A current conversion circuit, a flexible distribution area interconnection system and a control method

Abstract

This application provides a converter circuit, a flexible transformer substation interconnection system, and a control method, relating to the field of power electronics technology. The converter circuit includes an AC interface, an AC-side switch, an AC / DC conversion module, a DC bus, a DC-side switch, and a DC interface. The AC interface includes a three-phase AC interface and a neutral interface. The AC-side switch includes a three-phase AC switch and a neutral switch. The three-phase AC interface is connected to the three-phase AC terminals of the AC / DC conversion module via the three-phase AC switch. The DC terminal of the AC / DC conversion module is connected to the DC bus. The DC bus is connected to the DC interface via the DC-side switch. The neutral interface is connected to the midpoint of the DC bus via the neutral switch. The AC interface is used to connect the transformer of one transformer substation, and the DC interface is used to connect the DC interface of the converter circuit of the transformer of another transformer substation. This converter circuit can effectively limit the circulating current between transformer substations via the neutral switch or the DC-side switch in the AC-side switch, and it has low cost and high versatility.

Description

Technical Field

[0001] This application relates to the field of power electronics technology, and more specifically, to a converter circuit, a flexible transformer interconnection system, and a control method. Background Technology

[0002] The low-voltage flexible interconnection system interconnects the AC sides of multiple transformer substations through AC / DC bidirectional conversion power electronic devices, enabling the closed-loop operation of different power supply substations. However, in the low-voltage flexible interconnection system, a neutral current may occur between substations. If the value of the neutral current is too large, it will affect the leakage protection of the substation and cause the power supply to the substation to be disconnected.

[0003] To prevent excessive circulating current from causing power outages in distribution areas, existing technologies employ power frequency transformers and high-frequency isolation transformers in series with the AC system to effectively isolate circulating current paths between distribution areas. However, considering the actual operational needs of the distribution network, power frequency transformers and high-frequency transformers increase the system's operating costs and hardware costs. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of the prior art by providing a converter circuit, a flexible transformer interconnection system, and a control method to solve the technical problem of excessively large neutral circulating current in the prior art.

[0005] To achieve the above objectives, the technical solutions adopted in the embodiments of this application are as follows:

[0006] In a first aspect, embodiments of this application provide a converter circuit, which includes: an AC interface, an AC-side switch, an AC-DC conversion module, a DC bus, a DC-side switch, and a DC interface;

[0007] The AC interface includes a three-phase AC interface and a neutral wire interface; the AC side switch includes a three-phase AC switch and a neutral wire switch; the three-phase AC interface is connected to the three-phase AC terminals of the AC-DC conversion module through the three-phase AC switch; the DC terminal of the AC-DC conversion module is connected to the DC bus; and the DC bus is connected to the DC interface through the DC side switch.

[0008] The neutral wire interface is connected to the midpoint of the DC bus via the neutral wire switch; the AC interface is used to connect to the transformer of one distribution area, and the DC interface is used to connect to the DC interface of the converter circuit corresponding to the transformer of another distribution area.

[0009] Optionally, the converter circuit further includes: a filtering module;

[0010] The three-phase AC interface is connected to the three first terminals of the filter module via the three-phase AC switch, and the three second terminals of the filter module are connected to the three-phase AC terminals of the AC-DC conversion module.

[0011] Optionally, the filtering module is connected to the neutral wire switch.

[0012] Optionally, the AC / DC conversion module includes at least two AC / DC conversion units;

[0013] The AC side switch includes at least two sets of AC switches, the DC side switch includes at least two sets of DC switches, and the DC interface includes at least two sets of DC interfaces.

[0014] The three-phase AC switches in the at least two sets of AC switches are respectively connected to the three-phase AC terminals of the at least two AC-DC conversion units; the DC terminals of the at least two AC-DC conversion units are connected to the DC bus, and the DC bus is respectively connected to the at least two sets of DC switches.

[0015] Two sets of DC interfaces;

[0016] 5. The neutral wire switches of at least two sets of AC switches are all connected to the midpoint of the DC bus;

[0017] The DC interface formed by connecting at least two sets of DC interfaces in parallel is used to connect the DC interface of the converter circuit corresponding to the transformer in the other transformer area.

[0018] Optionally, the DC bus is provided with two sets of capacitors connected in series, and the midpoint of the DC bus is the midpoint of the two sets of capacitors.

[0019] 0. In a second aspect, embodiments of this application provide a flexible transformer interconnection system, wherein the flexible transformer interconnection...

[0020] The system includes: at least two converter circuits and a control module; wherein each converter circuit is the converter circuit described in the first aspect above;

[0021] The AC interfaces of the at least two converter circuits are respectively used to connect to the transformers of at least two distribution areas.

[0022] The DC interface of each converter circuit is connected to the DC interface of the other converter circuits 5 in the at least two converter circuits.

[0023] The control module is connected to the AC side switch and the DC side switch in the at least two converter circuits.

[0024] Thirdly, embodiments of this application provide a flexible transformer area control method, applied to a control module in the flexible transformer area interconnection system described in the second aspect above. The flexible transformer area control method includes:

[0025] When the flexible distribution area interconnection system is in grid-connected mode, it is determined whether the three-phase output signals of at least two distribution areas' transformers meet the preset three-phase balance conditions.

[0026] If the three-phase output signal of the first target transformer in the at least two transformer substations does not meet the preset three-phase balance condition, calculate the unbalanced electrical parameters of the first target transformer based on the three-phase output signal of the first target transformer.

[0027] Based on the unbalanced electrical parameters of the first target transformer, determine the number of target switch groups corresponding to the first target transformer;

[0028] Based on the number of target switch groups, the DC side switches of the target switch groups in the target converter circuit connected to the first target transformer are controlled to be disconnected.

