A method and system for derating control of a bridge arm multiplexing converter

Abstract

The application discloses a capacity reduction control method and system for a bridge arm multiplexing converter, and belongs to the technical field of converter control. The method is as follows: obtaining a current three-phase modulation wave and calculating a current modulation ratio; when the current modulation ratio meets a preset first boundary interval, obtaining a first target three-phase modulation wave according to the current modulation ratio, a preset implicit function equation and the current three-phase modulation wave, so as to perform capacity reduction control on the bridge arm multiplexing converter according to the first target modulation wave; when the current modulation ratio meets a preset second boundary interval, setting a double-frequency circulating current amplitude reference value according to a preset value, obtaining a second target three-phase modulation wave based on the current modulation ratio, the double-frequency circulating current amplitude reference value, an alternating current side fundamental wave current amplitude, a preset bridge arm cycle energy balance constraint and the current three-phase modulation wave, so as to perform capacity reduction control on the bridge arm multiplexing converter according to the second target modulation wave, and realizing differentiated capacity reduction control in different modulation ratio intervals.

Description

Technical Field

[0001] This invention relates to the field of converter control technology, and in particular to a derating control method and system for a bridge arm multiplexer converter. Background Technology

[0002] High-power energy storage emergency power supplies, as mobile power supply devices with rapid response capabilities, have broad application prospects in various emergency power supply scenarios. Modular multilevel converters, with their advantages of high modularity, strong scalability, and low output harmonic content, have been widely used in high-voltage power conversion and energy storage power supply fields. Traditional modular multilevel converters have two bridge arms per phase unit, resulting in low overall submodule utilization and high converter size and cost, making them difficult to adapt to the space constraints of vehicle-mounted mobile scenarios. To reduce the capacitance value of submodules and achieve converter lightweighting, existing technologies typically use circulating current components to suppress submodule capacitor voltage fluctuations, and there are also related control schemes that widen the modulation operating range by injecting third-harmonic common-mode voltage.

[0003] However, the aforementioned derating control schemes are constrained by the energy balance conditions of the bridge arm cycle, and can only achieve good capacitor voltage fluctuation suppression under fixed modulation ratio conditions. They cannot adapt to the operational requirements of wide-range power regulation in emergency power supplies. When the modulation ratio changes dynamically with the load power, the capacitor derating effect will significantly decrease. Furthermore, existing derating control does not design interval-specific adaptation strategies for the topology characteristics of bridge arm multiplexed converters. The coordination method between third-harmonic voltage injection and circulating current derating control is simplistic, making it difficult to maintain a stable capacitor derating effect across a wide modulation ratio range. This restricts the widespread application of bridge arm multiplexed converters in high-power emergency power supply scenarios. Summary of the Invention

[0004] This invention provides a derating control method and system for bridge arm multiplexed converters, which can solve the technical problems in the prior art where the traditional single third-harmonic injection strategy cannot be adapted to the wide modulation ratio operating range of bridge arm multiplexed converters and the submodule capacitor voltage ripple suppression effect is insufficient, and realize differentiated derating control in different modulation ratio ranges.

[0005] This invention provides a derating control method for a bridge arm multiplexer converter, applicable to a bridge arm multiplexer converter, the method comprising: The inner loop current control calculation is performed on the pre-acquired three-phase AC side voltage, three-phase AC side current, active power command and reactive power command to obtain the current three-phase modulation wave; The current modulation ratio is calculated based on the real-time acquired fundamental voltage amplitude and DC bus voltage. When the current modulation ratio is determined to meet the preset first boundary interval, the first third harmonic voltage injection coefficient is calculated according to the current modulation ratio and the preset implicit function equation. The first target three-phase modulation wave is obtained based on the first third harmonic voltage injection coefficient and the current three-phase modulation wave. The bridge arm multiplex converter is then de-capacitated according to the first target modulation wave. When the current modulation ratio is determined to meet the preset second boundary interval, the second harmonic circulating current amplitude reference value is set according to the preset value. The second harmonic voltage injection coefficient is calculated based on the current modulation ratio, the second harmonic circulating current amplitude reference value, the AC side fundamental current amplitude, and the preset bridge arm periodic energy balance constraint. The second target three-phase modulation wave is obtained based on the second harmonic voltage injection coefficient and the current three-phase modulation wave. The bridge arm multiplexed converter is then derated according to the second target modulation wave.

[0006] The above-mentioned scheme proposes a segmented derating control method applicable to bridge arm multiplexed converters. First, a basic three-phase modulation wave is generated by inner-loop current control and the real-time modulation ratio is calculated. Then, based on the two preset boundary intervals of the modulation ratio, the third-harmonic voltage injection coefficient is calculated using two rules: implicit function equation and bridge arm periodic energy balance constraint. The coefficients are then superimposed to generate the corresponding target modulation wave to perform derating control. This solves the technical problems that the traditional single third-harmonic injection strategy cannot adapt to the wide modulation ratio operating range of bridge arm multiplexed converters and the sub-module capacitor voltage ripple suppression effect is insufficient, thus realizing differentiated derating control in different modulation ratio intervals.

[0007] Further, when the current modulation ratio determines that it conforms to a preset first boundary interval, a first third harmonic voltage injection coefficient is calculated based on the current modulation ratio and a preset implicit function equation. A first target three-phase modulation wave is obtained based on the first third harmonic voltage injection coefficient and the current three-phase modulation wave. Then, based on the first target modulation wave, bridge arm layered voltage division and submodule switching drive actions are performed to derating control of the bridge arm multiplexed converter; including: When the current modulation ratio determines that it conforms to a preset first boundary interval: The first third harmonic voltage injection coefficient is calculated based on the current modulation ratio and the preset implicit function equation; The first third harmonic voltage is determined based on the first third harmonic voltage injection coefficient; The first third harmonic voltage is superimposed on the current three-phase modulated wave to obtain the first target three-phase modulated wave; The bridge arm layered voltage division and submodule switching drive actions are executed according to the first target modulation wave to perform derating control on the bridge arm multiplexed converter.

[0008] Furthermore, after performing derating control on the bridge arm multiplexer converter according to the first target modulation wave, the method further includes: Real-time acquisition of AC side current amplitude, current three-phase AC side voltage, and current three-phase AC side current; Calculate the power factor angle based on the current three-phase AC side voltage and the current three-phase AC side current; The target second harmonic circulating current amplitude reference value and phase reference value are calculated based on the first third harmonic voltage injection coefficient, the current modulation ratio, and the power factor angle. The target second harmonic circulating current amplitude reference value and phase reference value are converted into a second harmonic compensation voltage. The second harmonic compensation voltage is then superimposed on the three-phase bridge arm circuit of the bridge arm multiplexer to cancel the circulating current of the bridge arm multiplexer.

[0009] Further, the calculation of the target second harmonic circulating current amplitude reference value and phase reference value based on the first third harmonic voltage injection coefficient, the current modulation ratio, and the power factor angle includes: For any single-phase bridge arm unit in the bridge arm multiplex converter; A simultaneous solution function is constructed based on the preset second harmonic power pulsation complete cancellation constraint and the preset bridge arm period energy balance constraint. Substituting the first third harmonic voltage injection coefficient, the current modulation ratio, the power factor angle, and the AC side fundamental current amplitude into the simultaneous solution function, the target second harmonic circulating current amplitude reference value and phase reference value are obtained.

[0010] The above solution, based on the third harmonic injection derating, adds a second harmonic circulating current cancellation control process. By collecting the operating parameters of the bridge arm submodule and the AC side, the power factor angle is calculated. Combined with the third harmonic injection coefficient, the current modulation ratio, and other parameters, the amplitude and phase reference values ​​of the target second harmonic circulating current are solved. This is converted into a second harmonic compensation voltage and superimposed on the three-phase bridge arm circuit to actively cancel the second harmonic power pulsation component in the bridge arm. This further reduces the voltage fluctuation rate of the submodule capacitor and solves the technical problem that the third harmonic voltage injection will introduce additional second harmonic power pulsation and aggravate the voltage fluctuation of the submodule capacitor.

[0011] Furthermore, it also includes: When the current modulation ratio enters the preset transition interval from the preset first boundary interval, the target second harmonic circulating current amplitude reference value is subjected to attenuation smoothing switching processing based on the current modulation ratio until the target second harmonic circulating current amplitude reference value is switched to the second harmonic circulating current amplitude reference value. When the current modulation ratio enters the preset transition interval from the preset second boundary interval, the second harmonic current amplitude reference value is subjected to a rising smooth switching process based on the current modulation ratio until the second harmonic current amplitude reference value is switched to the target second harmonic current amplitude reference value.

[0012] The above scheme adds a smooth switching mechanism for modulation ratio operation across intervals. When the modulation ratio enters the preset transition interval from the first boundary interval or the second boundary interval, a smooth switching process of attenuation or increase is performed on the reference value of the second harmonic circulating current amplitude, so as to realize the smooth transition between the two control modes without impact, effectively improve the dynamic stability of the converter operating across intervals, and solve the technical problem of sudden change of second harmonic circulating current when the modulation ratio fluctuates at the interval boundary, which causes bridge arm current impact and capacitor voltage oscillation.

[0013] Furthermore, the bridge arm multiplexing converter includes three single-phase bridge arm units, each of which includes several bridge arm sub-modules and several redundant sub-modules, and further includes: Real-time acquisition of the operating data of several bridge arm sub-modules corresponding to several bridge arm sub-modules; obtaining the total number of single-phase fault modules based on the operating data of several bridge arm sub-modules; and identifying several faulty bridge arm sub-modules. When the total number of single-phase fault modules determines that the preset first level of fault tolerance conditions are met, a sub-module voltage constant command is output, and based on the sub-module voltage constant command, several faulty bridge arm sub-modules are replaced with several redundant sub-modules to perform fault tolerance on the bridge arm multiplexed converter. When the total number of single-phase fault modules determines that the preset second-level fault tolerance condition is met, the fault module disconnection action is performed on several faulty bridge arm sub-modules. The sub-module operating voltage and the current number of operating sub-modules are calculated based on the total number of single-phase fault modules and the DC bus voltage. The bridge arm multiplex converter is then derated according to the sub-module operating voltage and the current number of operating sub-modules. When the total number of single-phase fault modules determines that the preset third-level fault tolerance condition is met, a safe shutdown action is triggered on the bridge arm multiplex converter.

