Topological structure and operation strategy of hybrid multi-infeed direct current system

Abstract

The invention discloses a topological structure and an operation strategy of a hybrid multi-infeed direct current system. The hybrid multi-infeed direct-current system is fed into the receiving-end alternating-current system in a partitioned manner, an inverter of at least one receiving-end alternating-current system is an HCC converter, and the HCC converter is formed by replacing part or all of thyristors in an LCC converter with a full-control device, so that reactive power compensation can be provided for an adjacent direct-current power transmission system when a fault occurs; the problem of simultaneous commutation failure or successive commutation failure of the MIDC system is solved, and the problem of concurrent commutation failure of a non-fault end valve group is solved. When a fault is detected, the reactive output power of the HCC current converter and / or the new energy power generation device is increased, reactive dynamic support is carried out, the influence of the defects of reactive compensation equipment on the hybrid multi-infeed direct current system can be reduced, and the equipment cost and the power loss are reduced. The topological structure and the operation strategy of the hybrid multi-infeed direct current system can restrain commutation failure, and are of great significance to guarantee safe and stable operation of a power grid.

Description

Technical Field

[0001] The present invention relates to the technical field of direct current transmission, and in particular to a hybrid multi-feed direct current system topology structure and operation strategy. Background Art

[0002] High-voltage direct current transmission is the transmission of high-voltage direct current from one place to another. When it arrives at a certain place, it must be converted into a voltage that can be used locally. This location is the drop point. With the increase in the demand for transmission capacity, more and more direct current drop points have begun to appear at the load center, thus forming a multi-infeed direct current (MIDC) transmission system. The rapid development of MIDC has met the growing demand for energy transmission to a certain extent.

[0003] However, the increase in DC drop points also makes the coupling characteristics of the power grid more complicated. In the multi-infeed DC system, there is electrical coupling between different layers of valve groups on the DC inverter side and between different DCs, and the transient characteristics of the system are more complicated. In addition to the first and subsequent commutation failures of the fault-end valve group in the multi-infeed DC system, there is also the concurrent commutation failure problem of the non-fault-end valve group. The system commutation failure problem is particularly prominent. Once a short-circuit fault occurs in the receiving-end power grid, it may cause simultaneous commutation failure or successive commutation failure in multiple inverter stations, resulting in the interruption of power transmission of multiple DC lines, which seriously endangers the safety of the power grid. Summary of the invention

[0004] In order to solve the above problems, the inventors have made the present invention, and provide a hybrid multi-infeed DC system topology structure and operation strategy through specific implementation methods.

[0005] In a first aspect, an embodiment of the present invention provides a hybrid multi-infeed DC system topology structure, wherein the hybrid multi-infeed DC system is partitioned and fed into a receiving-end AC system, and the inverter of at least one receiving-end AC system is an HCC converter, and the HCC converter is an LCC converter in which some or all thyristors are replaced with fully controlled devices.

[0006] Optionally, the hybrid multi-infeed DC system includes multiple receiving-end AC systems, each receiving-end AC system includes a rectifier and an inverter, each receiving-end AC system is connected to a commutation busbar that is electrically adjacent, and the commutation busbar is connected to the flexible DC grid through a voltage source converter.

[0007] Optionally, at least one single valve in the HCC converter includes an active turn-off thyristor valve string or a hybrid thyristor valve string, wherein the active turn-off thyristor valve string includes a plurality of fully-controlled devices connected in series, and the hybrid thyristor valve string includes thyristors and fully-controlled devices connected in series.

[0008] Optionally, the single valve further includes a separate lightning arrester, a static voltage-equalizing resistor and a dynamic voltage-equalizing circuit, and at least one fully-controlled device is respectively connected in parallel to the separate lightning arrester, the static voltage-equalizing resistor and the dynamic voltage-equalizing circuit.

[0009] Optionally, the dynamic voltage balancing circuit includes a capacitor and a resistor connected in series.

[0010] Optionally, the fully-controlled device is a reverse-resistance IGCT, and when commutation fails, the reverse-resistance IGCT is actively shut down to perform forced commutation.

