DC power transmission receiving end and DC power transmission system
By introducing inverter circuits and back-to-back converter groups into the DC transmission system, the problems of commutation failure and insufficient reactive power compensation in the traditional DC transmission system during AC faults have been solved, achieving higher system stability and voltage regulation capability.
Patent Information
- Application Number
- CN202522441821.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2025-11-18
- Publication Date
- 2025-12-23
- Estimated Expiration
- 2035-11-18
AI Technical Summary
Traditional DC transmission systems are prone to commutation failures when the AC grid is disturbed or faulted, and reactive power compensation methods are insufficient in dynamic response capability, affecting system stability and efficiency.
The system employs an inverter circuit, a first transformer, and a back-to-back converter group. The back-to-back converter group consists of two converters connected in series. The inverter circuit is connected to the DC transmission line, and the transformer is connected to the AC power grid. The back-to-back converters provide instantaneous voltage support during AC faults, compensate for reactive power demand in real time, and enhance system robustness.
It significantly reduces the possibility of commutation failure, improves the stability and robustness of DC transmission receiving-end systems, enhances reactive power compensation capabilities, and improves the system's voltage regulation capabilities.
Smart Images
Figure CN223713595U_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the field of direct current transmission, in particular to a direct current transmission receiving end and a direct current transmission system. BACKGROUND
[0002] As a highly efficient and large-capacity power transmission method, high voltage direct current (HVDC) plays a crucial role in global energy transmission networks.
[0003] However, in traditional converter commutation technology, when the AC grid connected to the converter is subjected to disturbances or faults, the commutation process of the HVDC system is easily affected, thereby causing commutation failure. Commutation failure not only leads to the interruption of DC power transmission, but also triggers a series of chain reactions such as overvoltage, overcurrent, and even the shutdown of the entire system, posing a significant threat to the safe and stable operation of the power system.
[0004] In addition, the converter consumes a large amount of reactive power during operation, which poses potential pressure on the voltage stability and overall operation efficiency of the AC system. Traditional reactive power compensation methods, such as AC filters or shunt capacitor banks, can provide certain reactive power support, but their dynamic response capability in the transient process of the power grid is insufficient, making it difficult to meet the changes in system reactive power demand in a timely manner, especially in the case of sudden faults or large load fluctuations. CONTENT OF THE INVENTION
[0005] The main purpose of the present application is to provide a direct current transmission receiving end and a direct current transmission system to at least solve the problem of how to improve the stability of the direct current transmission receiving end system in the prior art.
[0006] In order to achieve the above-mentioned purpose, according to one aspect of the present application, a direct current transmission receiving end is provided, comprising: an inverter circuit, a first transformer, and a back-to-back converter group, the back-to-back converter group comprising two converters connected in series back-to-back, a first end of the inverter circuit being used for connecting a direct current transmission line, a first end of the first transformer and a first end of the back-to-back converter group being electrically connected with a second end of the inverter circuit respectively, a second end of the first transformer and a second end of the back-to-back converter group being used for connecting an alternating current grid respectively, the two converters being electrically connected at the direct current side, an alternating current side of one of the converters being electrically connected with the inverter circuit, and an alternating current side of the other of the converters being electrically connected with the alternating current grid.
[0007] Optionally, the direct current transmission receiving end further comprises a second transformer and a third transformer, wherein the second transformer is connected in parallel or series with the first transformer, and the third transformer is connected in parallel or series with the first transformer.
[0008] Optionally, the second transformer is connected in parallel with the first transformer, the third transformer is connected in parallel with the first transformer, and the two converters are first converters, wherein each of the first converters comprises three phases, each phase comprising a first upper bridge arm and a first lower bridge arm, each of the first upper bridge arms and the first lower bridge arms being formed by cascading a plurality of first converter sub-modules, and each of the first converters further comprises a first inductor module, the first inductor module comprising a plurality of first inductors, each of the first inductors having a first end electrically connected to a connection branch of the first upper bridge arm and the first lower bridge arm, and each of the first inductors having a second end for connecting to the AC power grid.