[0014] The above scheme proposes a hierarchical fault-tolerant control process. By collecting the operating data of each bridge arm submodule in real time, the total number of single-phase faulty modules is counted. Three levels of fault tolerance conditions are matched according to the number of faults, and hierarchical processing is performed respectively: replacement of redundant submodules, submodule boosting and derating operation, and triggering safe shutdown. By constructing a multi-level fault tolerance mechanism, the fault tolerance capability of the converter is improved. The system can be stably operated or safely shut down under different fault levels, improving the overall operational reliability. This solves the technical problems of traditional redundancy fault tolerance strategies having a single level, the system being unable to continue operating after the redundant submodules are exhausted, and insufficient operational reliability.

[0015] This invention provides a derating control system for a bridge arm multiplexer converter, applicable to a bridge arm multiplexer converter, comprising a modulation calculation module and a third-harmonic voltage injection module, wherein: The modulation calculation module is used to perform inner-loop current control calculations on the pre-acquired three-phase AC side voltage, three-phase AC side current, active power command, and reactive power command to obtain the current three-phase modulation wave; and to calculate the current modulation ratio based on the real-time acquired fundamental voltage amplitude and DC bus voltage. The third-harmonic voltage injection module is used to calculate the first third-harmonic voltage injection coefficient according to the current modulation ratio and the preset implicit function equation when the current modulation ratio determines that it meets the preset first boundary interval. Based on the first third-harmonic voltage injection coefficient and the current three-phase modulation wave, the first target three-phase modulation wave is obtained, and the bridge arm multiplexed converter is de-capacitated according to the first target modulation wave. The third-harmonic voltage injection module is also used to, when the current modulation ratio determines that the current condition meets the preset second boundary interval, set a second harmonic circulating current amplitude reference value according to a preset value, calculate a second third harmonic voltage injection coefficient based on the current modulation ratio, the second harmonic circulating current amplitude reference value, the AC side fundamental current amplitude, and the preset bridge arm periodic energy balance constraint, obtain a second target three-phase modulation wave based on the second third harmonic voltage injection coefficient and the current three-phase modulation wave, and then perform derating control on the bridge arm multiplexed converter according to the second target modulation wave.

[0016] The above scheme constructs a derating control system adapted to bridge arm multiplexed converters. A modulation calculation module is set up to complete the generation of basic three-phase modulation waves and real-time modulation ratio calculation. A third-harmonic voltage injection module is set up to calculate the third-harmonic injection coefficients and generate target modulation waves according to two preset modulation ratio intervals, and execute interval-based derating control. Through modular functional units, interval-based differentiated third-harmonic injection control is realized, which broadens the applicability of derating control and provides a stable system execution carrier for wide-range derating operation of bridge arm multiplexed converters.

[0017] Furthermore, the system also includes a second-harmonic circulating current control module, wherein: The second harmonic circulating current control module is used after the third harmonic voltage injection module performs derating control on the arm-type multiplexer converter according to the first target modulation wave: real-time acquisition of AC side current amplitude, current three-phase AC side voltage, and current three-phase AC side current; calculation of power factor angle based on the current three-phase AC side voltage and current; calculation of target second harmonic circulating current amplitude reference value and phase reference value based on the first third harmonic voltage injection coefficient, current modulation ratio, and power factor angle; conversion of the target second harmonic circulating current amplitude reference value and phase reference value into second harmonic compensation voltage, and superimposition of the second harmonic compensation voltage in the three-phase arm circuit of the arm-type multiplexer converter to perform circulating current cancellation on the arm-type multiplexer converter.

[0018] Furthermore, the bridge arm multiplexing converter includes three single-phase bridge arm units, each of which includes several bridge arm sub-modules and several redundant sub-modules. The system also includes a fault-tolerant control module, wherein: The fault-tolerant control module is used to acquire in real time the operating data of several bridge arm sub-modules corresponding to several bridge arm sub-modules, obtain the total number of single-phase fault modules based on the operating data of several bridge arm sub-modules, and determine several faulty bridge arm sub-modules; when it is determined that the total number of single-phase fault modules meets the preset first level of fault tolerance conditions, a sub-module voltage constant command is output, and several faulty bridge arm sub-modules are replaced with several redundant sub-modules based on the sub-module voltage constant command to perform fault tolerance on the bridge arm multiplexed converter; when it is determined that the total number of single-phase fault modules meets the preset second level of fault tolerance conditions, a fault module disconnection action is performed on several faulty bridge arm sub-modules, and the sub-module operating voltage and the current number of operating sub-modules are calculated based on the total number of single-phase fault modules and the DC bus voltage, thereby adjusting the bridge arm multiplexed converter to derated operation based on the sub-module operating voltage and the current number of operating sub-modules; when it is determined that the total number of single-phase fault modules meets the preset third level of fault tolerance conditions, a safe shutdown action is triggered on the bridge arm multiplexed converter.

[0019] Furthermore, the bridge arm multiplexer includes three single-phase bridge arm units. The system also includes an energy management module, a DC bus, and several overcharge ports, wherein: The DC bus is provided with several tap nodes that are electrically connected to several of the supercharging ports. Each of the single-phase bridge arm units is provided with several distribution switch nodes; A plurality of distribution switch nodes are electrically connected to the first terminals of a plurality of distribution switches, and the second terminals of a plurality of distribution switches are electrically connected to a plurality of supercharging ports; The energy management module is electrically connected to the control terminals of the distribution switches respectively; The energy management module is used to obtain the voltage requirement of the access load, output the distribution switch control command according to the voltage requirement of the access load, and control the target distribution switch in several distribution switch nodes to close based on the distribution switch control command, thereby forming the current access submodule group loop, and charging the access load through the current access submodule group loop.

[0020] The above solution adds a dynamic allocation function to the derating control system through the supercharging port. By setting tap nodes on the DC bus, configuring distribution switches and energy management modules, the target distribution switch is closed according to the required voltage of the connected load, forming a corresponding sub-module group circuit to charge the load. It can quickly match connected loads of different voltage levels, realize DC charging output of multiple voltage levels, effectively improve the system's scenario adaptability and application flexibility, and solve the technical problem that bridge arm multiplexed converters cannot adapt to the charging needs of loads of different voltage levels. Attached Figure Description

[0021] To more clearly illustrate the technical solution of this application, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0022] Figure 1 This is a schematic diagram of a derating control method for a bridge arm multiplexer converter provided in this embodiment; Figure 2 This is a schematic diagram of a DC supercharging port dynamic allocation device provided in this embodiment; Figure 3 This embodiment provides a schematic diagram of the three-phase main circuit topology of a bridge arm reusable modular multilevel converter derating control and fault tolerance system for a high-power charging and storage emergency power supply vehicle. Figure 4 This is a schematic diagram of a single-bridge arm submodule topology provided in this embodiment. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0024] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0025] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0026] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0027] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0028] In the description of the embodiments of this application, the term "multiple" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces).

[0029] In the description of the embodiments of this application, unless otherwise expressly specified and limited, technical terms such as "installation," "connection," "joining," and "fixing" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. For those skilled in the art, the specific meaning of the above terms in the embodiments of this application can be understood according to the specific circumstances.

[0030] Example 1: like Figure 1As shown, this embodiment provides a derating control method for a bridge arm multiplexer converter, applied to a bridge arm multiplexer converter. The method includes: S1. Perform inner loop current control calculations on the pre-acquired three-phase AC side voltage, three-phase AC side current, active power command, and reactive power command to obtain the current three-phase modulation wave; S2. Calculate the current modulation ratio based on the real-time acquired fundamental voltage amplitude and DC bus voltage; S3. When the current modulation ratio is determined to meet the preset first boundary interval, the first third harmonic voltage injection coefficient is calculated according to the current modulation ratio and the preset implicit function equation. The first target three-phase modulation wave is obtained based on the first third harmonic voltage injection coefficient and the current three-phase modulation wave. The bridge arm multiplex converter is then de-capacitated according to the first target modulation wave. S4. When the current modulation ratio is determined to meet the preset second boundary interval, the second harmonic circulating current amplitude reference value is set according to the preset value. The second harmonic voltage injection coefficient is calculated based on the current modulation ratio, the second harmonic circulating current amplitude reference value, the AC side fundamental current amplitude, and the preset bridge arm periodic energy balance constraint. The second target three-phase modulation wave is obtained based on the second harmonic voltage injection coefficient and the current three-phase modulation wave. The bridge arm multiplexed converter is then derated according to the second target modulation wave.

[0031] In specific implementation, this embodiment is applied to a bridge arm multiplexed converter using a bridge arm multiplexed modular multilevel converter (AM-MMC) topology. This topology includes three single-phase bridge arm units: phase A, phase B, and phase C. Each single-phase bridge arm unit consists of three bridge arms: an upper bridge arm, a multiplexed bridge arm, and a lower bridge arm. Through time-division multiplexing technology, the redundant submodules of the multiplexed bridge arm can be used as common backups for both the upper and lower bridge arms simultaneously. This reduces the total number of bridge arm submodules by 25% while increasing the submodule utilization rate to 66.7% under the same level, significantly reducing the converter size. It is suitable for vehicle-mounted installation and avoids low submodule utilization and large system size.

[0032] Define the first third-harmonic voltage injection coefficient as: The current modulation ratio is m. When m∈[1.22,1.30], it is determined that the preset first boundary interval is met, and the circulating current control mode is adopted. The preset implicit function equation is: And (0≤k≤0.408), the specific design idea of ​​this preset implicit function equation will be elaborated in Embodiment 2, and will not be repeated here. When m∈[1.34,1.414], it is determined that it meets the preset second boundary interval, and the circulation suppression mode is adopted. At this time, the first third harmonic voltage injection coefficient is obtained according to the preset bridge arm periodic energy balance constraint. satisfy =6(1-0.5m²) / m². The specific design idea of ​​this formula will be elaborated in Example 2, and will not be repeated here.

