Alternating current conversion equipment

Abstract

The invention discloses alternating current conversion equipment, and belongs to the technical field of power conversion. In the alternating-current conversion equipment, an alternating-current conversion circuit is connected with an alternating-current source and a primary winding of a transformer, the alternating-current conversion circuit comprises at least one bridge arm, the two ends of the bridge arm are connected with the alternating-current source through bridge arm buses, the bridge arm comprises an upper bridge arm and a lower bridge arm which are connected in series, and each of the upper bridge arm and the lower bridge arm comprises two switching tubes. The two switch tubes of one of the upper bridge arm and the lower bridge arm are connected in series through common source electrodes, and the two switch tubes of the other one of the upper bridge arm and the lower bridge arm are connected in series through common drain electrodes; under the condition that the bridge arm is in the dead zone time period, the follow current module is provided with a follow current path, the alternating current conversion device is provided with a closed follow current loop, and the closed follow current loop comprises the follow current path, part of the switching tubes and the primary winding. According to the invention, a closed follow current loop is provided in a dead zone period, continuous current circulation is realized without interruption, tube pressure stress overshoot of a switching device is reduced, and the risk of damage to the switching device is reduced.

Description

Technical Field

[0001] This application relates to the field of power conversion technology, and more particularly to an AC conversion device. Background Technology

[0002] In single-stage AC-DC schemes, matrix-type single-stage AC-DC converters based on bidirectional switching structures have become an application solution. However, in this traditional matrix-type single-stage AC-DC converter, the bidirectional switching devices are distributed back to back, which means that the freewheeling current has no freewheeling loop during the dead time period, which can easily cause overshoot of tube voltage stress and damage the switching devices. Summary of the Invention

[0003] This application provides an AC converter that can provide a freewheeling current loop during the dead time period, thereby effectively reducing the overshoot of the switching device's voltage stress and reducing the risk of damage to the switching device.

[0004] In a first aspect, this application provides an AC conversion device, which includes: transformer; An AC converter circuit is provided, one end of which is configured to be connected to an AC source, and the other end of which is connected to the primary winding of a transformer. The AC converter circuit includes at least one bridge arm, with both ends of the bridge arm connected to the AC source via a bridge arm busbar. The bridge arm includes an upper bridge arm and a lower bridge arm connected in series. The connection node between the upper bridge arm and the lower bridge arm is connected to the primary winding. Both the upper bridge arm and the lower bridge arm include two switching transistors. The two switching transistors of one of the upper bridge arm and the lower bridge arm are connected in series with a common source, and the two switching transistors of the other of the upper bridge arm and the lower bridge arm are connected in series with a common drain. The freewheeling module has a freewheeling path when the bridge arm is in the dead time period. The AC converter has a closed freewheeling loop, which includes the freewheeling path, part of the switching transistors and the primary winding.

[0005] In some embodiments, when there is only one bridge arm and the bridge arms form a symmetrical half-bridge, one end of the freewheeling module is connected to the middle node of the two switching transistors in the upper bridge arm, and the other end of the freewheeling module is connected to the middle node of the two switching transistors in the lower bridge arm.

[0006] In some embodiments, the freewheeling module includes a first sub-freewheeling unit and a second sub-freewheeling unit. One end of the first sub-freewheeling unit is connected to the middle node of the two switching transistors of the upper bridge arm, and the other end of the first sub-freewheeling unit is connected to the bridge arm bus. One end of the second sub-freewheeling unit is connected to the middle node of the two switching transistors of the lower bridge arm, and the other end of the second sub-freewheeling unit is connected to the bridge arm bus. When the bridge arm is in a dead zone, the follow-through path includes at least one of the first sub-follow-through unit and the second sub-follow-through unit.

[0007] In some embodiments, the AC conversion device further includes: Bus capacitors are connected to the bridge arm bus and are connected in parallel with the bridge arm.

[0008] In some embodiments, when there is only one bridge arm and the bridge arm forms an asymmetrical half-bridge, one end of the freewheeling module is connected to the middle node of the two switching transistors in the upper bridge arm, and the other end of the freewheeling module is connected to the middle node of the two switching transistors in the lower bridge arm.

[0009] In some embodiments, the freewheeling module includes a third sub-freewheeling unit and a fourth sub-freewheeling unit. One end of the third sub-freewheeling unit is connected to the middle node of the two switching transistors of the upper bridge arm, and the other end of the third sub-freewheeling unit is connected to the bridge arm bus. One end of the fourth sub-freewheeling unit is connected to the middle node of the two switching transistors of the lower bridge arm, and the other end of the fourth sub-freewheeling unit is connected to the bridge arm bus. When the bridge arm is in a dead zone, the follow-through path includes at least one of the third and fourth sub-follow-through units.

[0010] In some embodiments, when there are two bridge arms and the two bridge arms have the same structure, the freewheeling module includes a fifth sub-freewheeling unit and a sixth sub-freewheeling unit. One end of the fifth sub-freewheeling unit is connected to the middle node of the two switching transistors of an upper bridge arm, and the other end of the fifth sub-freewheeling unit is connected to the middle node of the two switching transistors of any lower bridge arm. One end of the sixth sub-freewheeling unit is connected to the middle node of the two switching transistors of another upper bridge arm, and the other end of the sixth sub-freewheeling unit is connected to the middle node of the two switching transistors of the remaining lower bridge arm. When the bridge arm is in a dead zone, the follow-through path includes at least one of the fifth and sixth sub-follow-through units.

[0011] In some embodiments, at least one of the fifth sub-current relay unit and the sixth sub-current relay unit is composed of a plurality of current relay elements.

[0012] In some embodiments, when there are two bridge arms, and the two switches of the upper bridge arm of one of the two bridge arms are connected in series with a common source, and the two switches of the upper bridge arm of the other of the two bridge arms are connected in series with a common drain, the freewheeling module includes a seventh sub-freewheeling unit and an eighth sub-freewheeling unit. One end of the seventh sub-freewheeling unit is connected to the middle node of the two switches of one upper bridge arm, and the other end of the seventh sub-freewheeling unit is connected to the middle node of the two switches of another upper bridge arm. One end of the eighth sub-freewheeling unit is connected to the middle node of the two switches of one lower bridge arm, and the other end of the eighth sub-freewheeling unit is connected to the middle node of the two switches of another lower bridge arm. When the bridge arm is in a dead zone, the follow-through path includes at least one of the seventh and eighth sub-follow-through units.

[0013] In some embodiments, at least one of the seventh sub-current relay unit and the eighth sub-current relay unit is composed of a plurality of current relay elements.

[0014] In some embodiments, the AC conversion device further includes: AC / DC converter circuit, which is connected to the secondary winding of the transformer; An impedance network is connected between an AC converter circuit and the primary winding of a transformer, or between an AC / DC converter circuit and the secondary winding of a transformer.

[0015] Beneficial effects: This application provides an AC conversion device, which includes a transformer, an AC conversion circuit, and a freewheeling module. One end of the AC conversion circuit is configured to be connected to an AC source, and the other end of the AC conversion circuit is connected to the primary winding of the transformer. The AC conversion circuit includes at least one bridge arm, and the two ends of the bridge arm are respectively connected to the AC source through the bridge arm bus. The bridge arm includes an upper bridge arm and a lower bridge arm connected in series. The connection node between the upper bridge arm and the lower bridge arm is connected to the primary winding. Both the upper bridge arm and the lower bridge arm include two switching transistors. The two switching transistors of one of the upper bridge arm and the lower bridge arm are connected in series with a common source, and the two switching transistors of the other of the upper bridge arm and the lower bridge arm are connected in series with a common drain. When the bridge arm is in the dead time period, the freewheeling module has a freewheeling path, and the AC conversion device has a closed freewheeling loop. The closed freewheeling loop includes the freewheeling path, part of the switching transistors, and the primary winding. In this application, by connecting one switch in the upper and lower bridge arms with its common source in series and the other switch in the lower bridge arms with its common drain in series, the switches in both the upper and lower bridge arms form a bidirectional switching structure. This, combined with the freewheeling module providing the freewheeling path, ensures that the AC converter provides a closed freewheeling loop, including the freewheeling path, part of the switch, and the primary winding, regardless of whether the current is in the forward or reverse direction during the dead time period. This allows for continuous current flow without interruption, effectively reducing the overshoot of the switching device's voltage and lowering the risk of damage to the switching device. Attached Figure Description

[0016] Figure 1 A circuit diagram of an AC converter provided in an embodiment of this application; Figure 2 A circuit diagram illustrating a symmetrical half-bridge formed by bridge arms, provided as an embodiment of this application; Figure 3 A circuit diagram of a freewheeling module in a symmetrical half-bridge provided for an embodiment of this application; Figure 4 A circuit diagram of another symmetrical half-bridge freewheeling module provided in an embodiment of this application; Figure 5A circuit diagram of another symmetrical half-bridge freewheeling module provided in the embodiments of this application; Figure 6 A circuit diagram of another symmetrical half-bridge freewheeling module provided in the embodiments of this application; Figure 7 A circuit diagram illustrating an asymmetric half-bridge formed by bridge arms, provided as an embodiment of this application; Figure 8 A circuit diagram of an asymmetric half-bridge freewheeling module provided for an embodiment of this application; Figure 9 A circuit diagram of another asymmetric half-bridge freewheeling module provided for an embodiment of this application; Figure 10 A circuit diagram showing two identical bridge arm structures provided in an embodiment of this application; Figure 11 for Figure 10 A schematic diagram of current flow in a closed freewheeling circuit; Figure 12 for Figure 10 A schematic diagram of current flow in another closed freewheeling loop in a circuit; Figure 13 A circuit diagram of a freewheeling module with identical two bridge arm structures provided in an embodiment of this application; Figure 14 A circuit diagram of a freewheeling module with the same two bridge arm structures provided in an embodiment of this application; Figure 15 A circuit diagram of another freewheeling module with identical two bridge arm structures provided in this application embodiment; Figure 16 A circuit diagram of another freewheeling module with identical two bridge arm structures provided in this application embodiment; Figure 17 A circuit diagram of another freewheeling module with identical two bridge arm structures provided in this application embodiment; Figure 18 A circuit diagram of another freewheeling module with identical two bridge arm structures provided in this application embodiment; Figure 19 A circuit diagram of another freewheeling module with identical two bridge arm structures provided in this application embodiment; Figure 20 A circuit diagram of another freewheeling module with identical two bridge arm structures provided in this application embodiment; Figure 21 A circuit diagram of another freewheeling module with identical two bridge arm structures provided in this application embodiment; Figure 22A circuit diagram of another freewheeling module with identical two bridge arm structures provided in this application embodiment; Figure 23 A circuit diagram of another freewheeling module with identical two bridge arm structures provided in this application embodiment; Figure 24 A circuit diagram of another freewheeling module with identical two bridge arm structures provided in this application embodiment; Figure 25 A circuit diagram of another freewheeling module with identical two bridge arm structures provided in this application embodiment; Figure 26 A circuit diagram showing two bridge arm structures with different configurations is provided in this application embodiment; Figure 27 A circuit diagram of a freewheeling module with two different bridge arm structures provided in an embodiment of this application; Figure 28 A circuit diagram of a freewheeling module with different two bridge arm structures provided in an embodiment of this application; Figure 29 A circuit diagram of another freewheeling module with different two bridge arm structures provided in this application embodiment; Figure 30 A circuit diagram of another freewheeling module with different two bridge arm structures provided in this application embodiment; Figure 31 A circuit diagram of another AC converter provided in an embodiment of this application; Figure 32 A circuit diagram of another AC converter provided in the embodiments of this application; Figure 33 A circuit diagram of an AC / DC converter circuit provided in an embodiment of this application; Figure 34 A circuit diagram of another AC / DC conversion circuit provided in an embodiment of this application; Figure 35 A circuit diagram of yet another AC / DC conversion circuit provided in an embodiment of this application; Figure 36 A waveform diagram of an AC converter device for phase shift control provided in an embodiment of this application.

[0017] Explanation of reference numerals in the attached figures: 100. Transformer; 200. AC converter circuit; 210. Bridge arm; 211. Upper bridge arm; 212. Lower bridge arm; 220. Bridge arm bus; 230. Bus capacitor; 300, Streaming Module; 310, First Sub-Streaming Unit; 320, Second Sub-Streaming Unit; 330, Third Sub-Streaming Unit; 340, Fourth Sub-Streaming Unit; 350, Fifth Sub-Streaming Unit; 360, Sixth Sub-Streaming Unit; 370, Seventh Sub-Streaming Unit; 380, Eighth Sub-Streaming Unit; 400, Exchange Source; 500. AC / DC conversion circuit; 600, Impedance Network. Detailed Implementation

[0018] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the protection scope of this application.

[0019] In the embodiments of this application, "at least one" refers to one or more; "multiple" refers to two or more. In the description of this application, the terms "first," "second," "third," etc., are used only for the purpose of distinguishing descriptions and should not be construed as indicating or implying relative importance, nor should they be construed as indicating or implying order.

