A direct current power distribution system applied to a nuclear power plant

Abstract

The application belongs to the technical field of power distribution in nuclear power plants, and particularly relates to a direct current power distribution system applied to a nuclear power plant, comprising: at least two direct current topology power distribution lines for connecting different off-site high-voltage alternating current power sources, wherein the direct current topology power distribution lines comprise a common rectifier and two sub power distribution lines. Each of the two sub power distribution lines is arranged with a first power distribution voltage direct current bus, a second power distribution voltage direct current bus, two third power distribution voltage direct current buses, and a third power distribution voltage backup direct current bus, and the first and second third power distribution voltage direct current buses are used to provide third power distribution voltage direct current for the on-site load and third power distribution voltage alternating current through an inverter; one end of the rectifier is used to connect the off-site high-voltage alternating current power source, and the other end is connected to the two first power distribution voltage direct current buses respectively.

Description

Technical Field

[0001] This invention belongs to the field of power distribution technology in nuclear power plants, and specifically relates to a DC power distribution system applied in nuclear power plants. Background Technology

[0002] In existing small nuclear power plants, the power distribution system mostly uses traditional AC power distribution systems. However, AC power distribution systems also have some drawbacks, such as high line losses, numerous power supply access restrictions (such as phase and frequency), and the risk of common-cause faults. These problems not only result in poor power quality of AC power distribution systems, but also make it difficult to directly match with various types of load equipment, making them unsuitable for the stable operation of small nuclear power plants. Summary of the Invention

[0003] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide a brand-new DC power distribution system. Through specific analysis and research on the load characteristics of small nuclear power plants, the power distribution system structure is simplified and the reliability and stability of power supply within the plant are enhanced while ensuring the safety and stable operation of the nuclear power unit and its supporting processes.

[0004] This invention provides a DC power distribution system for a nuclear power plant, comprising: at least two DC topology distribution lines for connecting to different external high-voltage AC power sources; each DC topology distribution line includes a shared rectifier and two sub-distribution lines; wherein each sub-distribution line is equipped with a first distribution voltage DC bus, a second distribution voltage DC bus, two third distribution voltage DC buses, and a spare third distribution voltage DC bus; one end of the rectifier is used to connect to the external high-voltage AC power source, and the other end is respectively connected to the two first distribution voltage DC buses; the first distribution voltage DC bus is connected to the same sub-distribution line via a DC / DC converter. The DC bus of the second distribution voltage in the power distribution line is connected; the DC bus of the second distribution voltage is connected to the first DC bus of the third distribution voltage in the same sub-distribution line through a DC / DC converter; the DC bus of the second distribution voltage is also connected to the second DC bus of the third distribution voltage in the same sub-distribution line through a DC / DC converter; the standby DC bus of the third distribution voltage is connected to the first DC bus and the second DC bus of the third distribution voltage in the same sub-distribution line respectively; the first DC bus and the second DC bus of the third distribution voltage are used to provide DC power of the third distribution voltage to the loads in the plant, and to provide AC power of the third distribution voltage through an inverter.

[0005] In one embodiment of the present invention, it further includes: a power switching device, used to connect the rectifier of the DC topology distribution line to the external high-voltage AC power supply of another DC topology distribution line when the external high-voltage AC power supply of any DC topology distribution line fails.

[0006] In one embodiment of the present invention, the DC bus of the first distribution voltage is also connected to the DC bus of the first distribution voltage of a sub-distribution line in another DC topology distribution line through a DC tie circuit breaker.

[0007] In one embodiment of the present invention, the DC topology distribution line includes a DC bus with a first distribution voltage and a redundant DC bus; wherein, the DC bus with the first distribution voltage is connected to the DC bus with the first distribution voltage in another DC topology distribution line through a DC tie circuit breaker; the redundant DC bus with the first distribution voltage is connected to the redundant DC bus with the first distribution voltage in another DC topology distribution line through a DC tie circuit breaker.

