High-voltage direct-current power transmission system

Abstract

The invention provides a high-voltage direct-current power transmission system. The high-voltage direct-current power transmission system comprises a first current converter and a second current converter, each of the first converter and the second converter comprises at least two bridge arms. The first converter is used for converting the first DC voltage into a port voltage. The second converter is used for converting the port voltage into a second DC voltage. The port voltage is a direct-current voltage containing an alternating-current bias voltage. It can be seen that the number of bridge arms of the first current converter and the second current converter is small, voltage boosting, voltage reducing and long-distance energy transmission can be achieved by needing a small number of power electronic devices, the cost and loss of the high-voltage direct-current power transmission system can be reduced, and the high-voltage direct-current power transmission system is suitable for high-voltage medium-large-capacity (for example, the capacity is smaller than 200-400 MW and the like) direct-current power transmission scenes. According to the invention, the power exchange efficiency between the bridge arms is improved, and the bridge arms are enabled to have a greater control freedom degree and a faster power regulation speed.

Description

Technical Field

[0001] The present application relates to the field of power transmission technology, and in particular to a high voltage direct current power transmission system. Background Art

[0002] With the rapid development of power electronic devices, DC transmission technology based on power electronic devices has been widely used. At present, the first converter of the high-voltage direct current transmission system is an alternating current (AC) / direct current (DC) converter, and the second converter is a DC / AC converter. In conventional high-voltage direct current transmission systems, AC / DC converters and DC / AC converters mainly use thyristor-based converters, while AC / DC converters and DC / AC converters in flexible direct current transmission systems mainly use converters of power submodules composed of fully controlled devices such as insulated gate bipolar transistors (IGBTs).

[0003] Although the high-voltage direct current transmission system provided by the related technology can realize flexible interconnection of different voltage levels and is suitable for high-voltage and large-capacity direct current transmission, both the AC / DC converter and the DC / AC converter include six bridge arms, and since each bridge arm uses a large number of power electronic devices, the high-voltage direct current transmission system is costly and has large losses. Summary of the invention

[0004] In order to solve the problems of high cost and large loss in the prior art, the present application provides a high voltage direct current transmission system, which may include a first converter and a second converter. The first converter and the second converter each include at least two bridge arms.

[0005] The first converter is used to convert the first DC voltage into a port voltage.

[0006] The second converter is used to convert the port voltage into a second DC voltage.

[0007] The port voltage is a DC voltage containing an AC bias voltage.

[0008] Optionally, the first converter further includes a first DC port, a second DC port, a third DC port and a fourth DC port, and the second converter further includes a fifth DC port, a sixth DC port, a seventh DC port and an eighth DC port.

[0009] The first DC port and the second DC port constitute the first end of the first converter, and also serve as the first end of the high-voltage direct current transmission system. The third DC port and the fourth DC port constitute the second end of the first converter, the fifth DC port and the sixth DC port constitute the first end of the second converter, the third DC port is connected to the fifth DC port, and the fourth DC port is connected to the sixth DC port. The seventh DC port and the eighth DC port constitute the second end of the second converter, and also serve as the second end of the high-voltage direct current transmission system.

[0010] Exemplarily, the first end of the high-voltage direct current transmission system is an input end or an output end, and the second end of the high-voltage direct current transmission system is an output end or an input end. In other words, the high-voltage direct current transmission system can realize bidirectional power transmission.

[0011] In some possible implementations, the first converter or the second converter includes a first bridge arm, a second bridge arm, and a passive branch.

[0012] The first end of the first bridge arm and the passive branch are connected to serve as the third DC port or the fifth DC port. The second end of the first bridge arm is connected to the first end of the second bridge arm to serve as the first DC port or the seventh DC port. The second end of the second bridge arm and the passive branch are connected to serve as the second DC port, the fourth DC port, the sixth DC port and the eighth DC port.

[0013] Optionally, the passive branch includes a capacitor and a first inductor connected in series.

[0014] Furthermore, the first bridge arm and the second bridge arm both include a controlled voltage source.

[0015] The first bridge arm and / or the second bridge arm comprises a second inductor connected in series with the controlled voltage source.

