A linear motor drive system topology

Abstract

The utility model discloses a linear motor drive system topology, including at least one phase shifting transformer and at least two drive frequency cascaded circuit, phase shifting transformer primary side connects the power grid, and the input side of every drive frequency cascaded circuit is connected with all phase shifting transformer secondary side respectively, drive frequency cascaded circuit adopts the high voltage required for cascaded topology output drive linear motor, the at least two drive frequency cascaded circuit alternate output is for linear motor adjacent stator segment power supply, and the at least two drive frequency cascaded circuit of alternate output power supply share front end phase shifting transformer, has improved the utilization of front end phase shifting transformer, has reduced the deployment quantity of phase shifting transformer, has reduced linear motor electromagnetic traction drive power deployment cost, has saved deployment space simultaneously. In addition, through the targeted phase shifting design to phase shifting transformer primary winding and secondary winding, can reduce the network side power grid harmonic without increasing the filter.

Description

Technical Field

[0001] This utility model relates to the field of train control technology, and in particular to a topology of a linear motor drive system. Background Technology

[0002] High-speed maglev trains, with their advantages of rapid acceleration and low operating noise, represent an ideal solution for future rail transit. The core component enabling traction and levitation in high-speed maglev trains is the long-stator linear synchronous motor, whose performance directly impacts train operating efficiency. To improve efficiency, long-stator linear motors typically employ segmented power supply; the stator is divided into multiple segments, and only the segment where the mover (train) operates is powered by the corresponding linear motor traction drive. To ensure smooth forward movement or acceleration of the mover, the drive power supply must be switched to different stator segments via a switching switch. This has led to various long-stator segment switching techniques, such as the two-step method, the leapfrog method, and the three-step method. Based on the characteristics of linear motors, each traction substation typically has two sets of frequency converter drive power supplies connected to the stator windings of each linear motor segment via stator switching switches, depending on the switching technique used. Figure 1 As shown, each inverter drive power supply is equipped with a separate transformer. When the output of one inverter drive power supply is used to power the corresponding stator section of the linear motor, it not only increases the equipment cost but also wastes deployment space.

[0003] Therefore, traditional linear motor electromagnetic traction drive power supplies suffer from high deployment costs and large deployment space requirements. Summary of the Invention

[0004] The technical problem to be solved by this utility model is to provide a topology structure for a linear motor drive system, so as to solve the problems of high deployment cost and large deployment space of traditional linear motor electromagnetic traction drive power supplies.

[0005] This utility model provides a linear motor drive system topology, including at least one phase-shifting transformer and at least two drive frequency converter cascade circuits. The primary side of the phase-shifting transformer is connected to the power grid, and the input side of each drive frequency converter cascade circuit is connected to the secondary side of all phase-shifting transformers respectively. The at least two drive frequency converter cascade circuits alternately output power to adjacent stator sections of the linear motor.

[0006] Preferably, at least two drive frequency converter cascade circuits are simultaneously connected to the secondary side of a single phase-shifting transformer, and each secondary sub-winding of the phase-shifting transformer is simultaneously connected to the corresponding power unit input in each phase of the at least two drive frequency converter cascade circuits; or, at least two drive frequency converter cascade circuits are simultaneously connected to the secondary side of a single phase-shifting transformer, and each secondary sub-winding of the phase-shifting transformer is connected to the corresponding power unit input in each phase of one of the drive frequency converter cascade circuits, with the power unit inputs in different drive frequency converter cascade circuits connected to different and mutually isolated secondary sub-windings of the phase-shifting transformer.

[0007] Preferably, the drive frequency conversion cascade circuit adopts a cascaded topology to output the high voltage required to drive the linear motor. Each phase of the drive frequency conversion cascade circuit includes multiple cascaded power units. The output three phases of each three phases of the drive frequency conversion cascade circuit are connected in a star configuration and then connected to the three-phase windings of the corresponding stator segment of the linear motor through a switching switch.

[0008] Preferably, the drive frequency conversion cascade circuit adopts a cascaded topology to output the high voltage required to drive the linear motor. The drive frequency conversion cascade circuit includes at least one three-phase power circuit. Each phase of the three-phase power circuit includes multiple cascaded power units. The input side of the three-phase power circuit is connected to the secondary winding of the phase-shifting transformer. The output three phases of the three-phase power circuit are connected in a star configuration and then connected to the three-phase windings of the corresponding stator segment of the linear motor through a switching switch.