[0008] In one embodiment of the present invention, the DC bus of the first distribution voltage adopts a bipolar DC topology to provide the plant load with the first distribution voltage and half of the first distribution voltage DC power; the DC bus of the second distribution voltage adopts a bipolar DC topology to provide the plant load with the second distribution voltage and half of the second distribution voltage DC power.

[0009] In one embodiment of the present invention, the DC bus of the first distribution voltage also provides DC power of the fourth distribution voltage to the plant load through a DC / DC converter.

[0010] In one embodiment of the present invention, the DC bus of the first distribution voltage is also connected to the standby DC bus of the third distribution voltage in the same sub-distribution line via a DC / DC converter.

[0011] In one embodiment of the present invention, the DC bus of the second distribution voltage is also used to connect to a distributed energy system and / or an energy storage system.

[0012] In one embodiment of the present invention, the first DC bus of the third distribution voltage serves as a safety-grade power supply output, and the second DC bus of the third distribution voltage serves as a non-safety-grade power supply output; wherein, the first DC bus of the third distribution voltage is used to provide DC power of the third distribution voltage to the loads within the plant, and to provide AC power of the third distribution voltage through an inverter; the second DC bus of the third distribution voltage is only used to provide DC power of the third distribution voltage to the loads within the plant.

[0013] In one embodiment of the present invention, both the first DC bus and the second DC bus of the third power distribution voltage are connected to a backup power supply.

[0014] The beneficial effects of this invention are as follows: This invention adopts a global DC power distribution design, and for the first time applies the DC power distribution concept across the entire range of a small nuclear power plant. Except for retaining only the external high-voltage AC power input and the AC power supply for the plant's safety-grade UPS loads, all other power distribution uses DC power distribution technology, ensuring reliable and efficient power transmission and stable system operation. Furthermore, the DC power distribution design reduces the need for large-capacity power transformers in small nuclear power plants, saving equipment costs and floor space.

[0015] This invention simplifies the power switching scheme. By switching the power supply on the DC bus side of the first distribution voltage, the phase difference problem during AC system residual voltage switching can be avoided. Phase determination is not required, and the connection of another power supply can be completed quickly.

[0016] Meanwhile, the present invention also simplifies the power transmission and conversion process. For the original DC power load, it is directly powered by the DC bus without the need for a rectifier. Some loads that are essentially DC power are directly powered by the DC bus, eliminating the AC / DC / AC / DC conversion process in the power distribution path.

[0017] The present invention also provides an interface design for distributed energy systems and energy storage systems. By designing an interface for distributed energy systems and energy storage systems on the DC bus side of the second distribution voltage, the comprehensive utilization of distributed energy is realized, and the continuous power supply capability of small nuclear power plants under design basis accident and design extended operating conditions is improved. Attached Figure Description

[0018] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application. It is obvious that the drawings described below are merely some embodiments of this application, and those skilled in the art can obtain other drawings based on these drawings without any inventive effort.

[0019] Figure 1 A schematic diagram of the circuit topology of a traditional small nuclear power plant's AC power distribution system;

[0020] Figure 2 This is a schematic diagram of the power distribution path for a traditional DC load.

[0021] Figure 3 This is a schematic diagram of the power distribution path for a traditional UPS load.

[0022] Figure 4 This is a schematic diagram of a DC power distribution system applied to a nuclear power plant, provided in one embodiment of the present invention.

[0023] Figure 5This is a schematic diagram of the line topology of a DC power distribution system applied to a nuclear power plant, provided in one embodiment of the present invention. Detailed Implementation

[0024] To facilitate understanding of this application, a more complete description will be provided below with reference to the accompanying drawings, which illustrate embodiments of the present application. However, the present application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that the disclosure of this application will be thorough and complete.

[0025] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0026] It is understood that the terms "first," "second," etc., used herein may be used to describe various elements, but these elements are not limited by these terms. These terms are only used to distinguish one element from another. For example, without departing from the scope of this application, a first resistor may be referred to as a second resistor, and similarly, a second resistor may be referred to as a first resistor. Both the first resistor and the second resistor are resistors, but they are not the same resistor.