[0033] Determining the first and third harmonic voltage injection coefficients Or the second or third harmonic voltage injection coefficient Then, based on the first third harmonic voltage injection coefficient Or the second or third harmonic voltage injection coefficient A third harmonic zero-sequence voltage (i.e., the first third harmonic voltage or the second third harmonic voltage) is superimposed on the fundamental frequency modulation wave (i.e., the current three-phase modulation wave) to form a saddle wave (i.e., the first target three-phase modulation wave or the second target three-phase modulation wave). After adding the third harmonic zero-sequence voltage, the modulation wave changes from a sine wave to a saddle wave, and the maximum value it needs to reach is reduced, which can indirectly improve the utilization rate of DC voltage and increase the modulation ratio.

[0034] Optionally, the step of performing inner-loop current control calculations on the pre-acquired three-phase AC side voltage, three-phase AC side current, active power command, and reactive power command to obtain the current three-phase modulation waveform includes: obtaining active voltage, reactive voltage, active current, and reactive current based on the pre-acquired three-phase AC side voltage and three-phase AC side current; calculating active power and reactive power based on the active voltage, reactive voltage, active current, and reactive current; performing outer-loop power conversion on the pre-acquired active power command based on the active power and reactive power to obtain an active current command; performing outer-loop power conversion on the pre-acquired reactive power command based on the active power and reactive power to obtain a reactive current command; performing inner-loop current control calculations on the active current command, reactive current command, active current, reactive current, and the pre-acquired grid angular frequency and AC side equivalent inductance to obtain a three-phase fundamental modulation voltage command; and performing an inverse Parker transformation on the three-phase fundamental modulation voltage command to obtain the current three-phase modulation waveform.

[0035] In the specific implementation process, the three-phase AC side voltage is transformed into the synchronous rotating dq coordinate system to obtain the active voltage. reactive voltage and active current reactive current The active power P and reactive power Q can then be calculated as follows: ; Then the active power command is transmitted through the power outer loop. Reactive power command Convert to active current command and reactive current command As shown in the following formula: ; in, , , and These are the parameters set for the PI regulator in the overpower outer loop.

[0036] Then, the active current command and reactive current command are converted into a three-phase fundamental frequency modulated voltage command through the current inner loop control. and That is, the current three-phase modulation wave.

[0037] ; Where ω is the pre-acquired grid angular frequency, and L is the AC side equivalent inductance.

[0038] Finally and The current three-phase modulated wave in the stationary coordinate system is obtained by inverse Park transformation (i.e., the inverse Park transformation).

[0039] Optionally, when the current modulation ratio determines that the signal meets a preset first boundary interval, a first third-harmonic voltage injection coefficient is calculated based on the current modulation ratio and a preset implicit function equation. A first target three-phase modulation wave is obtained based on the first third-harmonic voltage injection coefficient and the current three-phase modulation wave. Then, based on the first target modulation wave, bridge arm layered voltage division and submodule switching drive actions are performed to derating control of the bridge arm multiplexed converter; including: When the current modulation ratio determines that it conforms to a preset first boundary interval: The first third harmonic voltage injection coefficient is calculated based on the current modulation ratio and the preset implicit function equation; The first third harmonic voltage is determined based on the first third harmonic voltage injection coefficient; The first third harmonic voltage is superimposed on the current three-phase modulated wave to obtain the first target three-phase modulated wave; The bridge arm layered voltage division and submodule switching drive actions are executed according to the first target modulation wave to perform derating control on the bridge arm multiplexed converter.

[0040] In the specific implementation process, the injected third-harmonic voltage for: ;in, The amplitude of the third harmonic voltage. The initial phase angle is the third harmonic voltage. In this embodiment, the initial phase of the zero-sequence voltage is set to be the same as the initial phase angle of phase A. Indicates the angular frequency of the power grid. =2πf, where f is the fundamental frequency of the power grid.

[0041] It should be noted that in bridge arm multiplexed (modular multilevel) converters, by adjusting... and This can break the strong binding relationship between the original modulation ratio and the amplitude and phase of the second harmonic circulating current, offset the second harmonic power pulsation of the bridge arm, widen the modulation ratio range in which the converter can operate stably, and reduce the voltage fluctuation rate of the submodule capacitor.

[0042] Optionally, after performing derating control on the bridge arm multiplexer converter according to the first target modulation wave, the method further includes: Real-time acquisition of AC side current amplitude, current three-phase AC side voltage, and current three-phase AC side current; Calculate the power factor angle based on the current three-phase AC side voltage and the current three-phase AC side current; The target second harmonic circulating current amplitude reference value and phase reference value are calculated based on the first third harmonic voltage injection coefficient, the current modulation ratio, and the power factor angle. The target second harmonic circulating current amplitude reference value and phase reference value are converted into a second harmonic compensation voltage. The second harmonic compensation voltage is then superimposed on the three-phase bridge arm circuit of the bridge arm multiplexer to cancel the circulating current of the bridge arm multiplexer.

[0043] It should be noted that the power factor angle It is the phase difference between the AC side voltage and current, determined by the load characteristics. This occurs when an emergency power vehicle is connected to the grid or charging an electric vehicle. The power factor angle reflects the ratio of active power to reactive power transmitted by the system. The angle between active power and apparent power is calculated using the following formula: .

[0044] In the specific implementation process, the second harmonic circulating current reference value and phase reference value Calculate using the following formula: ; Power factor λ=cos When the power factor λ is 1, the calculation process for the second harmonic circulating current reference value can be simplified to: ; When the power factor λ is not equal to 1, the following vector synthesis algorithm is used for calculation: .

[0045] This embodiment introduces a second-harmonic circulating current injection control method in a bridge arm multiplexed modular multilevel converter. By solving for the amplitude and phase of the second-harmonic circulating current adapted to the current operating conditions, it is injected into the bridge arm. This can completely suppress the second-harmonic fluctuation component contained in the average voltage of the sub-module to zero. Simulation and experimental verification show that the voltage fluctuation rate of the sub-module capacitor can be reduced by more than 75%, significantly reducing the capacitor voltage ripple amplitude, reducing the capacitor capacity selection requirements, and improving the bridge arm current stress.

[0046] Optionally, calculating the power factor angle based on the three-phase AC side voltage and the three-phase AC side current includes: obtaining active voltage, reactive voltage, active current, and reactive current based on the three-phase AC side voltage and the three-phase AC side current; calculating active power and reactive power based on the active voltage, reactive voltage, active current, and reactive current; and calculating the power factor angle based on the active power and reactive power.

[0047] Optionally, the calculation of the target second harmonic circulating current amplitude reference value and phase reference value based on the first third harmonic voltage injection coefficient, the current modulation ratio, and the power factor angle includes: For any single-phase bridge arm unit in the bridge arm multiplex converter; A simultaneous solution function is constructed based on the preset second harmonic power pulsation complete cancellation constraint and the preset bridge arm period energy balance constraint. Substituting the first third harmonic voltage injection coefficient, the current modulation ratio, the power factor angle, and the AC side fundamental current amplitude into the simultaneous solution function, the target second harmonic circulating current amplitude reference value and phase reference value are obtained.

[0048] In the specific implementation process, the pre-set constraint condition for complete cancellation of second harmonic power pulsation is as follows: ; The preset energy balance constraint for the bridge arm period is: ; Solving these equations simultaneously yields: .

[0049] Optional, also includes: When the current modulation ratio enters the preset transition interval from the preset first boundary interval, the target second harmonic circulating current amplitude reference value is subjected to attenuation smoothing switching processing based on the current modulation ratio until the target second harmonic circulating current amplitude reference value is switched to the second harmonic circulating current amplitude reference value. When the current modulation ratio enters the preset transition interval from the preset second boundary interval, the second harmonic current amplitude reference value is subjected to a rising smooth switching process based on the current modulation ratio until the second harmonic current amplitude reference value is switched to the target second harmonic current amplitude reference value.

[0050] It should be noted that in the circulating current suppression mode of this embodiment, the preset value of the second harmonic circulating current reference value is set to zero. By suppressing the second harmonic component in the circulating current, the capacitor voltage fluctuation rate is reduced by more than 60%.

[0051] In the specific implementation process, a preset transition range of 1.30 to 1.34 is set for the modulation ratio. When the current modulation ratio enters this transition range from the preset first boundary range, a smooth mode switch is triggered. Based on the real-time current modulation ratio, a decay-type smooth switching process is performed on the target second harmonic circulating current amplitude reference value, gradually transitioning the target second harmonic circulating current amplitude reference value to the steady-state second harmonic circulating current amplitude reference value. When the current modulation ratio enters this transition range from the preset second boundary range, a rising-type smooth switching process is performed on the steady-state second harmonic circulating current amplitude reference value based on the real-time current modulation ratio, gradually transitioning to the target second harmonic circulating current amplitude reference value. By replacing the hard-switching hysteresis logic with this segmented smooth transition logic, sudden changes in the arm circulating current can be avoided throughout the process, ensuring the stability of the converter during cross-multiplexing mode operation.

[0052] In the specific implementation process, this embodiment uses a derating controller to switch the operating mode (including circulating current control mode, circulating current suppression module and mode smooth switching) according to the current modulation ratio to realize the above-mentioned third harmonic injection and circulating current control regulation process.

[0053] It should be noted that this embodiment optimizes the traditional circulating current suppression strategy for bridge arm multiplexed modular multilevel converters by addressing the limitation of applicable operating conditions. While existing circulating current suppression strategies can reduce submodule capacitor voltage fluctuations, their stable operation relies on satisfying the periodic energy balance constraint between bridge arms. A strong coupling constraint exists between the modulation ratio and the amplitude and phase of the second harmonic circulating current, allowing for ideal capacitor fluctuation suppression only under a single fixed modulation ratio. When the active or reactive power command changes, the operating modulation ratio deviates from this fixed value, disrupting the periodic energy balance of the bridge arms and causing significant voltage imbalances in the submodule capacitors. Furthermore, the system cannot independently decouple and regulate active and reactive power. To address this deficiency and broaden the effective operating range of the circulating current suppression strategy, this embodiment superimposes a controllable amplitude third harmonic common-mode voltage onto the three-phase fundamental modulation wave. The third harmonic voltage injection coefficient is used as an independently adjustable control degree of freedom, and it works in conjunction with the second harmonic circulating current to collaboratively regulate the bridge arm energy distribution, ultimately achieving continuous and stable suppression of submodule capacitor voltage fluctuations across a wide modulation ratio operating range.