[0029] Optionally, determining the number of target switch groups corresponding to the first target transformer based on the unbalanced electrical parameters of the first target transformer includes:

[0030] The number of target switch groups is determined based on the unbalanced electrical parameters of the first target transformer and the single-phase rated electrical parameters of the target converter circuit.

[0031] Optionally, the method further includes:

[0032] If the three-phase output signal of the second target transformer in the transformers of the at least two transformer substations meets the preset three-phase balance condition, then both the AC side switch and the DC side switch in the converter circuit connected to the second target transformer will be closed.

[0033] Optionally, the method further includes:

[0034] Determine whether the neutral current of the neutral interface of the second target transformer meets the preset neutral current condition.

[0035] If the neutral current of the neutral interface of the third target transformer in the second target transformer does not meet the neutral current condition, then the neutral switch in the converter circuit connected to the third target transformer is opened.

[0036] Compared with the prior art, this application has the following beneficial effects:

[0037] This application provides a converter circuit, a flexible transformer substation interconnection system, and a control method. The converter circuit includes: an AC interface, an AC-side switch, an AC / DC conversion module, a DC bus, a DC-side switch, and a DC interface. The AC interface includes: a three-phase AC interface and a neutral interface. The AC-side switch includes: a three-phase AC switch and a neutral switch. The three-phase AC interface is connected to the three-phase AC terminals of the AC / DC conversion module through the three-phase AC switch. The DC terminal of the AC / DC conversion module is connected to the DC bus. The DC bus is connected to the DC interface through the DC-side switch. The neutral interface is connected to the midpoint of the DC bus through the neutral switch. The AC interface is used to connect the transformer of one transformer substation, and the DC interface is used to connect the DC interface of the converter circuit corresponding to the transformer of another transformer substation. This converter circuit can meet the functions of basic application scenarios (improving transformer substation overload, optimizing power supply quality, and reducing load transfer time). It can also promptly cut off the neutral circulating current loop through the neutral switch or the DC-side switch in the AC-side switch, effectively limiting the neutral circulating current between transformer substations. At the same time, it has low cost, high efficiency, small size, and high versatility. Attached Figure Description

[0038] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0039] Figure 1 This is a schematic diagram of a converter circuit provided in an embodiment of this application;

[0040] Figure 2 This is a schematic diagram of another converter circuit provided in an embodiment of this application;

[0041] Figure 3 This is a schematic diagram of another converter circuit provided in an embodiment of this application;

[0042] Figure 4 A schematic diagram of a flexible transformer interconnection system provided in this application embodiment;

[0043] Figure 5 A schematic diagram of another flexible transformer interconnection system provided in this application embodiment;

[0044] Figure 6 A schematic diagram of another flexible transformer interconnection system provided in this application embodiment;

[0045] Figure 7 A flowchart illustrating a flexible transformer area control method provided in an embodiment of this application;

[0046] Figure 8 This is a schematic diagram of another converter circuit provided in an embodiment of this application;

[0047] Figure 9 A flowchart illustrating another flexible transformer area control method provided in this application embodiment;

[0048] Figure 10 A schematic diagram of a flexible control unit for an embodiment of this application;

[0049] Figure 11 This is a schematic diagram of a control module provided in an embodiment of this application.

[0050] Icons: Converter circuit 1; AC interface 10; AC side switch 20; AC / DC conversion module 30; DC bus 40; DC side switch 50; DC interface 60; Transformer 2; Filter module 70; AC / DC conversion unit 301; AC switch 201; DC switch 501; Control module 3; Substation bus tie switch 4; Output distribution switch 5. Detailed Implementation

[0051] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments. The components of the embodiments of the present application described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0052] Therefore, the following detailed description of the embodiments of this application provided in the accompanying drawings is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments of the application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0053] In the description of this invention, the terms "first," "second," "third," etc., are used only for distinguishing descriptions and should not be construed as indicating or implying relative importance.

[0054] It should be noted that, where there is no conflict, the features in the embodiments of the present invention can be combined with each other.

[0055] To address the technical problem of excessively high neutral circulating current, this application provides a converter circuit, a flexible transformer interconnection system, and a control method. The neutral circulating current between transformer stations corresponding to the converter circuit can be controlled by the DC-side switch and the neutral switch of the converter circuit. It also has the advantages of low cost, high efficiency, and small size.

[0056] The following specific examples illustrate a converter circuit provided in the embodiments of this application. Figure 1 This is a schematic diagram of a converter circuit provided in an embodiment of this application, such as... Figure 1 As shown, the converter circuit 1 includes: AC interface 10, AC side switch 20, AC-DC conversion module 30, DC bus 40, DC side switch 50 and DC interface 60.

[0057] The AC interface 10 mainly consists of a three-phase four-wire AC interface A / B / C / N, including a three-phase AC interface and a neutral line interface. The three-phase AC interface is the A-phase AC interface, the B-phase AC interface, and the C-phase AC interface. The neutral line AC interface is the N-line AC interface, where the N-line can also be called the neutral line.

[0058] Corresponding to the three-phase AC interface and the neutral interface, the AC side switch 20 includes a three-phase AC switch and a neutral switch. The three-phase AC switch can be a three-channel switch or three single-channel switches; no specific limitation is made in this embodiment. The neutral switch is a single-channel switch. The neutral switch can also be referred to as the connection switch for the power grid neutral line.

