Flexible direct current back-to-back system converter online switching system

Abstract

The utility model discloses a flexible DC back-to-back system converter on-line switching system, and relates to the technical field of flexible DC power transmission. The device comprises two alternating current field areas and a valve body area, wherein each alternating current field area comprises an alternating current power grid, a first transformer connected to the alternating current power grid and a second transformer connected to the first alternating current power grid; the valve body area comprises two current converter sets, and the positive wire and the negative wire of each current converter are both provided with direct-current quick switches. According to the utility model, the on-line switching operation of any current converter is stopped without influencing the normal operation of the current converter which is put into operation, so that the operation flexibility and reliability of the flexible back-to-back system are improved.

Description

Technical Field

[0001] The utility model relates to the technical field of flexible direct current transmission, and more specifically to an online switching system for converters of a flexible direct current back-to-back system. Background Art

[0002] The development of power systems is bound to move towards networking, and the flexible DC back-to-back project is a typical application of AC power grid zone interconnection.

[0003] The Chinese patent "A main connection system for a back-to-back symmetrical monopole flexible DC system and its selection method" (application number: 202010078830.1) proposes a main connection system for a back-to-back symmetrical monopole flexible DC system. However, when the converter station on one side of the system is out of operation, the system power transmission is interrupted and cannot meet the N-1 requirement, which has a great impact on the stable operation of the system. The system's flexibility and reliability are insufficient.

[0004] Therefore, it is necessary to develop an online switching system for converters in a flexible DC back-to-back system, which can realize online switching of converters and improve the flexibility and reliability of back-to-back transmission systems. Utility Model Content

[0005] The purpose of the utility model is to overcome the shortcomings of the above-mentioned background technology and to provide an online switching system for converters of a flexible DC back-to-back system.

[0006] In order to achieve the above-mentioned purpose, the technical solution of the utility model is: a flexible DC back-to-back system converter online switching system, including two AC field areas and a valve body area, characterized in that: the AC field area includes an AC power grid, a first transformer connected to the AC power grid, and a second transformer connected to the first AC power grid;

[0007] The valve body area includes two sets of converter groups, each of which has a plurality of converters connected in parallel;

[0008] A part of the converters in one group of converter groups are connected to a first transformer in one AC field area, and another part of the converters are connected to a second transformer in one AC field area; a part of the converters in another group of converter groups are connected to a first transformer in another AC field area, and another part of the converters are connected to a second transformer in another AC field area;

[0009] The positive lines of some converters in each converter group are connected to one end of the positive busbar and the negative lines are connected to one end of the negative busbar, and the positive lines of other converters are connected to the other end of the positive busbar and the negative lines are connected to the other end of the negative busbar;

[0010] A DC fast switch is provided on both the positive line and the negative line of the converter.

[0011] In the above technical solution, the converter adopts a half-bridge topology power module.

[0012] In the above technical solution, the operation is to unlock any converter, and after entering into the constant DC voltage control, close the DC fast switch on the positive line and the negative line of any converter.

[0013] In the above technical solution, when the DC voltage deviation on both sides of the DC fast switch of any of the converters is less than a set threshold, the DC fast switch is closed.

[0014] In the above technical solution, the exit operation is to lock any converter, and after entering the DC side charging mode, separate the DC fast switches on the positive line and the negative line of any converter.

[0015] In the above technical solution, when the DC voltage deviation on both sides of any converter is less than a set threshold, the DC fast switch is closed.

[0016] In the above technical solution, the target value of the fixed DC voltage control is the actual operating DC voltage of the flexible DC back-to-back system.

[0017] Compared with the prior art, the utility model has the following advantages:

[0018] 1) The utility model realizes the online switching operation of shutting down any converter without affecting the normal operation of the converters already in operation, thereby improving the flexibility and reliability of the flexible back-to-back system operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a structural schematic diagram of the utility model.

[0020] Among them, 1-AC field area, 11-AC power grid, 12-first transformer, 13-second transformer, 2-valve body area, 21-converter group, 211-converter, 22-positive bus, 23-negative bus, 24-DC fast switch. DETAILED DESCRIPTION

[0021] The following is a detailed description of the implementation of the utility model in conjunction with the accompanying drawings, but they do not constitute a limitation of the utility model and are only used as examples. At the same time, the advantages of the utility model will become clearer and easier to understand through the description.