[0020] References such as “one embodiment” or “some embodiments” as described in this specification mean that one or more embodiments of this application include a specific feature, structure, or characteristic described in connection with that embodiment. Therefore, the terms “comprising,” “including,” “having,” and variations thereof, as used in this specification, mean “including, but not limited to,” unless otherwise specifically emphasized.

[0021] It should be noted that in the embodiments of this application, "and / or" describes the relationship between associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. In addition, the character " / ", unless otherwise specified, generally indicates that the associated objects before and after it are in an "or" relationship.

[0022] It should be noted that in the embodiments of this application, "connection" can be understood as electrical connection. The connection between two electrical components can be a direct or indirect connection between the two electrical components. For example, the connection between A and B can be a direct connection between A and B, or an indirect connection between A and B through one or more other electrical components.

[0023] With the development of the new energy vehicle industry, traditional on-board charger circuit topologies generally adopt a two-stage structure of PFC (Power Factor Correction) cascaded DC / DC converters, with a large electrolytic capacitor used in the intermediate bus for power decoupling. However, the two-stage structure is difficult to meet the system's requirements for high power density, longer service life, and low cost.

[0024] Single-stage AC-DC converters can meet the requirements of high power density, longer service life and low cost of systems. As a result, on-board chargers based on single-stage AC-DC converters have attracted attention as a better solution and have become a research hotspot in the industry.

[0025] In single-stage AC-DC converter schemes, a matrix-type single-stage AC-DC converter with a bidirectional switching structure can be used. However, in this traditional matrix-type single-stage AC-DC converter, the bidirectional switching devices are distributed back to back, which means that the freewheeling current has no freewheeling path during the dead time period, which can easily cause overshoot of the tube voltage stress and damage the switching devices.

[0026] In view of the above, this application provides an AC conversion device to solve at least one of the above-mentioned technical problems, which will be described in detail below.

[0027] Please see Figure 1 As shown. This application provides an AC conversion device, which includes: a transformer 100, an AC conversion circuit 200, and a freewheeling module 300; one end of the AC conversion circuit 200 is configured to be connected to an AC source 400, and the other end of the AC conversion circuit 200 is connected to the primary winding of the transformer 100. The AC conversion circuit 200 includes at least one bridge arm 210, and both ends of the bridge arm 210 are respectively connected to the AC source 400 through a bridge arm bus 220. The bridge arm 210 includes an upper bridge arm 211 and a lower bridge arm 212 connected in series. The connection node between the upper bridge arm 211 and the lower bridge arm 212 is connected to the primary winding. Both the upper bridge arm 211 and the lower bridge arm 212 include two switching transistors. The two switching transistors of one of the upper bridge arm 211 and the lower bridge arm 212 are connected in series with a common source, and the two switching transistors of the other of the upper bridge arm 211 and the lower bridge arm 212 are connected in series with a common drain. When the bridge arm 210 is in the dead time period, the freewheeling module 300 has a freewheeling path, and the AC conversion equipment has a closed freewheeling loop. The closed freewheeling loop includes the freewheeling path, part of the switching transistors, and the primary winding.

[0028] Transformer 100 is used to change the voltage level (step-up or step-down) and provide electrical isolation. The secondary voltage Vo of transformer 100 can be determined based on the voltage on the primary side of transformer 100 and the turns ratio of the primary and secondary windings.

[0029] The AC converter circuit 200 is used to convert the input AC power into AC power, providing a suitable AC signal for subsequent circuit transmission. One end of the AC converter circuit 200 is connected to the AC source 400, and the other end is connected to the primary winding of the transformer 100. The AC source 400 can be a grid AC source 400 or a new energy power generation AC source 400, etc.

[0030] Specifically, the AC converter circuit 200 includes at least one bridge arm 210. For each bridge arm 210, the bridge arm 210 is composed of an upper bridge arm 211 and a lower bridge arm 212 connected in series. That is, one end of the upper bridge arm 211 and one end of the lower bridge arm 212 are connected and have a connection node A. The connection node A is connected to the primary winding of the transformer 100. The other end of the upper bridge arm 211 and the other end of the lower bridge arm 212 are respectively connected to the AC source 400 through the bridge arm bus 220. Each of the upper bridge arm 211 and the lower bridge arm 212 includes two switching transistors. The two switching transistors of one of the upper bridge arm 211 and the lower bridge arm 212 are connected in series with a common source, and the two are connected in series with a common drain. That is, both the upper and lower bridge arms form a bidirectional switching structure. The two switching transistors in the upper bridge arm 211 and the lower bridge arm 212 are connected in reverse series. The series connection direction of the switching transistors in the upper bridge arm 211 and the lower bridge arm 212 that are also connected in the same direction is the same. Specifically, the overall conduction and cutoff of the upper bridge arm 211 and the lower bridge arm 212 can be controlled by controlling the conduction and cutoff of each switching transistor, thereby controlling the direction and magnitude of current flow, realizing the conversion of alternating current, and helping to provide an effective current path at a specific time.

[0031] For example, the switching transistors in bridge arm 210 can be insulated-gate bipolar transistors (IGBTs), silicon-based metal-oxide-semiconductor field-effect transistors (Si MOSFETs), or switching devices based on semiconductor materials such as silicon carbide (SiC) and gallium nitride (GaN). It should be noted that each switching transistor in bridge arm 210 is a switching transistor with a body diode. The body diodes of two switching transistors connected in series in phase have the same conduction direction, while the body diodes of two switching transistors connected in reverse phase have opposite conduction directions. Furthermore, the body diodes of the switching transistors can provide a current path when bridge arm 210 is in a dead time period.

[0032] For example, such as Figure 1As shown, taking an AC converter circuit 200 including a bridge arm 210 as an example, the upper bridge arm 211 includes switches S1 and S2 connected in series, and the lower bridge arm 212 includes switches S3 and S4 connected in series. The connection node between the upper bridge arm 211 and the lower bridge arm 212 is point A. The two ends of the bridge arm 210 are connected to the AC source 400 via the bridge arm bus 220, and the two ends of the lower bridge arm 212 are connected to the primary winding of the transformer 100. That is, one end of the lower bridge arm 212 is connected to the non-inverting terminal of the primary winding of the transformer 100 via point A, and the other end of the lower bridge arm 212 is connected to the inverting terminal of the primary winding of the transformer 100 via point B. Switches S1 and S2 are on one side of the connection node A, and switches S3 and S4 are on the other side of the connection node A. Since the two switches of one of the upper bridge arm 211 and the lower bridge arm 212 are connected in series with their common source terminals, and the two switches of the other of the upper bridge arm 211 and the lower bridge arm 212 are connected in series with their common drain terminals, the body diodes of switches S2 and S3, which are closer to the connection node A, have the same conduction direction. The body diodes of switches S1 and S4, which are farther from the connection node A, have the same conduction direction. The body diodes of switches S1 and S2 have opposite conduction directions, and the body diodes of switches S3 and S4 have opposite conduction directions.

[0033] The freewheeling module 300 provides an effective freewheeling path when the bridge arm 210 is in a dead-time period, enabling the AC converter to maintain current continuity with a closed freewheeling loop. This closed freewheeling loop includes the freewheeling path provided by the freewheeling module 300, a portion of the switching transistors, and the primary winding. The dead-time period refers to the period during which all switching transistors in the bridge arm 210 are temporarily disconnected to avoid short circuits. Based on the inductive characteristics of the primary winding of the transformer 100, its current cannot change abruptly. Therefore, during the dead-time period, a freewheeling loop is needed to maintain the original current flow direction, ensuring current continuity and protecting circuit components. Thus, in this embodiment, the freewheeling module 300 provides a freewheeling path, ensuring that when the bridge arm 210 is in a dead-time period, regardless of whether the current flows from point B into point A or out of point A to point B (i.e., regardless of whether the current flow is forward or reverse), the AC converter has a closed freewheeling loop, allowing the current to form a closed loop and ensuring current continuity.

[0034] For example, the freewheeling module 300 may include, but is not limited to, freewheeling components such as capacitors.

[0035] As can be seen, under normal operating conditions, the AC converter circuit 200 can control the alternating conduction and cutoff of the upper and lower bridge arms by controlling the switching transistors in the bridge arm 210, thereby adjusting the direction and magnitude of current flow and achieving AC conversion. During dead time periods, the current in the AC converter circuit 200 will have a freewheeling path provided by the freewheeling module 300, allowing the current to continue flowing in the closed freewheeling loop including the freewheeling path, part of the switching transistors, and the primary winding, ensuring current continuity and protecting circuit components.

[0036] It should be noted that the AC conversion equipment provided in this application embodiment can be applied to, but is not limited to, scenarios such as new energy grid connection, electric vehicle charging and discharging, microgrids, and energy storage systems. For example, it can be applied to, but is not limited to, products such as on-board chargers, charging piles, power converters, and microinverters.

[0037] Understandably, in this application, by connecting the common source of one switch in the upper bridge arm 211 and the common drain of the other switch in the lower bridge arm 212, both switches in the upper bridge arm 211 and the lower bridge arm 212 form a bidirectional switching structure. This, combined with the freewheeling path provided by the freewheeling module 300, ensures that during the dead time period, regardless of whether the current is forward or reverse, the AC converter provides a closed freewheeling loop including the freewheeling path, part of the switch, and the primary winding, achieving continuous current flow without interruption. This effectively reduces the overshoot of the switching device's voltage stress and lowers the risk of damage to the switching device. Furthermore, this application directly utilizes the body diodes of some switches in the bridge arm 210 topology as freewheeling elements included in the closed freewheeling loop, eliminating the need for additional dedicated freewheeling diodes and simplifying the circuit topology.

[0038] Please see Figure 2 As shown. In some embodiments, when there is only one bridge arm 210 and the bridge arms 210 form a symmetrical half-bridge, one end of the freewheeling module 300 is connected to the middle node of the two switching transistors in the upper bridge arm 211, and the other end of the freewheeling module 300 is connected to the middle node of the two switching transistors in the lower bridge arm 212.

[0039] It is important to understand that a symmetrical half-bridge is a bridge arm 210 in which the switching parameters of the upper and lower bridge arms are completely identical, and it is also equipped with two series resonant capacitors of the same capacity. The two ends of the primary winding of the transformer 100 are connected to the connection nodes between the upper and lower bridge arms and the nodes between the two capacitors, respectively. The driving timing is 180° complementary conduction with a dead zone. Voltage balance and stable energy conversion are achieved through the symmetrical layout of components.

[0040] Specifically, when there is only one bridge arm 210, and the bridge arm 210 forms a symmetrical half-bridge, the symmetrical half-bridge circuit includes one bridge arm 210 and two capacitors. The two capacitors are connected in series and then in parallel with the bridge arm 210. The bridge arm 210 includes an upper bridge arm 211 and a lower bridge arm 212. The specific structure of the upper and lower bridge arms is as described above and will not be repeated here. The two ends of the primary winding of the transformer 100 are respectively connected to the connection node A between the upper and lower bridge arms and the connection node C between the two capacitors. One end of the freewheeling module 300 is connected to the middle node of the two switching transistors in the upper bridge arm 211, and the other end of the freewheeling module 300 is connected to the middle node of the two switching transistors in the lower bridge arm 212. This allows the current to flow between the middle nodes of the two switching transistors in the upper bridge arm 211 and the middle nodes of the two switching transistors in the lower bridge arm 212 based on the freewheeling path provided by the freewheeling module 300. Thus, during dead time periods, the freewheeling module 300 can provide a freewheeling path between the middle nodes of the upper and lower bridge arms, allowing the current to flow between the upper and lower bridge arms based on the freewheeling path provided by the freewheeling module 300. In this way, the current continues in a closed freewheeling loop including the freewheeling path, part of the switching transistors, and the primary winding, maintaining current continuity.

[0041] Please see Figure 3 As shown, for example, the freewheeling module 300 may include capacitor C1. The two capacitors in the symmetrical half-bridge circuit are capacitors Cb1 and Cb2. The bridge arm 210 includes switching transistors S1 to S4. One end of capacitor C1 is connected between switching transistors S1 and S2, and the other end of capacitor C1 is connected between switching transistors S3 and S4. Therefore, capacitor C1 can provide a freewheeling path between the intermediate nodes of the upper and lower bridge arms when the bridge arm 210 is in a dead time period. Taking current flowing out from point A as positive and current flowing in from point A as negative, when the bridge arm 210 is in a dead time period, and the current direction in the AC converter is positive, the closed freewheeling loop provides a current path where the current flows from point A through the primary winding of transformer 100, sequentially through point C, capacitor Cb1, switching transistor S1, capacitor C1 in the freewheeling module 300, and switching transistor S3, before flowing out from point A, forming a current closed loop. When the current direction is reversed in the AC converter, the current flows in from point A, sequentially through switch S2, capacitor C1, switch S4, point C, and the primary winding of transformer 100 before flowing back into point A, forming a current closed loop. This ensures that the closed freewheeling circuit includes the freewheeling path provided by the freewheeling module 300, part of the switches, and the primary winding. It should be noted that the current direction during the dead time period inherits the current flow direction in the AC converter before the dead time period and maintains this direction unchanged due to the freewheeling characteristics of the primary winding.