[0009] Optionally, the second transformer is connected in series with the first transformer, the third transformer is connected in series with the first transformer, and the two converters are second converters, wherein each of the second converters comprises three phases, each phase comprising a second upper bridge arm and a second lower bridge arm, each of the second upper bridge arms and the second lower bridge arms being formed by cascading a plurality of second converter sub-modules, and each of the second converters further comprises a second inductor module, the second inductor module comprising a plurality of second inductors, each of the second inductors having a first end electrically connected to a connection branch of the second upper bridge arm and the second lower bridge arm, and each of the second inductors having a second end for connecting to the AC power grid; and a capacitor module, the capacitor module comprising a plurality of first capacitors, each of the first capacitors having a first end electrically connected to the second end of each of the second inductors, and each of the first capacitors having a second end electrically connected.
[0010] Optionally, the second transformer comprises a first primary winding and a first secondary winding, the second transformer is connected in parallel with the first transformer, the first primary winding is electrically connected to the second end of the inverter circuit, and the first secondary winding is electrically connected to the first end of the back-to-back converter group; or the second transformer is connected in series with the first transformer, a first end of the first primary winding is electrically connected to the second end of the inverter circuit, a second end of the first primary winding is electrically connected to the first end of the first transformer, and the first secondary winding is electrically connected to the first end of the back-to-back converter group.
[0011] Optionally, the third transformer comprises a second primary winding and a second secondary winding, the third transformer is connected in parallel with the first transformer, the second primary winding is electrically connected to the second end of the first transformer, and the second secondary winding is electrically connected to the second end of the back-to-back converter group; or the third transformer is connected in series with the first transformer, a first end of the second primary winding is electrically connected to the second end of the first transformer, a second end of the second primary winding is for connecting to the AC power grid, and the second secondary winding is electrically connected to the second end of the back-to-back converter group.
[0012] Optionally, the direct current sides of the two converters are electrically connected, wherein the converter is a voltage source converter or a current source converter.
[0013] Optionally, the back-to-back converter group further comprises a second capacitor, and the second capacitor is connected in parallel with the two voltage source converters respectively.
[0014] Optionally, the inverter circuit comprises at least one of a current source converter and a voltage source converter.
[0015] In order to achieve the above-mentioned purpose, according to an aspect of the present application, a direct current transmission system is provided, comprising a direct current transmission sending end and any one of the direct current transmission receiving ends.
[0016] The technical scheme of the present application provides a direct current transmission receiving end, the direct current transmission end comprising an inverter circuit, a first transformer and a back-to-back converter group, the back-to-back converter group comprising two converters connected in series back-to-back, the first end of the inverter circuit being used for connecting a direct current transmission line, the first end of the first transformer and the first end of the back-to-back converter group being electrically connected with the second end of the inverter circuit respectively, and the second end of the first transformer and the second end of the back-to-back converter group being used for connecting an alternating current power grid. The scheme connects one back-to-back converter to the direct current transmission receiving end, one end of which is connected with the alternating current power grid and the other end of which is connected with the secondary side power grid of the direct current transmission receiving end. During alternating current fault, the back-to-back converter can provide instantaneous voltage support, greatly reduce the possibility of commutation failure, enhance the system robustness, the back-to-back converter can compensate the reactive power demand of the converter in real time, participate in voltage regulation, and improve the stability of the direct current transmission receiving end system. BRIEF DESCRIPTION OF DRAWINGS
[0017] The drawings accompanying the specification of the present application form a part thereof, serve to provide further understanding of the present application, and together with the specification explain the present application, and do not constitute an improper limitation on the present application. In the drawings:
[0018] Figure 1 A circuit diagram of a first direct current transmission receiving end provided in an embodiment of the present application is shown;
[0019] Figure 2 A circuit diagram of a second direct current transmission receiving end provided in an embodiment of the present application is shown;
[0020] Figure 3 A circuit diagram of a third direct current transmission receiving end provided in an embodiment of the present application is shown;
[0021] Figure 4 A circuit diagram of a fourth direct current transmission receiving end provided in an embodiment of the present application is shown;
[0022] Figure 5 A circuit diagram of a fifth DC power receiving end is shown according to an embodiment of the present application.
