IGCT-based wind power flexible straight back-to-back sending test method and system

Abstract

The invention relates to the technical field of electric power engineering, and discloses a wind power flexible direct current back-to-back sending test method and system based on IGCT. In the system, one end of a sending end IGCT-MMC converter valve, one end of a diode and one end of an IGBT-MMC heterogeneous combined converter are connected with a wind field outlet bus, the other end of the sending end IGCT-MMC converter valve, the other end of the diode and the other end of the IGBT-MMC heterogeneous combined converter are connected with one end of a receiving end IGCT-MMC converter valve through a change-over switch, and the other end of the receiving end IGCT-MMC converter valve is connected with an alternating current power grid. Two working conditions of a double-IGCT-MMC back-to-back test and a sending-end heterogeneous combined converter and receiving-end IGCT-MMC back-to-back test can be realized, and the blank of a medium-voltage test platform integrating IGCT and diode rectification technologies is filled.

Description

Technical Field

[0001] This invention relates to the field of power engineering technology, specifically to a test method and system for wind power flexible DC back-to-back transmission based on IGCT. Background Technology

[0002] Flexible DC transmission technology has become the industry's recognized preferred method for transmitting offshore wind power resources due to its flexible operation mode, good system controllability, and the fact that it does not require voltage support from the sending and receiving AC power grids. In the field of deep-sea wind power, it is almost the only transmission technology solution.

[0003] To ensure the economic viability of deep-sea wind power projects, the key breakthroughs lie in making platform equipment lighter, more lightweight, and more compact. As a crucial piece of equipment for transmitting deep-sea wind power, the lightweight improvement of offshore wind power flexible DC converter valves is particularly important.

[0004] Currently, mainstream flexible DC transmission systems use IGBT-based converters. However, since mature IGBT specifications are mostly 3.3kV and 4.5kV, this results in a large number of cascaded sub-modules and large capacitor volumes, making it difficult to meet the lightweight requirements of deep-sea platforms. To address this issue, the industry has proposed two improvement approaches: one is to use IGCT power devices capable of high current and high voltage, reducing the number of cascaded sub-modules in the bridge arms by increasing the rated voltage of individual power modules, thus achieving converter lightweighting; the other is to integrate diode rectifier (DRU) technology to increase power delivery density and reduce sub-module capacitors, further optimizing the converter's size and weight.

[0005] However, the two improved technologies mentioned above are currently still in the simulation verification or small-scale grid-connected demonstration stage, lacking a medium-voltage test platform that can comprehensively integrate IGCT and diode rectification technologies. This makes it impossible to verify the reliability of the system, equipment, and devices through long-term real-world physical operation. Therefore, there is an urgent need to design a wind power flexible DC back-to-back medium-voltage transmission test system based on IGCT, to complete the key technology verification through the aforementioned pilot platform, and lay the foundation for subsequent promotion and application. Summary of the Invention

[0006] In view of this, the present invention provides a wind power flexible DC back-to-back transmission test method and system based on IGCT, so as to solve the problem that the existing technology lacks a medium-voltage test platform that can integrate IGCT and diode rectification technology.

[0007] In a first aspect, the present invention provides a wind power flexible DC back-to-back transmission test system based on IGCT, the system comprising: a transmitting-end IGCT-MMC converter valve, a diode and IGBT-MMC heterogeneous combination converter, a receiving-end IGCT-MMC converter valve, and a switching switch, wherein...

[0008] One end of the sending-end IGCT-MMC converter valve and one end of the diode and IGBT-MMC heterogeneous combined converter are both connected to the wind farm outlet bus. The other end of the sending-end IGCT-MMC converter valve and the other end of the diode and IGBT-MMC heterogeneous combined converter are both connected to one end of the receiving-end IGCT-MMC converter valve through the switching switch. The other end of the receiving-end IGCT-MMC converter valve is connected to the AC power grid.

[0009] This invention provides a wind power flexible DC back-to-back transmission test system based on IGCT. Through switch control, it can realize two operating conditions: dual IGCT-MMC back-to-back test and sending-end heterogeneous combined converter + receiving-end IGCT-MMC back-to-back test. It fills the gap in medium-voltage test platform integrating IGCT and diode rectification technology. Moreover, it can be based on the transformation of existing wind farms and is compatible with multiple technical routes. While ensuring the normal power generation of wind farms, it provides reliable verification support for the engineering promotion of new technologies for flexible DC transmission of wind power in deep-sea areas.

