A network topology for ac reconstruction of a dc transmission receiving end

Abstract

The application discloses a network topology of AC power reconstruction at a receiving end of DC power transmission and belongs to the technical field of power generation and power equipment. The network topology comprises a DC / AC converter connected with a DC power transmission line and used for converting DC power inputted by the DC power transmission line into AC power with adjustable frequency, size and phase; and a synchronous motor-synchronous generator set, wherein the AC power outputted by the DC / AC converter is connected to a stator side of the synchronous motor, drives the synchronous motor and a synchronous generator coaxially connected with the synchronous motor to rotate, the DC / AC converter drives the synchronous motor-synchronous generator set to start from static to variable frequency, and after the synchronous motor-synchronous generator set is started, the constant frequency output of the DC / AC converter drives the synchronous motor-synchronous generator set to rotate at a constant speed, and the synchronous generator outputs constant frequency AC power to be connected to an AC power grid at the receiving end. The application fundamentally solves the problem of AC power stability reconstruction at the receiving end of the DC power transmission.

Description

Technical Field

[0001] This invention belongs to the field of DC transmission receiving-end AC power reconstruction grid and power equipment technology for various power sources such as wind and solar new energy power generation. More specifically, it relates to a grid topology for DC transmission receiving-end AC power reconstruction. Background Technology

[0002] With the large-scale development of new energy power generation such as wind power and photovoltaics, especially the development and utilization of abundant wind and solar resources in western, northwestern and southwestern regions of my country, DC power transmission plays a vital role in my country's new power system, especially in long-distance and large-capacity power transmission scenarios such as "West-to-East Power Transmission", and has become one of the main transmission methods for long-distance power transmission such as wind and solar power generation.

[0003] Currently, the widely adopted DC transmission architecture both domestically and internationally works as follows: At the sending end, various power sources, such as wind and solar power, are converted into DC power via power electronic converters and transmitted to the receiving end via DC transmission lines; at the receiving end, the DC power is inverted back into AC power by power electronic converters and integrated into the receiving end's AC power grid. The core feature of this architecture is that both the sending and receiving ends must be directly connected to the AC power grid via power electronic converters, and these power electronic converters directly face the AC power grid.

[0004] However, the aforementioned DC transmission architecture has significant technical shortcomings in practical applications. Because the power electronic converters at both the sending and receiving ends are connected in series along the power transmission path, directly facing the AC grid, this effectively isolates the key system stability characteristics and mutual support capabilities between the source (sending) and load (receiving) power equipment. These isolated system stability characteristics include, but are not limited to, the rotational inertia of the power equipment, the transient support capability against faults, and the ability to suppress system oscillations and damping—all core technical indicators closely related to system stability. This leads to a series of stability problems known in the industry as "power electronic power systems," such as insufficient system synchronous inertia, inadequate transient stability support capabilities, and frequent and insufficient suppression of system oscillations and harmonics. In severe cases, these problems may induce large-scale power outages.

[0005] In-depth analysis shows that the root cause of the above-mentioned stability problem can be attributed to the following two points: First, the proportion of traditional synchronous generator sets in the system has been continuously declining, leading to a corresponding weakening of the system's inherent stability support capabilities (including synchronous inertia, transient stability support capabilities, and oscillation and harmonic suppression capabilities). In fact, the introduction of a large number of power electronic converters is itself a significant cause of system oscillations and harmonic generation. This change constitutes the fundamental reason for the frequent occurrence of stability problems in the new power system and is also the most essential difference between it and the traditional power system.

[0006] Secondly, in new energy power transmission systems, the series connection of power electronic converters disconnects the synchronous inertia and stability support capabilities of the source (sending) and load (receiving) equipment in the transmission path, further weakening the system's stability support capability and increasing the risk of system failures or even sudden large-scale power outages.

[0007] It is important to note that new power systems primarily powered by wind and solar power face two core fundamental issues: system power balance and system stability. Although these two issues appear related, they are essentially independent. Solving the safety and stability problems of new energy power systems primarily powered by wind and solar power requires effectively addressing both of these core fundamental issues simultaneously.

