A DC-DC power transmission system

Abstract

The present invention discloses a DC-DC power transmission system, including first and second DC ports, a DC-DC power converter and a unidirectional semiconductor switch; the positive and negative poles of the first DC port are respectively connected to the positive and negative poles of the DC input port of the power converter, and are also respectively connected to an external power supply DC system; the positive and negative poles of the second DC port are respectively connected to an external power receiving DC system, wherein the positive pole is connected to the positive pole of the DC output port of the power converter and the negative pole of the unidirectional semiconductor switch, and the negative pole is connected to the negative pole of the first DC port; the positive pole of the unidirectional semiconductor switch is connected to the negative pole of the DC output port of the power converter, and the positive pole of the first DC port is connected to the positive pole of the unidirectional semiconductor switch. The present invention connects a unidirectional semiconductor switch in reverse parallel between the positive and negative poles of the DC output port of the power converter, connects the positive pole of the input end of the power converter to the positive pole of the unidirectional semiconductor switch, and when the power converter fails due to a fault, the power transmission is restored through the unidirectional semiconductor switch, thereby improving the reliability of the power transmission system and greatly reducing the cost.

Description

Technical Field

[0001] The present invention belongs to the field of power transmission, and more specifically, relates to a DC-DC power transmission system. Background Art

[0002] With the development of distributed generation technology and DC distribution technology, the demand for renewable energy generation systems to be directly integrated into the DC distribution network through DC-DC power transmission systems is growing. In low-voltage and small-capacity DC-DC power transmission systems, basic DC-DC converters such as boost converters and buck-boost converters are the preferred technical solutions. However, when such technical solutions are applied to medium- and high-voltage large-capacity scenarios, they will face high technical difficulties and high costs, and have great limitations. In the field of medium- and high-voltage large-capacity DC-DC power transmission, DC-DC converter technical solutions represented by DC autotransformers and DC transformers based on dual active bridge (DAB) power units have received a lot of attention and research.

[0003] Patent No. 109600049A discloses a DC solid-state transformer. When the DC solid-state transformer is used to transmit power, the transmitted electric energy needs to undergo two conversions, that is, first converting DC electric energy into AC electric energy, and then further converting AC electric energy into DC electric energy. Due to the large number of power conversions, it will cause a large power loss. When the DC solid-state transformer is used in medium and high voltage applications, there are also defects such as a large number of power unit modules, a complex system and high cost. In addition, when the DC solid-state transformer fails, the energy transmission channel between different DC systems on the high and low voltage sides of the DC solid-state transformer will be interrupted, reducing the reliability of energy transmission. Patent 201410024869.X proposes a three-dimensional DC-DC converter for interconnecting two DC systems with different voltage levels, and its internal VSC converter unit adopts a three-phase voltage source converter structure. In medium and high voltage applications, Patent 201410024869.X can solve the shortcomings of a large number of power unit modules, a complex system, high cost and high loss in Patent 109600049A. However, when the VSC converter unit inside patent 201410024869.X fails due to a fault, the three-dimensional DC-DC converter will lose its power transmission capability, and there is also the problem of reliability of energy transmission.

[0004] Therefore, for the disclosed DC-DC converters (such as the boost converter, DC solid-state transformer, three-dimensional DC-DC converter, etc. mentioned above): on the one hand, when the DC-DC converter fails due to a fault, the energy transmission channel between the DC systems on both sides will be interrupted, so it is necessary to further improve the reliability of the above-mentioned technical solutions; on the other hand, when some of the existing disclosed technical solutions are applied to medium and high voltage occasions, there are technical difficulties, such as the large number and capacity of high-power unit modules, complex system and high cost. Summary of the invention

[0005] The present invention provides a DC-DC power transmission system for solving the technical problem in the existing power transmission system that when a DC-DC converter fails and cannot transmit power, power transmission is interrupted, which leads to high power transmission cost.

[0006] The technical solution of the present invention to solve the above technical problem is as follows: A DC-DC power transmission system includes a first DC port, a second DC port, a DC-DC power converter and a unidirectional semiconductor switch;

[0007] The positive and negative electrodes of the first DC port are respectively connected to the positive and negative electrodes of the DC input port of the DC-DC power converter, and are also respectively connected to the positive and negative ports of an external DC power supply system;

[0008] The positive and negative electrodes of the second DC port are respectively connected to the positive and negative ports of the DC system for receiving power, wherein the positive electrode is also connected to the positive electrode of the DC output port of the DC-DC power converter and the negative electrode of the unidirectional semiconductor switch, and the negative electrode is also connected to the negative electrode of the first DC port;

[0009] The positive pole of the unidirectional semiconductor switch is connected to the negative pole of the DC output port of the DC-DC power converter, and the positive pole of the first DC port is also connected to the positive pole of the unidirectional semiconductor switch.