[0022] Referring to the attached drawings, it can be seen that: a flexible DC back-to-back system converter online switching system includes two AC field areas 1 and a valve body area 2. The AC field area 1 includes an AC grid 11, a first transformer 12 connected to the AC grid 11, and a second transformer 13 connected to the first AC grid 11;

[0023] The valve body area 2 includes two sets of converter groups 21, and each set of converter groups 21 has a plurality of converters 211 connected in parallel;

[0024] A part of the converters 211 in one group of converter groups 21 is connected to the first transformer 12 in one AC field area 1, and another part of the converters 211 is connected to the second transformer 13 in one AC field area 1; a part of the converters 211 in another group of converter groups 21 is connected to the first transformer 12 in another AC field area 1, and another part of the converters 211 is connected to the second transformer 13 in another AC field area 1;

[0025] The positive line of a part of the converter 211 is connected to one end of the positive bus 22, and the negative line is connected to one end of the negative bus 23, and the positive line of another part of the converter 211 is connected to the other end of the positive bus 22, and the negative line is connected to the other end of the negative bus 23;

[0026] A DC fast switch 24 is provided on both the positive line and the negative line of the converter 211 .

[0027] The converter 211 adopts a half-bridge topology power module.

[0028] The operation of putting into operation is to unlock any converter 211 and after entering into the constant DC voltage control, close the DC fast switch 24 on the positive line and the negative line of any converter 211 .

[0029] When the DC voltage deviation at both sides of the DC fast switch 24 of any of the converters 211 is less than a set threshold, the DC fast switch 24 is closed.

[0030] The exit operation is to lock any converter 211 , and after entering the DC side charging mode, separate the DC fast switch 24 on the positive line and the negative line of any converter 211 .

[0031] When the DC voltage deviation on both sides of any converter 211 is less than a set threshold, the DC fast switch 24 is closed.

[0032] The target value of the fixed DC voltage control is the actual operating DC voltage of the flexible DC back-to-back system.

[0033] Example

[0034] A flexible DC back-to-back system converter online switching system, comprising two AC field areas 1 and a valve body area 2, wherein the AC field area 1 comprises an AC power grid 11, a first transformer 12 connected to the AC power grid 11, and a second transformer 13 connected to the first AC power grid 11; the valve body area 2 comprises two groups of converter groups 21, each of which has two converters 211 connected in parallel; one converter 211 in one of the converter groups 21 is connected to the first transformer 12 in one AC field area 1, and the other converter 211 is connected to the second transformer 13 in one AC field area 1 ; One converter 211 in another converter group 21 is connected to the first transformer 12 in another AC field area 1, and another converter 211 is connected to the second transformer 13 in another AC field area 1; the positive line of one converter 211 in each converter group 21 is connected to one end of the positive bus 22, and the negative line is connected to one end of the negative bus 23, and the positive line of another converter 211 is connected to the other end of the positive bus 22, and the negative line is connected to the other end of the negative bus 23; DC fast switches 24 are provided on the positive and negative lines of the converter 211. The converter 211 adopts a half-bridge topology power module.

[0035] The operation of the input is to unlock any converter 211, enter the fixed DC voltage control, and close the DC fast switch 24 on the positive line and negative line of any converter 211. When the DC voltage deviation on both sides of the DC fast switch 24 of any converter 211 is less than the set threshold, close the DC fast switch 24. The target value of the fixed DC voltage control is the actual operating DC voltage of the flexible DC back-to-back system.

[0036] When the inverter 211 needs to be put online, the inverter 211 is charged by the AC system, the fixed DC voltage is unlocked, and its DC voltage target value is set to the DC voltage value of the running back-to-back system. The DC fast switch 24 on the positive and negative lines of the inverter 211 is closed, and the inverter 211 is put into operation. At this time, the inverter 211 is converted to the constant power control mode, and then the power is increased or decreased according to system requirements.

[0037] The exit operation is to lock any converter 211, and after entering the DC side charging mode, separate the DC fast switch 24 on the positive line and the negative line of any converter 211. When the DC voltage deviation on both sides of any converter 211 is less than the set threshold, close the DC fast switch 24.

