A three-phase four-bridge-arm converter and control method

Abstract

The present invention relates to the field of converter technology, and discloses a three-phase four-bridge-arm converter and a control method. The three-phase four-bridge-arm converter adds a fourth bridge arm on the basis of the topology of the three-phase three-bridge-arm converter. The current requirement of the fourth bridge arm device is significantly less than the current requirement of the converter part device. Based on this converter, a control method for the three-phase four-bridge-arm converter is disclosed. The method monitors the three-phase output current in real time. When a sudden load change or grid-side fault causes a sudden increase in the three-phase output current, the method actively injects a tripled frequency current into the common-mode loop through the fourth bridge arm to limit the peak current of the converter part device. Under the premise that all devices in the device do not pass current, the device can withstand a larger output current, thereby improving the overload capacity and not significantly increasing the system cost.

Description

Technical Field

[0001] The present invention relates to the technical field of converters, and in particular to a three-phase four-bridge-arm converter and a control method thereof. Background Art

[0002] New energy power generation systems are mainly connected to the grid through power electronic converters. Different control methods of the converters will have different impacts on the characteristics of the grid. In the application scenarios of long-distance and large-capacity transmission of new energy, especially in the face of ultra-long-distance new energy transmission scenarios such as Shagohuang, grid-connected inverters have become one of the preferred technical solutions. However, the directly controlled object of grid-connected control is the port voltage, and the valve-side current of the converter may exceed the standard during a fault. At present, the traditional grid-connected converter based on IGBT (Insulated Gate Bipolar Transistor) devices can trigger protection when the valve-side current reaches 1.2 times the rated value. At this time, the grid-connected control strategy will degenerate into a grid-following strategy under current limiting, and the advantages of grid-connected control cannot be fully utilized.

[0003] The severely limited overcurrent capacity of grid-connected converters is a key factor limiting their flexible controllability and reliable support for the power grid. Existing solutions typically enhance the converter's short-term high overload capacity by selecting components with sufficient margin or implementing redundant configurations, which significantly increases system costs. Summary of the Invention

[0004] The present invention provides a three-phase four-bridge-arm converter and a control method. On the basis of a traditional three-phase three-bridge-arm converter, only a fourth bridge arm with low current requirement is added, thereby improving the overload capacity of the equipment without significantly increasing the system cost.

[0005] In view of this, a first aspect of the present invention provides a three-phase four-bridge-arm converter, comprising a DC part, a converter part, an output filter part, a fourth bridge arm, and a fourth bridge arm controller, wherein the fourth bridge arm, the DC part, the converter part, and the output filter part are sequentially connected in parallel;

[0006] The DC part includes two voltage-dividing capacitors, the two voltage-dividing capacitors are connected in series to form a voltage-dividing branch, and the neutral point of the voltage-dividing branch is grounded;

[0007] The conversion part is a three-phase three-bridge-arm converter;

[0008] The output filter part includes a three-phase filter inductor and a three-phase filter capacitor; one end of the three-phase filter inductor is electrically connected to the output end of the converter part, and the other end of the three-phase filter inductor is connected to the power grid; one end of the three-phase filter capacitor is connected to the line between the three-phase filter inductor and the power grid, and the other end of the three-phase filter capacitor is connected to the output port of the fourth bridge arm;

[0009] The fourth bridge arm is a half-bridge module, including two power switching tubes, each of which is anti-parallel connected to a freewheeling diode, and the connection point of the two power switching tubes is connected to the neutral point of the three-phase filter capacitor of the converter part;

[0010] The input end of the fourth bridge arm controller is respectively connected to the line between the three-phase filter inductor and the power grid, and the output end of the three-phase filter capacitor, and is used to actively control the triple frequency current injection of the fourth bridge arm according to the three-phase output current signal output by the three-phase three-bridge arm converter and the current measurement value of the fourth bridge arm.

[0011] In a second aspect, the present invention further provides a control method for the three-phase four-leg converter as described above, comprising:

[0012] Real-time monitoring of the three-phase output current signals of the three-phase three-bridge-arm converter, and extraction of the amplitude and phase of the three-phase output current signals;

[0013] performing a limiting process on the difference between the amplitude of the three-phase output current signal and a preset device threshold current, and amplifying the output signal after the limiting process by three times to obtain an amplified signal;

[0014] Multiplying the amplified signal with the output signal processed by the sine link to obtain the output signal of the triple frequency current outer loop, wherein the output signal processed by the sine link is obtained by adding the phase of the three-phase output current signal and the preset angular frequency and then processing it by the sine link;

[0015] The output signal of the triple frequency current outer loop is subtracted from the current measurement value of the fourth bridge arm and then input into the current inner loop controller to generate a modulation wave signal of the switch tube of the fourth bridge arm.