[0010] The beneficial effects of the present invention are as follows: the present invention connects a unidirectional semiconductor switch in reverse parallel between the positive and negative poles of the DC output port of the DC-DC power converter, and simultaneously connects the positive pole of the input end of the DC-DC power converter to the positive pole of the unidirectional semiconductor switch. When the DC-DC power converter inside the DC-DC power transmission system fails due to a fault, the power transmission between the power supply DC system and the power receiving DC system is automatically restored by the unidirectional semiconductor switch, and has a zero response time characteristic, avoiding the interruption of power transmission between the power supply DC system and the power receiving DC system, greatly improving the reliability and availability of the DC-DC power transmission system. In addition, by connecting the positive pole of the input end of the DC-DC power converter to the negative pole of the output end of the DC-DC power converter, and further connecting the negative pole of the input end of the DC-DC power converter to the negative pole of the second DC port, the design capacity and power loss of the DC-DC power converter can be reduced, thereby reducing the volume and cost of the DC-DC power converter, and greatly improving the economy of the DC-DC power transmission system.

[0011] Based on the above technical solution, the present invention can also be improved as follows.

[0012] Furthermore, the number of the DC-DC power converters is n, where n is a positive integer; and when n>1, the n DC-DC power converters are connected in combination, and the positive pole of the DC input port of one of the DC-DC power converters is connected to the positive pole of the first DC port; the negative pole of the DC input port of one of the DC-DC power converters is connected to the negative pole of the first DC port; the positive pole of the DC output port of one of the DC-DC power converters is connected to the positive pole of the second DC port, and the negative pole of the DC output port of one of the DC-DC power converters is connected to the positive pole of the unidirectional semiconductor switch.

[0013] Further, when n>1, the DC input ports of the n DC-DC power converters are respectively connected to the first DC port in parallel; the DC output ports of the n DC-DC power converters are respectively connected to the positive electrode of the second DC port and the positive electrode of the unidirectional semiconductor switch in parallel.

[0014] A further beneficial effect of the present invention is that the overall current transmission capacity of the DC-DC power converter part is increased by connecting a plurality of DC-DC power converter input ports and output ports in parallel, thereby achieving the purpose of improving the power transmission capacity.

[0015] Further, when n>1, the DC input ports of the n DC-DC power converters are respectively connected to the first DC port in parallel; the DC output ports of the n DC-DC power converters are connected in series, wherein the positive pole of the DC output port of one DC-DC power converter is connected to the positive pole of the second DC port, and the negative pole of the DC output port of one DC-DC power converter is connected to the positive pole of the unidirectional semiconductor switch.

[0016] A further beneficial effect of the present invention is that the overall current tolerance of the input port of the DC-DC power converter is increased by connecting the input ends of the DC-DC power converters in parallel, and the overall voltage tolerance of the output port of the DC-DC power converter is increased by connecting the output ends of the DC-DC power converters in series, thereby achieving the purpose of improving the overall power transmission capacity of the DC-DC power converter.

[0017] Further, when n>1, the DC input ports of the n DC-DC power converters are connected in series, wherein the positive pole of the DC input port of one DC-DC power converter is connected to the positive pole of the first DC port, and the negative pole of the DC input port of one DC-DC power converter is connected to the negative pole of the second DC port; the DC output ports of the n DC-DC power converters are connected in series, wherein the positive pole of the DC output port of one DC-DC power converter is connected to the positive pole of the second DC port, and the negative pole of the DC output port of one DC-DC power converter is connected to the positive pole of the unidirectional semiconductor switch.

[0018] A further beneficial effect of the present invention is that by connecting the input and output ends of each DC-DC power converter in series, the overall voltage tolerance of the input and output ports of the DC-DC power converter can be increased, thereby achieving the purpose of improving the power transmission capacity of the DC-DC power converter.