[0010] In one optional implementation, the switching switch includes: a first switch, a second switch, a third switch, a fourth switch, a fifth switch, and a sixth switch, wherein, One end of the first switch is connected to the other end of the sending end IGCT-MMC converter valve, the other end of the first switch is connected to the other end of the third switch and one end of the fifth switch respectively, and the other end of the fifth switch is connected to one end of the receiving end IGCT-MMC converter valve; One end of the second switch is connected to the other end of the sending end IGCT-MMC converter valve, the other end of the second switch is connected to the other end of the fourth switch and one end of the sixth switch respectively, and the other end of the sixth switch is connected to one end of the receiving end IGCT-MMC converter valve; One end of the third switch and one end of the fourth switch are both connected to the other end of the diode and IGBT-MMC heterogeneous combination converter.

[0011] In one alternative embodiment, the system further includes an on / off switch, one end of which is connected to the other end of the receiving-end IGCT-MMC converter valve, and the other end of which is connected to the AC power grid.

[0012] In one optional implementation, the system further includes an AC bypass branch, one end of which is connected to the wind farm outlet bus, and the other end of which is connected to the AC power grid.

[0013] In one optional implementation, the AC bypass branch includes: a seventh switch and an eighth switch, wherein, One end of the seventh switch is connected to the wind farm outlet bus, the other end of the seventh switch is connected to one end of the eighth switch, and the other end of the eighth switch is connected to the AC power grid.

[0014] In one optional implementation, the system further includes: a sending-end AC filter and a receiving-end AC filter, wherein, One end of the sending-end AC filter is connected to the wind farm outlet bus, and the other end of the sending-end AC filter is connected to one end of the sending-end IGCT-MMC converter valve and one end of the diode and IGBT-MMC heterogeneous combined converter, respectively. One end of the receiving-end AC filter is connected to the other end of the on / off switch, and the other end of the receiving-end AC filter is connected to the AC power grid.

[0015] Secondly, the present invention provides a wind power flexible DC back-to-back transmission test method based on IGCT, and a wind power flexible DC back-to-back transmission test system based on IGCT according to the first aspect above or any corresponding embodiment thereof, the method comprising: The control switch connects the sending end IGCT-MMC converter valve and the receiving end IGCT-MMC converter valve to simulate the back-to-back flexible direct transmission operation of the wind farm through IGCT-MMC converter valves at both ends. The control switch connects the diode and IGBT-MMC heterogeneous combination converter and the receiving end IGCT-MMC converter valve, simulating the back-to-back flexible direct transmission operation of the wind farm with the sending end being the diode and IGBT-MMC heterogeneous combination converter and the receiving end being the IGCT-MMC converter valve.

[0016] This invention provides a test method for flexible DC transmission of wind power based on IGCT. Through switch control, it can realize two operating conditions: dual IGCT-MMC back-to-back test and heterogeneous combined converter at the sending end + IGCT-MMC back-to-back test at the receiving end. It fills the gap in medium-voltage test platform integrating IGCT and diode rectification technology. Moreover, it can be based on the modification of existing wind farms and is compatible with multiple technical routes. While ensuring the normal power generation of wind farms, it provides reliable verification support for the engineering promotion of new flexible DC transmission technology for deep-sea wind power.

[0017] In one optional implementation, controlling the switching switch to connect the sending-end IGCT-MMC converter valve and the receiving-end IGCT-MMC converter valve includes: Close the first and second switches to connect the IGCT-MMC converter valve at the sending end; Close the fifth and sixth switches to connect the DC field to the receiving-end IGCT-MMC converter valve; Close the on / off switch to connect the receiving end IGCT-MMC converter valve to the AC power grid.

[0018] In one optional implementation, controlling the switching switch to connect the diode and the IGBT-MMC heterogeneous combination converter and the receiving-end IGCT-MMC converter valve includes: Close the third and fourth switches to connect the diode and the IGBT-MMC heterogeneous converter. Close the fifth and sixth switches to connect the DC field to the receiving-end IGCT-MMC converter valve; Close the on / off switch to connect the receiving end IGCT-MMC converter valve to the AC power grid.

