Medium-voltage alternating-current bidirectional flexible interconnection device

Abstract

The invention provides a medium-voltage alternating-current bidirectional flexible interconnection device, which belongs to the technical field of power distribution and comprises a first phase-shifting transformer, a second phase-shifting transformer and a three-phase current source type flexible power transmission unit, the three-phase current source type flexible power transmission unit is located between the first phase-shifting transformer and the second phase-shifting transformer, and the first medium-voltage bus and the second medium-voltage bus are located at the lower end of the total drop of any two active high voltages; and the three-phase current source type flexible power transmission unit is used for performing bidirectional scheduling on the alternating current electric energy between the first medium-voltage bus and the second medium-voltage bus under the control instruction. When temporary uneven energy distribution occurs between transformers in a power distribution network of two power distribution transformers, energy redistribution can be realized, and energy balance can be realized to the greatest extent.

Description

Technical Field

[0001] The present application belongs to the field of power distribution technology, and more specifically, relates to a medium voltage AC bidirectional flexible interconnection device. Background Art

[0002] In today's multi-distribution transformer distribution network, each distribution transformer is in an independent operation state. There is no conventional connection between the medium-voltage busbar sections, and the entire distribution system presents a typical radial structure. This situation will cause that when a transformer is overloaded, it cannot transmit energy to the transformer with lower load, resulting in uneven load and causing serious damage to the transformer.

[0003] Due to the existence of power generation equipment, when there is excess energy, the medium-voltage bus will transmit power in reverse, causing a large amount of electric energy that should have been reasonably used and consumed within the system to be lost during the transmission process, resulting in a huge waste of energy. The reverse power transmission may even trigger the malfunction of the power grid's protection device, causing unnecessary tripping of the power grid, affecting the power supply reliability of the power grid, and in severe cases, may cause large-scale power outages, causing significant impacts on social production and life.

[0004] When each distribution transformer is in an independent operation state, once the transformer fails, all the loads it carries will instantly lose power support, which will undoubtedly bring extremely serious losses and have a huge impact on production operations, residents' lives and other aspects. Summary of the invention

[0005] In view of the defects of the prior art, the purpose of this application is to provide a medium-voltage AC bidirectional flexible interconnection device, which aims to solve the problem that in today's multi-distribution transformer distribution network, each distribution transformer is in an independent operation state, and the entire distribution system has a radial structure. As a result, when a transformer is overloaded, energy cannot be transmitted to the transformer with a lower load, resulting in uneven load.

[0006] To achieve the above-mentioned object, the present application provides a medium voltage AC bidirectional flexible interconnection device, comprising: a first phase-shifting transformer, a second phase-shifting transformer, a controller and a three-phase current source type flexible power transmission unit;

[0007] One AC side of the three-phase current source flexible power transmission unit is connected to the secondary side of the first phase-shifting transformer; the other AC side of the three-phase current source flexible power transmission unit is connected to the secondary side of the second phase-shifting transformer; the primary side of the first phase-shifting transformer is connected to the first medium-voltage bus, and the primary side of the second phase-shifting transformer is connected to the second medium-voltage bus; the first medium-voltage bus and the second medium-voltage bus are located at the lower end of any two active high-voltage total drops; the controller is connected to the three-phase current source flexible power transmission unit;

[0008] The controller is used to issue control instructions according to the load status of the first medium-voltage bus and the second medium-voltage bus; the three-phase current source flexible power transmission unit is used to obtain corresponding trigger pulses from the control instructions, control the conduction or shutdown of the thyristor, and work in the rectification or inversion state; and bidirectionally dispatch AC power between the first medium-voltage bus and the second medium-voltage bus.

[0009] Further preferably, the three-phase current source type flexible power transmission unit is a current source type back-to-back converter.

[0010] Further preferably, the current source back-to-back converter is a three-phase active AC-DC-AC converter based on thyristors.

[0011] Further preferably, a DC reactor is provided between the rectification and the inversion of the current source type back-to-back converter, for providing energy storage and smoothing the DC current in the DC link.

