Topological structure of dual switched capacitor series DC transformer and inrush current suppression method

Abstract

The present application discloses a dual-switch capacitor series DC transformer topology structure and inrush current suppression method, the structure includes: n dual-switch capacitor series modules, n DAB modules, n is a positive integer; the dual-switch capacitor series module is connected in series with the high-voltage side of the DAB module to form a first unit; wherein the dual-switch capacitor series module includes: a first IGBT switch, a second IGBT switch, and a first capacitor; the emitter of the first IGBT switch is connected to the first end of the first capacitor, and the collector of the second IGBT switch is connected to the second end of the first capacitor; the high-voltage side of each first unit is connected in series in sequence, and the low-voltage side of each first unit is connected in parallel. The technical problem that the prior art cannot take into account both high efficiency and low cost on the basis of having fault self-clearing capability and inrush current suppression capability is solved.

Description

Technical Field

[0001] The present application relates to the technical field of transformers, and in particular to a dual-switch capacitor series DC transformer topology structure and an inrush current suppression method. Background Art

[0002] With the increasing number of DC loads such as electric vehicle charging and swapping stations and large data centers, as well as the high proportion of DC renewable energy power generation equipment such as photovoltaics and wind turbines, the source-load-storage DC characteristics of the current distribution network are becoming more and more obvious. Compared with the AC distribution network, the multi-terminal interconnected flexible DC distribution method has the characteristics of high energy transmission efficiency, low line loss, large-scale consumption of distributed power sources and access to energy storage equipment, and simpler and more flexible coordinated control of the entire network. Therefore, the DC distribution network is generally considered to be an important development direction of the future power system.

[0003] The DC transformer is an important interface between the multi-terminal flexible DC distribution network and the DC load and DC microgrid. In existing practical projects and academic research, the more mature DC transformer topology is the full-bridge + DAB module or half-bridge + DAB structure. The DC transformer with half-bridge + DAB structure has the ability to self-clear faults and suppress inrush current, but the half-bridge structure module generally works in switching mode and has low efficiency; the DC transformer with full-bridge + DAB structure has the ability to self-clear faults and suppress inrush current, but the full-bridge structure module generally works in switching mode and has low efficiency. In addition, the full-bridge structure contains the largest number of tubes and the highest cost. The topology of the DC transformer containing only the DAB module does not have the ability to self-clear faults and suppress inrush current. Summary of the invention

[0004] The purpose of the present application is to provide a dual-switch capacitor series DC transformer topology structure and an inrush current suppression method, which are used to solve the technical problem that the prior art cannot take into account both high efficiency and low cost while having fault self-clearing capability and inrush current suppression capability.

[0005] In view of this, the first aspect of the present application provides a dual-switch capacitor series DC transformer topology structure, comprising: n dual-switch capacitor series modules, n DAB modules, where n is a positive integer; the dual-switch capacitor series modules are connected in series with the high-voltage side of the DAB module to form a first unit;

[0006] The dual-switch capacitor series module includes: a first IGBT switch, a second IGBT switch, and a first capacitor; the emitter of the first IGBT switch is connected to the first end of the first capacitor, and the collector of the second IGBT switch is connected to the second end of the first capacitor;

[0007] The high-voltage side of each of the first units is connected in series in sequence, and the low-voltage side of each of the first units is connected in parallel.

[0008] Optionally, the DAB module is composed of a first full-bridge module, a high-frequency transformer, and a second full-bridge module connected in series.

[0009] Optionally, the first full-bridge module and the second full-bridge module are both composed of four IGBT switches with the same structure.

[0010] Optionally, the high voltage side of each of the first units is connected in series in sequence, specifically comprising:

[0011] The second IGBT switch of the dual-switch capacitor series module is connected to the first IGBT switch of the adjacent dual-switch capacitor series module.

[0012] Optionally, the low-voltage side of each of the first units is connected in parallel, specifically including:

[0013] The positive electrode of the DAB module is connected to the positive electrode of the adjacent DAB module, and the negative electrode of the DAB module is connected to the negative electrode of the adjacent DAB module.

[0014] Optionally, it further includes: a second capacitor; the second capacitor is connected between the positive and negative electrodes of the low-voltage side of the DAB module.