[0011] In a second aspect, an embodiment of the present invention provides a hybrid multi-infeed DC system operation strategy, comprising the following steps:

[0012] In a hybrid multi-infeed DC system, when a fault is detected, the reactive output power of the HCC converter and / or the renewable energy generation device is increased to provide reactive dynamic support.

[0013] Optionally, detecting a fault comprises the following steps: monitoring the commutation bus voltage and the arc extinction angle on the DC inverter side of an adjacent LCC DC transmission system according to a set period or in real time, and determining that a fault has occurred when the voltage is less than 0.8 pu or the arc extinction angle is less than 10 degrees.

[0014] Optionally, the hybrid multi-infeed DC system operation strategy further includes the following steps: when a preset recovery condition is met, the HCC converter and / or the new energy power generation device with increased reactive output power is restored to a normal operating state.

[0015] Optionally, the recovery condition is that the commutation bus voltage of the adjacent LCC DC transmission system is greater than 0.8pu and the arc extinction angle on the DC inverter side is greater than 10 degrees.

[0016] The beneficial effects of the above technical solution provided by the embodiment of the present invention include at least:

[0017] A hybrid multi-infeed DC system topology structure can provide reactive power compensation for adjacent DC transmission systems when a fault occurs and improve the operating characteristics of the system by introducing an HCC-HVDC system including an HCC converter; can solve the problem of simultaneous commutation failure or successive commutation failure in the multi-infeed DC transmission system by feeding the receiving-end AC system into the partitioned mode; can solve the problem of concurrent commutation failure of non-fault-end valve groups by outputting reactive power through the HCC-HVDC system and feeding the receiving-end AC system into the partitioned mode.

[0018] A hybrid multi-infeed DC system operation strategy can improve the system's dynamic reactive power support capability, thereby suppressing continuous commutation failures in the DC transmission system, and can partially or completely replace reactive power compensation equipment with high costs and large losses, thereby reducing investment in reactive power compensation equipment, reducing the impact of the shortcomings of reactive power compensation equipment on the hybrid multi-infeed DC system, and reducing the equipment cost and power loss of the hybrid multi-infeed DC system.

[0019] The above hybrid multi-infeed DC system topology and operation strategy can suppress commutation failure and is of great significance to ensuring the safe and stable operation of the power grid.

[0020] Other features and advantages of the present invention will be described in the following description, and partly become apparent from the description, or understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures particularly pointed out in the written description, claims, and drawings.

[0021] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0023] Figure 1 A topological diagram of a multi-input hybrid system in an embodiment of the present invention;

[0024] Figure 2 It is a structural diagram of a hybrid multi-feed DC system with zoned feeding in an embodiment of the present invention;

[0025] Figure 3 This is a topological structure diagram of HCC-HVDC in an embodiment of the present invention;

[0026] Figure 4 This is a flow chart of the operation strategy of the hybrid multi-infeed DC system in an embodiment of the present invention. DETAILED DESCRIPTION

[0027] The exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although the exemplary embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the present disclosure to those skilled in the art.

[0028] In order to solve the problems existing in the prior art, an embodiment of the present invention provides a hybrid multi-infeed DC system topology structure and operation strategy.

[0029] A multi-infeed DC system refers to a system in which two or more DC converters are fed into the same commutation bus, or connected to commutation buses with close electrical distances, thus forming a multi-infeed hybrid system. Its structure is as follows: Figure 1 shown. Figure 1 In the multi-infeed DC system, there are multiple receiving-end AC systems, each of which corresponds to a DC point, connected to the DC grid through the commutation bus to form multiple high-voltage DC systems (High Voltage Direct Current, HVDC), and there is impedance between the commutation buses. The multi-infeed structure brings new changes to the commutation failure problem of the AC / DC hybrid system. Since there is electrical coupling between different layers of valve groups on the DC inverter side and between different DCs in the multi-infeed DC system, it is easy to cause the adjacent DC systems to fail in commutation one after another, and the transient characteristics of the system are more complicated. Therefore, in addition to the first and subsequent commutation failure problems of the fault-end valve group, the multi-infeed DC system also adds the concurrent commutation failure problem of the non-fault-end valve group.