[0038] When the converter 211 needs to exit online, the converter 211 enters the DC side charging mode after locking operation, avoids the occurrence of system overvoltage or undervoltage by dynamically adjusting the number of sub-modules put into operation, disconnects the DC fast switch 24 on the positive line and negative line of the converter 211, and the converter 211 exits operation. Then, the AC side circuit breaker of the converter 211 is disconnected, and the converter 211 completely exits.

[0039] An online starting method of an online starting and stopping system of a converter of a flexible DC back-to-back system comprises the following steps:

[0040] Step 1: Close the AC circuit breaker of any converter 211 to enter the AC side charging mode;

[0041] Step 2: After the converter 211 is fully charged, it is unlocked and operated in a constant DC voltage mode, and the converter 211 does not exchange active power and reactive power with the AC system;

[0042] Step 3: After the DC voltage deviation on both sides of the DC fast switch 24 on the positive line and the negative line of the converter 211 is less than the set threshold, the DC fast switch 24 on the positive line and the negative line of the converter 211 is closed;

[0043] Step 4: After the converter 211 is successfully put into operation, it is changed to fixed active power control, and the power is increased or decreased according to actual demand.

[0044] An online exit method of an online switching-on and switching-off system of a flexible DC back-to-back system converter comprises the following steps:

[0045] Step 1: reduce the power of any converter 211 to 0 and lock the converter 211;

[0046] Step 2: The converter control system enters the DC side charging mode, and avoids overvoltage and overcurrent of the system by online switching of the submodules. After the DC voltage deviation on both sides of the DC fast switch is less than the set threshold, the DC fast switch 24 on the positive line and negative line of the converter 211 is disconnected;

[0047] Step 3: Disconnect the AC side circuit breaker of the converter 211, and the converter 211 exits the system.

[0048] It should be noted that the DC fast switch 24 has an initial DC current capacity of about 15A. To avoid continuous arcing during the breaking process, the DC fast switch 24 can only be opened when the voltage deviation on both sides is small.

[0049] It should be noted that any converter 211 in the present invention supports online switching.

[0050] Other parts not described belong to the prior art.

Claims

1. A flexible DC back-to-back system converter online switching system, comprising two AC field areas (1) and a valve body area (2), characterized in that: The AC field area (1) comprises an AC power grid (11), a first transformer (12) connected to the AC power grid (11), and a second transformer (13) connected to the first AC power grid (11); The valve body area (2) comprises two sets of converter groups (21), and each set of converter groups (21) has a plurality of converters (211) connected in parallel; A portion of the converters (211) in one converter group (21) is connected to a first transformer (12) in an AC field area (1), and another portion of the converters (211) is connected to a second transformer (13) in one AC field area (1); a portion of the converters (211) in another converter group (21) is connected to a first transformer (12) in another AC field area (1), and another portion of the converters (211) is connected to a second transformer (13) in another AC field area (1); The positive lines of some converters (211) in each converter group (21) are connected to one end of the positive bus bar (22), and the negative lines are connected to one end of the negative bus bar (23), and the positive lines of other converters (211) are connected to the other end of the positive bus bar (22), and the negative lines are connected to the other end of the negative bus bar (23); A direct current fast switch (24) is provided on both the positive line and the negative line of the converter (211).

2. According to claim 1, a flexible DC back-to-back system converter online switching system is characterized by: The converter (211) adopts a half-bridge topology power module.

3. According to claim 1, a flexible DC back-to-back system converter online switching system is characterized by: The input operation is to unlock any converter (211), enter constant DC voltage control, and then close the DC fast switch (24) on the positive line and negative line of any converter (211).

4. According to claim 3, a flexible DC back-to-back system converter online switching system is characterized in that: When the DC voltage deviation on both sides of the DC fast switch (24) of any converter (211) is less than a set threshold, the DC fast switch (24) is closed.

5. According to claim 1, a flexible DC back-to-back system converter online switching system is characterized by: The exit operation is to lock any converter (211), and after entering the DC side charging mode, separate the DC fast switch (24) on the positive line and the negative line of any converter (211).

6. The online switching system for converters of a flexible DC back-to-back system according to claim 5 is characterized in that: When the DC voltage deviation on both sides of any converter (211) is less than a set threshold, the DC fast switch (24) is closed.

7. The online switching system for converters of a flexible DC back-to-back system according to claim 3 is characterized in that: The target value of the fixed DC voltage control is the actual operating DC voltage of the flexible DC back-to-back system.

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