Cascaded H-bridge topology and control method

Abstract

A cascaded H-bridge topology and control method. The cascaded H-bridge topology includes: a three-phase cascaded H-bridge circuit, a first additional dynamic shunt branch, and a second additional dynamic shunt branch; the first additional dynamic shunt branch is connected in parallel with the cascaded H-bridge circuit of each phase, and a phase selection switch device is arranged between the first additional dynamic shunt branch and each phase power supply; the second additional dynamic shunt branch is connected in parallel with the cascaded H-bridge circuit of each phase, and a phase selection switch device is arranged between the second additional dynamic shunt branch and each phase power supply; the first additional dynamic shunt branch and the second additional dynamic shunt branch are connected in parallel. The cascaded H-bridge topology and control method provided by the embodiments of the present invention can avoid damage to the switching devices on the working bridge arm due to overcurrent by shunting current through the parallel connection of the additional dynamic shunt branch and the cascaded H-bridge circuit of each phase, and improve the safe grid connection ability of the cascaded H-bridge and the supporting ability for the stability of the power system.

Description

Technical Field

[0001] The present invention relates to the field of power electronics technology in power systems, and in particular, to a cascaded H-bridge topology and a control method. Background Art

[0002] With the continuous growth of the grid-connected capacity of wind power and photovoltaic power, the increasing number of energy storage devices and flexible DC transmission projects, cascaded H-bridges have been widely used in power systems, and the development trend of the power electronicization of the system has become increasingly prominent. Restricted by factors such as the low over-current tolerance of power electronic devices, after the grid-connected AC system is disturbed, the cascaded H-bridge has a risk of exiting operation due to over-current damage to the switching devices. In a power system where a large number of power electronic devices with cascaded H-bridge structures such as wind power, photovoltaic power, and energy storage are grid-connected, if the cascaded H-bridge fails or is disconnected from the grid due to over-current caused by AC system disturbances, it will bring a large amount of active power impact and reactive power impact to the system, thereby threatening the power angle stability, voltage stability, and frequency stability of the system. Therefore, it is urgent to study measures to improve the over-current tolerance of cascaded H-bridges. Summary of the Invention

[0003] In view of this, the present invention proposes a cascaded H-bridge topology and a control method, aiming to solve the problem that the existing cascaded H-bridge fails or is disconnected from the grid due to over-current.

[0004] In a first aspect, an embodiment of the present invention provides a cascaded H-bridge topology, characterized in that the cascaded H-bridge topology includes: a three-phase cascaded H-bridge circuit, a first additional dynamic shunt branch, and a second additional dynamic shunt branch; the first additional dynamic shunt branch is connected in parallel with the cascaded H-bridge circuit of each phase, and a phase selection switch device is provided between the first additional dynamic shunt branch and the power supply of each phase; the second additional dynamic shunt branch is connected in parallel with the cascaded H-bridge circuit of each phase, and a phase selection switch device is provided between the second additional dynamic shunt branch and the power supply of each phase; the first additional dynamic shunt branch and the second additional dynamic shunt branch are connected in parallel; wherein, the cascaded H-bridge circuit of each phase includes m series-connected H-bridge circuits; both the first additional dynamic shunt branch and the second additional dynamic shunt branch include n series-connected shunt circuits, and both m and n are positive integers.

[0005] Further, the shunt circuit includes a first shunt circuit branch and a second shunt circuit branch connected in parallel, and both the first shunt circuit branch and the second shunt circuit branch include an insulated gate bipolar transistor and a diode.

[0006] Further, each shunt circuit in the first additional dynamic shunt branch is connected in series in a first direction, and each shunt circuit in the second additional dynamic shunt branch is connected in series in a second direction, and the first direction is opposite to the second direction.

[0007] Further, the phase selection switch device is a gate turn-off thyristor.

[0008] Further, m = 4.

[0009] Further, n = 4.