[0027] It is understood that the term "connection" in the following embodiments should be understood as "electrical connection," "communication connection," etc., if the connected circuits, modules, units, etc., have electrical signal or data transmission with each other.

[0028] It is understandable that "at least one" refers to one or more, and "multiple" refers to two or more. "At least a part of an element" refers to part or all of an element.

[0029] When used herein, the singular forms of “a,” “an,” and “the” may also include the plural forms unless the context clearly indicates otherwise. It should also be understood that the terms “comprising / including” or “having,” etc., specify the presence of the stated features, wholes, steps, operations, components, parts, or combinations thereof, but do not preclude the possibility of the presence or addition of one or more other features, wholes, steps, operations, components, parts, or combinations thereof. Meanwhile, the term “and / or” as used in this specification includes any and all combinations of the associated listed items.

[0030] First, to facilitate a better understanding of the technical solutions provided in this application by those skilled in the art, the technical background of this application will now be further explained.

[0031] The electrical systems of traditional small nuclear power plants generally include an external power system connected to the power grid and an internal power system. The internal power system is further divided into three categories: normal AC plant auxiliary power system, backup AC plant auxiliary power system, and DC and AC uninterruptible power supply systems.

[0032] In the aforementioned power systems, apart from the safety-grade DC system designed to ensure the safe, stable, and controllable operation of the nuclear reactor and post-accident monitoring and handling, and the non-safety-grade DC system designed to power important process control systems and instruments that are not related to safety, the remaining power systems are all AC systems.

[0033] Therefore, the electrical system of a nuclear power plant generally adopts a radial power supply network, which provides multi-level and diversified power through external power sources, generators, diesel generator sets, and batteries, supplemented by traditional power switching technology, to meet the power needs of various processes and instrumentation and control systems in the nuclear power plant.

[0034] In practical applications, the power distribution lines of the electrical system in a traditional small nuclear power plant can be found in [reference needed]. Figure 1 As shown, this system can switch the power distribution line via a power switching device on the 35kV side when one 35kV power source is unavailable, allowing another 35kV power source to continue operating the four 10kV busbars via two main transformers. Therefore, the two main transformers of this system need to have sufficient capacity to operate all four 10kV busbars after a failure of one main transformer or two outgoing lines of that main transformer.

[0035] Correspondingly, since the above-mentioned power distribution lines use AC power distribution, they have the following shortcomings:

[0036] First, power switching is complex and carries the risk of failure, potentially even leading to reactor shutdown. To ensure the plant power system meets the N-1 reliability requirement, Figure 1 The power distribution line shown is designed with two-stage power switching: 35kV side power switching and 10kV side power switching. This power switching requires collecting voltage, current, and status data from relevant lines, buses, and switching devices, combined with factors such as monitoring system interlocking and control logic, to initiate the switching. Furthermore, due to phase differences in AC systems, the switching device must determine phase compatibility before synchronous closing can be achieved. These issues may lead to power switching failure. If the plant power supply cannot be restored within the specified time, it will cause reactor shutdown, thus affecting the stable operation of the nuclear power plant.

[0037] Secondly, line losses are significant, resulting in reactive power loss. Compared to DC power distribution, AC cables suffer from the skin effect, leading to higher resistance losses compared to DC cables. Furthermore, AC cable insulation also experiences dielectric and magnetic induction losses. In addition, traditional AC transformers and asynchronous motors consume substantial reactive power, reducing system transmission capacity, increasing power losses, and impacting transmission efficiency. Therefore, dedicated reactive power compensation devices are necessary.

