Redecoupling method and system under asymmetric bridge arm inductance of bipolar AC-AC frequency converter

Abstract

The invention discloses a redecoupling method and system under asymmetry of bridge arm inductance of a bipolar AC-AC frequency converter. The bipolar AC-AC frequency converter is of an ABC three-phase structure, each phase comprises an upper bridge arm and a lower bridge arm, each of the upper bridge arm and the lower bridge arm comprises n full-bridge sub-modules connected in series and a bridge arm inductor, and the inductance parameters of the upper bridge arm and the lower bridge arm are different. Single-frequency output of a power frequency side and single-frequency output of a low-frequency side are achieved by applying the processing frequency difference mode reference voltage and the low-frequency common mode reference voltage to the upper bridge arm and the lower bridge arm, and mutual coupling of the power frequency side and the low-frequency side caused by asymmetry of bridge arm inductance is eliminated by applying the processing frequency common mode reference voltage and the low-frequency difference mode reference voltage to the upper bridge arm and the lower bridge arm. According to the invention, by introducing a re-decoupling control strategy based on a common mode and a differential mode, re-decoupling of the bipolar AC-AC frequency converter under the condition of asymmetric parameters is realized, unexpected harmonic components are eliminated, and the safety and reliability of the bipolar AC-AC frequency converter are effectively improved.

Description

Technical Field

[0001] The present invention belongs to the field of multi-level power electronic converters, and in particular relates to a positive and negative bipolar modular multi-level AC-AC converter. Background Art

[0002] Compared to traditional industrial frequency AC transmission, low-frequency power transmission offers stronger transmission capacity, lower reactive power compensation requirements, and lower line losses. Consequently, it has attracted widespread attention in areas such as offshore wind power grid integration and long-distance AC transmission. AC-AC converters, as key devices connecting low-frequency AC systems with industrial frequency AC systems, play a crucial role in frequency-divided transmission.

[0003] Currently, there are three main technical solutions for AC-AC converters: back-to-back MMC, M3C, and Hexverter. Back-to-back MMC AC-AC converters are relatively mature, using two MMCs connected on the DC side for frequency conversion. Their control algorithms are relatively simple and easy to understand. However, the back-to-back MMC structure involves 12 bridge arms and a large number of submodules, resulting in larger equipment and higher construction costs.

[0004] The M3C type AC-AC inverter uses nine bridge arms. The reduced number of bridge arms effectively reduces manufacturing costs, but its internal circuits are relatively complex, with strong coupling between circuits and multiple circulation channels. These shortcomings increase the difficulty of M3C manufacturing and control.

[0005] Hexverter-type AC-AC converters further reduce manufacturing costs by using only six bridge arms. However, their topology has limited scalability and, to ensure proper operation, must strictly meet reactive power compensation requirements. This limits their control flexibility and makes them difficult to meet the complex and changing demands of industrial applications. Summary of the Invention

[0006] Technical Problem to be Solved by the Present Invention: To address the shortcomings of the prior art, the present invention aims to provide a re-decoupling strategy for bipolar cycloconverters with asymmetrical bridge arm inductances, thereby achieving optimized control of the bipolar cycloconverter under unbalanced inductance parameters between the upper and lower bridge arms. This strategy aims to eliminate the low-frequency interference current component on the power frequency side and the power frequency interference current component on the low-frequency side under unbalanced inductance parameters, thereby achieving re-decoupling of the power frequency and low-frequency sides, improving the output current waveform, and effectively enhancing the output power quality.

[0007] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0008] The bipolar AC-AC converter disclosed in the present invention has an ABC three-phase structure, each phase includes upper and lower bridge arms, each bridge arm includes n full-bridge sub-modules connected in series and a bridge arm inductor, wherein the bridge arm inductors have different inductance values; its low-frequency side is connected to the low-frequency power grid via a bipolar transformer, and the connection points of the upper and lower bridge arms of each phase are respectively connected to the industrial frequency power grid.

[0009] In each bridge arm, the full-bridge sub-module includes the first to fourth IGBTs and the first electrolytic capacitor, wherein the emitter of the first IGBT is connected to the collector of the second IGBT, and the connection point is used as the positive end of the full-bridge sub-module; the emitter of the third IGBT is connected to the collector of the fourth IGBT, and the connection point is used as the negative end of the full-bridge sub-module; the collector of the first IGBT, the collector of the third IGBT and the positive electrode of the first electrolytic capacitor are connected; the emitter of the second IGBT, the emitter of the fourth IGBT and the negative electrode of the first electrolytic capacitor are connected; and the first to fourth IGBTs are all connected with anti-parallel diodes.

