role in maintaining stable arc combustion and reducing arc interruption. Third, because the current in each power branch is relatively small, the bandwidth of the control loop can be designed to be higher. The module responds faster to load changes (such as arc length or impedance changes), completing current adjustment within microseconds, effectively suppressing the risk of damage to the anode and cathode from current surges during the "arc pulling" process.

[0038] To achieve precise current balance between the two current streams, the control circuit within the module, composed of a dedicated analog chip or a small DSP, receives sampling signals from the left and right current sensors respectively. The control circuit uses half of the preset total current command value as the current setpoint for each stream and performs independent current closed-loop control for each stream. By comparing the sampled values ​​of the two current streams in real time, the control circuit dynamically and independently fine-tunes the duty cycle of the PWM drive signals applied to the gates of the two IGBTs, ensuring a high degree of consistency between the two output currents under any dynamic and steady-state conditions.

[0039] In a more preferred implementation, the control circuit can also set the phase of the PWM signals driving the two IGBTs to be 180 degrees out of phase, i.e., employing interleaved parallel technology. In this mode, when one IGBT is on, the other is off. This interleaved operating mode causes the ripple of the two inductor currents to partially cancel each other out on the output bus, significantly reducing the total current ripple delivered to the plasma generator while doubling the ripple frequency, further improving the smoothness of the output current. This is extremely beneficial for maintaining stable plasma arc combustion. Simultaneously, the interleaved parallel connection also reduces the capacitance requirements of the input and output filter capacitors, which helps to reduce the module size.

[0040] The control unit, acting as the brain of the entire control cabinet, is typically a programmable logic controller (PLC) or an industrial computer. It collects operating parameters (such as input voltage, output current, temperature, and fault codes) from all AC / DC and DC / DC modules via a communication bus, and sends unified start / stop, voltage / current setpoint, and other control commands to each module based on instructions received from the power plant's distributed control system (DCS) (such as target power and arc ignition / termination signals) or preset ignition process curves. This centralized management and distributed control architecture ensures clear system logic and strong coordination.

[0041] To ensure high system reliability, this control cabinet employs multiple redundancy and protection designs. Multiple AC / DC rectifier modules constitute an N+1 redundant power supply system. This means that when a module fails, the control unit immediately identifies the fault and automatically shuts it down. Simultaneously, the current sharing reference of the remaining modules is adjusted, allowing them to continue providing full power. The entire switching process is seamless and does not interrupt the plasma arc. Faulty modules support hot-swapping, allowing maintenance personnel to replace them without system power outages. In terms of safety protection, in addition to the overvoltage, overcurrent, and overtemperature protection functions inherent in each module, an isolation transformer added to the cabinet input provides double electrical isolation between the power grid and the load circuit, preventing load-side faults from backflushing the power grid. The entire control cabinet uses an IP54 protection-rated enclosure and features a rationally designed forced-air cooling system to adapt to the harsh operating environment of power plants.

[0042] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely preferred examples and are not intended to limit the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A plasma intelligent ignition control cabinet, characterized in that, include: At least one AC / DC rectifier module is used to convert alternating current into high-voltage direct current. The AC / DC rectifier module includes an active power factor correction circuit and a resonant isolated DC / DC converter circuit connected in sequence. The active power factor correction circuit is used to correct the power factor of the input AC power and generate intermediate DC power. The resonant isolated DC / DC converter circuit is used to convert the intermediate DC power into stable high-voltage direct current. At least one DC / DC step-down module, the input of which is connected in parallel with the output of the AC / DC rectifier module, is used to step down the high voltage DC power and convert it into low voltage high current DC power suitable for driving the plasma generator. The control unit is communicatively connected to the AC / DC rectifier module and the DC / DC buck module, respectively, and is used to coordinate and control the operating status of each module according to the preset plasma ignition process parameters.

2. The plasma intelligent ignition control cabinet according to claim 1, characterized in that, The resonant isolated DC / DC converter circuit is an LLC resonant full-bridge converter circuit.

3. The plasma intelligent ignition control cabinet according to claim 1, characterized in that, The AC / DC rectifier module further includes a digital signal processor, which is used to execute a voltage and current dual closed-loop control algorithm to control the switching frequency and duty cycle of the active power factor correction circuit and the resonant isolated DC / DC converter circuit.

4. The plasma intelligent ignition control cabinet according to claim 1, characterized in that, The DC / DC step-down module includes two step-down chopper circuits connected in parallel at the input and output. The topologies of the two step-down chopper circuits are completely symmetrical and are used to share the total current output to the plasma generator.

5. The plasma intelligent ignition control cabinet according to claim 4, characterized in that, The phase difference between the switching transistor drive signals of the two buck chopper circuits is 180 degrees.

6. The plasma intelligent ignition control cabinet according to claim 1, characterized in that, The DC / DC buck module also includes current sensors for sampling the output current of the two buck chopper circuits respectively, and a control circuit electrically connected to the current sensors. The control circuit is configured to dynamically adjust the duty cycle of the two buck chopper circuits based on the sampled current value so as to balance the output current of the two circuits.

7. The plasma intelligent ignition control cabinet according to claim 1, characterized in that, The control unit is configured to adjust the output voltage reference of each AC / DC rectifier module based on the average total output current of the multiple AC / DC rectifier modules and the real-time output current of each AC / DC rectifier module, so as to achieve output current sharing among the multiple AC / DC rectifier modules.

8. The plasma intelligent ignition control cabinet according to claim 7, characterized in that, The multiple AC / DC rectifier modules connected in parallel are configured in an N+1 redundancy mode that supports hot-swapping.

9. The plasma intelligent ignition control cabinet according to claim 1, characterized in that, It also includes an isolation transformer, the secondary side of which is connected to the input terminal of the AC / DC rectifier module, and the primary side of which is used to connect to a three-phase AC power grid.

10. The plasma intelligent ignition control cabinet according to claim 1, characterized in that, The control unit communicates with the AC / DC rectifier module and the DC / DC buck module via a CAN bus or industrial Ethernet.

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