[0059] The three-phase AC interface is connected to the three-phase AC terminals of the AC-DC converter module 30 via a three-phase AC switch. The three-phase AC switch is used to connect or disconnect the circuit connection between the three-phase AC interface and the AC-DC converter module 30. The AC-DC converter module 30 can convert the AC power transmitted from the three-phase AC interface into DC power.

[0060] The DC terminal of the AC / DC converter module 30 is connected to the DC bus 40, and the neutral terminal is connected to the midpoint of the DC bus 40 through the neutral switch, so that the electrical energy of the AC interface 10 returns to the neutral terminal of the AC interface 10 through the AC / DC converter module 30, the midpoint of the DC bus 40, and the neutral switch in sequence, forming a circuit loop.

[0061] In this embodiment, the AC / DC conversion module 30 can be a three-phase full-bridge topology, including six switching transistors. Of course, it can also be a three-level topology, a multi-level topology, a parallel type or an interleaved parallel type topology. No specific limitation is made in this embodiment.

[0062] The AC interface 10 is used to connect to a transformer 2 in a distribution area to receive AC power output from the transformer 2, or to supply three-phase four-wire power to the transformer 2. The transformer 2 can be connected to AC distribution interfaces (UA, UB, UC, UN) that distribute power to it.

[0063] The DC bus 40 is connected to the DC interface 60 via a DC-side switch 50. The DC-side switch 50 can be a two-channel switch or two single-channel switches; no specific limitation is made in this embodiment. The DC interface 60 includes a positive interface DC+ and a negative interface DC-. The DC interface 60 can be used to connect DC loads to supply power to them.

[0064] In this embodiment, the DC interface 60 is also used to connect to the DC interface 60 of the converter circuit 1 corresponding to the transformer 2 of another transformer area, so that the electrical energy of the AC interface 10 passes sequentially through the AC-DC conversion module 30, the DC side switch 50, the DC interface 60, the DC interface 60 of the converter circuit 1 corresponding to the transformer 2 of another transformer area, the neutral wire switch of the converter circuit 1 corresponding to the transformer 2 of another transformer area connected to ground, the neutral wire switch of the converter circuit 1 corresponding to the transformer 2 of another transformer area connected to ground, and the neutral wire interface in the AC interface 10 to form a neutral loop.

[0065] The DC-side switch 50 can be used to connect or disconnect the circulating current loop between one transformer substation and another. Furthermore, the AC / DC converter module 30 can convert DC power to AC power.

[0066] The neutral circulating current is mainly determined by the equivalent impedance of the DC bus of the converter circuit 1 corresponding to one transformer substation, the equivalent impedance of the DC bus of the converter circuit 1 corresponding to another transformer substation, the equivalent impedance of the neutral switch and grounding of the converter circuit 1 corresponding to transformer 25 in one transformer substation, and the equivalent impedance of the neutral switch and grounding of the converter circuit 1 corresponding to transformer 2 in another transformer substation. If the equivalent impedances of the two DC buses are equal and the equivalent impedances of the two groundings are both zero, the neutral circulating current forming the neutral circulating current loop is half of the single-phase current of one transformer substation. At this time, the neutral circulating current is relatively large.

[0067] To prevent excessive neutral current from causing a power outage in the transformer substation, the neutral wire switch or DC side switch in this embodiment can be controlled to promptly cut off the neutral current loop and effectively limit it.

[0068] The midline circulation between the two regions.

[0069] This application provides a converter circuit that can meet the functional requirements of basic application scenarios (improving overload conditions in transformer substations, optimizing power supply quality, and reducing load transfer time), and can also be used through an AC side switch.

[0070] The neutral wire switch or DC side switch can promptly cut off the neutral wire circulating current loop, effectively limiting the neutral wire circulating current between stations. At the same time, it is low in cost, high in efficiency, small in size, and highly versatile.

[0071] In the above Figure 1Based on the schematic diagram of a converter circuit shown, this application also provides another converter circuit. Optionally, Figure 2 This is a schematic diagram of another converter circuit provided in an embodiment of this application, as shown below. Figure 2 As shown, the converter circuit 1 also includes a filter module 70.

[0072] The three-phase AC interface is connected to the three first terminals of the filter module 70 via a three-phase AC switch, and the three second terminals of the filter module 70 are connected to the three-phase AC terminals of the AC-DC conversion module 30.

[0073] The filtering module 70 can be a three-phase filter, for example, an LCL filter, an LLCL filter, or other filters, but no specific limitations are made in this embodiment.

[0074] In this embodiment, the filtering module 70 includes multiple inductors, multiple capacitors, and multiple resistors.

[0075] The 5-filter module 70 can also be connected to a neutral wire switch, which can improve filtering efficiency compared to not connecting a neutral wire switch.

[0076] Effect.

[0077] Another converter circuit provided in this application embodiment further includes a filter module. The three-phase AC interface is connected to the three first terminals of the filter module through a three-phase AC switch. The three second terminals of the filter module are connected to the three-phase AC terminals of the AC-DC conversion module. The filter module is connected to a neutral wire switch to achieve the filtering function.

[0078] In the above Figure 1 Based on the schematic diagram of a converter circuit shown, this application also provides another converter circuit. Optionally, Figure 3 This is a schematic diagram of another converter circuit provided in an embodiment of this application, as shown below. Figure 3 As shown, the AC / DC conversion module 30 may further include at least two AC / DC conversion units 301. This embodiment uses two AC / DC conversion units 301 as an example for detailed explanation.

[0079] The AC side switch 20 includes at least two sets of AC switches 201, wherein the three-phase AC switches in the at least two sets of AC switches 201 are respectively connected to the three-phase AC terminals of at least two AC-DC conversion units 301.