[0054] Optionally, the bridge arm multiplexing converter includes three single-phase bridge arm units, each of which includes several bridge arm sub-modules and several redundant sub-modules, and further includes: Real-time acquisition of the operating data of several bridge arm sub-modules corresponding to several bridge arm sub-modules; obtaining the total number of single-phase fault modules based on the operating data of several bridge arm sub-modules; and identifying several faulty bridge arm sub-modules. When the total number of single-phase fault modules determines that the preset first level of fault tolerance conditions are met, a sub-module voltage constant command is output, and based on the sub-module voltage constant command, several faulty bridge arm sub-modules are replaced with several redundant sub-modules to perform fault tolerance on the bridge arm multiplexed converter. When the total number of single-phase fault modules determines that the preset second-level fault tolerance condition is met, the fault module disconnection action is performed on several faulty bridge arm sub-modules. The sub-module operating voltage and the current number of operating sub-modules are calculated based on the total number of single-phase fault modules and the DC bus voltage. The bridge arm multiplex converter is then derated according to the sub-module operating voltage and the current number of operating sub-modules. When the total number of single-phase fault modules determines that the preset third-level fault tolerance condition is met, a safe shutdown action is triggered on the bridge arm multiplex converter.

[0055] In practical implementation, in any single-phase bridge arm unit of the bridge arm multiplexing converter, each bridge arm is composed of several bridge arm sub-modules (i.e., half-bridge sub-modules) connected in series. Each bridge arm sub-module integrates an energy storage battery unit and a capacitor. Switches K1 and K2 are respectively installed between the upper bridge arm and the multiplexing bridge arm, and between the multiplexing bridge arm and the lower bridge arm. By controlling the opening and closing of these switches, the multiplexing bridge arm can be connected in series with either the upper or lower bridge arm at different times, forming an equivalent upper bridge arm or an equivalent lower bridge arm, thus achieving time-division multiplexing. Within one power frequency cycle, when the equivalent upper bridge arm reference voltage is higher than the equivalent lower bridge arm reference voltage, the upper bridge arm multiplexing mode is used; otherwise, the lower bridge arm multiplexing mode is used. The common connection point of the upper bridge arms of the three single-phase bridge arm units forms the positive terminal of the DC bus, and the common connection point of the lower bridge arms forms the negative terminal of the DC bus. The DC bus voltage... The value is determined by the number of bridge arm submodules with constant input in each phase. M represents the number of submodules per bridge arm (including redundant submodules). This is the rated voltage of the bridge arm submodule.

[0056] In a specific implementation process, the present embodiment provides a bypass switch array for completing bypass operation of faulty sub-modules under fault conditions; the multiplexed bridge arm of the bridge-arm multiplexed modular multilevel converter in the present solution can call redundant sub-modules in the bridge arm in a time-division manner. Compared with the traditional MMC, in the present embodiment, the upper bridge arm, the multiplexed bridge arm and the lower bridge arm are each configured with redundant sub-modules accounting for 10% of the total number of the bridge arm, and the redundancy management unit performs hierarchical fault-tolerant control according to the numerical relationship between the number of faulty sub-modules N1 and the number of redundant sub-modules N2. The number of redundant sub-modules per phase unit satisfies N2=32N×10%, and the hierarchical fault-tolerant control strategy set in the present embodiment is as follows: When the first hierarchical fault-tolerant condition N1≤N is satisfied, a sub-module voltage constant command is output to execute a hot standby fault-tolerant strategy that maintains constant sub-module voltage, that is, hot standby redundant sub-modules are directly used to replace faulty sub-modules to put into operation, and the rated working voltage of the sub-modules remains unchanged; When the second hierarchical fault-tolerant condition N2<N1≤0.243N is satisfied, a fault-tolerant strategy for maintaining constant total bridge arm voltage is executed: the faulty module is directly cut off, the faulty bridge arm sub-modules are bypassed by using the bypass switch array, no additional redundant sub-modules are put into operation, the remaining healthy sub-modules jointly bear the DC bus voltage, and the working voltage of the sub-modules after adjustment is recalculated according to the current number of faults , and the control device is controlled to enter a derated operation state; When the third hierarchical fault-tolerant condition N1>0.243N is satisfied, the safety shutdown protection action of the bridge-arm multiplexed converter is directly triggered.

[0057] wherein the DC bus voltage satisfies the relational expression , in which N is the number of continuously put-in sub-modules per phase under rated working conditions, N2 is the number of redundant sub-modules, N1 is the number of faulty sub-modules, is the working voltage of the sub-modules after fault-tolerant adjustment. According to the specification, the maximum continuous operating voltage of the capacitor shall not exceed 1.15 times the rated voltage, that is, the constraint condition ≤1.15 , the sub-module voltage under rated working conditions , substituting it into the constraint inequality gives N1≤0.143N through derivation; comprehensively considering the redundant capacity and the capacitor voltage withstand limit, the maximum allowable total number of faulty sub-modules of a single bridge arm of the system N3=N2+0.143N=0.243N.

[0058] For example, in one embodiment, the rated number of submodules continuously operating in a single bridge arm is ten, with one redundant standby submodule configured accordingly, resulting in a total of one redundant submodule per bridge arm. When the total number of faulty submodules is no greater than the number of redundant submodules in a single bridge arm (i.e., only one faulty submodule occurs), the system executes the first-level fault-tolerant control logic. First, it closes the bypass switch associated with the faulty submodule to complete the faulty branch isolation. Then, it engages the hot standby redundant submodule within this bridge arm to replace the faulty module and participate in the operation, maintaining the rated operating voltage of the submodules constant throughout the process, and the overall output operating characteristics of the converter remain unaffected. If another faulty submodule subsequently occurs, and the total number of faults exceeds the number of redundant submodules in a single bridge arm, the system switches to execute the second-level fault-tolerant control logic. No new redundant standby submodules are added, and all remaining healthy submodules share the DC bus voltage. Under this condition, a total of twenty-eight healthy submodules participate in the voltage bearing. The actual operating voltage of the submodules is recalculated based on the total DC bus voltage and the current number of healthy submodules, and the equipment enters a derating operation state, still maintaining continuous external power supply. In this embodiment, the rated number of continuously engaged submodules per phase unit is twenty. The calculated maximum number of faulty submodules that the system can withstand is 24.3% of the total number of rated engaged submodules, corresponding to approximately 4.86 faults. When the total number of faulty submodules reaches five or more, exceeding the system's fault tolerance limit, the controller triggers a safe shutdown of the converter and outputs a fault alarm signal.

[0059] The hierarchical fault-tolerant control strategy designed in this embodiment adopts a hot standby replacement fault-tolerant mode that maintains constant submodule voltage when the number of faulty submodules is not greater than the number of redundant submodules in the system; when the number of faulty submodules is greater than the number of redundant submodules in the system, it switches to a fault-tolerant operation mode that maintains constant bridge arm voltage. The maximum number of faulty submodules that this hierarchical fault-tolerant scheme can withstand can reach 24.3% of the total number of submodules in the bridge arm.

[0060] It should be noted that this embodiment designs a hierarchical fault-tolerant control strategy for a bridge arm multiplexing modular multilevel converter. The total number of sub-modules in each of the upper bridge arm, multiplexing bridge arm, and lower bridge arm is denoted as M, of which the number of normally operating sub-modules continuously engaged under rated operating conditions is M1, and the number of redundant sub-modules configured in a single bridge arm satisfies M3 = 0.1M1. The redundant sub-arms within the multiplexing bridge arm can be time-division multiplexed, serving as backup for the upper bridge arm under multiplexing conditions and as backup for the lower bridge arm under multiplexing conditions. Compared with traditional MMC, the equivalent redundancy carrying capacity per phase unit is increased by 25%, and the total number of redundant sub-modules required for the same fault tolerance capacity is reduced by 25%.

[0061] In the specific implementation process, the control scheme of this embodiment is divided into four parts: The first part is a dual closed-loop control system, which adopts the control architecture of the traditional modular multilevel converter with an outer power loop and an inner current loop; the second part is to use a third-harmonic voltage injection module to calculate the amplitude and phase angle of the third-harmonic zero-sequence voltage based on the current modulation ratio, and to superimpose a third-harmonic zero-sequence voltage with an amplitude of k times the fundamental amplitude (0≤k≤0.408) onto the three-phase modulated wave; the third part is to use a second-harmonic circulating current control module to substitute the current modulation ratio and power factor angle into the corresponding simultaneous equations to solve the second-harmonic circulating current control module. The first part consists of a frequency-doubled circulating current amplitude reference value and a phase reference value. A dq transformation is applied to the second-harmonic circulating current reference value, followed by PI closed-loop regulation and an inverse Park transformation to generate the bridge arm common-mode voltage. Closed-loop control of the common-mode voltage ensures the actual circulating current tracks the reference value, offsetting the second-harmonic fluctuation component of the submodule capacitor voltage, reducing capacitor voltage fluctuation rate, and allowing for smaller capacitor values. The fourth part is the equivalent bridge arm modulation stage. Based on the bridge arm switching state, the equivalent bridge arm modulation wave is distributed to the upper bridge arm, multiplexed bridge arm, and lower bridge arm. This, combined with the submodule voltage equalization algorithm, outputs the drive signal for each submodule. Closed-loop regulation of the bridge arm common-mode voltage ensures the actual circulating current tracks the reference value, thereby suppressing the second-harmonic fluctuation component of the submodule capacitor voltage, reducing capacitor voltage fluctuation rate, and allowing the use of smaller capacitance values ​​for capacitors.

[0062] To address the limitations of traditional derating control, which operates only at a single modulation ratio and has a narrow applicability, this embodiment proposes a third-harmonic voltage injection and second-harmonic circulating current coupling control strategy. This strategy injects an adjustable-amplitude third-harmonic zero-sequence voltage into the bridge arm reference voltage, breaking the original constraint of the bridge arm energy balance condition on the modulation ratio. This expands the effective modulation ratio range of the second-harmonic circulating current suppression strategy from a fixed value of m=1.414 to 1.34–1.414, while simultaneously enabling stable operation of the circulating current control at a modulation ratio covering 1.22–1.3, effectively suppressing submodule capacitor voltage fluctuations over a wide operating range.