[0042] Please see Figure 4 to Figure 6As shown, in some embodiments, the current-carrying module 300 includes a first sub-current-carrying unit 310 and a second sub-current-carrying unit 320. One end of the first sub-current-carrying unit 310 is connected to the intermediate node of the two switching transistors of the upper bridge arm 211, and the other end of the first sub-current-carrying unit 310 is connected to the bridge arm bus 220. One end of the second sub-current-carrying unit 320 is connected to the intermediate node of the two switching transistors of the lower bridge arm 212, and the other end of the second sub-current-carrying unit 320 is connected to the bridge arm bus 220. When the bridge arm 210 is in a dead time period, the current-carrying path includes at least one of the first sub-current-carrying unit 310 and the second sub-current-carrying unit 320.

[0043] It should be understood that one end of the first sub-freezing unit 310 is connected to the intermediate node of the two switching transistors of the upper bridge arm 211, and the other end of the first sub-freezing unit 310 is connected to the bridge arm bus 220. The first sub-freezing unit 310 provides a current path between the intermediate node of the two switching transistors of the upper bridge arm 211 and the bridge arm bus 220. One end of the second sub-freezing unit 320 is connected to the intermediate node of the two switching transistors of the lower bridge arm 212, and the other end of the second sub-freezing unit 320 is connected to the bridge arm bus 220. The second sub-freezing unit 320 provides a current path between the intermediate node of the two switching transistors of the lower bridge arm 212 and the bridge arm bus 220. Furthermore, in the case of a dead time period, the freewheeling path includes a current path provided by at least one of the first sub-freezing unit 310 and the second sub-freezing unit 320, allowing current to continue flowing in a closed freewheeling loop including the freewheeling path, part of the switching transistors, and the primary winding, thus maintaining current continuity.

[0044] It should be noted that both ends of bridge arm 210 are connected to AC source 400 via bridge arm bus 220, i.e., bridge arm bus 220 includes an upper bus and a lower bus. The upper bus is connected to upper bridge arm 211, and the lower bus is connected to lower bridge arm 212. One end of the first sub-freezing unit 310 is connected to the midpoint of the two switching transistors of upper bridge arm 211, and the other end of the first sub-freezing unit 310 can be connected to either the upper or lower bus. Similarly, one end of the second sub-freezing unit 320 is connected to the midpoint of the two switching transistors of lower bridge arm 212, and the other end of the second sub-freezing unit 320 is connected to either the upper or lower bus.

[0045] It should also be noted that when there is only one bridge arm 210, and the bridge arms 210 form a symmetrical half-bridge, the freewheeling module 300 can provide multiple possible freewheeling paths. Specifically, in some examples, the freewheeling path includes a first sub-freewheeling unit 310; in other examples, the freewheeling path includes a second sub-freewheeling unit 320; and in still other examples, the freewheeling path includes both the first sub-freewheeling unit 310 and the second sub-freewheeling unit 320. During the actual operation of the bridge arm 210 in the dead time period, the specific freewheeling path is determined by the inherent topology of the circuit itself and the real-time current direction during the dead time period, thus automatically and uniquely determining the freewheeling path. The specific freewheeling path will adaptively adjust according to different circuit topology details, ensuring that the current, whether forward or reverse, can continue to flow without interruption through a closed freewheeling loop during the dead time period.

[0046] like Figure 4 As shown, in some examples, one end of the first sub-freezing unit 310 is connected to the intermediate node of the two switching transistors of the upper bridge arm 211, and the other end of the first sub-freezing unit 310 is connected to the upper bus. One end of the second sub-freezing unit 320 is connected to the intermediate node of the two switching transistors of the lower bridge arm 212, and the other end of the second sub-freezing unit 320 is connected to the lower bus. The freewheeling path includes one of the first sub-freezing unit 310 and the second sub-freezing unit 320.

[0047] For example, the first sub-freewheeling unit 310 includes capacitor C2, the second sub-freewheeling unit 320 includes capacitor C3, the two capacitors in the symmetrical half-bridge circuit are capacitors Cb1 and Cb2, and the bridge arm 210 includes switching transistors S1 to S4. When the bridge arm 210 is in the dead time period, the freewheeling path includes either the first sub-freewheeling unit 310 or the second sub-freewheeling unit 320. Specifically, taking current flowing out from point A as positive and current flowing in from point A as negative, when the bridge arm 210 is in the dead time period, and the current direction in the AC converter is positive, the freewheeling path includes the second sub-freewheeling unit 320. That is, the loop path provided by the closed freewheeling loop is that the current flows from point A through the primary winding of transformer 100, sequentially through point C, capacitor Cb2, capacitor C3, and switching transistor S3, and then flows out from point A, forming a current closed loop. In the case of reverse current direction in AC conversion equipment, the freewheeling path includes the first sub-freewheeling unit 310. After the current flows in from point A, it sequentially passes through switch S2, capacitor C2, capacitor Cb1, point C, and the primary winding of transformer 100 before flowing back into point A, forming a current closed loop.

[0048] like Figure 5As shown, in some other examples, one end of the first sub-freezing unit 310 is connected to the intermediate node of the two switching transistors of the upper bridge arm 211, and the other end of the first sub-freezing unit 310 is connected to the lower bus. One end of the second sub-freezing unit 320 is connected to the intermediate node of the two switching transistors of the lower bridge arm 212, and the other end of the second sub-freezing unit 320 is connected to the upper bus. The freewheeling path includes one of the first sub-freezing unit 310 and the second sub-freezing unit 320.

[0049] For example, the first sub-freewheeling unit 310 includes capacitor C2, the second sub-freewheeling unit 320 includes capacitor C3, the two capacitors in the symmetrical half-bridge circuit are capacitors Cb1 and Cb2, and the bridge arm 210 includes switching transistors S1 to S4. When the bridge arm 210 is in the dead time period, and the current direction in the AC converter is positive, the freewheeling path includes the second sub-freewheeling unit 320. When the current direction in the AC converter is reverse, the freewheeling path includes the first sub-freewheeling unit 310. It should be noted that the specific closed freewheeling loop path in the AC converter can be determined according to its inherent circuit topology and the current direction during the dead time period, and will not be described in detail here.

[0050] like Figure 6 In some other examples, as shown, one end of the first sub-freezing unit 310 is connected to the intermediate node of the two switching transistors in the upper bridge arm 211, and the other end of the first sub-freezing unit 310 is connected to the upper bus. One end of the second sub-freezing unit 320 is connected to the intermediate node of the two switching transistors in the lower bridge arm 212, and the other end of the second sub-freezing unit 320 is connected to the upper bus. The freewheeling path includes a flow path provided by at least one of the first sub-freezing unit 310 and the second sub-freezing unit 320.

[0051] For example, the first sub-freewheeling unit 310 includes capacitor C2, the second sub-freewheeling unit 320 includes capacitor C3, the two capacitors in the symmetrical half-bridge circuit are capacitors Cb1 and Cb2, and the bridge arm 210 includes switching transistors S1 to S4. When the bridge arm 210 is in the dead time period, and the current direction in the AC converter is positive, the freewheeling path may include the second sub-freewheeling unit 320. When the current direction in the AC converter is reverse, the freewheeling path may include the first sub-freewheeling unit 310, or the freewheeling path may include both the first sub-freewheeling unit 310 and the second sub-freewheeling unit 320. When the freewheeling path includes both the first sub-freewheeling unit 310 and the second sub-freewheeling unit 320, that is, the loop path provided by the closed freewheeling loop can be that the current flows in from point A, sequentially passes through switching transistor S2, capacitor C2, capacitor C3, switching transistor S4, capacitor Cb2, point C, and the primary winding of transformer 100 before flowing back into point A, forming a current closed loop.

[0052] It should be noted that the first sub-freezing unit 310 and the second sub-freezing unit 320 may also have other connection structures. For example, one end of the first sub-freezing unit 310 may be connected to the intermediate node of the two switching transistors of the upper bridge arm 211, and the other end of the first sub-freezing unit 310 may be connected to the lower bus. One end of the second sub-freezing unit 320 may be connected to the intermediate node of the two switching transistors of the lower bridge arm 212, and the other end of the second sub-freezing unit 320 may be connected to the lower bus. As another example, the first sub-freezing unit 310 and the second sub-freezing unit 320 may include multiple freewheeling capacitors. Besides the exemplary structures described above, those skilled in the art can derive more connection forms that satisfy the freewheeling function based on the technical concept of this application; related embodiments will not be described in detail here.

[0053] Please see Figure 7 As shown, in some embodiments, the AC conversion device further includes a bus capacitor 230, which is connected to the bridge arm bus 220 and is connected in parallel with the bridge arm 210.

[0054] It is important to understand that the two ends of the bus capacitor 230 are connected to the upper bus and the lower bus, respectively. The bus capacitor 230 not only stabilizes the bus voltage and absorbs voltage ripple in the circuit, but also provides a current path between the upper and lower buses when the bridge arm 210 is in the dead time period. During the dead time period, when the closed freewheeling loop needs to form a current path across the two bridge arm buses 220, the bus capacitor 230 can provide a current path between the two bridge arm buses 220. Thus, the closed freewheeling loop can be incorporated into the bus capacitor 230, allowing the current to freewheel in the closed freewheeling loop that includes the freewheeling path, part of the switching diode, the primary winding, and the bus capacitor 230, maintaining current continuity.

[0055] Please continue reading. Figure 7 As shown, in some embodiments, when there is only one bridge arm 210 and the bridge arm 210 forms an asymmetrical half-bridge, one end of the freewheeling module 300 is connected to the middle node of the two switching transistors in the upper bridge arm 211, and the other end of the freewheeling module 300 is connected to the middle node of the two switching transistors in the lower bridge arm 212.

[0056] It is important to understand that an asymmetrical half-bridge refers to a bridge arm 210 paired with a bus capacitor 230. The bus capacitor 230 is connected in parallel with a single bridge arm 210. The two ends of the primary winding of the transformer 100 are respectively connected to the two ends of the lower bridge arm 212. The driving timing can be flexibly adjusted according to the driving strategy, without the need to maintain strict symmetry.

[0057] Specifically, when there is only one bridge arm 210, and the bridge arm 210 forms an asymmetrical half-bridge, the asymmetrical half-bridge circuit includes one bridge arm 210 and a bus capacitor 230. The bus capacitor 230 is connected in parallel with the bridge arm 210. The bridge arm 210 includes an upper bridge arm 211 and a lower bridge arm 212. The specific structures of the upper and lower bridge arms are as described above and will not be repeated here. The two ends of the primary winding of the transformer 100 are respectively connected to the two ends of the lower bridge arm 212, that is, the two ends of the primary winding of the transformer 100 are respectively connected to points A and B. One end of the freewheeling module 300 is connected to the middle node of the two switching transistors in the upper bridge arm 211, and the other end of the freewheeling module 300 is connected to the middle node of the two switching transistors in the lower bridge arm 212, so that the freewheeling module 300 can provide a freewheeling path between the middle nodes of the two switching transistors in the upper bridge arm 211 and the middle nodes of the two switching transistors in the lower bridge arm 212. The bus capacitor 230 is connected to both the upper and lower buses, thus providing a current path between them. Therefore, during the dead time period, in some examples, the current continues in a closed freewheeling loop including the freewheeling path, part of the switching transistor, and the primary winding, maintaining current continuity. In other examples, the current continues in a closed freewheeling loop including the bus capacitor 230, the freewheeling path, part of the switching transistor, and the primary winding, maintaining current continuity.

[0058] like Figure 7 As shown, for example, the freewheeling module 300 may include capacitor C5, bus capacitor 230 is C4, and bridge arm 210 includes switching transistors S1 to S4. One end of capacitor C5 is connected between switching transistors S1 and S2, and the other end of capacitor C5 is connected between switching transistors S3 and S4. Capacitor C5 can provide a freewheeling path for the upper and lower bridge arms when bridge arm 210 is in a dead time period. Taking current flowing out from point A as positive and current flowing in from point A as negative, when bridge arm 210 is in a dead time period, and the current direction in the AC converter is positive, the current flows through a closed freewheeling loop including bus capacitor 230, the freewheeling path, part of the switching transistors, and the primary winding. The loop path provided by the closed freewheeling loop is that the current flows from point A through the primary winding of transformer 100, sequentially through point B, capacitor C4, switching transistor S1, capacitor C5 in the freewheeling module 300, and switching transistor S3, before flowing out from point A, forming a current closed loop. In AC converters, when the current direction is reversed, the current continues in a closed freewheeling circuit that includes a freewheeling path, part of the switching transistors, and the primary winding. The loop path provided by the closed freewheeling circuit is that the current flows in from point A, passes through switching transistor S2, capacitor C5, switching transistor S4, point B, and the primary winding of transformer 100 before flowing back into point A, forming a current closed loop.