[0080] The DC-side switch 50 includes at least two sets of DC switches 501, and the DC interface 60 includes at least two sets of DC interfaces. The DC terminals of at least two AC / DC conversion units 301 are connected to the DC bus, and the DC bus is connected to at least two sets of DC interfaces through at least two sets of DC switches 501.

[0081] The neutral wire switches of at least two sets of AC switches 201 are connected to the midpoint of the DC bus, and the DC interface 60 of at least two sets of DC interfaces connected in parallel is used to connect to the DC interface 60 of the converter circuit corresponding to the transformer of another substation.

[0082] Figure 3 This can also be referred to as a schematic diagram of multi-machine parallel power expansion of modular converters. When the front ends of at least two sets of AC switches are connected and the rear ends of at least two sets of DC switches are connected in parallel, modular expansion can be carried out through these multiple AC-DC conversion units. When each set of DC switches is disconnected, the converter circuit of another transformer station without DC side connection can be in single-machine operation mode. Although the active power transfer between transformer stations is not realized, the converter circuit can output reactive power and three-phase unbalanced power to the three-phase four-wire (A-phase line, B-phase line, C-phase line, N-line) connected to the transformer to optimize the power supply quality of the transformer station.

[0083] Another converter circuit provided in this application embodiment includes an AC / DC conversion module comprising: at least two AC / DC conversion units; an AC-side switch comprising: at least two sets of AC switches; a DC-side switch comprising: at least two sets of DC switches; and a DC interface comprising: at least two sets of DC interfaces. The three-phase AC switches in the at least two sets of AC switches are respectively connected to the three-phase AC terminals of the at least two AC / DC conversion units. The DC terminals of the at least two AC / DC conversion units are connected to a DC bus. The DC bus is respectively connected to at least two sets of DC interfaces through at least two sets of DC switches. The neutral wire switches of the at least two sets of AC switches are all connected to the midpoint of the DC bus. The DC interface of the at least two sets of DC interfaces connected in parallel is used to connect to the DC interface of the converter circuit corresponding to the transformer in another distribution area. Through at least two AC / DC conversion units, at least two sets of AC switches, and at least two sets of DC switches, both neutral wire circulating current control and modular capacity expansion are achieved.

[0084] In the above Figure 1 Based on the schematic diagram of one converter circuit shown, this application embodiment also provides another converter circuit. Optionally, two sets of capacitors are provided on the DC bus 40 in series, with the midpoint of the DC bus 40 being the midpoint of the two sets of capacitors.

[0085] In this embodiment, the capacitor can reduce the voltage fluctuation of the DC bus 40 and also achieve the function of filtering.

[0086] like Figure 1 The diagram shows two sets of capacitors connected in series. Each set of capacitors includes one capacitor, and the midpoint between the two capacitors is the midpoint of the DC bus 40.

[0087] Each group of capacitors may also include two, three, or more capacitors connected in series, and no specific limitation is made in the embodiments of this application.

[0088] Another converter circuit provided in this application embodiment has two sets of capacitors connected in series on the DC bus, with the midpoint of the DC bus being the midpoint of the two sets of capacitors, in order to achieve filtering and reduce voltage fluctuations on the DC bus.

[0089] In the above Figures 1-3 Based on the embodiments described above, this application also provides a flexible transformer interconnection system. Optionally, Figure 4 A schematic diagram of a flexible transformer interconnection system provided in this application embodiment is shown below. Figure 4 As shown, the flexible transformer interconnection system includes: at least two converter circuits 1 and a control module 3. This application uses two converter circuits 1 as an example for specific explanation and illustration, and... Figure 4 Each converter circuit 1 in the example is explained in detail using an AC / DC conversion unit 301.

[0090] The AC interfaces 10 of at least two converter circuits 1 are respectively used to connect the transformers 2 of at least two substations, and the DC interfaces 60 of each converter circuit 1 are connected to the DC interfaces 60 of other converter circuits 1 in at least two converter circuits.

[0091] like Figure 4 As shown, there are two transformers 2 in two distribution areas, denoted as T1 and T2 respectively. The low-voltage distribution area is generally a neutral grounding system, that is, the neutral line is grounded (PE). RP1 and RP2 are the equivalent resistances of the neutral grounding of the two distribution areas.

[0092] With both AC-side switch 20 and DC-side switch 50 closed Figure 4 The following explanation uses the C-phase line as an example. Within half a cycle, the current loop for the local transformer area corresponding to T1 is as follows: the current of the C-phase line of transformer T1 flows sequentially through the C-phase line of the AC power grid (or the C-phase line of AC interface 10), the filter module, the upper C-phase tube, the half-capacitor on the bus, and the N-line back to the C-phase line of the AC power grid; the current loop (circuit) for the other transformer area corresponding to T2 is as follows: the current of the C-phase line of transformer T1 flows sequentially through the C-phase line of the AC power grid, the filter module, the upper C-phase tube, the positive line of the DC interface, the half-capacitor C1 on the bus of the other transformer area, the N-line, the grounding resistor RP2, and the grounding resistor RP1 back to the N-line of the AC power grid in this transformer area, and then back to the C-phase line of the power grid.

[0093] Figure 5 A schematic diagram of another flexible transformer interconnection system provided in this application embodiment is shown below. Figure 5 As shown, this is the current loop of this area and the current loop of another area in the other half cycle of the C phase line. The difference between this current loop and the current loop of the above half cycle is that the current flows through the lower tube S6 of the C phase and the lower half capacitor C2 of the bus.