[0019] Further, when n>1, the DC input ports of the n DC-DC power converters are connected in series, wherein the positive pole of the DC input port of one DC-DC power converter is connected to the positive pole of the first DC port, and the negative pole of the DC input port of one DC-DC power converter is connected to the negative pole of the second DC port; the DC output ports of the n DC-DC power converters are connected in parallel, and are respectively connected to the positive pole of the second DC port and the positive pole of the unidirectional semiconductor switch.

[0020] A further beneficial effect of the present invention is that by connecting the input ends of the DC-DC power converters in series, the overall voltage tolerance of the input port of the DC-DC power converter part can be increased, and by connecting the output ports of the DC-DC power converters in parallel, the overall current tolerance of the output port of the DC-DC power converter part can be increased, thereby greatly improving the overall power transmission capacity of the DC-DC power converter part.

[0021] Furthermore, the n DC-DC power converters have the same topological structure.

[0022] A further beneficial effect of the present invention is that the manufacturing difficulty of the n DC-DC power converters can be simplified.

[0023] Further, the n DC-DC power converters are independently selected from:

[0024] DC-DC power converter based on dual active bridges, bidirectional LLC resonant converter, bidirectional LLC converter with added auxiliary inductor, bidirectional LLC converter with added auxiliary capacitor, resonant converter based on dual active bridges, resonant converter based on half-bridge, BOOST converter, BUCK-BOOST converter, bidirectional half-bridge converter.

[0025] A further beneficial effect of the present invention is that the application field of the DC-DC power transmission system is expanded.

[0026] Furthermore, the unidirectional semiconductor switch is a diode valve group.

[0027] A further beneficial effect of the present invention is that the diode valve group can enable the power transmission branch after the DC-DC power converter fails to have better active opening and closing capabilities, thereby increasing the controllability of the branch. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a schematic diagram of an existing DC-DC converter;

[0029] Figure 2 A schematic diagram of a DC-DC power transmission system provided by an embodiment of the present invention;

[0030] Figure 3 A schematic diagram of a low-cost and high-reliability DC-DC power transmission system provided by an embodiment of the present invention;

[0031] Figure 4 A specific schematic diagram of another low-cost and high-reliability DC-DC power transmission system provided by an embodiment of the present invention;

[0032] Figure 5A specific schematic diagram of another low-cost and high-reliability DC-DC power transmission system provided by an embodiment of the present invention;

[0033] Figure 6 A specific schematic diagram of another low-cost and high-reliability DC-DC power transmission system provided by an embodiment of the present invention;

[0034] Figure 7 A specific schematic diagram of another low-cost and high-reliability DC-DC power transmission system provided by an embodiment of the present invention;

[0035] Figure 8 A schematic diagram of a bidirectional LLC resonant converter;

[0036] Fig. 9 A schematic diagram of a bidirectional LLC converter with an additional auxiliary inductor;

[0037] Fig.10 A schematic diagram of a bidirectional LLC converter with an additional auxiliary capacitor;

[0038] Fig.11 A schematic diagram of a bidirectional full-bridge LLC converter;

[0039] Fig.12 A schematic diagram of a bidirectional half-bridge LLC resonant converter;

[0040] Fig.13 A schematic diagram of a bidirectional half-bridge converter.

[0041] In all the drawings, the same figure numbers are used to represent the same elements or structures, among which: 1. power supply DC system, 2. power receiving DC system, 3. dual active bridge inverter, 31. inverter bridge, 32. rectifier bridge, 4. power transmission system, 40. first DC port, 41. second DC port, 42. DC-DC power converter, 43. unidirectional semiconductor switch. DETAILED DESCRIPTION

[0042] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0043] like Figure 1As shown, a specific schematic diagram of an existing DC-DC power converter 3 for transmitting electric energy between a power supply DC system 1 and a power receiving DC system 2 is shown. When the electric energy of the power supply DC system 1 is transmitted to the power receiving DC system 2, it must first be converted into electric energy in the form of high-frequency AC through the inverter bridge 31 inside the DC-DC power converter 3, and then converted into electric energy in the form of DC through the rectifier bridge 32 inside the DC-DC power converter 3. It can be seen that the power transmission process needs to go through a two-stage conversion of DC-AC-DC, and the capacity design of the inverter unit 31 and the rectifier unit 32 needs to be designed according to the size of the actual transmission capacity, resulting in a large capacity requirement for power electronic devices inside the DC-DC power converter. On the other hand, when the DC-DC power converter 3 fails due to a fault, the power transmission between the power supply DC system 1 and the power receiving DC system 2 is interrupted, and energy cannot be transmitted further.