[0015] The second aspect of the present application further provides an inrush current suppression method for a dual-switch capacitor series DC transformer, characterized in that the method is applied to the dual-switch capacitor series DC transformer topology structure described in the first aspect, and comprises:

[0016] S1. Continuously monitor the high-voltage side of the DC transformer. When an overcurrent fault occurs on the high-voltage side of the DC transformer, lock the dual-switch capacitor series module and keep the DAB module in operation;

[0017] S2, determine whether the overcurrent fault occurs again within the preset time range, if so, execute step S3, otherwise execute step S4;

[0018] S3, shutting down the DC transformer;

[0019] S4, restarting the dual-switch capacitor series module.

[0020] Optionally, the preset time range is 2 ms.

[0021] Compared with the prior art, the advantages of the embodiments of the present application are:

[0022] The present application provides a dual-switch capacitor series DC transformer topology structure, comprising: n dual-switch capacitor series modules, n DAB modules, n is a positive integer; the dual-switch capacitor series module is connected in series with the high-voltage side of the DAB module to form a first unit; wherein the dual-switch capacitor series module comprises: a first IGBT switch, a second IGBT switch, and a first capacitor; the emitter of the first IGBT switch is connected to the first end of the first capacitor, and the collector of the second IGBT switch is connected to the second end of the first capacitor; the high-voltage side of each first unit is connected in series in sequence, and the low-voltage side of each first unit is connected in parallel.

[0023] In the DC transformer topology of the present application, in normal mode, the two IGBT switches of the dual-switch capacitor series module work in a normally on state, the capacitor can be charged and discharged, and the voltage on the high-voltage side is maintained stable. When a bipolar short circuit occurs on the DC side of the flexible DC distribution network, the two IGBT switches of the dual-switch capacitor series module work in a locked state, thereby blocking the capacitor from discharging to the outside, and the external current will not flow into the capacitor of the DC transformer. Since the switch capacitor module only works in a charging state during normal operation, no large current flows through it, because its working efficiency is very high; the DC transformer of the present application has fault self-clearing capability, inrush current suppression capability, high efficiency, simple structure and low economic cost; thereby solving the technical problem that the prior art cannot take into account both high efficiency and low cost on the basis of having fault self-clearing capability and inrush current suppression capability. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the specific implementation methods of the present application or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0025] Figure 1 A schematic diagram of a dual-switched capacitor series DC transformer topology structure provided in an embodiment of the present application;

[0026] Figure 2 A method for suppressing inrush current of a dual-switch capacitor series DC transformer provided in an embodiment of the present application;

[0027] Figure 3 A schematic diagram of a locked state mode of a dual-switched capacitor series DC transformer topology structure provided in an embodiment of the present application;

[0028] Figure 4 A schematic diagram of potential inrush current flow paths of a dual-switch capacitor series DC transformer topology structure provided in an embodiment of the present application. DETAILED DESCRIPTION

[0029] The technical solution of the present application will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the present application, rather than all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present application.

[0030] In the description of the present application, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, 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 limiting the present application. In addition, the terms "first", "second", and "third" are used for descriptive purposes only, and cannot be understood as indicating or implying relative importance.

[0031] Unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0032] See also Figure 1 , a dual-switched capacitor series DC transformer topology structure provided in an embodiment of the present application includes:

[0033] n dual-switch capacitor series modules and n DAB modules, where n is a positive integer; the dual-switch capacitor series modules are connected in series with the high-voltage side of the DAB module to form a first unit.

[0034] like Figure 1 As shown, the left dotted line block diagram shows a dual-switch capacitor series module, and the right dotted line block diagram shows a DAB module. For the convenience of description, the two are connected in series to form a first unit. The DC transformer of the present application is composed of multiple DAB modules and multiple dual-switch capacitor series modules.

[0035] The dual-switch capacitor series module comprises: a first IGBT switch (T1), a second IGBT switch (T2), and a first capacitor (V1); the emitter of the first IGBT switch (T1) is connected to the first end of the first capacitor (V1), and the collector of the second IGBT switch (T2) is connected to the second end of the first capacitor (V1).

[0036] The high voltage side of each first unit is connected in series in sequence, and the low voltage side of each first unit is connected in parallel.

[0037] It should be noted that if Figure 1 As shown, the high voltage side of each first unit is connected in series in sequence, specifically: the second IGBT switch of the dual-switch capacitor series module is connected to the first IGBT switch (T1) of the adjacent dual-switch capacitor series module.

[0038] The low voltage side of each first unit is connected in parallel, specifically: the positive pole of the DAB module is connected to the positive pole of the adjacent DAB module, and the negative pole of the DAB module is connected to the negative pole of the adjacent DAB module.