[0019] In an optional implementation, the method further includes: During non-test periods or DC system faults, only the AC bypass branch is controlled to conduct. Attached Figure Description

[0020] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0021] Figure 1 This is a schematic diagram of the wind power flexible DC back-to-back transmission test system based on IGCT according to an embodiment of the present invention; Figure 2 This is another principle block diagram of the wind power flexible DC back-to-back transmission test system based on IGCT according to an embodiment of the present invention; Figure 3 This is a topology diagram of a wind power flexible DC back-to-back transmission test system based on IGCT according to an embodiment of the present invention. Figure 4 This is a schematic diagram of the current flow of a wind power flexible DC back-to-back transmission test system based on IGCT according to an embodiment of the present invention. Figure 5 This is another schematic diagram of the current flow of the wind power flexible DC back-to-back transmission test system based on IGCT according to an embodiment of the present invention; Figure 6 This is another schematic diagram of the current flow of the wind power flexible DC back-to-back transmission test system based on IGCT according to an embodiment of the present invention; Figure 7 This is another principle block diagram of the wind power flexible DC back-to-back transmission test system based on IGCT according to an embodiment of the present invention; Figure 8 This is a schematic flowchart of a wind power flexible DC back-to-back transmission test method based on IGCT according to an embodiment of the present invention. Detailed Implementation

[0022] 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 invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0024] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can also refer to the internal connection of two components; and they can refer to a wireless connection or a wired connection. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0025] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0026] This invention provides a wind power flexible DC back-to-back transmission test system based on IGCT. For example... Figure 1 As shown, it includes: a sending-end IGCT-MMC converter valve, a diode and IGBT-MMC heterogeneous combined converter, a receiving-end IGCT-MMC converter valve, and a switching switch. One end of the sending-end IGCT-MMC converter valve and one end of the diode and IGBT-MMC heterogeneous combined converter are connected to the wind farm outlet bus. The other end of the sending-end IGCT-MMC converter valve and the other end of the diode and IGBT-MMC heterogeneous combined converter are connected to one end of the receiving-end IGCT-MMC converter valve via the switching switch. The other end of the receiving-end IGCT-MMC converter valve is connected to the AC power grid.

[0027] Specifically, the sending-end IGCT-MMC converter valve rectifies the AC power output from the wind farm into DC power, while reducing the number of cascaded sub-modules compared to traditional IGBT converters. The diode and IGBT-MMC heterogeneous converter is used to improve power delivery density and reduce sub-module capacitance through diode rectification technology, further optimizing the converter's lightweight effect. The receiving-end IGCT-MMC converter valve inverts the DC power transmitted from the sending-end converter valve into AC power that meets grid requirements, and uses IGCT devices throughout the process to ensure consistency in the receiving-end technology route and avoid interference from multiple device types in test results.

[0028] The switch is used to build a dual IGCT test route, where only one of the two sender-end converter valves is operational at any given time. When simulating a back-to-back flexible DC power transmission operation via IGCT-MMC converter valves at both ends to verify the reliability of the new IGCT power devices and the feasibility of the entire system, the switch is used to connect both the sender-end and receiver-end IGCT-MMC converter valves. When simulating a back-to-back flexible DC power transmission operation via a diode and IGBT-MMC heterogeneous converter at the sender end and an IGCT-MMC converter valve at the receiver end, the switch is used to connect both the diode and IGBT-MMC heterogeneous converter and the receiver-end IGCT-MMC converter valve.

[0029] This invention provides a wind power flexible DC back-to-back transmission test system based on IGCT. Through switch control, it can realize two operating conditions: dual IGCT-MMC back-to-back test and sending-end heterogeneous combined converter + receiving-end IGCT-MMC back-to-back test. It fills the gap in medium-voltage test platform integrating IGCT and diode rectification technology. Moreover, it can be based on the transformation of existing wind farms and is compatible with multiple technical routes. While ensuring the normal power generation of wind farms, it provides reliable verification support for the engineering promotion of new technologies for flexible DC transmission of wind power in deep-sea areas.