[0010] In a second aspect, an embodiment of the present invention further provides a control method for a cascaded H-bridge topology, which is applied to the cascaded H-bridge topology according to any one of claims 1-6. It is characterized in that the grid AC side A, B, and C phase currents are respectively I asum 、I bsum 、I csum , the phase selection switch devices between the first additional dynamic shunt branch and the A, B, and C phase power supplies are respectively T an 、T bn 、T cn , the phase selection switch devices between the second additional dynamic shunt branch and the A, B, and C phase power supplies are respectively T ap 、T bp 、T cp , and the control method includes: according to the phase with the maximum positive current in the I asum 、I bsum 、I csum , correspondingly turn on the phase selection switch devices T ap 、T bp 、T cp , so that the second additional dynamic shunt branch shunts the phase with the maximum positive current in parallel; or according to the phase with the maximum negative current in the I asum 、I bsum 、I csum , correspondingly turn on the phase selection switch devices T an 、T bn 、T cn , so that the first additional dynamic shunt branch shunts the phase with the maximum negative current in parallel.

[0011] Further, the step of correspondingly turning on the phase selection switch devices T asum 、T bsum 、T csum according to the phase with the maximum positive current in the I ap 、T bp 、T cp , includes: if I asum > 0 and I asum > I bsum 、I asum > I csum , then turn on T ap ; if I bsum> 0 and I bsum > I asum 、I bsum > I csum ,then turn on T bp ; If I csum > 0 and I csum > I asum 、I csum > I bsum ,then turn on T cp .

[0012] Further, according to the I asum 、I bsum 、I csum in the phase with the maximum reverse current, correspondingly turn on the phase selection switch device T an 、T bn 、T cn , including: If I asum <0 and |I asum | > |I bsum |、|I asum | > |I csum |, then turn on T an ; If I bsum <0 and |I bsum | > |I asum |、|I bsum | > |I csum |, then turn on T bn ; If I csum <0 and |I csum | > |I asum |、|I csum | > |I bsum |, then turn on T cn .

[0013] In a third aspect, an embodiment of the present invention further provides a computer-readable storage medium, on which a computer program is stored, and when the program is executed by a processor, the method provided in any of the above embodiments is implemented.

[0014] The cascaded H-bridge topology structure and control method provided by the embodiments of the present invention can shunt current by connecting the first additional dynamic shunt branch and the second additional dynamic shunt branch in parallel with the cascaded H-bridge circuit of each phase, which can avoid damage to the switching devices on the working bridge arm due to overcurrent, and improve the safe grid connection ability of the cascaded H-bridge and the supporting ability for the stability of the power system. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 Shows a schematic structural diagram of a cascaded H-bridge topology structure according to an embodiment of the present invention;

[0016] Figure 2A schematic diagram showing the division of the working regions of the AC-side current of the cascaded H-bridge topology according to an embodiment of the present invention;

[0017] Figures 3(a) to 3(f) showing according to an embodiment of the present invention Figure 2 A dynamic shunt schematic diagram of the cascaded H-bridge topology in the 6 working regions shown;

[0018] Figure 4 A schematic diagram of a test system for the cascaded H-bridge topology according to an embodiment of the present invention;

[0019] Fig. 5(a) shows a schematic diagram of the three-phase currents of the power grid and the AC side of the cascaded H-bridge under the test conditions according to an embodiment of the present invention; Fig. 5(b) shows a schematic diagram of the currents of the first additional dynamic shunt branch and the second additional dynamic shunt branch under the test conditions according to an embodiment of the present invention; Fig. 5(c) shows a schematic diagram of the three-phase output current of the cascaded H-bridge and the currents of the working bridge arms of the first three-phase H-bridge when the second additional dynamic shunt branch p is conducting under the test conditions according to an embodiment of the present invention; Fig. 5(d) shows a schematic diagram of the three-phase output current of the cascaded H-bridge and the currents of the working bridge arms of the first three-phase H-bridge when the first additional dynamic shunt branch n is conducting under the test conditions according to an embodiment of the present invention. Detailed implementation manners

[0020] Now, exemplary embodiments of the present invention will be introduced with reference to the accompanying drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. These embodiments are provided to disclose the present invention in detail and completely, and to fully convey the scope of the present invention to those skilled in the art. The terms in the exemplary embodiments shown in the drawings are not limitations to the present invention. In the drawings, the same units / components are denoted by the same reference numerals.

