DC power transmission system, control method for DC power transmission system, and DC power transmission device

Abstract

The invention relates to a direct-current power transmission system, a control method of the direct-current power transmission system and a direct-current power transmission device.The direct-current power transmission system comprises a voltage conversion circuit, a switching circuit and a conversion transmission circuit, and the voltage conversion circuit is used for connecting a first voltage circuit of a first voltage level and a second voltage circuit of a second voltage level; electric energy of the first voltage circuit is converted and unidirectionally transmitted to the second voltage circuit; the switching circuit is connected with the first voltage circuit and the conversion transmission circuit; the conversion transmission circuit is also connected with the third voltage circuit, and is used for converting the electric energy of the third voltage circuit into the electric energy of the first voltage level, and transmitting the electric energy to the first voltage circuit under the condition that the switching circuit is switched on. When the system needs to be started, the switching circuit is switched on, the first voltage circuit is charged through the conversion transmission circuit, the first voltage circuit serving as an energy sending end can be started smoothly, and therefore the charging starting problem in the one-way direct-current power transmission system is solved.

Description

Technical Field

[0001] This application relates to the field of DC power transmission technology, and in particular to a DC power transmission system, a control method and apparatus for a DC power transmission system, a DC power transmission device, and a computer-readable storage medium. Background Technology

[0002] In the field of DC power transmission technology, when electrical energy is designed to flow unidirectionally from one end (energy sending end) to the other end (energy receiving end), this network topology exhibits the characteristics of unidirectional power transmission. Due to its advantages such as simple equipment structure and good technical and economic efficiency, unidirectional power transmission DC networks have become an important technical means for realizing the large-scale power transmission from renewable energy bases.

[0003] Power electronic systems typically require charging of their internal components before startup. However, in unidirectional power transmission network structures, the traditional method of charging the sending network from the receiving end becomes difficult to implement because electrical energy cannot flow in reverse. Therefore, in DC systems with unidirectional power transmission, achieving charging startup at the sending end has become a pressing problem. Summary of the Invention

[0004] Therefore, it is necessary to provide a DC transmission system, a control method for the DC transmission system, a device for the DC transmission system, a DC transmission device, and a computer-readable storage medium that can realize the reliable startup of the sending end of the DC transmission system.

[0005] In a first aspect, this application provides a direct current transmission system, comprising:

[0006] A voltage conversion circuit connects a first voltage circuit and a second voltage circuit; the first voltage level of the first voltage circuit and the second voltage level of the second voltage circuit are different; the voltage conversion circuit is used to convert the electrical energy of the first voltage circuit to the second voltage level and transmit it unidirectionally to the second voltage circuit;

[0007] A switching circuit, wherein the first terminal of the switching circuit is connected to the first voltage circuit;

[0008] A conversion transmission circuit is used to connect the second terminal of the switching circuit and the third voltage circuit; the conversion transmission circuit is used to convert the electrical energy of the third voltage circuit to electrical energy of the first voltage level; when the switching circuit is turned on, the electrical energy of the first voltage level converted by the conversion transmission circuit is fed back to the first voltage circuit through the switching circuit to start the first voltage circuit.

[0009] In one embodiment, the second terminal of the switching circuit is connected to the second voltage circuit, and the conversion transmission circuit is connected to the second voltage circuit and the third voltage circuit.

[0010] In one embodiment, the conversion transmission circuit includes a converter connected to a second terminal of the switching circuit and the third voltage circuit.

[0011] In one embodiment, the conversion transmission circuit includes a DC-DC module connected to a second terminal of the switching circuit and the third voltage circuit.

[0012] In one embodiment, the switching circuit includes a switching component, a first end of which is connected to the first voltage circuit, and a second end of which is used to connect to the conversion transmission circuit.

[0013] In one embodiment, the switching circuit includes a switching component and a current limiting circuit, a first terminal of the switching component is connected to the first voltage circuit, and a second terminal of the switching component is connected to the conversion transmission circuit through the current limiting circuit.

[0014] In one embodiment, the current limiting circuit includes a current limiting resistor, the first end of which is connected to the second end of the switching circuit, and the second end of which is used to connect to the conversion transmission circuit.

[0015] In one embodiment, the current limiting circuit includes an inductor, a first end of which is connected to a second end of the switching circuit, and the second end of which is used to connect to the conversion transmission circuit.

[0016] Secondly, this application provides a control method for a DC transmission system, the DC transmission system including a voltage conversion circuit, a switching circuit, and a conversion transmission circuit; the voltage conversion circuit connects a first voltage circuit and a second voltage circuit, the first voltage level of the first voltage circuit and the second voltage level of the second voltage circuit being different; the voltage conversion circuit is used to convert electrical energy from the first voltage circuit to the second voltage level and transmit it unidirectionally to the second voltage circuit; the first terminal of the switching circuit is connected to the first voltage circuit, the second terminal is connected to the conversion transmission circuit, and the conversion transmission circuit is also used to connect to a third voltage circuit; the method includes:

[0017] Receive start signal;

[0018] In response to the start signal, the switching circuit is controlled to turn on, and the conversion and transmission circuit is controlled to convert the electrical energy of the third voltage circuit to the electrical energy of the first voltage level; the electrical energy of the first voltage level converted by the conversion and transmission circuit is fed back to the first voltage circuit through the switching circuit to start the first voltage circuit.

[0019] In one embodiment, the second terminal of the switching circuit is connected to the second voltage circuit, and the conversion transmission circuit is connected to the second voltage circuit and the third voltage circuit; the method further includes:

[0020] When the first voltage circuit has been started, the switching circuit is controlled to disconnect.

[0021] When the switching circuit is open, the voltage conversion circuit is controlled to convert the electrical energy of the first voltage circuit to the second voltage level and transmit it unidirectionally to the second voltage circuit.

[0022] The conversion and transmission circuit is controlled to deliver electrical energy from the second voltage circuit to the third voltage circuit.