[0039] Furthermore, in a specific implementation, the DAB module is composed of a first full-bridge module, a high-frequency transformer, and a second full-bridge module connected in series.

[0040] It can be understood that the DC transformer topology structure of the present application is composed of a plurality of first units connected in series on the high voltage side and in parallel on the low voltage side. Figure 1 The first unit shown is composed of a dual-switch capacitor series module and a DAB module. The dual-switch capacitor series module consists of two IGBT switches T1 and T2 connected in series on both sides of the first capacitor, and the two IGBT switches T1 and T2 are in opposite directions. When the IGBT switches T1 and T2 are turned on at the same time, the capacitor can be charged; when the IGBT switches T1 and T2 are turned off at the same time, the capacitor will not provide a discharge channel to the external circuit. The DAB module consists of a first full-bridge module (S 1P , S 2P , S 3P , S 4P Four IGBT switches), high-frequency transformer (n:1), second full-bridge module (S 1S , S 2S , S 3S , S 4S Four IGBT switch tubes) are connected in series

[0041] In the DC transformer topology of the present application, in normal mode, the two IGBT switches of the dual-switch capacitor series module work in a normally on state, the capacitor can be charged and discharged, and the voltage on the high-voltage side is maintained stable. When a bipolar short circuit occurs on the DC side of the flexible DC distribution network, the two IGBT switches of the dual-switch capacitor series module work in a locked state, thereby blocking the capacitor from discharging externally, and external current will not flow into the capacitor of the DC transformer. This working state is as follows Figure 3 As shown. During normal operation, the switched capacitor module only works in a charging state and no large current flows, because its working efficiency is very high.

[0042] The following is a comparison of the characteristics of the DC transformer topology of the present application and the topology of various types of existing DC transformers:

[0043]

[0044]

[0045] The above is an embodiment of a dual-switch capacitor series DC transformer topology structure provided in an embodiment of the present application, and the following is an embodiment of an inrush current suppression method for a dual-switch capacitor series DC transformer provided in an embodiment of the present application.

[0046] It should be noted that, in order to facilitate analysis, the inventors considered the inrush effect of the energy injected by the single-ended converter station into the DC transformer when the power was redistributed due to AC disturbance causing the converter station to lock up and causing a step-like and large fluctuation in the power flow of the remaining ports. Figure 4 The potential path of inrush current in the DC transformer based on full-bridge + DAB module in actual operation of the project shown. Figure 4 It can be seen that when the converter station I is locked, the power flow of the converter station II must find a flow path instantly, and the H-bridge structure of the DC transformer provides a loop for the transfer of the power flow. The instantaneous power flow forms a loop through the H-bridge anti-parallel diode of the DC transformer, which is the mechanism of the DC transformer inrush current.

[0047] At the same time, the inventors discovered through research that the surge phenomenon caused by instantaneous current redistribution in a multi-terminal interconnected system is not a DC system fault condition.

[0048] Therefore, this embodiment proposes an inrush current suppression method (a surge current temporary lockout suppression strategy) for a dual-switch capacitor series DC transformer based on the DC transformer topology of the present application. It can be understood that after the DC transformer is locked, the overcurrent will be suppressed and quickly restored to normal value, and the command to disconnect the high and low voltage side circuit breakers will not be executed at this time. Since the overcurrent protection threshold has sufficient margin for short-circuit faults, for temporary overcurrent faults caused by power step conditions, a temporary lockout suppression strategy can be added on the basis of the original protection. The temporary lockout function only locks the dual-switch capacitor series module, and the DAB module is always in operation.

[0049] See also Figure 2 , a method for suppressing inrush current of a dual-switch capacitor series DC transformer provided in an embodiment of the present application includes:

[0050] Step 101, continuously monitor the high voltage side of the DC transformer. When an overcurrent fault occurs on the high voltage side of the DC transformer, lock the dual-switch capacitor series module and keep the DAB module in operation.

[0051] Step 102 , determine whether the overcurrent fault occurs again within a preset time range, if so, execute step 103 , otherwise execute step 104 .

[0052] Step 103: Shut down the DC transformer.

[0053] Step 104: Restart the dual-switch capacitor series module.