[0008] Therefore, in view of the above-mentioned technical defects, this invention proposes a network topology for AC power reconstruction at the receiving end of DC transmission, which is particularly necessary to solve the problems of insufficient system synchronization inertia, lack of transient stability support capability, and frequent and insufficient suppression capability of system oscillations and harmonics in power systems. Summary of the Invention

[0009] To address the shortcomings and improvement needs of existing technologies, this invention provides a network topology for AC power reconstruction at the receiving end of DC transmission. Its purpose is to completely eliminate the problem of DC transmission receiving-end power electronic converters directly facing and connecting to the receiving-end AC grid. This fundamentally solves the problem of AC power stability during DC transmission receiving-end reconstruction in existing new power systems, avoiding AC grid stability issues caused by various faults in the receiving-end AC grid, as well as various fault impacts and potential damage or fault protection issues on numerous power electronic converters in DC transmission, especially the sending-end converter and the original receiving-end converter.

[0010] To achieve the above objectives, according to one aspect of the present invention, a network topology for AC power reconstruction at the receiving end of a DC transmission line is provided, comprising: DC / AC converter: Connected to a DC transmission line, it is used to convert the input DC power into AC power with adjustable frequency, magnitude, and phase. Synchronous motor-generator set: This includes a synchronous motor and a synchronous generator coaxially connected to it. The synchronous motor is connected between a DC / AC converter and the synchronous generator. The AC output of the DC / AC converter is connected to the stator side of the synchronous motor, driving the synchronous motor and the coaxially connected synchronous generator to rotate. The DC / AC converter drives the synchronous motor set to rotate. The DC / AC converter drives the synchronous motor-generator set to start from rest to rated speed via frequency conversion. After the synchronous motor-generator set has started, the constant frequency output of the DC / AC converter drives the synchronous motor-generator set to rotate synchronously at a constant speed. The synchronous generator outputs constant frequency AC power which is connected to the receiving end AC power grid. The magnitude of the DC voltage on the input side of the DC / AC converter matches the magnitude of the operating voltage on the stator side of the synchronous motor.

[0011] In summary, the above-described technical solutions conceived in this invention can achieve the following beneficial effects: (1) This invention fundamentally eliminates the stability problems of the DC transmission receiving-end AC system caused by "power electronic" and significantly improves the physical synchronous inertia of the receiving-end AC grid. The present invention adopts the technical solution of "DC / AC converter + synchronous motor - synchronous generator coaxial unit" to transmit DC power to the receiving end. The DC power transmitted to the receiving end is driven by a synchronous motor with constant frequency control to drive a synchronous generator set connected coaxially to generate AC power at a constant frequency, thereby realizing the reconstruction of the AC power at the receiving end of the DC transmission or its integration into the receiving-end AC grid. That is, the synchronous motor with constant frequency control rotates at a constant speed to drive the synchronous generator to generate constant frequency AC power, reconstructing the AC power at the receiving end or integrating it into the receiving-end AC grid. This is the traditional synchronous generator directly facing the receiving-end AC grid and directly connected to the receiving-end AC grid. This topology fundamentally eliminates the series of stability problems of the "power electronic power system" caused by the use of power electronic converters directly facing the receiving-end AC grid and directly connected to the receiving-end AC grid at the existing DC transmission receiving end, including but not limited to: reduced system synchronous inertia, insufficient transient support capability, easy occurrence of oscillations and harmonics and lack of suppression capability. Meanwhile, the coaxially connected synchronous motor unit structure can provide nearly twice the physical synchronous inertia of a synchronous motor of the same capacity. Its inertia level is superior to that of traditional thermal power units and hydropower units, which can effectively ensure the safe and stable operation of the receiving-end AC power grid.

[0012] (2) It possesses active hard support capability, fast response speed, and stronger transient stability and frequency and voltage stabilization capabilities. Even when DC transmission power fluctuates or the receiving-end system / equipment malfunctions, this invention can still drive and maintain the synchronous motor-synchronous generator set at constant speed and frequency through constant frequency output control of the DC / AC converter, ensuring the stability of the synchronous generator's output voltage and frequency, and achieving active hard support for the receiving-end AC grid frequency. Simultaneously, by adjusting the excitation of the synchronous generator, reactive power can be compensated, voltage stabilized, and system stability significantly improved. The synchronous motor's synchronous power angle characteristic, within its static stability range, can adapt to fluctuations in wind and solar power generation or DC transmission receiving-end power, effectively maintaining its own speed stability. In particular, the synchronous motor's dynamic self-response to such power fluctuations is an electromagnetic dynamic self-response process, with a response speed significantly faster than that of traditional thermal power units and hydropower units to changes in prime mover driving power. Similarly, the synchronous generator's synchronous power angle characteristic can also adapt to active power fluctuations within its static stability range, maintaining speed and frequency stability. By rationally controlling the rotor excitation current of the synchronous generator, the system voltage stability can be further supported and maintained. Therefore, the topology proposed in this invention has stronger transient stability support capabilities as well as frequency and voltage stabilization capabilities, and can fundamentally solve the problem of safe and stable operation of DC transmission receiving-end AC power reconstruction or integration into the receiving-end AC power grid.