[0010] The bipolar transformer includes two secondary windings W1 and W2, where W1 is the positive winding and adopts the Y0 connection method, and W2 is the negative winding and adopts the Y6 connection method; the three-phase ports of the secondary winding W1 are respectively connected to the upper end of the three-phase upper bridge arm; the three-phase ports of the secondary winding W2 are respectively connected to the lower end of the three-phase lower bridge arm.

[0011] In view of the above bipolar cycloconverter structure, the present invention first proposes a re-decoupling method for the bipolar cycloconverter under the asymmetric inductance of the bridge arm, specifically:

[0012] The power frequency common-mode reference voltage, power frequency differential-mode reference voltage, low-frequency common-mode reference voltage, and low-frequency differential-mode reference voltage are applied to the upper and lower bridge arms of each phase. The bridge arm reference voltage is the sum of the four reference voltages; among them, the power frequency differential-mode reference voltage and the low-frequency common-mode reference voltage are used to realize the frequency output of the power frequency side and the low-frequency side respectively, and the power frequency common-mode reference voltage and the low-frequency differential-mode reference voltage are used to eliminate the mutual interference between the power frequency and the low frequency caused by the asymmetry of the bridge arm inductance.

[0013] Furthermore, the power frequency differential mode reference voltage is obtained by the following steps:

[0014] S101, in the dq coordinate system, according to the power frequency reference current i gd_ref and i gq_ref , the dq component u of the power frequency differential mode reference voltage is obtained through PI control diff_gd and u diff_gq :

[0015]

[0016] Among them, K p and K i is the control parameter of PI control, igd and i gq is the dq component of the power frequency current, u gd and u gq is the dq component of the power frequency voltage, ω g is the power frequency angular frequency, L G is the equivalent inductance on the power frequency side;

[0017] S102, u diff_gd and u diff_gq At the power frequency angular frequency ω g Down-converted to the abc three-phase coordinate system, the power frequency differential mode reference voltage u is obtained diff_gj , j = a, b, c.

[0018] Furthermore, the low-frequency common-mode reference voltage is obtained by the following steps:

[0019] S201, in the dq coordinate system, according to the low-frequency reference current i ld_ref and i lq_ref The dq component u of the low-frequency common-mode reference voltage is calculated by the following formula: com_ld and u com_lq :

[0020]

[0021] Among them, i ld and i lq is the dq component of the low-frequency current, u ld and u lq is the dq component of the low-frequency voltage, ω l is the low-frequency corner frequency, L L is the low-frequency side equivalent inductance, k l is the bipolar transformer ratio; K p and K i is the control parameter of PI control;

[0022] S202. Will u com_ld and u com_lq At low angular frequency ω l Down-converted to the abc three-phase coordinate system, the low-frequency common-mode reference voltage u is obtained com_lj , j = a, b, c.

[0023] Furthermore, the power frequency common mode reference voltage is obtained by the following steps:

[0024] S301, filter out the power frequency interference current component in the low frequency current, and convert it to the dq coordinate system to obtain the low frequency side power frequency interference current i l_gd and i l_gq ;

[0025] S302, in the dq coordinate system, il_gd and i l_gq Suppress it to 0, and calculate the dq component u of the power frequency common mode reference voltage by the following formula com_gd and u com_gq :

[0026]

[0027] Among them, ω g is the power frequency angular frequency, ΔL is the difference between the upper and lower bridge arm inductances;

[0028] S303, u com_gd and u com_gq At the power frequency angular frequency ω g Down-converted to the abc three-phase coordinate system, the power frequency common mode reference voltage u is obtained com_gj , j = a, b, c.

[0029] Furthermore, the low-frequency differential mode reference voltage is obtained by the following steps:

[0030] S401, filter out the low-frequency interference current component from the power frequency current, and convert it to the dq coordinate system to obtain the power frequency side low-frequency interference current i g_ld and i g_lq ;

[0031] S402, in the dq coordinate system, i g_ld and i g_lq Suppress it to 0, and calculate the dq component u of the low-frequency differential mode reference voltage by the following formula diff_ld and u diff_lq :

[0032]

[0033] Among them, ω l is the low-frequency angular frequency, ΔL is the difference between the upper and lower bridge arm inductances;

[0034] S403, u diff_ld and u diff_lq At the angular frequency ω l Down-converted to the abc three-phase coordinate system, the low-frequency differential mode reference voltage u is obtained diff_lj , j = a, b, c.

