Power-asymmetric bidirectional direct-current converter, and direct-current power transmission system

Abstract

Disclosed in the embodiments of the present disclosure are a power-asymmetric bidirectional direct-current converter, and a direct-current power transmission system. The power-asymmetric bidirectional direct-current converter comprises: a first fully controlled circuit, a transformer, a diode rectifier circuit and a second fully controlled circuit, wherein the first fully controlled circuit is used for converting a first direct-current voltage into a first alternating-current voltage or converting the first alternating-current voltage into the first direct-current voltage and outputting same; the transformer is used for transforming the voltage level of the first alternating-current voltage or transforming the voltage level of a second alternating-current voltage; the diode rectifier circuit is used for converting the second alternating-current voltage obtained by means of transformation into a second direct-current voltage and outputting same; and the second fully controlled circuit is used for converting the second direct-current voltage into a second alternating-current voltage and transmitting same to the transformer.

Description

A power asymmetric bidirectional DC-DC converter and DC transmission system

[0001] Cross-reference to related applications

[0002] This disclosure is based on Chinese Patent Application No. 202410674869.8, filed on May 28, 2024, entitled "A Power Asymmetric Bidirectional DC-DC Converter and DC Transmission System", and claims priority to that Chinese Patent Application, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This disclosure relates to the field of DC power transmission technology, and in particular to a power asymmetric bidirectional DC converter and a DC power transmission system. Background Technology

[0004] New energy DC aggregation and networking technology has the technical advantages of large-scale aggregation and wide-area interconnection. DC converters, as bridges between various DC voltages, are the core part of DC transmission systems.

[0005] DC-DC converters provided by related technologies typically employ a face-to-face topology. A face-to-face topology can include two fully controlled circuits, one acting as an inverter and the other as a rectifier, thereby achieving voltage conversion and power control.

[0006] However, due to the large number of fully controlled semiconductor devices in the fully controlled circuit, the DC-DC converter has high cost and significant operating losses. Summary of the Invention

[0007] This disclosure provides a power asymmetric bidirectional DC-DC converter and a DC transmission system, which solves the problems of high cost and large operating losses of DC-DC converters in related technologies.

[0008] On one hand, this disclosure provides a power asymmetric bidirectional DC-DC converter, including: a first fully controlled circuit, a transformer, a diode rectifier circuit, and a second fully controlled circuit. The first fully controlled circuit is connected to the transformer, and both the diode rectifier circuit and the second fully controlled circuit are connected to the transformer.

[0009] The first fully controlled circuit is used to: convert the first DC voltage into the first AC voltage, or convert the first AC voltage into the first DC voltage and output it.

[0010] The transformer is used to: transform the voltage level of a first AC voltage and transmit the transformed second AC voltage to a diode rectifier circuit. Alternatively, the transformer is used to transform the voltage level of a second AC voltage and transmit the transformed first AC voltage to a first fully controlled circuit. The first AC voltage and the second AC voltage have different voltage levels.

[0011] The diode rectifier circuit is used to: convert a second AC voltage into a second DC voltage and output it;

[0012] The second fully controlled circuit is used to convert the second DC voltage into a second AC voltage and transmit it to the transformer.

[0013] In some possible implementations, the transformer is also used to transmit the second AC voltage to the second fully controlled circuit.

[0014] The second fully controlled circuit is also used to convert the second AC voltage into a second DC voltage and output it.

[0015] In some possible implementations, the first fully controlled circuit adopts a three-phase bridge topology or a modular multilevel topology.

[0016] In some possible implementations, the diode rectifier circuit employs a six-pulse rectifier circuit.

[0017] In some possible implementations, the transformer includes a first winding, a second winding, and a third winding.