[0023] In one embodiment, controlling the switching circuit to turn on and controlling the conversion transmission circuit to convert the electrical energy of the third voltage circuit to the electrical energy of the first voltage level includes:

[0024] The conversion and transmission circuit is controlled to convert the electrical energy provided by the third voltage circuit;

[0025] When the conversion and transmission circuit converts the electrical energy provided by the third voltage circuit to the first voltage level, the switching circuit is controlled to be turned on.

[0026] In one embodiment, controlling the switching circuit to turn on and controlling the conversion transmission circuit to convert the electrical energy of the third voltage circuit to the electrical energy of the first voltage level includes:

[0027] Control the switching circuit to conduct;

[0028] When the switching circuit is turned on, the conversion and transmission circuit is controlled to convert the electrical energy provided by the third voltage circuit to electrical energy at the first voltage level.

[0029] Thirdly, this application provides a DC power transmission device, including a first voltage circuit, a second voltage circuit, a third voltage circuit, a controller, and a DC power transmission system as described above, wherein the controller is used to execute the steps of the control method described above.

[0030] Fourthly, this application provides a control device for a DC transmission system, the DC transmission system including a voltage conversion circuit, a switching circuit, and a conversion transmission circuit; the voltage conversion circuit connects a first voltage circuit and a second voltage circuit, the first voltage level of the first voltage circuit and the second voltage level of the second voltage circuit being different; the voltage conversion circuit is used to convert electrical energy from the first voltage circuit to the second voltage level and transmit it unidirectionally to the second voltage circuit; the first terminal of the switching circuit is connected to the first voltage circuit, the second terminal is connected to the conversion transmission circuit, and the conversion transmission circuit is also used to connect to a third voltage circuit; the device includes:

[0031] The signal receiving module is used to receive the start signal;

[0032] The power transmission control module is used to respond to the start signal, control the switching circuit to turn on, and control the conversion transmission circuit to convert the electrical energy of the third voltage circuit to the electrical energy of the first voltage level; the electrical energy of the first voltage level converted by the conversion transmission circuit is fed back to the first voltage circuit through the switching circuit to start the first voltage circuit.

[0033] Fifthly, this application provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, performs the following steps:

[0034] Receive start signal;

[0035] In response to the start signal, the switching circuit is controlled to turn on, and the conversion and transmission circuit is controlled to convert the electrical energy of the third voltage circuit to the electrical energy of the first voltage level; the electrical energy of the first voltage level converted by the conversion and transmission circuit is fed back to the first voltage circuit through the switching circuit to start the first voltage circuit.

[0036] The aforementioned DC transmission system, control method, apparatus, DC transmission device, and computer-readable storage medium include a voltage conversion circuit, a switching circuit, and a conversion transmission circuit. The voltage conversion circuit connects a first voltage circuit and a second voltage circuit. The first voltage level of the first voltage circuit and the second voltage level of the second voltage circuit are different. The voltage conversion circuit converts the electrical energy of the first voltage circuit to the second voltage level and transmits it unidirectionally to the second voltage circuit. The first terminal of the switching circuit is connected to the first voltage circuit, and the second terminal is connected to the conversion transmission circuit. The conversion transmission circuit also connects to a third voltage circuit. The conversion transmission circuit converts the electrical energy of the third voltage circuit to the electrical energy of the first voltage level. When the switching circuit is on, the electrical energy of the first voltage level converted by the conversion transmission circuit is fed back to the first voltage circuit through the switching circuit to start the first voltage circuit. Thus, when the DC transmission system needs to be started, turning on the switching circuit and charging the first voltage circuit through the conversion transmission circuit enables the first voltage circuit, as the energy sending end, to start smoothly. This solves the charging and starting problem in unidirectional DC transmission systems and promotes the engineering and practical application of unidirectional power transmission DC technology. Attached Figure Description

[0037] To more clearly illustrate the technical solutions in the embodiments of this application or the conventional technology, the drawings used in the description of the embodiments or the conventional technology will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0038] Figure 1 This is a schematic diagram of a DC transmission system according to one embodiment;

[0039] Figure 2 This is a schematic diagram of a DC transmission system according to another embodiment;

[0040] Figure 3 This is a schematic diagram of the circuit structure of a DC transmission system according to one embodiment;

[0041] Figure 4 This is a flowchart illustrating a control method for a DC transmission system according to one embodiment.

[0042] Figure 5 This is a block diagram of a control device for a DC power transmission system according to an embodiment. Detailed Implementation

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] Direct current (DC) transmission technology is a power transmission technology that transmits electrical energy in direct current (DC) form, offering advantages such as large transmission capacity and long distances. Further research by the inventors revealed that by utilizing the unidirectional nature of new energy power generation equipment or loads to simplify the topology of power electronic equipment in DC transmission networks, costs can be reduced. Therefore, the designed unidirectional power transmission DC system possesses significant advantages such as simple equipment structure and good technical and economic efficiency, making it a crucial technical means for realizing large-scale transmission of new energy from power plants.

[0050] However, this simplification also leads to a decrease in flexibility, such as how to start up a DC transmission system with unidirectional power transmission. It is understandable that power electronic systems typically contain components that require charging to start (such as capacitors), and system startup often requires charging these components first. The unidirectional transmission structure makes it difficult to charge the sending-end network through the energy receiving end.

[0051] Specifically, when a DC transmission system is a unidirectional power transmission system, such as a renewable energy integration system, the electricity generated by the renewable energy source is first connected to the medium- and low-voltage DC bus, and then converted to a high-voltage level through a DC-DC (Direct Current-to-Direct Current) converter before being transmitted through the high-voltage system. During this process, if the medium- and low-voltage system needs to be started through the high-voltage system, a charging problem arises. This is because DC-DC converters are typically designed for unidirectional operation, meaning they can only transfer electrical energy from the low-voltage side to the high-voltage side and cannot perform reverse charging. For similar reasons, the same problem exists in power supply systems. When the high-voltage bus needs to be converted to a low-voltage level through a unidirectional DC-DC converter, how to charge the high-voltage system or equipment from the low-voltage side becomes a challenge.