[0023] In the above drawings, reference numerals:
[0024] 10, inverter circuit; 20, first transformer; 30, back-to-back converter group; 31, converter; 32, second capacitor; 311, first converter; 312, first upper bridge arm; 313, first lower bridge arm; 314, first inductor module; 321, second converter; 322, second upper bridge arm; 323, second lower bridge arm; 324, second inductor module; 325, capacitor module; 40, AC power grid; 50, second transformer; 60, third transformer. DETAILED DESCRIPTION
[0025] It should be noted that the embodiments and features of the embodiments in the present application can be combined with each other without conflict. The technical solutions in the embodiments of the present application will be described in detail below with reference to the drawings and in combination with the embodiments.
[0026] In order to enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, not all. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor should be within the scope of protection of the present application.
[0027] It should be noted that the terms "first", "second" and the like in the specification and claims of the present application and the above-mentioned drawings are used to distinguish similar objects, and do not necessarily indicate a specific order or sequence. It should be understood that the data thus used can be interchanged under appropriate circumstances, so that the embodiments of the present application described herein can be implemented. In addition, the terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusion, for example, a process, system, product or device including a series of steps or units does not necessarily limit to those steps or units clearly listed, but can include other steps or units not clearly listed or inherent to these processes, products or devices.
[0028] As introduced in the background, the stability of the DC power receiving end system in the prior art is not ideal. To solve the above problems, the embodiments of the present application provide a DC power receiving end and a DC power transmission system.
[0029] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application.
[0030] Figures 1 to 5 is a circuit diagram of a first direct current transmission receiving end according to an embodiment of the present application. As shown in Figures 1 to 5 , it comprises:
[0031] an inverter circuit 10, a first transformer 20, and a back-to-back converter group 30, the back-to-back converter group 30 comprising two converters 31 connected in back-to-back series, a first end of the inverter circuit 10 being used for connecting a direct current transmission line, a first end of the first transformer 20 and a first end of the back-to-back converter group 30 being electrically connected to a second end of the inverter circuit 10 respectively, a second end of the first transformer 20 and a second end of the back-to-back converter group 30 being used for connecting an alternating current power grid 40 respectively, the two converters 31 connected in back-to-back series being electrically connected at the direct current side of the two converters 31, an alternating current side of one converter 31 being connected to the inverter circuit 10, and an alternating current side of the other converter 31 being electrically connected to the alternating current power grid 40.
[0032] Specifically, the inverter circuit 10 is used for converting direct current into alternating current and inputting the alternating current to one end of the back-to-back converter group 30. In actual application, the inverter circuit 10 can comprise a current source type converter or a voltage source type converter. The first transformer 20 is a converter transformer of the inverter circuit 10, and is used for reducing the voltage of the alternating current power grid 40 to the rated voltage of the inverter circuit 10. The type of the converter 31 in the back-to-back converter group 30 is not limited in the present application, and can be selected by those skilled in the art according to actual conditions. In actual application, the back-to-back converter group 30 can be controlled to provide reactive power support to the inverter circuit 10 through direct current voltage control or voltage compensation control, and the control modes of the two converters 31 in the back-to-back converter group 30 can be the same or different.
[0033] Through the embodiment, a direct current transmission receiving end is provided. The direct current transmission end comprises an inverter circuit, a first transformer, and a back-to-back converter group. The back-to-back converter group comprises two converters connected in back-to-back series. A first end of the inverter circuit is used for connecting a direct current transmission line. A first end of the first transformer and a first end of the back-to-back converter group are electrically connected to a second end of the inverter circuit respectively. A second end of the first transformer and a second end of the back-to-back converter group are used for connecting an alternating current power grid. The present scheme connects one back-to-back converter to the direct current transmission receiving end. One end of the back-to-back converter is connected to the alternating current power grid, and the other end is connected to the auxiliary side power grid of the direct current transmission receiving end. During alternating current fault, the back-to-back converter can provide instantaneous voltage support, greatly reduce the possibility of commutation failure, enhance the system robustness, and compensate the reactive power demand of the converter in real time, participate in voltage regulation, and improve the stability of the direct current transmission receiving end system.