[0013] (3) Simplify the system architecture and eliminate the risk of large-scale power outages from the source. After adopting the topology of this invention, the AC grid at the receiving end of the DC transmission line does not need to be configured or can be significantly reduced in terms of inertia and stability support equipment such as flywheel energy storage, SVG, and traditional synchronous condensers. While fundamentally solving the system stability problem, it can simplify the system equipment composition and complexity, reconstruct the theoretical and technical system of the new energy power system, and bring the system structure and stability back to the level of the traditional AC synchronous grid. As a result, it can avoid large-scale power outages caused by faults and protection actions of DC transmission power equipment or power electronic conversion equipment from the source. DC transmission power fluctuations and system transient stability problems can be dealt with relatively independently. This invention focuses on solving system stability problems (including insufficient synchronous inertia, insufficient fault stability support, insufficient system oscillation and harmonic suppression capabilities, etc.), realizing frequency and voltage stability of the AC grid at the receiving end of the DC transmission line, effectively ensuring the safe and stable operation of the system, and in particular, fundamentally avoiding sudden power outages similar to the "2025.04.28" European blackout.

[0014] (4) The technology is mature and reliable, the cost is low, it is easy to promote, and its industrial application value is significant. This invention relies on mature synchronous motor technology and reliable power electronics technology. Synchronous motor equipment has advantages such as mature technology, serialization, long service life (usually more than 30 years), high reliability, and lower cost than power electronic equipment of the same capacity. The DC / DC converter, DC / AC converter and other power electronic equipment used in this invention achieve electrical isolation between the power electronic converter and the AC grid at the receiving end through the synchronous motor. Any faults in the AC grid at the receiving end are directly faced by the synchronous generator and synchronous motor unit, and the relevant power electronic converters do not need to directly bear various faults and impacts of the AC grid. Therefore, the power electronic converters in the topology of this invention only need to be designed and manufactured according to normal working conditions, without the need to consider special functions and capabilities such as fault support or impact. The DC transmission lines and systems before the receiving end of the DC transmission are only responsible for transmitting the source power to the receiving end, and similarly do not need to consider the stability support and fault impact of AC grid faults at the receiving end. This invention can be directly applied to the reconstruction of AC power at the receiving end of newly built DC transmission lines or its integration into the receiving-end AC grid. It can also be used to upgrade existing DC transmission receiving-end AC grids, making it easy to implement and highly scalable. When combined with appropriate measures to mitigate fluctuations in wind and solar power generation or DC transmission power, it can fundamentally solve the problem of wind and solar power curtailment, promote the large-scale, efficient transmission and consumption of wind and solar power, and achieve a disruptive transformation in the stability reconstruction of the new energy power system.

[0015] (5) Flexible application scenarios. The DC transmission receiving-end AC power reconstruction network topology proposed in this invention can be used in any scenario where DC power transmission is used to transmit electrical energy to the receiving end and then perform AC power reconstruction or merge into the receiving end AC power grid.

[0016] (6) Compatible with multiple types of synchronous motors. This invention is applicable to various types of synchronous motors, such as electrically excited and permanent magnet synchronous motors and synchronous generators, as well as various motor combinations.