[0063] In summary, this embodiment provides an integrated solution for emergency power vehicles, applicable to high-power charging and storage emergency power vehicle technology scenarios. It enables derating control and fault tolerance of the bridge arm reusable MMC for high-power charging and storage emergency power vehicles, integrating and adapting the lightweight topology of the bridge arm reusable MMC, wide modulation ratio derating control, and hierarchical fault tolerance control to form a complete technical solution suitable for vehicle-mounted mobile energy storage charging and discharging conditions.

[0064] Example 2: This embodiment provides a design selection process for the third-harmonic voltage injection coefficient, specifically including: First, to determine the magnitude relationship between the third harmonic voltage and the fundamental frequency voltage, this embodiment defines the third harmonic voltage injection coefficient k as the amplitude of the injected third harmonic voltage. With fundamental frequency voltage amplitude The ratio: ; Taking phase A as an example, the expression for the target modulation wave (including the first target modulation wave and the second target modulation wave) after the injection of a third harmonic voltage is as follows: ; Simplifying it using the double-angle formula, we get: ; To obtain the maximum value, this embodiment differentiates the above equation and sets its derivative to 0. The corresponding extreme point should then satisfy the following equation: ; This yields the maximum value of the saddle wave. for: ; This shows that after adding a third harmonic voltage, the modulation ratio m becomes the original value. When k=0.408, the maximum value of the saddle wave is the same as the amplitude of the original fundamental function. Therefore, in order to improve the DC voltage utilization rate, the maximum value of the synthesized saddle wave needs to be smaller than the amplitude of the original fundamental function. The maximum amplitude of the added third harmonic voltage is 0.408 times the amplitude of the fundamental wave.

[0065] It should be noted that, under ideal conditions, the power on the DC side is completely transferred to the AC side, achieving power balance. In this case, the DC side current... and AC side current amplitude The following preset bridge arm period energy balance constraints should be met: .

[0066] In practical engineering, to ensure that no tri-frequency voltage appears on the AC side, this embodiment uses a third-harmonic zero-sequence voltage injection to maintain the phase of the injected voltage consistent with the phase of the fundamental frequency voltage. At this time, the phase of the third-harmonic voltage applied to each phase unit is the same. Based on this, the reference voltage of phase A of the converter after the third-harmonic voltage is applied is obtained. The expression is as follows: ; Phase A equivalent upper bridge arm voltage and equivalent lower bridge arm voltage It can be represented as follows: ; In AM-MMC's upper arm multiplexing mode, the upper arm and the multiplexed arm constitute an equivalent upper arm, which equally shares the reference voltage of the equivalent upper arm. The lower arm alone constitutes an equivalent lower arm, and the A-phase upper arm outputs an instantaneous voltage. Instantaneous output voltage of the lower bridge arm of phase A Instantaneous voltage of phase A forward multiplexing bridge arm Instantaneous voltage of phase A negative multiplexed bridge arm Instantaneous voltage of the intermediate multiplexed bridge arm of phase A The following equation should be satisfied: ; In the AM-MMC lower arm multiplexing mode, the following equation should be satisfied: ; In AM-MMC, the DC-side current is evenly distributed among the three-phase symmetrical arms. If we ignore the higher harmonic currents and only consider the second harmonic circulating current of the arms, the circulating current of the upper arm in the multiplexing mode can be expressed as follows: ; The bridge arm circulation in the lower bridge arm reuse mode can be expressed as follows: ; in, This represents the instantaneous circulating current of the upper arm of phase A (the component of the arm current that circulates only within the phase unit after removing the load current). This indicates the instantaneous circulation of the lower arm of phase A. This indicates the instantaneous circulation in the intermediate multiplex arm of phase A. This represents the constant DC current component input to the DC side, and is the DC reference component of the circulating current. This represents the amplitude of the second harmonic circulating current, i.e., the reference value for the target second harmonic circulating current amplitude. The initial phase angle represents the second harmonic circulation current, i.e., the phase reference value.

[0067] Based on the above formula, due to different electrical angle applications and different multiplexing modes: ;when At that time, the instantaneous power of the upper bridge arm is obtained. Satisfy the following formula: ; when At that time, the instantaneous power of the upper bridge arm was obtained. Satisfy the following formula: ; Under the premise that the converter can operate stably, the exchange power of the DC side and the AC side should be consistent, that is, to meet the preset bridge arm periodic energy balance constraint provided above. Within one operating cycle, the energy of each of the three bridge arms remains balanced. The instantaneous power expression structure of the three bridge arms in each phase unit is the same. Taking the upper bridge arm of phase A as an example for analysis, the following equation should be satisfied: ; Solving the above system of equations yields the following objective function: ; Therefore, this embodiment introduces a third-harmonic voltage injection strategy on the basis of the original control logic of the bridge arm multiplexed modular multilevel converter. After adopting this strategy, the modulation ratio and the amplitude and phase of the second harmonic circulating current in the system no longer maintain a unique coupling constraint relationship. The amplitude of the third harmonic voltage becomes an independent and adjustable control degree of freedom. By changing the amplitude of the third harmonic voltage injection, the energy balance constraint condition of the bridge arm period can be flexibly adjusted, and the strong binding relationship between the modulation ratio and the second harmonic circulating current can be released. This allows the converter to meet the energy balance requirements under different modulation ratio conditions, achieve stable operation over a wide modulation ratio range, and effectively solve the limitation that the traditional circulating current suppression strategy can only play a role under a single fixed modulation ratio.

[0068] After implementing derating control by injecting a third-harmonic voltage, this embodiment further implements circulating current control to achieve circulating current cancellation in order to reduce the voltage fluctuation rate of the bridge arm submodule.

[0069] First, define the switching functions for the three arms of each single-phase bridge arm unit. Taking phase A as an example, the switching functions for the three arms are as follows: ; in, , , These represent the average switching functions of the upper arm, multiplexed arm, and lower arm in the A-phase arm unit, respectively; N / 2 represents the number of arm sub-modules contained in each arm. , , These represent the switching state of the i-th bridge arm submodule in the upper bridge arm, multiplexed bridge arm, and lower bridge arm, respectively. When the switching function is 1, it indicates that the bridge arm submodule is in the operating state. When the switching function is 0, it indicates that the bridge arm submodule is in the off operating state. When the switching state function is -1, it indicates that the bridge arm submodule is in the negative level operating state.

[0070] Based on this, the voltage of each bridge arm can be expressed by a switching function as shown in the following equation: ; In the formula, , , These represent the capacitor voltages of the i-th sub-module of the upper, multiplexed, and lower bridge arms of phase A, respectively. , , These represent the AC fluctuation components in the voltage of the middle arm submodules of the upper, multiplexed, and lower arms of phase A, respectively. This represents the DC component of the capacitor voltage in each bridge arm submodule, typically the capacitor's rated voltage, which satisfies... .

[0071] In practical engineering applications, the number of bridge arm submodules is typically no less than 100, and the switching frequency is sufficiently high. Under this premise, when this embodiment adopts a third harmonic voltage injection strategy, the switching function of each bridge arm exhibits time-division multiplexing characteristics, and its spectrum contains only the fundamental frequency component and the third harmonic component. Based on the aforementioned calculation process, it can be obtained that during the upper bridge arm multiplexing period, the switching functions of the multiplexed bridge arm and the upper bridge arm are the same, as shown in the following formula: ; During the lower bridge arm reuse period, the switching functions of the reused bridge arm and the lower bridge arm are the same, as shown in the following formula: ; Therefore, in the upper arm multiplexing mode, the average submodule current of the three arms of phase A is... , and The following formulas are shown respectively: ; ; ; In the lower arm multiplexing mode, the average submodule current of the three arms of phase A is... , and The following formulas are shown respectively: ; ; ; Based on the preset bridge arm periodic energy balance constraint, it can be seen that the DC current component of the average current of each bridge arm submodule is 0, and the average current of each bridge arm submodule contains no DC component, only AC component, and the energy stored in the capacitor is in dynamic equilibrium. Due to the addition of third harmonic voltage injection, the average current of the bridge arm submodule generates new harmonic currents such as fourth and fifth harmonics, and the contents of the fundamental frequency current, second harmonic current, and third harmonic current also change.

[0072] It is important to clarify that the types of current harmonics in each bridge arm remain consistent across different times and bridge arms. Therefore, the types of harmonic voltages generated by harmonic currents on each bridge arm are also the same. Similar to traditional two-arm modular multilevel converters (MMCs), AM-MMCs typically introduce submodule voltage equalization control to ensure energy balance among submodules within the same bridge arm. A common voltage equalization strategy is based on a sorting algorithm to determine the switching state of submodules: during the bridge arm charging phase, submodules with lower voltages are prioritized for switching; during the discharging phase, submodules with higher voltages are prioritized for switching. With an average switching frequency maintained at approximately 200Hz, the deviation of the capacitor voltage of each submodule can typically be limited to within 3%. Therefore, the voltage of each submodule in the bridge arm can be approximated as equal to the average voltage of the submodule, thus using an average capacitor to represent the entire bridge arm.

[0073] When using an equivalent capacitance When replacing each bridge arm submodule, its expression can be written as follows: ; Where C represents the capacitance value of each bridge arm submodule.

[0074] definition , and These are the average submodule voltages of the three arms in a bridge arm multiplexed modular multilevel converter, and their expressions can be obtained by averaging the voltages of all submodules in the bridge arm: ; During the upper bridge arm reuse period, the current flowing through the upper bridge arm and the reused bridge arm is the same, and the calculated average voltage of the submodule is also the same. Substituting the current expression obtained earlier into the average voltage expression above, we can obtain: ; ; During the lower bridge arm reuse period, the current flowing through the lower bridge arm and the reused bridge arm is the same, and the calculated average voltage of the submodule is also the same. Substituting the current expression obtained earlier into the average voltage expression above, we can obtain: ; ; To minimize the voltage fluctuation of the submodules, analysis based on the aforementioned expression for the average voltage of the submodules shows that the second-order component accounts for the highest proportion of the average voltage of each bridge arm submodule. Therefore, this embodiment uses a method to suppress the second-order component in the submodule voltage by adjusting the second-order circulating current. When this component is controlled to zero, the following equation based on the preset constraint condition of complete cancellation of second-order power pulsation must be satisfied: ; Converting it to vector form yields the vector composition algorithm shown in the following equation: ; By simultaneously applying the pre-set second harmonic power pulsation complete cancellation constraint and the pre-set bridge arm period energy balance constraint, a simultaneous solution function is obtained, and solving it yields: ; If operating on the AC side under conditions where the power factor is always 1 and the power factor angle is always 0, the above equation can be simplified to the following relationship between the target second harmonic circulating current amplitude reference value and phase reference value and the first and third harmonic voltage injection coefficients and the current modulation ratio: ; Substituting the simplified result into the target solution function obtained earlier, we can obtain the preset implicit function equation for the first third harmonic voltage injection coefficient and the current modulation ratio as shown in the following equation: ; This indicates that, under ideal operating conditions, there is an implicit functional relationship between the amplitude of the injected third harmonic voltage and the modulation ratio. Furthermore, based on the solution process described earlier, to improve DC voltage utilization, the amplitude of the injected third harmonic voltage needs to be limited; specifically, its ratio k to the fundamental voltage amplitude should be controlled at 0. Within the range of 0.408. Under this condition, the second harmonic component in the average voltage of the submodule can be effectively suppressed by controlling the circulating current of the bridge arm, thereby reducing the voltage fluctuation rate of the submodule. After introducing the third harmonic voltage injection, the modulation ratio range for derating control of the converter is expanded to 1.22. 1.3 further verifies that the coupling control strategy has a wider range of applications and greater flexibility.