[0018] The DC terminal of the first fully controlled circuit serves as the first DC terminal of the power asymmetric bidirectional DC-DC converter. The AC terminal of the first fully controlled circuit is connected to the first winding. The AC terminal of the diode rectifier circuit is connected to the second winding. The AC terminal of the second fully controlled circuit is connected to the third winding. The DC terminals of the diode rectifier circuit and the second fully controlled circuit are connected to serve as the second DC terminal of the power asymmetric bidirectional DC-DC converter.

[0019] In some other possible implementations, the second fully controlled circuit includes a voltage source converter and a regulating circuit. The regulating circuit includes a high-voltage bridge arm and a low-voltage bridge arm connected in series.

[0020] The AC terminal of the voltage source converter serves as the AC terminal of the second fully controlled circuit. The first DC terminal of the voltage source converter is connected to the second terminal of the high-voltage bridge arm. The first DC terminal of the voltage source converter is also connected to the first terminal of the low-voltage bridge arm. The first terminal of the high-voltage bridge arm is connected to the first DC terminal of the diode rectifier circuit. The second terminal of the low-voltage bridge arm, the second DC terminal of the diode rectifier circuit, and the second DC terminal of the voltage source converter are connected.

[0021] In some possible implementations, both the high-voltage arm and the low-voltage arm include multiple sub-modules connected in series.

[0022] In one example, the submodule includes a capacitor, an inductor, a first insulated-gate bipolar transistor, and a diode;

[0023] The collector of the first insulated-gate bipolar transistor is connected to the positive terminal of the capacitor, serving as the first terminal of the submodule; the emitter of the first insulated-gate bipolar transistor, the first terminal of the inductor, and the cathode of the diode are connected; the anode of the diode serves as the second terminal of the submodule; the negative terminal of the capacitor is connected to the second terminal of the inductor, serving as the third terminal of the submodule.

[0024] In another example, the submodule includes a capacitor, an inductor, a first insulated-gate bipolar transistor, and a second insulated-gate bipolar transistor;

[0025] The collector of the first insulated-gate bipolar transistor is connected to the positive terminal of the capacitor, serving as the first terminal of the submodule; the emitter of the first insulated-gate bipolar transistor, the first terminal of the inductor, and the collector of the second insulated-gate bipolar transistor are connected; the emitter of the second insulated-gate bipolar transistor serves as the second terminal of the submodule; the negative terminal of the capacitor is connected to the second terminal of the inductor, serving as the third terminal of the submodule.

[0026] In some possible implementations, the voltage source converter adopts a two-level topology, a diode-clamped topology, a flying capacitor topology, or a modular multilevel topology.

[0027] In another aspect, embodiments of this disclosure provide a DC transmission system, which includes the aforementioned power asymmetric bidirectional DC-DC converter.

[0028] Compared with the prior art, the beneficial effects of the embodiments of this disclosure are as follows:

[0029] This disclosure provides a power asymmetric bidirectional DC-DC converter, comprising: a first fully controlled circuit, a transformer, a diode rectifier circuit, and a second fully controlled circuit. The first fully controlled circuit is connected to the transformer, and both the diode rectifier circuit and the second fully controlled circuit are connected to the transformer. The first fully controlled circuit is used to convert a first DC voltage into a first AC voltage, or to convert the first AC voltage into a first DC voltage and output it. The transformer is used to change the voltage level of the first AC voltage and transmit the resulting second AC voltage to the diode rectifier circuit, or to change the voltage level of the second AC voltage and transmit the resulting first AC voltage to the first fully controlled circuit, wherein the first AC voltage and the second AC voltage have different voltage levels. The diode rectifier circuit is used to convert the second AC voltage into a second DC voltage and output it. The second fully controlled circuit is used to convert the second DC voltage into a second AC voltage and transmit it to the transformer. In this embodiment, the semiconductor devices used in the diode rectifier circuit are all uncontrollable diodes, thereby greatly reducing the cost of the DC-DC converter and reducing its operating losses.

