A method and system for hierarchical control of a neutral beam high voltage power supply

Abstract

This invention relates to the field of power supply control, specifically to a hierarchical control method and system for a neutral-beam ultra-high voltage power supply. For each power conversion unit, the target value of the DC bus voltage of the phase-controlled rectifier is determined based on a comparison between the output voltage reference value and a preset voltage threshold. If the actual bus voltage deviates from the target value, the output of the phase-controlled rectifier is adjusted until the target is met. After each bus voltage reaches the target, the initial duty cycle of the three-level inverter is calculated based on the output voltage reference value and the actual bus voltage, and the inverter output is controlled to obtain the actual output voltage. If the actual output voltage deviates from the reference value, the inverter duty cycle is adjusted step-by-step from the series start stage to the end stage until the output voltage of each stage meets the requirements. This method ensures that the bus voltages of each stage do not interfere with each other, eliminating the phenomenon in traditional schemes where adjusting the voltage of one stage causes fluctuations in other stages through bus coupling.

Description

Technical Field

[0001] This invention relates to the field of power supply control, and specifically to a method and system for hierarchical control of a neutral-beam ultra-high voltage power supply. Background Technology

[0002] In the field of nuclear fusion energy research, the neutral beam injection system is one of the key devices for achieving nuclear fusion plasma heating and current driving. The neutral beam negative ion source, as the core component of the neutral beam injection system, directly determines the energy, intensity, and stability of the neutral beam through its acceleration performance. To ensure that the neutral beam negative ion source can generate a high-energy negative ion beam that meets the requirements of a nuclear fusion device, five independent accelerating electrodes are needed to accelerate the negative ions. This requires each accelerating electrode to be equipped with a corresponding ultra-high voltage power supply, and the power supply voltage of each electrode must be independently and precisely adjustable according to the experimental conditions.

[0003] Currently, the power supply for the accelerating electrodes of neutral beam negative ion sources mostly adopts a traditional centralized power control scheme, that is, a single control system uniformly regulates the DC bus voltage of all accelerating electrodes. However, this control method has certain drawbacks: due to the coupling effect of the power supply circuits of the five accelerating electrodes, a single control system cannot achieve independent and precise adjustment of the voltage of each electrode. When the voltage of one electrode needs to be adjusted, it is very easy to interfere with the power supply stability of other electrodes, resulting in energy fluctuations in the neutral beam. Summary of the Invention

[0004] The purpose of this invention is to provide a hierarchical control method and system for neutral beam ultra-high voltage power supplies, which solves the problems in the prior art.

[0005] This invention is achieved through the following technical solution:

[0006] In a first aspect, embodiments of the present invention provide a hierarchical control method for a neutral-beam ultra-high voltage power supply, wherein the neutral-beam ultra-high voltage power supply includes multi-stage power conversion units connected in series, each stage of the power conversion unit including a phase-controlled rectifier and a three-level inverter connected in sequence, and the method includes:

[0007] For each power conversion unit, the target value of the DC bus voltage of the DC bus of the phase-controlled rectifier in the power conversion unit is determined based on the comparison result between the output voltage reference value of the power conversion unit and the preset voltage threshold.

[0008] If the deviation between the actual bus voltage and the target value of the DC bus voltage does not meet the DC bus voltage requirement, the output of the phase-controlled rectifier is adjusted until the actual bus voltage meets the DC bus voltage requirement.

[0009] Once the actual bus voltage of each stage reaches the target value of the DC bus voltage, for each stage of the power conversion unit, the initial duty cycle of the three-level inverter in the power conversion unit is calculated based on the output voltage reference value and the adjusted actual bus voltage.

[0010] The output AC voltage of the three-level inverter is controlled according to the initial duty cycle to obtain the actual output voltage of the power conversion unit.

[0011] If the deviation between the actual output voltage and the output voltage reference value does not meet the output voltage requirement, the duty cycle of the three-level inverter in each stage is adjusted sequentially from the starting stage to the ending stage in the series connection until the actual output voltage of each stage meets the output voltage requirement.

[0012] Preferably, determining the target DC bus voltage of the DC bus of the phase-controlled rectifier in the power conversion unit based on the comparison result between the output voltage reference value of the power conversion unit and the preset voltage threshold includes:

[0013] The comparison result is obtained by comparing the output voltage reference value with the preset voltage threshold, wherein the preset voltage threshold is obtained based on the single-stage rated output voltage;

[0014] If the comparison result shows that the output voltage reference value exceeds the preset voltage threshold, then the DC bus voltage target value is set to the preset maximum value.

[0015] If the comparison result shows that the output voltage reference value does not exceed the preset voltage threshold, then the target value of the DC bus voltage is calculated according to the preset formula.

[0016] Preferably, adjusting the output of the phase-controlled rectifier until the actual bus voltage meets the DC bus voltage requirement includes:

[0017] The direction of the deviation is obtained based on the deviation between the actual bus voltage and the target value of the DC bus voltage;

[0018] If the deviation direction is that the actual bus voltage is lower than the target value of the DC bus voltage, then reduce the firing angle of the thyristors in the phase-controlled rectifier to obtain an increased actual bus voltage;

[0019] If the deviation direction is that the actual bus voltage is higher than the target value of the DC bus voltage, then increase the firing angle of the thyristors in the phase-controlled rectifier to obtain a reduced actual bus voltage;

[0020] Repeatedly adjust the output of the phase-controlled rectifier until the deviation between the actual bus voltage and the target value of the DC bus voltage does not exceed the preset bus voltage deviation threshold.

[0021] Preferably, the three-level inverter is a neutral-point clamped three-level inverter, comprising four power switching transistors and two clamping diodes; the step of controlling the output AC voltage of the three-level inverter according to the initial duty cycle to obtain the actual output voltage of the power conversion unit includes:

[0022] Based on the initial duty cycle and the DC bus voltage, a timing combination of three output states—positive level, zero level, and negative level—is obtained.

[0023] The output AC voltage is obtained by controlling the on and off of the four power switching transistors according to the timing combination.

[0024] Preferably, when the deviation between the actual output voltage of a certain power conversion unit and the output voltage reference value is detected to exceed a preset fault threshold, the method further includes:

[0025] Based on the deviation exceeding the preset fault threshold, the corresponding level is marked as an abnormal level;

[0026] Based on the position of the abnormal stage in the series connection, while keeping the electrical connection state between the abnormal stage and other normal stages unchanged, the actual output voltage after compensation is obtained by gradually fine-tuning the duty cycle of the three-level inverter of the abnormal stage.

[0027] Based on the update deviation between the compensated actual output voltage and the output voltage reference value, determine whether the update deviation has been reduced to within the preset fault threshold.

[0028] If the update deviation is not reduced to within the preset fault threshold after a preset number of fine adjustments, the bypass switch is controlled according to the position of the abnormal level to remove the abnormal level from the series connection, and the remaining normal level sequence is obtained.

[0029] Based on the difference between the total output voltage reference value and the sum of the actual output voltages of the remaining normal stages, the output voltage reference value allocation scheme for each remaining normal stage is recalculated to obtain the updated output voltage reference values ​​for each stage.

[0030] Secondly, embodiments of the present invention provide a neutral beam ultra-high voltage power supply system, comprising:

[0031] Power grid supply end;

[0032] At least one phase-shifting transformer, the input terminal of which is electrically connected to the power grid supply terminal;

[0033] The series-connected multi-stage power conversion unit includes a phase-controlled rectifier and a three-level inverter connected in sequence. The input terminal of the phase-controlled rectifier is electrically connected to the output terminal of the phase-shifting transformer. The output terminal of the three-level inverter of each stage of the power conversion unit serves as the high-voltage DC output terminal of each stage, and the high-voltage DC output terminals of each stage are connected in series to form the total high-voltage DC output terminal of the system.

[0034] The control system is electrically connected to each stage of the phase-controlled rectifier and each stage of the three-level inverter. The control system determines the target DC bus voltage of the phase-controlled rectifier in each stage based on a comparison between the output voltage reference value and a preset voltage threshold. It adjusts the output of the phase-controlled rectifier according to the deviation between the actual bus voltage and the target DC bus voltage until the actual bus voltage reaches the target DC bus voltage. After the actual bus voltage of each stage reaches the target DC bus voltage, it calculates the initial duty cycle of the three-level inverter in each stage based on the output voltage reference value and the adjusted actual bus voltage. It controls the output AC voltage of the three-level inverter according to the initial duty cycle to obtain the actual output voltage of each stage. When the deviation between the actual output voltage and the output voltage reference value does not meet the output voltage requirement, it adjusts the duty cycle of the three-level inverter in each stage sequentially from the starting stage to the ending stage in the series connection until the actual output voltage of each stage meets the output voltage requirement.

[0035] Preferably, the at least one phase-shifting transformer includes two phase-shifting transformers; the input terminals of the two phase-shifting transformers are electrically connected to the power grid supply terminal, and the output terminals are electrically connected to the input terminals of each stage of the phase-controlled rectifier, and the output AC currents of the two phase-shifting transformers have a 15-degree phase difference.