[0021] Unless otherwise specified, the terms (including scientific and technical terms) used herein have the ordinary meaning understood by those skilled in the art. Additionally, it can be understood that the terms defined in a commonly used dictionary should be understood to have a meaning consistent with the context of their relevant fields, and should not be construed as idealized or overly formal meanings.

[0022] Figure 1 A schematic diagram of the structure of the cascaded H-bridge topology according to an embodiment of the present invention.

[0023] As Figure 1 shown, the cascaded H-bridge topology includes:

[0024] A three-phase cascaded H-bridge circuit, a first additional dynamic shunt branch, and a second additional dynamic shunt branch;

[0025] The first additional dynamic shunt branch is connected in parallel with the cascaded H-bridge circuit of each phase, and a phase selection switch device is provided between the first additional dynamic shunt branch and the power supply of each phase;

[0026] The second additional dynamic shunt branch is connected in parallel with the cascaded H-bridge circuit of each phase, and a phase selection switch device is provided between the second additional dynamic shunt branch and the power supply of each phase;

[0027] The first additional dynamic shunt branch and the second additional dynamic shunt branch are connected in parallel;

[0028] Wherein, the cascaded H-bridge circuit of each phase includes m series-connected H-bridge circuits;

[0029] Both the first additional dynamic shunt branch and the second additional dynamic shunt branch include n series-connected shunt circuits, and both m and n are positive integers.

[0030] In the above embodiment, by connecting the first additional dynamic shunt branch, the second additional dynamic shunt branch in parallel with the cascaded H-bridge circuit of each phase for current shunting, it is possible to avoid damage to the switching devices on the working bridge arm due to overcurrent, and improve the safe grid connection ability of the cascaded H-bridge and the supporting ability for the stability of the power system.

[0031] Further, the shunt circuit includes a first shunt circuit branch and a second shunt circuit branch connected in parallel, and both the first shunt circuit branch and the second shunt circuit branch include an insulated gate bipolar transistor and a diode.

[0032] Further, each shunt circuit in the first additional dynamic shunt branch is connected in series in a first direction, and each shunt circuit in the second additional dynamic shunt branch is connected in series in a second direction, and the first direction is opposite to the second direction.

[0033] Further, the phase selection switch device is a gate turn-off thyristor.

[0034] Further, m = 4.

[0035] Further, n = 4.

[0036] Specifically, as Figure 1 shown, the cascaded H-bridge of each phase is composed of four series-connected H-bridge circuits. The H-bridge circuits constituting the cascaded H-bridge of phase A are sequentially numbered as H-B A01 , H-B A02 , H-B A03 , H-B A04 , and A01-1, A01-2, A01-3, A01-4 are respectively the switching devices on the working bridge arm of the H-bridge H-B of phase A A01 , and A02-1, A02-2, A02-3, A02-4 are respectively the switching devices on the working bridge arm of the H-bridge H-B of phase A A02The switching devices on the working bridge arm, A03-1, A03-2, A03-3, and A03-4 are respectively the A-phase H-bridge H-B A03 The switching devices on the working bridge arm, A04-1, A04-2, A04-3, and A04-4 are respectively the A-phase H-bridge H-B A04 The switching devices on the working bridge arm; the switching devices on the B-phase and C-phase cascaded H-bridge working bridge arms are numbered according to the same rule.