[0030] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and are not intended to limit this disclosure. Attached Figure Description

[0031] To more clearly illustrate the technical solutions in this disclosure or the prior art, the accompanying drawings used in the description of the embodiments of this disclosure or the prior art will be briefly introduced below. Obviously, the accompanying drawings described below are some embodiments of this disclosure. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0032] Figure 1 is a schematic structural diagram of a power asymmetric bidirectional DC-DC converter provided in an embodiment of this disclosure;

[0033] Figure 2 is another schematic structural diagram of the power asymmetric bidirectional DC-DC converter provided in the embodiments of this disclosure;

[0034] Figure 3 is a schematic structural diagram of a diode rectifier circuit provided in an embodiment of this disclosure;

[0035] Figure 4a is a schematic structural diagram of a first fully controlled circuit provided in an embodiment of this disclosure;

[0036] Figure 4b is another schematic structural diagram of the first fully controlled circuit provided in the embodiment of this disclosure;

[0037] Figure 4c is another schematic structural diagram of the first fully controlled circuit provided in the embodiments of this disclosure;

[0038] Figure 5 is a schematic structural diagram of a second fully controlled circuit provided in an embodiment of this disclosure;

[0039] Figure 6a is a schematic structural diagram of a high-voltage bridge arm / low-voltage bridge arm provided in an embodiment of this disclosure;

[0040] Figure 6b is another schematic structural diagram of the high-voltage bridge arm / low-voltage bridge arm provided in the embodiments of this disclosure;

[0041] Figure 7a is a schematic structural diagram of a voltage source converter provided in an embodiment of this disclosure;

[0042] Figure 7b is another schematic structural diagram of the voltage source converter provided in the embodiment of this disclosure;

[0043] Figure 7c is another schematic structural diagram of the voltage source converter provided in the embodiment of this disclosure;

[0044] Figure 7d is another schematic structural diagram of the voltage source converter provided in the embodiment of this disclosure. Detailed Implementation

[0045] The technical solutions in this disclosure will now be described with reference to the accompanying drawings of the embodiments thereof.

[0046] The terms "first," "second," etc., used in the embodiments, claims, and drawings of this disclosure are for distinguishing purposes only and should not be construed as indicating or implying relative importance or order. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion, such as including a series of steps or units. A method, system, product, or apparatus is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0047] It should be understood that in this disclosure, "at least one item" means one or more, and "more than one" means two or more. "And / or" is used to describe the relationship between related objects, indicating that three relationships can exist. For example, "A and / or B" can represent three cases: only A exists, only B exists, and both A and B exist simultaneously, where A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects are in an "or" relationship. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, at least one of a, b, or c can represent: a, b, c, "a and b", "a and c", "b and c", or "a and b and c", where a, b, and c can be single or multiple.

[0048] This disclosure provides a power asymmetric bidirectional DC-DC converter, as shown in Figures 1 and 2. The power asymmetric bidirectional DC-DC converter 10 may include a first fully controlled circuit 1, a transformer 2, a diode rectifier circuit 3, and a second fully controlled circuit 4. The first fully controlled circuit 1 is connected to the transformer 2, and both the diode rectifier circuit 3 and the second fully controlled circuit 4 are connected to the transformer 2.

[0049] The first fully controlled circuit 1 is used to: convert the first DC voltage DC1 into the first AC voltage AC1, or convert the first AC voltage AC1 into the first DC voltage DC1 and output it.

[0050] Transformer 2 is used to: transform the voltage level of the first AC voltage AC1 and transmit the transformed second AC voltage AC2 to the diode rectifier circuit 3. Alternatively, transformer 2 is used to transform the voltage level of the second AC voltage AC2 and transmit the transformed first AC voltage AC1 to the first fully controlled circuit 1. The first AC voltage AC1 and the second AC voltage AC2 have different voltage levels. In this embodiment, the voltage level of the first AC voltage AC1 may be lower than the voltage level of the second AC voltage AC2.