[0012] Further preferably, based on the multi-pulse energy transmission technology, n groups of current source back-to-back converters are arranged between the first phase-shift converter and the second phase-shift converter to construct a 6n pulse medium voltage AC bidirectional flexible interconnection device, which is used to increase the transmission power and reduce the primary side harmonic content of the first phase-shift transformer or the second phase-shift transformer; wherein the phase shift angle of the first phase-shift transformer and the second phase-shift transformer is 360° / 6n; the primary side of the first phase-shift transformer or the second phase-shift transformer contains only 6nk±1 harmonics, wherein n is the number of modules of the current source back-to-back converter; k is a positive integer; and when multiple modules of the current source back-to-back converter transmit electric energy, they can only be transmitted in one direction to avoid the formation of circulating currents between modules to cause damage to the device.

[0013] Further preferably, two groups of current source back-to-back converters are arranged between the first phase-shifting converter and the second phase-shifting converter to construct a 12-pulse medium-voltage AC bidirectional flexible interconnection device, the phase shift angle of the first phase-shifting transformer or the second phase-shifting transformer is 30°, and the primary side of the first phase-shifting transformer or the second phase-shifting transformer contains only 12k±1 harmonics.

[0014] Further preferably, three groups of current source back-to-back converters are arranged between the first phase-shifting converter and the second phase-shifting converter to construct an 18-pulse medium-voltage AC bidirectional flexible interconnection device, the phase shift angle of the first phase-shifting transformer or the second phase-shifting transformer is 20°, and the primary side of the first phase-shifting transformer or the second phase-shifting transformer contains only 18k±1 harmonics.

[0015] Further preferably, four groups of current source back-to-back converters are arranged between the first phase-shifting converter and the second phase-shifting converter to construct a 24-pulse medium-voltage AC bidirectional flexible interconnection device, the phase shift angle of the first phase-shifting transformer or the second phase-shifting transformer is 15°, and the primary side of the first phase-shifting transformer or the second phase-shifting transformer contains only 24k±1 harmonics.

[0016] In general, the above technical solutions conceived by this application have the following beneficial effects compared with the prior art:

[0017] The present application provides a medium-voltage AC bidirectional flexible interconnection device, wherein a three-phase current source type flexible power transmission unit is located between the secondary side of the first phase-shifting transformer and the secondary side of the second phase-shifting transformer; the three-phase current source type flexible power transmission unit is used to bidirectionally dispatch AC power between the first medium-voltage bus and the second medium-voltage bus under control instructions. Based on this, when temporary energy inequality occurs between transformers in a distribution network of two distribution transformers, the excess energy on the primary side of the first phase-shifting transformer or the second phase-shifting transformer with excess energy is exchanged through the back-to-back converter connected to the secondary side to achieve energy redistribution and maximize energy balance.

[0018] The present application provides a medium-voltage AC bidirectional flexible interconnection device, in which a smoothing reactor is used on the DC side of a back-to-back converter. When the rectifier side converts AC power into DC power, the DC voltage will still contain a certain ripple; the DC reactor can reduce this ripple, making the DC voltage more stable, and the reactor can limit the rising rate of the fault current, thereby protecting other power electronic components from damage.

[0019] The present application provides a medium-voltage AC bidirectional flexible interconnection device, in which the current source type back-to-back converter part adopts multi-pulse technology, which can not only improve the capacity demand of the flexible interconnection so that it can meet the use in the medium and high voltage environment, but also can reduce the harmonic content of the voltage measurement by offsetting low-order harmonics, reduce the pollution of harmonic current on the grid side, and improve the efficiency of energy transmission of the interconnection device. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a schematic diagram of a 12-pulse medium voltage AC bidirectional flexible interconnection device provided in an embodiment of the present application;

[0021] Figure 2 This is a schematic diagram of an 18-pulse medium voltage AC bidirectional flexible interconnection device provided in an embodiment of the present application;

[0022] Figure 3 This is a schematic diagram of a 24-pulse medium voltage AC bidirectional flexible interconnection device provided in an embodiment of the present application;

[0023] Figure 4is a schematic diagram of a 6n pulse medium voltage AC bidirectional flexible interconnection device provided in an embodiment of the present application, where n is the number of modules of a current source type back-to-back converter;

[0024] Figure 5 It is a single back-to-back converter provided in an embodiment of the present application;

[0025] Figure 6 It is an application example of the medium voltage flexible interconnection device provided in the embodiment of the present application;

[0026] Marking Description:

[0027] 1-10kV switchgear; 2-phase-shifting transformer at end I; 3-phase-shifting transformer at end II; 4-medium-voltage busbar at end I; 5-medium-voltage busbar at end II; 6-back-to-back converter; 7-smoothing reactor; 8-thyristor. DETAILED DESCRIPTION

[0028] The embodiments of the present application are described below in conjunction with the drawings in the embodiments of the present application.