[0037] In addition to the above three-phase cascaded H-bridge circuit, the cascaded H-bridge topology further includes a first additional dynamic shunt branch n and a second additional dynamic shunt branch p. I p 、I n are respectively the total current of the first additional dynamic shunt branch n and the total current of the second additional dynamic shunt branch p. The first additional dynamic shunt branch n includes four series-connected shunt circuits B N01 、B N02 、B N03 、B N04 . The shunt circuit B N01 includes a first shunt circuit branch B N01-1 and a second shunt circuit branch B N01-2 . The first shunt circuit branch B N01-1 includes an insulated gate bipolar transistor N01-1 and a diode. The second shunt circuit branch B N01-2 includes an insulated gate bipolar transistor N01-2 and a diode. The insulated gate bipolar transistors in the shunt circuits B N02 、B N03 、B N04 are numbered according to the same rule, and these insulated gate bipolar transistors serve as the shunt switching devices of the first additional dynamic shunt branch n. The second additional dynamic shunt branch p includes four series-connected shunt circuits B P01 、B P02 、B P03 、B P04 . The shunt circuit B P01 includes a first shunt circuit branch B P01-1 and a second shunt circuit branch B P01-2 . The first shunt circuit branch B P01-1 includes an insulated gate bipolar transistor P01-1 and a diode. The second shunt circuit branch B P01-2 includes an insulated gate bipolar transistor P01-2 and a diode. The insulated gate bipolar transistors in the shunt circuits B P02 、B P03 、B P04 are numbered according to the same rule, and these insulated gate bipolar transistors serve as the shunt switching devices of the second additional dynamic shunt branch p.

[0038] The first additional dynamic shunt branch n is respectively connected in parallel with the cascaded H-bridge circuits of phases A, B, and C, and phase-selection switch devices T an , T bn , T cn are provided between the first additional dynamic shunt branch n and the power supplies of phases A, B, and C respectively; the second additional dynamic shunt branch p is respectively connected in parallel with the cascaded H-bridge circuits of phases A, B, and C, and phase-selection switch devices T ap , T bp , T cp are provided between the second additional dynamic shunt branch p and the power supplies of phases A, B, and C respectively. The phase-selection switch devices T an , T bn , T cn , T ap , T bp , T cp are all gate turn-off thyristors.

[0039] The present invention also provides a control method for a cascaded H-bridge topology, which is applied to the cascaded H-bridge topology provided in any of the above embodiments. The grid AC-side phase A, B, and C currents are respectively I asum , I bsum , I csum . The phase-selection switch devices between the first additional dynamic shunt branch and the power supplies of phases A, B, and C are respectively T an , T bn , T cn . The phase-selection switch devices between the second additional dynamic shunt branch and the power supplies of phases A, B, and C are respectively T ap , T bp , T cp . The control method includes:

[0040] According to the phase with the maximum positive current among I asum , I bsum , I csum , the corresponding phase-selection switch devices T ap , T bp , T cp are turned on to enable the second additional dynamic shunt branch to perform parallel shunting on the phase with the maximum positive current; or

[0041] According to the phase with the maximum negative current among I asum , I bsum , I csum , the corresponding phase-selection switch devices T an , T bn , T cn are turned on to enable the first additional dynamic shunt branch to perform parallel shunting on the phase with the maximum negative current.

[0042] In the above embodiments, by turning on the phase selection switch device corresponding to the phase with the maximum value among the three-phase currents, the first additional dynamic shunt branch or the second additional dynamic shunt branch is turned on to shunt the switch device on the working bridge arm of the H-bridge, which can prevent the switch device on the working bridge arm from exiting operation or being damaged due to overcurrent, and improve the safe grid connection ability of the cascaded H-bridge and the supporting ability for the stability of the power system.

[0043] Figure 2 FIG. shows a schematic diagram of the division of the working area of the AC-side current of the cascaded H-bridge topology according to an embodiment of the present invention. As Figure 2 shown, the current flow conditions of the first additional dynamic shunt branch, the second additional dynamic shunt branch, and the working bridge arm of the cascaded H-bridge are divided into 6 working areas. When the switch devices on the working bridge arm of the three-phase cascaded H-bridge are turned on in the corresponding working areas, the phase selection switch devices are respectively T an 、T bn 、T cn or T ap 、T bp 、T cp , generating an additional dynamic shunt branch in parallel with it to share the current flowing through the switch device.