[0094] Loop analysis reveals that the circulating current is primarily determined by the equivalent impedance of capacitors C1 or C2 in converter circuit 1 of transformer area T1, the equivalent impedance of capacitors C1 or C2 in converter circuit 1 of transformer area T2, the equivalent impedance of RP1, and the equivalent impedance of RP2. In the worst-case scenario, when the equivalent impedances of RP1 and RP2 are both zero, the equivalent impedance of capacitors C1 or C2 in converter circuit 1 of transformer area T1 is equal to the equivalent impedance of capacitors C1 or C2 in converter circuit 1 of transformer area T2. In this case, the circulating current in transformer area T2 is half of the C-phase current in transformer area T1. Therefore, the neutral-line circulating current between transformer areas is relatively large.

[0095] The control module 3 is connected to the AC side switch 20 and the DC side switch 50 in at least two converter circuits 1 to control the closing or opening of the AC side switch 20 and the DC side switch 50, thereby realizing the connection or disconnection of the neutral circulating current.

[0096] When the AC / DC conversion module includes at least two AC / DC conversion units, each converter circuit 1 includes at least two AC / DC conversion units. Figure 6 A schematic diagram of another flexible transformer interconnection system provided in this application embodiment is shown below. Figure 6 As shown, each converter circuit 1 is explained in detail using two AC / DC conversion units 301 as an example.

[0097] The control module 3 is connected to at least two sets of AC switches 201 in the AC side switch 20 and at least two sets of DC switches 501 in the DC side switch 50 in the converter circuit 1.

[0098] If the circulating current is too large, it can be reduced by disconnecting some of the DC switches 501 or some of the AC switches 201 in the DC-side switch 50. Alternatively, the circulating current can be cut off by disconnecting all the DC switches 501 or all the AC switches 201 in the DC-side switch 50.

[0099] This application provides a flexible transformer substation interconnection system, comprising: at least two converter circuits and a control module. The AC interfaces of the at least two converter circuits are respectively used to connect to the transformers of at least two transformer substations. The DC interface of each converter circuit is connected to the DC interfaces of other converter circuits in the at least two converter circuits. The control module is connected to the AC side switch and the DC side switch in the at least two converter circuits. By controlling the AC side switch and the DC side switch in the at least two converter circuits through the control module, the neutral circulating current can be effectively controlled. This control of the neutral circulating current can be achieved by cutting off the neutral circulating current or reducing the neutral circulating current.

[0100] In the above Figure 6 Based on the embodiments described above, this application also provides a flexible transformer area control method. Optionally, Figure 7 This is a flowchart illustrating a flexible transformer area control method provided in an embodiment of this application, as shown below. Figure 7 As shown, this method is applied to the control module of the aforementioned flexible transformer interconnection system. The method includes:

[0101] S701, when the flexible distribution transformer interconnection system is in grid-connected mode, determines whether the three-phase output signals of at least two distribution transformers meet the preset three-phase balance conditions.

[0102] Regarding the invocation strategy, if it is determined that the flexible distribution transformer interconnection system is in off-grid mode (such as AC constant voltage, AC inverter, etc.), the AC side switch 20 of the distribution transformer is in the open state. In another case, the bus tie switch 4 of the distribution transformer is in the open state in off-grid mode. Specifically, Figure 8 This is a schematic diagram of another converter circuit provided in an embodiment of this application, as shown below. Figure 8 As shown, the transformer is connected to the bus tie cabinet, which includes: the distribution area bus tie switch, the bus tie copper bus, and the output distribution switch 5. There are generally multiple sets of output distribution switches. One set of output distribution switches is connected to the converter circuit, and the other sets of output distribution switches are connected to the load. If it is determined that the flexible distribution area interconnection system is in off-grid mode (such as AC constant voltage, AC inverter, etc.), the distribution area bus tie switch is in the open state. At the same time, according to the power and load of the converter circuit, the other sets of output distribution switches except for the set of output distribution switches connected to the converter circuit can be disconnected. When in the open state, the distribution area load is directly connected to the AC side of the converter circuit, so there is no circulating current problem. At the same time, when in offline mode, it is not necessary to determine whether the three phases are balanced. At this time, all AC-DC conversion units are considered not to need to be regrouped and adopt the full parallel mode.

[0103] If it is determined that the flexible distribution transformer interconnection system is in grid-connected mode (such as DC droop, DC constant voltage, AC constant power, etc.), determine whether the three-phase output signals of the transformers in at least two distribution transformers meet the preset three-phase balance conditions.

[0104] The three-phase output signal can be the three-phase output current or the three-phase output power of the transformer, and the corresponding preset three-phase balance condition can be that the vector sum of the three-phase output current is zero or the vector sum of the three-phase output power is zero.

[0105] S702, if the three-phase output signal of the first target transformer in at least two transformer substations does not meet the preset three-phase balance condition, calculate the unbalanced electrical parameters of the first target transformer based on the three-phase output signal of the first target transformer.

[0106] If the three-phase output signal of the first target transformer does not meet the preset three-phase balance condition, that is, the vector sum of the three-phase output current of the first target transformer is not zero, or the vector sum of the three-phase output power of the first target transformer is not zero, the unbalanced electrical parameters of the first target transformer are calculated based on the three-phase output signal of the first target transformer. The unbalanced electrical parameters are unbalanced current or unbalanced power.

[0107] For example, if the output power of phase A, phase B, and phase C of the first target transformer is 80kW, 100kW, and 120kW respectively, then the unbalanced power is -20kW, 0kW, and 20kW. This unbalanced power can be calculated by subtracting the average power of the three-phase output power from the output power of each phase.

[0108] In this embodiment, the calculation method for unbalanced current is the same as that for unbalanced power, and will not be elaborated further here. Therefore, the unbalanced electrical parameters can be calculated by subtracting the average electrical parameters of the three-phase output signals from the electrical parameters of each phase's output signals.