[0016] Preferably, the method further comprises:

[0017] By modulating the modulation wave signal of the switch tube of the fourth bridge arm, an output voltage of the fourth bridge arm is obtained;

[0018] The actual current value of the fourth bridge arm is sampled to obtain a current measurement value of the fourth bridge arm.

[0019] Preferably, the current flowing through the current conversion part is the result of superimposing the output current value of the fourth bridge arm on the three-phase output current value.

[0020] In a third aspect, the present invention further provides a control system for the three-phase four-bridge-arm converter as described above, comprising:

[0021] A signal monitoring module is used to monitor the three-phase output current signals of the three-phase three-bridge-arm converter in real time and extract the amplitude and phase of the three-phase output current signals;

[0022] a signal limiting module, configured to perform limiting processing after subtracting the amplitude of the three-phase output current signal from a preset device threshold current, and amplify the output signal after the limiting processing by three times to obtain an amplified signal;

[0023] a signal frequency multiplication module, configured to multiply the amplified signal by the output signal processed by the sine link to obtain an output signal of the tripled frequency current outer loop, wherein the output signal processed by the sine link is obtained by adding the phase of the three-phase output current signal to a preset angular frequency and then processing it by the sine link;

[0024] The signal modulation module is used to input the difference between the output signal of the triple frequency current outer loop and the current measurement value of the fourth bridge arm into the current inner loop controller to generate a modulation wave signal for the switch tube of the fourth bridge arm.

[0025] Preferably, the system further includes:

[0026] a modulation module, configured to obtain an output voltage of the fourth bridge arm by modulating the modulation wave signal of the switch tube of the fourth bridge arm;

[0027] The sampling module is used to sample the actual current value of the fourth bridge arm to obtain the current measurement value of the fourth bridge arm.

[0028] Preferably, the system further includes:

[0029] The current superposition module is used to superimpose the output current value of the fourth bridge arm on the three-phase output current value as the current flowing through the conversion part.

[0030] In a fourth aspect, the present invention further provides an electronic device comprising a memory and a processor, wherein the memory stores a computer program, and when the computer program is executed by the processor, the processor executes the steps of the control method of the three-phase four-bridge-arm converter as described above.

[0031] In a fifth aspect, the present invention further provides a computer-readable storage medium having a computer program stored thereon, which implements the steps of the control method of the three-phase four-bridge-arm converter as described above when the computer program is executed.

[0032] In a sixth aspect, the present invention also provides a computer program product, comprising a computer program stored on a non-transitory computer-readable storage medium, wherein the computer program comprises program instructions, wherein when the program instructions are executed by a computer, the computer is caused to execute the steps of the control method of the three-phase four-bridge-arm converter as described above.

[0033] It can be seen from the above technical solutions that the present invention has the following advantages:

[0034] The three-phase four-bridge-arm converter proposed in the present invention only adds a fourth bridge arm with low current requirement on the basis of the traditional three-phase three-bridge-arm converter topology. Through the structural design of the fourth bridge arm, the fourth bridge arm controller is used to perform triple frequency current active injection control on the fourth bridge arm according to the three-phase output current signal output by the three-phase three-bridge-arm converter and the current measurement value of the fourth bridge arm. The proposed triple frequency current active injection control method is adopted, which can improve the short-term overload capacity of the equipment without significantly increasing the cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 A schematic structural diagram of a three-phase four-bridge-arm converter provided in an embodiment of the present invention;

[0036] Figure 2 An equivalent circuit diagram of a three-phase four-bridge-arm converter provided by an embodiment of the present invention;

[0037] Figure 3 A common-mode equivalent circuit diagram of a three-phase four-bridge-arm converter provided by an embodiment of the present invention;

[0038] Figure 4 A differential-mode equivalent circuit diagram of a three-phase four-bridge-arm converter provided by an embodiment of the present invention;

[0039] Figure 5 A flow chart of a control method for a three-phase four-leg converter provided by an embodiment of the present invention;

[0040] Figure 6 A control block diagram of the fourth bridge arm provided in an embodiment of the present invention;

[0041] Figure 7 A schematic structural diagram of a control system for a three-phase four-leg converter provided by an embodiment of the present invention;

[0042] Figure 8 A schematic structural diagram of an electronic device provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0043] In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0044] It should be noted that the terms "including" and "having" and any variations thereof in the specification and claims of the present invention and the above-mentioned drawings are intended to cover non-exclusive inclusions. For example, a process, method, system, product or apparatus comprising a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or are inherent to these processes, methods, products or apparatuses.