[0009] Preferably, the number of secondary sub-windings of the phase-shifting transformer is consistent with the number of power units in each phase of the three-phase power circuit. Each secondary sub-winding of the phase-shifting transformer is connected in a delta configuration with extended sides. The phase shift angle θ between adjacent secondary sub-windings is 360 / (6*N), where N is the number of secondary sub-windings of the phase-shifting transformer. Each power unit in each phase of the three-phase power circuit is connected to one secondary sub-winding of the phase-shifting transformer.

[0010] Preferably, the secondary windings of the phase-shifting transformer are symmetrically distributed with respect to the primary winding, either leading or lagging behind it.

[0011] Preferably, when the number of phase-shifting transformers is greater than or equal to 2, the primary winding of the phase-shifting transformer adopts an extended delta design for phase shifting, and the phase shift angle φ = 360 / (6*N*n) + (360*k) / (6*N), where n is the number of phase-shifting transformers participating in the phase shifting, and k is an integer coefficient, k = 1, 2, ... n.

[0012] Preferably, the power unit includes a three-phase rectifier circuit, a DC bus capacitor bank, and an H-bridge inverter unit connected in sequence.

[0013] Preferably, the three-phase rectifier circuit adopts a controllable three-phase rectifier topology or an uncontrolled three-phase rectifier topology; when the three-phase rectifier circuit adopts an uncontrolled three-phase rectifier topology, the power unit further includes a braking circuit connected in parallel with the DC bus capacitor bank.

[0014] Preferably, the H-bridge inverter unit adopts a two-level H-bridge structure or a three-level H-bridge structure. The three-level H-bridge structure includes a T-shaped three-level H-bridge unit, an NPC three-level H-bridge unit, or an ANPC three-level H-bridge unit.

[0015] The aforementioned linear motor drive system topology includes at least one phase-shifting transformer and at least two cascaded drive frequency converter circuits. The primary side of the phase-shifting transformer is connected to the power grid, and the input side of each cascaded drive frequency converter circuit is connected to the secondary side of all phase-shifting transformers. The cascaded drive frequency converter circuits output the high voltage required to drive the linear motor using a cascaded topology. The at least two cascaded drive frequency converter circuits alternately output power to adjacent stator sections of the linear motor. The at least two cascaded drive frequency converter circuits that alternately output power share the front-end phase-shifting transformer, which improves the utilization rate of the front-end phase-shifting transformer, reduces the number of phase-shifting transformers deployed, reduces the deployment cost of the electromagnetic traction drive power supply for the linear motor, and saves deployment space. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the topology of a traditional linear motor electromagnetic traction drive power supply.

[0017] Figure 2 This is a schematic diagram of the electromagnetic traction drive power supply topology of a long stator twelve-phase linear motor in one embodiment of the present invention.

[0018] Figure 3 This is a schematic diagram of the secondary connection structure of a single phase-shifting transformer in one embodiment of the present invention;

[0019] Figure 4 This is a schematic diagram of the secondary connection structure of a single phase-shifting transformer in another embodiment of the present invention;

[0020] Figure 5 This is a schematic diagram of the power unit circuit topology in one embodiment of the present invention;

[0021] Figure 6 This is a schematic diagram of the power unit circuit topology in another embodiment of the present invention;

[0022] Figure 7 This is a schematic diagram of the circuit topology of a T-shaped three-level H-bridge unit;

[0023] Figure 8 A schematic diagram of the circuit topology of an NPC three-level H-bridge unit;

[0024] Figure 9 A schematic diagram of the circuit topology of the ANPC three-level H-bridge unit;

[0025] Figure 10 This is a schematic diagram of a phase-shifting transformer with a Y-connected primary winding connected in parallel.

[0026] Figure 11 This is a schematic diagram of a phase-shifting transformer with a primary winding connected in a delta configuration. Detailed Implementation

[0027] To enable those skilled in the art to more clearly understand the purpose, technical solution and advantages of this utility model, the present utility model will be further described below in conjunction with the accompanying drawings and embodiments.