[0016] In some other possible implementations, the first converter or the second converter includes a first bridge arm, a second bridge arm, a third bridge arm, and a fourth bridge arm.

[0017] The first ends of the first bridge arm and the third bridge arm are respectively connected to serve as a third DC port or a fifth DC port.

[0018] The second end of the first bridge arm is connected to the first end of the second bridge arm as the first DC port or the seventh DC port. Alternatively, the second end of the first bridge arm is connected to the first end of the second bridge arm as the first DC port or the seventh DC port, and the second end of the third bridge arm is connected to the first end of the fourth bridge arm as the thirteenth DC port of the first converter or the fourteenth DC port of the second converter. Alternatively, the second end of the first bridge arm, the first end of the second bridge arm, the second end of the first bridge arm and the first end of the fourth bridge arm are connected as the first DC port or the seventh DC port.

[0019] The second ends of the second bridge arm and the fourth bridge arm are respectively connected to serve as the second DC port, the fourth DC port, the sixth DC port and the eighth DC port.

[0020] Furthermore, the first bridge arm, the second bridge arm, the third bridge arm and the fourth bridge arm all include a controlled voltage source.

[0021] The first bridge arm and / or the second bridge arm comprises a second inductor connected in series with the corresponding controlled voltage source, and the third bridge arm and / or the fourth bridge arm comprises a third inductor connected in series with the corresponding controlled voltage source.

[0022] In some other possible implementations, the first converter or the second converter includes a first bridge arm, a second bridge arm, a third bridge arm, a fourth bridge arm, a fifth bridge arm, and a sixth bridge arm. The first converter also includes a ninth DC port and a tenth DC port, and the second converter also includes an eleventh DC port and a twelfth DC port.

[0023] The first ends of the first bridge arm, the third bridge arm and the fifth bridge arm are respectively connected to serve as a third DC port or a fifth DC port.

[0024] The second end of the first bridge arm is connected to the first end of the second bridge arm as the first DC port or the seventh DC port. The second end of the third bridge arm is connected to the first end of the fourth bridge arm as the ninth DC port or the eleventh DC port. The second end of the fifth bridge arm is connected to the first end of the sixth bridge arm as the tenth DC port or the twelfth DC port. Alternatively, the second end of the first bridge arm, the second end of the third bridge arm, the second end of the fifth bridge arm, the first end of the second bridge arm, the first end of the fourth bridge arm and the first end of the sixth bridge arm are connected as the first DC port or the seventh DC port.

[0025] The second ends of the second bridge arm, the fourth bridge arm and the sixth bridge arm are respectively connected to serve as the second DC port, the fourth DC port, the sixth DC port and the eighth DC port.

[0026] Further, the first bridge arm, the second bridge arm, the third bridge arm, the fourth bridge arm, the fifth bridge arm and the sixth bridge arm include a controlled voltage source.

[0027] The first bridge arm and / or the second bridge arm also includes a second inductor connected in series with the corresponding controlled voltage source, the third bridge arm and / or the fourth bridge arm also includes a third inductor connected in series with the corresponding controlled voltage source, and the fifth bridge arm and / or the sixth bridge arm also includes a fourth inductor connected in series with the corresponding controlled voltage source.

[0028] Exemplarily, the controlled voltage source includes a half-bridge topology and / or a full-bridge topology.

[0029] Furthermore, there are one or more half-bridge topology structures and one or more full-bridge topology structures.

[0030] Compared with the prior art, the beneficial effects of this application are:

[0031] The high-voltage direct current transmission system provided in the present application may include a first converter and a second converter. The first converter and the second converter each include at least two bridge arms. The first converter is used to convert a first DC voltage into a port voltage. The second converter is used to convert the port voltage into a second DC voltage. The port voltage is a DC voltage containing an AC bias voltage. It can be seen that the number of bridge arms of the first converter and the second converter in the present application is small, which can reduce the cost and loss of the high-voltage direct current transmission system.

[0032] In the present application, fewer power electronic devices are required in the first converter and the second converter to achieve voltage boosting, voltage reduction and long-distance transmission of energy, and can be applied to high-voltage and medium-capacity (for example, less than 200-400MW, etc.) DC transmission scenarios.