[0038] Third, the numerous power transmission and conversion stages increase power loss and negatively impact power supply reliability. Small nuclear power plants contain a large number of DC loads, particularly non-safety-grade DC equipment in instrumentation and control systems. Traditional power distribution methods typically require AC rectification to convert AC to DC power, such as... Figure 2 As shown. For loads requiring an AC uninterruptible power supply (UPS), it is also necessary to rectify the AC power to DC power, and then invert the DC power back to AC power for supply, such as... Figure 3 As shown, the power supply path for the aforementioned load has numerous switching points and potential failure points, which hinders power supply reliability and increases energy loss due to the switching equipment.

[0039] Fourth, AC power grids are not conducive to the direct integration of distributed renewable energy sources. Small nuclear power plants, due to their flexibility, can typically be coupled with distributed clean energy systems. However, typical energy storage systems (ESS) and photovoltaic power generation systems generally require inverters to convert electrical energy into AC before they can be connected to the grid. Figure 1 AC power distribution system in China.

[0040] Fifth, large-capacity transformers require additional land, such as Figure 1 The two transformer areas shown require an additional 200m² of land area.

[0041] Therefore, this application designs a novel DC power distribution system, aiming to solve the problems of complex power switching and high risk of power failure and reactor shutdown, numerous power transmission and conversion links, high power transmission line losses, and the convenience of distributed new energy access.

[0042] Example 1

[0043] Please see Figure 4 , 5As shown, a DC power distribution system for nuclear power plants adopts a completely new line topology. While ensuring the safe and stable operation of the nuclear reactor safety system and supporting process systems, the power distribution system structure is simplified. Specifically, it includes at least two DC topology power distribution lines 10, which can be applied to small nuclear power plants (dual-reactor nuclear power plants) with one or two nuclear power units. The number of DC topology power distribution lines 10 can also be added according to the number of nuclear power units in the plant, and it is not limited to dual-reactor DC power distribution topology design.

[0044] The two DC topology distribution lines 10 are used to introduce two independent external high-voltage AC power supplies, such as... Figure 5 As shown, it is equipped with two high-voltage AC busbars 9AHA and 9AHB, and adopts a single busbar segmented connection. Each busbar segment connects to an external high-voltage AC power supply line and a DC topology distribution line 10.

[0045] In addition, the two high-voltage AC busbars are connected to the DC topology distribution line 10 through a power switching device, thereby ensuring that the two DC topology distribution lines 10 can be powered normally when any external high-voltage AC power supply fails or becomes unavailable.

[0046] Specifically, in practical applications, when the two external high-voltage AC power supplies are operating normally, the two high-voltage AC busbars 9AHA and 9AHB and the corresponding power switching devices operate simultaneously. If one external high-voltage AC power supply fails or becomes unavailable, the power switching device will automatically connect the DC topology distribution line 10 of that line to the other external high-voltage AC power supply to ensure that the DC topology distribution line 10 of that line is uninterrupted.

[0047] It should be noted that each DC topology distribution line 10 consists of a rectifier 11 and two sub-distribution lines 12. The two sub-distribution lines 12 share the same rectifier. One end of the rectifier 11 is connected to an external high-voltage AC power supply via a high-voltage AC bus, and the other end is connected to the two sub-distribution lines 12.

[0048] Considering the existence of the power switching device, a modular multilevel bidirectional converter (MMC) is used as the rectifier 11 in this embodiment. It can convert the AC power from the external high-voltage AC power supply into DC power and distribute it to the two sub-distribution lines 12. It can also automatically switch to another external high-voltage AC power supply when the connected external high-voltage AC power supply fails or becomes unavailable. There is no need to configure two devices, the power switching device and the rectifier, thereby reducing the footprint and equipment purchase cost.

[0049] For details on the connection methods between the two MMCs and the two external high-voltage AC power supplies, please refer to [link / reference needed]. Figure 5As shown, no further details will be provided. Modifications and refinements made by those skilled in the art to the embodiments of the present invention without departing from the spirit of the present invention still fall within the scope of the invention application patent.