[0017] (7) Facilitates the construction of a multi-energy complementary AC power grid, minimizes the energy storage equipment configuration requirements, and improves the system's economy and reliability. This invention can construct an AC power grid at the DC transmission receiving end that includes wind power, photovoltaic power, thermal power, hydropower, nuclear power, energy storage, and other complementary energy sources, which is beneficial for achieving power balance in the AC power grid system. Utilizing the flexible and deep adjustment capabilities of thermal power, hydropower, and other power sources integrated into the same AC power grid, the system power fluctuation problem caused by the volatility and intermittency of wind and solar power can be effectively compensated and balanced. Based on the above technical advantages, the energy storage equipment (especially chemical energy storage equipment) configured in the AC power grid system can be reduced to a minimum capacity, which is beneficial for improving the overall system's economy and long-term reliable and stable operation capability, and fully utilizing wind and solar power resources while configuring as little energy storage capacity as possible. Attached Figure Description

[0018] Figure 1 The diagram shown is a network topology diagram for AC power reconstruction at the receiving end of a DC transmission line according to an embodiment of the present invention.

[0019] Figure 2 The diagram shown is a network topology diagram for AC power reconstruction at the receiving end of a DC transmission line, according to an embodiment of the present invention.

[0020] Figure 3 The diagram shown is a network topology diagram for AC power reconstruction at the receiving end of a DC transmission line according to an embodiment of the present invention.

[0021] Figure 4 The diagram shown is a network topology diagram for AC power reconstruction at the receiving end of a DC transmission line, according to an embodiment of the present invention. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0023] In this invention, the terms "first," "second," etc. (if present) in the invention and the accompanying drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence.

[0024] This invention reconstructs a highly stable AC power grid at the receiving end of a DC transmission line by rebuilding AC power based on a traditional synchronous generator. This AC power is then integrated and constructed from multiple sources, including thermal power, hydropower, wind power, photovoltaic power, nuclear power, wave power, tidal power, and energy storage equipment, creating a unified AC power grid with high stability. The solution of this invention enables the reconstructed AC power at the DC transmission receiving end to provide support for the stability of new power systems, even surpassing that of traditional thermal and hydropower units. Therefore, rebuilding AC power based on traditional synchronous generators at the DC transmission receiving end and integrating it into a robust, unified AC power grid is fundamentally necessary and urgent for fundamentally solving the stability problems of new power systems.

[0025] The DC transmission receiving-end AC power reconstruction network topology disclosed in this invention will be described below with specific embodiments. In this invention, the same type or function of individual units or components have the same name.

[0026] Example 1: This invention discloses a network topology for AC power reconstruction at the receiving end of a DC transmission line, such as... Figure 1 As shown, it includes: DC / AC converter: Connected to a DC transmission line, it is used to convert the input DC power into AC power with adjustable frequency, magnitude, and phase to drive the synchronous motor connected to it. The AC side of the DC / AC converter is connected to the stator side of the synchronous motor. Synchronous motor-generator set: This includes a synchronous motor and a synchronous generator coaxially connected to it. The synchronous motor is connected between a DC / AC converter and the synchronous generator. The AC power output from the DC / AC converter is connected to the stator side of the synchronous motor, driving the synchronous motor and the coaxially connected synchronous generator to rotate. The DC / AC converter drives the synchronous motor set to rotate, and drives the synchronous motor-generator set to start from rest at rated speed via frequency conversion. After the synchronous motor-generator set has started, the constant frequency output of the DC / AC converter drives the synchronous motor-generator set to rotate synchronously at a constant speed. The synchronous generator outputs constant frequency AC power to rebuild or feed into the receiving-end AC power grid. The magnitude of the DC voltage at the receiving end of the DC transmission line matches the magnitude of the operating voltage on the stator side of the DC / AC converter and the synchronous motor connected to it. This invention utilizes the adaptive characteristic of the synchronous motor's synchronous power angle to changes in active power. Within its static stability range, it can adapt to fluctuations in the active power of the DC transmission while maintaining a constant rotational speed, thereby ensuring the stability of the synchronous generator's generating frequency.

[0027] Furthermore, the AC power generated by the synchronous motor-synchronous generator set can be rebuilt or incorporated into the receiving-end AC grid. This can also form a receiving-end AC grid that integrates multiple energy sources, such as thermal power, hydropower, and even nuclear power, all based on AC power generated by synchronous generators. This can balance and compensate for the volatility and intermittency of wind and solar power generation or DC transmission power to a certain extent, reduce the configuration capacity of energy storage equipment, and further improve the safety, stability, reliability, and economy of the receiving-end AC grid.