[0033] The DC / DC converter provided by the related technology needs to add a filter or an additional energy balancing bridge arm on the low-voltage side to maintain the voltage on the low-voltage side. The present application can directly match the external DC power supply or load by controlling the voltage on the low-voltage side, so it is more economical.

[0034] The related technology provides a voltage-divider DC / DC converter in which the controllable voltage output voltages of the two bridge arms are as close in amplitude as possible and opposite in phase, resulting in a low power exchange efficiency between the two bridge arms. However, the present application does not require the DC voltage to be maintained constant, and the port voltage is a DC voltage containing an AC bias voltage, thereby improving the power exchange efficiency between the bridge arms and allowing the bridge arms to have greater control freedom and faster power regulation speed.

[0035] Compared with the flexible DC transmission system based on MMC converter in the related technology, the present application not only has fewer bridge arms, but also does not require a converter transformer. Ideally, the distribution power on the power supply side can even be directly boosted by the first converter for high-voltage DC long-distance transmission, and then reduced to the voltage required by the load through the second converter, reducing multiple intermediate AC-DC conversion and AC-AC conversion links, thereby saving the cost of high-voltage DC transmission.

[0036] The high-voltage direct current transmission system provided in the present application can directly integrate distributed renewable energy sources along the transmission lines, and can also directly supply power to multiple loads along the long-distance transmission lines from the collected distributed renewable energy sources, thereby increasing the reliability and redundancy of the high-voltage direct current transmission system. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the technical solutions in the present application or the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0038] Figure 1 A schematic structural diagram of a high voltage direct current transmission system in an embodiment of the present application;

[0039] Figure 2a A schematic structural diagram of a single-phase converter in an embodiment of the present application;

[0040] Figure 2b Another schematic structural diagram of a single-phase converter in an embodiment of the present application;

[0041] Figure 2c Another schematic structural diagram of a single-phase converter in an embodiment of the present application;

[0042] Figure 3a A schematic structural diagram of a two-phase converter in an embodiment of the present application;

[0043] Figure 3b is another schematic structural diagram of a two-phase converter in an embodiment of the present application;

[0044] Figure 3c is another schematic structural diagram of a two-phase converter in an embodiment of the present application;

[0045] Figure 4a A schematic structural diagram of a three-phase converter in an embodiment of the present application;

[0046] Figure 4b Another schematic structural diagram of a three-phase converter in an embodiment of the present application;

[0047] Figure 5a A schematic structural diagram of a half-bridge topology structure in an embodiment of the present application;

[0048] Figure 5b A schematic structural diagram of a full-bridge topology structure in an embodiment of the present application;

[0049] Figure 6 A schematic structural diagram of a high voltage direct current transmission system in an embodiment of the present application;

[0050] Figure 7 Schematic diagram of the waveform of the port voltage of the first converter in the embodiment of the present application;

[0051] Figure 8Schematic diagram of the waveform of the port voltage of the second converter in the embodiment of the present application;

[0052] Fig. 9 Schematic diagram of the waveform of the direct current of the transmission line in the embodiment of the present application. DETAILED DESCRIPTION

[0053] The technical solution in this application will be described below in conjunction with the accompanying drawings.

[0054] The terms "first", "second", etc. in the specification embodiments, claims, and drawings of the present application are only used for the purpose of distinguishing descriptions, and cannot be understood as indicating or implying relative importance, nor can they be understood as indicating or implying order. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, including a series of steps or units. The method, system, product, or device is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products, or devices.

[0055] It should be understood that in the present application, "at least one (item)" means one or more, and "plurality" means two or more. "And / or" is used to describe the association relationship of associated objects, indicating that three relationships may exist. For example, "A and / or B" can mean: only A exists, only B exists, and A and B exist at the same time, where A and B can be singular or plural. The character " / " generally indicates that the objects associated before and after are in an "or" relationship. "At least one of the following" or similar expressions refers 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 mean: a, b, c, "a and b", "a and c", "b and c", or "a and b and c", where a, b, c can be single or multiple.