[0028] This utility model provides a linear motor drive system topology, including at least one phase-shifting transformer and at least two drive frequency converter cascaded circuits. The primary side of the phase-shifting transformer is connected to the power grid, and the input side of each drive frequency converter cascaded circuit is connected to the secondary side of all phase-shifting transformers respectively. The drive frequency converter cascaded circuits use a cascaded topology to output the high voltage required to drive the linear motor. The at least two drive frequency converter cascaded circuits alternately output power to adjacent stator sections of the linear motor.

[0029] like Figure 2 As shown, in one embodiment of this utility model, the electromagnetic traction drive power supply topology for a long stator twelve-phase linear motor includes four phase-shifting transformers (phase-shifting transformers 1-4) and eight three-phase power circuits. Four of the three-phase power circuits (three-phase power circuits 1-4) constitute a twelve-phase output drive frequency converter cascade circuit to power the odd-numbered stator segments of the linear motor; the other four three-phase power circuits (three-phase power circuits 5-8) constitute another twelve-phase output drive frequency converter cascade circuit to power the even-numbered stator segments of the linear motor; the two drive frequency converter cascade circuits alternately output power to adjacent stator segments of the linear motor.

[0030] The outputs of each three-phase power circuit are connected in a star configuration. Each drive frequency converter cascade circuit has four three-phase outputs. The outputs of each drive frequency converter cascade circuit are connected to a series of switching switches. These switching switches are connected to the stator windings of the linear motors respectively. According to the sequence number of the stator segments of the linear motors they are connected to, the switching switches are divided into odd-numbered segment switching switches and even-numbered segment switching switches.

[0031] The four phase-shifting transformers (phase-shifting transformers 1-4) are connected one-to-one with four three-phase power circuits (three-phase power circuits 1-4) to form the input of one drive frequency converter cascade circuit. The four phase-shifting transformers (phase-shifting transformers 1-4) are also connected one-to-one with four other three-phase power circuits (three-phase power circuits 5-8) to form the input of another drive frequency converter cascade circuit. The total capacity of the four phase-shifting transformers is the rated power required to drive the stator section of a single linear motor. The two drive frequency converter cascade circuits, which alternately output power, share the front-end phase-shifting transformer, improving the utilization rate of the front-end phase-shifting transformer, reducing the number of phase-shifting transformers deployed, lowering the deployment cost of the linear motor electromagnetic traction drive power supply, and saving deployment space.

[0032] like Figure 3 As shown, phase-shifting transformer 1 is simultaneously connected to three-phase power circuit 1 and three-phase power circuit 5, meaning that the secondary winding of a single phase-shifting transformer is simultaneously connected to a three-phase power circuit with two cascaded drive frequency converter circuits. Each phase of the three-phase power circuit includes multiple cascaded power units, where power units A1 to AN are multiple cascaded power units of phase A, power units B1 to BN are multiple cascaded power units of phase B, and power units C1 to CN are multiple cascaded power units of phase C. The input side of the three-phase power circuit is connected to the secondary winding of the phase-shifting transformer. The output three phases of the three-phase power circuit are connected in a star configuration and then connected to the three-phase windings of the corresponding stator segment of the linear motor via a switching switch, outputting the high voltage required to drive the linear motor.

[0033] The secondary winding of the phase-shifting transformer has N secondary sub-windings corresponding to the number of power units cascaded in each phase of the three-phase power circuit. Each secondary sub-winding is connected one-to-one with one of the N power units in each phase of the three-phase power circuit. Each secondary sub-winding is an extended delta connection. The phase shift angle θ between adjacent secondary sub-windings is determined according to the number of power units. Simultaneously, each secondary sub-winding is symmetrically distributed relative to the primary winding, either leading or lagging behind, while ensuring the phase shift angle between them, further reducing harmonics. Since four phase-shifting transformers are used, the primary windings of the phase-shifting transformers can be connected in an extended delta connection (e.g., ...). Figure 11 Phase shifting is performed, with the phase shift angle φ determined by the phase shift angle of the secondary winding and the number of phase shifts in the primary winding, in order to reduce power grid harmonics during operation.

[0034] The phase shift angle θ between adjacent secondary windings of a phase-shifting transformer can be obtained using the following formula:

[0035] θ=360 / (6*N) (1);

[0036] The phase shift angle φ of the primary winding of the corresponding phase-shifting transformer can be obtained according to the following formula:

[0037] φ=360 / (6*N*n)+(360*k) / (6*N) (2);

[0038] Where N is the number of secondary windings of the phase-shifting transformer, n is the number of phase-shifting transformers participating in the phase shift, and k is an integer coefficient, k = 1, 2, ... n.