[0051] The diode rectifier circuit 3 is used to convert the second AC voltage AC2 into a second DC voltage DC2 and output it.

[0052] The second fully controlled circuit 4 is used to convert the second DC voltage DC2 into the second AC voltage AC2 and transmit it to the transformer 2.

[0053] The embodiments disclosed herein can realize the transmission of high power from the first fully controlled circuit 1 through the transformer 2 to the diode rectifier circuit 3 (which can be understood as forward power transmission), and can also realize the transmission of low power from the second fully controlled circuit 4 through the transformer 2 to the first fully controlled circuit 1 (which can be understood as reverse power transmission).

[0054] In some possible implementations, transformer 2 is also used to transmit the second AC voltage AC2 to the second fully controlled circuit 4. Transformer 2 can achieve electrical safety isolation.

[0055] The second full control circuit 4 is also used to: convert the second AC voltage AC2 into the second DC voltage DC2 and output it.

[0056] It is understood that the second fully controlled circuit 4 in this embodiment can convert the second DC voltage DC2 into the second AC voltage AC2 and transmit it to the transformer 2, and can also convert the second AC voltage AC2 from the transformer 2 into the second DC voltage DC2 and output it. In this way, the second fully controlled circuit 4 has the function of bidirectional power transmission, thereby realizing the bidirectional power transmission of the power asymmetric bidirectional DC-DC converter 10 and improving the power transmission efficiency and control flexibility of the power asymmetric bidirectional DC-DC converter 10.

[0057] In some possible implementations, as shown in Figure 1, the diode rectifier circuit 3 employs a six-pulse rectifier circuit. The transformer 2 includes a first winding 21, a second winding 22, and a third winding 23.

[0058] The DC terminal of the first fully controlled circuit 1 serves as the first DC terminal of the power asymmetric bidirectional DC-DC converter 10. The AC terminal of the first fully controlled circuit 1 is connected to the first winding 21. The AC terminal of the six-pulse rectifier circuit is connected to the second winding 22. The AC terminal of the second fully controlled circuit 4 is connected to the third winding 23. The DC terminals of the diode rectifier circuit 3 and the second fully controlled circuit 4 are connected to serve as the second DC terminal of the power asymmetric bidirectional DC-DC converter 10.

[0059] In some possible implementations, as shown in Figure 2, the diode rectifier circuit 3 can also be a twelve-pulse rectifier circuit. Based on Figure 1, the transformer 2 can also include a fourth winding 24. The fourth winding 24 can be connected to the AC terminal of the twelve-pulse rectifier circuit.

[0060] Figure 3 is a schematic structural diagram of a diode rectifier circuit provided in an embodiment of this disclosure. As shown in Figure 3, the diode rectifier circuit 3 adopts a six-pulse rectifier circuit. Each rectifier bridge arm may include multiple diodes connected in series, and each diode may be connected in parallel with a resistor-capacitor (RC) buffer branch. The RC buffer branch may include a resistor R and a capacitor C connected in series.

[0061] In some possible implementations, the first fully controlled circuit 1 is a three-phase bridge topology or a modular multilevel topology.

[0062] For example, the first fully controlled circuit 1 can be a three-phase bridge topology consisting of insulated gate bipolar transistors (IGBTs) connected in series, as shown in Figure 4a.

[0063] For example, the first fully controlled circuit 1 can be a three-phase bridge topology consisting of integrated gate-commutated thyristors (IGCTs) connected in series, as shown in Figure 4b.

[0064] For example, the first fully controlled circuit 1 can be a modular multilevel topology, as shown in Figure 4c. In Figure 4c, the sub-modules of the modular multilevel topology can be half-bridge sub-modules or full-bridge sub-modules, and this embodiment of the present disclosure is not limited thereto.

[0065] The AC side voltage (i.e., AC1) of the first fully controlled circuit 1 can be phase-locked and voltage / current dual closed-loop controlled, thereby obtaining the first AC voltage with the desired amplitude and frequency.