[0044] like Figure 2 As shown, this embodiment provides a DC-DC power transmission system 4, including a first DC port 40, a second DC port 41, a DC-DC power converter 42 and a unidirectional semiconductor switch 43. The positive and negative poles of the first DC port are respectively connected to the positive and negative poles of the DC input port of the DC-DC power converter, and are also externally connected to the positive and negative ports of the power supply DC system; the positive and negative poles of the second DC port are respectively externally connected to the positive and negative ports of the power receiving DC system, wherein the positive pole is also connected to the positive pole of the DC output port of the DC-DC power converter and the negative pole of the unidirectional semiconductor switch, and the negative pole is also connected to the negative pole of the first DC port; the positive pole of the unidirectional semiconductor switch is connected to the negative pole of the DC output port of the DC-DC power converter, and the positive pole of the first DC port is also connected to the positive pole of the unidirectional semiconductor switch.

[0045] It should be noted that a unidirectional semiconductor switch is a semiconductor switch device with restrictions on both the opening and current flow directions. This device will only be turned on when the closing requirements are met in the high and low potential directions, and thus the current flow direction is also limited. For example, diode valve groups, half-controlled semiconductor devices (such as thyristors), fully controlled semiconductor devices (such as insulated gate bipolar transistors IGBTs), etc. are all unidirectional semiconductor switches, where, for example, the anode of the diode valve group is the positive electrode of the above-mentioned unidirectional semiconductor switch, and the cathode of the diode valve group is the negative electrode of the above-mentioned unidirectional semiconductor switch.

[0046] By connecting a unidirectional semiconductor switch in reverse parallel between the positive and negative poles of the DC output port of the DC-DC power converter, and at the same time connecting the positive pole of the input end of the DC-DC power converter to the positive pole of the unidirectional semiconductor switch, when the DC-DC power converter inside the DC-DC power transmission system fails due to a fault, the power transmission between the power supply DC system and the power receiving DC system is automatically restored through the unidirectional semiconductor switch, which has a zero response time characteristic, avoids causing the power transmission interruption between the power supply DC system and the power receiving DC system, and greatly improves the reliability and availability of the DC-DC power transmission system. In addition, by connecting the positive pole of the input end of the DC-DC power converter to the negative pole of the output end of the DC-DC power converter, and further connecting the negative pole of the input end of the DC-DC power converter to the negative pole of the second DC port, the design capacity and power loss of the DC-DC power converter can be reduced, thereby reducing the volume and cost of the DC-DC power converter, and greatly improving the economy of the DC-DC power transmission system.

[0047] For example, Figure 3 As shown, it includes a first DC port 40, a second DC port 41, and a DC-DC power converter 42, and the unidirectional semiconductor switch 43 is a diode valve group 43. The first DC port 40 is connected to the power supply DC system 1, and the positive pole of the first DC port 40 is connected to the positive pole of the power supply DC system 1, and the negative pole of the first DC port 40 is connected to the negative pole of the power supply DC system 1; the second DC port 41 is connected to the power receiving DC system 2, and the positive pole of the second DC port 41 is connected to the positive pole of the power receiving DC system 2, and the negative pole of the second DC port 41 is connected to the negative pole of the power receiving DC system 2; the first DC port 40 is also connected to the DC input port of the DC-DC power converter 42, and the positive pole of the first DC port 40 is connected to the positive pole of the DC input port of the DC-DC power converter 42, and the negative pole of the first DC port 40 is connected to the DC input The positive pole of the second DC port 41 is also connected to the positive pole of the DC output port of the DC-DC power converter 42, and the negative pole of the second DC port 41 is also connected to the negative pole of the DC input port of the DC-DC power converter 42; and, the positive pole of the DC input port of the DC-DC power converter 42 is connected to the negative pole of the DC output port of the DC-DC power converter 42; the diode valve group 43 is bridged between the positive and negative poles of the DC output port of the DC-DC power converter 42, and the anode of the diode valve group 43 is connected to the negative pole of the DC output port of the DC-DC power converter 42, and the cathode of the diode valve group 43 is connected to the positive pole of the DC output port of the DC-DC power converter 42.