[0050] Therefore, considering both reliability and economy, the traditional AC power switching method is retained between the external high-voltage AC power system and the internal power distribution lines, employing a double-ended ring external power supply network design. However, the external high-voltage AC power system no longer requires a transformer, significantly reducing the project's footprint.

[0051] Furthermore, each sub-distribution line 12 is equipped with DC busbars of different distribution voltages to ensure power output at multiple voltage levels. Specifically, it includes a DC busbar with a first distribution voltage, a DC busbar with a second distribution voltage, two DC busbars with a third distribution voltage, and a spare DC busbar with a third distribution voltage.

[0052] It should be noted that this embodiment mainly targets the power distribution lines within a small nuclear power plant. The first, second, and third power distribution voltages are exemplified by ±10kV, ±750V, and ±220V, respectively. However, this is not intended to limit the applicable scenarios of this application. It is also compatible with other multi-voltage-level nuclear power plant power distribution scenarios. The first, second, and third power distribution voltages can be freely configured without any limitation. Modifications and refinements made by those skilled in the art to the embodiments of this invention without departing from the spirit of this invention still fall within the scope of the invention application patent of this invention.

[0053] Specifically, such as Figure 5 As shown, the single-line DC topology distribution line 10 includes two ±10kV DC bus sections to construct the ±10kV DC distribution areas of the two sub-distribution lines 12. The two DC topology distribution lines 10 include four ±10kV DC bus sections: 9DHA, 9DHB, 9DHC, and 9DHD. Specifically, 9DHA and 9DHC belong to the two ±10kV DC bus sections of the left-hand single-line DC topology distribution line 10; one is in a normal arrangement, and the other is redundant, thus constructing two redundant ±10kV DC distribution areas. Similarly, 9DHB and 9DHD belong to the two ±10kV DC bus sections of the right-hand single-line DC topology distribution line 10; again, one is in a normal arrangement, and the other is redundant.

[0054] Furthermore, a DC tie circuit breaker is installed between 9DHA and 9DHB, and between 9DHC and 9DHD. This means that the ±10kV DC busbars conventionally arranged in one DC topology distribution line 10 are connected to the ±10kV DC busbars conventionally arranged in another DC topology distribution line 10 via DC tie circuit breakers. The redundant ±10kV DC busbars in the two DC topology distribution lines 10 are also connected via DC tie circuit breakers. This ensures that if any ±10kV DC busbar fails, the incoming power supply (MMC) of the other ±10kV DC busbar can be used to power the current sub-distribution line 12, ensuring that all four sub-distribution lines 12 can operate normally. In practical applications, when the ±10kV DC distribution area is operating normally, all four ±10kV DC busbars operate simultaneously, and all DC tie circuit breakers are open. If a busbar fault occurs or its incoming power supply is unavailable, the system will switch to another MMC with four ±10kV DC busbars via a DC tie circuit breaker.

[0055] Of course, it is also possible to connect the ±10kV DC bus conventionally arranged in one DC topology distribution line 10 with the ±10kV DC bus redundantly arranged in another DC topology distribution line 10 through a DC tie circuit breaker, and there are no restrictions on this.

[0056] In addition, the ±10kV DC bus adopts a bipolar DC topology, which can provide two voltages, 10kV and 20kV, making it easier to reduce the power loss of the power supply circuit for high-power electrical equipment of different power levels, reduce the cable selection specifications, and save investment.

[0057] For equipment that cannot be converted to operate on DC power, an inverter can be configured additionally.

[0058] Therefore, the four ±10kV DC bus sections can supply the high-power loads required for the normal operation of the two nuclear power reactors within the plant, as well as the downstream bidirectional DC / DC converters. In one specific embodiment, the ±10kV DC bus can directly provide medium-voltage DC loads, or the voltage output can be adjusted via the DC / DC converter to provide DC power at the fourth distribution voltage, supplying power for lighting or maintenance equipment within the plant.