[0029] like Figure 1 As shown, the present application provides a medium voltage AC bidirectional flexible interconnection device, including: a first phase-shifting transformer, a second phase-shifting transformer, a controller and a current source type back-to-back converter;

[0030] The current source type back-to-back converter is connected between the first phase-shifting transformer and the second phase-shifting transformer. The first phase-shifting transformer and the second phase-shifting transformer are respectively connected between the medium-voltage busbars at the lower end of the two 220kV (high voltage) main step-downs with return power, forming a flexible interconnection between different medium-voltage busbars; the controller is connected to the three-phase current source flexible power transmission unit;

[0031] Among them, the primary side of the first phase-shifting transformer and the primary side of the second phase-shifting transformer are both connected to the medium-voltage bus, and the secondary side of the first phase-shifting transformer and the secondary side of the second phase-shifting transformer are respectively connected to the two ends of the current source back-to-back converter, so that the energy of two different medium-voltage bus transformers can borrow and support each other;

[0032] More specifically, a DC reactor (also called a smoothing reactor or a DC side inductor) is provided between the rectifier and the inverter of the current source type back-to-back converter. It is a key component used in power electronic systems. Its main purpose is to provide energy storage and smooth DC current in the DC link.

[0033] Further preferably, the controller is used to issue control instructions according to the load status of the first medium-voltage bus and the second medium-voltage bus; the current source back-to-back converter is a three-phase active AC-DC-AC converter constructed based on thyristors, and a corresponding trigger pulse is obtained in the control instruction to control the conduction or shutdown of the thyristors, so that the current source back-to-back converter can arbitrarily dispatch AC power from any AC bus to another AC bus in both directions without the need for switching through any electrical switches, thereby realizing flexible dispatch of AC power.

[0034] More specifically, a current-source back-to-back converter can only transmit useful power, and a current-source back-to-back converter can only transmit power in one direction when multiple modules transmit power, to avoid the formation of circulating currents between modules that may harm the system.

[0035] More specifically, when temporary energy inequality occurs between transformers in a power distribution network of two distribution transformers, the excess energy on the primary side of the first phase-shifting transformer or the second phase-shifting transformer with excess energy is redistributed through energy interaction through a back-to-back converter connected to the secondary side, thereby achieving energy balance to the greatest extent; wherein the primary sides of the first phase-shifting transformer and the second phase-shifting transformer are connected to different medium-voltage busbars, and the first phase-shifting transformer and the second phase-shifting transformer are connected through a three-phase current source type flexible power transmission unit connected to the secondary side; wherein the three-phase current source type flexible power transmission unit in this embodiment is a current source type back-to-back converter; more specifically, the current source type back-to-back converter in this embodiment is a three-phase active AC-DC-AC converter based on thyristors;

[0036] Further preferably, the power that can be transmitted by the single-circuit module of the back-to-back converter is limited, and the harmonic content on the grid side is large, resulting in low energy transmission efficiency. The medium-voltage AC bidirectional flexible interconnection device can be as follows Figure 1 The 12-pulse medium voltage AC bidirectional flexible interconnection device shown in FIG. Figure 2 The 18-pulse medium voltage AC bidirectional flexible interconnection device shown or Figure 3 The 24-pulse medium voltage AC bidirectional flexible interconnection device shown;

[0037] More generally, the medium voltage AC bidirectional flexible interconnection device may be a 6n pulse medium voltage AC bidirectional flexible interconnection device; wherein n is the number of modules of the current source back-to-back converter; a plurality of current source back-to-back converters may be arranged between the first phase-shifting transformer and the second phase-shifting transformer, wherein the phase shift angle between the first phase-shifting transformer and the second phase-shifting transformer is 360° / 6n;

[0038] like Figure 1As shown, the 12-pulse medium voltage AC bidirectional flexible interconnection device has a phase shift angle of 30°, and the grid-side current of the first phase-shifting transformer or the second phase-shifting transformer of the 12-pulse medium voltage AC bidirectional flexible interconnection device contains only 12k±1 (k=1, 2, 3, ...) harmonics, and the lowest harmonic is 11th;