[0056] The present application provides a high voltage direct current transmission system, such as Figure 1 As shown. The high voltage direct current transmission system 10 includes a first converter 1 and a second converter 2. The first converter 1 and the second converter 2 each include at least two bridge arms ( Figure 1 (a) The example includes two bridge arms.

[0057] The first converter 1 is used to: convert the first DC voltage U dc1 Convert to port voltage.

[0058] The second converter 2 is used to convert the port voltage into a second DC voltage U dc2 .

[0059] It is conceivable that the first converter 1 and the second converter 2 may be connected via a transmission line such as a cable. dc3 The port voltage may be a DC voltage including an AC bias voltage.

[0060] Optional, such as Figure 1 As shown, the first converter 1 further includes a first DC port P1, a second DC port P2, a third DC port P3 and a fourth DC port P4, and the second converter 2 further includes a fifth DC port P5, a sixth DC port P6, a seventh DC port P7 and an eighth DC port P8.

[0061] Among them, the first DC port P1 and the second DC port P2 can constitute the first end of the first converter 1 (which can be the input end / output end of the first converter 1), and also serve as the first end of the high-voltage direct current transmission system 10 (which can be the input end or output end of the high-voltage direct current transmission system 10). The third DC port P3 and the fourth DC port P4 constitute the second end of the first converter 1 (which can be the output end / input end of the first converter 1), the fifth DC port P5 and the sixth DC port P6 constitute the first end of the second converter 2 (which can be the input end / output end of the first converter 1), the third DC port P3 is connected to the fifth DC port P5, and the fourth DC port P4 is connected to the sixth DC port P6. The seventh DC port P7 and the eighth DC port P8 constitute the second end of the second converter 2 (which can be the output end / input end of the second converter 2), and also serve as the second end of the high-voltage direct current transmission system 10 (which can be the output end or input end of the high-voltage direct current transmission system 10).

[0062] For example, the first end of the HVDC transmission system 10 may be an input end or an output end, and the second end of the HVDC transmission system 10 may be an output end or an input end. In other words, the HVDC transmission system 10 can realize bidirectional power transmission.

[0063] Optionally, the first converter 1 is used as a sending-end converter, and the second converter 2 is used as a receiving-end converter. Then, the port voltage at the second end of the first converter 1 (i.e., the port voltage U dc3 ) is greater than the port voltage of the first end of the second converter 2 (which can be represented by U dc4 That is to say, there will be some power loss during the power transmission process.

[0064] Figure 1In the illustrated embodiment, the first converter 1 includes a first bridge arm 11, a second bridge arm 12 and a passive branch 17, wherein the passive branch 17 includes a capacitor C1 and a first inductor L11 connected in series. The second converter 2 includes a first bridge arm 21, a second bridge arm 22 and a passive branch 27, wherein the passive branch 27 includes a capacitor C2 and a first inductor L12 connected in series.

[0065] In some possible implementations, the first converter 1 or the second converter 2 includes a first bridge arm, a second bridge arm, and a passive branch.

[0066] The first end of each of the first bridge arm and the passive branch is connected to serve as the third DC port P3 or the fifth DC port P5. The second end of the first bridge arm is connected to the first end of the second bridge arm to serve as the first DC port P1 or the seventh DC port P7. The second end of each of the second bridge arm and the passive branch is connected to serve as the second DC port P2, the fourth DC port P4, the sixth DC port P6 and the eighth DC port P8. It can be seen that the first converter 1 or the second converter 2 is a single-phase converter.

[0067] The embodiment of the present application takes the first converter 1 as an example to introduce the specific structure of the single-phase converter.

[0068] like Figure 2a , Figure 2b and Figure 2c As shown, the first converter 1 includes a first bridge arm 11 (upper bridge arm), a second bridge arm 12 (lower bridge arm) and a passive branch 17 .

[0069] The first ends of the first bridge arm 11 and the passive branch 17 are connected to form a third DC port P3. The second end of the first bridge arm 11 is connected to the first end of the second bridge arm 12 to form a first DC port P1. The second ends of the second bridge arm 12 and the passive branch 17 are connected to form a second DC port P2 and a fourth DC port P4.

[0070] Optionally, the passive branch 17 includes a capacitor C1 and a first inductor L11 connected in series.