[0045] The severely limited overcurrent capacity of grid-connected converters is one of the key factors limiting their flexible controllability and reliable support for the power grid. Existing solutions generally enhance the converter's short-term high overload capacity by selecting components with sufficient margin or implementing redundant configurations, but this significantly increases system costs. Therefore, it is necessary to optimize topology and control to improve the equipment's short-term overload capacity without significantly increasing system costs.

[0046] Existing solutions generally select devices with sufficient margin to improve the converter's short-term high-load capability, which significantly increases system complexity and increases system cost.

[0047] In view of this, the embodiment of the present invention provides a three-phase four-bridge-arm converter, which improves the short-term overload capacity of the equipment without significantly increasing the system cost through topology and control optimization. Figure 1 As shown, it includes a DC part, a current conversion part, an output filtering part, a fourth bridge arm, and a fourth bridge arm controller. The fourth bridge arm, the DC part, the current conversion part, and the output filtering part are connected in parallel in sequence.

[0048] The DC part includes two voltage-dividing capacitors, which are connected in series to form a voltage-dividing branch. The neutral point O of the voltage-dividing branch is grounded. The voltage-dividing branch is connected to the DC source V dc connect;

[0049] The conversion part is a three-phase three-bridge-arm converter.

[0050] The topology of the three-phase three-leg converter may be a T-type three-level converter, an ANPC converter, etc., which is not limited here.

[0051] The output filter part includes a three-phase filter inductor L and a three-phase filter capacitor C; one end of the three-phase filter inductor L is electrically connected to the output end of the converter part (the three-phase bridge arms a, b, and c of the converter part), and the other end of the three-phase filter inductor L is connected to the grid V a 、V b 、V c One end of the three-phase filter capacitor C is connected to the three-phase filter inductor L and the grid V a 、V b 、V c On the line between, the other end of the three-phase filter capacitor C is connected to the output port of the fourth bridge arm;

[0052] The fourth bridge arm is a half-bridge module, including two power switching tubes, each power switching tube is anti-parallel connected to a freewheeling diode, and the connection point of the two power switching tubes is connected to the neutral point of the three-phase filter capacitor C of the conversion part.

[0053] The input end of the fourth bridge arm controller is respectively connected to the line between the three-phase filter inductor and the power grid, and the output end of the three-phase filter capacitor, and is used to actively control the triple frequency current injection of the fourth bridge arm according to the three-phase output current signal output by the three-phase three-bridge arm converter and the current measurement value of the fourth bridge arm.

[0054] in, Figure 1 i in aT 、i bT 、i cT They represent the output currents of the three-phase two-level bridge arms a, b, and c of the three-phase three-bridge-arm converter, and are also the currents flowing through the devices in each bridge arm. ao 、i bo 、i co Represent the three-phase load currents of A, B, and C respectively, and N represents the neutral point of the load.

[0055] It should be noted that the three-phase four-bridge-arm converter proposed in the present invention adds a fourth bridge arm on the basis of the topology of the three-phase three-bridge-arm converter, and the current requirement of the fourth bridge arm is significantly smaller than that of the other bridge arm devices.

[0056] The equivalent circuit of the three-phase four-bridge-arm converter proposed in the present invention is as follows: Figure 2 As shown, where v oCM is the common mode voltage, v aoDM 、v boDM 、v coDM They are the three-phase differential mode voltage, i oCM is the load common mode current, i aoDM 、i boDM 、i coDM They are three-phase differential mode current, v Cfa 、v Cfb 、vCfc They are the three-phase capacitor voltages, v do is the output voltage of the fourth bridge arm.

[0057] According to KVL and KCL theorems, we can get:

[0058] (1)

[0059] (2)

[0060] based on Figure 2 The equivalent circuit shown in Figure 1 is summed up to derive the common-mode equivalent circuit of this topology. Figure 3 As shown. According to the common mode equivalent circuit and Figure 2 , we can further deduce the differential mode equivalent circuit as Figure 4 As shown, where i xoDM (x=a, b, c) represents the differential-mode output current of the three-phase bridge arms A, B, and C in the converter section.