[0039] like Figure 2 As shown, the 18-pulse medium voltage AC bidirectional flexible interconnection device has a phase shift angle of 20°, and the grid-side current of the first phase-shifting transformer or the second phase-shifting transformer of the 18-pulse medium voltage AC bidirectional flexible interconnection device contains only 18k±1 (k=1, 2, 3, ...) harmonics, and the lowest harmonic is 17th;

[0040] like Figure 3 As shown, the 24-pulse medium voltage AC bidirectional flexible interconnection device has a phase shift angle of 15°, and the grid-side (primary-side) current of the first phase-shifting transformer or the second phase-shifting transformer of the 24-pulse medium voltage AC bidirectional flexible interconnection device contains only 24k±1 (k=1, 2, 3, ...) harmonics, and the lowest harmonic is 23;

[0041] from Figures 1 to 3 It can be seen that the multi-pulse energy transmission technology selects the appropriate number of pulses based on capacity requirements, so that the medium-voltage network side can effectively offset the above-mentioned specific harmonics while meeting the energy requirements, greatly reducing the harmonic content and significantly improving the harmonic pollution in the power grid.

[0042] More specifically, as the number of pulses increases, the transmitted power can be increased; at the same time, the multi-pulse output technology can reduce the low-order harmonics on the grid side of the transformer, reduce the harmonic content, and improve the transmission efficiency factor of electric energy.

[0043] More specifically, Figure 4 As shown, the three-phase active AC-DC-AC converter based on thyristors is a three-phase bridge-type six-pulse rectifier / inverter circuit, which can achieve continuous adjustment of the secondary side output voltage of the first phase-shifting transformer and the second phase-shifting transformer by changing the trigger angle α.

[0044] Example

[0045] In the existing multi-distribution transformer distribution network, each distribution transformer is in an independent operation state, there is no conventional connection between the sections of the medium-voltage busbars, and the entire distribution system presents a typical radial structure; in this embodiment, a medium-voltage AC bidirectional flexible interconnection device is arranged between two medium-voltage busbars connected to the two 220kV total step-down sides with return power, so as to form a flexible interconnection between different medium-voltage busbars;

[0046] Figure 1It is a schematic diagram of the structure of a 12-pulse medium-voltage AC bidirectional flexible interconnection device provided in an embodiment of the present application. A 6-loop output through a phase-shifting transformer and two back-to-back converter modules 7 are arranged between a first medium-voltage bus 4 and a second medium-voltage bus 5 to form a flexible interconnection device with two medium-voltage ports. The two ports are respectively connected to medium-voltage busbars of different sections to achieve flexible interconnection between different medium-voltage busbars.

[0047] Figure 2 It is a schematic diagram of the structure of an 18-pulse medium-voltage AC bidirectional flexible interconnection device provided in an embodiment of the present application. A 9-loop output through a phase-shifting transformer and three back-to-back converter modules 7 are arranged between a first medium-voltage bus 4 and a second medium-voltage bus 5 to form a flexible interconnection device with two medium-voltage ports. The two ports are respectively connected to medium-voltage busbars of different sections to achieve flexible interconnection between different medium-voltage busbars.

[0048] Figure 3 It is a schematic diagram of the structure of a 24-pulse medium-voltage AC bidirectional flexible interconnection device provided in an embodiment of the present application. A 12-loop output through a phase-shifting transformer and four groups of back-to-back converter modules 7 are arranged between a first medium-voltage bus 4 and a second medium-voltage bus 5 to form a flexible interconnection device with two medium-voltage ports. The two ports are respectively connected to medium-voltage busbars of different sections to realize flexible interconnection between different medium-voltage busbars.

[0049] Figure 4 It is a structural schematic diagram of a 6n pulse medium voltage AC bidirectional flexible interconnection device provided in an embodiment of the present application. A 3n loop outputted by a phase-shifting transformer and n back-to-back converter 7 modules are arranged between a first medium voltage bus 4 and a second medium voltage bus 5 to form a flexible interconnection device with two medium voltage ports. The two ports are respectively connected to medium voltage buses of different sections to realize flexible interconnection between different medium voltage buses.