[0036] Preferably, each power conversion unit further includes two choke inductors and two DC filter capacitors; the two choke inductors are connected in series in the positive and negative branches of the DC output terminal of the phase-controlled rectifier, respectively, and the two DC filter capacitors are connected in parallel between the positive and negative terminals, forming a two-stage inductor-capacitor filter structure to suppress current ripple and voltage ripple of the DC bus voltage.

[0037] Preferably, the three-level inverter is a neutral-point clamped three-level inverter, and each stage of the three-level inverter includes a first upper-arm fully controlled device, a second upper-arm fully controlled device, a first lower-arm fully controlled device, a second lower-arm fully controlled device, an upper half-arm clamping diode, a lower half-arm clamping diode, and a DC bus midpoint, wherein:

[0038] The collector of the first upper arm fully controlled device is connected to the positive terminal of the DC bus, and the emitter is connected to the collector of the second upper arm fully controlled device. The emitter of the second upper arm fully controlled device serves as the AC output terminal of the three-level inverter.

[0039] The collector of the first lower bridge arm fully controlled device is connected to the AC output terminal of the three-level inverter, and the emitter is connected to the collector of the second lower bridge arm fully controlled device. The emitter of the second lower bridge arm fully controlled device is connected to the negative terminal of the DC bus.

[0040] The anode of the upper half-bridge arm clamping diode is connected to the midpoint of the DC bus, and the cathode is connected to the connection point between the emitter of the first upper half-bridge arm fully controlled device and the collector of the second upper half-bridge arm fully controlled device.

[0041] The cathode of the lower half-bridge arm clamping diode is connected to the midpoint of the DC bus, and the anode is connected to the connection point between the emitter of the first lower half-bridge arm fully controlled device and the collector of the second lower half-bridge arm fully controlled device.

[0042] By combining the on and off states of the first upper bridge arm control device, the second upper bridge arm control device, the first lower bridge arm control device, and the second lower bridge arm control device, a positive level state, a zero level state, and a negative level state are output. The positive level is half of the DC bus voltage, the zero level is zero, and the negative level is half of the negative DC bus voltage.

[0043] Preferably, each power conversion unit further includes a step-up transformer and a rectifier and filter unit that are electrically connected in sequence to the output of the three-level inverter. The rectifier and filter unit includes a high-voltage uncontrolled rectifier and an RC filter circuit. The RC filter circuit is composed of a filter resistor and a filter capacitor connected in series.

[0044] The control system includes a bus voltage detection unit, an output voltage detection unit, and a step-by-step adjustment control unit. The input terminal of the bus voltage detection unit is electrically connected to the DC bus output terminal of each stage phase-controlled rectifier to collect the actual bus voltage. The input terminal of the output voltage detection unit is electrically connected to the output terminal of each stage RC filter circuit to collect the actual output voltage. The input terminal of the step-by-step adjustment control unit is electrically connected to the output terminals of the bus voltage detection unit and the output terminal of the output voltage detection unit, respectively. The output terminal of the step-by-step adjustment control unit is electrically connected to the trigger terminal of each stage phase-controlled rectifier and the switching transistor control terminal of each stage three-level inverter, respectively, to calculate the duty cycle and perform step-by-step adjustment.

[0045] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0046] By independently determining the target DC bus voltage for each power conversion unit and adjusting the phase-controlled rectifier to ensure the actual bus voltage meets the standard, the voltages of each stage of the bus are free from interference, eliminating the phenomenon in traditional schemes where adjusting the voltage of one stage causes fluctuations in other stages through bus coupling. After the bus voltage meets the standard, the initial duty cycle of the three-level inverter is calculated based on the output voltage reference value and the actual bus voltage. Since the bus voltage has been matched according to the comparison between the reference value and the threshold, the initial duty cycle naturally falls within the range of low inverter output ripple, which is beneficial for the three-level inverter. Its inherent multi-level output characteristics effectively reduce DC voltage ripple after boost rectification. When the actual output voltage deviates from the reference value, the duty cycle is finely adjusted step by step from the series start stage to the end stage. The lower stage voltage is stabilized first, and then the adjustment is made step by step to avoid chain fluctuations during the adjustment process. At the same time, the combination of coarse adjustment of the bus voltage and fine adjustment of the duty cycle utilizes the rectifier's wide range of adjustment capabilities to quickly approach the target, and utilizes the inverter's high response speed to achieve precise compensation. Thus, the stability and adjustment accuracy of the output voltage are improved without increasing the control complexity. Attached Figure Description

[0047] To more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of the present invention and should not be considered as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort. In the drawings:

[0048] Figure 1 A schematic flowchart of the neutral beam ultra-high voltage power supply hierarchical control method provided by the present invention;

[0049] Figure 2 A schematic diagram of the neutral beam ultra-high voltage power supply system provided by the present invention;

[0050] Figure 3 The schematic diagram of the phase-shifting transformer and phase-controlled rectifier provided by this invention;

[0051] Figure 4 The schematic diagram of phase a of the three-level inverter provided by this invention;

[0052] Figure 5 This is the timing diagram for triggering all controllable devices in phase a of a three-level inverter.

[0053] The attached diagram shows the markings and corresponding component names:

[0054] 1-Power grid supply terminal, 2-Primary outdoor equipment, 3-Phase shifting transformer, 4-Phase controlled rectifier, 5-Three-level inverter, 6-Step-up transformer, 7-Rectifier and filter unit, 8-High voltage uncontrolled rectifier, 9-Filter resistor, 10-Filter capacitor, 11-Choke inductor, 12-DC filter capacitor, 13-Upper half-bridge arm clamping diode, 14-Lower half-bridge arm clamping diode, 15-First upper half-bridge arm fully controlled device, 16-Second upper half-bridge arm fully controlled device, 17-First lower half-bridge arm fully controlled device, 18-Second lower half-bridge arm fully controlled device. Detailed Implementation

[0055] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and accompanying drawings. The illustrative embodiments and descriptions of the present invention are only used to explain the present invention and are not intended to limit the present invention.

[0056] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising..." does not exclude the presence of additional identical elements in the process, method, article, or apparatus that includes said element.

[0057] It should be noted that all actions involving the acquisition of signals, information, or data in this invention are carried out in compliance with the relevant data protection laws and regulations of the locality and with authorization from the owner of the relevant device.

[0058] Example 1

[0059] Please see Figure 1 This invention provides a hierarchical control method for a neutral-beam ultra-high voltage power supply. The neutral-beam ultra-high voltage power supply includes multiple power conversion units connected in series. Each power conversion unit includes a phase-controlled rectifier and a three-level inverter connected in sequence.

[0060] A multi-stage power conversion unit refers to a device that processes input electrical energy sequentially through multiple independent power conversion links, with each link including rectification and inversion stages, ultimately connecting and superimposing the high-voltage DC outputs of each stage in series. For example, in a neutral beam negative ion source power supply scenario, a five-stage power conversion unit is used in series, with a single-stage rated output of 200kV and a maximum output of 1000kV for the five stages in series.

[0061] A phase-controlled rectifier is a rectifier device that controls the magnitude of the DC output voltage by adjusting the firing angle of the thyristors. For example, when the firing angle decreases, the DC bus voltage output by the rectifier increases; when the firing angle increases, the DC bus voltage decreases. This device converts alternating current (AC) to direct current (DC), providing an adjustable DC bus voltage for subsequent inverters.

[0062] A three-level inverter is a DC-to-AC converter capable of outputting positive, zero, and negative voltage levels. For example, when the DC bus voltage is 6kV, a three-level inverter can output AC voltage steps of +3kV, 0V, and -3kV respectively. Compared to a two-level inverter, a three-level inverter has smaller voltage steps and a smoother output waveform.

[0063] The method includes:

[0064] S1. For each stage of power conversion unit, the target value of the DC bus voltage of the DC bus of the phase-controlled rectifier in the power conversion unit is determined based on the comparison result between the output voltage reference value of the power conversion unit and the preset voltage threshold.

[0065] The output voltage reference value is the DC high voltage value that the operator or host computer sets for each stage of the power conversion unit. For example, based on the nuclear fusion experiment conditions, the operator sets the first stage output to 150kV, the second stage output to 180kV, the third stage output to 120kV, etc., and these values ​​are the output voltage reference values ​​for each stage.

[0066] The preset voltage threshold is a critical voltage value used to determine whether to maintain the DC bus voltage at its maximum value. For example, when the rated output voltage of a single stage is 200kV, the preset voltage threshold is set to 140kV. When the output voltage reference value exceeds 140kV, the DC bus voltage should be set to its maximum value to ensure that the inverter has sufficient regulation margin.

[0067] The target DC bus voltage is the ideal DC voltage value that each stage of the phase-controlled rectifier needs to output. This value is determined by comparing the output voltage reference value with the preset voltage threshold: if the output voltage reference value exceeds the preset voltage threshold, the target DC bus voltage is set to the preset maximum value; if it does not exceed the threshold, it is calculated according to a pre-established matching formula.