[0061] The current flowing through each device in the bridge arm in the conversion part, that is, the three-phase output current signal i xT , expressed as:

[0062]

[0063] From formula (3), we can get that by controlling the output current value i of the fourth bridge arm d The current flowing through each device in the bridge arm of the converter can be controlled, achieving the goal of increasing the load current without increasing the device current without increasing the margin of traditional two-level and three-level topology devices. This allows the device to withstand a larger load current during a fault, improving the device's overload capacity.

[0064] thus, Figure 5 The flowchart of a control method of the three-phase four-bridge-arm converter provided by the present invention is illustrated.

[0065] The present invention provides a control method for the above-mentioned three-phase four-bridge-arm converter, comprising:

[0066] Step S1: monitor the three-phase output current signals of the three-phase three-bridge-arm converter in real time, and extract the amplitude and phase of the three-phase output current signals.

[0067] Step S2: performing a limiting process on the amplitude of the three-phase output current signal after subtracting the amplitude from the preset device threshold current, and amplifying the output signal after the limiting process by three times to obtain an amplified signal.

[0068] Step S3: multiplying the amplified signal by the output signal processed by the sine link to obtain the output signal of the tripled frequency current outer loop, wherein the output signal processed by the sine link is obtained by adding the phase of the three-phase output current signal and the preset angular frequency and then processing it by the sine link;

[0069] Step S4: Subtract the output signal of the triple frequency current outer loop from the current measurement value of the fourth bridge arm and input the resultant signal into the current inner loop controller to generate a modulation wave signal for the switch tube of the fourth bridge arm.

[0070] This control method monitors the three-phase output current in real time. When a sudden load change or grid-side fault causes a sudden increase in the three-phase output current, it actively injects a tripled frequency current into the common-mode loop through the fourth bridge arm to limit the peak current of the converter components. Under the premise that all components in the device do not overcurrent, the equipment can withstand a larger output current, thereby improving the overload capacity without significantly increasing the system cost.

[0071] In some embodiments, the control method further includes:

[0072] Step S41, performing modulation through the modulation wave signal of the switch tube of the fourth bridge arm to obtain the output voltage of the fourth bridge arm;

[0073] Step S42: Sampling the actual current value of the fourth bridge arm to obtain a current measurement value of the fourth bridge arm.

[0074] Specifically, if Figure 6 As shown, Figure 6 The control block diagram of the fourth bridge arm is shown. The present invention provides a control method for the three-phase four-bridge-arm converter as described above, comprising: real-time monitoring of the three-phase output current signal i xT , input to the amplitude extraction link |Am| and phase extraction link θ(x), and obtain the three-phase output current signal i xT The amplitude and phase of the device threshold current I Tlim The difference is used as the input signal of the limiting link, and the phase is added to the angular frequency 3×2π as the input signal of the sin link. Sin represents a sinusoidal signal with an amplitude of 1 generated according to the input phase. The output signal of the limiting link is tripled and multiplied with the output signal of the sin link to obtain the output signal of the tripled frequency current outer loop.

[0075] The output signal of the triple frequency current outer loop is used as the input signal of the triple frequency current inner loop, and is compared with the current measurement value of the fourth bridge arm (the actual current value of the fourth bridge arm and the sampling coefficient H i The difference is calculated and used as the current inner loop controller G CM (s) is the input signal of the current inner loop controller G CM The output signal of (s) is the modulation wave v of the fourth bridge armdo *.

[0076] v do *After the modulation step K PWM Get the output voltage v of the fourth bridge arm do , the output voltage of the fourth bridge arm v do and common mode voltage vo CM Acting together on the inductor L and the capacitor C, the actual current value of the fourth bridge arm i is obtained d .

[0077] Among them, the limit link means that when the input signal is less than 0, the output signal of this link is equal to 0, and when the input signal is greater than 0 and less than 0.15I Tlim When the output signal of this link is equal to the input signal, when the output signal is greater than 0.15I Tlim When the output signal is equal to 0.15I Tlim .