[0052] Based on this, a DC power transmission system is provided. In one embodiment, such as... Figure 1 As shown, the DC transmission system 100 includes a voltage conversion circuit 110. The voltage conversion circuit 110 connects a first voltage circuit 200 and a second voltage circuit 300; the first voltage level of the first voltage circuit 200 and the second voltage level of the second voltage circuit 300 are different. The voltage conversion circuit 110 is used to convert the electrical energy of the first voltage circuit 200 to the second voltage level and transmit it unidirectionally to the second voltage circuit 300.

[0053] The voltage levels of the first voltage circuit 200 and the second voltage circuit 300 can be set according to actual conditions during implementation. For example, the first voltage level can be 100kV and the second voltage level can be 200kV. In this case, the DC transmission system is a unidirectional power transmission system, the first voltage circuit 200 is a 100kV low-voltage circuit system, such as a new energy access system, and the second voltage circuit 300 is a 200kV high-voltage circuit system, such as a high-voltage system for transmitting electrical energy. In other embodiments, the first voltage level of the first voltage circuit 200 can be 200kV and the second voltage level of the second voltage circuit 300 can be 100kV; in this case, the DC transmission system is a unidirectional power supply system.

[0054] It is understood that the voltage levels in this embodiment are for illustrative purposes only and are not intended to limit the voltage levels of the first voltage circuit 200 and the second voltage circuit 300. In specific applications, the voltage levels of the first voltage circuit 200 and the second voltage circuit 300 can also be other voltage values, such as 500KV, 660KV, 800KV, etc.

[0055] The voltage conversion circuit 110 is capable of performing DC-DC conversion, and can be, for example, a DC transformer. The topology of the voltage conversion circuit 110 is not limited; for example, the topology of the voltage conversion circuit 110 can be a T-connected DC transformer topology or other unidirectional topology.

[0056] The voltage conversion circuit 110 is used to convert electrical energy at a first voltage level provided by the first voltage circuit 200 into electrical energy at a second voltage level, and transmit it unidirectionally to the second voltage circuit 300. Thus, after the DC transmission system is started, the voltage conversion circuit 110 can realize the unidirectional transmission of electrical energy from the first voltage circuit 200 to the second voltage circuit 300, with the first voltage circuit 200 acting as the energy sender and the second voltage circuit 300 acting as the energy receiver.

[0057] Since the voltage conversion circuit 110 is a DC transformer that transmits power in one direction, the electrical energy from the second voltage circuit 300 cannot be transmitted in reverse to the first voltage circuit 200 through the voltage conversion circuit 110. Therefore, the first voltage circuit 200 cannot obtain electrical energy from the second voltage circuit 300 to start charging.

[0058] The DC transmission system 100 also includes a switching circuit 120 and a conversion transmission circuit 130. A first terminal of the switching circuit 120 is connected to a first voltage circuit 200, and a second terminal of the switching circuit 120 is connected to the conversion transmission circuit 130. The conversion transmission circuit 130 is also connected to a third voltage circuit 400. The conversion transmission circuit 130 is used to convert the electrical energy from the third voltage circuit to electrical energy at the first voltage level. When the switching circuit 120 is turned on, the electrical energy at the first voltage level converted by the conversion transmission circuit 130 is fed back to the first voltage circuit 200 through the switching circuit 120 to activate the first voltage circuit 200.

[0059] In this embodiment, "reverse transmission" refers to the fact that during system startup, the direction of the current supplied by the conversion and transmission circuit 130 to the first voltage circuit 200 is opposite to the unidirectional current direction during normal system operation. It can be understood that after the DC transmission system starts up, it operates normally. During normal system operation, the electrical energy of the first voltage circuit 200 is unidirectionally transmitted to the second voltage circuit 300 through the voltage conversion circuit 110. Therefore, the current direction during system startup is opposite to the current direction during normal system operation. Thus, through this "reverse transmission" of electrical energy, the first voltage circuit 200 can be successfully charged and started.

[0060] The third voltage circuit 400 can be a DC voltage circuit or an AC voltage circuit. Furthermore, the voltage level of the third voltage circuit 400 can be set according to specific circumstances, and this embodiment does not limit this.

[0061] When the third voltage circuit 400 is a DC voltage circuit, the conversion transmission circuit 130 can perform DC-DC conversion to convert the electrical energy of the third voltage circuit 400 to the first voltage level. When the third voltage circuit 400 is an AC voltage circuit, the conversion transmission circuit 130 can perform AC-DC (Alternating Current and Direct Current) conversion to convert the AC electrical energy of the third voltage circuit 400 to the DC electrical energy of the first voltage level.

[0062] The control method of the switch circuit 120 is not unique. In some embodiments, the controlled terminal of the switch circuit 120 can be connected to a controller. When the system needs to be started, the controller outputs a control signal to the switch circuit 120 to control the switch circuit 120 to conduct. In other embodiments, the controlled terminal of the switch circuit 120 can also be manually controlled, so that when the system needs to be started, a professional can manually control the switch circuit 120 to conduct.

[0063] When the switching circuit 120 is turned on, the DC power of the first voltage level obtained by the conversion and transmission circuit 130 is transmitted to the first voltage circuit 200 via the switching circuit 120, so that the components in the first voltage circuit 200 that need to be charged and started can be charged and started.

[0064] The aforementioned DC power transmission system 100 includes a voltage conversion circuit 110, a switching circuit 120, and a conversion transmission circuit 130. The voltage conversion circuit 110 is used to connect a first voltage circuit 200 and a second voltage circuit 300. The first voltage level of the first voltage circuit 200 and the second voltage level of the second voltage circuit 300 are different. The voltage conversion circuit 110 is used to convert the electrical energy of the first voltage circuit 200 to the second voltage level and transmit it unidirectionally to the second voltage circuit 300. The first end of the switching circuit 120 is connected to the first voltage circuit 200, and the second end is connected to the conversion transmission circuit 130. The conversion transmission circuit 130 is also used to connect to a third voltage circuit 400. The conversion transmission circuit 130 is used to convert the electrical energy of the third voltage circuit 400 to the electrical energy of the first voltage level. When the switching circuit 120 is turned on, the electrical energy of the first voltage level converted by the conversion transmission circuit 130 is fed back to the first voltage circuit 200 through the switching circuit 120 to start the first voltage circuit 200. Therefore, when the DC transmission system needs to be started, the switching circuit 120 is turned on, and the first voltage circuit 200 is charged through the conversion and transmission circuit 130, enabling the first voltage circuit 200, which serves as the energy delivery end, to start smoothly. This solves the charging and starting problem in unidirectional DC transmission systems and promotes the engineering and practical application of DC technology for unidirectional power transmission.