[0028] Furthermore, in the network topology of DC transmission receiving-end AC reconstruction, the DC bus is located between the DC / AC converter and the DC transmission line. The input side of the DC / AC converter is connected to the DC bus, and the output side of the DC / AC converter is connected to the stator side of the synchronous motor.

[0029] In this invention, the synchronous motor includes: an electrically excited synchronous motor with an external DC excitation current applied to the rotor, or a permanent magnet synchronous motor, either of which is acceptable. When it is an electrically excited synchronous motor, it also includes a DC excitation controller that is matched with it and a synchronous generator that is coaxially connected to the synchronous motor, such as an electrically excited synchronous generator with an external DC excitation current applied to the rotor, or a permanent magnet synchronous generator. Generally, it is an electrically excited synchronous generator. When it is an electrically excited synchronous generator, it also includes a DC excitation controller that is matched with it. The AC power output by the synchronous generator is reconstructed or fed into the receiving-end AC power grid.

[0030] Example 2: In another embodiment, the network topology for DC transmission receiving-end AC power reconstruction disclosed in this invention is as follows: Figure 2 As shown, it includes: a DC bus, a DC / DC converter, a DC / AC converter, and a synchronous motor-synchronous generator set. Components with the same name have the same function and purpose in this invention, and will not be described in detail to avoid redundancy.

[0031] In one implementation, when the DC voltage level at the receiving end of the DC transmission line does not match the stator voltage level of the DC / AC converter and the synchronous motor driven by it, the receiving end network topology also includes a DC / DC converter. This DC / DC converter transforms the DC voltage level at the receiving end of the DC transmission line to a DC voltage level that matches the stator voltage level of the DC / AC converter and the synchronous motor driven by it. The input side or output side of the DC / DC converter is connected to the DC bus. In other words, the DC bus can be located on either the input side or the output side of the DC / DC converter without restriction.

[0032] Compared to the DC transmission receiving-end AC power reconstruction network topology in Example 1, the DC / DC converter is used to transform the DC voltage at the receiving end of the DC transmission line to a DC voltage level that matches the stator voltage level of the DC / AC converter and the synchronous motor driven by it. This application scenario is applicable when the DC voltage output from the DC transmission line does not match the stator voltage level of the DC / AC converter and the synchronous motor driven by it in the network topology of this invention, and it is necessary to transform it to a DC voltage level that matches the stator voltage level of the DC / AC converter and the synchronous motor driven by it. In the application scenario of Example 1, where the DC voltage output from the DC transmission line can match the stator voltage level of the DC / AC converter and the synchronous motor driven by it, it can be used directly without transformation by a DC / DC converter.

[0033] Optional, such as Figure 2As shown in the diagram, the dashed lines indicate the optional positions of the DC bus, meaning the DC bus can be connected to... Figure 2 It can be connected to either the input or output side of the DC / DC converter.

[0034] Furthermore, in another application scenario, when the magnitude of the DC voltage at the receiving end of the DC transmission line does not match the magnitude of the stator voltage of the connected DC / AC converter and the synchronous motor driven by it, the network topology for reconstructing the AC power at the receiving end of the DC transmission line includes multiple DC / AC converters operating in parallel between the DC / AC converter and the DC transmission line, as well as a first DC bus and a second DC bus. The multiple parallel-operating DC / AC converters are located between the first DC bus and the second DC bus. Each DC / AC converter... The input side is connected to the first DC bus, the output side of each DC / DC converter is connected to the second DC bus, the DC transmission line is connected to the first DC bus, the input side of the DC / AC converter is connected to the second DC bus, and multiple DC / DC converters operating in parallel are used to convert the DC voltage at the receiving end of the DC transmission line to a DC voltage level that matches the voltage level of the stator side of the DC / AC converter and the synchronous motor driven after it, and then feed it into the second DC bus, and then connect it to the stator side of the synchronous motor driven after it through the DC / AC converter.

[0035] Example 3: In another embodiment, the network topology for DC transmission receiving-end AC power reconstruction disclosed in this invention is as follows: Figure 3 As shown, it includes: a DC bus, a DC / DC converter, a DC / AC converter, a synchronous motor-synchronous generator set, and a synchronous motor auxiliary braking device, such as a braking resistor, for assisting in braking the synchronous motor-synchronous generator set, accelerating the braking or deceleration of the synchronous motor-synchronous generator set. The synchronous motor auxiliary braking device is connected to the stator side of the synchronous motor or the synchronous motor auxiliary braking device is connected to the stator side of the synchronous generator.