[0109] S703, based on the unbalanced electrical parameters of the first target transformer, determine the number of target switch groups corresponding to the first target transformer.

[0110] The number of target switch groups corresponds to the number of target AC / DC conversion units, so as to adjust the imbalance of the three-phase output signal of the first target transformer through the AC / DC conversion units corresponding to the number of target AC / DC conversion units.

[0111] S704, based on the number of target switch groups, controls the DC side switches of the target switch groups in the target converter circuit connected to the first target transformer to be disconnected.

[0112] The DC-side switches for the target number of switch groups can be any DC-side switches that meet the target number of switch groups. For example, the DC-side switches for the target number of switch groups can be randomly selected, or the DC-side switches for the target number of switch groups can be selected sequentially according to the connection order, or the DC-side switches for the target number of switch groups can be selected in other ways. No specific restrictions are imposed in the embodiments of this application.

[0113] Even with a large neutral current, the neutral circulating current is reduced because the DC-side switches of the target number of switch groups are disconnected. Therefore, the neutral circulating current can be effectively controlled by controlling the closing or opening of the DC-side switches based on whether there are unbalanced electrical parameters.

[0114] Optionally, this method is a center-circulating current control method when the primary objective is to address imbalances. Based on the target number of switch groups, the DC-side switches of the target switch groups in the target converter circuit connected to the first target transformer are opened, while the other DC-side switches are closed. This means that the AC / DC conversion units corresponding to the other DC-side switches are used for load transfer.

[0115] Optionally, if the priority is to supply power to the load, the DC side switches of the number of target switch groups in the target converter circuit connected to the first target transformer can be disconnected, provided that the power or current to be supplied is met. If the converter circuit cannot meet the power or current to be supplied, no imbalance processing is performed.

[0116] This application provides a flexible transformer substation control method, comprising: when the flexible transformer substation interconnection system is in grid-connected mode, determining whether the three-phase output signals of transformers in at least two substations meet preset three-phase balance conditions; if the three-phase output signal of the first target transformer in the at least two substations does not meet the preset three-phase balance conditions, calculating the unbalanced electrical parameters of the first target transformer based on the three-phase output signal of the first target transformer, determining the number of target switch groups corresponding to the first target transformer based on the unbalanced electrical parameters of the first target transformer, and controlling the DC-side switches of the target switch groups in the target converter circuit connected to the first target transformer to be disconnected based on the number of target switch groups, thereby effectively controlling the neutral circulating current by controlling the closing or opening of the DC-side switches through the unbalanced electrical parameters.

[0117] In the above Figure 7 Based on the flexible distribution area control method shown, this application embodiment also provides a method for determining the number of target switch groups. Optionally, the above method S703, determining the number of target switch groups corresponding to the first target transformer based on the unbalanced electrical parameters of the first target transformer, includes:

[0118] The number of target switch groups is determined based on the unbalanced electrical parameters of the first target transformer and the single-phase rated electrical parameters of the target converter circuit.

[0119] The number of target switch groups or target AC / DC conversion units required for the unbalanced electrical parameters can be calculated by using the ratio of the unbalanced electrical parameters to the single-phase rated electrical parameters of the target converter circuit.

[0120] For example, if the output power of phases A, B, and C of the first target transformer is 80kW, 100kW, and 120kW respectively, and the unbalanced power is -20kW, 0kW, and 20kW, then for a 60kW AC / DC converter unit, the single-phase rated electrical parameters are 20kW, and the ratios are 1, 0, and 1 respectively. Therefore, an AC / DC converter unit is called to remove the unbalanced power, and the DC side switch of that AC / DC converter unit is disconnected.

[0121] Optionally, if the ratio is less than an integer, it can be processed by adding one and rounding down.

[0122] This application provides a method for determining the number of target switch groups. Based on the unbalanced electrical parameters of a first target transformer and the single-phase rated electrical parameters of a target converter circuit, the number of target switch groups is determined, and then the DC-side switches of the target number of switch groups are controlled to be disconnected. The AC / DC conversion unit corresponding to the number of target switch groups can adjust the unbalance.

[0123] In the above Figure 7 Based on the flexible transformer area control method shown, this application embodiment also provides another flexible transformer area control method. Optionally, the above method further includes:

[0124] If the three-phase output signal of the second target transformer in at least two transformer substations meets the preset three-phase balance condition, then both the AC side switch and the DC side switch in the converter circuit connected to the second target transformer will be closed.

[0125] The preset three-phase balance condition is that the vector sum of the three-phase output currents is zero, or the vector sum of the three-phase output power is zero.

[0126] For example, if the three-phase output signal of the second target transformer is that the output power of phases A, B, and C are all 100kW, then the three-phase output signal of the second target transformer meets the preset three-phase balance condition, and both the AC side switch and the DC side switch in the converter circuit connected to the second target transformer are closed. At this time, even if there is a circulating current path, because the three phases are balanced current or balanced power, there is no neutral current or a relatively small neutral circulating current.

[0127] Optionally, if the three-phase output signal changes, when balanced, the output power and output current of the AC-DC converter are redistributed according to the balanced power or balanced current; when unbalanced, the output power and output current of the AC-DC converter are redistributed according to the unbalanced power or unbalanced current.

[0128] The embodiment of this application provides a flexible transformer substation control method. If the three-phase output signal of the second target transformer in at least two transformer substations meets the preset three-phase balance condition, then the AC side switch and DC side switch in the converter circuit connected to the second target transformer are closed. At this time, there is no neutral current or there is a relatively small neutral circulating current.