[0071] Furthermore, both the first bridge arm 11 and the second bridge arm 12 include a controlled voltage source. In the embodiment of the present application, the first bridge arm 11 includes a controlled voltage source S1, and the second bridge arm 12 includes a controlled voltage source S2.

[0072] like Figure 2a As shown, the first bridge arm 11 includes a controlled voltage source S1 and a second inductor L21 connected in series with the controlled voltage source S1. Figure 2b As shown, the second bridge arm 12 includes a controlled voltage source S2 and a second inductor L22 connected in series with the controlled voltage source S2. Figure 2cAs shown, the first bridge arm 11 includes a controlled voltage source S1 and a second inductor L21 connected in series with the controlled voltage source S1, and the second bridge arm 12 includes a controlled voltage source S2 and a second inductor L22 connected in series with the controlled voltage source S2. That is, both the first bridge arm 11 and the second bridge arm 12 include a controlled voltage source. The first bridge arm 11 and / or the second bridge arm 12 include a second inductor connected in series with the controlled voltage source.

[0073] In some other possible implementations, the first converter 1 or the second converter 2 includes a first bridge arm, a second bridge arm, a third bridge arm and a fourth bridge arm.

[0074] The first ends of the first bridge arm and the third bridge arm are respectively connected to serve as the third DC port P3 or the fifth DC port P5.

[0075] The second end of the first bridge arm is connected to the first end of the second bridge arm to serve as the first DC port P1 or the seventh DC port P7. Alternatively, the second end of the first bridge arm is connected to the first end of the second bridge arm to serve as the first DC port P1 or the seventh DC port P7, and the second end of the third bridge arm is connected to the first end of the fourth bridge arm to serve as the thirteenth DC port P13 of the first converter 1 (see Figure 3b ) or the fourteenth DC port of the second converter 2. Alternatively, the second end of the first bridge arm, the first end of the second bridge arm, the second end of the first bridge arm and the first end of the fourth bridge arm are connected to serve as the first DC port P1 or the seventh DC port P7.

[0076] The second ends of the second bridge arm and the fourth bridge arm are respectively connected to serve as the second DC port P2, the fourth DC port P4, the sixth DC port P6 and the eighth DC port P8.

[0077] It can be seen that the first converter 1 or the second converter 2 is a two-phase converter.

[0078] The embodiment of the present application takes the first converter 1 as an example to introduce the specific structure of the two-phase converter.

[0079] like Figure 3a , Figure 3b and Figure 3c The first converter 1 includes a first bridge arm 11 (upper bridge arm), a second bridge arm 12 (lower bridge arm), a third bridge arm 13 (upper bridge arm) and a fourth bridge arm 14 (lower bridge arm).

[0080] The first ends of the first bridge arm 11 and the third bridge arm 13 are connected to form a third DC port P3. The second end of the first bridge arm 11 is connected to the first end of the second bridge arm 12 to form a first DC port. The second ends of the second bridge arm 12 and the fourth bridge arm 14 are connected to form a second DC port and a fourth DC port P4.

[0081] like Figure 3aAs shown, the first ends of the first bridge arm 11 and the third bridge arm 13 are connected to form a third DC port P3. The second end of the first bridge arm 11 is connected to the first end of the second bridge arm 12 to form a first DC port P1. The second ends of the second bridge arm 12 and the fourth bridge arm 14 are connected to form a second DC port P2 and a fourth DC port P4.

[0082] like Figure 3b As shown, the second end of the first bridge arm 11 is connected to the first end of the second bridge arm 12 as the first DC port P, and the second end of the third bridge arm 13 is connected to the first end of the fourth bridge arm 14 as the thirteenth DC port P13. The second ends of the second bridge arm 12 and the fourth bridge arm 14 are respectively connected to form the second DC port P2 and the fourth DC port P4.

[0083] like Figure 3c As shown, the second end of the first bridge arm 11 is connected to the first end of the second bridge arm 12 as the first DC port P1, and the second end of the first bridge arm 11, the first end of the second bridge arm 12, the second end of the first bridge arm 11 and the first end of the fourth bridge arm 14 are connected as the first DC port P1. The second ends of the second bridge arm 12 and the fourth bridge arm 14 are respectively connected as the second DC port P2 and the fourth DC port P4.