[0065] In one embodiment, the second terminal of the switching circuit 120 is connected to the second voltage circuit 300, and the conversion transmission circuit 130 is connected to the second voltage circuit 300 and the third voltage circuit 400.

[0066] In this embodiment, the switching circuit 120 and the voltage conversion circuit 110 are connected in parallel between the first voltage circuit 200 and the second voltage circuit 300. The conversion transmission circuit 130 is connected to the second terminal of the switching circuit 120 via the second voltage circuit 300.

[0067] The topology of the second voltage circuit 300 can be configured according to actual conditions. For example, the second voltage circuit 300 includes a DC bus of a second voltage level, a switching circuit 120 and a voltage conversion circuit 110 connected in parallel between the first voltage circuit 200 and the DC bus, and a conversion transmission circuit 130 connected to the DC bus and the third voltage circuit 400. The second voltage circuit 300 can also be a DC transmission network of a second voltage level, with the DC transmission network connecting the voltage conversion circuit 110, the switching circuit 120, and the third voltage circuit 400 respectively.

[0068] The conversion and transmission circuit 130 is connected between the second voltage circuit 300 and the third voltage circuit 400. The conversion and transmission circuit 130 is also used to convert the electrical energy of the second voltage circuit 300 into electrical energy that matches the voltage level and voltage form (AC or DC) of the third voltage circuit 400 during normal operation of the DC transmission system after the first voltage circuit 200 is started, and then transmit it to the third voltage circuit 400.

[0069] Specifically, when the DC transmission system needs to be started, the switching circuit 120 is turned on, the voltage conversion circuit 110 is bypassed, and the conversion transmission circuit 130 converts the electrical energy provided by the third voltage circuit 400 into electrical energy of the first voltage level, and provides it to the first voltage circuit 200 through the switching circuit 120 so that the first voltage circuit 200 is charged and started.

[0070] After the first voltage circuit 200 is started, the switching circuit 120 is disconnected. The voltage conversion circuit 110 converts the electrical energy of the first voltage circuit 200 into electrical energy of the second voltage level and transmits it unidirectionally to the second voltage circuit 300. Then, the conversion and transmission circuit 130 converts the electrical energy of the second voltage circuit 300 into a voltage level and voltage form (AC or DC) that matches the third voltage circuit 400 and transmits it to the third voltage circuit 400, thereby supplying power to the load connected to the third voltage circuit 400.

[0071] In this embodiment, by connecting the second terminal of the switching circuit 120 to the second voltage circuit 300 and using the conversion and transmission circuit 130 to connect the second voltage circuit 300 and the third voltage circuit 400, the system can flexibly obtain starting power from the third voltage circuit 400 and charge it for startup when needed, thus eliminating the need for additional starting equipment and simplifying the topology of the power transmission system. Through the parallel connection and timely disconnection of the switching circuit 120, the system can smoothly transition between the startup and normal operation phases. After system startup is complete, the voltage conversion circuit 110 can efficiently convert the electrical energy of the first voltage circuit 200 into electrical energy of the second voltage level and transmit it to the second voltage circuit 300. This energy conversion and transmission is unidirectional, reducing unnecessary energy loss and improving system efficiency.

[0072] It should be noted that the switching circuit 120 turning on and the conversion and transmission circuit 130 performing power conversion can be performed simultaneously or sequentially. In some embodiments, the switching circuit 120 turning on and the conversion and transmission circuit 130 performing power conversion sequentially makes it easier to monitor and control the system state of each process.

[0073] The order in which the switching circuit 120 turns on and the conversion and transmission circuit 130 performs the power conversion is not unique. In some embodiments, the conversion and transmission circuit 130 first converts the power provided by the third voltage circuit 400. After the conversion and transmission circuit 130 has converted the power provided by the third voltage circuit 400 to a certain extent, such as reaching the first voltage level, the switching circuit 120 turns on again to send the power at the first voltage level obtained by the conversion and transmission circuit 130 back to the first voltage circuit 200, thereby activating the first voltage circuit 200.

[0074] Since the conversion and transmission circuit 130 has completed the conversion of electrical energy before the switching circuit 120 is turned on, once the switching circuit 120 is turned on, it can stably provide electrical energy that meets the requirements of the first voltage circuit 200. Therefore, this method is beneficial to protect the first voltage circuit 200.

[0075] In other embodiments, the switching circuit 120 can be turned on first. When the switching circuit 120 is turned on, the conversion and transmission circuit 130 converts the electrical energy provided by the third voltage circuit 400 into electrical energy at the first voltage level, and sends it back to the first voltage circuit 200 through the switching circuit 120 so that the first voltage circuit 200 is started.

[0076] By turning on the switching circuit 120 first, the electrical energy converted by the conversion and transmission circuit 130 can be transmitted to the first voltage circuit 200 in a timely manner, thereby reducing the waiting time before system startup and meeting the requirements for rapid system startup.

[0077] In actual implementation, the conversion transmission circuit 130 can be configured according to specific circumstances. In some embodiments, the conversion transmission circuit 130 includes a converter connected to the second terminal of the switching circuit 120 and the third voltage circuit 400.

[0078] A converter is a device that performs AC-DC conversion, consisting of one or more converter bridges. When the third voltage circuit 400 is an AC circuit, the converter can convert the AC power of the third voltage circuit 400 into DC power of the first voltage level and supply it to the first voltage circuit 200. The converter can also convert the power of the second voltage circuit 300 into AC power that matches the third voltage circuit 400 and supply it to the third voltage circuit 400.