[0039] See Figure 3 Since the number of cascaded power units in each phase of the three-phase power circuit is 6, i.e., N=6, the number of secondary windings of the phase-shifting transformer is correspondingly 6, with a phase shift angle of 10°. The phase shift angles of the 6 secondary windings relative to the primary side without phase shifting the reference voltage are 25°, 15°, 5°, -5°, -15°, and -25°, respectively, which is equivalent to achieving a 36-pulse phase shift effect, thereby reducing grid harmonics. In this embodiment, since there are four phase-shifting transformers, the phase shift design is considered after the primary side is connected in parallel in pairs. At this time, n=2, and the phase shift angle is (5+10k)°. Taking k=1, the phase shift angle is 15°, which is equivalent to achieving a 72-pulse phase shift effect compared to the grid side. If the primary sides of all four phase-shifting transformers are connected in a delta connection for phase shifting, then n=4, and the phase shift angle is 12.5°, which is equivalent to achieving a 144-pulse phase shift effect.

[0040] See Figure 5 The power unit comprises a three-phase rectifier circuit, a DC bus capacitor bank, and an H-bridge inverter unit connected in sequence. The input of the three-phase rectifier circuit is connected to the secondary winding of the phase-shifting transformer, converting AC to DC voltage. After being filtered by the DC bus capacitor bank, the DC voltage is supplied to the H-bridge inverter unit. Combined with the corresponding modulation algorithm in the software, the switching elements in the H-bridge inverter unit are controlled to switch on and off, synthesizing a stepped wave equivalent to a sine wave. Finally, the wave is switched by a switching switch to supply power to the corresponding stator segment of the linear motor, driving the linear motor mover to run.

[0041] In this embodiment, the three-phase rectifier circuit adopts an uncontrolled three-phase rectifier topology, and the power unit further includes a braking circuit connected in parallel with the DC bus capacitor bank. Of course, in other embodiments, the three-phase rectifier circuit can also adopt a controlled three-phase rectifier topology, which does not require a braking circuit, such as... Figure 6 As shown.

[0042] In this embodiment, the H-bridge inverter unit adopts a two-level H-bridge structure; of course, in other embodiments, the H-bridge inverter unit can also adopt a three-level H-bridge structure, including a T-shaped three-level H-bridge unit, an NPC three-level H-bridge unit, or an ANPC three-level H-bridge unit, such as... Figure 7-9 As shown.

[0043] In other embodiments, for a long stator twelve-phase linear motor, it is possible to... Figure 2Based on the electromagnetic traction drive power supply topology of the long stator twelve-phase linear motor shown, more drive frequency conversion cascade circuits are constructed by adding three-phase power circuits, thereby realizing 3, 4 or even more twelve-phase outputs, with each twelve-phase output being 4 three-phase outputs.

[0044] based on Figure 2 The electromagnetic traction drive power supply topology for the twelve-phase linear motor with a long stator shown can also be adjusted according to the number of phases of the linear motor, thereby enabling power supply to the corresponding stator segments of linear motors with different numbers of phases.

[0045] Specifically, based on the number of phases of the linear motor, M outputs corresponding to the number of phases can be configured. For example, a three-phase linear motor can be configured with M*three-phase outputs, a six-phase linear motor with M*six-phase outputs, and a twelve-phase motor with M*twelve-phase outputs, where M≥2.

[0046] In some embodiments, at least two drive frequency converter cascade circuits are simultaneously connected to the secondary side of a single phase-shifting transformer, and each secondary sub-winding of the phase-shifting transformer is simultaneously connected to the input of the corresponding power unit in each phase of the at least two drive frequency converter cascade circuits.