[0059] Please see Figure 8 to Figure 9As shown, in some embodiments, the current-carrying module 300 includes a third sub-current-carrying unit 330 and a fourth sub-current-carrying unit 340. One end of the third sub-current-carrying unit 330 is connected to the intermediate node of the two switching transistors of the upper bridge arm 211, and the other end of the third sub-current-carrying unit 330 is connected to the bridge arm bus 220. That is, the other end of the third sub-current-carrying unit 330 can be connected to either the upper bus or the lower bus. One end of the fourth sub-current-carrying unit 340 is connected to the intermediate node of the two switching transistors of the lower bridge arm 212, and the other end of the fourth sub-current-carrying unit 340 is connected to the bridge arm bus 220. That is, the other end of the fourth sub-current-carrying unit 340 can be connected to either the upper bus or the lower bus. When the bridge arm 210 is in a dead time period, the current-carrying path includes at least one of the third sub-current-carrying unit 330 and the fourth sub-current-carrying unit 340.

[0060] It should be understood that one end of the third sub-freezing unit 330 is connected to the intermediate node of the two switching transistors of the upper bridge arm 211, and the other end of the third sub-freezing unit 330 is connected to the bridge arm bus 220. Therefore, the third sub-freezing unit 330 provides a current path between the intermediate node of the two switching transistors of the upper bridge arm 211 and the bridge arm bus 220. One end of the fourth sub-freezing unit 340 is connected to the intermediate node of the two switching transistors of the lower bridge arm 212, and the other end of the fourth sub-freezing unit 340 is connected to the bridge arm bus 220. Therefore, the fourth sub-freezing unit 340 provides a current path between the intermediate node of the two switching transistors of the lower bridge arm 212 and the bridge arm bus 220. Furthermore, in the case of a dead time period, the freewheeling path includes a current path provided by at least one of the third sub-freezing unit 330 and the fourth sub-freezing unit 340, allowing current to continue flowing in the closed freewheeling loop and maintaining current continuity. It should be noted that, in some examples, the closed freewheeling path may include the freewheeling path, part of the switching transistor, and the primary winding. In other examples, the closed freewheeling path may include the bus capacitor 230, the freewheeling path, part of the switching transistor, and the primary winding. The specific path is determined based on the current direction during the dead time and the specific circuit topology.

[0061] It should be noted that when there is only one bridge arm 210, and the bridge arm 210 forms an asymmetrical half-bridge, the freewheeling module 300 can provide multiple possible freewheeling paths. That is, in some examples, the freewheeling path includes a third sub-freewheeling unit 330; in other examples, the freewheeling path includes a fourth sub-freewheeling unit 340; in still other examples, the freewheeling path includes both the third sub-freewheeling unit 330 and the fourth sub-freewheeling unit 340. During the actual operation of the dead time period of the bridge arm 210, the specific freewheeling path is determined by the inherent topology of the circuit itself and the real-time current direction during the dead time period, thereby automatically and uniquely determining the freewheeling path. The specific freewheeling path will adaptively adjust according to the different circuit topology details, so that the current during the dead time period, whether forward or reverse, can be ensured to flow continuously without interruption through a closed freewheeling loop.

[0062] like Figure 8 As shown, in some examples, one end of the third sub-freezing unit 330 is connected to the intermediate node of the two switching transistors of the upper bridge arm 211, and the other end of the third sub-freezing unit 330 is connected to the upper bus. One end of the fourth sub-freezing unit 340 is connected to the intermediate node of the two switching transistors of the lower bridge arm 212, and the other end of the fourth sub-freezing unit 340 is connected to the lower bus. The freewheeling path includes at least one of the third sub-freezing unit 330 and the fourth sub-freezing unit 340. That is, the freewheeling path may include the third sub-freezing unit 330, the freewheeling path may include the fourth sub-freezing unit 340, or the freewheeling path may include both the third sub-freezing unit 330 and the fourth sub-freezing unit 340.

[0063] For example, the third sub-freewheeling unit 330 includes capacitor C5, the fourth sub-freewheeling unit 340 includes capacitor C6, the bus capacitor 230 is C4, and the bridge arm 210 includes switching transistors S1 to S4. When the bridge arm 210 is in the dead time period, the freewheeling path includes one of the first sub-freewheeling unit 310 and the second sub-freewheeling unit 320. Specifically, taking current flowing out from point A as positive and current flowing in from point A as negative, when the bridge arm 210 is in the dead time period, and the current direction in the AC converter is positive, the freewheeling path includes the fourth sub-freewheeling unit 340. The current then freewheels in a closed freewheeling loop including the freewheeling path, part of the switching transistors, and the primary winding. In AC converters where the current direction is reversed, the freewheeling path may include a third sub-freewheeling unit 330, or it may include a third sub-freewheeling unit 330 and a fourth sub-freewheeling unit 340. In this case, the current freewheels in a closed freewheeling loop that includes the bus capacitor 230, the freewheeling path, part of the switching transistor, and the primary winding.

[0064] like Figure 9As shown, in some other examples, one end of the third sub-freezing unit 330 is connected to the intermediate node of the two switching transistors of the upper bridge arm 211, and the other end of the third sub-freezing unit 330 is connected to the lower bus. One end of the fourth sub-freezing unit 340 is connected to the intermediate node of the two switching transistors of the lower bridge arm 212, and the other end of the fourth sub-freezing unit 340 is connected to the upper bus. The freewheeling path includes a flow path provided by at least one of the third sub-freezing unit 330 and the fourth sub-freezing unit 340. That is, the freewheeling path may include the third sub-freezing unit 330, the freewheeling path may include the fourth sub-freezing unit 340, or the freewheeling path may include both the third sub-freezing unit 330 and the fourth sub-freezing unit 340.

[0065] For example, the third sub-freewheeling unit 330 includes capacitor C5, the fourth sub-freewheeling unit 340 includes capacitor C6, the bus capacitor 230 is C4, and the bridge arm 210 includes switching transistors S1 to S4. When the bridge arm 210 is in the dead time period and the current direction in the AC converter is positive, the freewheeling path may include the fourth sub-freewheeling unit 340, and the current will continue in a closed freewheeling loop including the bus capacitor 230, the freewheeling path, part of the switching transistors, and the primary winding. The freewheeling path may also include the third sub-freewheeling unit 330 and the fourth sub-freewheeling unit 340, and the current will continue in a closed freewheeling loop including the freewheeling path, part of the switching transistors, and the primary winding. In AC converters, when the current direction is reversed, if the freewheeling path includes the third sub-freewheeling unit 330, the current will continue in a closed freewheeling loop including the freewheeling path, part of the switching transistor, and the primary winding. The freewheeling path may also include the third sub-freewheeling unit 330 and the fourth sub-freewheeling unit 340, in which case the current will continue in a closed freewheeling loop including the bus capacitor 230, the freewheeling path, part of the switching transistor, and the primary winding.

[0066] It should also be noted that the third sub-freezing unit 330 and the fourth sub-freezing unit 340 may also have other connection structures. For example, one end of the third sub-freezing unit 330 may be connected to the intermediate node of the two switching transistors of the upper bridge arm 211, and the other end of the third sub-freezing unit 330 may be connected to the upper bus. One end of the fourth sub-freezing unit 340 may be connected to the intermediate node of the two switching transistors of the lower bridge arm 212, and the other end of the fourth sub-freezing unit 340 may be connected to the upper bus. Alternatively, the other ends of both the third sub-freezing unit 330 and the fourth sub-freezing unit 340 may be connected to the lower bus. Furthermore, the third sub-freezing unit 330 and the fourth sub-freezing unit 340 may include multiple freewheeling capacitors. In addition to the exemplary structures described above, those skilled in the art can derive more connection forms that satisfy the freewheeling function based on the technical concept of this application; related embodiments will not be described in detail here.

[0067] Please see Figure 10 to Figure 13As shown, when there are two bridge arms 210 and the two bridge arms 210 have the same structure, the freewheeling module 300 includes a fifth sub-freewheeling unit 350 and a sixth sub-freewheeling unit 360. One end of the fifth sub-freewheeling unit 350 is connected to the middle node of the two switching transistors of an upper bridge arm 211, and the other end of the fifth sub-freewheeling unit 350 is connected to the middle node of the two switching transistors of any lower bridge arm 212. One end of the sixth sub-freewheeling unit 360 is connected to the middle node of the two switching transistors of another upper bridge arm 211, and the other end of the sixth sub-freewheeling unit 360 is connected to the middle node of the two switching transistors of the remaining lower bridge arm 212. When the bridge arm 210 is in a dead time period, the freewheeling path includes at least one of the fifth sub-freewheeling unit 350 and the sixth sub-freewheeling unit 360.

[0068] It should be understood that when there are two bridge arms 210, and the two bridge arms 210 have the same structure, both bridge arms 210 include an upper bridge arm 211 and a lower bridge arm 212. The specific structures of the upper and lower bridge arms are as described above and will not be repeated here. In this application, the bridge arm 210 located on the left in the attached figure is defined as the first bridge arm 210, and the bridge arm 210 located on the right is defined as the second bridge arm 210. The two ends of the primary winding of the transformer 100 are respectively connected to the connection nodes between the upper and lower bridge arms in the first bridge arm 210 and the connection nodes between the upper and lower bridge arms in the second bridge arm 210, that is, the two ends of the primary winding of the transformer 100 are respectively connected to points A and C. One end of the fifth sub-freezing unit 350 is connected to the intermediate node of the two switches in one upper bridge arm 211, and the other end is connected to the intermediate node of the two switches in any one lower bridge arm 212. The fifth sub-freezing unit 350 provides a current path between the two connected intermediate nodes. One end of the sixth sub-freezing unit 360 is connected to the intermediate node of the two switches in another upper bridge arm 211, and the other end is connected to the intermediate node of the two switches in the remaining lower bridge arm 212. The sixth sub-freezing unit 360 provides a current path between the two connected intermediate nodes. Furthermore, in the case of a dead time period, the freewheeling path includes the current path provided by at least one of the fifth sub-freezing unit 350 and the sixth sub-freezing unit 360, allowing current to continue flowing in the closed freewheeling loop and maintaining current continuity. It should be noted that in some examples, the closed freewheeling path may include the freewheeling path, some switches, and the primary winding. In other examples, the closed freewheeling path may include the bus capacitor 230, the freewheeling path, part of the switching transistor, and the primary winding. The specific details are determined based on the current direction during the dead time and the specific circuit topology.

[0069] It should be noted that when there is only one bridge arm 210 and the two bridge arms 210 have the same structure, the freewheeling module 300 can provide multiple possible freewheeling paths. Specifically, in some examples, the freewheeling path includes the fifth sub-freewheeling unit 350; in other examples, the freewheeling path includes the sixth sub-freewheeling unit 360; and in still other examples, the freewheeling path includes both the fifth sub-freewheeling unit 350 and the sixth sub-freewheeling unit 360. During the actual operation of the bridge arm 210 in the dead time period, the specific freewheeling path is determined by the inherent topology of the circuit itself and the real-time current direction during the dead time period, thus automatically and uniquely determining the freewheeling path. The specific freewheeling path will adaptively adjust according to different circuit topology details, ensuring that the current, whether forward or reverse, can continue to flow without interruption through a closed freewheeling loop during the dead time period.

[0070] like Figure 10 to 12 As shown, in some examples, one end of the fifth sub-freezing unit 350 is connected to the intermediate node of the two switching transistors of the upper bridge arm 211 of the first bridge arm 210, and the other end of the fifth sub-freezing unit 350 is connected to the intermediate node of the two switching transistors of the lower bridge arm 212 of the second bridge arm 210. One end of the sixth sub-freezing unit 360 is connected to the intermediate node of the two switching transistors of the upper bridge arm 211 of the second bridge arm 210, and the other end of the sixth sub-freezing unit 360 is connected to the intermediate node of the two switching transistors of the lower bridge arm 212 of the first bridge arm 210. When the bridge arm 210 is in a dead time period, the freewheeling path includes either the fifth sub-freezing unit 350 or the sixth sub-freezing unit 360. That is, the freewheeling path may include the fifth sub-freezing unit 350, and the freewheeling path may also include the sixth sub-freezing unit 360.

[0071] like Figure 10 As shown, for example, the fifth sub-freewheeling unit 350 includes capacitor C7, the sixth sub-freewheeling unit 360 includes capacitor C8, the first bridge arm 210 includes switching transistors S1 to S4, the second bridge arm 210 includes switching transistors S5 to S8, one end of capacitor C7 is connected between switching transistors S1 and S2, and the other end of capacitor C7 is connected between switching transistors S7 and S8; one end of capacitor C8 is connected between switching transistors S5 and S6, and the other end of capacitor C8 is connected between switching transistors S3 and S4. Current flowing out of point A is considered positive, and current flowing into point A is considered negative. When bridge arm 210 is in the dead zone, and the current direction in the AC converter is positive, the freewheeling path includes the sixth sub-freewheeling unit 360. The current flows through a closed freewheeling loop that includes the freewheeling path, part of the switching transistors, and the primary winding. The loop path provided by the closed freewheeling loop is that the current flows from point A through the primary winding of transformer 100, sequentially through point C, switching transistor S6, capacitor C8, and switching transistor S3, and then flows out from point A, forming a current closed loop.Figure 11 As shown. In the AC converter equipment, when the current direction is reversed, the freewheeling path includes the fifth sub-freewheeling unit 350. The current freewheels in a closed freewheeling loop that includes the freewheeling path, part of the switching transistors, and the primary winding. The loop path provided by the closed freewheeling loop is that the current flows in from point A, sequentially through switching transistor S2, capacitor C7, switching transistor S7, point C, and the primary winding of transformer 100 before flowing back into point A, forming a current closed loop, as shown. Figure 12 As shown.