[0066] In some embodiments, as shown in Figures 1 and 2, the second fully controlled circuit 4 includes a voltage source converter (VSC) 41 and a regulating circuit 42. The AC terminal of the voltage source converter 41 serves as the AC terminal of the second fully controlled circuit 4. The first DC terminal of the voltage source converter 41 is connected to the second terminal of the high-voltage bridge arm. The first DC terminal of the voltage source converter 41 is also connected to the first terminal of the low-voltage bridge arm. The first terminal of the high-voltage bridge arm is connected to the first DC terminal of the diode rectifier circuit 3. The second terminal of the low-voltage bridge arm, the second DC terminal of the diode rectifier circuit 3, and the second DC terminal of the voltage source converter 41 are connected.

[0067] In some possible implementations, the voltage source converter 41 has reactive power compensation and active filtering functions, which can filter out low-order harmonics generated on the AC side by the diode rectifier circuit 3.

[0068] The voltage source converter 41 can invert the second DC voltage DC2 into the second AC voltage AC2. It also takes into account the load distribution between the diode rectifier circuit 3 and the voltage source converter 41 during power forward transmission. It is necessary to sample the AC side voltage (i.e., the second AC voltage AC2), AC side current and DC side current of the voltage source converter 41. Through closed-loop control, the second AC voltage AC2 can be stabilized while ensuring that the diode rectifier circuit 3 can stably output the second DC voltage DC2.

[0069] The regulating circuit 42 includes a high-voltage bridge arm and a low-voltage bridge arm connected in series. The high-voltage bridge arm may include submodules SMD11 to SMD1M connected in series. The low-voltage bridge arm may include submodules SMD21 to SMD2N connected in series.

[0070] Understandably, the regulating circuit 42 may also include only the high-voltage bridge arm, as shown in Figure 5.

[0071] In one example, as shown in Figure 6a, the high-voltage bridge arm / low-voltage bridge arm includes submodules SM1 and SM2 connected in series. Submodules SM1 and SM2 each include a capacitor C, an inductor L, a first insulated-gate bipolar transistor IGBT1, and a diode D.

[0072] In submodule SM1, the collector of the first insulated-gate bipolar transistor (IGBT1) is connected to the positive terminal of capacitor C, serving as the first terminal of submodule SM1. The emitter of the first IGBT1, the first terminal of inductor L, and the cathode of diode D are connected. The anode of diode D serves as the second terminal of submodule SM1. The negative terminal of capacitor C is connected to the second terminal of inductor L, serving as the third terminal of submodule SM1.

[0073] In submodule SM2, the collector of the first insulated-gate bipolar transistor (IGBT1) is connected to the positive terminal of capacitor C, serving as the first terminal of submodule SM2. The emitter of the first IGBT1, the first terminal of inductor L, and the cathode of diode D are connected. The anode of diode D serves as the second terminal of submodule SM2. The negative terminal of capacitor C is connected to the second terminal of inductor L, serving as the third terminal of submodule SM2.

[0074] The third end of submodule SM1 can be connected to the first end of submodule SM2, and the second end of submodule SM1 can be connected to the third end of submodule SM2. It can be seen that the high-voltage bridge arm / low-voltage bridge arm shown in Figure 6a is a unidirectional topology.

[0075] In another example, as shown in Figure 6b, the high-voltage bridge arm / low-voltage bridge arm includes submodules SM1 and SM2 connected in series. Submodules SM1 and SM2 each include a capacitor C, an inductor L, a first insulated-gate bipolar transistor (IGBT1), and a second insulated-gate bipolar transistor (IGBT2). Both IGBT1 and IGBT2 may have diodes connected in anti-parallel.