[0030] In one alternative implementation, such as Figure 2 As shown, the system also includes: an on / off switch, one end of which is connected to the other end of the receiving end IGCT-MMC converter valve, and the other end of which is connected to the AC power grid.

[0031] Specifically, the on / off switch directly determines whether the electrical energy output by the receiving-end converter valve is connected to the power grid. In this embodiment of the invention, the on / off switch includes switch S9. When switch S9 is closed, the other end of the receiving-end IGCT-MMC converter valve is connected to the AC power grid, and the electrical energy output by the receiving-end converter valve is connected to the power grid; when switch S9 is open, the other end of the receiving-end IGCT-MMC converter valve is disconnected from the AC power grid, and the electrical energy output by the receiving-end converter valve cannot be connected to the power grid.

[0032] In one alternative implementation, such as Figure 3 As shown, the switching system includes: a first switch S1, a second switch S2, a third switch S3, a fourth switch S4, a fifth switch S5, and a sixth switch S6. One end of the first switch S1 is connected to the other end of the sending-end IGCT-MMC converter valve. The other end of the first switch S1 is connected to the other ends of both the third switch S3 and the fifth switch S5. The other end of the fifth switch S5 is connected to the first end of the receiving-end IGCT-MMC converter valve. One end of the second switch S2 is connected to the other end of the sending-end IGCT-MMC converter valve. The other end of the second switch S2 is connected to the other ends of both the fourth switch S4 and the sixth switch S6. The other end of the sixth switch S6 is connected to the first end of the receiving-end IGCT-MMC converter valve. One end of the third switch S3 and one end of the fourth switch S4 are both connected to the other end of the diode and IGBT-MMC heterogeneous converter.

[0033] Specifically, disconnect the third switch S3 and the fourth switch S4, close the first switch S1 and the second switch S2, and connect the sending-end IGCT-MMC converter valve; close the fifth switch S5 and the sixth switch S6 to connect the DC field to the receiving-end IGCT-MMC converter valve. Close the on / off switch S9 to connect the receiving-end IGCT-MMC converter valve to the AC grid. The wind farm power is sent from the sending-end (left) IGCT-MMC converter valve to the receiving-end (right) IGCT-MMC converter valve and finally connected to the grid. This simulates the back-to-back flexible DC transmission operation of the wind farm through IGCT-MMC converter valves at both ends, verifying the reliability of the new IGCT power device and the feasibility of the entire system scheme, laying the foundation for subsequent engineering promotion. See the schematic diagram of the current flow under this condition. Figure 4 .

[0034] Disconnect the first switch S1 and the second switch S2, close the third switch S3 and the fourth switch S4 to connect the diode and IGBT-MMC heterogeneous converter; close the fifth switch S5 and the sixth switch S6 to connect the DC field and the receiving-end IGCT-MMC converter valve; close the on / off switch S9 to connect the receiving-end IGCT-MMC converter valve to the AC grid. The wind farm power is transmitted from the sending-end DRU+IGBT-MMC converter valve to the receiving-end IGCT-MMC converter valve and finally connected to the grid, thus simulating the back-to-back flexible DC transmission operation of the wind farm via a diode and IGBT-MMC heterogeneous converter at the sending end and an IGCT-MMC converter valve at the receiving end. Here, DRU (Diode Rectifier Unit) refers to the diode rectifier valve. See the schematic diagram of the current flow under this condition. Figure 5 .

[0035] In one alternative implementation, such as Figure 3-6As shown, the system also includes an AC bypass branch, one end of which is connected to the wind farm outlet bus, and the other end of which is connected to the AC power grid.

[0036] Specifically, to achieve short-circuit control of the back-to-back system and ensure power supply to the wind farm, this system is equipped with a dedicated AC circuit breaker. Its core function is to provide a stable AC transmission channel to the wind farm through the bypass test circuit during non-test periods or when the DC system fails, thereby ensuring that the wind farm's power generation and normal operation are not affected. At the same time, this AC circuit breaker can be directly replaced by the original system's 35kV AC switch, effectively reducing system modification and construction costs.