[0078] like Figure 7 As shown, the present invention further provides a control system for the three-phase four-bridge-arm converter as described above, comprising:

[0079] The signal monitoring module 101 is used to monitor the three-phase output current signals of the three-phase three-bridge-arm converter in real time and extract the amplitude and phase of the three-phase output current signals;

[0080] The signal limiting module 102 is used to perform a limiting process on the amplitude of the three-phase output current signal after subtracting the amplitude from the preset device threshold current, and amplify the output signal after the limiting process by three times to obtain an amplified signal;

[0081] The signal frequency multiplication module 103 is used to multiply the amplified signal by the output signal processed by the sine link to obtain the output signal of the tripled frequency current outer loop, wherein the output signal processed by the sine link is the phase of the three-phase output current signal plus the preset angular frequency and then processed by the sine link;

[0082] The signal modulation module 104 is used to calculate the difference between the output signal of the triple frequency current outer loop and the current measurement value of the fourth bridge arm and input the result to the current inner loop controller to generate a modulation wave signal for the switch tube of the fourth bridge arm.

[0083] In some embodiments, the system further comprises:

[0084] a modulation module, configured to obtain an output voltage of the fourth bridge arm by modulating the modulation wave signal of the switch tube of the fourth bridge arm;

[0085] The sampling module is used to sample the actual current value of the fourth bridge arm to obtain the current measurement value of the fourth bridge arm.

[0086] In some embodiments, the system further comprises:

[0087] The current superposition module is used to superimpose the output current value of the fourth bridge arm on the three-phase output current value as the current flowing through the conversion part.

[0088] like Figure 8 As shown, the present invention also provides an electronic device 10, including a memory 20 and a processor 30, wherein a computer program is stored in the memory 20, and when the computer program is executed by the processor 30, the processor 30 executes the steps of the control method of the three-phase four-bridge-arm converter as described above.

[0089] The present invention also provides a computer-readable storage medium having a computer program stored thereon, which implements the steps of the control method of the three-phase four-bridge-arm converter as described above when the computer program is executed.

[0090] The present invention also provides a computer program product, which includes a computer program stored on a non-transitory computer-readable storage medium, and the computer program includes program instructions, wherein when the program instructions are executed by a computer, the computer executes the steps of the control method of the three-phase four-bridge-arm converter as described above.

[0091] Those skilled in the art will clearly understand that, for the convenience and brevity of description, the specific working processes of the above-described systems, electronic devices, computer storage media, and computer program products can refer to the corresponding processes in the aforementioned method embodiments and will not be repeated here.

[0092] In several embodiments provided by the present invention, it is understood that each box in the flow chart or block diagram can represent a module, program segment or part of the code, and the module, program segment or part of the code contains one or more executable instructions for realizing the specified logical function. It should also be noted that in some alternative implementations, the functions marked in the box can also occur in a different order than that marked in the accompanying drawings. For example, two consecutive boxes can actually be executed substantially in parallel, and they can sometimes be executed in the opposite order, depending on the functions involved.

[0093] In the several embodiments provided by the present invention, it should be understood that the disclosed systems, electronic devices, computer storage media, computer program products and methods can be implemented in other ways. For example, the device embodiments described above are merely illustrative. For example, the division of units is only a logical function division. In actual implementation, there may be other division methods, such as multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be through some interfaces, indirect coupling or communication connection of devices or units, which can be electrical, mechanical or other forms.

[0094] Units described as separate components may or may not be physically separate, and components shown as units may or may not be physical units, that is, they may be located in one place or distributed across multiple network units. Some or all of these units may be selected to achieve the purpose of this embodiment according to actual needs.

[0095] In addition, the functional units in the various embodiments of the present invention may be integrated into a single processing unit, each unit may exist physically separately, or two or more units may be integrated into a single unit. The aforementioned integrated units may be implemented in the form of hardware or software functional units.

[0096] If the integrated unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, or the portion that contributes to the prior art, or all or part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions for executing all or part of the steps of the various embodiments of the method of the present invention via a computer device (which can be a personal computer, server, or network device, etc.). The aforementioned storage medium includes various media that can store program code, such as USB flash drives, mobile hard drives, read-only memories (ROMs), random access memories (RAMs), magnetic disks, or optical disks.