[0050] The use of multi-pulse technology in the current source back-to-back converter can not only increase the capacity requirements of flexible interconnection to meet the use in medium and high voltage environments, but also reduce the harmonic content of voltage measurement by offsetting low-order harmonics, reduce the pollution of harmonic current on the grid side, and improve the efficiency of energy transmission of interconnected devices.

[0051] Based on Figure 5 The three-phase active AC-DC-AC converter constructed by the thyristor shown can arbitrarily dispatch AC power from any AC bus to another AC bus under control instructions without the need for switching through any electrical switches, thereby realizing flexible dispatch of AC power.

[0052] The DC side of the back-to-back converter uses smoothing reactors. When the rectifier side converts AC power into DC power, the DC voltage will still contain a certain amount of ripple. The DC reactor can reduce this ripple, making the DC voltage more stable, and the reactor can limit the rising rate of the fault current, thereby protecting other power electronic components from damage.

[0053] It is connected to two different sections of medium-voltage busbars through phase-shifting transformers and back-to-back converters. When a transformer is overloaded or fails, the interconnected transformer can absorb and transmit energy, so that the distribution transformers can transfer and distribute energy, support each other's power, and serve as emergency backup for each other.

[0054] Figure 6 This is an application example of the medium-voltage flexible interconnection device provided in the embodiment of the present application: when the load on the medium-voltage bus becomes smaller, or when a distribution transformer distribution system is overloaded, the distribution control center adjusts the working status of each converter, calls on the excess capacity of other distribution transformers, realizes mutual borrowing of capacity, realizes controllable transmission and utilization of energy, and prevents the distribution transformer from reversely supplying power to the superior power grid, causing a large amount of energy loss.

[0055] In summary, compared with the prior art, the present application has the following advantages:

[0056] The medium-voltage AC bidirectional flexible interconnection device provided in the present application finds out two different groups of medium-voltage busbars at the two 220kV main step-down ends with returned power, and constructs a set of two-end flexible interconnections between the two groups of medium-voltage busbars through two groups of phase-shifting transformers and current source back-to-back converters. The device can reduce the peak-to-valley difference, realize flexible load balancing, bidirectional energy interaction, and bidirectional capacity borrowing and support between different distribution transformers, can adjust the maximum demand from different external lines, and can actively dispatch the flow of electric energy, give priority to sending excess energy of the generator set to other working section buses, and prevent excess electric energy from flowing into the power grid.

[0057] It should be understood that expressions such as "including" and "may include" that may be used in the present application indicate the existence of the disclosed functions, operations, or constituent elements, and do not limit one or more additional functions, operations, and constituent elements. In the present application, terms such as "including" and / or "having" may be interpreted as indicating specific characteristics, numbers, operations, constituent elements, components, or combinations thereof, but may not be interpreted as excluding the existence or possibility of adding one or more other characteristics, numbers, operations, constituent elements, components, or combinations thereof.

[0058] In addition, in the present application, the expression "and / or" includes any and all combinations of the associated listed words. For example, the expression "A and / or B" may include A, may include B, or may include both A and B.

[0059] In the description of the embodiments of the present application, it should be noted that, unless otherwise clearly specified and limited, the term "connection" should be understood in a broad sense. For example, "connection" can be a detachable connection or a non-detachable connection; it can be a direct connection or an indirect connection through an intermediate medium. Among them, "fixed connection" means that the relative position relationship after connection remains unchanged. "Rotational connection" means that the two are connected to each other and can rotate relative to each other after connection. "Sliding connection" means that the two are connected to each other and can slide relative to each other after connection. The directional terms mentioned in the embodiments of the present application, such as "top", "bottom", "inside", "outside", "left", "right", etc., are only reference directions of the accompanying drawings. Therefore, the directional terms used are for better and clearer explanation and understanding of the embodiments of the present application, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the embodiments of the present application.

[0060] In addition, in the embodiments of the present application, the mathematical concepts mentioned are symmetry, equality, parallelism, verticality, etc. These limitations are all for the current state of the art, rather than being absolutely strict definitions in a mathematical sense, and allow a small amount of deviation, approximation to symmetry, approximation to equality, approximation to parallelism, approximation to verticality, etc. are all possible. For example, A and B are parallel, which means that A and B are parallel or approximately parallel, and the angle between A and B can be between 0 and 10 degrees. A and B are perpendicular, which means that A and B are perpendicular or approximately perpendicular, and the angle between A and B can be between 80 and 100 degrees.