[0079] The number of converters and their specific connection structure are not limited; those skilled in the art can select an appropriate number and connect them according to the specific circumstances.

[0080] In practical applications, DC transmission systems are designed with multiple converters to achieve functions such as inversion. By using converters to charge the energy sending end during system startup, no additional components are needed, making the system cost more controllable.

[0081] In other embodiments, the conversion transmission circuit includes a DC-DC module connected to the second terminal of the switching circuit 120 and the third voltage circuit 400.

[0082] The DC-DC module can be an integrated functional module or a DC-DC conversion circuit, depending on the specific requirements. When the third voltage circuit 400 is a DC circuit, the DC-DC module can convert the electrical energy from the third voltage circuit 400 into electrical energy at the first voltage level, supplying it to the first voltage circuit 200. The DC-DC module can also convert the electrical energy from the second voltage circuit 300 into electrical energy matching that of the third voltage circuit 400, supplying it to the third voltage circuit 400.

[0083] In this embodiment, the DC-DC module has different functions during system startup and normal system operation. Therefore, it is not necessary to set up separate circuits or modules for each stage. The circuit structure is simple and easy to implement.

[0084] In some embodiments, the switching circuit 120 includes a switching component, a first end of which is connected to a first voltage circuit 200, and a second end of which is used to connect to a conversion transmission circuit 130.

[0085] The controlled end of the switch assembly can be connected to a controller and controlled by the control signals issued by the controller; or it can be manually controlled by professionals, and the specific control method is not limited.

[0086] The type of switching component is not unique; it can be a mechanical switch, a semiconductor switch, or any other type of electronic switch. The first and second terminals of the switching component need to be determined in conjunction with the type of switching component. The number of switching components can be one or multiple, depending on the specific circumstances.

[0087] In this embodiment, by setting a switch component, the circuit path between the first voltage circuit 200 and the conversion transmission circuit 130 can be flexibly connected or disconnected. The system structure is simple and clear and easy to maintain.

[0088] In some embodiments, the switching circuit 120 includes a switching component and a current limiting circuit. The first end of the switching component is connected to the first voltage circuit 200, and the second end of the switching component is connected to the conversion transmission circuit 130 through the current limiting circuit.

[0089] When the system needs to start, the conversion and transmission circuit 130 starts working, converting the electrical energy provided by the third voltage circuit 400 into electrical energy of the first voltage level, and feeding it back to the first voltage circuit 200 through the current limiting circuit and the switching circuit 120. The current limiting circuit is used to ensure that the current flowing through the switching assembly does not exceed a certain current value, thereby protecting the switching assembly and the first voltage circuit 200.

[0090] The structure of the current limiting circuit is not unique. In some embodiments, the current limiting circuit includes a current limiting resistor, the first end of which is connected to the second end of the switching circuit 120, and the second end of which is used to connect to the conversion transmission circuit 130.

[0091] By setting a current-limiting resistor, the current flowing through the switching assembly can be limited, thus protecting the switching assembly and the first voltage circuit 200. Current-limiting resistors are low-cost, effectively controlling system costs.

[0092] In some embodiments, the current limiting circuit includes an inductor, with a first end connected to a second end of the switching circuit 120 and the second end of the inductor used to connect to the conversion transmission circuit 130.

[0093] By utilizing the inductive properties of inductors, the rate of change of current can be limited, thereby limiting current and protecting downstream circuits, while also reducing electromagnetic interference in the circuit.

[0094] To better understand the above embodiments, a detailed explanation is provided below with reference to an optional embodiment. The DC transmission system 100 includes a voltage conversion circuit 110, a switching circuit 120, and a conversion and transmission circuit 130. In one embodiment, please refer to... Figure 3 The first voltage circuit 200, serving as the energy sending end of the power grid circuit, includes a first DC bus connected to it and a circuit (not shown) requiring charging for startup. The voltage level of the first DC bus is a first voltage level V1. The second voltage circuit 300, serving as the energy receiving end of the power grid circuit, includes a second DC bus and a third DC bus connected to it. The voltage levels of both the second and third DC buses are second voltage levels V2.

[0095] The voltage conversion circuit 110 uses a DC transformer, which includes a 3-phase DC conversion module. Each phase DC conversion module includes a bridge arm consisting of multiple energy conversion sub-modules cascaded together (SM) and a reactor (L) connected in series, and two sets of switches. The common connection terminal of the two sets of switches connected in series is connected to the first end of the bridge arm. The first end of the two sets of switches connected in series is used to connect to the first DC bus, the second end of the two sets of switches connected in series is used to connect to the second DC bus, and the second end of the bridge arm serves as the grounding terminal. The grounding terminal and the third DC bus are connected to the conversion transmission circuit 130, which is also connected to the third voltage circuit.

[0096] The number of phases in the DC-DC converter module can be adjusted based on factors such as capacity requirements, voltage level, current withstand parameters of each device in the cascaded energy conversion submodule structure, and cost. The number of submodules in the cascaded energy conversion submodule structure is also not limited; those skilled in the art can set it according to specific circumstances.

[0097] The structure of the energy conversion submodule SM is not unique; it can be either a full-bridge submodule or a half-bridge submodule. Therefore, the bridge arm can be composed of a cascaded half-bridge submodule structure connected in series with a reactor L, or a cascaded full-bridge submodule structure connected in series with a reactor L.

[0098] Each group of switches may include one or more switching devices. A switching device may consist of multiple power electronic devices connected in series. Power electronic devices include fully controlled devices (such as IGBTs or GTOs) and their anti-parallel diodes, semi-controlled devices (such as thyristors), or diodes.

[0099] In this embodiment, each set of switches includes a switching device. After switching devices S1 and S2 are connected in series, the end of switching device S1 not connected to switching device S2 and the end of switching device S2 not connected to switching device S1 serve as the first and second ends of the two sets of switches connected in series, respectively. For example, the end of switching device S1 not connected to switching device S2 is used to connect to the first DC bus, and the end of switching device S2 not connected to switching device S1 is connected to the second DC bus. The end of the reactor L in the bridge arm not connected to the cascaded energy conversion submodule SM structure is used to connect to the ground terminal. The specific connection relationships of other phase DC-DC conversion modules in this embodiment are not described in detail.