[0035] Furthermore, in the described heavy decoupling strategy under the asymmetric bridge arm inductance of the bipolar cycloconverter, the power frequency side and the low frequency side can be exchanged with each other. After the power frequency side and the low frequency side are exchanged with each other, the power frequency common-mode reference voltage and the low-frequency differential-mode reference voltage are used to realize the frequency output of each of the power frequency side and the low frequency side, and the low-frequency common-mode reference voltage and the power frequency differential-mode reference voltage are used to eliminate the mutual interference between the power frequency and the low frequency caused by the asymmetric bridge arm inductance.

[0036] Secondly, the present invention also proposes an electronic system, comprising: at least one processor; and a memory communicatively connected to the at least one processor; wherein the memory stores instructions that can be executed by the at least one processor, and the instructions are executed by the at least one processor to enable the at least one processor to perform the method steps of the present invention.

[0037] Finally, the present invention also provides a computer-readable storage medium storing computer instructions, wherein the computer instructions are used to enable the computer to execute the method steps of the present invention.

[0038] By adopting the above technical solution, compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0039] 1. The present invention proposes a re-decoupling strategy for a bipolar cycloconverter with asymmetric bridge arm inductance. By applying four reference voltage components in the bridge arm, namely, a power frequency common-mode reference voltage, a low-frequency common-mode reference voltage, a power frequency differential-mode reference voltage, and a low-frequency differential-mode reference voltage, the strategy eliminates the power frequency current on the low-frequency side and the low-frequency current on the power frequency side while ensuring effective output on the power frequency side and the low-frequency side, thereby achieving re-decoupling of the bipolar cycloconverter.

[0040] 2. The present invention proposes a heavy decoupling strategy for bipolar AC-AC inverters with asymmetric bridge arm inductance. This strategy can effectively reduce the harmonic content in the output currents on the power frequency side and the low frequency side when the inductance is asymmetric due to manufacturing, failure, aging and other problems. This strategy can also improve the output current waveform and power quality, and can enhance the stability of the power grid on the power frequency side and the low frequency side. It has high industrial value.

[0041] 3. The heavy decoupling strategy under the asymmetric bridge arm inductance of the bipolar cycloconverter proposed in the present invention can reduce the internal harmonic distribution of the bipolar cycloconverter, thereby reducing unnecessary power loss generated inside the bipolar cycloconverter, improving the operating efficiency of the bipolar cycloconverter, and improving the operation of the power switching device, and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0043] Figure 1 1 is a schematic diagram of the topological structure of a bipolar cycloconverter according to an embodiment of the present invention.

[0044] Figure 2 2 is a schematic diagram of the full-bridge submodule structure of an embodiment of the present invention.

[0045] Figure 3 It is a flow chart of the method of the present invention. DETAILED DESCRIPTION

[0046] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. 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 any creative efforts shall fall within the scope of protection of the present invention.

[0047] like Figure 1 As shown, the present invention is a heavy decoupling strategy under the asymmetric inductance of the bridge arm of a bipolar cycloconverter, and the controlled system consists of two main parts: the first part is a bipolar cycloconverter, and the bipolar cycloconverter is an ABC three-phase structure, each phase includes an upper bridge arm and a lower bridge arm, and the upper and lower bridge arms respectively include n full-bridge sub-modules connected in series and a bridge arm reactor, wherein the inductance values of the bridge arm reactors are different; the second part is a bipolar transformer, and the bipolar transformer includes two secondary windings W1 and W2, wherein W1 is a positive winding, adopts a Y0 connection method, and W2 is a negative winding, adopts a Y6 connection method; the three-phase ports of the secondary winding W1 are respectively connected to the upper end of the three-phase upper bridge arm; the three-phase ports of the secondary winding W2 are respectively connected to the lower end of the three-phase lower bridge arm. In the proposed bipolar AC-AC converter, the power frequency side of the bipolar AC-AC converter is connected to the power frequency grid at the connection point of the upper and lower bridge arms, and the low frequency side is connected to the low frequency grid via the primary winding W0 of the bipolar transformer.

[0048] like Figure 2 As shown, the full-bridge submodule of the bipolar AC-AC converter includes first to fourth IGBTs and a first electrolytic capacitor, wherein the emitter of the first IGBT is connected to the collector of the second IGBT, and the connection point is used as the positive end of the full-bridge submodule; the emitter of the third IGBT is connected to the collector of the fourth IGBT, and the connection point is used as the negative end of the full-bridge submodule; the collector of the first IGBT, the collector of the third IGBT and the positive electrode of the first electrolytic capacitor are connected; the emitter of the second IGBT, the emitter of the fourth IGBT and the negative electrode of the first electrolytic capacitor are connected; and the first to fourth IGBTs are all connected with anti-parallel diodes.