[0068] Specifically, the control system receives an independent output voltage reference value for each stage and compares this value with a preset voltage threshold of 140kV. When the reference value is greater than 140kV, it means that the three-level inverter needs a larger voltage regulation range to output the target high voltage. Therefore, the target DC bus voltage is set to a maximum value of 6kV to ensure that the inverter has sufficient regulation margin. When the reference value is less than or equal to 140kV, the target DC bus voltage is calculated according to a pre-fitted matching formula. This formula ensures that the inverter's duty cycle is always in the range with the minimum output ripple. After the above processing, each stage obtains a target DC bus voltage value that matches the output voltage requirement of that stage. This avoids the drawbacks of using a uniform bus voltage for all stages in traditional schemes: when the bus voltage is too high, the inverter's duty cycle is too small, causing increased ripple; when the bus voltage is too low, the inverter cannot output the required voltage.

[0069] In some embodiments, determining the target DC bus voltage of the phase-controlled rectifier in the power conversion unit based on a comparison between the output voltage reference value of the power conversion unit and a preset voltage threshold includes:

[0070] The comparison result is obtained by comparing the output voltage reference value with the preset voltage threshold, wherein the preset voltage threshold is obtained based on the single-stage rated output voltage;

[0071] If the comparison result shows that the output voltage reference value exceeds the preset voltage threshold, then the DC bus voltage target value is set to the preset maximum value.

[0072] If the comparison result shows that the output voltage reference value does not exceed the preset voltage threshold, then the target value of the DC bus voltage is calculated according to the preset formula.

[0073] The rated output voltage of a single stage refers to the maximum DC high voltage value that each power conversion unit can stably output under normal operating conditions. For example, in a five-stage series system, the rated output voltage of a single stage is 200kV, which means that the maximum designed output capacity of each stage is 200kV, and the maximum capacity of five stages in series is 1000kV.

[0074] The preset maximum value is the upper limit that the DC bus voltage of the phase-controlled rectifier can be set to. For example, when the output voltage reference value is high, in order to ensure that the three-level inverter has sufficient adjustment margin, the target value of the DC bus voltage is set to 6kV, which is the preset maximum value.

[0075] The preset formula is a pre-established mathematical relationship used to calculate the target value of the DC bus voltage based on the output voltage reference value. This formula can be in the form of a fitting function or a piecewise function, and its design goal is to ensure that the duty cycle of the three-level inverter is always in the range with the minimum output voltage ripple and the fastest response speed.

[0076] Specifically, the control system acquires the output voltage reference value for each stage and compares it with a preset voltage threshold. The preset voltage threshold is determined based on the rated output voltage of a single stage. For example, if the rated output voltage of a single stage is 200kV, the threshold is set to 140kV, which is 70% of the rated value. The comparison yields two results: when the output voltage reference value exceeds the preset voltage threshold, it indicates that the stage requires a higher output voltage, and the inverter needs a larger voltage regulation range. In this case, the DC bus voltage target value is directly set to the preset maximum value. When the output voltage reference value does not exceed the preset voltage threshold, it indicates that the output demand is relatively low. In this case, instead of using a fixed maximum value, the DC bus voltage target value is calculated according to a preset formula, ensuring that the calculated target value guarantees that the inverter duty cycle falls within the optimal operating range. Through the above branching process, each stage obtains a DC bus voltage target value that matches its own output demand, laying the foundation for the subsequent low-ripple output of the inverter.

[0077] S2. If the deviation between the actual bus voltage of the DC bus and the target value of the DC bus voltage does not meet the DC bus voltage requirement, then adjust the output of the phase-controlled rectifier until the actual bus voltage meets the DC bus voltage requirement.

[0078] The actual bus voltage is the DC voltage value currently output by each stage of the phase-controlled rectifier, measured by a voltage detection device. For example, the measurement shows that the actual bus voltage of a certain stage is 5.8kV, while the target value of the DC bus voltage for that stage is 6.0kV, resulting in a deviation of 0.2kV.

[0079] The DC bus voltage requirement refers to the limit on the allowable deviation between the actual bus voltage and the target DC bus voltage value. For example, the deviation is required to be no more than ±1%, meaning that the requirement is met when the actual bus voltage is within 99% to 101% of the target value.

[0080] Specifically, the control system acquires the actual bus voltage of each stage through a voltage detection device and calculates the deviation between this voltage and the corresponding target DC bus voltage value. If the deviation exceeds ±1%, it is determined that the DC bus voltage requirement is not met. At this point, the thyristor firing angle of the phase-controlled rectifier is adjusted: when the actual bus voltage is lower than the target value, the firing angle is decreased to increase the rectifier output; when the actual bus voltage is higher than the target value, the firing angle is increased to decrease the rectifier output. After each adjustment, the actual bus voltage is re-detected, and the above process is repeated until the deviation falls within the allowable range. Because each stage of the phase-controlled rectifier is adjusted independently, adjusting the firing angle of one stage will not affect the bus voltage of other stages. Ultimately, the actual bus voltage of all stages stabilizes near the target value, providing a precise DC input power supply for the subsequent inverter, while eliminating the voltage fluctuation problem caused by inter-stage coupling in traditional solutions.

[0081] In some embodiments, adjusting the output of the phase-controlled rectifier until the actual bus voltage meets the DC bus voltage requirement includes:

[0082] The direction of the deviation is obtained based on the deviation between the actual bus voltage and the target value of the DC bus voltage;

[0083] If the deviation direction is that the actual bus voltage is lower than the target value of the DC bus voltage, then reduce the firing angle of the thyristors in the phase-controlled rectifier to obtain an increased actual bus voltage;

[0084] If the deviation direction is that the actual bus voltage is higher than the target value of the DC bus voltage, then increase the firing angle of the thyristors in the phase-controlled rectifier to obtain a reduced actual bus voltage;

[0085] Repeatedly adjust the output of the phase-controlled rectifier until the deviation between the actual bus voltage and the target value of the DC bus voltage does not exceed the preset bus voltage deviation threshold.

[0086] Among them, the thyristor is a semi-controlled power switching device used in a phase-controlled rectifier to control the current conduction angle. By changing the timing of the trigger pulse applied to the gate of the thyristor, the conduction start point of the thyristor within the AC voltage cycle can be controlled, thereby adjusting the magnitude of the DC voltage output by the rectifier.

[0087] The firing angle is the electrical angle between the zero-crossing of the AC voltage and the activation of the thyristor, usually denoted by α. The larger the firing angle, the later the thyristor turns on, and the lower the DC voltage output by the rectifier; the smaller the firing angle, the earlier the thyristor turns on, and the higher the DC voltage output.

[0088] The bus voltage deviation threshold is the maximum allowable deviation between the actual bus voltage and the target DC bus voltage. For example, when the threshold is set to ±1%, the actual bus voltage is considered to meet the DC bus voltage requirement as long as it falls within 99% to 101% of the target value.

[0089] Specifically, the control system calculates the difference between the actual bus voltage and the target DC bus voltage, determining the direction of the deviation based on the sign of the difference. When the actual bus voltage is lower than the target value, the deviation is negative. In this case, the thyristor firing angle is reduced, causing the thyristor to conduct earlier in the AC cycle, resulting in a higher DC voltage output from the phase-controlled rectifier, and consequently, an increase in the actual bus voltage. When the actual bus voltage is higher than the target value, the deviation is positive. In this case, the thyristor firing angle is increased, causing the thyristor to conduct later, resulting in a lower DC voltage output from the rectifier, and consequently, a decrease in the actual bus voltage. After each firing angle adjustment, the actual bus voltage is re-detected and compared with the target value to calculate the new deviation, repeating the above adjustment process. When the absolute value of the deviation between the actual bus voltage and the target value does not exceed the preset bus voltage deviation threshold, the adjustment stops, indicating that the actual bus voltage of that stage meets the requirements. Since each stage of the phase-controlled rectifier is adjusted independently, changes in the firing angle only affect the bus voltage of that stage and do not interfere with the voltages of other stages in the series connection.

[0090] S3. When the actual bus voltage of each stage reaches the target value of the DC bus voltage, for each stage of power conversion unit, calculate the initial duty cycle of the three-level inverter in the power conversion unit based on the output voltage reference value and the adjusted actual bus voltage.

[0091] The initial duty cycle is a pulse width ratio used to initially control the output of the three-level inverter, calculated based on the output voltage reference value and the actual bus voltage that has reached the target. For example, for an output voltage reference value of 150kV and an actual bus voltage of 6kV, the duty cycle is calculated to be 0.6 based on the inverter gain relationship, indicating that the positive level output time accounts for 60% within one switching cycle.

[0092] Specifically, after confirming that the actual bus voltage of all stages has reached the target value, the control system performs an initial duty cycle calculation for each stage. For a given stage, given the output voltage reference value and the stabilized actual bus voltage, the initial duty cycle is calculated based on the linear relationship between the output voltage and duty cycle of the three-level inverter. This duty cycle represents the proportion of the positive level output duration within one switching cycle. Since the actual bus voltage has been pre-matched according to the output voltage reference value, the calculated initial duty cycle naturally falls within the inverter's optimal operating range, meaning the duty cycle is neither too small nor too large, thus avoiding a surge in output voltage ripple caused by extreme duty cycles. Each stage is calculated independently without interference.

[0093] S4. Control the output AC voltage of the three-level inverter according to the initial duty cycle to obtain the actual output voltage of the power conversion unit;

[0094] The actual output voltage is the DC high voltage value finally output by each power conversion unit, measured by a detection device. This voltage is the result after passing through three-level inversion, boost, rectification, and filtering stages. For example, the measurement shows that the actual output voltage of a certain stage is 148kV, while the reference value is 150kV, with a deviation of 2kV.