[0129] Based on the above embodiments, this application also provides another flexible transformer area control method. Optionally, Figure 9 A flowchart illustrating another flexible transformer area control method provided in this application embodiment is shown below. Figure 9 As shown, the above method also includes:

[0130] S901, determine whether the neutral current of the neutral interface of the second target transformer meets the preset neutral current condition.

[0131] In some more stringent neutral current requirements, the neutral current needs to be sufficiently small (based on the preset neutral current condition).

[0132] In this application scenario, when there is imbalance, the DC-side switch is open, and the target AC-DC converter unit does not participate in the neutral current circulation. When there is balance, both the AC-side switch and the DC-side switch are closed, which may generate a small neutral current circulation. Therefore, it is necessary to compare and judge this neutral current circulation with the preset neutral current condition.

[0133] S902, if the neutral current of the neutral interface of the third target transformer in the second target transformer does not meet the neutral current condition, then the neutral switch in the converter circuit connected to the third target transformer is opened.

[0134] If the neutral current of the neutral interface of the third target transformer in the second target transformer does not meet the neutral current condition, the neutral circulating current corresponding to the equalization is still relatively large. Therefore, the neutral switch in the converter circuit connected to the third target transformer can be controlled to open and cut off the neutral circulating current to meet some stricter neutral circulating current requirements.

[0135] This application provides a flexible transformer substation control method that determines whether the neutral current of the neutral interface of the second target transformer meets the preset neutral current condition. If the neutral current of the neutral interface of the third target transformer in the second target transformer does not meet the neutral current condition, the neutral switch in the converter circuit connected to the third target transformer is controlled to be disconnected in order to meet some stricter neutral circulating current requirements during equalization.

[0136] Based on the above embodiments, a simulation system for a dual-area interconnection system under the PSIM software environment was built. Through simulation, under unbalanced current conditions (extreme simulation of phase A current of 67A), after the DC side switch is disconnected, the current flowing through area T2 is almost zero because there is no circulating current path. Under balanced current conditions (simulating three phases), the neutral current of the interconnection system based on the three-phase half-bridge four-wire converter is small in both area T1 and area T2, with an effective value of about 400mA.

[0137] The following describes a charging control device, a first control board, and a storage medium provided in this application for implementation. The specific implementation process and technical effects are described above and will not be repeated below.

[0138] Figure 10This is a schematic diagram of a flexible control unit for an embodiment of this application, as shown below. Figure 9 As shown, the flexible control unit includes:

[0139] The judgment module 1001 is used to determine whether the three-phase output signals of at least two transformer substations meet the preset three-phase balance conditions when the flexible transformer substation interconnection system is in grid-connected mode.

[0140] The calculation module 1002 is used to calculate the unbalanced electrical parameters of the first target transformer based on the three-phase output signal of the first target transformer if the three-phase output signal of the first target transformer in at least two transformer substations does not meet the preset three-phase balance condition.

[0141] The determination module 1003 is used to determine the number of target switch groups corresponding to the first target transformer based on the unbalanced electrical parameters of the first target transformer.

[0142] The first control module 1004 is used to control the DC side switches of the target switch group in the target converter circuit connected to the first target transformer to be disconnected according to the number of target switch groups.

[0143] Optionally, the determining module 1003 is specifically used to determine the number of target switch groups based on the unbalanced electrical parameters of the first target transformer and the single-phase rated electrical parameters of the target converter circuit.

[0144] The second control module 1005 is used to control both the AC side switch and the DC side switch in the converter circuit connected to the second target transformer to close if the three-phase output signal of the second target transformer in at least two transformer substations meets the preset three-phase balance condition.

[0145] The third control module 1006 is used to determine whether the neutral current of the neutral interface of the second target transformer meets the preset neutral current condition; if the neutral current of the neutral interface of the third target transformer in the second target transformer does not meet the neutral current condition, the neutral switch in the converter circuit connected to the third target transformer is controlled to open.

[0146] These modules can be one or more integrated circuits configured to implement the above methods, such as one or more Application Specific Integrated Circuits (ASICs), one or more digital signal processors (DSPs), or one or more Field Programmable Gate Arrays (FPGAs). Alternatively, when a module is implemented using processing element scheduler code, the processing element can be a general-purpose processor, such as a Central Processing Unit (CPU) or other processor capable of calling program code. Furthermore, these modules can be integrated together as a system-on-a-chip (SOC).

[0147] Figure 11 This is a schematic diagram of a control module provided in an embodiment of this application. The control module may be a device with computing processing capabilities.

[0148] The control module includes a processor 1101, a storage medium 1102, and a bus 1103. The processor 1101 and the storage medium 1102 are connected via the bus 1103.

[0149] Storage medium 1102 is used to store programs, and processor 1101 calls the programs stored in storage medium 1102 to execute the above method embodiments. The specific implementation and technical effects are similar, and will not be described again here.

[0150] Optionally, the present invention also provides a program product, such as a computer-readable storage medium, including a program that, when executed by a processor, is used to perform the above-described method embodiments.

[0151] In the several embodiments provided by this invention, it should be understood that the disclosed apparatus and methods can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative; for instance, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces; the indirect coupling or communication connection between apparatuses or units may be electrical, mechanical, or other forms.

[0152] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0153] Furthermore, the functional units in the various embodiments of the present invention can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or in the form of hardware plus software functional units.