[0037] Furthermore, the AC bypass branch includes: a seventh switch S7 and an eighth switch S8. One end of the seventh switch S7 is connected to the wind farm's outlet bus, and the other end of the seventh switch S7 is connected to one end of the eighth switch S8. The other end of the eighth switch S8 is connected to the AC power grid. When the system needs to switch to AC bypass power supply mode, the seventh switch S7 and the eighth switch S8 are closed, and all other switches are opened. At this time, the power output from the wind farm can be directly connected to the AC power grid through the AC bypass branch, and the entire DC back-to-back system is in a shutdown state, with only the AC bypass branch operating independently to ensure wind power transmission. See the schematic diagram of the current flow under this condition. Figure 6 .

[0038] In one alternative implementation, such as Figure 7 As shown, the system also includes a sending-end AC filter and a receiving-end AC filter. One end of the sending-end AC filter is connected to the wind farm outlet bus, and the other end is connected to one end of the sending-end IGCT-MMC converter valve and one end of the diode and IGBT-MMC heterogeneous converter. One end of the receiving-end AC filter is connected to the other end of the on / off switch, and the other end is connected to the AC power grid.

[0039] Specifically, the sending-end AC filter is used to filter out harmonics on the sending-end AC side, ensuring the quality of AC power at the sending end. The receiving-end AC filter is used to filter out harmonics on the receiving-end AC side, ensuring the quality of power connected to the AC power grid.

[0040] Furthermore, the wind power flexible DC back-to-back medium-voltage transmission test system based on IGCT also includes a sending-end connection transformer area and a DC field area. One end of the sending-end connection transformer area is connected to the sending-end AC filter, and the other end is connected to one end of the sending-end IGCT-MMC converter valve and one end of the diode-IGBT-MMC heterogeneous converter. One end of the DC field area is connected to the other end of the sending-end IGCT-MMC converter valve and the other end of the diode-IGBT-MMC heterogeneous converter, and the other end is connected to the receiving-end IGCT-MMC converter valve. In this embodiment, the sending-end connection transformer area integrates a start-up circuit area to achieve voltage matching and system start-up control between the wind farm and the sending-end valve group area. The DC field area is used to achieve DC power transmission and DC-side power quality control between the sending-end and receiving-end valve group areas.

[0041] This invention proposes a wind power flexible DC back-to-back medium-voltage transmission test system based on IGCT, which can simultaneously verify and has the following three effective advantages: First, it has a simple structure and low construction cost of the pilot test platform, and can be modified in existing onshore wind farms; second, it can effectively build a full-chain, full-stage technology research and verification system of "simulation verification - dynamic model pilot test - physical pilot test"; third, it can simultaneously accommodate multiple technical routes, including wind turbine AC transmission, wind turbine transmission via IGCT-MMC back-to-back test system, wind turbine transmission via a diode valve and IGBT-MMC heterogeneous new converter at the sending end, and wind turbine transmission via IGCT-MMC back-to-back test system at the receiving end.

[0042] The proposed solution can be extended to future offshore wind power transmission scenarios. It can verify control strategies for new technology routes, equipment development, and the reliability of continuous equipment operation. Specifically, it can test and verify the performance of new equipment and devices such as IGCT-MMC and diode valves in long-term operation of offshore wind power transmission systems via flexible direct current transmission. Technologies that pass performance verification can significantly reduce platform size and achieve lightweight converter valves. Furthermore, the medium-voltage back-to-back system in flexible direct current transmission plays a crucial role in the entire wind power transmission process. The design proposed in this invention has advantages such as high reliability, flexible operation and scheduling, economic rationality, and convenient maintenance and operation.

[0043] This invention provides a test method for wind power flexible DC back-to-back transmission based on IGCT. Figures 1-7 The wind power flexible DC back-to-back transmission test system based on IGCT shown is as follows: Figure 8 As shown, the test method for wind power flexible DC back-to-back transmission based on IGCT includes: Step S11: Control the switching switch to connect the sending end IGCT-MMC converter valve and the receiving end IGCT-MMC converter valve to simulate the back-to-back flexible direct transmission operation of the wind farm through IGCT-MMC converter valves at both ends.