[0034] In the specific implementation process, as shown in Figure 2As shown, the DC power receiving end further comprises a second transformer 50 and a third transformer 60, wherein the second transformer 50 is connected in parallel or in series with the first transformer 20, and the third transformer 60 is connected in parallel or in series with the first transformer 20. In the case of series connection of the second transformer 50 and the first transformer 20, the second transformer 50 can further provide a charging voltage for the converter 31 in the back-to-back converter group 30; in the case of parallel connection of the second transformer 50 and the first transformer 20, the current of the converter 31 in the back-to-back converter group 30 can be merged into the inverter circuit side, which can further play a role in energy compensation, harmonic control, etc. The third transformer 60 can be used to isolate the converter 31 in the back-to-back converter group 30 from the AC power grid, and at the same time realize power conversion by means of the third transformer 60. In the case of series connection of the third transformer 60 and the first transformer 20, the output voltage of the converter 31 in the back-to-back converter group 30 can be connected in series to the AC power grid, thereby playing a role in voltage compensation; in the case of parallel connection of the third transformer 60 and the first transformer 20, the output current of the converter 31 in the back-to-back converter group 30 can be merged into the AC power grid, thereby further playing a role in auxiliary energy sending.
[0035] Specifically, the parallel or series connection of the second transformer 50 and the first transformer 20 means that the second transformer 50 is in parallel or series connection with the three-phase AC line, and the same applies to the third transformer 60. The second transformer 50 is used to isolate the inverter circuit and the converter 31 in the back-to-back converter group 30, and at the same time realize power conversion by means of the second transformer 50. The types and connection modes of the second transformer 50 and the third transformer 60 can be the same or different. For example, the second transformer 50 and the third transformer 60 are both connected in series with the first transformer 20; the second transformer 50 and the third transformer 60 are both connected in parallel with the first transformer 20; one of the second transformer 50 and the third transformer 60 is connected in parallel with the first transformer 20, and the other is connected in series. In actual application, the selection of the parallel and series connection modes depends on the specific application requirements. The parallel connection is suitable for occasions where current capacity needs to be increased and system redundancy needs to be improved, while the series connection is suitable for scenarios where voltage needs to be boosted or voltage distribution needs to be realized in a high-voltage system.
[0036] In order to further provide stable current for the second transformer and the third transformer, as shown in the figure, the DC power receiving end further comprises a fourth transformer 70 and a fifth transformer 80, wherein the fourth transformer 70 is connected in parallel or in series with the second transformer 50, and the fifth transformer 80 is connected in parallel or in series with the third transformer 60. In the case of series connection of the fourth transformer 70 and the second transformer 50, the fourth transformer 70 can further provide a charging voltage for the converter 31 in the back-to-back converter group 30; in the case of parallel connection of the fourth transformer 70 and the second transformer 50, the current of the converter 31 in the back-to-back converter group 30 can be merged into the inverter circuit side, which can further play a role in energy compensation, harmonic control, etc. The fifth transformer 80 can be used to isolate the converter 31 in the back-to-back converter group 30 from the AC power grid, and at the same time realize power conversion by means of the fifth transformer 80. In the case of series connection of the fifth transformer 80 and the third transformer 60, the output voltage of the converter 31 in the back-to-back converter group 30 can be connected in series to the AC power grid, thereby playing a role in voltage compensation; in the case of parallel connection of the fifth transformer 80 and the third transformer 60, the output current of the converter 31 in the back-to-back converter group 30 can be merged into the AC power grid, thereby further playing a role in auxiliary energy sending. Figure 3As shown, the second transformer 50 of this application is connected in parallel with the first transformer 20, and the third transformer 60 is connected in parallel with the first transformer 20. Both converters 31 are first converters 311. The first converter 311 includes three phases, each phase including a first upper bridge arm 312 and a first lower bridge arm 313. Each of the first upper bridge arm 312 and the first lower bridge arm 313 is formed by cascading multiple first converter submodules. The first converter 311 also includes a first inductor module 314. The first inductor module 314 includes multiple first inductors. The first end of each of the first inductors is electrically connected to the connecting branch of the first upper bridge arm 312 and the first lower bridge arm 313, and the second end of each of the first inductors is used to connect to the AC power grid.