[0072] like Figure 13 As shown, in some other examples, one end of the fifth sub-freezing unit 350 is connected to the middle node of the two switching transistors of the upper bridge arm 211 of the first bridge arm 210, and the other end of the fifth sub-freezing unit 350 is connected to the middle node of the two switching transistors of the lower bridge arm 212 of the first bridge arm 210. One end of the sixth sub-freezing unit 360 is connected to the middle node of the two switching transistors of the upper bridge arm 211 of the second bridge arm 210, and the other end of the sixth sub-freezing unit 360 is connected to the middle node of the two switching transistors of the lower bridge arm 212 of the second bridge arm 210. When the bridge arm 210 is in a dead time period, the freewheeling path includes the fifth sub-freezing unit 350 and the sixth sub-freezing unit 360.

[0073] like Figure 13 As shown, for example, the fifth sub-freewheeling unit 350 includes capacitor C7, the sixth sub-freewheeling unit 360 includes capacitor C8, the first bridge arm 210 includes switching transistors S1 to S4, the second bridge arm 210 includes switching transistors S5 to S8, one end of capacitor C7 is connected between switching transistors S1 and S2, and the other end of capacitor C7 is connected between switching transistors S3 and S4, one end of capacitor C8 is connected between switching transistors S5 and S6, and the other end of capacitor C8 is connected between switching transistors S7 and S8. When bridge arm 210 is in the dead time period, and the current direction in the AC converter is positive, the freewheeling path includes the fifth sub-freewheeling unit 350 and the sixth sub-freewheeling unit 360, and the current freewheels in a closed freewheeling loop including the bus capacitor 230, the freewheeling path, part of the switching transistors, and the primary winding. In AC converters, when the current direction is reversed, the freewheeling path includes the fifth sub-freewheeling unit 350 and the sixth sub-freewheeling unit 360, and the current freewheels in a closed freewheeling loop including the bus capacitor 230, the freewheeling path, part of the switching transistor and the primary winding.

[0074] In some embodiments, at least one of the fifth sub-current relay unit 350 and the sixth sub-current relay unit 360 is composed of a plurality of current relay elements.

[0075] In other words, in some examples, the fifth sub-freezing unit 350 may include multiple freezing elements, and the sixth sub-freezing unit 360 may include a single freezing element. In other examples, the fifth sub-freezing unit 350 may include a single freezing element, and the sixth sub-freezing unit 360 may include multiple freezing elements. In still other examples, the fifth sub-freezing unit 350 may include multiple freezing elements, and the sixth sub-freezing unit 360 may include multiple freezing elements. It should be noted that the line containing each freezing element in the fifth sub-freezing unit 350 and the sixth sub-freezing unit 360 can provide a current flow path. Furthermore, in the case of dead time, the freezing path includes the flow path provided by at least one of the fifth sub-freezing unit 350 and the sixth sub-freezing unit 360. That is, the freezing path includes the current flow path provided by all the freezing elements included in at least one of the fifth sub-freezing unit 350 and the sixth sub-freezing unit 360, so that the current can continue in the closed freezing loop, maintaining current continuity.

[0076] Please see Figure 14 to Figure 17 As shown, in some examples, the fifth sub-freezing unit 350 consists of a single freezing element, and the sixth sub-freezing unit 360 consists of multiple freezing elements. It should be understood that one end of a freezing element in the fifth sub-freezing unit 350 can be connected to the intermediate node of the two switching transistors in an upper bridge arm 211, and the other end of the freezing element can be connected to the intermediate node of the two switching transistors in any lower bridge arm 212. Thus, the fifth sub-freezing unit 350 can provide a current flow path between the two connected intermediate nodes. Multiple freezing elements in the sixth sub-freezing unit 360 can be connected in series. The multiple freezing elements in the sixth sub-freezing unit 360 can be connected in series through the bridge arm bus 220, meaning that current can flow between the two intermediate nodes connected to the sixth sub-freezing unit 360 through multiple freezing elements and the bridge arm bus 220. Multiple current-carrying elements in the sixth sub-current-carrying unit 360 can also be connected in series through the bridge arm bus 220 and the bus capacitor 230. That is, current can flow between the two intermediate nodes connected by the sixth sub-current-carrying unit 360 through multiple current-carrying elements, the bridge arm bus 220 and the bus capacitor 230.

[0077] like Figure 14As shown, for example, the fifth sub-freezing unit 350 includes capacitor C7, and the sixth sub-freezing unit 360 includes two freezing elements: capacitors C9 and C10. The first bridge arm 210 includes switching transistors S1 to S4, and the second bridge arm 210 includes switching transistors S5 to S8. One end of capacitor C7 is connected between switching transistors S1 and S2, and the other end of capacitor C7 is connected between switching transistors S7 and S8. One end of capacitor C9 is connected between switching transistors S5 and S6, and the other end of capacitor C9 is connected to the upper bus. One end of capacitor C10 is connected between switching transistors S3 and S4, and the other end of capacitor C10 is connected to the upper bus. Furthermore, capacitor C9 provides a flow path between the intermediate node between switching transistors S5 and S6 and the upper bus, and capacitor C10 provides a flow path between the intermediate node between switching transistors S3 and S4 and the upper bus. Thus, the two intermediate nodes connected to the sixth sub-freezing unit 360 achieve flow through multiple freezing elements and the upper bus. Specifically, when bridge arm 210 is in the dead zone and the current direction in the AC converter is positive, the freewheeling path includes the sixth sub-freewheeling unit 360, and the current freewheels in a closed freewheeling loop including the freewheeling path, part of the switching transistor, and the primary winding. When the current direction in the AC converter is reverse, the freewheeling path may include the fifth sub-freewheeling unit 350, and the current freewheels in a closed freewheeling loop including the freewheeling path, part of the switching transistor, and the primary winding.

[0078] like Figure 15 As shown, for example, the other end of capacitor C9 and the other end of capacitor C10 are connected to the lower busbar, and the rest of the circuit structure is the same as... Figure 14 The same applies here, so it will not be repeated. Furthermore, capacitor C9 provides a current path between the intermediate node between switching transistors S5 and S6 and the lower busbar, and capacitor C10 provides a current path between the intermediate node between switching transistors S3 and S4 and the lower busbar. Thus, the two intermediate nodes connected to the sixth sub-freezing unit 360 achieve current flow through multiple freezing elements and the lower busbar. Specifically, when bridge arm 210 is in the dead time period, and the current direction in the AC converter is positive, the freezing path includes the sixth sub-freezing unit 360, and the current flows in a closed freezing loop including the freezing path, part of the switching transistors, and the primary winding. When the current direction in the AC converter is reversed, the freezing path may include the fifth sub-freezing unit 350, and the current flows in a closed freezing loop including the freezing path, part of the switching transistors, and the primary winding.

[0079] like Figure 16 As shown, for example, the other end of capacitor C9 is connected to the lower busbar, and the other end of capacitor C10 is connected to the upper busbar; the rest of the circuit structure is the same. Figure 14The same applies here, so it will not be repeated. Furthermore, capacitor C9 provides a current path between the intermediate node between switching transistors S5 and S6 and the lower busbar, and capacitor C10 provides a current path between the intermediate node between switching transistors S3 and S4 and the upper busbar. Thus, the two intermediate nodes connected to the sixth sub-freewheeling unit 360 achieve current flow through multiple freewheeling elements, the upper busbar, the lower busbar, and the busbar capacitor 230. Specifically, when the bridge arm 210 is in the dead zone, and the current direction in the AC converter is positive, the freewheeling path includes the sixth sub-freewheeling unit 360, and the current flows through a closed freewheeling loop including the busbar capacitor 230, the freewheeling path, part of the switching transistors, and the primary winding. When the current direction in the AC converter is reversed, the freewheeling path may include the fifth sub-freewheeling unit 350, and the current flows through a closed freewheeling loop including the freewheeling path, part of the switching transistors, and the primary winding.

[0080] like Figure 17 As shown, for example, the other end of capacitor C9 is connected to the upper busbar, and the other end of capacitor C10 is connected to the lower busbar; the rest of the circuit structure is the same. Figure 14 The same applies here, so it will not be repeated. Furthermore, capacitor C9 provides a current path between the intermediate node between switching transistors S5 and S6 and the upper busbar, and capacitor C10 provides a current path between the intermediate node between switching transistors S3 and S4 and the lower busbar. Thus, the two intermediate nodes connected to the sixth sub-freewheeling unit 360 achieve current flow through multiple freewheeling elements, the upper busbar, the lower busbar, and the busbar capacitor 230. Specifically, when the bridge arm 210 is in the dead zone, and the current direction in the AC converter is positive, the freewheeling path includes the sixth sub-freewheeling unit 360, and the current flows through a closed freewheeling loop including the busbar capacitor 230, the freewheeling path, part of the switching transistors, and the primary winding. When the current direction in the AC converter is reversed, the freewheeling path may include the fifth sub-freewheeling unit 350, and the current flows through a closed freewheeling loop including the freewheeling path, part of the switching transistors, and the primary winding.

[0081] Please see Figure 18 to Figure 21As shown, in some examples, the fifth sub-freezing unit 350 consists of a single freezing element, and the sixth sub-freezing unit 360 consists of multiple freezing elements. It should be understood that one end of a freezing element in the sixth sub-freezing unit 360 can be connected to the intermediate node of the two switching transistors in an upper bridge arm 211, and the other end of the freezing element can be connected to the intermediate node of the two switching transistors in any lower bridge arm 212. Thus, the sixth sub-freezing unit 360 can provide a current flow path between the two connected intermediate nodes. Multiple freezing elements in the fifth sub-freezing unit 350 can be connected in series. These multiple freezing elements can be connected in series via the bridge arm bus 220, meaning that current can flow between the two intermediate nodes connected to the fifth sub-freezing unit 350 through multiple freezing elements and the bridge arm bus 220. Multiple current-carrying elements in the fifth sub-current-carrying unit 350 can also be connected in series through the bridge arm bus 220 and the bus capacitor 230. That is, the current can flow between the two intermediate nodes connected by the fifth sub-current-carrying unit 350 through multiple current-carrying elements, the bridge arm bus 220 and the bus capacitor 230.

[0082] like Figure 18 As shown, for example, the fifth sub-freezing unit 350 includes two freezing elements, capacitors C11 and C12, and the sixth sub-freezing unit 360 includes one freezing element, capacitor C8. The first bridge arm 210 includes switching transistors S1 to S4, and the second bridge arm 210 includes switching transistors S5 to S8. One end of capacitor C8 is connected between switching transistors S5 and S6, and the other end of capacitor C8 is connected between switching transistors S3 and S4. One end of capacitor C11 is connected between switching transistors S1 and S2, and the other end of capacitor C11 is connected to the upper bus. One end of capacitor C12 is connected between switching transistors S7 and S4, and the other end of capacitor C12 is connected to the upper bus. Furthermore, capacitor C11 provides a current path between the intermediate node between switching transistors S1 and S2 and the upper busbar, and capacitor C12 provides a current path between the intermediate node between switching transistors S7 and S8 and the upper busbar. Thus, the two intermediate nodes connected to the fifth sub-freewheeling unit 350 achieve current flow through multiple freewheeling elements and the upper busbar. Specifically, when bridge arm 210 is in the dead time period, and the current direction in the AC converter is positive, the freewheeling path includes the sixth sub-freewheeling unit 360, and the current flows through a closed freewheeling loop including the freewheeling path, part of the switching transistors, and the primary winding. When the current direction in the AC converter is reversed, the freewheeling path may include the fifth sub-freewheeling unit 350, and the current flows through a closed freewheeling loop including the freewheeling path, part of the switching transistors, and the primary winding.

[0083] like Figure 19 As shown, for example, the other end of capacitor C11 is connected to the lower busbar, the other end of capacitor C12 is connected to the lower busbar, and the rest of the circuit structure is the same as...Figure 18 The same applies here, so it will not be repeated. Furthermore, capacitor C11 provides a current path between the connected intermediate node and the lower busbar, and capacitor C12 provides a current path between the connected intermediate node and the lower busbar. Thus, the two intermediate nodes connected to the fifth sub-freezing unit 350 achieve current flow through multiple freezing elements and the upper busbar. Specifically, when the bridge arm 210 is in the dead zone, and the current direction in the AC converter is positive, the freezing path includes the sixth sub-freezing unit 360, and the current flows through a closed freezing loop including the freezing path, part of the switching transistor, and the primary winding. When the current direction in the AC converter is reversed, the freezing path may include the fifth sub-freezing unit 350, and the current flows through a closed freezing loop including the freezing path, part of the switching transistor, and the primary winding.