[0059] One DC topology distribution line 10 also includes two ±750V DC bus sections to construct the ±750V DC distribution areas of the two sub-distribution lines 12. The two DC topology distribution lines 10 include four ±750V DC bus sections: 1DHA, 1DHB, 2DHB, and 2DHA. 1DHA and 1DHB belong to the two ±750V DC bus sections of the left-hand DC topology distribution line 10; one is in a normal arrangement, and the other is redundant, thus constructing two redundant ±750V DC distribution areas. 2DHB and 2DHA belong to the two ±750V DC bus sections of the right-hand DC topology distribution line 10; similarly, one is in a normal arrangement, and the other is redundant.

[0060] Each ±750V DC bus is connected to a corresponding ±10kV DC bus via a bidirectional DC / DC converter, serving as the power supply for the ±750V DC bus.

[0061] It should be noted that this DC power distribution area takes into account high-power electrical equipment such as pumps, valves, and fans with rated voltage below 500V, and also considers the convenience of energy storage and distributed energy access.

[0062] In practical applications, multiple load centers can be set up according to the power load distribution of a small nuclear power plant to supply power to process, instrumentation and control, lighting, and maintenance equipment within the plant. For equipment that cannot be converted to DC operation, additional inverters can be configured. Load centers located on the nuclear island can be configured with corresponding independent power supply sequences based on the safety level system configuration of the small reactor; load centers located near distributed energy systems can be equipped with distributed energy or energy storage system interfaces to connect them to the ±750V integrated DC system.

[0063] Understandably, ESS or distributed energy systems can also serve as one of the backup power sources for small nuclear power plants, adding an extra means of power supply and effectively improving the ability to provide continuous power supply under design-baseline accidents and design-extended operating conditions.

[0064] In addition, the ±750V DC bus also adopts a bipolar DC topology, which can provide two voltages, 750V and 1500V, to facilitate the use of electrical equipment with different power levels. This will not be described in detail.

[0065] One DC topology distribution line 10 also includes four ±220V DC bus sections to construct the ±220V DC distribution areas of the two sub-distribution lines 12. Each sub-distribution line 12 includes two ±220V DC distribution areas: one is a safety-grade ±220V DC distribution area, and the other is a non-safety-grade ±220V DC distribution area. Accordingly, one DC topology distribution line 10 can provide four power supply channels for the nuclear power unit reactor.

[0066] Each ±220V DC bus is equipped with a DC / DC converter, a battery bank, and an inverter. Correspondingly, the ±750V DC bus provides the first DC power supply through the DC / DC converter, the ±220V backup DC bus provides the second DC power supply, and the battery bank provides the third DC power supply.

[0067] It should be added that each of the two ±220V DC busbars has an additional ±220V backup DC busbar to provide backup power for lighting, ventilation, DC and UPS equipment that need to operate under LOOP (loss of external AC power) conditions.

[0068] Specifically, the ±220V backup DC bus is connected to two DC power sources: one is connected to the ±10kV DC bus of the current sub-distribution line 12 via a bidirectional DC / DC converter, and the other is connected to a backup power source, such as a diesel generator set. Correspondingly, when the sub-distribution line 12 is operating normally, it is powered by the ±10kV DC bus through the DC / DC converter. Under LOOP conditions, the backup power source (diesel generator set) automatically starts to supply power to the ±220V DC bus.

[0069] In response, under LOOP conditions, if the ±220V DC bus loses its first DC power supply and the normal power supply of the ±220V backup DC bus is also lost, the backup power supply (diesel generator set) of the ±220V backup DC bus can continue to provide a second DC power supply through the ±220V backup DC bus.

[0070] In addition, if none of the above power sources are available, the DC power supply to the ±220V DC bus is provided by a directly connected battery pack.

[0071] It should also be noted that in safety-grade ±220V DC power distribution areas, the corresponding ±220V DC bus can directly provide 220V DC power, or provide 220V AC power through an inverter installed in conjunction with it, to meet the power requirements of the load. In contrast, in non-safety-grade ±220V DC power distribution areas, the corresponding ±220V DC bus can only provide 220V DC power, specifically limited by the safety-grade and non-safety-grade power supply standards within the nuclear power plant.