[0075] In practical applications, conventional circulating current suppression strategies can significantly reduce the voltage fluctuation amplitude of submodule capacitors in bridge arm multiplexed modular multilevel converters, effectively reducing voltage fluctuation rate. However, this control method is limited by bridge arm energy balance constraints, achieving ideal suppression effects only under a single fixed modulation ratio condition, resulting in a narrow applicable range and stringent requirements on system operating conditions. This embodiment additionally introduces a third-harmonic voltage injection control method, using the third-harmonic voltage amplitude as an independently adjustable control quantity. This decouples the strong relationship between the modulation ratio and the second-harmonic circulating current, effectively widening the modulation ratio range that can be covered by the converter's stable operation.

[0076] In practical implementation, the second harmonic is the main component of the circulating current in the bridge arm. In this embodiment, the circulating current suppression strategy used for circulating current cancellation is mainly to suppress the second harmonic circulating current in the bridge arm current to 0, that is... =0, substituting it into the objective function and simplifying, we get: ; Therefore, the relationship between the modulation ratio and the amplitude of the third harmonic voltage required to satisfy energy balance is as follows: ; It should be noted that the parameter k (corresponding to the second and third harmonic voltage injection coefficients) is controlled within the range of 0. 0.408 corresponds to a modulation ratio m in the range of 1.34. 1.414.

[0077] Example 3: This embodiment includes a derating controller comprising a third-harmonic voltage injection module and a second-harmonic circulating current control module. The original fundamental component of the three-phase modulation wave is set. The third-harmonic voltage injection module generates a third-harmonic voltage reference signal, which is then superimposed on the original fundamental modulation component to generate an updated modulation wave. The second-harmonic circulating current control module automatically switches the corresponding control mode based on the system's real-time modulation ratio. When the system modulation ratio m = 1.26, the controller operates in circulating current control mode. Substituting the modulation ratio into a preset implicit function equation yields a third-harmonic injection coefficient of approximately 0.1. Under the condition of a system power factor of 1, the second-harmonic circulating current amplitude reference value and the second-harmonic circulating current phase reference value are obtained as 0. The proportional resonant controller performs closed-loop regulation of the bridge arm common-mode voltage, ensuring that the actual circulating current of the bridge arm accurately tracks the aforementioned second-harmonic circulating current reference value. Based on actual test results, after implementing this control strategy, the voltage fluctuation rate of the upper arm submodule decreased from 28% to 7%, a reduction of 75%, and the second harmonic fluctuation component in the arm submodule voltage decreased from 155V to 15V. When the system modulation ratio m=1.38, the controller switches to circulating current suppression mode. The third harmonic injection coefficient is calculated to be approximately 0.1667 using the corresponding formula. Under this condition, the reference value of the second harmonic circulating current amplitude, I_2, is 0, achieving complete suppression of the second harmonic circulating current. Based on actual test data, after adopting this control scheme, the voltage fluctuation rate of the multiplexed arm submodule decreased from 15.6% to 5.8%, a reduction of 62.6%, while the peak arm current decreased from 1143A to 837A.

[0078] Example 4: This embodiment provides a derating control system for a bridge arm multiplexer converter, applied to the bridge arm multiplexer converter, to implement a derating control method for a bridge arm multiplexer converter as described in Embodiment 1, including a modulation calculation module and a third-harmonic voltage injection module, wherein: The modulation calculation module is used to perform inner-loop current control calculations on the pre-acquired three-phase AC side voltage, three-phase AC side current, active power command, and reactive power command to obtain the current three-phase modulation wave; and to calculate the current modulation ratio based on the real-time acquired fundamental voltage amplitude and DC bus voltage. The third-harmonic voltage injection module is used to calculate the first third-harmonic voltage injection coefficient according to the current modulation ratio and the preset implicit function equation when the current modulation ratio determines that it meets the preset first boundary interval. Based on the first third-harmonic voltage injection coefficient and the current three-phase modulation wave, the first target three-phase modulation wave is obtained, and the bridge arm multiplexed converter is de-capacitated according to the first target modulation wave. The third-harmonic voltage injection module is also used to, when the current modulation ratio determines that the current condition meets the preset second boundary interval, set a second harmonic circulating current amplitude reference value according to a preset value, calculate a second third harmonic voltage injection coefficient based on the current modulation ratio, the second harmonic circulating current amplitude reference value, the AC side fundamental current amplitude, and the preset bridge arm periodic energy balance constraint, obtain a second target three-phase modulation wave based on the second third harmonic voltage injection coefficient and the current three-phase modulation wave, and then perform derating control on the bridge arm multiplexed converter according to the second target modulation wave.

[0079] Optionally, the system also includes a second-harmonic circulating current control module, wherein: The second harmonic circulating current control module is used after the third harmonic voltage injection module performs derating control on the bridge arm multiplexer converter according to the first target modulation wave: real-time acquisition of AC side current amplitude, current three-phase AC side voltage, and current three-phase AC side current; calculation of power factor angle based on the current three-phase AC side voltage and current; calculation of target second harmonic circulating current amplitude reference value and phase reference value based on the first third harmonic voltage injection coefficient, current modulation ratio, and power factor angle; conversion of the target second harmonic circulating current amplitude reference value and phase reference value into second harmonic compensation voltage, and superimposition of the second harmonic compensation voltage in the three-phase bridge arm circuit of the bridge arm multiplexer converter to perform circulating current cancellation on the bridge arm multiplexer converter.

[0080] Optionally, the bridge arm multiplexed converter includes three single-phase bridge arm units, each of which includes several bridge arm sub-modules and several redundant sub-modules. The system also includes a fault-tolerant control module, wherein: The fault-tolerant control module is used to acquire in real time the operating data of several bridge arm sub-modules corresponding to several bridge arm sub-modules, obtain the total number of single-phase fault modules based on the operating data of several bridge arm sub-modules, and determine several faulty bridge arm sub-modules; when it is determined that the total number of single-phase fault modules meets the preset first level of fault tolerance conditions, a sub-module voltage constant command is output, and several faulty bridge arm sub-modules are replaced with several redundant sub-modules based on the sub-module voltage constant command to perform fault tolerance on the bridge arm multiplexed converter; when it is determined that the total number of single-phase fault modules meets the preset second level of fault tolerance conditions, a fault module disconnection action is performed on several faulty bridge arm sub-modules, and the sub-module operating voltage and the current number of operating sub-modules are calculated based on the total number of single-phase fault modules and the DC bus voltage, thereby adjusting the bridge arm multiplexed converter to derated operation based on the sub-module operating voltage and the current number of operating sub-modules; when it is determined that the total number of single-phase fault modules meets the preset third level of fault tolerance conditions, a safe shutdown action is triggered on the bridge arm multiplexed converter.

[0081] Optionally, the bridge arm multiplexer includes three single-phase bridge arm units. The system also includes an energy management module, a DC bus, and several overcharge ports, wherein: The DC bus is provided with several tap nodes that are electrically connected to several of the supercharging ports. Each of the single-phase bridge arm units is provided with several distribution switch nodes; A plurality of distribution switch nodes are electrically connected to the first terminals of a plurality of distribution switches, and the second terminals of a plurality of distribution switches are electrically connected to a plurality of supercharging ports; The energy management module is electrically connected to the control terminals of the distribution switches respectively; The energy management module is used to obtain the voltage requirement of the access load, output the distribution switch control command according to the voltage requirement of the access load, and control the target distribution switch in several distribution switch nodes to close based on the distribution switch control command, thereby forming the current access submodule group loop, and charging the access load through the current access submodule group loop.

[0082] In one specific embodiment, this embodiment sets up multiple DC supercharging ports, each connected to a different tap node of the DC bus. The number of series-connected submodules to each charging port is dynamically configured using a submodule allocation switch matrix, allowing the port output voltage to range from 0 to U. dcThe range is continuously adjustable, forming a dynamic allocation device for DC supercharging ports, capable of adapting to the charging needs of electric vehicles with various voltage platforms such as 400V, 800V, and 1000V. The specific process of the dynamic allocation method for the DC supercharging port submodule used in this embodiment is as follows: The system pre-sets multiple fixed tap nodes on the DC bus, and the tap voltage can be selected from U... dc / 5、2U dc / 5、3U dc / 5、4U dc The system is divided into five equal segments, with each segment's tap node corresponding to an independent submodule group. When an electric vehicle connects to the supercharging port, the energy management module obtains the required voltage V of the connected load uploaded by the vehicle's battery management system. It then selects the submodule group whose output voltage best matches the required voltage, issues a control command to the distribution switch to close the corresponding target distribution switch, and establishes a power supply circuit between the currently connected submodule group and the charging port. The output voltage of the submodule group is the sum of the number of series-connected bridge arm submodules (n) and the bridge arm module voltage (U). c The product of the load demand voltage and the tap position voltage; if there is a deviation between the load demand voltage and the tap position voltage, the drive duty cycle of the sub-module group can be adjusted within the ±5% voltage range to achieve precise matching of the output voltage; under the condition of simultaneous charging of multiple ports, the power demand of each port and the remaining available power of the corresponding sub-module group can be collected through the energy management module, and the output duty cycle of each sub-module group can be dynamically adjusted through the weighted proportional allocation algorithm to achieve balanced power distribution of multiple charging ports. The response time of the entire power distribution adjustment is less than 10ms.