[0047] For example, a single phase-shifting transformer is simultaneously connected to both drive frequency converter cascade circuit 1 and drive frequency converter cascade circuit 2 on its secondary side. Each drive frequency converter cascade circuit outputs a three-phase output. The number of power units cascaded in each phase of the drive frequency converter cascade circuit is 6. The number of secondary sub-windings on the secondary side of the phase-shifting transformer is 3*6. Each secondary three-phase winding is connected to the three-phase input of the corresponding power unit in drive frequency converter cascade circuit 1 and drive frequency converter cascade circuit 2. That is, the corresponding power unit inputs of drive frequency converter cascade circuit 1 and drive frequency converter cascade circuit 2 are connected in parallel to their corresponding secondary sub-windings of the phase-shifting transformer. Generally, the configuration can be based on the transformer winding design. The first secondary three-phase sub-winding is connected to the first power unit in the three phases of drive frequency converter cascade circuit 1 and the first power unit in the three phases of drive frequency converter cascade circuit 2. The second secondary sub-winding is connected to the second power unit in the three phases of drive frequency converter cascade circuit 1 and the second power unit in the three phases of drive frequency converter cascade circuit 2. The third secondary sub-winding is connected to the third power unit in the three phases of drive frequency converter cascade circuit 1 and the third power unit in the three phases of drive frequency converter cascade circuit 2, and so on.

[0048] In other embodiments, at least two drive frequency converter cascade circuits are simultaneously connected to the secondary side of a single phase-shifting transformer. Each secondary sub-winding of the phase-shifting transformer is connected to the corresponding power unit input in each phase of one of the drive frequency converter cascade circuits. The power unit inputs in different drive frequency converter cascade circuits are connected to different secondary sub-windings of the phase-shifting transformer.

[0049] For example, a single phase-shifting transformer's secondary side is simultaneously connected to both drive frequency converter cascade circuit 1 and drive frequency converter cascade circuit 2. Each drive frequency converter cascade circuit outputs a three-phase output. The number of power units cascaded in each phase of the drive frequency converter cascade circuit is 6. The number of secondary sub-windings on the secondary side of the phase-shifting transformer is 2*3*6. The three-phase inputs of each phase power unit in drive frequency converter cascade circuit 1 and drive frequency converter cascade circuit 2 are respectively connected to different mutually isolated three-phase sub-windings of the corresponding phase-shifting transformer to prevent mutual interference during operation. This configuration is generally based on the transformer winding design. Figure 4 As shown, the first secondary sub-winding is connected to the first power unit of the three phases in the drive frequency converter cascade circuit 1; the second secondary sub-winding is connected to the second power unit of the three phases in the drive frequency converter cascade circuit 1; the third secondary sub-winding is connected to the third power unit of the three phases in the drive frequency converter cascade circuit 1; and so on. The seventh secondary sub-winding is connected to the first power unit of the three phases in the drive frequency converter cascade circuit 2; the eighth secondary sub-winding is connected to the second power unit of the three phases in the drive frequency converter cascade circuit 2; the ninth secondary sub-winding is connected to the third power unit of the three phases in the drive frequency converter cascade circuit 2; and so on.

[0050] In some preferred embodiments, the number of phase-shifting transformers can be determined according to the number of phases of the motor, ensuring that the total capacity equals the rated power required to drive the stator segment of a single-phase linear motor. For example, one phase-shifting transformer corresponds to a three-phase linear motor, two phase-shifting transformers correspond to a six-phase linear motor, and four phase-shifting transformers correspond to a twelve-phase linear motor. Each secondary winding of the phase-shifting transformer adopts a delta connection for phase shifting design, and is symmetrically distributed with leading or lagging behind the primary winding. The phase shift angle θ between adjacent secondary windings is 360 / (6*N), where N is the number of secondary windings of the phase-shifting transformer. When the number of phase-shifting transformers is greater than or equal to 2, phase shifting processing can be performed on the primary winding of the phase-shifting transformer (e.g., Figure 11 As shown), it is also possible to omit the phase-shifting process for the primary winding of the phase-shifting transformer (e.g., Figure 10 As shown), when performing phase shifting, the primary winding of the phase shifting transformer adopts an extended triangle design for phase shifting, and the phase shift angle φ=360 / (6*N*n)+(360*k) / (6*N), where n is the number of phase shifting transformers participating in phase shifting, and k is an integer coefficient, k=1,2,…n.

[0051] In summary, the linear motor drive system topology provided by this invention improves the utilization rate of the front-end phase-shifting transformer by sharing a common front-end phase-shifting transformer, reduces the number of phase-shifting transformers deployed, lowers the deployment cost of the linear motor electromagnetic traction drive power supply, and saves deployment space. Furthermore, by implementing targeted phase-shifting designs on the primary and secondary windings of the phase-shifting transformer, grid-side harmonics can be reduced without adding filters.