[0076] In submodule SM1, the collector of the first insulated-gate bipolar transistor (IGBT1) is connected to the positive terminal of capacitor C, serving as the first terminal of submodule SM1. The emitter of the first IGBT1 is connected to the first terminal of inductor L and the collector of the second IGBT2. The emitter of the second IGBT1 serves as the second terminal of submodule SM1. The negative terminal of capacitor C is connected to the second terminal of inductor L, serving as the third terminal of submodule SM1.

[0077] In submodule SM2, the collector of the first insulated-gate bipolar transistor (IGBT1) is connected to the positive terminal of capacitor C, serving as the first terminal of submodule SM2. The emitter of the first IGBT1 is connected to the first terminal of inductor L and the collector of the second IGBT2. The emitter of the second IGBT1 serves as the second terminal of submodule SM2. The negative terminal of capacitor C is connected to the second terminal of inductor L, serving as the third terminal of submodule SM2.

[0078] The third terminal of submodule SM1 can be connected to the first terminal of submodule SM2, and the second terminal of submodule SM1 can be connected to the third terminal of submodule SM2. It can be seen that the high-voltage bridge arm / low-voltage bridge arm shown in Figure 6b is a bidirectional topology.

[0079] The capacitor voltage and branch current of each submodule can be collected, and the energy balance and power stable transmission within the regulating circuit 42 can be achieved through voltage equalization control between submodules.

[0080] In some possible implementations, the voltage source converter 41 adopts a two-level topology as shown in Figure 7a, a diode-clamped (NPC) topology as shown in Figure 7b, a flying capacitor (FC) topology as shown in Figure 7c, or a modular multilevel (MMC) topology as shown in Figure 7d.

[0081] This disclosure also provides a DC power transmission system that may include the aforementioned power asymmetric bidirectional DC converter.

[0082] In some possible implementations, a DC transmission system may include two power asymmetric bidirectional DC-DC converters. One acts as the transmitter and the other as the receiver, enabling power transmission between DC systems of different voltage levels.

[0083] The above are merely embodiments of this disclosure and are not intended to limit this disclosure. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this disclosure shall be included within the scope of the claims of this disclosure pending approval. Industrial applicability

[0084] This disclosure provides a power asymmetric bidirectional DC-DC converter and a DC transmission system, including: a first fully controlled circuit, a transformer, a diode rectifier circuit, and a second fully controlled circuit; the first fully controlled circuit is connected to the transformer, and both the diode rectifier circuit and the second fully controlled circuit are connected to the transformer; the first fully controlled circuit is used to convert a first DC voltage into a first AC voltage, or to convert the first AC voltage into a first DC voltage and output it; the transformer is used to change the voltage level of the first AC voltage and transmit the resulting second AC voltage to the diode rectifier circuit, or to change the voltage level of the second AC voltage and transmit the resulting first AC voltage to the first fully controlled circuit, wherein the first AC voltage and the second AC voltage have different voltage levels; the diode rectifier circuit is used to convert the second AC voltage into a second DC voltage and output it; the second fully controlled circuit is used to convert the second DC voltage into a second AC voltage and transmit it to the transformer, and the semiconductor devices used in the diode rectifier circuit are all uncontrollable diodes, thereby greatly reducing the cost of the DC-DC converter and reducing the operating losses of the DC-DC converter.

Claims

1. A power asymmetrical bidirectional DC converter, comprising: The first full-control circuit, the transformer, the diode rectifier circuit and the second full-control circuit; the first full-control circuit is connected with the transformer, and the diode rectifier circuit and the second full-control circuit are both connected with the transformer; The first full-control circuit is used for converting a first direct current voltage into a first alternating current voltage, or converting the first alternating current voltage into the first direct current voltage and outputting; The transformer is used for transforming voltage levels of the first alternating current voltage and transmitting a second alternating current voltage obtained by transformation to the diode rectifier circuit, or transforming voltage levels of the second alternating current voltage and transmitting the first alternating current voltage obtained by transformation to the first full-control circuit; wherein the voltage levels of the first alternating current voltage and the second alternating current voltage are different from each other; The diode rectifier circuit is used for converting the second alternating current voltage into a second direct current voltage and outputting; The second full-control circuit is used for converting the second direct current voltage into the second alternating current voltage and transmitting to the transformer.