[0048] When the DC-DC power converter 42 is operating normally, the electric energy transmitted from the positive electrode of the first DC port enters the positive electrode of the DC input port of the DC-DC power converter 42 and flows from the negative electrode of the DC input port of the DC-DC power converter 42 into the negative electrode of the first DC port. After being converted by the DC-DC power converter 42, the electric energy is output through the positive electrode of the DC output port of the DC-DC power converter 42 and flows into the positive electrode of the second DC port to supply power to the receiving DC system. At this time, the receiving DC system forms a power supply circuit through the negative electrode of the second DC port and the negative electrode of the first DC port. In this case, due to the limitation of the current flow of the diode valve group, no current flows through the current branch from the positive electrode of the first DC port to the negative electrode of the DC output port of the DC-DC power converter 42.

[0049] When the DC-DC power converter 42 fails or is actively locked, the electric energy transmitted from the positive electrode of the first DC port directly enters the negative electrode of the DC output port of the DC-DC power converter 42 and supplies power to the receiving DC system through the diode valve group. This electric energy transmission branch after the DC-DC power converter fails has the ability to be actively opened and closed, which increases the controllability of the branch.

[0050] Preferably, the number of the above-mentioned DC-DC power converters is n, where n is a positive integer; and when n>1, the n DC-DC power converters are connected in combination, and the positive pole of the DC input port of one of the DC-DC power converters is connected to the positive pole of the first DC port; the negative pole of the DC input port of one of the DC-DC power converters is connected to the negative pole of the first DC port; the positive pole of the DC output port of one of the DC-DC power converters is connected to the positive pole of the second DC port, and the negative pole of the DC output port of one of the DC-DC power converters is connected to the anode of the diode valve group.

[0051] There is no limit to the number of DC-DC power converters used, and when there are multiple power converters, the multiple power converters can be connected in various ways, as long as there is a positive and negative input port and a positive and negative output port respectively connected, the compatibility of the power transmission system with the DC-DC power converter is greatly improved.

[0052] Preferably, when n>1, such as Figure 4 As shown, the DC input ports of n DC-DC power converters are connected in parallel to the first DC port respectively; the DC output ports of n DC-DC power converters are connected in parallel to the positive electrode of the second DC port and the anode of the diode valve group respectively.

[0053] The overall current transmission capacity of the DC-DC power converter part is increased by connecting a plurality of DC-DC power converter input ports and output ports in parallel, thereby achieving the purpose of improving the power transmission capacity.

[0054] Preferably, when n>1, such as Figure 5 As shown, the DC input ports of n DC-DC power converters are connected in parallel to the first DC port respectively; the DC output ports of n DC-DC power converters are connected in series, wherein the positive pole of the DC output port of one DC-DC power converter is connected to the positive pole of the second DC port, and the negative pole of the DC output port of one DC-DC power converter is connected to the anode of the diode valve group.

[0055] The overall current tolerance of the input port of the DC-DC power converter is increased by connecting the input ends of the DC-DC power converters in parallel, and the overall voltage tolerance of the output port of the DC-DC power converter is increased by connecting the output ends of the DC-DC power converters in series, thereby achieving the purpose of improving the overall power transmission capacity of the DC-DC power converter.

[0056] Preferably, when n>1, such as Figure 6 As shown, the DC input ports of n DC-DC power converters are connected in series, wherein the positive pole of the DC input port of one DC-DC power converter is connected to the positive pole of the first DC port, and the negative pole of the DC input port of one DC-DC power converter is connected to the negative pole of the second DC port; the DC output ports of n DC-DC power converters are connected in series, wherein the positive pole of the DC output port of one DC-DC power converter is connected to the positive pole of the second DC port, and the negative pole of the DC output port of one DC-DC power converter is connected to the anode of the diode valve group.

[0057] By connecting the input and output ends of each DC-DC power converter in series, the overall voltage tolerance of the input and output ports of the DC-DC power converter can be increased, thereby achieving the purpose of improving the power transmission capacity of the DC-DC power converter.

[0058] Preferably, when n>1, such as Figure 7As shown, the DC input ports of n DC-DC power converters are connected in series, wherein the positive pole of the DC input port of one DC-DC power converter is connected to the positive pole of the first DC port, and the negative pole of the DC input port of one DC-DC power converter is connected to the negative pole of the second DC port; the DC output ports of n DC-DC power converters are connected in parallel, and are respectively connected to the positive pole of the second DC port and the anode of the diode valve group.