[0072] It should also be noted that the circuit breakers on the two DC topology distribution lines 10 mentioned above can be arranged according to actual needs, and there are no restrictions on this. Modifications and refinements made by those skilled in the art to the embodiments of the present invention without departing from the spirit of the present invention still fall within the scope of the invention application patent of the present invention.

[0073] Based on the above, the ±10kV DC distribution area, the ±750V DC distribution area, and the ±220V DC distribution area together form one sub-distribution line 12, while the redundant two sub-distribution lines 12 can ensure the continuous and stable normal operation of the current nuclear power unit and its electrical equipment.

[0074] In summary, the DC power distribution line topology provided in this application can be directly applied to the power distribution system of a small nuclear power plant, and brings the following technical benefits:

[0075] It simplifies the power switching scheme of the power distribution system, improves the reliability of power supply, and the power switching adopted on the ±10kV DC bus side is based on DC power distribution technology, which can avoid the phase difference problem when switching the residual voltage of the AC system. It can quickly complete the connection of another power source without phase determination.

[0076] This significantly reduces the number of power transmission and conversion steps in the power distribution system, thereby reducing potential failure points and further improving power supply reliability. For example, the MMC device in this embodiment can be compared to a high-voltage station transformer in a traditional AC power distribution system. By treating them as voltage conversion devices, for DC loads in the DC power distribution system, there is no need to configure a rectifier as in a traditional AC power distribution system; instead, power is supplied directly through the DC bus. For loads supplied by non-safety-grade AC uninterruptible power supplies in a traditional AC power distribution system, the AC power needs to be rectified to DC power first, and then the DC power needs to be inverted back to AC power for supply. Given that a large proportion of this load uses AC power input (or at least one power source is AC), but the device has a rectifier inside to power the internal components of the load, the electrical load is essentially operating on DC power. The DC power distribution system can change this part of the load to be directly powered by a 220V non-safety-grade DC bus, eliminating the AC / DC / AC / DC conversion process in a traditional AC power distribution system.

[0077] This DC power distribution system reduces power transmission losses, eliminates the need for reactive power compensation equipment, and improves the utilization rate of plant power. The system eliminates the skin effect problem of AC cables in traditional AC power distribution systems, as well as the dielectric loss and magnetic induction loss problems present in the insulation layer of AC cables. This reduces power transmission losses throughout the power distribution system and improves power utilization efficiency. Furthermore, since the DC power distribution system eliminates reactive power loss, it also saves on reactive power compensation devices, eliminating the need for investment in such equipment.

[0078] This increases the flexibility and convenience of the power distribution system in incorporating distributed energy systems and energy storage systems, strengthens the depth of the power system in small nuclear power plants, effectively couples distributed clean energy systems, and achieves comprehensive utilization of clean energy. Typical clean energy systems, such as fuel cells, distributed photovoltaic systems, and ESS (Electrical Storage System), operate in direct current (DC), and the interface equipment and control technology required for connecting to DC power distribution systems are relatively simple. However, for wind power systems, wind turbines generate randomly fluctuating alternating current (AC), requiring AC / DC / AC conversion for grid connection. Therefore, their connection can eliminate the DC / AC conversion process, making it more flexible and convenient. Furthermore, small nuclear power plants equipped with distributed energy systems or energy storage systems have a richer power supply depth and stronger continuous power supply capabilities under design-baseline accidents and design-extended operating conditions.

[0079] Direct current (DC) can fully leverage its inherent advantages and improve the power quality of the system. In AC power distribution systems, voltage fluctuations, flicker, and harmonics can all affect or even damage the electrical equipment in small nuclear power plants. DC power distribution systems, due to their inherent characteristics, avoid these problems, effectively improving power distribution quality and contributing to the safe and stable operation of plant equipment.