[0036] Specifically, a grid topology for DC transmission receiving-end AC power reconstruction also includes: a transfer switch, wherein the synchronous motor auxiliary braking device is connected to the stator side of the synchronous motor through the transfer switch, or the synchronous motor auxiliary braking device is connected to the stator side of the synchronous generator through the transfer switch.

[0037] The difference between Example 3 and Example 2 is that, optionally, a synchronous motor auxiliary braking device, such as a braking resistor or other braking device, can be connected via a transfer switch on the stator side of the synchronous motor in the synchronous motor-synchronous generator set or on the stator side of the synchronous generator. This allows for auxiliary braking of the synchronous motor-synchronous generator set when necessary, accelerating the braking or deceleration of the synchronous motor set. Apart from this, the other components, their functions, working processes, and operating characteristics are the same as in Example 2.

[0038] Example 4: In another embodiment, the network topology for DC transmission receiving-end AC power reconstruction disclosed in this invention is as follows: Figure 4 As shown.

[0039] like Figure 4 As shown, the network topology for the AC power reconstruction at the receiving end of the DC transmission line includes: DC transmission line, DC bus, DC / AC converter, synchronous motor-synchronous generator set, and synchronous motor auxiliary braking device.

[0040] The difference between Example 4 and Example 1 is that, optionally, a synchronous motor auxiliary braking device, such as a braking resistor or other braking device, can be connected via a transfer switch on the stator side of the synchronous motor in the synchronous motor-synchronous generator set or on the stator side of the synchronous generator. This allows for auxiliary braking of the synchronous motor-synchronous generator set when necessary, accelerating the braking or deceleration of the synchronous motor set. Apart from this, the other components, their functions, working processes, and operating characteristics are the same as in Example 1.

[0041] Optionally, the sending end of the DC power transmission disclosed in this invention is connected to various power sources at the sending end, including but not limited to electricity generated by various energy sources such as wind power, photovoltaic power, thermal power, hydropower, nuclear power, wave power, and tidal power.

[0042] It should be noted that in the DC transmission receiving-end AC power reconstruction network topology disclosed in this invention, the synchronous motor-synchronous generator set is driven by a DC / AC converter with constant frequency output, thus achieving constant speed synchronous rotation of the synchronous motor-synchronous generator set and ensuring constant frequency AC power output from the synchronous generator. Due to the adaptive characteristics of the synchronous motor and synchronous generator's synchronous power angle to power changes, within its static stability range, it can adapt to the fluctuations in wind and solar power generation and DC transmission power, while still maintaining a constant speed of the synchronous motor and a stable frequency of AC power output from the synchronous generator coaxially driven by the synchronous motor. Combined with the regulation of the rotor excitation current of the synchronous motor and synchronous generator (parallel excitation synchronous motor), it not only ensures the stability of the synchronous motor-synchronous generator set operation, but also ensures the appropriate overload capacity of the synchronous motor and the reliable frequency and voltage stabilization output capability of the synchronous generator. Due to the large inertia of the synchronous motor-synchronous generator set (nearly twice the rotational inertia of a synchronous generator of the same capacity), the electromagnetic dynamic rapid response characteristics of the synchronous motor as the prime mover of the synchronous generator, and the strong transient stability support capability and suppression and damping capability of the synchronous generator for system oscillations and harmonics, the grid topology of this DC transmission receiving-end AC power reconstruction has many outstanding advantages in terms of system stability support capability as described above. It can fundamentally overcome a series of prominent stability problems in the current DC transmission receiving-end "power electronic" AC power reconstruction, and can significantly improve the safety and reliability of DC transmission operation before the receiving end. In particular, by using the synchronous motor-synchronous generator set, it completely isolates the DC transmission from various faults and the series of stability problems caused by them in the receiving-end AC grid. This can greatly simplify the development difficulty of the power electronic converter used in this DC transmission and receiving-end AC grid reconstruction, significantly improve its operational safety, reliability and lifespan, and reduce its manufacturing cost. It is no longer necessary to consider the prominent problems of dealing with the impact and stability support capability caused by various faults in the receiving-end AC grid.