[0083] In a specific application, the DC supercharging port dynamic allocation device, such as Figure 2As shown, DC+ is the positive terminal of the DC bus, DC- is the negative terminal of the DC bus, the reference potential of the negative terminal of the DC bus is 0V, and the total voltage of the DC bus T0 = 1000V; SM1 to SM10 are 10 bridge arm sub-modules arranged in series, which together form the DC bus voltage divider unit; T0, T1, T2, T3, and T4 represent the output voltage levels to ground corresponding to different tap nodes on the DC bus, where T0 is the total DC bus voltage level of 1000V, T1 is the tap voltage of 800V after SM1 and SM2 are connected in series, T2 is the tap voltage of 600V after SM1 to SM4 are connected in series, T3 is the tap voltage of 400V after SM1 to SM6 are connected in series, and T4 is the tap voltage of 200V after SM1 to SM8 are connected in series; K1, K2, K3, K4 is the distribution switch that makes up the submodule distribution switch matrix. One end of each distribution switch corresponds to the DC bus voltage divider tap node, and the other end is uniformly connected to the electric vehicle charging port (i.e., the supercharging port). The control terminals of all distribution switches are electrically connected to the energy management module. EV represents the electric vehicle that serves as the charging load. The energy management module is the main control unit of this system. It can collect the required voltage uploaded by the electric vehicle EV in real time, and issue distribution switch control commands according to the required voltage to control the target distribution switches in K1 to K4 to close, and conduct the corresponding tap voltage divider submodule group to complete the charging voltage matching. In the attached figure, the dashed line is the control terminal signal line of the energy management module connecting each distribution switch, and the red solid line is the power circuit that supplies power to the electric vehicle at the 800V voltage level when K1 is closed.

[0084] The aforementioned device has five tap nodes on the DC bus, corresponding to voltage output levels of 200V, 400V, 600V, 800V, and 1000V respectively. Taking the 800V voltage platform electric vehicle access condition as an example, when the on-board BMS battery management system reports a required voltage of 780V to the energy management module, the energy management module automatically selects the 800V submodule group that best matches the requirement. This submodule group consists of 10 bridge arm submodules with a single module voltage of 100V connected in series. The controller issues a command to close the corresponding distribution switch, connecting the submodule group to the electric vehicle charging port. Since the load required voltage of 780V is 2.5% lower than the 800V voltage, the system uniformly adjusts the drive duty cycle of all submodules in this group to 97.5%, completing the precise matching of the charging output voltage. In the case of multi-port synchronous charging, each charging port uploads its required power to the energy management module in real time. The module uses a weighted proportional allocation algorithm to dynamically correct the output duty cycle of each sub-module group, and the overall power utilization rate of the system can reach more than 95%.

[0085] Optionally, this embodiment also includes a redundant fault-tolerant controller, which comprises a fault detection and location unit, a bypass switch array, and a redundancy management unit. The fault detection and location unit collects real-time operating data of each sub-module, such as voltage, current, and temperature, to identify faults such as IGBT open / short circuits and capacitor short circuits, and accurately locates the fault point. The specific fault determination logic is as follows: For IGBT open-circuit and short-circuit faults, identification is achieved by comparing the drive signal with the actual output voltage of the submodule. When the drive signal is in the active state (T1 is on, T2 is off) and the bridge arm current is in the capacitor discharge direction, if the output voltage is lower than 0.5... If the circuit continues for multiple switching cycles, then T1 is determined to be open; when the drive signal is in the off state (T1 off, T2 on), the output voltage remains above 0.5V. T1 is determined to be short-circuited; the drive signal indicates that the output voltage remains below 0.5V when in the active state. The system determines that T2 is short-circuited and, after identifying the IGBT short-circuit fault, directly triggers the bypass action.

[0086] For capacitor faults, if the capacitor voltage is lower than 0.1 times the rated capacitor voltage for multiple consecutive sampling periods, and the output voltage of the submodule port is also lower than 0.1 times the rated capacitor voltage when the drive signal is in the active state, the capacitor is determined to be short-circuited; if the bridge arm current flows into the submodule during charging and the capacitor voltage does not rise for a long time, or if the capacitor voltage does not show a downward trend during discharging, the capacitor is determined to be open-circuited.

[0087] Meanwhile, the characteristics of the bridge arm current are used to help identify open circuit faults: Fourier decomposition of the bridge arm current is performed. If the DC component amplitude continuously exceeds 5% of the rated current, an open circuit fault is determined. The branch current of the submodule is collected. When the drive signal is turned on, the corresponding IGBT branch current approaches zero, indicating an open circuit fault. When the drive signal is turned off, if there is still current in the branch, it is determined that the IGBT is short-circuited or the diode is damaged.

[0088] For overheating faults, NTC thermistors or IPM built-in temperature sensors are used to monitor the junction temperature of the devices. If the junction temperature of silicon-based IGBT exceeds 150°C or the junction temperature of silicon carbide MOSFET exceeds 175°C and continues to exceed the protection delay, an overheating fault is determined. Short circuit faults will cause a sudden temperature rise. When the temperature change rate dT / dt is greater than 100°C / s, the emergency protection of the equipment is directly triggered.

[0089] Based on this, this embodiment also includes an energy management system, which monitors the SOC of each energy storage battery, the capacitor voltage of each submodule, the bridge arm current, and the DC bus voltage, and communicates with the derating controller and the redundancy fault-tolerant controller to coordinate system operation.

[0090] This embodiment provides a derating control method, or system, for a bridge arm multiplexed converter, which has the following beneficial technical effects: It adopts a bridge arm multiplexed modular multilevel converter topology, reducing the total number of sub-modules by 25%, increasing sub-module utilization from 50% to 66.7%, and increasing overall power density by more than 50%, making it suitable for the limited on-board installation space of emergency power vehicles; combined with a coordinated control strategy of third-harmonic voltage injection and second-harmonic circulating current coupling, the effective modulation ratio range for derating control can be widened from a single fixed value of 1.414 to 1.22~1.414, reducing sub-module capacitor voltage fluctuation by 60%~75%, and reducing capacitor selection value by 30%~40%; forward charging and reverse energy storage discharge power transmission reuse the same control architecture, enabling bidirectional... The operating efficiency deviation is less than 0.5%, ensuring high-efficiency operation in both charging and storage modes. Relying on reused bridge arms, redundant submodules are shared in a time-sharing manner, reducing the number of redundant submodules required for the same fault tolerance by 25%. With a tiered fault-tolerant control strategy, the system can withstand a maximum faulty submodule count of up to 24.3% of the total number of bridge arm submodules, exceeding the fault tolerance limit of traditional modular multilevel converter solutions and significantly improving the overall power supply reliability. The DC supercharging port directly relies on the modular multilevel converter submodules for voltage-sharing power supply, eliminating the need for additional independent DC-DC converters and reducing the overall hardware cost for expanding multiple charging ports by over 90%. The dynamic allocation and adjustment response time of submodules is less than 10ms, and the overall system power utilization rate can reach over 95%. In summary, this embodiment integrates a lightweight topology of the bridge arm reuse-type modular multilevel converter, a wide modulation ratio derating control strategy, and a tiered redundancy fault-tolerant control scheme, comprehensively improving the overall power density, all-condition adaptability, and fault-tolerant reliability of the high-power charging and storage emergency power supply vehicle, possessing high engineering implementation and promotional application value.

[0091] Example 5: like Figure 3 As shown, this embodiment provides a three-phase main circuit topology for a bridge arm reuse type modular multilevel converter derating control and fault tolerance system for high-power charging and storage emergency power vehicles. The main body of the topology adopts a bridge arm reuse type modular multilevel converter. The system is set up with three independent phase units A, B, and C. Each phase unit is divided into three branches: upper bridge arm, reuse bridge arm, and lower bridge arm. In the figure, the blue module represents the upper bridge arm sub-module, the yellow module represents the reuse bridge arm sub-module, and the light cyan module represents the lower bridge arm module. A set of switching switches is configured between each phase upper bridge arm branch and the reuse bridge arm branch. The corresponding switch for phase A is... Switch B corresponds to C corresponding switch Another set of switching switches is configured between the reused bridge arm branch and the lower bridge arm branch, with switch A corresponding to the switch. Switch B corresponds to C corresponding switch . , , These are the A, B, and C phase AC voltage output ports, respectively. , , , , , The bridge arm inductors are connected in series at the beginning and end of each bridge arm to suppress bridge arm circulating currents and fault inrush currents. to This represents M sub-modules arranged in series within a single bridge arm. The common terminals at the top of all three-phase upper bridge arms converge to form the positive terminal of the DC bus, and the common terminals at the bottom of all three-phase lower bridge arms converge to form the negative terminal of the DC bus; the total DC bus voltage is... The voltage divider on both the positive and negative sides of the DC bus is... The rated voltage of a single submodule is The DC bus voltage satisfies the following relationship: .

[0092] In this embodiment, the topology of the single-bridge arm submodule is as follows: Figure 4 As shown, a half-bridge architecture is used, in which... For the upper bridge arm power switching transistor, The lower bridge arm power switch can be either an IGBT or a SiC MOSFET. To and Anti-parallel freewheeling diodes To and Anti-parallel freewheeling diodes; The submodule outputs voltage at its port, with the upper end of the port being positive and the lower end being negative. C is the branch current flowing into the submodule; C is the parallel buffer capacitor of the submodule. The rated voltage of the capacitor is [voltage value missing]. The battery (Bat) is the energy storage battery unit. The capacitor (C) and the energy storage battery (Bat) are connected in parallel to form the energy support branch of the submodule. The capacitor (C) is used to absorb high-frequency voltage ripple in the circuit and provide instantaneous charging and discharging power, while the energy storage battery (Bat) undertakes the task of steady-state energy throughput. This half-bridge submodule relies on the coordinated switching of two power switches to achieve two operating states: submodule on and off. The parallel-connected capacitor and energy storage battery can work together to smooth power fluctuations and reduce the current ripple stress of the energy storage battery.