[0100] In practical applications, by controlling switching devices S1, S2, S3, S4, S5, and S6 according to actual needs, the electrical energy provided by the first DC bus at the first voltage level V1 can be converted to the second voltage level V2 and transmitted unidirectionally to the second DC bus.

[0101] The switching circuit 120 includes a switching component K and a current-limiting resistor R. The first end of the switching component K is connected to the first DC bus, and the second end of the switching component K is connected to the second DC bus through the current-limiting resistor R. The second DC bus is connected to the third DC bus, and the third DC bus is connected to the third voltage circuit through the conversion and transmission circuit 130.

[0102] When the system needs to be started, the control switch component K is turned on, and the conversion and transmission circuit 130 is controlled to convert the electrical energy provided by the third voltage circuit to the electrical energy of the first voltage level V1. The energy is then fed back to the first DC bus through the current limiting resistor R and the switch component K, thereby enabling the components in the circuit that need to be charged to start to charge and start.

[0103] By adding at least one switching component K between different levels of power grid circuits, current can flow between different levels of power grid circuits (e.g., high-voltage side circuit and low-voltage side circuit), with the current direction opposite to the normal unidirectional current direction (see the directions of current I1 and current I2 in the figure), thereby enabling charging of the other side circuit that needs charging.

[0104] In this method, the switching component K can be activated first, and then the converter can be controlled to boost the voltage and charge. Alternatively, the converter can be boosted to a certain level (such as the first voltage level V1) first, and then the switching component K can be operated to bypass the DC transformer. In this case, the current-limiting resistor or inductor can prevent overcurrent.

[0105] The conversion transmission circuit 130 can be a converter. Since there are often multiple converters in a DC network, the voltage is boosted by the converter and then switched by the switching component K to introduce the voltage of the converter into the grid circuit on the side that needs to be charged, thus realizing the charging start of the sending grid.

[0106] It is understood that the structural description of the first voltage circuit 200 and the second voltage circuit 300 in this embodiment is for the purpose of better understanding the principle of the DC transmission system 100. In actual implementation, the first voltage circuit 200 and the second voltage circuit 300 may also include other circuits. For example, the first voltage circuit 200 may also include a new energy access system connected to the first DC bus. The new energy access system is used to access new energy power generation modules, which include, but are not limited to, wind power generation modules, solar power generation modules, etc.

[0107] This embodiment does not limit the startup method of the second voltage circuit 300. Exemplarily, the conversion and transmission circuit 130 can also convert the electrical energy of the third voltage circuit to the second voltage level and transmit it to the second voltage circuit 300, thereby starting the second voltage circuit 300. The second voltage circuit 300 can also be connected to an independent startup circuit, which charges the second voltage circuit 300 to start it up.

[0108] Therefore, by setting the switching component K, the charging start-up problem in a unidirectional DC transmission system can be solved. The circuit structure is simple, easy to implement, and low in cost, which can further promote the engineering and practical application of DC technology for unidirectional power transmission.

[0109] Based on the same inventive concept, this application also provides a control method for the aforementioned DC transmission system. Specifically, the control method for the DC transmission system is applied to a DC transmission device, which includes a first voltage circuit, a second voltage circuit, a third voltage circuit, a controller, and a DC transmission system.

[0110] DC transmission systems can use the parameters mentioned above. Figure 1 The system includes a voltage conversion circuit, a switching circuit, and a conversion transmission circuit connected to the controller. The voltage conversion circuit connects a first voltage circuit and a second voltage circuit, where the first voltage level of the first voltage circuit and the second voltage level of the second voltage circuit are different. The voltage conversion circuit converts the electrical energy of the first voltage circuit to the second voltage level and transmits it unidirectionally to the second voltage circuit. The first terminal of the switching circuit is connected to the first voltage circuit, and the second terminal is connected to the conversion transmission circuit, which is also used to connect to a third voltage circuit. The controller receives a start signal; in response to the start signal, it controls the switching circuit to conduct and controls the conversion transmission circuit to convert the electrical energy of the third voltage circuit to the electrical energy of the first voltage level. The electrical energy of the first voltage level converted by the conversion transmission circuit is fed back to the first voltage circuit through the switching circuit to start the first voltage circuit.

[0111] In one exemplary embodiment, such as Figure 4 As shown, a control method for a DC transmission system is provided. Taking the application of this method to a controller as an example, the method includes the following steps 502 and 504. Wherein:

[0112] Step 502: Receive the start signal.

[0113] The start signal can be sent to the controller by professionals as needed, or it can be generated by the controller based on received system operating parameters or detection parameters.

[0114] Step 504: In response to the start signal, control the switch circuit to turn on, and control the conversion and transmission circuit to convert the electrical energy of the third voltage circuit to the electrical energy of the first voltage level; the electrical energy of the first voltage level converted by the conversion and transmission circuit is fed back to the first voltage circuit through the switch circuit to start the first voltage circuit.

[0115] By controlling the electrical energy at the first voltage level obtained by the conversion and transmission circuit when the switching circuit is on, the electrical energy can be fed back to the first voltage circuit through the switching circuit, thus starting the first voltage circuit. Therefore, when the DC transmission system needs to be started, the first voltage circuit, as the energy sending end, can be charged and started, solving the charging and starting problem in unidirectional DC transmission systems and promoting the engineering and practical application of DC technology for unidirectional power transmission.

[0116] In one embodiment, please refer to Figure 2 The second terminal of the switching circuit is connected to the second voltage circuit, and the conversion transmission circuit is connected to both the second and third voltage circuits. The control method for this DC transmission system also includes the following steps:

[0117] When the first voltage circuit has been started, the control switch circuit is disconnected;

[0118] When the switching circuit is open, the control voltage conversion circuit converts the electrical energy of the first voltage circuit to the second voltage level and transmits it unidirectionally to the second voltage circuit.

[0119] The control conversion and transmission circuit transfers electrical energy from the second voltage circuit to the third voltage circuit.