[0084] like Figure 20 As shown, for example, the other end of capacitor C11 is connected to the upper busbar, and the other end of capacitor C12 is connected to the lower busbar; the rest of the circuit structure is the same. Figure 18 The same applies here, so it will not be repeated. Furthermore, capacitor C11 provides a current path between the connected intermediate node and the upper busbar, and capacitor C12 provides a current path between the connected intermediate node and the lower busbar. Thus, the two intermediate nodes connected to the fifth sub-freewheeling unit 350 achieve current flow through multiple freewheeling elements, the upper busbar, the lower busbar, and the busbar capacitor 230. Specifically, when the bridge arm 210 is in a dead time period, and the current direction in the AC converter is positive, the freewheeling path includes the sixth sub-freewheeling unit 360, and the current flows in a closed freewheeling loop including the freewheeling path, part of the switching transistor, and the primary winding. When the current direction in the AC converter is reversed, the freewheeling path may include the fifth sub-freewheeling unit 350, and the current flows in a closed freewheeling loop including the busbar capacitor 230, the freewheeling path, part of the switching transistor, and the primary winding.

[0085] like Figure 21 As shown, for example, the other end of capacitor C11 is connected to the lower busbar, and the other end of capacitor C12 is connected to the upper busbar; the rest of the circuit structure is the same. Figure 18The same applies here, so it will not be repeated. Furthermore, capacitor C11 provides a flow path between the connected intermediate node and the lower busbar, and capacitor C12 provides a flow path between the connected intermediate node and the upper busbar. Thus, the two intermediate nodes connected to the fifth sub-freewheeling unit 350 achieve flow through multiple freewheeling elements, the upper busbar, the lower busbar, and the busbar capacitor 230. Specifically, when the bridge arm 210 is in the dead zone, and the current direction in the AC converter is positive, the freewheeling path includes the sixth sub-freewheeling unit 360, and the current flows in a closed freewheeling loop including the freewheeling path, part of the switching transistor, and the primary winding. When the current direction in the AC converter is reversed, the freewheeling path may include the fifth sub-freewheeling unit 350, and the current flows in a closed freewheeling loop including the busbar capacitor 230, the freewheeling path, part of the switching transistor, and the primary winding.

[0086] Please see Figure 22 to Figure 25 As shown, in some examples, the fifth sub-freezing unit 350 is composed of multiple freezing elements, and the sixth sub-freezing unit 360 is composed of multiple freezing elements. It should be understood that the multiple freezing elements in the fifth sub-freezing unit 350 can be connected in series. The multiple freezing elements in the fifth sub-freezing unit 350 can be connected in series via the bridge arm bus 220, meaning that current can flow between the two intermediate nodes connected to the fifth sub-freezing unit 350 through the multiple freezing elements and the bridge arm bus 220. Alternatively, the multiple freezing elements in the fifth sub-freezing unit 350 can be connected in series via the bridge arm bus 220 and the bus capacitor 230, meaning that current can flow between the two intermediate nodes connected to the fifth sub-freezing unit 350 through the multiple freezing elements, the bridge arm bus 220, and the bus capacitor 230. Similarly, multiple current-carrying elements in the sixth sub-current-carrying unit 360 can be connected in series. These multiple current-carrying elements can be connected in series via the bridge arm bus 220, meaning that current can flow between the two intermediate nodes connected to the sixth sub-current-carrying unit 360 through multiple current-carrying elements and the bridge arm bus 220. Alternatively, the multiple current-carrying elements in the sixth sub-current-carrying unit 360 can also be connected in series via the bridge arm bus 220 and the bus capacitor 230, meaning that current can flow between the two intermediate nodes connected to the sixth sub-current-carrying unit 360 through multiple current-carrying elements, the bridge arm bus 220, and the bus capacitor 230.

[0087] like Figure 22As shown, for example, the fifth sub-freezing unit 350 includes two freezing elements, capacitors C13 and C16, and the sixth sub-freezing unit 360 includes two freezing elements, capacitors C14 and C15. The first bridge arm 210 includes switching transistors S1 to S4, and the second bridge arm 210 includes switching transistors S5 to S8. One end of capacitor C13 is connected between switching transistors S1 and S2, and the other end of capacitor C13 is connected to the upper bus. One end of capacitor C14 is connected between switching transistors S3 and S4, and the other end of capacitor C14 is connected to the lower bus. One end of capacitor C15 is connected between switching transistors S5 and S6, and the other end of capacitor C15 is connected to the upper bus. One end of capacitor C16 is connected between switching transistors S7 and S8, and the other end of capacitor C16 is connected to the lower bus. Specifically, when bridge arm 210 is in the dead zone and the current direction in the AC converter is positive, the freewheeling path includes the sixth sub-freewheeling unit 360, and the current freewheels in a closed freewheeling loop including the bus capacitor 230, the freewheeling path, part of the switching transistor, and the primary winding. When the current direction in the AC converter is reverse, the freewheeling path may include the fifth sub-freewheeling unit 350, and the current freewheels in a closed freewheeling loop including the bus capacitor 230, the freewheeling path, part of the switching transistor, and the primary winding.

[0088] like Figure 23 As shown, for example, the other ends of capacitors C13, C14, C15, and C16 are connected to the busbar, and the rest of the circuit structure is the same. Figure 22 The same applies here, so it will not be repeated. Specifically, when bridge arm 210 is in the dead zone, and the current direction in the AC converter is positive, the freewheeling path includes the sixth sub-freewheeling unit 360, so the current freewheels in a closed freewheeling loop including the freewheeling path, part of the switching transistor, and the primary winding. When the current direction in the AC converter is reversed, the freewheeling path may include the fifth sub-freewheeling unit 350, so the current freewheels in a closed freewheeling loop including the freewheeling path, part of the switching transistor, and the primary winding.

[0089] like Figure 24 As shown, for example, the other ends of capacitors C13, C14, C15, and C16 are connected to the lower busbar, and the rest of the circuit structure is the same. Figure 22The same applies here, so it will not be repeated. Specifically, when bridge arm 210 is in the dead zone, and the current direction in the AC converter is positive, the freewheeling path includes the sixth sub-freewheeling unit 360, so the current freewheels in a closed freewheeling loop including the freewheeling path, part of the switching transistor, and the primary winding. When the current direction in the AC converter is reversed, the freewheeling path may include the fifth sub-freewheeling unit 350, so the current freewheels in a closed freewheeling loop including the freewheeling path, part of the switching transistor, and the primary winding.

[0090] like Figure 25 As shown, for example, the other end of capacitor C13 is connected to the lower busbar, the other end of capacitor C14 is connected to the upper busbar, the other end of capacitor C15 is connected to the lower busbar, and the other end of capacitor C16 is connected to the upper busbar. The remaining circuit structure is the same. Figure 22 The same applies here, and will not be repeated. Specifically, when bridge arm 210 is in the dead zone, and the current direction in the AC converter is positive, the freewheeling path includes the sixth sub-freewheeling unit 360, and the current freewheels in a closed freewheeling loop including the bus capacitor 230, the freewheeling path, part of the switching transistor, and the primary winding. When the current direction in the AC converter is reversed, the freewheeling path may include the fifth sub-freewheeling unit 350, and the current freewheels in a closed freewheeling loop including the bus capacitor 230, the freewheeling path, part of the switching transistor, and the primary winding.

[0091] It should be noted that the above examples are only for scenarios where there are two bridge arms 210 and the two bridge arms 210 have the same structure. They are illustrative examples of the circuit structure of the freewheeling module 300, which includes a fifth sub-freewheeling unit 350 and a sixth sub-freewheeling unit 360, and are not the only limitation on the technical solution of this application. Specifically, the connection structure of the fifth sub-freewheeling unit 350 and the sixth sub-freewheeling unit 360 can adopt other adaptation forms, and the number of freewheeling capacitors included in them can also be more than two, as long as the freewheeling function requirements during the dead time period can be met. Furthermore, the freewheeling paths in the above examples are not unique limitations; the circuit itself has the potential to provide multiple freewheeling paths. During the actual operation of the bridge arm 210 during the dead time period, the specific freewheeling path is determined by the inherent topology of the circuit and the real-time current direction at the moment of the dead time, thus automatically forming a unique freewheeling path adapted to the current operating condition. In addition to the above exemplary structures and path configurations, those skilled in the art can derive more unit connection forms and path design schemes that can realize the freewheeling function based on the technical concept of this application. Related embodiments will not be described in detail here.

[0092] Please see Figure 26As shown, in some embodiments, when there are two bridge arms 210, and the two switches of the upper bridge arm 211 of one of the two bridge arms 210 are connected in series with a common source, and the two switches of the upper bridge arm 211 of the other of the two bridge arms 210 are connected in series with a common drain, the freewheeling module 300 includes a seventh sub-freewheeling unit 370 and an eighth sub-freewheeling unit 380. One end of the seventh sub-freewheeling unit 370 is connected to the middle node of the two switches of one upper bridge arm 211, and the other end of the seventh sub-freewheeling unit 370 is connected to the middle node of the two switches of the other upper bridge arm 211. One end of the eighth sub-freewheeling unit 380 is connected to the middle node of the two switches of one lower bridge arm 212, and the other end of the eighth sub-freewheeling unit 380 is connected to the middle node of the two switches of the other lower bridge arm 212. When the bridge arm 210 is in a dead time period, the freewheeling path includes at least one of the seventh sub-freewheeling unit 370 and the eighth sub-freewheeling unit 380.

[0093] It's important to understand that when there are two bridge arms 210, and in one bridge arm 210, the two switches of the upper bridge arm 211 are connected in series with a common source, while in the other bridge arm 210, the two switches of the upper bridge arm 211 are connected in series with a common drain, resulting in the following: in one bridge arm 210, the two switches of the upper bridge arm 211 are connected in series with a common source, and the two switches of the lower bridge arm 212 are connected in series with a common drain; in the other bridge arm 210, the two switches of the upper bridge arm 211 are connected in series with a common drain, and the two switches of the lower bridge arm 212 are connected in series with a common source. In other words, the circuit structures of the two bridge arms 210 are different.

[0094] In this embodiment of the application, the bridge arm 210 on the left side of the figure is defined as the first bridge arm 210, and the bridge arm 210 on the right side is defined as the second bridge arm 210. The two ends of the primary winding of the transformer 100 are respectively connected to the connection node between the upper and lower bridge arms in the first bridge arm 210 and the connection node between the upper and lower bridge arms in the second bridge arm 210. That is, the two ends of the primary winding of the transformer 100 are respectively connected to point A and point C. One end of the seventh sub-current freewheeling unit 370 is connected to the intermediate node of the two switching transistors of one upper bridge arm 211, and the other end of the seventh sub-current freewheeling unit 370 is connected to the intermediate node of the two switching transistors of another upper bridge arm 211. The seventh sub-current freewheeling unit 370 is used to provide a flow path between the intermediate nodes of the two switching transistors of the upper bridge arm 211 of one bridge arm 210 and the intermediate nodes of the two switching transistors of the upper bridge arm 211 of another bridge arm 210. One end of the eighth sub-current freewheeling unit 380 is connected to the intermediate node of the two switching transistors of one lower bridge arm 212, and the other end of the eighth sub-current freewheeling unit 380 is connected to the intermediate node of the two switching transistors of another lower bridge arm 212. The eighth sub-current freewheeling unit 380 is used to provide a flow path between the intermediate nodes of the two switching transistors of the lower bridge arm 212 of one bridge arm 210 and the intermediate nodes of the two switching transistors of the lower bridge arm 212 of another bridge arm 210. Furthermore, during the dead time period, the freewheeling path includes a current path provided by at least one of the seventh sub-freewheeling unit 370 and the eighth sub-freewheeling unit 380, allowing current to continue flowing in the closed freewheeling loop and maintaining current continuity. It should be noted that in some examples, the closed freewheeling path may include the freewheeling path, a portion of the switching transistor, and the primary winding. In other examples, the closed freewheeling path may include the bus capacitor 230, the freewheeling path, a portion of the switching transistor, and the primary winding. The specific path is determined based on the current direction during the dead time period and the specific circuit topology.

[0095] It should be noted that when there is only one bridge arm 210, and the two bridge arms 210 have different structures, the freewheeling module 300 can provide multiple possible freewheeling paths. Specifically, in some examples, the freewheeling path includes the seventh sub-freewheeling unit 370; in other examples, the freewheeling path includes the eighth sub-freewheeling unit 380; and in still other examples, the freewheeling path includes both the seventh sub-freewheeling unit 370 and the eighth sub-freewheeling unit 380. During the actual operation of the bridge arm 210 in the dead time period, the specific freewheeling path is determined by the inherent topology of the circuit itself and the real-time current direction during the dead time period, thus automatically and uniquely determining the freewheeling path.

[0096] like Figure 26As shown, in some examples, one end of the seventh sub-freezing unit 370 is connected to the intermediate node of the two switching transistors of the upper bridge arm 211 of the first bridge arm 210, and the other end of the seventh sub-freezing unit 370 is connected to the intermediate node of the two switching transistors of the upper bridge arm 211 of the second bridge arm 210. One end of the eighth sub-freezing unit 380 is connected to the intermediate node of the two switching transistors of the lower bridge arm 212 of the first bridge arm 210, and the other end of the eighth sub-freezing unit 380 is connected to the intermediate node of the two switching transistors of the lower bridge arm 212 of the second bridge arm 210. When the bridge arm 210 is in a dead time period, the freewheeling path includes either the seventh sub-freezing unit 370 or the eighth sub-freezing unit 380. That is, the freewheeling path may include the seventh sub-freezing unit 370, or it may include the eighth sub-freezing unit 380.