[0044] Figures 3(a) to 3(f) FIG. shows the dynamic shunt schematic diagram of the cascaded H-bridge topology in the 6 working areas provided according to an embodiment of the present invention. It should be noted that, in order to highlight the shunt conditions in each working area, Figure 2 only the conduction conditions of the switch devices with shunt paths in the working area are drawn in, and the working modes of the remaining switch devices are omitted. Figures 3(a) to 3(f)

[0045] As shown in FIG. 3(a), in working area ①, I asum >0 and I asum >I bsum 、I asum >I csum , T ap is turned on, corresponding to the conduction of P01-1, P01-2, P02-1, P02-2,..., P04-2 and their anti-parallel diodes to form the second additional dynamic shunt branch p, which shares 50% of I A01 with the working bridge arms of the A-phase H-bridge circuits H-B A02 、H-B A03 、H-B A04 、H-B asum csum .

[0046] As shown in FIG. 3(b), in working area ②, I csum <0 and |I csum |>|I asum |、|Icsum |>|I bsum |, T cn Conducts, corresponding to the conduction of N01-1, N01-2, N02-1, N02-2,..., N04-2 and their anti-parallel diodes, and forms the first additional dynamic shunt branch n, which shares 50% of I with the working bridge arms of the C-phase H-bridge circuits H-B C01 、H-B C02 、H-B C03 、H-B C04 respectively csum 。

[0047] As shown in Fig. 3(c), in working region ③, I bsum > 0 and I bsum > I asum 、I bsum > I csum ,T bp conducts, corresponding to the conduction of P01-1, P01-2, P02-1, P02-2,..., P04-2 and their anti-parallel diodes, and forms the second additional dynamic shunt branch p, which shares 50% of I with the working bridge arms of the B-phase H-bridge circuits H-B B01 、H-B B02 、H-B B03 、H-B B04 respectively bsum 。

[0048] As shown in Fig. 3(d), in working region ④, I asum < 0 and |I asum | > |I bsum |、|I asum | > |I csum |,T an conducts, corresponding to the conduction of N01-1, N01-2, N02-1, N02-2,..., N04-2 and their anti-parallel diodes, and forms the first additional dynamic shunt branch n, which shares 50% of I with the working bridge arms of the A-phase H-bridge circuits H-B A01 、H-B A02 、H-B A03 、H-B A04 respectively asum 。

[0049] As shown in Fig. 3(e), in working region ⑤, I csum > 0 and I csum > I asum 、I csum > I bsum ,T cpConduct, corresponding to the conduction of P01-1, P01-2, P02-1, P02-2, ..., P04-2 and their anti-parallel diodes, and form the second additional dynamic shunt branch p, which shares 50% of I with the working bridge arms of the C-phase H-bridge circuit H-B C01 、H-B C02 、H-B C03 、H-B C04 respectively csum 。

[0050] As shown in Fig. 3(f), in the working region ⑥, I bsum <0 and |I bsum | > |I asum |, |I bsum | > |I csum |, T bn conducts, corresponding to the conduction of N01-1, N01-2, N02-1, N02-2, ..., N04-2 and their anti-parallel diodes, and forms the first additional dynamic shunt branch n, which shares 50% of I with the working bridge arms of the B-phase H-bridge circuit H-B B01 、H-B B02 、H-B B03 、H-B B04 respectively bsum 。

[0051] Figure 4 shows a schematic diagram of a test system for a cascaded H-bridge topology according to an embodiment of the present invention. Build a test system as shown in Figure 4 in a simulation software to test the cascaded H-bridge topology