2. The power asymmetric bidirectional direct current converter according to claim 1, wherein The transformer is further used for transmitting the second alternating current voltage to the second full-control circuit; The second full-control circuit is further used for converting the second alternating current voltage into the second direct current voltage and outputting.

3. The power asymmetric bidirectional DC-DC converter according to claim 1 or 2, wherein, The transformer comprises a first winding, a second winding and a third winding; A direct current end of the first full-control circuit is used as a first direct current end of the power asymmetric bidirectional direct current converter, an alternating current end of the first full-control circuit is connected with the first winding, an alternating current end of the diode rectifier circuit is connected with the second winding, an alternating current end of the second full-control circuit is connected with the third winding, and a direct current end of the diode rectifier circuit and a direct current end of the second full-control circuit are connected with each other and used as a second direct current end of the power asymmetric bidirectional direct current converter.

4. The power-asymmetric bidirectional DC converter of claim 3, wherein, The first full-control circuit adopts a three-phase bridge topology or a modular multi-level topology.

5. The power asymmetric bidirectional DC-DC converter according to claim 3 or 4, wherein, The diode rectifier circuit adopts a six-pulse rectifier circuit.

6. The power-asymmetric bidirectional DC converter according to any of claims 3 to 5, wherein, The second full-control circuit comprises a voltage source converter and a regulating circuit; the regulating circuit comprises a high-voltage bridge arm and a low-voltage bridge arm connected in series; An alternating current end of the voltage source converter is used as an alternating current end of the second full-control circuit, a first direct current end of the voltage source converter is connected with a second end of the high-voltage bridge arm, the first direct current end of the voltage source converter is also connected with a first end of the low-voltage bridge arm, a first end of the high-voltage bridge arm is connected with a first direct current end of the diode rectifier circuit, a second end of the low-voltage bridge arm, a second direct current end of the diode rectifier circuit and a second direct current end of the voltage source converter are connected.

7. The power-asymmetric bidirectional DC converter of claim 6, wherein, The high-voltage bridge arm and the low-voltage bridge arm each comprise a plurality of sub-modules connected in series.

8. The power-asymmetric bidirectional DC converter of claim 7, wherein, The sub-module comprises a capacitor, an inductor, a first insulated gate bipolar transistor and a diode; The collector of the first insulated gate bipolar transistor is connected with the positive electrode end of the capacitor, as the first end of the sub-module; the emitter of the first insulated gate bipolar transistor, the first end of the inductor and the cathode of the diode are connected; the anode of the diode is as the second end of the sub-module; the negative electrode end of the capacitor is connected with the second end of the inductor, as the third end of the sub-module.

9. The power-asymmetric bidirectional DC converter according to claim 7 or 8, wherein, The sub-module comprises a capacitor, an inductor, a first insulated gate bipolar transistor and a second insulated gate bipolar transistor; The collector of the first insulated gate bipolar transistor is connected with the positive electrode end of the capacitor, as the first end of the sub-module; the emitter of the first insulated gate bipolar transistor, the first end of the inductor and the collector of the second insulated gate bipolar transistor are connected; the emitter of the second insulated gate bipolar transistor is as the second end of the sub-module; the negative electrode end of the capacitor is connected with the second end of the inductor, as the third end of the sub-module.

10. The power-asymmetric bidirectional DC converter according to any of claims 6 to 9, wherein, The voltage source converter adopts a two-level topology structure, a diode clamped topology structure, a flying capacitor topology structure or a modular multilevel topology structure. 11.A direct current power transmission system comprising the power asymmetric bidirectional direct current converter according to any one of claims 1 to 10.

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