[0030] like Figure 2The hybrid multi-feed DC system structure with partitioned feeding shown, an embodiment of the present invention provides a hybrid multi-feed DC system topology structure, the hybrid multi-feed DC system is partitioned to feed the receiving end AC system, at least one inverter of the receiving end AC system is an HCC converter (Hybrid Commutated Converter, HCC), and the HCC converter is a LCC converter in which part or all of the thyristors are replaced with fully controlled devices. The LCC converter uses semi-controlled thyristors as the main power devices. The thyristors (Silicon Controlled Rectifier, SCR) can only control the opening, not the closing, and are prone to commutation failure under AC grid faults, harmonics and other working conditions. The HCC converter replaces part or all of the thyristors in the LCC converter with fully controlled devices to achieve active shutdown and partitioned feeding, which can suppress commutation failure, force commutation when commutation fails, and can also reduce the successive commutation failures of adjacent DC systems. The receiving-end AC system including the HCC converter corresponds to the HCC high-voltage direct current transmission system (HCC-HVDC), and the other receiving-end AC systems correspond to the line-commutated converter high-voltage direct current transmission system (Line-Commutated Converter High Voltage Direct Current, LCC-HVDC). HCC-HVDC is to add a fully controlled reverse-resistance IGCT (Integrated Gate-Commutated Thyristor) device to the conventional thyristor valve of the LCC-HVDC system, and use the reverse-resistance IGCT to replace the thyristor. During normal operation, the reverse-resistance IGCT exhibits thyristor characteristics, and only when the commutation fails does the IGCT force commutation to intervene. Reverse resistance refers to the ability to withstand reverse voltage. The HCC-HVDC system can also use other reverse-resistance fully-controlled devices, such as reverse-resistance IGBT (Insulated Gate Bipolar Transistor). Figure 2 The hybrid multi-infeed DC system topology based on HCC-HVDC shown in the figure, on the one hand, can provide reactive power to the adjacent system at the time of fault occurrence by introducing HCC-HVDC, thereby improving the operating characteristics of the system; on the other hand, the problem of simultaneous commutation failure or successive commutation failure in the multi-infeed DC system can be solved by feeding the receiving-end system into the partition.

[0031] In some specific embodiments, Figure 2As shown, the hybrid multi-infeed DC system includes multiple receiving-end AC systems, each receiving-end AC system includes a rectifier and an inverter, each receiving-end AC system is connected to a commutation busbar with an electrical proximity, and the commutation busbar is connected to a flexible DC grid through a voltage source converter (VSC). The flexible DC grid includes new energy power generation devices, such as wind power devices and photovoltaic power generation devices.

[0032] In some specific embodiments, Figure 3 As shown, at least one single valve in the HCC converter includes an active shut-off thyristor valve string or a hybrid thyristor valve string. The active shut-off thyristor valve string, also called a turn-off thyristor valve string, includes a plurality of fully controlled devices (IGCT1, IGCT2 to IGCTm) connected in series. The hybrid thyristor valve string includes thyristors (SCR1 to SCRn) and fully controlled devices (IGCT1 to IGCTm) connected in series. Compared with the HCC converter, the LCC converter uses a thyristor valve string (SCR1, SCR2 to SCRn), such as Figure 3 As shown, the single valve of the LCC converter is composed of a thyristor valve string and cannot be actively shut down. The turn-off thyristor valve string (active shut-off thyristor valve string) or hybrid thyristor valve string of the HCC converter can control the shutdown, thereby suppressing commutation failure and forcing commutation when commutation fails. At the same time, combined with partition feeding, it can reduce the successive commutation failures of adjacent DC systems. Figure 3 The n or m here only represents an integer and does not limit the quantity or quantitative relationship.