[0043] This invention applies to the network topology embodiments of DC transmission receiving-end AC power reconstruction or integration into the receiving-end AC power grid. In each diagram, corresponding to the DC / DC converter and DC / AC converter in the network system, this represents the topological function within the block diagram. In actual manufacturing and application, each block diagram can be an independent unit or a combination of each other into a single unit.

[0044] This invention applies to a set of generator systems formed by "DC / AC converter → synchronous motor → synchronous generator set" in the network topology embodiments of DC transmission receiving-end AC power reconstruction or merging into the receiving-end AC power grid. Depending on the transmission capacity of the DC transmission line, it can be flexibly configured as one or several sets of such generator systems in parallel. The capacities of the parallel generator systems can be the same or different. The DC / DC converters that are optionally connected in front of them can also be flexibly configured as one or several sets in parallel. The capacities of the parallel sets can be the same or different.

[0045] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A network topology for AC power reconstruction at the receiving end of a DC transmission line, characterized in that, include: DC / AC converter: Connected to a DC transmission line, it is used to convert the input DC power into AC power with adjustable frequency, magnitude, and phase. Synchronous motor-generator set: This includes a synchronous motor and a synchronous generator coaxially connected to it. The synchronous motor is connected between a DC / AC converter and the synchronous generator. The AC power output from the DC / AC converter is connected to the stator side of the synchronous motor. The AC power drives the synchronous motor and the synchronous generator coaxially connected to it to rotate. The DC / AC converter drives the synchronous motor set to rotate. The DC / AC converter drives the synchronous motor-generator set to start from rest to rated speed via frequency conversion. After the synchronous motor-generator set has started, the constant frequency output of the DC / AC converter drives the synchronous motor-generator set to rotate synchronously at a constant speed. The synchronous generator outputs constant frequency AC power which is connected to the receiving end AC power grid. The magnitude of the DC voltage on the input side of the DC / AC converter is matched with the magnitude of the operating voltage on the stator side of the synchronous motor connected to it.

2. The network topology for DC transmission receiving-end AC power reconstruction according to claim 1, characterized in that, The DC / AC converter is connected to the DC transmission line via the DC bus.

3. The network topology for DC transmission receiving-end AC power reconstruction according to claim 1, characterized in that, It also includes a DC / DC converter, which converts the DC voltage at the receiving end of the DC transmission to a DC voltage level that matches the stator voltage level of the DC / AC converter connected to it and the synchronous motor driven by it.

4. The network topology for DC transmission receiving-end AC power reconstruction according to claim 3, characterized in that, The input side of the DC / DC converter is connected to the DC bus connected to the DC transmission line, and the output side of the DC / DC converter is connected to the input side of the DC / AC converter.

5. The network topology for DC transmission receiving-end AC power reconstruction according to claim 3, characterized in that, The input side of the DC / DC converter is connected to the DC transmission line, the output side of the DC / DC converter is connected to the DC bus, and the input side of the DC / AC converter is connected to the DC bus.

6. The network topology for DC transmission receiving-end AC power reconstruction according to claim 1, characterized in that, It also includes multiple DC / DC converters, which operate in parallel to convert the DC voltage at the receiving end of the DC transmission line to a DC voltage level that matches the stator voltage level of the DC / AC converters connected to it and the synchronous motors driven by them. The input side of each DC / DC converter is connected to a first DC bus, and the output side of each DC / DC converter is connected to a second DC bus. The first DC bus is connected to the DC transmission line, and the second DC bus is connected to the input side of the DC / AC converter.

7. The network topology for DC transmission receiving-end AC power reconstruction according to claim 1, characterized in that, It also includes a synchronous motor auxiliary braking device, which includes a braking resistor for assisting in braking the synchronous motor-synchronous generator set, accelerating the braking or deceleration of the synchronous motor-synchronous generator set. The synchronous motor auxiliary braking device is connected to the stator side of the synchronous motor or the synchronous motor auxiliary braking device is connected to the stator side of the synchronous generator.

8. The network topology for AC power reconstruction at the receiving end of a DC transmission line according to claim 1, characterized in that, It also includes a transfer switch, through which the synchronous motor auxiliary braking device is connected to the stator side of the synchronous motor, or through which the synchronous motor auxiliary braking device is connected to the stator side of the synchronous generator.

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