[0061] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any person skilled in the art who is familiar with the present technical field can easily think of changes or substitutions within the technical scope disclosed in the present application, which should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A medium voltage AC bidirectional flexible interconnection device, characterized in that: include: A first phase-shifting transformer, a second phase-shifting transformer, a controller, and a three-phase current source type flexible power transmission unit; One AC side of the three-phase current source flexible power transmission unit is connected to the secondary side of the first phase-shifting transformer; the other AC side of the three-phase current source flexible power transmission unit is connected to the secondary side of the second phase-shifting transformer; the primary side of the first phase-shifting transformer is connected to the first medium-voltage bus, and the primary side of the second phase-shifting transformer is connected to the second medium-voltage bus; the first medium-voltage bus and the second medium-voltage bus are located at the lower ends of any two active high-voltage total drops; the controller is connected to the three-phase current source flexible power transmission unit; The controller is used to issue control instructions according to the load status of the first medium-voltage bus and the second medium-voltage bus; the three-phase current source flexible power transmission unit is used to obtain corresponding trigger pulses from the control instructions, control the conduction or shutdown of the thyristor, and work in the rectification or inversion state; and bidirectionally dispatch AC power between the first medium-voltage bus and the second medium-voltage bus.

2. The medium voltage AC bidirectional flexible interconnection device according to claim 1, characterized in that: The three-phase current source type flexible power transmission unit is a current source type back-to-back converter.

3. The medium voltage AC bidirectional flexible interconnection device according to claim 2, characterized in that: The current source back-to-back converter is a three-phase active AC-DC-AC converter based on thyristors.

4. The medium voltage AC bidirectional flexible interconnection device according to claim 2 or 3, characterized in that: A DC reactor is arranged between the rectification and the inversion of the current source type back-to-back converter, which is used to provide energy storage and smooth DC current in the DC link.

5. The medium voltage AC bidirectional flexible interconnection device according to claim 2 or 4, characterized in that: Based on the multi-pulse energy transmission technology, n groups of current source back-to-back converters are arranged between the first phase-shift converter and the second phase-shift converter to construct a 6n pulse medium voltage AC bidirectional flexible interconnection device, which is used to improve the transmission power and reduce the primary side harmonic content of the first phase-shift transformer or the second phase-shift transformer; wherein the phase shift angle of the first phase-shift transformer and the second phase-shift transformer is 360° / 6n; the primary side of the first phase-shift transformer or the second phase-shift transformer contains only 6nk±1 harmonics, wherein n is the number of modules of the current source back-to-back converter; k is a positive integer; and when multiple modules of the current source back-to-back converter transmit electric energy, they can only be transmitted in one direction.

6. The medium voltage AC bidirectional flexible interconnection device according to claim 5, characterized in that: Two groups of current source back-to-back converters are arranged between the first phase-shifting converter and the second phase-shifting converter to construct a 12-pulse medium-voltage AC bidirectional flexible interconnection device. The phase shift angle of the first phase-shifting transformer or the second phase-shifting transformer is 30°, and the primary side of the first phase-shifting transformer or the second phase-shifting transformer contains only 12k±1 harmonics.

7. The medium voltage AC bidirectional flexible interconnection device according to claim 5, characterized in that: Three groups of current source back-to-back converters are arranged between the first phase-shifting converter and the second phase-shifting converter to construct an 18-pulse medium-voltage AC bidirectional flexible interconnection device. The phase shift angle of the first phase-shifting transformer or the second phase-shifting transformer is 20°, and the primary side of the first phase-shifting transformer or the second phase-shifting transformer contains only 18k±1 harmonics.

8. The medium voltage AC bidirectional flexible interconnection device according to claim 5, characterized in that: Four groups of current source back-to-back converters are arranged between the first phase-shifting converter and the second phase-shifting converter to construct a 24-pulse medium-voltage AC bidirectional flexible interconnection device. The phase shift angle of the first phase-shifting transformer or the second phase-shifting transformer is 15°, and the primary side of the first phase-shifting transformer or the second phase-shifting transformer contains only 24k±1 harmonics.

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