[0044] Specifically, disconnect the third switch S3 and the fourth switch S4, close the first switch S1 and the second switch S2 to connect the sending-end IGCT-MMC converter valve; close the fifth switch S5 and the sixth switch S6 to connect the DC field to the receiving-end IGCT-MMC converter valve; close the on / off switch S9 to connect the receiving-end IGCT-MMC converter valve to the AC grid. The wind farm power is transmitted from the sending-end (left) IGCT-MMC converter valve to the receiving-end (right) IGCT-MMC converter valve and finally connected to the grid. This simulates the back-to-back flexible DC power transmission operation of the wind farm through IGCT-MMC converter valves at both ends, verifying the reliability of the new IGCT power devices and the feasibility of the entire system scheme, laying the foundation for subsequent engineering promotion. See the schematic diagram of the current flow under this condition. Figure 4 .

[0045] Step S12: Control the switching switch to connect the diode and IGBT-MMC heterogeneous combination converter and the receiving end IGCT-MMC converter valve to simulate the back-to-back flexible direct transmission operation of the wind farm with the sending end being the diode and IGBT-MMC heterogeneous combination converter and the receiving end being the IGCT-MMC converter valve.

[0046] Specifically, disconnect the first switch S1 and the second switch S2, close the third switch S3 and the fourth switch S4 to connect the diode and IGBT-MMC heterogeneous converter; close the fifth switch S5 and the sixth switch S6 to connect the DC field to the receiving-end IGCT-MMC converter valve; close the on / off switch S9 to connect the receiving-end IGCT-MMC converter valve to the AC grid. The wind farm power is transmitted from the sending-end DRU+IGBT-MMC converter valve to the receiving-end IGCT-MMC converter valve and finally connected to the grid, thus simulating the back-to-back flexible DC transmission operation of the wind farm via a diode and IGBT-MMC heterogeneous converter at the sending end and an IGCT-MMC converter valve at the receiving end. See the schematic diagram of the current flow under this condition. Figure 5 .

[0047] This invention provides a test method for flexible DC transmission of wind power based on IGCT. Through switch control, it can realize two operating conditions: dual IGCT-MMC back-to-back test and heterogeneous combined converter at the sending end + IGCT-MMC back-to-back test at the receiving end. It fills the gap in medium-voltage test platform integrating IGCT and diode rectification technology. Moreover, it can be based on the modification of existing wind farms and is compatible with multiple technical routes. While ensuring the normal power generation of wind farms, it provides reliable verification support for the engineering promotion of new flexible DC transmission technology for deep-sea wind power.

[0048] In one alternative implementation, the method further includes: Step S13: During non-test periods or DC system faults, only the AC bypass branch is controlled to be turned on.

[0049] Specifically, during non-testing periods or when a DC system fault occurs, a stable AC power transmission channel is provided to the wind farm through the bypass test circuit, ensuring that the wind farm's power generation and normal operation are not affected. When the system needs to switch to AC bypass power transmission mode, the seventh switch S7 and the eighth switch S8 are closed, and all other switches are opened. At this time, the power output of the wind farm can be directly connected to the AC grid through the AC bypass branch, and the entire DC back-to-back system is in a shutdown state, with only the AC bypass branch operating independently to ensure wind power transmission. See the schematic diagram of the current flow under this condition. Figure 6 .

[0050] Although embodiments of the invention have been described in conjunction with the accompanying drawings, those skilled in the art can make various modifications and variations without departing from the spirit and scope of the invention, and such modifications and variations all fall within the scope defined by the appended claims.

Claims

1. An IGCT-based wind power flexible back-to-back sending-out test system, characterized in that, The system comprises a sending-end IGCT-MMC converter valve, a diode and IGBT-MMC heterogeneous combined converter, a receiving-end IGCT-MMC converter valve and a switching switch, wherein, One end of the sending-end IGCT-MMC converter valve and one end of the diode and IGBT-MMC heterogeneous combined converter are connected with a wind farm outlet bus, the other end of the sending-end IGCT-MMC converter valve and the other end of the diode and IGBT-MMC heterogeneous combined converter are connected with one end of the receiving-end IGCT-MMC converter valve through the switching switch, and the other end of the receiving-end IGCT-MMC converter valve is connected with an AC power grid.