[0033] In some specific embodiments, Figure 3 As shown, the single valve also includes a separate arrester MOV, a static voltage grading resistor R d and a dynamic voltage-equalizing circuit RC, at least one fully-controlled device is respectively connected in parallel with the separate lightning arrester, the static voltage-equalizing resistor and the dynamic voltage-equalizing circuit. Figure 3 In the example, each fully controlled device in series is connected in parallel with a separate arrester, a static voltage-equalizing resistor, and a dynamic voltage-equalizing circuit. The separate arrester is used for overvoltage protection, and the separate arrester has a compact structure and occupies a small space. The static voltage-equalizing resistor and the dynamic voltage-equalizing circuit are used to equalize the voltage of the fully controlled devices in series.

[0034] In some specific embodiments, Figure 3 As shown, the dynamic voltage balancing circuit includes a capacitor C connected in series d and resistor R d .

[0035] In some specific embodiments, Figure 3As shown, the fully controlled device is a reverse-resistance IGCT. When commutation fails, the reverse-resistance IGCT is actively turned off to perform forced commutation.

[0036] In the embodiment corresponding to the hybrid multi-infeed DC system topology, by introducing an HCC-HVDC system including an HCC converter, reactive power compensation can be provided to adjacent DC transmission systems when a fault occurs, thereby improving the operating characteristics of the system; by feeding the receiving-end AC system into the partitioned feeder, the problem of simultaneous commutation failure or successive commutation failure in the multi-infeed DC transmission system can be solved; by outputting reactive power through the HCC-HVDC system and feeding the receiving-end AC system into the partitioned feeder, the problem of concurrent commutation failure of the non-fault end valve group can be solved. The above-mentioned hybrid multi-infeed DC system topology can suppress commutation failure, which is of great significance to ensuring the safe and stable operation of the power grid.

[0037] Suppressing the commutation failure of the DC transmission system is the key to maintaining the stability of the AC-DC hybrid system. At present, reactive power compensation equipment is generally installed to improve the dynamic reactive power support capacity of the system, thereby suppressing the continuous commutation failure of the DC transmission system. However, reactive power compensation equipment has the disadvantages of high cost, high loss, large footprint, slow response, and possible over-compensation when the load is low. Another embodiment of the present invention provides a hybrid multi-input DC system operation strategy, the process of which is as follows: Figure 4 As shown, the following steps are included:

[0038] In a hybrid multi-infeed DC system, when a fault is detected, the reactive output power of the HCC converter and / or the renewable energy generation device is increased to provide dynamic reactive support. By controlling the reactive output power of the HCC converter and / or the renewable energy generation device to provide reactive compensation, the dynamic reactive support capability of the system is improved, and the investment in reactive compensation equipment can be reduced, thereby reducing the impact of the shortcomings of reactive compensation equipment on the hybrid multi-infeed DC system. Figure 4 As shown, by adjusting the active power and reactive power output by the HCC-HVDC system, wind power device and photovoltaic power generation device, the reactive output of the HCC converter, wind power device and photovoltaic power generation device on the HCC-HVDC inverter side is increased in the event of a fault, and reactive dynamic support is provided to achieve the purpose of suppressing continuous commutation failure of the adjacent LCC DC transmission system.

[0039] In some specific embodiments, Figure 4 As shown, fault detection includes the following steps: monitoring the commutation bus voltage and the arc extinction angle of the DC inverter side of the adjacent LCC DC transmission system according to a set period or in real time, and determining that a fault occurs when the voltage is less than 0.8pu or the arc extinction angle is less than 10 degrees.

[0040] In some specific embodiments, the hybrid multi-feed DC system operation strategy further includes the following steps: when the preset recovery conditions are met, the HCC converter and / or the new energy power generation device with increased reactive output power is restored to a normal operating state. The active power and reactive power output by the HCC-HVDC system, the wind power device and the photovoltaic power generation device are adjusted to a normal operating state, the reactive dynamic support is suspended, the receiving end AC system is restored to stability, and the adjacent LCC-HVDC DC transmission system operates normally.

[0041] In some specific embodiments, the recovery condition is that the commutation bus voltage of the adjacent LCC DC transmission system is greater than 0.8 pu, and the arc extinction angle on the DC inverter side is greater than 10 degrees.