[0052] In the simulation, start to judge the startup criterion of the additional dynamic shunt branch phase selection switch device at 0.15 Figures 5(a) to 5(d) shows a schematic diagram of the current waveforms of each branch of the cascaded H-bridge topology under the test conditions provided by the embodiment of the present invention. It can be seen that when the amplitudes of the three-phase currents I asum 、I bsum 、I csum on the AC side of the power grid are relatively large, there is a risk that the device will be damaged and the cascaded H-bridge will fail to operate when this current flows through the switch devices of the working bridge arms of the cascaded H-bridge. Enable the additional dynamic shunt branch at the 0.15 s moment. Fig. 5(a) shows a schematic diagram of the three-phase currents on the power grid and the AC side of the cascaded H-bridge under the test conditions provided by the embodiment of the present invention. It can be seen from Fig. 5(a) that starting from 0.15 s, the three-phase currents I a 、I b 、I cThe amplitudes of the currents are reduced to half of the previous values, and the shunting effect is obvious. FIG5( b ) shows the first additional dynamic shunting branch current I under the test condition provided by the embodiment of the present invention. n and the second additional dynamic shunt branch current I p The first H bridge (HB A01 HB B01 HB C01 5(c) shows the current flowing through HB when the second additional dynamic shunt branch p is turned on under the test conditions provided by the embodiment of the present invention. A01 HB B01 HB C01 The current I of the switch device on the working bridge arm A01-4 ,I B01-4 ,I C01-4 5(d) shows the current flowing through HB when the first additional dynamic shunt branch n is turned on under the test conditions provided by the embodiment of the present invention. A01 HB B01 HB C01 The current I of the switch device on the working bridge arm A01-1 ,I B01-1 ,I C01-1 It can be seen that the current of the switching devices on the working bridge arm of the H-bridge circuit is significantly reduced due to the additional dynamic shunt branch, and the amplitude is reduced to half of the original, that is, 1 / 2I asum 、1 / 2I bsum 、1 / 2I csum Since the four H-bridge circuits of each phase are in series, the currents flowing through different switch devices of the cascaded H-bridge of the same phase at the same time are equal, so the same conclusion will be obtained by analyzing the currents of other working bridge arms in the novel cascaded H-bridge structure proposed in this embodiment.

[0053] It can be seen from the simulation results that the new cascade H-bridge proposed in the embodiment of the present invention can significantly reduce the overcurrent of the switching devices of the working bridge arms of the cascade H-bridge caused by the AC system disturbance, and improve the operating reliability of the cascade H-bridge.

[0054] An embodiment of the present invention further provides a computer-readable storage medium on which a computer program is stored. When the program is executed by a processor, the method provided in any of the above embodiments is implemented.

[0055] The invention has been described above with reference to a few embodiments. However, it is readily apparent to a person skilled in the art that other embodiments than the ones disclosed above are equally within the scope of the invention, as defined by the appended patent claims.

[0056] Generally, all terms used in the claims are construed according to their ordinary meaning in the technical field, unless otherwise expressly defined therein. All references to "a / the [device, component, etc.]" are to be construed openly as at least one instance of the device, component, etc., unless otherwise expressly stated. The steps of any method disclosed herein need not be performed in the exact order disclosed, unless expressly stated.

[0057] Those skilled in the art will appreciate that the embodiments of the present application may be provided as a method, a system, or a computer program product. Accordingly, the present application may take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present application may take the form of a computer program product implemented on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) that contain computer-usable program code.

[0058] The present application is described with reference to the flowcharts and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the present application. It should be understood that each flow and / or block in the flowcharts and / or block diagrams, and combinations of flows and / or blocks in the flowcharts and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to the processors of general purpose computers, special purpose computers, embedded processors, or other programmable data processing devices to produce a machine, such that the instructions executed by the processors of the computer or other programmable data processing devices produce means for implementing the functions specified in Figure 1 one or more of the flows Figure 1 or blocks or combinations of blocks.

[0059] These computer program instructions can also be stored in a computer-readable memory that can direct a computer or other programmable data processing device to operate in a particular manner, such that the instructions stored in the computer-readable memory produce a manufacture including instruction means that implement the functions specified in Figure 1 one or more of the flows Figure 1 or blocks or combinations of blocks.

[0060] These computer program instructions can also be loaded onto a computer or other programmable data processing device, such that a series of operational steps are performed on the computer or other programmable device to produce a computer-implemented process, and thus the instructions executed on the computer or other programmable device provide steps for implementing the functions specified in Figure 1 one or more of the flows Figure 1 or blocks or combinations of blocks.