2. The IGCT-based wind power flexible back-to-back HVDC transmission test system of claim 1, wherein, The switching switch comprises a first switch, a second switch, a third switch, a fourth switch, a fifth switch and a sixth switch, wherein, One end of the first switch is connected with the other end of the sending-end IGCT-MMC converter valve, the other end of the first switch is connected with the other end of the third switch and one end of the fifth switch respectively, and the other end of the fifth switch is connected with one end of the receiving-end IGCT-MMC converter valve; One end of the second switch is connected with the other end of the sending-end IGCT-MMC converter valve, the other end of the second switch is connected with the other end of the fourth switch and one end of the sixth switch respectively, and the other end of the sixth switch is connected with one end of the receiving-end IGCT-MMC converter valve; One end of the third switch and one end of the fourth switch are connected with the other end of the diode and IGBT-MMC heterogeneous combined converter.

3. The IGCT-based wind power flexible back-to-back HVDC transmission test system of claim 1, wherein, The system further comprises an on-off switch, one end of the on-off switch is connected with the other end of the receiving-end IGCT-MMC converter valve, and the other end of the on-off switch is connected with the AC power grid.

4. The IGCT-based wind power flexible back-to-back HVDC transmission test system of claim 1, wherein, The system further comprises an AC bypass branch, one end of the AC bypass branch is connected with the wind farm outlet bus, and the other end of the AC bypass branch is connected with the AC power grid.

5. The IGCT-based wind power flexible back-to-back HVDC transmission test system of claim 4, wherein, The AC bypass branch comprises a seventh switch and an eighth switch, wherein, One end of the seventh switch is connected with the wind farm outlet bus, the other end of the seventh switch is connected with one end of the eighth switch, and the other end of the eighth switch is connected with the AC power grid.

6. The IGCT-based wind power flexible back-to-back HVDC transmission test system of claim 3, wherein, The system further comprises a sending-end AC filter and a receiving-end AC filter, wherein, One end of the sending-end AC filter is connected with the wind farm outlet bus, and the other end of the sending-end AC filter is connected with one end of the sending-end IGCT-MMC converter valve and one end of the diode and IGBT-MMC heterogeneous combined converter respectively; One end of the receiving-end AC filter is connected with the other end of the on-off switch, and the other end of the receiving-end AC filter is connected with the AC power grid.

7. A test method for IGCT-based wind power flexible back-to-back sending out, characterized in that, The IGCT-based wind power flexible HVDC back-to-back transmission test system based on any one of claims 1-6, the method comprising: controlling the switching switch to connect the sending-end IGCT-MMC converter valve and the receiving-end IGCT-MMC converter valve, so as to simulate the wind farm operating in a back-to-back HVDC external transmission mode with both ends being IGCT-MMC converter valves; Controlling the switching switches to connect the diode and IGBT-MMC hybrid combined converter and the receiving end IGCT-MMC converter valve, simulating the back-to-back HVDC external sending operation condition of the wind farm with the diode and IGBT-MMC hybrid combined converter at the sending end and the IGCT-MMC converter valve at the receiving end.

8. The IGCT-based wind power flexible back-to-back sending-out test method according to claim 7, characterized in that, Controlling the switching switches to connect the sending end IGCT-MMC converter valve and the receiving end IGCT-MMC converter valve, comprising: closing the first switch and the second switch to connect the sending end IGCT-MMC converter valve; closing the fifth switch and the sixth switch to connect the DC field and the receiving end IGCT-MMC converter valve; closing the on-off switch to connect the receiving end IGCT-MMC converter valve and the AC power grid.

9. The IGCT-based wind power flexible back-to-back sending-out test method according to claim 7, characterized in that, Controlling the switching switches to connect the diode and IGBT-MMC hybrid combined converter and the receiving end IGCT-MMC converter valve, comprising: closing the third switch and the fourth switch to connect the diode and IGBT-MMC hybrid combined converter; closing the fifth switch and the sixth switch to connect the DC field and the receiving end IGCT-MMC converter valve; closing the on-off switch to connect the receiving end IGCT-MMC converter valve and the AC power grid.

10. The IGCT-based wind power flexible back-to-back sending-out test method according to claim 7, characterized in that, The method further comprises: only controlling the AC bypass branch to be conductive during a non-test period or a DC system fault.

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