[0042] In the embodiment corresponding to the hybrid multi-feed DC system operation strategy, the dynamic reactive power support capability of the system can be improved, thereby suppressing the continuous commutation failure of the DC transmission system, and can partially or completely replace the reactive compensation equipment with high cost and large loss, which can reduce the investment in reactive compensation equipment, reduce the impact of the shortcomings of reactive compensation equipment on the hybrid multi-feed DC system, and reduce the equipment cost and power loss of the hybrid multi-feed DC system. The above hybrid multi-feed DC system operation strategy can suppress commutation failure, which is of great significance to ensuring the safe and stable operation of the power grid.

[0043] Those skilled in the art can change the above sequence without departing from the protection scope of the present disclosure.

[0044] Any modification, supplement and equivalent replacement made within the scope of the principles of the present invention shall still fall within the scope of the patent coverage of the present invention. The "connection" mentioned above, unless otherwise stated, represents the logical relationship of current transmission and does not necessarily represent a direct electrical connection. The present invention is not limited to the above voltage levels, which are only the voltage levels in the embodiments.

Claims

1. A hybrid multi-infeed DC system topology, characterized in that: The hybrid multi-infeed DC system feeds the receiving-end AC system in sections, and the inverter of at least one receiving-end AC system is an HCC converter, wherein part or all of the thyristors in the HCC converter are replaced with fully controlled devices.

2. The hybrid multi-infeed DC system topology structure according to claim 1, characterized in that: The hybrid multi-infeed DC system includes multiple receiving-end AC systems, each receiving-end AC system includes a rectifier and an inverter, each receiving-end AC system is connected to a commutation busbar with a close electrical distance, and the commutation busbar is connected to the flexible DC grid through a voltage source converter.

3. The hybrid multi-infeed DC system topology structure according to claim 1, characterized in that: At least one single valve in the HCC converter includes an active turn-off thyristor valve string or a hybrid thyristor valve string, wherein the active turn-off thyristor valve string includes a plurality of fully-controlled devices connected in series, and the hybrid thyristor valve string includes thyristors and fully-controlled devices connected in series.

4. The hybrid multi-infeed DC system topology structure according to claim 3, characterized in that: The single valve also includes a separate lightning arrester, a static voltage-equalizing resistor and a dynamic voltage-equalizing circuit, and at least one fully-controlled device is connected in parallel to the separate lightning arrester, the static voltage-equalizing resistor and the dynamic voltage-equalizing circuit respectively.

5. The hybrid multi-infeed DC system topology structure according to claim 4, characterized in that: The dynamic voltage balancing loop includes a capacitor and a resistor connected in series.

6. The hybrid multi-infeed DC system topology structure according to claim 4, characterized in that: The fully controlled device is a reverse-resistance IGCT, which is actively turned off to perform forced commutation when commutation fails.

7. A hybrid multi-infeed DC system operation strategy, characterized in that: The following steps are involved: In a hybrid multi-infeed DC system, when a fault is detected, the reactive output power of the HCC converter and / or the renewable energy generation device is increased to provide reactive dynamic support.

8. The hybrid multi-infeed DC system operation strategy according to claim 7, characterized in that: Detecting a fault includes the following steps: The commutation bus voltage of the adjacent LCC DC transmission system and the arc extinction angle on the DC inverter side are monitored in a set period or in real time. When the voltage is less than 0.8 pu, or the arc extinction angle is less than 10 degrees, it is determined that a fault has occurred.

9. The hybrid multi-infeed DC system operation strategy according to claim 7, characterized in that: The hybrid multi-feed DC system operation strategy further includes the following steps: When the preset recovery conditions are met, the HCC converter and / or the new energy power generation device that increases the reactive output power is restored to a normal operating state.

10. The hybrid multi-infeed DC system operation strategy according to claim 9, characterized in that: The recovery conditions are that the commutation bus voltage of the adjacent LCC DC transmission system is greater than 0.8pu and the arc extinction angle on the DC inverter side is greater than 10 degrees.

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