[0097] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A three-phase four-bridge-arm converter, characterized in that: It includes a DC part, a current conversion part, an output filtering part, a fourth bridge arm, and a fourth bridge arm controller, wherein the fourth bridge arm, the DC part, the current conversion part, and the output filtering part are sequentially connected in parallel; The DC part includes two voltage-dividing capacitors, the two voltage-dividing capacitors are connected in series to form a voltage-dividing branch, and the neutral point of the voltage-dividing branch is grounded; The conversion part is a three-phase three-bridge-arm converter; The output filter part includes a three-phase filter inductor and a three-phase filter capacitor; one end of the three-phase filter inductor is electrically connected to the output end of the converter part, and the other end of the three-phase filter inductor is connected to the power grid; one end of the three-phase filter capacitor is connected to the line between the three-phase filter inductor and the power grid, and the other end of the three-phase filter capacitor is connected to the output port of the fourth bridge arm; The fourth bridge arm is a half-bridge module, including two power switching tubes, each of which is anti-parallel connected to a freewheeling diode, and the connection point of the two power switching tubes is connected to the neutral point of the three-phase filter capacitor of the converter part; The input end of the fourth bridge arm controller is respectively connected to the line between the three-phase filter inductor and the power grid, and the output end of the three-phase filter capacitor, and is used to perform triple frequency current active injection control on the fourth bridge arm according to the three-phase output current signal output by the three-phase three-bridge arm converter and the current measurement value of the fourth bridge arm; The control method of the three-phase four-bridge-arm converter includes: Real-time monitoring of the three-phase output current signals of the three-phase three-bridge-arm converter, and extraction of the amplitude and phase of the three-phase output current signals; performing a limiting process on the difference between the amplitude of the three-phase output current signal and a preset device threshold current, and amplifying the output signal after the limiting process by three times to obtain an amplified signal; Multiplying the amplified signal with the output signal processed by the sine link to obtain the output signal of the triple frequency current outer loop, wherein the output signal processed by the sine link is obtained by adding the phase of the three-phase output current signal and the preset angular frequency and then processing it by the sine link; The output signal of the triple frequency current outer loop is subtracted from the current measurement value of the fourth bridge arm and then inputted into the current inner loop controller to generate a modulation wave signal of the switch tube of the fourth bridge arm; The control method of the three-phase four-bridge-arm converter further includes: By modulating the modulation wave signal of the switch tube of the fourth bridge arm, an output voltage of the fourth bridge arm is obtained; Sampling the actual current value of the fourth bridge arm to obtain a current measurement value of the fourth bridge arm; The current flowing through the conversion part is the result of superimposing the output current value of the fourth bridge arm on the three-phase output current value.

2. A control system for a three-phase four-bridge-arm converter according to claim 1, characterized in that: include: A signal monitoring module is used to monitor the three-phase output current signals of the three-phase three-bridge-arm converter in real time and extract the amplitude and phase of the three-phase output current signals; a signal limiting module, configured to perform limiting processing after subtracting the amplitude of the three-phase output current signal from a preset device threshold current, and amplify the output signal after the limiting processing by three times to obtain an amplified signal; a signal frequency multiplication module, configured to multiply the amplified signal by the output signal processed by the sine link to obtain an output signal of the tripled frequency current outer loop, wherein the output signal processed by the sine link is obtained by adding the phase of the three-phase output current signal to a preset angular frequency and then processing it by the sine link; a signal modulation module, configured to calculate the difference between the output signal of the triple frequency current outer loop and the current measurement value of the fourth bridge arm and input the resultant difference to the current inner loop controller to generate a modulation wave signal for the switch tube of the fourth bridge arm; Also includes: a modulation module, configured to obtain an output voltage of the fourth bridge arm by modulating the modulation wave signal of the switch tube of the fourth bridge arm; a sampling module, configured to sample the actual current value of the fourth bridge arm to obtain a current measurement value of the fourth bridge arm; The current superposition module is used to superimpose the output current value of the fourth bridge arm on the three-phase output current value as the current flowing through the conversion part.

3. An electronic device, characterized in that: The system comprises a memory and a processor, wherein a computer program is stored in the memory, and when the computer program is executed by the processor, the processor executes the steps of the control method of the three-phase four-bridge-arm converter according to claim 1.

4. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed, the steps of the control method of the three-phase four-leg converter according to claim 1 are implemented.

5. A computer program product, characterized in that The computer program product includes a computer program stored on a non-transitory computer-readable storage medium, wherein the computer program includes program instructions, wherein when the program instructions are executed by a computer, the computer is caused to perform the steps of the control method for the three-phase four-bridge-leg converter according to claim 1.

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