[0037] In some other embodiments, the first converter 311 described above may be a current source converter used to output current to the second transformer 50 and the third transformer 60 described above.
[0038] like Figure 4 As shown, the second transformer 50 is connected in series with the first transformer 20, and the third transformer 60 is connected in series with the first transformer 20. Both converters 31 are second converters 321, wherein each second converter 321 includes three phases, each phase including a second upper bridge arm 322 and a second lower bridge arm 323. Each second upper bridge arm 322 and the second lower bridge arm 323 is formed by cascading multiple second converter submodules. The second converter 321 also includes: a second inductor module 324, which includes multiple second inductors. The first end of each second inductor is electrically connected to the connecting branch of the second upper bridge arm 322 and the second lower bridge arm 323, and the second end of each second inductor is used to connect to the AC power grid; and a capacitor module 325, which includes multiple first capacitors. The first end of each first capacitor is electrically connected to the second end of each second inductor, and the second end of each first capacitor is electrically connected to... The above settings can provide a stable current for the second transformer 50 and the third transformer 60.
[0039] In some other embodiments, the second converter can be a voltage source converter for outputting voltage to the second transformer 50 and the third transformer 60.
[0040] In order to further provide a stable current to the second transformer, the second transformer includes a first primary winding and a first secondary winding. The second transformer is connected in parallel with the first transformer. The first primary winding is electrically connected to the second terminal of the inverter circuit, and the first secondary winding is electrically connected to the first terminal of the back-to-back converter group.
[0041] Specifically, when the second transformer is connected in parallel to the three-phase AC line, the first primary winding (i.e. the primary side) and the first secondary winding (i.e. the secondary side) are respectively connected to two ends of the same circuit.
[0042] In some other embodiments, the second transformer includes a first primary winding and a first secondary winding, the second transformer is connected in series with the first transformer, a first end of the first primary winding is electrically connected to the second end of the inverter circuit, a second end of the first primary winding is electrically connected to the first end of the first transformer, and the first secondary winding is electrically connected to the first end of the back-to-back converter group. The above arrangement can further provide a stable voltage for the second transformer.
[0043] Specifically, when the second transformer is connected in parallel to the three-phase AC line, the first primary winding (i.e. the primary side) and the first secondary winding (i.e. the secondary side) are respectively connected to two ends of the same circuit.
[0044] The third transformer includes a second primary winding and a second secondary winding, the third transformer is connected in parallel with the first transformer, the second primary winding is electrically connected to the second end of the first transformer, and the second secondary winding is electrically connected to the second end of the back-to-back converter group. The above arrangement can further provide a stable current for the third transformer.
[0045] Specifically, when the third transformer is connected in parallel to the three-phase AC line, the second primary winding (i.e. the primary side) and the second secondary winding (i.e. the secondary side) are respectively connected to two ends of the same circuit.
[0046] In some other embodiments, the third transformer is connected in series with the first transformer, a first end of the second primary winding is electrically connected to the second end of the first transformer, a second end of the second primary winding is used to connect to the AC power grid, and the second secondary winding is electrically connected to the second end of the back-to-back converter group. The above arrangement can further provide a stable voltage for the third transformer.
[0047] Specifically, when the third transformer is connected in parallel to the three-phase AC line, the second primary winding (i.e. the primary side) and the second secondary winding (i.e. the secondary side) are respectively connected to two ends of the same circuit.
[0048] In some other specific embodiments, the DC sides of the two converters are electrically connected, wherein the converters are voltage source converters or current source converters. The use of voltage source converters can improve control flexibility and further quickly respond to various power system requirements, and the use of current source converters can further reduce the load of system control and reduce costs.