[0061] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: it is still possible to modify the specific implementation manners of the present invention or make equivalent substitutions, and any modification or equivalent substitution that does not depart from the spirit and scope of the present invention shall be covered by the protection scope of the claims of the present invention.

Claims

1. A cascaded H-bridge topology, characterized in that, the cascaded H-bridge topology includes: a three-phase cascaded H-bridge circuit, a first additional dynamic shunt branch and a second additional dynamic shunt branch; the first additional dynamic shunt branch is connected in parallel with the cascaded H-bridge circuit of each phase, and a phase selection switch device is arranged between the first additional dynamic shunt branch and each phase power supply; the second additional dynamic shunt branch is connected in parallel with the cascaded H-bridge circuit of each phase, and a phase selection switch device is arranged between the second additional dynamic shunt branch and each phase power supply; the first additional dynamic shunt branch and the second additional dynamic shunt branch are connected in parallel; wherein, the cascaded H-bridge circuit of each phase includes m series-connected H-bridge circuits; both the first additional dynamic shunt branch and the second additional dynamic shunt branch include n series-connected shunt circuits, and both m and n are positive integers.

2. The cascaded H-bridge topology according to claim 1, characterized in that, the shunt circuit includes a first shunt circuit branch and a second shunt circuit branch connected in parallel, and both the first shunt circuit branch and the second shunt circuit branch include an insulated gate bipolar transistor and a diode.

3. The cascaded H-bridge topology according to claim 1, characterized in that, each shunt circuit in the first additional dynamic shunt branch is connected in series in a first direction, each shunt circuit in the second additional dynamic shunt branch is connected in series in a second direction, and the first direction is opposite to the second direction.

4. The cascaded H-bridge topology according to any one of claims 1-3, characterized in that, the phase selection switch device is a gate turn-off thyristor.

5. The cascaded H-bridge topology according to claim 1, characterized in that, m＝4。 6. The cascaded H-bridge topology according to claim 1, characterized in that, n＝4。 7. A control method for a cascaded H-bridge topology, applied to the cascaded H-bridge topology according to any one of claims 1-6, characterized in that, The grid AC side A, B, and C phase currents are I asum , I bsum , I csum , and the phase selection switch devices between the first additional dynamic shunt branch and the A, B, and C phase power supplies are T an , T bn , T cn , and the phase selection switch devices between the second additional dynamic shunt branch and the A, B, and C phase power supplies are T ap , T bp , T cp , and the control method includes: According to the phase among the said I asum 、I bsum 、I csum with the maximum positive current, correspondingly turn on the phase-selection switch devices T ap 、T bp 、T cp so that the second additional dynamic shunt branch performs parallel shunting on the phase with the maximum positive current; or According to the phase among the I asum 、I bsum 、I csum with the maximum reverse current, correspondingly turn on the phase-selection switch devices T an 、T bn 、T cn so that the first additional dynamic shunt branch performs parallel shunting on the phase with the maximum reverse current.

8. The control method according to claim 7, characterized in that, The phase with the maximum positive current among the said I asum 、I bsum 、I csum correspondingly conducts the phase selection switch devices T ap 、T bp 、T cp , including: If I asum > 0 and I asum > I bsum 、I asum > I csum , then turn on T ap ; If I bsum > 0 and I bsum > I asum 、I bsum > I csum , then turn on T bp ; If I csum > 0 and I csum > I asum 、I csum > I bsum , then turn on T cp .

9. The control method according to claim 7, characterized in that, The phase with the maximum reverse current among the I asum , I bsum , I csum corresponds to conducting the phase selection switch devices T an , T bn , T cn , including: If I asum < 0 and |I asum | > |I bsum |, |I asum | > |I csum |, then turn on T an ; If I bsum < 0 and |I bsum | > |I asum |, |I bsum | > |I csum |, then turn on T bn ; If I csum < 0 and |I csum | > |I asum |, |I csum | > |I bsum |, then turn on T cn .

10. A computer-readable storage medium, on which a computer program is stored, characterized in that, when the program is executed by a processor, the method according to any one of claims 7-9 is implemented.

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