[0049] refer to Figure 3 As shown, the re-decoupling method of the bipolar cycloconverter bridge arm inductance asymmetry proposed by the present invention applies a power frequency common mode reference voltage u to the upper and lower bridge arms. com_gj , power frequency differential mode reference voltage u diff_gj , low frequency common mode reference voltage u com_lj , low frequency differential mode reference voltage u diff_ljThere are four reference voltages (j=a, b, c), and the bridge arm reference voltage is the sum of the four.

[0050] Among them, the power frequency differential mode reference voltage and the low frequency common mode reference voltage are used to realize the frequency output of the power frequency side and the low frequency side respectively, and the power frequency common mode reference voltage and the low frequency differential mode reference voltage are used to eliminate the mutual interference between the power frequency and the low frequency caused by the asymmetry of the bridge arm inductance.

[0051] When the heavy decoupling control strategy is implemented for the bipolar AC-AC converter under the condition of asymmetric bridge arm inductance, the power frequency differential mode reference voltage is obtained by the following method:

[0052] S1, in the dq coordinate system, according to the power frequency reference current i gd_ref and i gq_ref , the dq component u of the power frequency differential mode reference voltage is obtained through proportional integral (PI) control diff_gd and u diff_gq :

[0053]

[0054] Among them, K p and K i is the control parameter of PI control, i gd and i gq is the dq component of the power frequency current, u gd and u gq is the dq component of the power frequency voltage, ω g is the power frequency angular frequency, L G is the equivalent inductance on the power frequency side.

[0055] S2, u diff_gd and u diff_gq At the angular frequency ω g Down-converted to the power frequency differential mode reference voltage u in the abc three-phase coordinate system diff_gj .

[0056] When the heavy decoupling control strategy is implemented for the bipolar cycloconverter under the condition of asymmetric bridge arm inductance, the low-frequency common-mode reference voltage is obtained by:

[0057] S1, in the dq coordinate system, according to the low-frequency reference current i ld_ref and i lq_ref The dq component u of the low-frequency common-mode reference voltage is calculated by the following formula: com_ld and u com_lq :

[0058]

[0059] Among them, i ld and i lqis the dq component of the low-frequency current, u ld and u lq is the dq component of the low-frequency voltage, ω l is the low-frequency corner frequency, L L is the low-frequency side equivalent inductance, k l is the bipolar transformer ratio.

[0060] S2, u com_ld and u com_lq At the angular frequency ω l Down-converted to the low-frequency common-mode reference voltage u in the abc three-phase coordinate system com_lj .

[0061] When the heavy decoupling control strategy is implemented for the bipolar AC-AC converter under the condition of asymmetric bridge arm inductance, the power frequency common mode reference voltage is obtained by the following method:

[0062] S1. Filter out the power frequency interference current component in the low frequency current and convert it to the dq coordinate system to obtain the power frequency interference current i on the low frequency side. l_gd and i l_gq .

[0063] S2. In the dq coordinate system, i l_gd and i l_gq Suppress it to 0, and calculate the dq component u of the power frequency common mode reference voltage by the following formula com_gd and u com_gq :

[0064]

[0065] Where ΔL is the difference between the upper and lower arm inductances.

[0066] S3. Will u com_ld and u com_lq At the angular frequency ω g Down-converted to the power frequency common mode reference voltage u in the abc three-phase coordinate system com_g j.

[0067] When the heavy decoupling control strategy is implemented for the bipolar cycloconverter under the condition of asymmetric bridge arm inductance, the low-frequency differential mode reference voltage is obtained by:

[0068] S1. Filter out the low-frequency interference current component from the power frequency current and convert it to the dq coordinate system to obtain the power frequency side low-frequency interference current i g_ld and i g_lq .

[0069] S2. In the dq coordinate system, i g_ld and i g_lq Suppress it to 0, and calculate the dq component u of the low-frequency differential mode reference voltage by the following formuladiff_ld and u diff_lq :

[0070]

[0071] S3. Will u diff_ld and u diff_lq At the angular frequency ω l Down-converted to the low-frequency differential mode reference voltage u in the abc three-phase coordinate system diff_lj .