[0084] Optionally, the first bridge arm 11, the second bridge arm 12, the third bridge arm 13 and the fourth bridge arm 14 all include controlled voltage sources. In the embodiment of the present application, the first bridge arm 11 includes a controlled voltage source S1, the second bridge arm 12 includes a controlled voltage source S2, the third bridge arm 13 includes a controlled voltage source S3, and the fourth bridge arm 114 includes a controlled voltage source S4.

[0085] like Figure 3a , Figure 3b and Figure 3c The first bridge arm 11 includes a controlled voltage source S1 and a second inductor L21 connected in series with the controlled voltage source S1. The third bridge arm 13 includes a controlled voltage source S3 and a second inductor L23 connected in series with the controlled voltage source S3. The second bridge arm 12 includes a controlled voltage source S2. The fourth bridge arm 14 includes a controlled voltage source S4.

[0086] Of course, the first bridge arm 11 may not be provided with the second inductor, and the second bridge arm 12 may be provided with the second inductor. Alternatively, the first bridge arm 11 and the second bridge arm 12 may both be provided with the second inductor. Similarly, the third bridge arm 13 may not be provided with the second inductor, and the fourth bridge arm 14 may be provided with the second inductor. Alternatively, the third bridge arm 13 and the fourth bridge arm 14 may both be provided with the second inductor.

[0087] That is, the first bridge arm 11 and / or the second bridge arm 12 includes a second inductor L21 connected in series with the corresponding controlled voltage source, and the third bridge arm 13 and / or the fourth bridge arm 14 includes a third inductor L22 connected in series with the corresponding controlled voltage source.

[0088] In some other possible implementations, the first converter 1 or the second converter 2 includes a first bridge arm, a second bridge arm, a third bridge arm, a fourth bridge arm, a fifth bridge arm and a sixth bridge arm. The first converter 1 also includes a ninth DC port P9 (see Figure 4a ) and the tenth DC port P10 (see Figure 4a ), the second converter 2 also includes an eleventh DC port and a twelfth DC port.

[0089] The first ends of the first bridge arm, the third bridge arm and the fifth bridge arm are respectively connected to serve as the third DC port P3 or the fifth DC port P5.

[0090] The second end of the first bridge arm is connected to the first end of the second bridge arm as the first DC port or the seventh DC port. The second end of the third bridge arm is connected to the first end of the fourth bridge arm as the ninth DC port or the eleventh DC port. The second end of the fifth bridge arm is connected to the first end of the sixth bridge arm as the tenth DC port or the twelfth DC port. Alternatively, the second end of the first bridge arm, the second end of the third bridge arm, the second end of the fifth bridge arm, the first end of the second bridge arm, the first end of the fourth bridge arm and the first end of the sixth bridge arm are connected as the first DC port or the seventh DC port.

[0091] The second ends of the second bridge arm, the fourth bridge arm and the sixth bridge arm are respectively connected to serve as the second DC port P2, the fourth DC port P4, the sixth DC port and the eighth DC port.

[0092] It can be seen that the first converter 1 or the second converter 2 is a three-phase converter.

[0093] The embodiment of the present application takes the first converter 1 as an example to introduce the specific structure of the three-phase converter.

[0094] like Figure 4a and Figure 4b As shown, the first converter 1 includes a first bridge arm 11 (upper bridge arm), a second bridge arm 12 (lower bridge arm), a third bridge arm 13 (upper bridge arm), a fourth bridge arm 14 (lower bridge arm), a fifth bridge arm 15 (upper bridge arm) and a sixth bridge arm 16 (lower bridge arm). Figure 4a , the first converter 1 further includes a ninth DC port P9 and a tenth DC port P10.

[0095] The first bridge arm 11 includes a controlled voltage source S1 and a second inductor L21 connected in series with the controlled voltage source S1. The third bridge arm 13 includes a controlled voltage source S3 and a second inductor L23 connected in series with the controlled voltage source S3. The fifth bridge arm 15 includes a controlled voltage source S5 and a second inductor L25 connected in series with the controlled voltage source S3. The second bridge arm 12 includes a controlled voltage source S2, the fourth bridge arm 14 includes a controlled voltage source S4, and the sixth bridge arm 16 includes a controlled voltage source S6.