[0054] In specific applications, when an overcurrent fault occurs on the high-voltage side of the DC transformer, the controller sends a temporary lockout + DAB operation command to the module control board for the dual-switch capacitor series module. At this time, the module changes from the normal operating state to the dual-switch capacitor series module lockout + DAB operation state. Since this overcurrent process is short, the controller executes the temporary lockout control logic, and detects whether the system has a new overcurrent fault again within 2ms. If not, the lockout and restart logic and restart command are executed, and the normal operation of the system is controlled to the low-voltage side voltage mode. During the temporary lockout recovery and startup process, if the ±10kV side overcurrent occurs again, the DC transformer is shut down to avoid repeated grid connection of the DC transformer due to grid connection failure and other factors.

[0055] This embodiment provides a dual-switch capacitor series module temporary blocking + DAB non-blocking suppression strategy, which enhances the inrush current suppression capability by connecting the DAB module in series, and temporarily blocking and restoring to improve the operating reliability of the system equipment.

[0056] It should be understood that in the present application, "at least one (item)" means one or more, and "plurality" means two or more. "And / or" is used to describe the association relationship of associated objects, indicating that three relationships may exist. For example, "A and / or B" can mean: only A exists, only B exists, and A and B exist at the same time, where A and B can be singular or plural. The character " / " generally indicates that the objects associated before and after are in an "or" relationship. "At least one of the following" or similar expressions refers to any combination of these items, including any combination of single or plural items. For example, at least one of a, b or c can mean: a, b, c, "a and b", "a and c", "b and c", or "a and b and c", where a, b, c can be single or multiple.

[0057] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit it. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A dual-switch capacitor series DC transformer topology structure, characterized in that: include: n dual-switch capacitor series modules, n DAB modules, n is a positive integer; The dual-switched capacitor series module is connected in series with the high-voltage side of the DAB module to form a first unit; The dual-switch capacitor series module includes: a first IGBT switch, a second IGBT switch, and a first capacitor; the emitter of the first IGBT switch is connected to the first end of the first capacitor, and the collector of the second IGBT switch is connected to the second end of the first capacitor; The high-voltage side of each of the first units is connected in series in sequence, and the low-voltage side of each of the first units is connected in parallel; In normal mode, the first IGBT switch and the second IGBT switch operate in a normally on state, the first capacitor can be charged and discharged, and the voltage on the high-voltage side is maintained stable; when a bipolar short circuit occurs on the DC side of the flexible DC distribution network, the first IGBT switch and the second IGBT switch operate in a locked state, thereby blocking the first capacitor from discharging to the outside, and external current will not flow into the capacitor of the DC transformer.

2. The dual-switched capacitor series DC transformer topology structure according to claim 1, characterized in that: The DAB module is composed of a first full-bridge module, a high-frequency transformer, and a second full-bridge module connected in series.

3. The dual-switch capacitor series DC transformer topology structure according to claim 2 is characterized in that: The first full-bridge module and the second full-bridge module are both composed of four IGBT switches with the same structure.

4. The dual-switched capacitor series DC transformer topology structure according to claim 1, characterized in that: The high-voltage sides of each of the first units are sequentially connected in series, specifically comprising: The second IGBT switch of the dual-switch capacitor series module is connected to the first IGBT switch of the adjacent dual-switch capacitor series module.

5. The dual-switched capacitor series DC transformer topology structure according to claim 1, characterized in that: The low-voltage side of each of the first units is connected in parallel, specifically comprising: The positive electrode of the DAB module is connected to the positive electrode of the adjacent DAB module, and the negative electrode of the DAB module is connected to the negative electrode of the adjacent DAB module.

6. The dual-switch capacitor series DC transformer topology structure according to claim 1, characterized in that: Also includes: The second capacitor is connected between the positive and negative electrodes of the low voltage side of the DAB module.

7. A method for suppressing inrush current of a dual-switch capacitor series DC transformer, characterized in that: The method applied to the dual-switched capacitor series DC transformer topology structure according to any one of claims 1 to 6 comprises: S1. Continuously monitor the high-voltage side of the DC transformer. When an overcurrent fault occurs on the high-voltage side of the DC transformer, lock the dual-switch capacitor series module and keep the DAB module in operation; S2, determine whether the overcurrent fault occurs again within the preset time range, if so, execute step S3, otherwise execute step S4; S3, shutting down the DC transformer; S4, restarting the dual-switch capacitor series module.

8. The method for suppressing inrush current of a dual-switch capacitor series DC transformer according to claim 7, characterized in that: The preset time range is 2ms.

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