[0052] The above description is merely a preferred embodiment of the present utility model and is not intended to limit the present utility model in any way. Those skilled in the art can make various equivalent changes and improvements based on the above embodiments. All equivalent changes or modifications made within the scope of the claims should fall within the protection scope of the present utility model.

Claims

1. A linear motor drive system topology, characterized by: It includes at least one phase-shifting transformer and at least two drive frequency converter cascade circuits. The primary side of the phase-shifting transformer is connected to the power grid, and the input side of each drive frequency converter cascade circuit is connected to the secondary side of all phase-shifting transformers respectively. The at least two drive frequency converter cascade circuits alternately output power to adjacent stator sections of the linear motor.

2. The linear motor drive system topology as described in claim 1, characterized in that: At least two drive frequency converter cascade circuits are simultaneously connected to the secondary side of a single phase-shifting transformer, and each secondary winding of the phase-shifting transformer is simultaneously connected to the corresponding power unit input in each phase of the at least two drive frequency converter cascade circuits. Alternatively, at least two drive frequency converter cascade circuits are simultaneously connected to the secondary side of a single phase-shifting transformer. Each secondary sub-winding of the phase-shifting transformer is connected to the corresponding power unit input in each phase of one of the drive frequency converter cascade circuits. The power unit inputs in different drive frequency converter cascade circuits are connected to different and mutually isolated secondary sub-windings of the phase-shifting transformer.

3. The linear motor drive system topology of claim 1, wherein: The drive frequency converter cascade circuit adopts a cascaded topology to output the high voltage required to drive the linear motor. Each phase of the drive frequency converter cascade circuit includes multiple cascaded power units. The output three phases of each three phases of the drive frequency converter cascade circuit are connected in a star configuration and then connected to the three-phase windings of the corresponding stator segment of the linear motor through a switching switch.

4. The linear motor drive system topology of claim 1, wherein: The drive frequency conversion cascade circuit adopts a cascaded topology to output the high voltage required to drive the linear motor. The drive frequency conversion cascade circuit includes at least one three-phase power circuit. Each phase of the three-phase power circuit includes multiple cascaded power units. The input side of the three-phase power circuit is connected to the secondary winding of the phase-shifting transformer. The output three phases of the three-phase power circuit are connected in a star configuration and then connected to the three-phase windings of the corresponding stator segment of the linear motor through a switching switch.

5. The linear motor drive system topology of claim 4, wherein: The number of secondary sub-windings of the phase-shifting transformer is the same as the number of power units in each phase of the three-phase power circuit. Each secondary sub-winding of the phase-shifting transformer is connected in a delta configuration. The phase shift angle θ between adjacent secondary sub-windings is 360 / (6*N), where N is the number of secondary sub-windings of the phase-shifting transformer. Each power unit in each phase of the three-phase power circuit is connected to one secondary sub-winding of the phase-shifting transformer.

6. The linear motor drive system topology of claim 5, wherein: The secondary windings of the phase-shifting transformer are symmetrically distributed with respect to the primary winding, either leading or lagging behind it.

7. The linear motor drive system topology of claim 5, wherein: When the number of phase-shifting transformers is greater than or equal to 2, the primary winding of the phase-shifting transformer adopts an extended delta design for phase shifting, and the phase shift angle φ = 360 / (6*N*n) + (360*k) / (6*N), where n is the number of phase-shifting transformers participating in the phase shifting, and k is an integer coefficient, k = 1, 2, ... n.

8. The linear motor drive system topology as described in claim 3 or 4, characterized in that: The power unit includes a three-phase rectifier circuit, a DC bus capacitor bank, and an H-bridge inverter unit connected in sequence.

9. The linear motor drive system topology of claim 8, wherein: The three-phase rectifier circuit adopts a controlled three-phase rectifier topology or an uncontrolled three-phase rectifier topology; when the three-phase rectifier circuit adopts an uncontrolled three-phase rectifier topology, the power unit also includes a braking circuit connected in parallel with the DC bus capacitor bank.

10. The linear motor drive system topology of claim 8, wherein: The H-bridge inverter unit adopts a two-level H-bridge structure or a three-level H-bridge structure. The three-level H-bridge structure includes a T-shaped three-level H-bridge unit, an NPC three-level H-bridge unit, or an ANPC three-level H-bridge unit.

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