[0097] like Figure 26 As shown, for example, the seventh sub-freezing unit 370 includes capacitor C17, the eighth sub-freezing unit 380 includes capacitor C18, the first bridge arm 210 includes switching transistors S1 to S4, the second bridge arm 210 includes switching transistors S5 to S8, one end of capacitor C17 is connected between switching transistors S1 and S2, and the other end of capacitor C17 is connected between switching transistors S5 and S6, one end of capacitor C18 is connected between switching transistors S3 and S4, and the other end of capacitor C18 is connected between switching transistors S7 and S8. When bridge arm 210 is in the dead time period, and the current direction in the AC converter is positive, the freewheeling path includes the eighth sub-freezing unit 380, and the current freewheels in a closed freewheeling loop including the freewheeling path, part of the switching transistors, and the primary winding. In AC converters, when the current direction is reversed, the freewheeling path includes the seventh sub-freewheeling unit 370, and the current freewheels in a closed freewheeling loop that includes the freewheeling path, part of the switching transistor and the primary winding.

[0098] In some embodiments, at least one of the seventh sub-current relay unit 370 and the eighth sub-current relay unit 380 is composed of a plurality of current relay elements.

[0099] In other words, in some examples, the seventh sub-freezing unit 370 may include multiple freezing elements, and the eighth sub-freezing unit 380 may include a single freezing element. In other examples, the seventh sub-freezing unit 370 may include a single freezing element, and the eighth sub-freezing unit 380 may include multiple freezing elements. In still other examples, the seventh sub-freezing unit 370 may include multiple freezing elements, and the eighth sub-freezing unit 380 may include multiple freezing elements. It should be noted that the line containing each freezing element in the seventh sub-freezing unit 370 and the eighth sub-freezing unit 380 can provide a current flow path. Furthermore, in the case of dead time, the freezing path includes the flow path provided by at least one of the seventh sub-freezing unit 370 and the eighth sub-freezing unit 380. That is, the freezing path includes the current flow path provided by all the freezing elements included in at least one of the seventh sub-freezing unit 370 and the eighth sub-freezing unit 380, so that the current can continue in the closed freezing loop, maintaining current continuity.

[0100] It should be noted that the multiple current-carrying elements in the seventh sub-current-carrying unit 370 can be connected in series. These multiple current-carrying elements can be connected in series via the bridge arm bus 220, meaning that current can flow between the two intermediate nodes connected to the seventh sub-current-carrying unit 370 through the multiple current-carrying elements and the bridge arm bus 220. Alternatively, the multiple current-carrying elements in the seventh sub-current-carrying unit 370 can also be connected in series via the bridge arm bus 220 and the bus capacitor 230, meaning that current can flow between the two intermediate nodes connected to the seventh sub-current-carrying unit 370 through the multiple current-carrying elements, the bridge arm bus 220, and the bus capacitor 230. Similarly, the multiple current-carrying elements in the eighth sub-current-carrying unit 380 can be connected in series. These multiple current-carrying elements can be connected in series via the bridge arm bus 220, meaning that current can flow between the two intermediate nodes connected to the eighth sub-current-carrying unit 380 through the multiple current-carrying elements and the bridge arm bus 220. Multiple current-carrying elements in the eighth sub-current-carrying unit 380 can also be connected in series through the bridge arm bus 220 and the bus capacitor 230. That is, the current can flow between the two intermediate nodes connected by the eighth sub-current-carrying unit 380 through multiple current-carrying elements, the bridge arm bus 220 and the bus capacitor 230.

[0101] Specifically, in some examples, the seventh sub-current continuing unit 370 may include multiple current continuing elements, and the eighth sub-current continuing unit 380 may include one current continuing element. Taking the seventh sub-current continuing unit 370 as an example, if it includes two current continuing elements, one end of one current continuing element is connected to the intermediate node of the two switching transistors of the upper bridge arm 211 of the first bridge arm 210, and the other end of the current continuing element can be connected to either the upper bus or the lower bus; one end of the other current continuing element is connected to the intermediate node of the two switching transistors of the upper bridge arm 211 of the second bridge arm 210, and the other end of the current continuing element can be connected to either the upper bus or the lower bus; one end of the current continuing element in the eighth sub-current continuing unit 380 is connected to the intermediate node of the two switching transistors of the lower bridge arm 212 of the first bridge arm 210, and the other end of the current continuing element in the eighth sub-current continuing unit 380 is connected to the intermediate node of the two switching transistors of the lower bridge arm 212 of the second bridge arm 210.

[0102] In other examples, the seventh sub-current continuing unit 370 may include one current continuing element, and the eighth sub-current continuing unit 380 may include multiple current continuing elements. Taking the eighth sub-current continuing unit 380 as an example, if one end of the current continuing element of the eighth sub-current continuing unit 380 is connected to the intermediate node of the two switching transistors of the lower bridge arm 212 of the first bridge arm 210, and the other end of the current continuing element can be connected to either the upper bus or the lower bus; one end of the other current continuing element is connected to the intermediate node of the two switching transistors of the lower bridge arm 212 of the second bridge arm 210, and the other end of the current continuing element can be connected to either the upper bus or the lower bus; one end of the current continuing element in the seventh sub-current continuing unit 370 is connected to the intermediate node of the two switching transistors of the upper bridge arm 211 of the first bridge arm 210, and the other end of the current continuing element in the seventh sub-current continuing unit 370 is connected to the intermediate node of the two switching transistors of the upper bridge arm 211 of the second bridge arm 210.

[0103] Please see Figure 27 to Figure 31In other examples, the seventh sub-current relay unit 370 may include multiple current relays, and the eighth sub-current relay unit 380 may include multiple current relays. Taking the seventh sub-current continuing unit 370 and the eighth sub-current continuing unit 380, which include two current continuing elements, as an example, one end of the current continuing element of the eighth sub-current continuing unit 380 is connected to the intermediate node of the two switching transistors of the lower bridge arm 212 of the first bridge arm 210, and the other end of the current continuing element can be connected to either the upper bus or the lower bus; one end of the other current continuing element is connected to the intermediate node of the two switching transistors of the lower bridge arm 212 of the second bridge arm 210, and the other end of the current continuing element can be connected to either the upper bus or the lower bus; one end of the current continuing element of the seventh sub-current continuing unit 370 is connected to the intermediate node of the two switching transistors of the upper bridge arm 211 of the first bridge arm 210, and the other end of the current continuing element can be connected to either the upper bus or the lower bus; one end of the other current continuing element is connected to the intermediate node of the two switching transistors of the upper bridge arm 211 of the second bridge arm 210, and the other end of the current continuing element can be connected to either the upper bus or the lower bus.

[0104] like Figure 27 As shown, for example, the seventh sub-freezing unit 370 includes two freezing elements, capacitor C19 and capacitor C21, and the eighth sub-freezing unit 380 includes two freezing elements, capacitor C20 and capacitor C22. The first bridge arm 210 includes switching transistors S1 to S4, and the second bridge arm 210 includes switching transistors S5 to S8. One end of capacitor C19 is connected between switching transistors S1 and S2, and the other end of capacitor C19 is connected to the upper bus. One end of capacitor C20 is connected between switching transistors S3 and S4, and the other end of capacitor C20 is connected to the lower bus. One end of capacitor C21 is connected between switching transistors S5 and S6, and the other end of capacitor C21 is connected to the upper bus. One end of capacitor C22 is connected between switching transistors S7 and S8, and the other end of capacitor C22 is connected to the lower bus. Specifically, when bridge arm 210 is in the dead zone and the current direction in the AC converter is positive, the freewheeling path includes the eighth sub-freewheeling unit 380, and the current freewheels in a closed freewheeling loop including the freewheeling path, part of the switching transistor, and the primary winding. When the current direction in the AC converter is reverse, the freewheeling path may include the seventh sub-freewheeling unit 370, and the current freewheels in a closed freewheeling loop including the freewheeling path, part of the switching transistor, and the primary winding.

[0105] like Figure 28 As shown, for example, the other ends of capacitors C19, C20, C22, and C21 are connected to the busbar, and the rest of the circuit structure is the same. Figure 27The same applies, so it will not be repeated here. Specifically, when bridge arm 210 is in the dead zone, and the current direction in the AC converter is positive, the freewheeling path includes the eighth sub-freewheeling unit 380, so the current freewheels in a closed freewheeling loop including the freewheeling path, part of the switching transistor, and the primary winding. When the current direction in the AC converter is reversed, the freewheeling path may include the seventh sub-freewheeling unit 370, so the current freewheels in a closed freewheeling loop including the freewheeling path, part of the switching transistor, and the primary winding. It should be noted that when bridge arm 210 is in the dead zone and the current direction in the AC converter is positive, the freewheeling path also includes the seventh sub-freewheeling unit 370 and the eighth sub-freewheeling unit 380. The current flows in a closed freewheeling loop that includes the freewheeling path, part of the switching transistors and the primary winding. The loop path provided by the closed freewheeling loop is that the current flows from point A through the primary winding of transformer 100 in sequence through point C, switching transistor S7, capacitor C22, capacitor C21, switching transistor S5, switching transistor S1, capacitor C19, capacitor C20, and switching transistor S3 before flowing out from point A, forming a current closed loop.

[0106] like Figure 29 As shown, for example, the other ends of capacitors C19, C20, C22, and C21 are connected to the lower busbar, and the rest of the circuit structure is the same as... Figure 27 The same applies, so it will not be repeated here. Specifically, when bridge arm 210 is in the dead zone, and the current direction in the AC converter is positive, the freewheeling path includes the eighth sub-freewheeling unit 380, so the current freewheels in a closed freewheeling loop including the freewheeling path, part of the switching transistor, and the primary winding. When the current direction in the AC converter is reversed, the freewheeling path may include the seventh sub-freewheeling unit 370, so the current freewheels in a closed freewheeling loop including the freewheeling path, part of the switching transistor, and the primary winding.

[0107] like Figure 30 As shown, for example, the other end of capacitor C19 is connected to the lower busbar, the other end of capacitor C20 is connected to the upper busbar, the other end of capacitor C21 is connected to the lower busbar, and the other end of capacitor C22 is connected to the upper busbar. The remaining circuit structure is the same. Figure 27 The same applies, so it will not be repeated here. Specifically, when bridge arm 210 is in the dead zone, and the current direction in the AC converter is positive, the freewheeling path includes the eighth sub-freewheeling unit 380, so the current freewheels in a closed freewheeling loop including the freewheeling path, part of the switching transistor, and the primary winding. When the current direction in the AC converter is reversed, the freewheeling path may include the seventh sub-freewheeling unit 370, so the current freewheels in a closed freewheeling loop including the freewheeling path, part of the switching transistor, and the primary winding.

[0108] It should be noted that the above examples are only for scenarios where there are two bridge arms 210 and the two bridge arms 210 have the same structure. They are illustrative examples of the circuit structure of the freewheeling module 300, which includes a seventh sub-freewheeling unit 370 and an eighth sub-freewheeling unit 380, and are not the only limitation on the technical solution of this application. Specifically, the connection structure of the seventh sub-freewheeling unit 370 and the eighth sub-freewheeling unit 380 can adopt other adaptation forms, and the number of freewheeling capacitors included in them can also be more than two, as long as the freewheeling function requirements during the dead time period can be met. Furthermore, the freewheeling paths in the above examples are not unique limitations; the circuit itself has the potential to provide multiple freewheeling paths. During the actual operation of the bridge arm 210 during the dead time period, the specific freewheeling path is determined by the inherent topology of the circuit and the real-time current direction at the moment of the dead time, thus automatically forming a unique freewheeling path adapted to the current operating condition. In addition to the above exemplary structures and path configurations, those skilled in the art can derive more unit connection forms and path design schemes that can realize the freewheeling function based on the technical concept of this application. Related embodiments will not be described in detail here.

[0109] Please see Figure 31 As shown, in some embodiments, the AC conversion device further includes: an AC / DC conversion circuit 500 and an impedance network 600, wherein the AC / DC conversion circuit 500 is connected to the secondary winding of the transformer 100; the impedance network 600 is connected between the AC conversion circuit 200 and the primary winding of the transformer 100, or the impedance network 600 is connected between the AC / DC conversion circuit 500 and the secondary winding of the transformer 100.

[0110] Impedance network 600 is used to optimize the energy transmission path through impedance characteristics, suppressing harmonics, stabilizing the system, and improving overall efficiency and reliability. Impedance network 600 can be an inductor or a combination of inductor and capacitor. Impedance network 600 can be located between the primary circuit and transformer 100, or between transformer 100 and secondary circuit. For example, if impedance network 600 is an inductor, it can be placed between primary circuits, or between secondary circuits. If impedance network 600 is a combination of inductor and capacitor, the inductor can be placed between primary circuits, or between secondary circuits; the capacitor can be placed between primary circuits, or between secondary circuits.