[0072] When the bipolar AC-AC converter implements a heavy decoupling control strategy under the condition of asymmetric bridge arm inductance, its power frequency side and low frequency side can be interchanged. After the power frequency side and the low frequency side are interchanged, the power frequency common-mode reference voltage and the low frequency differential-mode reference voltage are used to realize the frequency output of the power frequency side and the low frequency side respectively, and the low frequency common-mode reference voltage and the power frequency differential-mode reference voltage are used to eliminate the mutual interference between the power frequency and low frequency caused by the asymmetric bridge arm inductance.

[0073] Example 2:

[0074] This embodiment proposes an electronic system, comprising: at least one processor; and a memory communicatively connected to the at least one processor; wherein the memory stores instructions executable by the at least one processor, and the instructions are executed by the at least one processor to enable the at least one processor to perform the method steps described in the present invention.

[0075] Example 3:

[0076] This embodiment provides a computer-readable storage medium storing computer instructions, wherein the computer instructions are used to enable the computer to execute the method steps described in the present invention.

[0077] It should be noted that the processing flow of Examples 2 to 3 corresponds to the specific steps of the method provided in the embodiment of the present invention, and has the functional modules and beneficial effects corresponding to the execution method. For technical details not fully described in this embodiment, please refer to the method provided in the embodiment of the present invention.

[0078] The program code for implementing the methods of the present application can be written in any combination of one or more programming languages. Such program code can be provided to a processor or controller of a general-purpose computer, a special-purpose computer, or other programmable data processing device, so that when the program code is executed by the processor or controller, the functions / operations specified in the flow charts and / or block diagrams are implemented. The program code can be executed entirely on the machine, partially on the machine, as a stand-alone software package, partially on the machine and partially on a remote machine, or entirely on a remote machine or server.

[0079] In the context of the present application, a machine-readable medium can be a tangible medium that can contain or store a program for use by an instruction execution system, device or equipment or used in combination with an instruction execution system, device or equipment. A machine-readable medium can be a machine-readable signal medium or a machine-readable storage medium. A machine-readable medium can include, but is not limited to, an electronic, magnetic, optical, electromagnetic, infrared or semiconductor system, device or equipment, or any suitable combination of the foregoing. A more specific example of a machine-readable storage medium can include an electrical connection based on one or more lines, a portable computer disk, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber, a portable compact disk read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing.

[0080] Throughout this specification, references to terms such as "one embodiment," "example," or "specific example" indicate that the specific features, structures, materials, or characteristics described in conjunction with that embodiment or example are included in at least one embodiment or example of the present invention. In this specification, schematic representations of these terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0081] The basic principles, main features, and advantages of the present invention are shown and described above. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are merely illustrative of the principles of the present invention. Various changes and modifications may be made to the present invention without departing from the spirit and scope of the present invention, and such changes and modifications fall within the scope of the invention as claimed.

Claims

1. A re-decoupling method for bipolar cycloconverter with asymmetric bridge arm inductance, wherein the bipolar cycloconverter has a three-phase structure, each phase comprising an upper bridge arm and a lower bridge arm, each of which comprises n full-bridge submodules connected in series and a bridge arm reactor, wherein the bridge arm reactors have different inductance values; the low-frequency side of the bipolar cycloconverter is connected to a low-frequency power grid via a bipolar transformer, and the connection points of the upper and lower bridge arms of each phase are respectively connected to the power frequency power grid, characterized in that: The control method is: Apply power frequency common mode reference voltage, power frequency differential mode reference voltage, low frequency common mode reference voltage, and low frequency differential mode reference voltage to the upper and lower bridge arms of each phase. The bridge arm reference voltage is the sum of the four reference voltages. The power frequency differential mode reference voltage and the low frequency common mode reference voltage are used to realize the frequency output of the power frequency side and the low frequency side respectively, and the power frequency common mode reference voltage and the low frequency differential mode reference voltage are used to eliminate the mutual interference between the power frequency and the low frequency caused by the asymmetry of the bridge arm inductance.

2. The method according to claim 1, wherein: The power frequency differential mode reference voltage is obtained by the following steps: S101, in the dq coordinate system, according to the power frequency reference current i gd_ref and i gq_ref , the dq component u of the power frequency differential mode reference voltage is obtained through PI control diff_gd and u diff_gq : Among them, K p and K i is the control parameter of PI control, i gd and i gq is the dq component of the power frequency current, u gd and u gq is the dq component of the power frequency voltage, ω g is the power frequency angular frequency, L G is the equivalent inductance on the power frequency side; S102, u diff_gd and u diff_gq At the power frequency angular frequency ω g Down-converted to the abc three-phase coordinate system, the power frequency differential mode reference voltage u is obtained diff_gj , j = a, b, c.