[0049] The voltage source converter (VSC) can be a two-level voltage source converter, a three-level voltage source converter, a modular multilevel converter (MMC), a neutral point clamped multilevel converter (NPC) and a flying capacitor multilevel converter (FCMC). The two-level voltage source converter is composed of two switching devices and an anti-parallel diode in each bridge arm, which can generate two voltage levels. Compared with the two-level VSC, the three-level VSC has three switching states in each bridge arm, which can output three voltage levels, thereby reducing the harmonic of the output voltage and improving the efficiency. The MMC is a new type of VSC, which forms a multi-level output by connecting multiple sub-modules in series. Each sub-module contains a capacitor and two switching devices, which can provide higher voltage and current levels while reducing harmonics. The NPC is a multi-level VSC that forms a multi-level output by clamping the midpoint voltage. The FCMC uses flying capacitors to maintain the balance of the midpoint voltage and forms a multi-level output, which is particularly suitable for situations that require voltage balance control.
[0050] In some specific embodiments, the converter is a voltage source converter, and the converter includes three phases, each phase including two bridge arms. Each bridge arm is composed of MOSFET half-bridge sub-modules and thyristor-diode inverse resistance sub-modules that are alternately cascaded. The MOSFET half-bridge sub-modules can bear high-frequency (>5 kHz) PWM signals and reactive harmonic compensation. The thyristor-diode inverse resistance sub-modules can be triggered only in fault transient state, providing a surge through capacity of more than 50 kA / μs, forming a "transient composite valve", which can further improve the stability of the back-to-back converter group, thereby further improving the stability of the DC power receiving end.
[0051] The current source converter (CSC) can be a PWM current source converter, a thyristor-controlled current source converter, and a resonant current source converter (RCSC). The PWM current source converter uses PWM technology to control the current, and generally requires a large inductance on the DC side for filtering to maintain a constant current. The thyristor-controlled current source converter uses thyristors as switching devices, and the thyristors control the current output of the converter by controlling the firing angle. The RCSC uses resonance elements in the circuit to control the current by using the resonance principle, and is generally used in low-frequency and high-frequency inverter applications.
[0052] To further improve the rectification effect of the above-mentioned back-to-back converter group, as shown in Figure 5 The back-to-back converter group further includes a second capacitor 32, and the second capacitor 32 is connected in parallel with the two voltage source converters.
[0053] In some embodiments, the DC power receiving end further includes an energy storage device, the energy storage device is electrically connected to the second capacitor, and the second capacitor is a super capacitor. The super capacitor can provide instantaneous high-power support for the DC power receiving end, and the energy storage device can provide continuous energy support for the DC power receiving end to maintain long-time operation. By combining the hybrid energy storage mode of the super capacitor and the energy storage device, the energy density and power density of the DC power receiving end can be further considered.
[0054] In actual applications, the energy storage device can be a lithium ion battery energy storage device, a superconducting magnetic energy storage device, a flywheel energy storage device, a super capacitor energy storage device, and a hydrogen energy storage device. In the case of power loss of the entire station, that is, the AC bus voltage of the DC power receiving end is 0, or the frequency is lost, the connection between the back-to-back converter group and the AC power grid is disconnected, the energy storage device and the super capacitor are activated, and the converter operates in a constant voltage and constant frequency mode. After the super capacitor takes on the main power output and supports the voltage establishment, a small amplitude sweep signal is injected. After detecting the local load access and the voltage or frequency stabilization, the converter switches to active power control and reactive power control, and the reactive power support function is restored.
[0055] The second capacitor can be a super capacitor. In some embodiments, the capacitance of the second capacitor ranges from 0.5F to 1.5F.
[0056] The embodiments of the present application also provide a DC power transmission system, which includes a DC power transmission sending end and any one of the above-mentioned DC power transmission receiving ends.