[0111] Please see Figure 32 As shown, the impedance network 600 may include an inductor Lr and a capacitor Cr, and both the inductor Lr and the capacitor Cr are disposed between the primary circuit and the primary side.

[0112] The AC / DC converter circuit 500 serves as the secondary circuit of the transformer 100, converting the AC voltage output from the secondary side of the transformer 100 into a DC voltage to supply power to the DC side. Alternatively, the AC / DC converter circuit 500 can also convert the DC voltage on the DC side into an AC voltage and input it to the transformer 100. Generally, the AC / DC converter circuit 500 includes multiple switching transistors (such as IGBTs or MOSFETs), and the output voltage waveform is adjusted by controlling the on and off states of the switching transistors, thereby realizing the conversion from DC to AC or vice versa.

[0113] Please refer to the following: Figure 32 to Figure 35 As shown. Exemplarily, the AC / DC converter circuit 500 may include, but is not limited to, a half-bridge circuit or a full-bridge circuit.

[0114] For example, such as Figure 32 and Figure 33 As shown, the AC / DC converter circuit 500 includes a full-bridge circuit composed of switching transistors S9, S10, S11, and S12, as well as a DC blocking capacitor Cs and a capacitor C23.

[0115] For example, such as Figure 34 As shown, the AC / DC converter circuit 500 includes a half-bridge circuit composed of switching transistor S9 and switching transistor S10, as well as a DC blocking capacitor Cs and a capacitor C23.

[0116] For example, such as Figure 35 As shown, the AC / DC converter circuit 500 includes a half-bridge circuit composed of switching transistor S9 and switching transistor S10, and also includes DC blocking capacitor Cs, capacitor C23, capacitor C24 and capacitor C25.

[0117] It should be noted that if the capacitor in impedance network 600 is located between transformer 100 and the secondary circuit, then... Figure 33 and Figure 34 The AC / DC conversion circuit 500 in the circuit may not include a DC blocking capacitor Cs, and the capacitor in the impedance network 600 may be used as a DC blocking capacitor.

[0118] Through the above technical solution, this application provides an AC converter device. The two transistors in the upper bridge arm 211 and the two transistors in the lower bridge arm 212 of this AC converter device form a bidirectional switching structure. The two inner transistors in each bridge arm 210 are aligned in the same direction, as are the two outer transistors. Simultaneously, the bus capacitor 230 is connected in parallel with the bridge arm 210. Each bidirectional switch intermediate node is connected to a corresponding freewheeling element in the freewheeling module 300. The freewheeling element in the freewheeling module 300 provides a freewheeling path during the dead time period. This ensures that, regardless of whether the current is forward or reverse during the dead time period, the AC converter device provides a closed freewheeling loop including the freewheeling path, part of the switching transistors, and the primary winding, achieving continuous current flow without interruption. This effectively reduces the overshoot of the switching device's voltage stress and lowers the risk of damage to the switching device. Furthermore, this application not only possesses the core functions of a traditional matrix topology, enabling direct single-stage AC-DC energy transmission, but also directly utilizes the body diodes of some switching transistors in the bridge arm 210 topology as freewheeling elements included in the closed freewheeling loop, eliminating the need for additional dedicated freewheeling diodes and simplifying the circuit topology. Furthermore, during the positive and negative half-cycles of the AC circuit, the freewheeling capacitor in the freewheeling module 300 of this application is charged and discharged only in one half-cycle, thereby reducing energy loss in half-cycle; while in the other half-cycle, the freewheeling capacitor is connected in parallel across the bus capacitor 230, which can improve the filtering performance of the bus capacitor and thus improve the overall circuit performance of the AC converter.

[0119] Furthermore, the control strategy for the AC converter proposed above can employ phase-shift control, frequency conversion control, or a combination of both. Phase-shift control includes external phase shifting, external phase shifting + internal phase shifting (primary-side internal phase shifting, secondary-side internal phase shifting, or primary-secondary-side internal phase shifting). For example, using... Figure 32 The AC converter structure shown is an example; the following will be combined with... Figure 36 As shown, each phase-shift control method is explained.

[0120] like Figure 36 As shown in the figure, α is the outward phase shift angle, β is the inward phase shift angle of the primary side, γ is the inward phase shift angle of the secondary side, and V... AC for Figure 13 The voltage between points A and C, V DE for Figure 13 The voltage between points D and E in the middle. Figure 36 Figure (a) shows the waveform corresponding to using only the external phase shift control between the primary and secondary sides. It can be seen that, with external phase shift control alone, V... AC and V DE There is an external phase shift angle α between them, which reflects the phase difference between the primary and secondary driving signals. The effective overlap time of the primary and secondary voltages can be adjusted by changing α, thereby controlling the power transmission. Figure 36Figure (b) shows the waveform corresponding to the addition of the inner phase shift control on the secondary side based on the outer phase shift. It can be seen that this method introduces the inner phase shift angle β on the secondary side based on the outer phase shift angle α. Power control can be achieved by adjusting the outer phase shift angle α and the inner phase shift angle β on the secondary side together. Figure 36 Figure (c) shows the waveform corresponding to the addition of the primary side's internal phase shift control on the basis of the external phase shift. It can be seen that this method introduces the primary side's internal phase shift angle β on the basis of the external phase shift angle α. Power control is achieved by adjusting the external phase shift angle α and the primary side's internal phase shift angle β together. Figure 36 Figure (d) shows the waveforms corresponding to the addition of internal phase shift control on the primary and secondary sides based on the external phase shift. It can be seen that this method introduces the internal phase shift angle β on the primary side and the internal phase shift angle γ on the secondary side based on the external phase shift angle α. Through the joint adjustment of the external phase shift angle α, the internal phase shift angle β on the primary side and the internal phase shift angle γ on the secondary side, more flexible power and voltage regulation can be achieved.

[0121] The waveform diagrams above illustrate various phase-shift control methods. Based on phase-shift control strategies such as "external phase shift" and "external phase shift + internal phase shift," dynamic adjustment of the switching frequency can be additionally introduced for control. This means that control is not limited to adjusting the phase shift angle (α, β, γ) to control power and voltage; frequency conversion control is also achieved by real-time changes in the operating frequency of the switching transistors in the converter. This works in conjunction with phase-shift control to achieve superior conversion performance. It should be noted that different topologies or application requirements may allow for the selection of one or a combination of the above phase-shift control methods, used in conjunction with frequency conversion control. Specific details regarding the driving timing and parameter optimization of phase-shift control can be adjusted using conventional techniques in this field combined with the control logic of this invention, and all such adjustments fall within the scope of this invention.

[0122] In the above embodiments, the descriptions of each embodiment have different focuses. For parts not described in detail in a certain embodiment, please refer to the relevant descriptions in other embodiments.

[0123] The above are merely preferred embodiments of this application and are not intended to limit this application in any way. Although this application has disclosed preferred embodiments as above, it is not intended to limit this application. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the technical solution of this application. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of this application without departing from the scope of the technical solution of this application shall still fall within the scope of the technical solution of this application.

Claims

1. An alternating current conversion device, characterized by, The AC conversion device comprises: a transformer (100); an AC conversion circuit (200), one end of the AC conversion circuit (200) being configured to be connected with an AC source (400), the other end of the AC conversion circuit (200) being connected with a primary winding of the transformer (100), the AC conversion circuit (200) comprising at least one bridge arm (210), two ends of the bridge arm (210) being connected with the AC source (400) through a bridge arm bus (220) respectively, the bridge arm (210) comprising a series connection of an upper bridge arm (211) and a lower bridge arm (212), a connection node between the upper bridge arm (211) and the lower bridge arm (212) being connected with the primary winding, the upper bridge arm (211) and the lower bridge arm (212) each comprising two switching tubes, and the two switching tubes of one of the upper bridge arm (211) and the lower bridge arm (212) being connected in common source, and the two switching tubes of the other of the upper bridge arm (211) and the lower bridge arm (212) being connected in common drain; a freewheeling module (300), the freewheeling module (300) having a freewheeling path in the case that the bridge arm (210) is in a dead time period, the AC conversion device having a closed freewheeling loop, the closed freewheeling loop comprising the freewheeling path, part of the switching tubes and the primary winding.

2. The alternating current conversion device of claim 1, wherein, In the case that the number of the bridge arms (210) is one and the bridge arm (210) constitutes a symmetric half-bridge, one end of the freewheeling module (300) is connected with a middle node of the two switching tubes of the upper bridge arm (211), and the other end of the freewheeling module (300) is connected with a middle node of the two switching tubes of the lower bridge arm (212).

3. The AC conversion device according to claim 2, characterized by The freewheeling module (300) comprises a first sub-freewheeling unit (310) and a second sub-freewheeling unit (320), one end of the first sub-freewheeling unit (310) being connected with the middle node of the two switching tubes of the upper bridge arm (211), the other end of the first sub-freewheeling unit (310) being connected with the bridge arm bus (220), one end of the second sub-freewheeling unit (320) being connected with the middle node of the two switching tubes of the lower bridge arm (212), and the other end of the second sub-freewheeling unit (320) being connected with the bridge arm bus (220). In the case that the bridge arm (210) is in a dead time period, the freewheeling path comprises at least one of the first sub-freewheeling unit (310) and the second sub-freewheeling unit (320).

4. The AC conversion device of claim 1, wherein The AC conversion device further comprises: a bus capacitor (230), the bus capacitor (230) being connected with the bridge arm bus (220), and the bus capacitor (230) being connected with the bridge arm (210) in parallel.

5. The AC conversion device of claim 4, wherein In the case that the number of the bridge arms (210) is one and the bridge arm (210) constitutes an asymmetric half-bridge, one end of the freewheeling module (300) is connected with a middle node of the two switching tubes of the upper bridge arm (211), and the other end of the freewheeling module (300) is connected with a middle node of the two switching tubes of the lower bridge arm (212).

6. The AC conversion device of claim 5, wherein The freewheeling module (300) comprises a third sub-freewheeling unit (330) and a fourth sub-freewheeling unit (340), one end of the third sub-freewheeling unit (330) is connected with the middle node of the two switch tubes of the upper bridge arm (211), the other end of the third sub-freewheeling unit (330) is connected with the bridge arm bus (220), one end of the fourth sub-freewheeling unit (340) is connected with the middle node of the two switch tubes of the lower bridge arm (212), the other end of the fourth sub-freewheeling unit (340) is connected with the bridge arm bus (220); In the case that the bridge arm (210) is in a dead time period, the freewheeling path comprises at least one of the third sub-freewheeling unit (330) and the fourth sub-freewheeling unit (340).

7. The AC conversion device of claim 1, wherein In the case that the number of the bridge arms (210) is two and the two bridge arms (210) are structurally identical, the freewheeling module (300) comprises a fifth sub-freewheeling unit (350) and a sixth sub-freewheeling unit (360), one end of the fifth sub-freewheeling unit (350) is connected with the middle node of the two switch tubes of one upper bridge arm (211), the other end of the fifth sub-freewheeling unit (350) is connected with the middle node of the two switch tubes of any one lower bridge arm (212), one end of the sixth sub-freewheeling unit (360) is connected with the middle node of the two switch tubes of the other upper bridge arm (211), the other end of the sixth sub-freewheeling unit (360) is connected with the middle node of the two switch tubes of the remaining one lower bridge arm (212); In the case that the bridge arm (210) is in a dead time period, the freewheeling path comprises at least one of the fifth sub-freewheeling unit (350) and the sixth sub-freewheeling unit (360).

8. The AC conversion device of claim 7, wherein At least one of the fifth sub-freewheeling unit (350) and the sixth sub-freewheeling unit (360) is composed of a plurality of freewheeling components.

9. The AC conversion device of claim 1, wherein, In the case that the number of the bridge arms (210) is two and the two bridge arms (210) are structurally identical, the freewheeling module (300) comprises a fifth sub-freewheeling unit (350) and a sixth sub-freewheeling unit (360), one end of the fifth sub-freewheeling unit (350) is connected with the middle node of the two switch tubes of one upper bridge arm (211), the other end of the fifth sub-freewheeling unit (350) is connected with the middle node of the two switch tubes of any one lower bridge arm (212), one end of the sixth sub-freewheeling unit (360) is connected with the middle node of the two switch tubes of the other upper bridge arm (211), the other end of the sixth sub-freewheeling unit (360) is connected with the middle node of the two switch tubes of the remaining one lower bridge arm (212); In the case that the bridge arm (210) is in a dead time period, the freewheeling path comprises at least one of the seventh sub-freewheeling unit (370) and the eighth sub-freewheeling unit (380).

10. The AC conversion device of claim 9, wherein At least one of the seventh sub-continuity unit (370) and the eighth sub-continuity unit (380) is composed of a plurality of continuity components.

11. The AC conversion device of claim 1, wherein The AC conversion device further comprises: An AC-DC conversion circuit (500) connected with the secondary winding of the transformer (100); An impedance network (600) connected between the AC conversion circuit (200) and the primary winding of the transformer (100), or connected between the AC-DC conversion circuit (500) and the secondary winding of the transformer (100). An impedance network (600) connected between the AC conversion circuit (200) and the primary winding of the transformer (100), or connected between the AC-DC conversion circuit (500) and the secondary winding of the transformer (100).

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