[0095] Specifically, the control system sends trigger pulses to the power switches of the three-level inverter based on the calculated initial duty cycle. The inverter outputs an AC voltage consisting of positive, zero, and negative levels according to the duty cycle sequence. This AC voltage is stepped up to the high-voltage level by a step-up transformer, then converted into pulsating DC by an uncontrolled rectifier, and finally filtered to remove residual ripple, yielding the actual output voltage of each stage. Because the inverter uses a three-level topology, the height of each voltage step in the output waveform is only half that of the DC bus voltage, resulting in naturally smaller ripple in the DC voltage obtained after step-up rectification. Simultaneously, since the actual bus voltage has been precisely adjusted to the target value and the duty cycle is within the optimal range, the initial actual output voltage is already close to the reference value with minimal deviation.

[0096] In some embodiments, the three-level inverter is a neutral-point clamped three-level inverter, comprising four power switching transistors and two clamping diodes; the step of controlling the output AC voltage of the three-level inverter according to the initial duty cycle to obtain the actual output voltage of the power conversion unit includes:

[0097] Based on the initial duty cycle and the DC bus voltage, a timing combination of three output states—positive level, zero level, and negative level—is obtained.

[0098] The output AC voltage is obtained by controlling the on and off of the four power switching transistors according to the timing combination.

[0099] Among them, the neutral-point clamped three-level inverter is an inverter topology that introduces the DC bus neutral point potential into the bridge arm through clamping diodes, enabling the inverter to output three different voltage levels. In this topology, each bridge arm consists of four power switches and two clamping diodes. The clamping diodes clamp the voltage at the connection point of the switches to the DC bus neutral point, so that the voltage stress on the switches is only half that of the DC bus voltage.

[0100] Power switching transistors are semiconductor devices in a three-level inverter used to perform turn-on and turn-off operations to change the current path. They are such as integrated gate commutated thyristors or injection-enhanced gate transistors. Each switching transistor receives a control pulse and is approximately short-circuited when on and approximately open-circuited when off. The combined state of the four switching transistors determines the output voltage of the inverter.

[0101] A clamping diode is a unidirectional conductive device connected between the midpoint of the DC bus and the connection point of the bridge arm switch transistor to limit the voltage amplitude across the switch transistor. The clamping diode of the upper bridge arm clamps the potential of the upper bridge arm switch transistor connection point to no higher than the midpoint potential, and the clamping diode of the lower bridge arm clamps the potential of the lower bridge arm switch transistor connection point to no lower than the midpoint potential, thereby preventing the switch transistor from being subjected to excessive voltage.

[0102] Positive level is a voltage state output by a three-level inverter, with an amplitude of half that of the DC bus voltage. When the two upper power switches in the inverter bridge arm are turned on and the two lower power switches are turned off, the voltage at the output terminal connected to the positive terminal of the DC bus and the midpoint is positive level.

[0103] Zero level is a voltage state output by a three-level inverter, with an amplitude of zero. When the second upper switch and the first lower switch in the inverter bridge arm are simultaneously turned on, and the remaining switches are turned off, the output terminal is connected to the midpoint of the DC bus, and the output voltage is zero.

[0104] A negative voltage level is a voltage state output by a three-level inverter, with an amplitude of half the negative DC bus voltage. When the two lower power switches in the inverter bridge arm are turned on and the two upper power switches are turned off, the voltage connected to the negative terminal of the DC bus and the midpoint at the output terminal is a negative voltage level.

[0105] Timing sequence refers to the sequence of positive, zero, and negative output states arranged in chronological order within a switching cycle, along with the duration ratio of each state. By adjusting the duty cycle of each level state in the timing sequence, AC output voltages of different magnitudes and waveforms can be synthesized.

[0106] Specifically, the control system determines the duration and order of occurrence of the three output states—positive, zero, and negative—within a switching cycle based on the initial duty cycle and the current stage's DC bus voltage, thus obtaining a timing combination. For example, when a higher AC voltage is required, the positive duty cycle is larger; when a lower voltage is required, the positive duty cycle is smaller, and a negative level may be inserted. The control system sends turn-on or turn-off commands to the control electrodes of the four power switches according to the timing combination: when a positive level is required, the two upper power switches are turned on and the two lower ones are turned off; when a zero level is required, the two middle switches are turned on and the two outer ones are turned off; when a negative level is required, the two lower switches are turned on and the two upper ones are turned off. Clamping diodes limit the voltage at the switch connection points to near the DC bus midpoint potential during switch switching, preventing the switches from experiencing stress exceeding half the DC bus voltage. The alternating on and off of the four switching transistors generates a multi-level stepped waveform at the AC output of the inverter. The voltage step height in this waveform is only half that of the DC bus voltage, resulting in a lower harmonic content. Consequently, the DC voltage ripple obtained after subsequent boost rectification is also reduced.

[0107] S5. If the deviation between the actual output voltage and the output voltage reference value does not meet the output voltage requirement, the duty cycle of the three-level inverter in each stage is adjusted sequentially from the starting stage to the ending stage in the series connection until the actual output voltage of each stage meets the output voltage requirement.

[0108] The output voltage requirement is a comprehensive limitation on the deviation between the actual output voltage and the reference value for each stage, typically including three indicators: stability, absolute deviation, and ripple. For example, the requirement is that the stability should not exceed ±2%, the deviation should not exceed ±5kV, and the ripple should not exceed ±3%.

[0109] In a series connection, the starting stage refers to the stage located at the lowest potential when multiple power conversion units are connected in series, and the ending stage refers to the stage located at the highest potential. For example, in a five-stage series power supply, the stage with the lowest output voltage is the starting stage, and the stage with the highest output voltage is the ending stage. The adjustment sequence proceeds from the starting stage to the ending stage.

[0110] Specifically, the control system detects the actual output voltage of each stage and compares it with the corresponding output voltage reference value to determine whether the deviation meets the three indicators of stability, absolute deviation, and ripple. If all stages meet the requirements, the current duty cycle remains unchanged, and the system enters steady-state operation. If at least one stage does not meet the requirements, adjustments are made stage by stage in sequence from the starting stage to the ending stage in the series connection. First, the starting stage is adjusted by fine-tuning the duty cycle of the three-level inverter at that stage: increasing the duty cycle raises the actual output voltage, decreasing the duty cycle lowers the actual output voltage, until the actual output voltage of that stage meets all requirements. Then, the duty cycle of that stage is fixed, and the same fine-tuning operation is performed on the next stage, and so on until the ending stage also meets the requirements. Since the total series voltage is the sum of the voltages of each stage, prioritizing the adjustment of the starting stage can stabilize the base potential of the series circuit. Subsequent adjustments at higher stages will not impact the already stabilized lower stages, avoiding the coupling phenomenon in traditional schemes where adjusting one stage causes fluctuations in other stages. The entire adjustment process uses closed-loop feedback, and the system is re-detected after each fine-tuning to ensure that the final output voltage of each stage reaches the preset accuracy.

[0111] In some embodiments, when the deviation between the actual output voltage of a certain power conversion unit and the output voltage reference value is detected to exceed a preset fault threshold, the method further includes:

[0112] Based on the deviation exceeding the preset fault threshold, the corresponding level is marked as an abnormal level;

[0113] Based on the position of the abnormal stage in the series connection, while keeping the electrical connection state between the abnormal stage and other normal stages unchanged, the actual output voltage after compensation is obtained by gradually fine-tuning the duty cycle of the three-level inverter of the abnormal stage.

[0114] Based on the update deviation between the compensated actual output voltage and the output voltage reference value, determine whether the update deviation has been reduced to within the preset fault threshold.

[0115] If the update deviation is not reduced to within the preset fault threshold after a preset number of fine adjustments, the bypass switch is controlled according to the position of the abnormal level to remove the abnormal level from the series connection, and the remaining normal level sequence is obtained.

[0116] Based on the difference between the total output voltage reference value and the sum of the actual output voltages of the remaining normal stages, the output voltage reference value allocation scheme for each remaining normal stage is recalculated to obtain the updated output voltage reference values ​​for each stage.

[0117] The preset fault threshold is a critical deviation value used to determine whether a power conversion unit has experienced a serious abnormality. When the deviation between the actual output voltage and the reference output voltage exceeds this threshold, it is considered that the unit cannot be quickly restored to normal through conventional fine-tuning and needs to enter the fault handling process.

[0118] An abnormal level refers to a power conversion unit where the deviation between the actual output voltage and the output voltage reference value exceeds a preset fault threshold. This marking is used to distinguish this level from other normally operating levels, so that targeted compensation or shutdown measures can be taken subsequently.

[0119] A bypass switch is a switching device connected in parallel across the high-voltage DC output terminals of each power conversion unit. When the bypass switch is closed, that stage is short-circuited and disconnected from the series circuit, its output voltage no longer participates in the series superposition, and the current bypasses that stage to continue flowing to the subsequent stages.

[0120] The remaining normal stage sequence refers to the set of power conversion units that still operate normally after one or more abnormal stages have been removed from the series connection, arranged in their original series sequence.