[0120] In this embodiment, when the DC transmission system needs to be started, the control switch circuit is turned on, the voltage conversion circuit is bypassed, and the conversion transmission circuit is controlled to charge the first voltage circuit.

[0121] After the first voltage circuit starts up, the control switch circuit disconnects and controls the voltage conversion circuit to convert the electrical energy from the first voltage circuit to electrical energy at the second voltage level, and transmits it unidirectionally to the second voltage circuit. Then, the control conversion and transmission circuit converts the electrical energy from the second voltage circuit to a voltage level and form (AC or DC) matching the third voltage circuit and transmits it to the third voltage circuit, thereby powering the load connected to the third voltage circuit. This unidirectional energy conversion and transmission reduces unnecessary energy loss and improves system efficiency.

[0122] In one embodiment, the step of controlling the switching circuit to turn on and controlling the conversion transmission circuit to convert the electrical energy of the third voltage circuit to the electrical energy of the first voltage level includes:

[0123] The control conversion transmission circuit converts the electrical energy supplied by the third voltage circuit;

[0124] When the conversion and transmission circuit converts the electrical energy provided by the third voltage circuit to the first voltage level, the control switch circuit is turned on to send the electrical energy of the first voltage level obtained by the conversion and transmission circuit back to the first voltage circuit, so that the first voltage circuit is started.

[0125] In this embodiment, the conversion and transmission circuit has completed the conversion of electrical energy before the switching circuit is turned on. Once the switching circuit is turned on, it can stably provide electrical energy that meets the requirements of the first voltage circuit, thereby helping to protect the first voltage circuit.

[0126] In one embodiment, the step of controlling the switching circuit to turn on and controlling the conversion transmission circuit to convert the electrical energy of the third voltage circuit to the first voltage level includes:

[0127] The control switch circuit is turned on;

[0128] When the switching circuit is on, the control conversion transmission circuit converts the electrical energy provided by the third voltage circuit to electrical energy at the first voltage level, and feeds it back to the first voltage circuit through the switching circuit so that the first voltage circuit can be started.

[0129] In this embodiment, by turning on the switching circuit first, the electrical energy converted by the conversion and transmission circuit can be transmitted to the first voltage circuit in a timely manner, thereby reducing the waiting time before the system starts up and thus meeting the requirements for rapid system startup.

[0130] It should be understood that although the steps in the flowcharts of the embodiments described above are shown sequentially according to the arrows, these steps are not necessarily executed in the order indicated by the arrows. Unless explicitly stated herein, there is no strict order restriction on the execution of these steps, and they can be executed in other orders. Moreover, at least some steps in the flowcharts of the embodiments described above may include multiple steps or multiple stages. These steps or stages are not necessarily completed at the same time, but can be executed at different times. The execution order of these steps or stages is not necessarily sequential, but can be performed alternately or in turn with other steps or at least some of the steps or stages of other steps.

[0131] Based on the same inventive concept, this application also provides a control device for a DC transmission system to implement the control method for the DC transmission system described above. The solution provided by this device is similar to the solution described in the above method. Therefore, the specific limitations in one or more embodiments of the control device for a DC transmission system provided below can be found in the limitations of the control method for the DC transmission system described above, and will not be repeated here.

[0132] In one exemplary embodiment, such as Figure 5 As shown, a control device for a DC transmission system is provided, comprising: a signal receiving module 602 and a transmission control module 604, wherein:

[0133] Signal receiving module 602 is used to receive the start signal;

[0134] The power transmission control module 604 is used to control the switching circuit to conduct in response to the start signal, and to control the conversion transmission circuit to convert the electrical energy of the third voltage circuit to the electrical energy of the first voltage level; the electrical energy of the first voltage level converted by the conversion transmission circuit is fed back to the first voltage circuit through the switching circuit so as to start the first voltage circuit.

[0135] In one embodiment, the power transmission control module 604 is further configured to: control the switching circuit to disconnect when the first voltage circuit has been started; control the voltage conversion circuit to convert the electrical energy of the first voltage circuit to the second voltage level and transmit it unidirectionally to the second voltage circuit when the switching circuit is disconnected; and control the conversion transmission circuit to deliver the electrical energy of the second voltage circuit to the third voltage circuit.

[0136] In one embodiment, the power transmission control module 604 is further configured to control the conversion transmission circuit to convert the electrical energy provided by the third voltage circuit; when the conversion transmission circuit converts the electrical energy provided by the third voltage circuit to a first voltage level, the control switch circuit is turned on to send the electrical energy of the first voltage level obtained by the conversion transmission circuit back to the first voltage circuit, so as to start the first voltage circuit.

[0137] In one embodiment, the power transmission control module 604 is further configured to control the switching circuit to conduct; when the switching circuit is conducted, it controls the conversion transmission circuit to convert the electrical energy provided by the third voltage circuit to electrical energy at the first voltage level, and feeds it back to the first voltage circuit through the switching circuit to start the first voltage circuit.

[0138] The various modules in the control device of the aforementioned DC transmission system can be implemented entirely or partially through software, hardware, or a combination thereof. These modules can be embedded in the processor of a computer device in hardware form or independent of it, or stored in the memory of a computer device in software form, so that the processor can call and execute the operations corresponding to each module.

[0139] In one embodiment, a DC transmission device is provided, including a first voltage circuit, a second voltage circuit, a third voltage circuit, a controller, and a DC transmission system. The DC input system can be configured as described in the above embodiments, and will not be repeated here. The controller is used to execute the steps of the control method of the DC transmission system, and the steps of the control method of the DC transmission system can be configured as described in the above embodiments.

[0140] In one embodiment, a computer-readable storage medium is provided having a computer program stored thereon that, when executed by a processor, implements the steps in the above method embodiments.