[0154] The integrated units implemented as software functional units described above can be stored in a computer-readable storage medium. These software functional units, stored in a storage medium, include several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) or processor to execute some steps of the methods described in the various embodiments of the present invention. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0155] The above are merely specific embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A converter circuit, characterized in that, include: AC interface, AC side switch, AC / DC conversion module, DC bus, DC side switch and DC interface; The AC interface includes a three-phase AC interface and a neutral wire interface; the AC side switch includes a three-phase AC switch and a neutral wire switch; the three-phase AC interface is connected to the three-phase AC terminals of the AC-DC conversion module through the three-phase AC switch; the DC terminal of the AC-DC conversion module is connected to the DC bus; and the DC bus is connected to the DC interface through the DC side switch. The neutral wire interface is connected to the midpoint of the DC bus via the neutral wire switch; the AC interface is used to connect to the transformer of one distribution area, and the DC interface is used to connect to the DC interface of the converter circuit corresponding to the transformer of another distribution area. The converter circuit is applied to a flexible transformer interconnection system, which includes at least two converter circuits and a control module. The control module is connected to the AC-side switch and the DC-side switch in the at least two converter circuits. The control module is configured to perform the following steps: When the flexible distribution area interconnection system is in grid-connected mode, it is determined whether the three-phase output signals of the transformers in at least two distribution areas meet the preset three-phase balance conditions. If the three-phase output signal of the first target transformer in the at least two transformer substations does not meet the preset three-phase balance condition, the unbalanced electrical parameters of the first target transformer are calculated based on the three-phase output signal of the first target transformer. The number of target switch groups corresponding to the first target transformer is determined based on the unbalanced electrical parameters of the first target transformer. Based on the number of target switch groups, the DC side switches of the target switch groups in the target converter circuit connected to the first target transformer are controlled to be disconnected.

2. The converter circuit according to claim 1, characterized in that, The converter circuit also includes: a filter module; The three-phase AC interface is connected to the three first terminals of the filter module via the three-phase AC switch, and the three second terminals of the filter module are connected to the three-phase AC terminals of the AC-DC conversion module.

3. The converter circuit according to claim 2, characterized in that, The filtering module is connected to the neutral wire switch.

4. The converter circuit according to claim 1, characterized in that, The AC / DC conversion module includes at least two AC / DC conversion units; The AC side switch includes at least two sets of AC switches, the DC side switch includes at least two sets of DC switches, and the DC interface includes at least two sets of DC interfaces. The three-phase AC switches in the at least two sets of AC switches are respectively connected to the three-phase AC terminals of the at least two AC-DC conversion units; the DC terminals of the at least two AC-DC conversion units are connected to the DC bus, and the DC bus is respectively connected to the at least two sets of DC interfaces through the at least two sets of DC switches. The neutral wire switches of the at least two sets of AC switches are all connected to the midpoint of the DC bus; the DC interface of the at least two sets of DC interfaces connected in parallel is used to connect to the DC interface of the converter circuit corresponding to the transformer of the other substation.

5. The converter circuit according to claim 1, characterized in that, The DC bus is equipped with two sets of capacitors connected in series, with the midpoint of the DC bus being the midpoint of the two sets of capacitors.

6. A flexible transformer substation interconnection system, characterized in that, include: At least two converter circuits and a control module; wherein each converter circuit is a converter circuit as described in any one of claims 1-5 above; The AC interfaces of the at least two converter circuits are respectively used to connect to the transformers of at least two substations, and the DC interface of each converter circuit is connected to the DC interface of other converter circuits in the at least two converter circuits. The control module is connected to the AC side switch and the DC side switch in the at least two converter circuits; The control module is configured to perform the following steps: When the flexible distribution area interconnection system is in grid-connected mode, it is determined whether the three-phase output signals of at least two distribution areas' transformers meet the preset three-phase balance conditions. If the three-phase output signal of the first target transformer in the at least two transformer substations does not meet the preset three-phase balance condition, calculate the unbalanced electrical parameters of the first target transformer based on the three-phase output signal of the first target transformer. Based on the unbalanced electrical parameters of the first target transformer, determine the number of target switch groups corresponding to the first target transformer; Based on the number of target switch groups, the DC side switches of the target switch groups in the target converter circuit connected to the first target transformer are controlled to be disconnected.

7. A flexible transformer area control method, characterized in that, The method, applied to the control module in the flexible transformer interconnection system of claim 6, comprises: When the flexible distribution area interconnection system is in grid-connected mode, it is determined whether the three-phase output signals of at least two distribution areas' transformers meet the preset three-phase balance conditions. If the three-phase output signal of the first target transformer in the at least two transformer substations does not meet the preset three-phase balance condition, calculate the unbalanced electrical parameters of the first target transformer based on the three-phase output signal of the first target transformer. Based on the unbalanced electrical parameters of the first target transformer, determine the number of target switch groups corresponding to the first target transformer; Based on the number of target switch groups, the DC side switches of the target switch groups in the target converter circuit connected to the first target transformer are controlled to be disconnected.

8. The flexible transformer area control method according to claim 7, characterized in that, The step of determining the number of target switch groups corresponding to the first target transformer based on the unbalanced electrical parameters of the first target transformer includes: The number of target switch groups is determined based on the unbalanced electrical parameters of the first target transformer and the single-phase rated electrical parameters of the target converter circuit.

9. The flexible transformer area control method according to claim 7, characterized in that, The method further includes: If the three-phase output signal of the second target transformer in the transformers of the at least two transformer substations meets the preset three-phase balance condition, then both the AC side switch and the DC side switch in the converter circuit connected to the second target transformer will be closed.

10. The flexible transformer area control method according to claim 9, characterized in that, The method further includes: Determine whether the neutral current of the neutral interface of the second target transformer meets the preset neutral current condition. If the neutral current of the neutral interface of the third target transformer in the second target transformer does not meet the neutral current condition, then the neutral switch in the converter circuit connected to the third target transformer is opened.

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