[0121] The total output voltage reference value refers to the final total high-voltage DC value expected to be output by the system, which is equal to the sum of the output voltage reference values ​​of all stages. For example, in a five-stage series system, when the reference value of each stage is 200kV, the total output voltage reference value is 1000kV.

[0122] The allocation scheme refers to the voltage setting plan for redistributing the total output voltage reference value to the remaining normal stages after some stages are removed. For example, after one stage is removed, the remaining four stages need to share the total voltage originally borne by the five stages, and each stage obtains a new output voltage reference value.

[0123] Specifically, the control system continuously monitors the actual output voltage of each stage. When the deviation between the actual output voltage of a stage and the reference output voltage exceeds a preset fault threshold, the stage is marked as an abnormal stage. For units marked as abnormal stages, physical disconnection is not performed initially. Instead, the electrical connection between the unit and other stages in the series circuit remains unchanged, and an attempt is made to compensate for the voltage deviation by gradually fine-tuning the duty cycle of the three-level inverter of that stage. After each fine-tuning attempt, the actual output voltage after compensation is re-detected, the updated deviation from the reference value is calculated, and it is determined whether the deviation has decreased to within the preset fault threshold. If, after a preset number of fine-tuning attempts, the updated deviation still fails to decrease to within the threshold, it indicates that the stage has a serious fault that cannot be recovered by duty cycle adjustment. At this time, based on the abnormal stage's position in the series connection, the bypass switch connected in parallel to the output terminal of that stage is closed, disconnecting the abnormal stage from the series circuit. After disconnection, the remaining normal stage sequence is obtained, and each stage in this sequence maintains its original series order. The control system calculates the total additional voltage that the remaining normal stages need to bear based on the difference between the total output voltage reference value and the sum of the actual output voltages of the remaining normal stages. Then, according to a certain principle (such as proportional allocation or allocation based on rated capacity), it recalculates the output voltage reference value for each remaining normal stage, resulting in an updated allocation scheme. The updated reference values ​​are sent to each normal stage controller, and the system continues to operate under the new reference values. This hierarchical processing method allows the system to maintain overall output through compensation or bypass in the event of a single-stage failure, preventing the entire power supply system from shutting down due to a single-stage failure.

[0124] Example 2

[0125] Please see Figure 2 This invention provides a neutral beam ultra-high voltage power supply system, comprising:

[0126] Power supply terminal 1;

[0127] At least one phase-shifting transformer 3, the input terminal of which is electrically connected to the power grid supply terminal 1;

[0128] The series-connected multi-stage power conversion units include a phase-controlled rectifier 4 and a three-level inverter 5 connected in sequence. The input terminal of the phase-controlled rectifier 4 is electrically connected to the output terminal of the phase-shifting transformer 3. The output terminal of the three-level inverter 5 of each stage of the power conversion unit serves as the high-voltage DC output terminal of each stage, and the high-voltage DC output terminals of each stage are connected in series to form the total high-voltage DC output terminal of the system.

[0129] The control system is electrically connected to each stage of the phase-controlled rectifier 4 and each stage of the three-level inverter 5. The control system determines the target DC bus voltage of the phase-controlled rectifier 4 in each stage based on a comparison between the output voltage reference value and a preset voltage threshold. It adjusts the output of the phase-controlled rectifier 4 according to the deviation between the actual bus voltage and the target DC bus voltage until the actual bus voltage reaches the target DC bus voltage. After the actual bus voltage of each stage reaches the target DC bus voltage, it calculates the initial duty cycle of the three-level inverter 5 in each stage based on the output voltage reference value and the adjusted actual bus voltage. It controls the output AC voltage of the three-level inverter 5 according to the initial duty cycle to obtain the actual output voltage of each stage. When the deviation between the actual output voltage and the output voltage reference value does not meet the output voltage requirement, it adjusts the duty cycle of the three-level inverter 5 in each stage sequentially from the starting stage to the ending stage in the series connection until the actual output voltage of each stage meets the output voltage requirement.

[0130] Among them, grid power supply terminal 1 is the energy input interface of the entire UHV power supply system, connecting to the external power frequency AC grid to provide raw power to the system. Grid power supply terminal 1 receives 35kV power frequency AC power, which, after subsequent conversion, meets the power requirements of the system when operating at full load, matching the total power corresponding to the highest output voltage of the five-stage series connection.

[0131] The phase-shifting transformer 3 is a specially designed power frequency transformer. Its input end is connected to the power grid supply end 1, and its output end is connected to the phase-controlled rectifiers 4 at each stage. The phase-shifting transformer 3 is used to offset the harmonic current generated when the subsequent five-stage phase-controlled rectifiers are working, thereby reducing harmonic pollution of the power grid by the rectifier stage and improving the system power factor. Secondly, it transforms the grid voltage to a voltage level suitable for the input of the phase-controlled rectifier 4.

[0132] The control system is an automatic control device electrically connected to each stage of phase-controlled rectifier 4 and each stage of three-level inverter 5, and is responsible for executing the hierarchical decoupling control strategy. The control system receives the output voltage reference values ​​set by the host computer for each stage, and sends trigger angle adjustment commands to the phase-controlled rectifier 4 and duty cycle control pulses to the three-level inverter 5 according to the hierarchical control process by detecting the actual bus voltage and the actual output voltage.

[0133] Among them, such as Figure 2As shown, in some embodiments, a primary outdoor device 2 is also included. The primary outdoor device 2 is located between the power grid supply terminal 1 and the phase-shifting transformer 3. The primary outdoor device 2 contains a vacuum circuit breaker and a soft starter cabinet. The vacuum circuit breaker is responsible for switching the main circuit of the system on and off. In case of a fault, it can quickly cut off the current to prevent the fault from spreading to the power grid or subsequent equipment. The soft starter cabinet gradually increases the output voltage through thyristor voltage regulation during startup, suppressing the inrush current at the beginning of power transmission (such as avoiding the inrush current of the phase-shifting transformer), and protecting the transformer, rectifier and other devices from overcurrent damage.

[0134] Among them, such as Figure 2 As shown, in some embodiments, the at least one phase-shifting transformer 3 includes a first phase-shifting transformer and a second phase-shifting transformer; the input terminals of the first phase-shifting transformer and the second phase-shifting transformer are respectively electrically connected to the power grid supply terminal 1, the output terminals of the first phase-shifting transformer and the second phase-shifting transformer are respectively electrically connected to the input terminals of each stage of the phase-controlled rectifier 4, and there is a 15-degree phase difference between the output AC power of the first phase-shifting transformer and the output AC power of the second phase-shifting transformer.

[0135] Specifically, the primary windings of the first and second phase-shifting transformers use the same connection method, such as a star connection, to ensure that the input voltages of the two transformers are in phase. The secondary windings of the two transformers use different phase-shifting connections: the secondary winding of the first phase-shifting transformer uses a star connection, while the secondary winding of the second phase-shifting transformer uses a delta connection, or both use an extended delta connection but with different turns ratios. By designing the connection method of the secondary windings, a 15-degree phase difference is created between the three-phase AC voltages output by the first and second phase-shifting transformers. Specifically, when the secondary output voltage of the first phase-shifting transformer is in phase with the primary winding (0-degree phase shift), and the secondary output voltage of the second phase-shifting transformer lags behind the primary winding by 15 degrees, a 15-degree phase difference is formed between the AC outputs of the two transformers.

[0136] The input terminals of the first and second phase-shifting transformers are connected in parallel to the power grid supply terminal 1, receiving the same primary voltage. The output terminals of the first and second phase-shifting transformers are connected to the AC input terminals of each stage of the phase-controlled rectifier 4. Because the outputs of the two phase-shifting transformers 3 have a 15-degree phase difference, the harmonic currents generated by the corresponding phase-controlled rectifiers 4 during operation have a mutual cancellation characteristic. For example, the characteristic harmonic generated by a 6-pulse rectifier is 6k±1 (k=1,2,3...). When the two rectifier inputs differ by 15 degrees, the harmonics of the same order generated by the two rectifiers differ by 180 degrees, canceling each other out when superimposed on the grid side. After the two phase-shifting transformers 3 work together, they effectively achieve a 24-pulse rectification effect, increasing the lowest-order characteristic harmonic in the harmonic current flowing into the grid from the 5th and 7th to the 23rd and 25th, reducing the total harmonic distortion rate. Meanwhile, the increased pulse number of the rectifier raises the frequency and reduces the amplitude of the DC bus voltage ripple at the output of phase-controlled rectifier 4, easing the burden on subsequent filtering circuits. This 15-degree phase difference setting does not require additional filtering devices; it can be achieved solely through the phase-shifting design of the transformer windings, reducing the system's harmonic mitigation costs.

[0137] Among them, such as Figure 3 As shown, in some embodiments, each power conversion unit further includes two choke inductors 11 and two DC filter capacitors 12; the two choke inductors 11 are connected in series in the positive and negative branches of the DC output terminal of the phase-controlled rectifier 4, respectively, and the two DC filter capacitors 12 are connected in parallel between the positive and negative terminals to form a two-stage inductor-capacitor filter structure, which is used to suppress the current ripple and voltage ripple of the DC bus voltage.