3. The method according to claim 1, wherein: The low-frequency common-mode reference voltage is obtained by the following steps: S201, in the dq coordinate system, according to the low-frequency reference current i ld_ref and i lq_ref The dq component u of the low-frequency common-mode reference voltage is calculated by the following formula: com_ld and u com_lq : Among them, i ld and i lq is the dq component of the low-frequency current, u ld and u lq is the dq component of the low-frequency voltage, ω l is the low-frequency corner frequency, L L is the low-frequency side equivalent inductance, k l is the bipolar transformer ratio; K p and K i is the control parameter of PI control; S202. Will u com_ld and u com_lq At low angular frequency ω l Down-converted to the abc three-phase coordinate system, the low-frequency common-mode reference voltage u is obtained com_lj , j = a, b, c.

4. The method according to claim 1, wherein The power frequency common-mode reference voltage is obtained by the following steps: S301, filter out the power frequency interference current component in the low frequency current, and convert it to the dq coordinate system to obtain the low frequency side power frequency interference current i l_gd and i l_gq ; S302, in the dq coordinate system, i l_gd and i l_gq Suppress it to 0, and calculate the dq component u of the power frequency common mode reference voltage by the following formula com_gd and u com_gq : Among them, ω g is the power frequency angular frequency, ΔL is the difference between the upper and lower bridge arm inductances; S303, u com_gd and u com_gq At the power frequency angular frequency ω g Down-converted to the abc three-phase coordinate system, the power frequency common mode reference voltage u is obtained com_gj , j = a, b, c.

5. The method according to claim 1, wherein: The low-frequency differential mode reference voltage is obtained by the following steps: S401, filter out the low-frequency interference current component from the power frequency current, and convert it to the dq coordinate system to obtain the power frequency side low-frequency interference current i g_ld and i g_lq ; S402, in the dq coordinate system, i g_ld and i g_lq Suppress it to 0, and calculate the dq component u of the low-frequency differential mode reference voltage by the following formula diff_ld and u diff_lq : Among them, ω l is the low-frequency angular frequency, ΔL is the difference between the upper and lower bridge arm inductances; S403, u diff_ld and u diff_lq At the angular frequency ω l Down-converted to the abc three-phase coordinate system, the low-frequency differential mode reference voltage u is obtained diff_lj , j = a, b, c.

6. The method according to any one of claims 1 to 5, characterized in that: When the connection positions of the power frequency side and the low frequency side with the bipolar AC-AC converter are swapped, the power frequency common-mode reference voltage and the low frequency differential-mode reference voltage are used to achieve the frequency output of the power frequency side and the low frequency side respectively, and the low frequency common-mode reference voltage and the power frequency differential-mode reference voltage are used to eliminate the mutual interference between the power frequency and low frequency caused by the asymmetry of the bridge arm inductance.

7. The method according to claim 1, characterized in that The bipolar transformer includes two secondary windings W1 and W2, where W1 is the positive winding and adopts the Y0 connection method, and W2 is the negative winding and adopts the Y6 connection method; the three-phase ports of the secondary winding W1 are respectively connected to the upper end of the three-phase upper bridge arm; the three-phase ports of the secondary winding W2 are respectively connected to the lower end of the three-phase lower bridge arm.

8. The method according to claim 1, wherein: The full-bridge submodule includes the first to fourth IGBTs and a first electrolytic capacitor, wherein the emitter of the first IGBT is connected to the collector of the second IGBT, and the connection point is used as the positive end of the full-bridge submodule; the emitter of the third IGBT is connected to the collector of the fourth IGBT, and the connection point is used as the negative end of the full-bridge submodule; the collector of the first IGBT, the collector of the third IGBT and the positive electrode of the first electrolytic capacitor are connected; the emitter of the second IGBT, the emitter of the fourth IGBT and the negative electrode of the first electrolytic capacitor are connected; and the first to fourth IGBTs are all connected with anti-parallel diodes.

9. An electronic system comprising: at least one processor; and a memory communicatively connected to the at least one processor; wherein the memory stores instructions executable by the at least one processor, characterized in that the instructions are executed by the at least one processor so that the at least one processor can execute the method described in any one of claims 1-8.

10. A computer-readable storage medium storing computer instructions, characterized in that: The computer instructions are used to enable the computer to execute the method according to any one of claims 1 to 8.

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