[0141] Those skilled in the art will understand that all or part of the processes in the above embodiments can be implemented by a computer program instructing related hardware. The computer program can be stored in a non-volatile computer-readable storage medium, and when executed, it can include the processes of the embodiments described above. Any references to memory, databases, or other media used in the embodiments provided in this application can include at least one of non-volatile memory and volatile memory. Non-volatile memory can include read-only memory (ROM), magnetic tape, floppy disk, flash memory, optical memory, high-density embedded non-volatile memory, resistive random access memory (ReRAM), magnetic random access memory (MRAM), ferroelectric random access memory (FRAM), phase change memory (PCM), graphene memory, etc. Volatile memory can include random access memory (RAM) or external cache memory, etc. By way of illustration and not limitation, RAM can take many forms, such as Static Random Access Memory (SRAM) or Dynamic Random Access Memory (DRAM). The databases involved in the embodiments provided in this application may include at least one type of relational database and non-relational database. Non-relational databases may include, but are not limited to, blockchain-based distributed databases. The processors involved in the embodiments provided in this application may be general-purpose processors, central processing units, graphics processing units, digital signal processors, programmable logic devices, quantum computing-based data processing logic devices, artificial intelligence (AI) processors, etc., and are not limited to these.

[0142] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this application.

[0143] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of this patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this application should be determined by the appended claims.

Claims

1. A DC transmission system, characterized in that, include: A voltage conversion circuit connects a first voltage circuit and a second voltage circuit; the first voltage level of the first voltage circuit and the second voltage level of the second voltage circuit are different. The voltage conversion circuit is used to convert the electrical energy of the first voltage circuit to the second voltage level and transmit it unidirectionally to the second voltage circuit; A switching circuit, wherein the first terminal of the switching circuit is connected to the first voltage circuit; A conversion transmission circuit is used to connect the second terminal of the switching circuit and the third voltage circuit; the conversion transmission circuit is used to convert the electrical energy of the third voltage circuit to electrical energy of the first voltage level; when the switching circuit is turned on, the electrical energy of the first voltage level converted by the conversion transmission circuit is fed back to the first voltage circuit through the switching circuit to start the first voltage circuit.

2. The DC transmission system according to claim 1, characterized in that, The second terminal of the switching circuit is connected to the second voltage circuit, and the conversion transmission circuit is connected to the second voltage circuit and the third voltage circuit.

3. The DC transmission system according to claim 1 or 2, characterized in that, The conversion transmission circuit includes a converter, which is connected to the second terminal of the switching circuit and the third voltage circuit.

4. The DC transmission system according to claim 1 or 2, characterized in that, The conversion transmission circuit includes a DC-DC module, which is connected to the second terminal of the switching circuit and the third voltage circuit.

5. The DC transmission system according to claim 1 or 2, characterized in that, The switching circuit includes a switching component, a first end of which is connected to the first voltage circuit, and a second end of which is used to connect to the conversion transmission circuit.

6. The DC transmission system according to claim 1 or 2, characterized in that, The switching circuit includes a switching component and a current limiting circuit. The first end of the switching component is connected to the first voltage circuit, and the second end of the switching component is connected to the conversion and transmission circuit through the current limiting circuit.

7. The DC transmission system according to claim 6, characterized in that, The current limiting circuit includes a current limiting resistor. The first end of the current limiting resistor is connected to the second end of the switching circuit, and the second end of the current limiting resistor is used to connect to the conversion transmission circuit.

8. The DC transmission system according to claim 6, characterized in that, The current limiting circuit includes an inductor, the first end of which is connected to the second end of the switching circuit, and the second end of which is used to connect to the conversion transmission circuit.

9. A control method for a DC transmission system, characterized in that, The DC transmission system includes a voltage conversion circuit, a switching circuit, and a conversion transmission circuit; the voltage conversion circuit is connected to a first voltage circuit and a second voltage circuit, wherein the first voltage level of the first voltage circuit and the second voltage level of the second voltage circuit are different. The voltage conversion circuit is used to convert the electrical energy of the first voltage circuit to the second voltage level and transmit it unidirectionally to the second voltage circuit; the first terminal of the switching circuit is connected to the first voltage circuit, and the second terminal is connected to the conversion and transmission circuit, which is also used to connect to a third voltage circuit; the method includes: Receive start signal; In response to the start signal, the switching circuit is controlled to turn on, and the conversion and transmission circuit is controlled to convert the electrical energy of the third voltage circuit to the electrical energy of the first voltage level; the electrical energy of the first voltage level converted by the conversion and transmission circuit is fed back to the first voltage circuit through the switching circuit to start the first voltage circuit.

10. The control method for a DC transmission system according to claim 9, characterized in that, The second terminal of the switching circuit is connected to the second voltage circuit, and the conversion transmission circuit is connected to the second voltage circuit and the third voltage circuit; the method further includes: When the first voltage circuit has been started, the switching circuit is controlled to disconnect. When the switching circuit is open, the voltage conversion circuit is controlled to convert the electrical energy of the first voltage circuit to the second voltage level and transmit it unidirectionally to the second voltage circuit. The conversion and transmission circuit is controlled to deliver electrical energy from the second voltage circuit to the third voltage circuit.

11. The control method for a DC transmission system according to claim 9, characterized in that, The control of the switching circuit to conduct and the control of the conversion and transmission circuit to convert the electrical energy of the third voltage circuit to the electrical energy of the first voltage level include: The conversion and transmission circuit is controlled to convert the electrical energy provided by the third voltage circuit; When the conversion and transmission circuit converts the electrical energy provided by the third voltage circuit to the first voltage level, the switching circuit is controlled to be turned on.

12. The control method for a DC transmission system according to claim 9, characterized in that, The control of the switching circuit to conduct and the control of the conversion and transmission circuit to convert the electrical energy of the third voltage circuit to the electrical energy of the first voltage level include: Control the switching circuit to conduct; When the switching circuit is turned on, the conversion and transmission circuit is controlled to convert the electrical energy provided by the third voltage circuit to electrical energy at the first voltage level.

13. A DC transmission device, characterized in that, The system includes a first voltage circuit, a second voltage circuit, a third voltage circuit, a controller, and a DC transmission system as described in any one of claims 1-8, wherein the controller is used to execute the steps of the control method for the DC transmission system as described in any one of claims 9-12.

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