[0057] In particular, the above-mentioned DC power transmission system can be one of a two-terminal DC power transmission system, a multi-terminal DC power transmission system, a light high-voltage DC power transmission system, a DC networking system, a hybrid DC power transmission system, a submarine DC power transmission system, a renewable energy-based DC power transmission system, and an urban DC power distribution network. The two-terminal DC power transmission system includes two converter stations, one for rectification (converting AC to DC) and the other for inversion (converting DC back to AC). The multi-terminal DC power transmission system allows the transmission and distribution of DC power among three or more converter stations, improving the flexibility and reliability of the power transmission network. The light high-voltage DC power transmission system uses voltage source converter (VSC) technology, which has advantages such as fast response, easy control, and bidirectional power transmission. The DC networking system connects multiple DC power transmission lines and converter stations through a DC grid, enabling networked transmission and management of power. The hybrid DC power transmission system combines line-commutated converters (LCC) based on thyristors and voltage source converters (VSC) based on fully controlled devices to leverage the advantages of both technologies, typically used to connect different types of AC grids or enhance system stability. The submarine DC power transmission system is used for underwater cable power transmission, as DC power has lower losses in cables than AC power, making it more economical and efficient for underwater power transmission. The renewable energy-based DC power transmission system can be combined with renewable energy generation systems such as wind power and solar power to achieve long-distance power transmission and flexible interconnection of power grids. In some large cities or areas with high power demand, urban DC power distribution networks can reduce power loss, improve power supply efficiency and reliability.
[0058] The technical features of the above-mentioned embodiments can be combined in any manner. To make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described, but as long as the combinations of the technical features do not contradict, they should be considered within the scope of the present disclosure.
[0059] It should also be noted that the terms "comprising", "including", or any other variant thereof are intended to cover non-exclusive inclusion, so that processes, products or devices including a series of elements not only include those elements, but also include other elements not explicitly listed or inherent to such processes, products or devices. Without more limitations, the element defined by the phrase "including a" does not exclude the presence of additional identical elements in the process, product or device including the element.
[0060] From the above description, it can be seen that the above-mentioned embodiments of the present application achieve the following technical effects:
[0061] 1) The direct current transmission receiving end of the application, the direct current transmission end comprises an inverter circuit, a first transformer and a back-to-back converter group, the back-to-back converter group comprises two converters connected in back-to-back series, the first end of the inverter circuit is used for connecting a direct current transmission line, the first end of the first transformer and the first end of the back-to-back converter group are respectively electrically connected with the second end of the inverter circuit, and the second end of the first transformer and the second end of the back-to-back converter group are respectively used for connecting an alternating current power grid. The scheme connects one back-to-back converter to the direct current transmission receiving end, one end of which is connected with the alternating current power grid and the other end of which is connected with the secondary side power grid of the direct current transmission receiving end. During an alternating current fault, the back-to-back converter can provide instantaneous voltage support, greatly reduce the possibility of commutation failure, enhance the robustness of the system, the back-to-back converter can compensate the reactive power demand of the converter in real time, participate in voltage regulation, and improve the stability of the direct current transmission receiving end system.
[0062] 2) The direct current transmission system of the application, comprising a direct current transmission sending end and any one of the above-mentioned direct current transmission receiving end. The direct current transmission end comprises an inverter circuit, a first transformer and a back-to-back converter group, the back-to-back converter group comprises two converters connected in back-to-back series, the first end of the inverter circuit is used for connecting a direct current transmission line, the first end of the first transformer and the first end of the back-to-back converter group are respectively electrically connected with the second end of the inverter circuit, and the second end of the first transformer and the second end of the back-to-back converter group are respectively used for connecting an alternating current power grid. The scheme connects one back-to-back converter to the direct current transmission receiving end, one end of which is connected with the alternating current power grid and the other end of which is connected with the secondary side power grid of the direct current transmission receiving end. During an alternating current fault, the back-to-back converter can provide instantaneous voltage support, greatly reduce the possibility of commutation failure, enhance the robustness of the system, the back-to-back converter can compensate the reactive power demand of the converter in real time, participate in voltage regulation, and improve the stability of the direct current transmission receiving end system, thereby further improving the stability of the direct current transmission system.
[0063] The above only describes the preferred embodiments of the application and is not intended to limit the application. Those skilled in the art can make various modifications and changes to the application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the application shall be included in the protection scope of the application.