[0059] By connecting the input ends of the DC-DC power converters in series, the overall voltage tolerance of the input port of the DC-DC power converter part can be increased. At the same time, by connecting the output ports of the DC-DC power converters in parallel, the overall current tolerance of the output port of the DC-DC power converter part can be increased, thereby greatly improving the overall power transmission capacity of the DC-DC power converter part.

[0060] Preferably, the n DC-DC power converters have the same topology.

[0061] Preferably, the n DC-DC power converters are independently selected from:

[0062] DC-DC power converter based on dual active bridge (DAB), bidirectional LLC resonant converter, bidirectional LLC converter with added auxiliary inductor, bidirectional LLC converter with added auxiliary capacitor, resonant converter based on dual active bridge (DAB), resonant converter based on half bridge, BOOST converter, BUCK-BOOST converter, bidirectional half-bridge converter.

[0063] are all well-known circuits in the industry. For example, a bidirectional LLC resonant converter such as Figure 8 As shown in Figure 2, the bidirectional LLC converter with auxiliary inductance is Fig. 9 As shown in Figure 2, the bidirectional LLC converter with additional auxiliary capacitors is Fig.10 As shown, the bidirectional full-bridge LLC converter is Fig.11 As shown in Figure 2, the bidirectional half-bridge LLC resonant converter is Fig.12 As shown in Figure 2, the bidirectional half-bridge converter is Fig.13 shown.

[0064] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A DC-DC power transmission system, characterized in that: It includes a first DC port, a second DC port, a DC-DC power converter and a unidirectional semiconductor switch; The positive and negative electrodes of the first DC port are respectively connected to the positive and negative electrodes of the DC input port of the DC-DC power converter, and are also respectively connected to the positive and negative ports of an external DC power supply system; The positive and negative electrodes of the second DC port are respectively connected to the positive and negative ports of the DC system for receiving power, wherein the positive electrode is also connected to the positive electrode of the DC output port of the DC-DC power converter and the negative electrode of the unidirectional semiconductor switch, and the negative electrode is also connected to the negative electrode of the first DC port; The positive electrode of the unidirectional semiconductor switch is connected to the negative electrode of the DC output port of the DC-DC power converter, and the positive electrode of the first DC port is also connected to the positive electrode of the unidirectional semiconductor switch; Wherein, the number of the DC-DC power converters is n, where n is a positive integer; and when n>1, the n DC-DC power converters are connected in combination, and the positive pole of the DC input port of one of the DC-DC power converters is connected to the positive pole of the first DC port; the negative pole of the DC input port of one of the DC-DC power converters is connected to the negative pole of the first DC port; the positive pole of the DC output port of one of the DC-DC power converters is connected to the positive pole of the second DC port, and the negative pole of the DC output port of one of the DC-DC power converters is connected to the positive pole of the unidirectional semiconductor switch; The n DC-DC power converters are independently selected from: DC-DC power converter based on dual active bridge, bidirectional LLC resonant converter, bidirectional LLC converter with added auxiliary inductor, bidirectional LLC converter with added auxiliary capacitor, resonant converter based on dual active bridge, resonant converter based on half bridge, BOOST converter, BUCK-BOOST converter, bidirectional half bridge converter; The unidirectional semiconductor switch is a diode valve group.

2. A DC-DC power transmission system according to claim 1, characterized in that: When n>1, the DC input ports of the n DC-DC power converters are respectively connected to the first DC port in parallel; the DC output ports of the n DC-DC power converters are respectively connected to the positive electrode of the second DC port and the positive electrode of the unidirectional semiconductor switch in parallel.

3. A DC-DC power transmission system according to claim 1, characterized in that: When n>1, the DC input ports of the n DC-DC power converters are respectively connected to the first DC port in parallel; and the DC output ports of the n DC-DC power converters are connected in series.

4. A DC-DC power transmission system according to claim 1, characterized in that: When n>1, the DC input ports of the n DC-DC power converters are connected in series; and the DC output ports of the n DC-DC power converters are connected in series.

5. A DC-DC power transmission system according to claim 1, characterized in that: When n>1, the DC input ports of the n DC-DC power converters are connected in series; the DC output ports of the n DC-DC power converters are connected in parallel, and are respectively connected to the positive electrode of the second DC port and the positive electrode of the unidirectional semiconductor switch.

6. A DC-DC power transmission system according to any one of claims 1 to 5, characterized in that: The n DC-DC power converters have the same topological structure.

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