[0138] Specifically, the choke inductor 11 is an inductor element connected in series in the DC output circuit, which uses the inductance to suppress current changes to smooth the pulsating current output of the rectifier. In this system, two choke inductors 11 are connected in series in the positive and negative branches of the DC output terminal of the phase-controlled rectifier 4, respectively, to suppress current ripple in the DC bus.

[0139] The DC filter capacitor 12 is a capacitor connected in parallel between the positive and negative terminals of the DC output. It utilizes the charging and discharging characteristics of a capacitor to filter out ripple components in the DC voltage. In this system, two DC filter capacitors 12 are connected in parallel between the positive and negative terminals to suppress voltage ripple in the DC bus voltage.

[0140] The inductor-capacitor two-stage filter structure refers to a filter circuit composed of a choke inductor 11 and a DC filter capacitor 12, arranged in the order of inductor first, then capacitor. The choke inductor 11 is connected in series in the branch to suppress current ripple, while the DC filter capacitor 12 is connected in parallel at the output terminal to suppress voltage ripple. The two work together to simultaneously attenuate both current and voltage ripple on the DC bus, thereby making the DC bus voltage smoother and more stable.

[0141] Among them, reference Figure 4 The schematic diagram of phase a of the three-level inverter shown is illustrated. In some embodiments, the three-level inverter 5 is a neutral-point clamped three-level inverter. Each stage of the three-level inverter 5 includes a first upper-arm fully controlled device 15, a second upper-arm fully controlled device 16, a first lower-arm fully controlled device 17, a second lower-arm fully controlled device 18, an upper half-arm clamping diode 13, a lower half-arm clamping diode 14, and a DC bus midpoint, wherein:

[0142] The collector of the first upper arm fully controlled device 15 is connected to the positive terminal of the DC bus, and the emitter is connected to the collector of the second upper arm fully controlled device 16. The emitter of the second upper arm fully controlled device 16 serves as the AC output terminal of the three-level inverter 5.

[0143] The collector of the first lower bridge arm fully controlled device 17 is connected to the AC output terminal of the three-level inverter 5, and the emitter is connected to the collector of the second lower bridge arm fully controlled device 18. The emitter of the second lower bridge arm fully controlled device 18 is connected to the negative terminal of the DC bus.

[0144] The anode of the upper half-bridge arm clamping diode 13 is connected to the midpoint of the DC bus, and the cathode is connected to the connection point between the emitter of the first upper half-bridge arm fully controlled device 15 and the collector of the second upper half-bridge arm fully controlled device 16.

[0145] The cathode of the lower half-bridge clamping diode 14 is connected to the midpoint of the DC bus, and the anode is connected to the connection point between the emitter of the first lower half-bridge fully controlled device 17 and the collector of the second lower half-bridge fully controlled device 18.

[0146] By combining the on and off states of the first upper bridge arm control device 15, the second upper bridge arm control device 16, the first lower bridge arm control device 17, and the second lower bridge arm control device 18, a positive level state, a zero level state, and a negative level state are output. The positive level is half of the DC bus voltage, the zero level is zero, and the negative level is half of the negative DC bus voltage.

[0147] Specifically, a neutral-point clamped three-level inverter is an inverter topology that clamps the output voltage to the DC bus neutral point potential using clamping diodes, thereby outputting three voltage levels. For example, when the DC bus voltage is 6kV, this inverter can output +3kV, 0V, and -3kV. Its advantage is that the voltage stress on each power switch is only half that of the DC bus voltage, resulting in a smoother output waveform.

[0148] The first upper arm fully controlled device 15 is a fully controlled power switch located on the side of the upper arm of the inverter near the positive terminal of the DC bus. The collector of this device is connected to the positive terminal of the DC bus, and the emitter is connected to the collector of the second upper arm fully controlled device 16. The two devices are connected in series to form the upper arm.

[0149] The second upper arm fully controlled device 16 is a fully controlled power switch located on the side of the upper arm of the inverter near the AC output terminal. The collector of this device is connected to the emitter of the first upper arm fully controlled device 15, which serves as the AC output terminal of the inverter. Together with the first upper arm fully controlled device 15, it realizes the switching control of the upper arm.

[0150] The first lower arm fully controlled device 17 is a fully controlled power switch located on the side of the lower arm of the inverter near the AC output terminal. The collector of this device is connected to the AC output terminal of the inverter, and the emitter is connected to the collector of the second lower arm fully controlled device 18. The two devices are connected in series to form the lower arm.

[0151] The second lower arm fully controlled device 18 is a fully controlled power switch located on the side of the lower arm of the inverter near the negative terminal of the DC bus. The collector of this device is connected to the emitter of the first lower arm fully controlled device 17, and the emitter is connected to the negative terminal of the DC bus. It works in conjunction with the first lower arm fully controlled device 17 to realize the switching control of the lower arm.

[0152] The upper half-arm clamping diode 13 is a diode that connects the midpoint of the DC bus to the middle node of the upper half-arm. The anode of this diode is connected to the midpoint of the DC bus, and the cathode is connected to the junction point of the emitter of the first upper half-arm fully controlled device 15 and the collector of the second upper half-arm fully controlled device 16, which is used to clamp the potential of the middle node of the upper half-arm to the midpoint potential.

[0153] The lower half-arm clamping diode 14 is a diode that connects the midpoint of the DC bus to the middle node of the lower half-arm. The cathode of this diode is connected to the midpoint of the DC bus, and the anode is connected to the junction point of the emitter of the first lower half-arm fully controlled device 17 and the collector of the second lower half-arm fully controlled device 18, which is used to clamp the potential of the middle node of the lower half-arm to the midpoint potential.

[0154] The DC bus midpoint is an intermediate potential point formed by two large capacitors connected in series, with a potential that is half the positive voltage of the DC bus. This midpoint serves as the reference potential for the clamping diodes, enabling the inverter to output a zero-level state.

[0155] The positive level state refers to the output state where the voltage at the AC output terminal of the inverter relative to the midpoint of the DC bus is positive and equal to half the DC bus voltage. In this state, the two fully controlled devices 15 and 16 of the upper bridge arm are turned on, and the two fully controlled devices 17 and 18 of the lower bridge arm are turned off, with the output current flowing from the upper bridge arm to the load.

[0156] The zero-level state refers to the output state where the AC output terminal potential of the inverter is equal to the DC bus midpoint potential. In this state, the second upper bridge arm fully controlled device 16 and the first lower bridge arm fully controlled device 17 are turned on, while the others are turned off. The output current flows to the midpoint and the load through the clamping diode, and the output voltage is zero.

[0157] The negative level state refers to the output state where the voltage at the AC output terminal of the inverter relative to the midpoint of the DC bus is negative and equal to half the DC bus voltage. In this state, the two fully controlled devices 17 and 18 of the lower bridge arm are turned on, and the two fully controlled devices 15 and 16 of the upper bridge arm are turned off, and the output current flows from the load to the lower bridge arm.

[0158] Specifically, refer to Figure 5 The diagram shows the triggering timing of the fully controlled devices on phase a of a three-level inverter. The control system generates the switching triggering sequence of the four fully controlled devices based on the initial duty cycle. Within one switching cycle, a specific switching sequence is used to avoid shoot-through short circuits between the upper and lower bridge arms. When a positive output level is required, the first upper bridge arm fully controlled device 15 and the second upper bridge arm fully controlled device 16 are simultaneously turned on, while the first lower bridge arm fully controlled device 17 and the second lower bridge arm fully controlled device 18 are turned off. Current flows from the positive terminal of the DC bus through the first upper bridge arm fully controlled device 15 and the second upper bridge arm fully controlled device 16 to the AC output terminal, and the output voltage is equal to half of the DC bus voltage. When a zero-level output is required, the second upper bridge arm fully controlled device 16 and the first lower bridge arm fully controlled device 17 are turned on, while the first upper bridge arm fully controlled device 15 and the second lower bridge arm fully controlled device 18 are turned off. The load current flows through the second upper bridge arm fully controlled device 16 to the midpoint via the upper half-bridge arm clamping diode 13, or flows out of the midpoint via the lower half-bridge arm clamping diode 14 and the first lower bridge arm fully controlled device 17, resulting in a zero output voltage. When a negative level output is required, the first lower bridge arm fully controlled device 17 and the second lower bridge arm fully controlled device 18 are turned on, while the first upper bridge arm fully controlled device 15 and the second upper bridge arm fully controlled device 16 are turned off. The current flows from the AC output terminal through the first lower bridge arm fully controlled device 17 and the second lower bridge arm fully controlled device 18 to the negative terminal of the DC bus, resulting in an output voltage that is half the negative DC bus voltage. When switching power levels, the process proceeds in the order of first turning off the currently conducting device, then turning on the device that needs to be turned on, with a dead time inserted between the two actions to completely avoid bridge arm shoot-through short circuits. By changing the duration ratio of the three power levels within a single switching cycle, the inverter output synthesizes an AC voltage with the required average value and frequency. Since the voltage across each power switch is only half the DC bus voltage when it is turned off, the switching stress on the devices is reduced, which helps improve operational reliability. Simultaneously, the increased number of output power levels reduces the voltage change step, making the output waveform closer to a sine wave, resulting in smaller DC ripple after subsequent boost rectification.