Claims
1. A direct current power transmission receiving end, characterized in that The application relates to a direct-current power transmission system, which comprises an inverter circuit, a first transformer and a back-to-back converter group, the back-to-back converter group comprises two converters connected in back-to-back series, the first end of the inverter circuit is used for connecting a direct-current transmission line, the first end of the first transformer and the first end of the back-to-back converter group are electrically connected with the second end of the inverter circuit respectively, the second end of the first transformer and the second end of the back-to-back converter group are used for connecting an alternating-current power grid respectively, the two converters are electrically connected at the direct-current side, the alternating-current side of one of the converters is electrically connected with the inverter circuit, and the alternating-current side of the other converter is electrically connected with the alternating-current power grid. The direct-current power transmission receiving end further comprises a second transformer and a third transformer, wherein the second transformer is connected in parallel or series with the first transformer, and the third transformer is connected in parallel or series with the first transformer.
2. The direct current power transmission receiving end according to claim 1, characterized in that The second transformer is connected in parallel with the first transformer, the third transformer is connected in parallel with the first transformer, and the two converters are first converters, wherein the first converter comprises three phases, each phase comprises a first upper bridge arm and a first lower bridge arm, each first upper bridge arm and first lower bridge arm is cascaded by a plurality of first converter sub-modules, the first converter further comprises a first inductor module, the first inductor module comprises a plurality of first inductors, the first end of each first inductor is electrically connected with the connection branch of the first upper bridge arm and the first lower bridge arm, and the second end of each first inductor is used for connecting the alternating-current power grid.
3. The direct current power transmission receiving end according to claim 2, characterized in that The second transformer is connected in series with the first transformer, the third transformer is connected in series with the first transformer, and the two converters are second converters, wherein the second converter comprises three phases, each phase comprises a second upper bridge arm and a second lower bridge arm, each second upper bridge arm and second lower bridge arm is cascaded by a plurality of second converter sub-modules, the second converter further comprises:
4. The direct current power transmission receiving end according to claim 2, characterized in that, a second inductor module, the second inductor module comprises a plurality of second inductors, the first end of each second inductor is electrically connected with the connection branch of the second upper bridge arm and the second lower bridge arm, and the second end of each second inductor is used for connecting the alternating-current power grid; a capacitor module, the capacitor module comprises a plurality of first capacitors, the first end of each first capacitor is electrically connected with the second end of each second inductor, and the second end of each first capacitor is electrically connected. The second transformer comprises a first primary winding and a first secondary winding, 5. The direct current power transmission receiving end according to claim 2, characterized in that, The second transformer is connected in parallel with the first transformer, the first primary winding is electrically connected with the second end of the inverter circuit, and the first secondary winding is electrically connected with the first end of the back-to-back converter group; or The second transformer is connected in series with the first transformer, the first end of the first primary winding is electrically connected with the second end of the inverter circuit, the second end of the first primary winding is electrically connected with the first end of the first transformer, and the first secondary winding is electrically connected with the first end of the back-to-back converter group. The third transformer comprises a second primary winding and a second secondary winding, 6. The direct current power transmission receiving end according to claim 2, characterized in that, The third transformer is connected in parallel with the first transformer, the second primary winding is electrically connected with the second end of the first transformer, and the second secondary winding is electrically connected with the second end of the back-to-back converter group; or, The third transformer is connected in series with the first transformer, the first end of the second primary winding is electrically connected with the second end of the first transformer, the second end of the second primary winding is used for connecting the AC power grid, and the second secondary winding is electrically connected with the second end of the back-to-back converter group.
7. The direct current power transmission receiving end according to claim 1, characterized in that, The direct current sides of the two converters are electrically connected, wherein the converter is a voltage source converter or a current source converter.
8. The direct current power transmission receiving end according to claim 7, characterized in that, The back-to-back converter group further comprises a second capacitor, and the second capacitor is connected in parallel with the two voltage source converters respectively.
9. The direct current power receiving end according to any one of claims 1 to 8, characterized in that, The inversion circuit comprises at least one of a current source converter and a voltage source converter.
10. A direct current power transmission system, characterized by The DC power transmission sending end and the DC power transmission receiving end in any one of claims 1 to 9.