[0080] The reduction in large-capacity power transformers saves floor space and reduces project investment. In this embodiment, the DC power distribution system only requires two bidirectional converters (MMCs) or additional bidirectional converters to achieve access and conversion of external AC power, eliminating the need for large-capacity power transformers. Therefore, a large transformer area is unnecessary, saving at least 200 m² of floor space for a small nuclear power plant with a dual-reactor design.

[0081] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A DC power distribution system for use in nuclear power plants, characterized in that, include: At least two DC topology power distribution lines are used to connect to different external high-voltage AC power sources; The DC topology distribution line includes a common rectifier and two sub-distribution lines; Each sub-distribution line shall be equipped with at least one DC bus of the first distribution voltage, one DC bus of the second distribution voltage, two DC bus of the third distribution voltage, and one spare DC bus of the third distribution voltage. One end of the rectifier is used to connect to the high-voltage AC power supply outside the plant, and the other end is connected to the DC bus of the two first distribution voltages respectively. The DC bus of the first distribution voltage is connected to the DC bus of the second distribution voltage in the same sub-distribution line through a DC / DC converter; and the DC bus of the first distribution voltage is also connected to the DC bus of the first distribution voltage of the sub-distribution line in another DC topology distribution line through a DC tie circuit breaker. The DC bus of the second distribution voltage is connected to the first DC bus of the third distribution voltage in the same sub-distribution line through a DC / DC converter; The DC bus of the second distribution voltage is also connected to the second DC bus of the third distribution voltage in the same sub-distribution line via a DC / DC converter. The standby DC bus of the third distribution voltage is connected to the first DC bus and the second DC bus of the third distribution voltage in the same sub-distribution line. The first and second DC buses of the third distribution voltage are used to provide DC power of the third distribution voltage to the loads in the plant, and AC power of the third distribution voltage through the inverter. A power switching device is used to connect the rectifier of the DC topology distribution line to the external high-voltage AC power supply of another DC topology distribution line when the external high-voltage AC power supply of any DC topology distribution line fails. The DC topology distribution line includes a DC bus with a first distribution voltage and a redundant DC bus; the DC bus with the first distribution voltage is connected to the DC bus with the first distribution voltage in another DC topology distribution line through a DC tie circuit breaker; the redundant DC bus with the first distribution voltage is connected to the redundant DC bus with the first distribution voltage in another DC topology distribution line through a DC tie circuit breaker. The DC bus of the first distribution voltage adopts a bipolar DC topology to provide DC power of the first distribution voltage and half of the first distribution voltage to the loads within the plant; the DC bus of the second distribution voltage adopts a bipolar DC topology to provide DC power of the second distribution voltage and half of the second distribution voltage to the loads within the plant.

2. The DC power distribution system for nuclear power plants according to claim 1, characterized in that, The DC bus of the first distribution voltage also provides DC power of the fourth distribution voltage to the loads in the plant through a DC / DC converter.

3. The DC power distribution system for nuclear power plants according to claim 1, characterized in that, The DC bus of the first distribution voltage is also connected to the standby DC bus of the third distribution voltage in the same sub-distribution line via a DC / DC converter.

4. The DC power distribution system for nuclear power plants according to claim 1, characterized in that, The DC bus of the second distribution voltage is also used to connect to distributed energy systems and / or energy storage systems.

5. The DC power distribution system for nuclear power plants according to claim 1, characterized in that, The first DC bus of the third distribution voltage serves as the power supply output for the safety level, while the second DC bus of the third distribution voltage serves as the power supply output for the non-safety level. The first DC bus of the third distribution voltage is used to provide DC power of the third distribution voltage to the loads in the plant, and AC power of the third distribution voltage is provided through the inverter. The second DC bus of the third distribution voltage is used only to provide DC power of the third distribution voltage to the loads within the plant.

6. The DC power distribution system for nuclear power plants according to claim 1, characterized in that, The first DC bus and the second DC bus of the third power distribution voltage are both connected to a backup power source.

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