[0093] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. A derating control method for a bridge arm multiplexer converter, characterized in that, Applied to bridge arm multiplex converters, the method includes: The inner loop current control calculation is performed on the pre-acquired three-phase AC side voltage, three-phase AC side current, active power command and reactive power command to obtain the current three-phase modulation wave; The current modulation ratio is calculated based on the real-time acquired fundamental voltage amplitude and DC bus voltage. When the current modulation ratio is determined to meet the preset first boundary interval, the first third harmonic voltage injection coefficient is calculated according to the current modulation ratio and the preset implicit function equation. The first target three-phase modulation wave is obtained based on the first third harmonic voltage injection coefficient and the current three-phase modulation wave. The bridge arm multiplex converter is then de-capacitated according to the first target modulation wave. When the current modulation ratio is determined to meet the preset second boundary interval, the second harmonic circulating current amplitude reference value is set according to the preset value. The second harmonic voltage injection coefficient is calculated based on the current modulation ratio, the second harmonic circulating current amplitude reference value, the AC side fundamental current amplitude, and the preset bridge arm periodic energy balance constraint. The second target three-phase modulation wave is obtained based on the second harmonic voltage injection coefficient and the current three-phase modulation wave. The bridge arm multiplexed converter is then derated according to the second target modulation wave.

2. The derating control method for a bridge arm multiplexer converter as described in claim 1, characterized in that, When the current modulation ratio is determined to meet the preset first boundary interval, the first third harmonic voltage injection coefficient is calculated according to the current modulation ratio and the preset implicit function equation. The first target three-phase modulation wave is obtained based on the first third harmonic voltage injection coefficient and the current three-phase modulation wave. Then, the bridge arm layered voltage division and sub-module switching drive action is performed according to the first target modulation wave to perform derating control on the bridge arm multiplexed converter. include: When the current modulation ratio determines that it conforms to a preset first boundary interval: The first third harmonic voltage injection coefficient is calculated based on the current modulation ratio and the preset implicit function equation; The first third harmonic voltage is determined based on the first third harmonic voltage injection coefficient; The first third harmonic voltage is superimposed on the current three-phase modulated wave to obtain the first target three-phase modulated wave; The bridge arm layered voltage division and submodule switching drive actions are executed according to the first target modulation wave to perform derating control on the bridge arm multiplexed converter.

3. The derating control method for a bridge arm multiplexer converter as described in claim 1, characterized in that, After performing derating control on the bridge arm multiplexer converter according to the first target modulation wave, the method further includes: Real-time acquisition of AC side current amplitude, current three-phase AC side voltage, and current three-phase AC side current; Calculate the power factor angle based on the current three-phase AC side voltage and the current three-phase AC side current; The target second harmonic circulating current amplitude reference value and phase reference value are calculated based on the first third harmonic voltage injection coefficient, the current modulation ratio, and the power factor angle. The target second harmonic circulating current amplitude reference value and phase reference value are converted into a second harmonic compensation voltage. The second harmonic compensation voltage is then superimposed on the three-phase bridge arm circuit of the bridge arm multiplexer to cancel the circulating current of the bridge arm multiplexer.

4. The derating control method for a bridge arm multiplexer converter as described in claim 3, characterized in that, The calculation of the target second harmonic circulating current amplitude reference value and phase reference value based on the first third harmonic voltage injection coefficient, the current modulation ratio, and the power factor angle includes: For any single-phase bridge arm unit in the bridge arm multiplex converter; A simultaneous solution function is constructed based on the preset second harmonic power pulsation complete cancellation constraint and the preset bridge arm period energy balance constraint. Substituting the first third harmonic voltage injection coefficient, the current modulation ratio, the power factor angle, and the AC side fundamental current amplitude into the simultaneous solution function, the target second harmonic circulating current amplitude reference value and phase reference value are obtained.

5. The derating control method for a bridge arm multiplexer converter as described in claim 3, characterized in that, Also includes: When the current modulation ratio enters the preset transition interval from the preset first boundary interval, the target second harmonic circulating current amplitude reference value is subjected to attenuation smoothing switching processing based on the current modulation ratio until the target second harmonic circulating current amplitude reference value is switched to the second harmonic circulating current amplitude reference value. When the current modulation ratio enters the preset transition interval from the preset second boundary interval, the second harmonic current amplitude reference value is subjected to a rising smooth switching process based on the current modulation ratio until the second harmonic current amplitude reference value is switched to the target second harmonic current amplitude reference value.

6. A derating control method for a bridge arm multiplexer converter as described in claim 3, wherein the bridge arm multiplexer converter comprises three single-phase bridge arm units, and any single-phase bridge arm unit comprises several bridge arm sub-modules and several redundant sub-modules, characterized in that... Also includes: Real-time acquisition of the operating data of several bridge arm sub-modules corresponding to several bridge arm sub-modules; obtaining the total number of single-phase fault modules based on the operating data of several bridge arm sub-modules; and identifying several faulty bridge arm sub-modules. When the total number of single-phase fault modules determines that the preset first level of fault tolerance conditions are met, a sub-module voltage constant command is output, and based on the sub-module voltage constant command, several faulty bridge arm sub-modules are replaced with several redundant sub-modules to perform fault tolerance on the bridge arm multiplexed converter. When the total number of single-phase fault modules determines that the preset second-level fault tolerance condition is met, the fault module disconnection action is performed on several faulty bridge arm sub-modules. The sub-module operating voltage and the current number of operating sub-modules are calculated based on the total number of single-phase fault modules and the DC bus voltage. The bridge arm multiplex converter is then derated according to the sub-module operating voltage and the current number of operating sub-modules. When the total number of single-phase fault modules determines that the preset third-level fault tolerance condition is met, a safe shutdown action is triggered on the bridge arm multiplex converter.

7. A derating control system for a bridge arm multiplexer converter, characterized in that, Applied to bridge arm multiplexed converters, it includes a modulation calculation module and a third-harmonic voltage injection module, wherein: The modulation calculation module is used to perform inner-loop current control calculations on the pre-acquired three-phase AC side voltage, three-phase AC side current, active power command, and reactive power command to obtain the current three-phase modulation wave; and to calculate the current modulation ratio based on the real-time acquired fundamental voltage amplitude and DC bus voltage. The third-harmonic voltage injection module is used to calculate the first third-harmonic voltage injection coefficient according to the current modulation ratio and the preset implicit function equation when the current modulation ratio determines that it meets the preset first boundary interval. Based on the first third-harmonic voltage injection coefficient and the current three-phase modulation wave, the first target three-phase modulation wave is obtained, and the bridge arm multiplexed converter is de-capacitated according to the first target modulation wave. The third-harmonic voltage injection module is also used to, when the current modulation ratio determines that the current condition meets the preset second boundary interval, set a second harmonic circulating current amplitude reference value according to a preset value, calculate a second third harmonic voltage injection coefficient based on the current modulation ratio, the second harmonic circulating current amplitude reference value, the AC side fundamental current amplitude, and the preset bridge arm periodic energy balance constraint, obtain a second target three-phase modulation wave based on the second third harmonic voltage injection coefficient and the current three-phase modulation wave, and then perform derating control on the bridge arm multiplexed converter according to the second target modulation wave.

8. A derating control system for a bridge arm multiplexer converter as described in claim 7, characterized in that, It also includes a second-harmonic circulating current control module, in which: The second harmonic circulating current control module is used after the third harmonic voltage injection module performs derating control on the bridge arm multiplexer converter according to the first target modulation wave: real-time acquisition of AC side current amplitude, current three-phase AC side voltage, and current three-phase AC side current; calculation of power factor angle based on the current three-phase AC side voltage and current; calculation of target second harmonic circulating current amplitude reference value and phase reference value based on the first third harmonic voltage injection coefficient, current modulation ratio, and power factor angle; conversion of the target second harmonic circulating current amplitude reference value and phase reference value into second harmonic compensation voltage, and superimposition of the second harmonic compensation voltage in the three-phase bridge arm circuit of the bridge arm multiplexer converter to perform circulating current cancellation on the bridge arm multiplexer converter.

9. A derating control system for a bridge arm multiplexer converter as described in claim 7, wherein the bridge arm multiplexer converter comprises three single-phase bridge arm units, and any single-phase bridge arm unit comprises several bridge arm sub-modules and several redundant sub-modules, characterized in that, The system also includes a fault-tolerant control module, in which: The fault-tolerant control module is used to acquire in real time the operating data of several bridge arm sub-modules corresponding to several bridge arm sub-modules, obtain the total number of single-phase fault modules based on the operating data of several bridge arm sub-modules, and determine several faulty bridge arm sub-modules; when it is determined that the total number of single-phase fault modules meets the preset first level of fault tolerance conditions, a sub-module voltage constant command is output, and several faulty bridge arm sub-modules are replaced with several redundant sub-modules based on the sub-module voltage constant command to perform fault tolerance on the bridge arm multiplexed converter; when it is determined that the total number of single-phase fault modules meets the preset second level of fault tolerance conditions, a fault module disconnection action is performed on several faulty bridge arm sub-modules, and the sub-module operating voltage and the current number of operating sub-modules are calculated based on the total number of single-phase fault modules and the DC bus voltage, thereby adjusting the bridge arm multiplexed converter to derated operation based on the sub-module operating voltage and the current number of operating sub-modules; when it is determined that the total number of single-phase fault modules meets the preset third level of fault tolerance conditions, a safe shutdown action is triggered on the bridge arm multiplexed converter.

10. A derating control system for a bridge arm multiplexer converter as described in claim 7, wherein the bridge arm multiplexer converter comprises three single-phase bridge arm units, characterized in that... The system also includes an energy management module, a DC bus, and several supercharging ports, among which: The DC bus is provided with several tap nodes that are electrically connected to several of the supercharging ports. Each of the single-phase bridge arm units is provided with several distribution switch nodes; A plurality of distribution switch nodes are electrically connected to the first terminals of a plurality of distribution switches, and the second terminals of a plurality of distribution switches are electrically connected to a plurality of supercharging ports; The energy management module is electrically connected to the control terminals of the distribution switches respectively; The energy management module is used to obtain the voltage requirement of the access load, output the distribution switch control command according to the voltage requirement of the access load, and control the target distribution switch in several distribution switch nodes to close based on the distribution switch control command, thereby forming the current access submodule group loop, and charging the access load through the current access submodule group loop.

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