[0159] In some embodiments, each power conversion unit further includes a step-up transformer 6 and a rectifier filter unit 7 that are sequentially electrically connected to the output of the three-level inverter 5. The rectifier filter unit 7 includes a high-voltage uncontrolled rectifier 8 and an RC filter circuit, which is composed of a filter resistor 9 and a filter capacitor 10 connected in series.

[0160] The control system includes a bus voltage detection unit, an output voltage detection unit, and a step-by-step adjustment control unit. The input terminal of the bus voltage detection unit is electrically connected to the DC bus output terminal of each stage phase-controlled rectifier 4 to collect the actual bus voltage. The input terminal of the output voltage detection unit is electrically connected to the output terminal of each stage RC filter circuit to collect the actual output voltage. The input terminal of the step-by-step adjustment control unit is electrically connected to the output terminals of the bus voltage detection unit and the output terminal of the output voltage detection unit, respectively. The output terminal of the step-by-step adjustment control unit is electrically connected to the trigger terminal of each stage phase-controlled rectifier 4 and the switching transistor control terminal of each stage three-level inverter 5, respectively, to calculate the duty cycle and perform step-by-step adjustment.

[0161] Among them, the step-up transformer 6 is a power frequency transformer that raises medium and low voltage AC power to high voltage levels. The input terminal of the step-up transformer 6 is connected to the AC output terminal of the three-level inverter 5, and the output terminal is connected to the rectifier and filter unit 7. For example, the three-level inverter 5 outputs several kilovolts of AC voltage, which is stepped up by the step-up transformer 6 to reach the high voltage AC power required for the rated output of 200kV per stage.

[0162] The rectifier and filter unit 7 is a combined device that converts high-voltage AC power into DC power and performs preliminary filtering. The input terminal of the rectifier and filter unit 7 is connected to the output terminal of the step-up transformer 6. It contains a high-voltage uncontrolled rectifier 8 and an RC filter circuit. The output terminal provides the actual DC output voltage for each stage.

[0163] The high-voltage uncontrolled rectifier 8 is a rectifier bridge composed of high-voltage diodes, used to rectify the high-voltage AC output from the step-up transformer 6 into pulsating DC. The high-voltage uncontrolled rectifier 8 employs an uncontrolled rectification method, meaning it does not require an external trigger signal and relies on the unidirectional conductivity of the diodes to complete the rectification. Its output is connected to an RC filter circuit to provide pulsating DC input for subsequent filtering.

[0164] The RC filter circuit is a first-order low-pass filter network consisting of a filter resistor 9 and a filter capacitor 10 connected in series. The RC filter circuit is connected in series at the output of the high-voltage uncontrolled rectifier 8 to filter out residual ripple voltage in the pulsating DC current. The filter resistor 9 limits the charging current of the filter capacitor 10 to prevent damage to the capacitor due to instantaneous large current; the filter capacitor 10 absorbs voltage fluctuations, making the output DC voltage smoother.

[0165] The filter resistor 9 is a resistor connected in series with the filter capacitor 10 in the RC filter circuit. One end of the filter resistor 9 is connected to the output terminal of the high-voltage uncontrolled rectifier 8, and the other end is connected to the positive terminal of the filter capacitor 10. When the system is powered on, the filter resistor 9 limits the charging current of the filter capacitor 10; when a short circuit and arcing occur in the load, the filter resistor 9 provides an energy release path for the filter capacitor 10, while suppressing the peak value of the capacitor discharge current.

[0166] Filter capacitor 10 is a capacitor component in the RC filter circuit used to store charge and filter out voltage ripple. The positive terminal of filter capacitor 10 is connected to one end of filter resistor 9, and the negative terminal is connected to the negative terminal of the DC bus. When the pulsating DC voltage fluctuates, filter capacitor 10 charges and discharges to stabilize the output voltage, further reducing the ripple amplitude.

[0167] The bus voltage detection unit is a sensor component used to measure the DC bus output voltage of each stage of the phase-controlled rectifier 4 in real time. The input terminal of the bus voltage detection unit is electrically connected to the DC bus output terminal of the phase-controlled rectifier 4 to acquire the DC bus voltage signal; the output terminal sends the acquired actual bus voltage value to the stage-by-stage adjustment control unit to provide feedback for closed-loop regulation.

[0168] The output voltage detection unit is a sensor component used to measure the DC high voltage output of each stage of the RC filter circuit in real time. The input terminal of the output voltage detection unit is electrically connected to the output terminal of the RC filter circuit to acquire the high voltage DC signal of the final output of each stage; the output terminal sends the actual output voltage value to the stage-by-stage adjustment control unit to determine whether the output voltage meets the set requirements.

[0169] The step-by-step adjustment control unit is the core calculation and command issuance module of the control system. Its input receives the actual bus voltage signal from the bus voltage detection unit and the actual output voltage signal from the output voltage detection unit. Its output is connected to the thyristor trigger terminals of each stage of the phase-controlled rectifier 4 and the power switch control terminals of each stage of the three-level inverter 5. Based on the received feedback signals and the reference values ​​set by the host computer, the step-by-step adjustment control unit calculates the firing angle adjustment of the phase-controlled rectifier 4 and the duty cycle of the three-level inverter 5, and issues adjustment commands step-by-step from the starting stage to the ending stage, achieving hierarchical decoupled control.

[0170] Specifically, the amplitude and frequency of the AC voltage output by the three-level inverter 5 are determined by the duty cycle, and this AC voltage is connected to the primary side of the step-up transformer 6. The step-up transformer 6 raises the medium- and low-voltage AC power to the high-voltage level according to the set transformation ratio, for example, raising it from several kilovolts to the high-voltage AC power required for the rated output of 200kV per stage. The high-voltage AC power is then rectified by the high-voltage uncontrolled rectifier 8 through a full-bridge rectifier, converting it into pulsating DC power. Since the high-voltage uncontrolled rectifier 8 uses diode uncontrolled rectification, the output waveform still contains a large pulsating component. This pulsating DC power enters an RC filter circuit consisting of a filter resistor 9 and a filter capacitor 10 connected in series. The filter resistor 9 limits the charging current of the filter capacitor 10, preventing excessive capacitor current at power-on and damage to the diodes or the capacitor itself; at the same time, when a short circuit arc occurs in the load, the filter resistor 9 provides a release path for the energy stored in the filter capacitor 10, suppressing the peak discharge current and protecting other components in the power supply system. The filter capacitor 10 uses its charging and discharging characteristics to absorb voltage fluctuations, smoothing the output voltage and ultimately obtaining the actual DC output voltage of each stage.

[0171] The bus voltage detection unit in the control system acquires the voltage at the DC bus output terminal of the phase-controlled rectifier 4 in real time and feeds this actual bus voltage back to the step-by-step adjustment control unit. The output voltage detection unit acquires the actual output voltage at the output terminal of the RC filter circuit in real time and also feeds it back to the step-by-step adjustment control unit. The step-by-step adjustment control unit compares the received actual bus voltage with the target DC bus voltage calculated based on the output voltage reference value. Based on the direction of the deviation, it sends a firing angle adjustment command to the thyristor firing terminals of the phase-controlled rectifier 4. Decreasing the firing angle increases the actual bus voltage, while increasing the firing angle decreases the actual bus voltage, until the actual bus voltage of all stages meets the requirements. Subsequently, the step-by-step adjustment control unit calculates the initial duty cycle of each stage of the three-level inverter 5 based on the output voltage reference value and the achieved actual bus voltage, and sends the corresponding switching timing signal to the switching transistor control terminal of each stage of the three-level inverter 5, causing the inverter to output the required AC voltage. Then, the control unit continuously receives the actual output voltage feedback from the output voltage detection unit and compares it with the output voltage reference value. The duty cycle of the three-level inverter 5 is finely adjusted step by step from the series start stage to the end stage until the actual output voltage of each stage meets the stability, deviation and ripple requirements.

[0172] Because each power conversion unit is equipped with an independent phase-controlled rectifier 4, a three-level inverter 5, a step-up transformer 6, a rectifier and filter unit 7, and an independent detection and control channel, the voltage regulation between each stage does not interfere with each other. The closed-loop feedback provided by the bus voltage detection unit and the output voltage detection unit enables the step-by-step adjustment control unit to accurately execute the sequential strategy of adjusting the starting stage first and then the ending stage, avoiding voltage fluctuations caused by inter-stage coupling in traditional centralized schemes. The filter resistor 9 and filter capacitor 10 in the RC filter circuit not only reduce the residual ripple of the output DC voltage, but also absorb and release energy in the event of load arcing faults, protecting the step-up transformer 6 and the high-voltage uncontrolled rectifier 8, and improving the system's survivability under frequent arcing conditions in nuclear fusion devices.

[0173] Those skilled in the art will understand that all or part of the steps of the above-described method embodiments can be implemented by hardware related to program instructions. The aforementioned program can be stored in a computer-readable storage medium. When executed, the program performs the steps of the above-described method embodiments; and the aforementioned storage medium includes various media capable of storing program code, such as ROM, RAM, magnetic disks, or optical disks.

[0174] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for graded control of a neutral-beam ultra-high voltage power supply, characterized in that, The neutral beam ultra-high voltage power supply includes a multi-stage power conversion unit connected in series. Each stage of the power conversion unit includes a phase-controlled rectifier and a three-level inverter connected in sequence. The method includes: For each power conversion unit, the target value of the DC bus voltage of the DC bus of the phase-controlled rectifier in the power conversion unit is determined based on the comparison result between the output voltage reference value of the power conversion unit and the preset voltage threshold. If the deviation between the actual bus voltage and the target value of the DC bus voltage does not meet the DC bus voltage requirement, the output of the phase-controlled rectifier is adjusted until the actual bus voltage meets the DC bus voltage requirement. Once the actual bus voltage of each stage reaches the target value of the DC bus voltage, for each stage of the power conversion unit, the initial duty cycle of the three-level inverter in the power conversion unit is calculated based on the output voltage reference value and the adjusted actual bus voltage. The output AC voltage of the three-level inverter is controlled according to the initial duty cycle to obtain the actual output voltage of the power conversion unit. If the deviation between the actual output voltage and the output voltage reference value does not meet the output voltage requirement, the duty cycle of the three-level inverter in each stage is adjusted sequentially from the starting stage to the ending stage in the series connection until the actual output voltage of each stage meets the output voltage requirement.

2. The method according to claim 1, characterized in that, The step of determining the target DC bus voltage of the DC bus of the phase-controlled rectifier in the power conversion unit based on the comparison result between the output voltage reference value of the power conversion unit and the preset voltage threshold includes: The comparison result is obtained by comparing the output voltage reference value with the preset voltage threshold, wherein the preset voltage threshold is obtained based on the single-stage rated output voltage; If the comparison result shows that the output voltage reference value exceeds the preset voltage threshold, then the DC bus voltage target value is set to the preset maximum value. If the comparison result shows that the output voltage reference value does not exceed the preset voltage threshold, then the target value of the DC bus voltage is calculated according to the preset formula.

3. The method according to claim 1, characterized in that, Adjusting the output of the phase-controlled rectifier until the actual bus voltage meets the DC bus voltage requirement includes: The direction of the deviation is obtained based on the deviation between the actual bus voltage and the target value of the DC bus voltage; If the deviation direction is that the actual bus voltage is lower than the target value of the DC bus voltage, then reduce the firing angle of the thyristors in the phase-controlled rectifier to obtain an increased actual bus voltage; If the deviation direction is that the actual bus voltage is higher than the target value of the DC bus voltage, then increase the firing angle of the thyristors in the phase-controlled rectifier to obtain a reduced actual bus voltage; Repeatedly adjust the output of the phase-controlled rectifier until the deviation between the actual bus voltage and the target value of the DC bus voltage does not exceed the preset bus voltage deviation threshold.

4. The method according to claim 1, characterized in that, The three-level inverter is a neutral-point clamped three-level inverter, comprising four power switching transistors and two clamping diodes; the step of controlling the output AC voltage of the three-level inverter according to the initial duty cycle to obtain the actual output voltage of the power conversion unit includes: Based on the initial duty cycle and the DC bus voltage, a timing combination of three output states—positive level, zero level, and negative level—is obtained. The output AC voltage is obtained by controlling the on and off of the four power switching transistors according to the timing combination.

5. The method according to claim 1, characterized in that, When the deviation between the actual output voltage of a certain power conversion unit and the output voltage reference value is detected to exceed a preset fault threshold, the method further includes: Based on the deviation exceeding the preset fault threshold, the corresponding level is marked as an abnormal level; Based on the position of the abnormal stage in the series connection, while keeping the electrical connection state between the abnormal stage and other normal stages unchanged, the actual output voltage after compensation is obtained by gradually fine-tuning the duty cycle of the three-level inverter of the abnormal stage. Based on the update deviation between the compensated actual output voltage and the output voltage reference value, determine whether the update deviation has been reduced to within the preset fault threshold. If the update deviation is not reduced to within the preset fault threshold after a preset number of fine adjustments, the bypass switch is controlled according to the position of the abnormal level to remove the abnormal level from the series connection, and the remaining normal level sequence is obtained. Based on the difference between the total output voltage reference value and the sum of the actual output voltages of the remaining normal stages, the output voltage reference value allocation scheme for each remaining normal stage is recalculated to obtain the updated output voltage reference values ​​for each stage.

6. A neutral-beam ultra-high voltage power supply system, characterized in that, include: Power grid supply end; At least one phase-shifting transformer, the input terminal of which is electrically connected to the power grid supply terminal; The series-connected multi-stage power conversion unit includes a phase-controlled rectifier and a three-level inverter connected in sequence. The input terminal of the phase-controlled rectifier is electrically connected to the output terminal of the phase-shifting transformer. The output terminal of the three-level inverter of each stage of the power conversion unit serves as the high-voltage DC output terminal of each stage, and the high-voltage DC output terminals of each stage are connected in series to form the total high-voltage DC output terminal of the system. The control system is electrically connected to each stage of the phase-controlled rectifier and each stage of the three-level inverter. The control system determines the target DC bus voltage of the phase-controlled rectifier in each stage based on a comparison between the output voltage reference value and a preset voltage threshold. It adjusts the output of the phase-controlled rectifier according to the deviation between the actual bus voltage and the target DC bus voltage until the actual bus voltage reaches the target DC bus voltage. After the actual bus voltage of each stage reaches the target DC bus voltage, it calculates the initial duty cycle of the three-level inverter in each stage based on the output voltage reference value and the adjusted actual bus voltage. It controls the output AC voltage of the three-level inverter according to the initial duty cycle to obtain the actual output voltage of each stage. When the deviation between the actual output voltage and the output voltage reference value does not meet the output voltage requirement, it adjusts the duty cycle of the three-level inverter in each stage sequentially from the starting stage to the ending stage in the series connection until the actual output voltage of each stage meets the output voltage requirement.

7. The system according to claim 6, characterized in that, The at least one phase-shifting transformer includes two phase-shifting transformers; the input terminals of the two phase-shifting transformers are electrically connected to the power grid supply terminal, and the output terminals are electrically connected to the input terminals of each stage of the phase-controlled rectifier, and the output AC current of the two phase-shifting transformers has a 15-degree phase difference.

8. The system according to claim 6, characterized in that, Each power conversion unit also includes two choke inductors and two DC filter capacitors; the two choke inductors are connected in series in the positive and negative branches of the DC output terminal of the phase-controlled rectifier, respectively, and the two DC filter capacitors are connected in parallel between the positive and negative terminals, forming a two-stage inductor-capacitor filter structure to suppress current ripple and voltage ripple of the DC bus voltage.

9. The system according to claim 6, characterized in that, The three-level inverter is a neutral-point clamped three-level inverter. Each stage of the three-level inverter includes a first upper-arm fully controlled device, a second upper-arm fully controlled device, a first lower-arm fully controlled device, a second lower-arm fully controlled device, an upper half-arm clamping diode, a lower half-arm clamping diode, and a DC bus midpoint, wherein: The collector of the first upper arm fully controlled device is connected to the positive terminal of the DC bus, and the emitter is connected to the collector of the second upper arm fully controlled device. The emitter of the second upper arm fully controlled device serves as the AC output terminal of the three-level inverter. The collector of the first lower bridge arm fully controlled device is connected to the AC output terminal of the three-level inverter, and the emitter is connected to the collector of the second lower bridge arm fully controlled device. The emitter of the second lower bridge arm fully controlled device is connected to the negative terminal of the DC bus. The anode of the upper half-bridge arm clamping diode is connected to the midpoint of the DC bus, and the cathode is connected to the connection point between the emitter of the first upper half-bridge arm fully controlled device and the collector of the second upper half-bridge arm fully controlled device. The cathode of the lower half-bridge arm clamping diode is connected to the midpoint of the DC bus, and the anode is connected to the connection point between the emitter of the first lower half-bridge arm fully controlled device and the collector of the second lower half-bridge arm fully controlled device. By combining the on and off states of the first upper bridge arm control device, the second upper bridge arm control device, the first lower bridge arm control device, and the second lower bridge arm control device, a positive level state, a zero level state, and a negative level state are output. The positive level is half of the DC bus voltage, the zero level is zero, and the negative level is half of the negative DC bus voltage.

10. The system according to claim 6, characterized in that, Each power conversion unit also includes a step-up transformer and a rectifier and filter unit that are electrically connected in sequence to the output of the three-level inverter. The rectifier and filter unit includes a high-voltage uncontrolled rectifier and an RC filter circuit. The RC filter circuit is composed of a filter resistor and a filter capacitor connected in series. The control system includes a bus voltage detection unit, an output voltage detection unit, and a step-by-step adjustment control unit. The input terminal of the bus voltage detection unit is electrically connected to the DC bus output terminal of each stage phase-controlled rectifier to collect the actual bus voltage. The input terminal of the output voltage detection unit is electrically connected to the output terminal of each stage RC filter circuit to collect the actual output voltage. The input terminal of the step-by-step adjustment control unit is electrically connected to the output terminals of the bus voltage detection unit and the output terminal of the output voltage detection unit, respectively. The output terminal of the step-by-step adjustment control unit is electrically connected to the trigger terminal of each stage phase-controlled rectifier and the switching transistor control terminal of each stage three-level inverter, respectively, to calculate the duty cycle and perform step-by-step adjustment.

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