[0096] Figure 4a In the embodiment, the first ends of the first bridge arm 11, the third bridge arm 13 and the fifth bridge arm 15 are connected to form a third DC port P3. The second end of the first bridge arm 11 is connected to the first end of the second bridge arm 12 to form a first DC port P1 or a seventh DC port P7. The second end of the third bridge arm 13 is connected to the first end of the fourth bridge arm 14 to form a ninth DC port P9. The second end of the fifth bridge arm 15 is connected to the first end of the sixth bridge arm 16 to form a tenth DC port P10. The second ends of the second bridge arm 12, the fourth bridge arm 14 and the sixth bridge arm 16 are connected to form a second DC port P2 and a fourth DC port P4.

[0097] Figure 4b In the embodiment, the first ends of the first bridge arm 11, the third bridge arm 13 and the fifth bridge arm 15 are connected to form a third DC port P3. The second end of the first bridge arm 11, the second end of the third bridge arm 13, the second end of the fifth bridge arm 15, the first end of the second bridge arm 12, the first end of the fourth bridge arm 14 and the first end of the sixth bridge arm 16 are connected to form a first DC port P1. The second ends of the second bridge arm 12, the fourth bridge arm 14 and the sixth bridge arm 16 are connected to form a second DC port P2 and a fourth DC port P4.

[0098] Further, the first bridge arm, the second bridge arm, the third bridge arm, the fourth bridge arm, the fifth bridge arm and the sixth bridge arm include a controlled voltage source.

[0099] The first bridge arm and / or the second bridge arm also includes a second inductor connected in series with the corresponding controlled voltage source, the third bridge arm and / or the fourth bridge arm also includes a third inductor connected in series with the corresponding controlled voltage source, and the fifth bridge arm and / or the sixth bridge arm also includes a fourth inductor connected in series with the corresponding controlled voltage source. That is to say, only one of the first bridge arm and the second bridge arm may be provided with the second inductor, or both bridge arms may be provided with the second inductor. Similarly, only one of the third bridge arm and the fourth bridge arm may be provided with the second inductor, or both bridge arms may be provided with the second inductor. Only one of the fifth bridge arm and the sixth bridge arm may be provided with the second inductor, or both bridge arms may be provided with the second inductor.

[0100] like Figure 4a and Figure 4bAs shown, the first bridge arm 11 includes a controlled voltage source S1 and a second inductor L21 connected in series with the controlled voltage source S1, the third bridge arm 13 includes a controlled voltage source S3 and a second inductor L23 connected in series with the controlled voltage source S3, and the fifth bridge arm 15 includes a controlled voltage source S5 and a second inductor L25 connected in series with the controlled voltage source S5. The second bridge arm 12 includes a controlled voltage source S2, the fourth bridge arm 14 includes a controlled voltage source S4, and the sixth bridge arm 16 includes a controlled voltage source S6.

[0101] Exemplarily, each of the above-mentioned controlled voltage sources may include: Figure 5a The half-bridge topology shown and / or Figure 5b The full-bridge topology shown. Both the half-bridge topology and the full-bridge topology can be one or more. That is, each controlled voltage source can include one or more half-bridge structures, or one or more full-bridge structures, or one or more half-bridge structures and one or more full-bridge structures.

[0102] like Figure 5a As shown, the half-bridge topology may include capacitor C2, IGBT1 and IGBT2. Figure 5b As shown, the full-bridge topology may include capacitor C2, IGBT1, IGBT2, IGBT3 and IGBT4.

[0103] Of course, in addition to the above-mentioned single-phase converter, two-phase converter and three-phase converter, the first converter 1 and the second converter 2 can also be converters with more phases, which will not be described in detail in the embodiments of the present application.

[0104] For example Figure 6 In the high-voltage direct current transmission system shown in FIG. 1 , the first direct current voltage U dc1 and the second DC voltage U dc2 is 100 kV, the first converter 1 (as the sending end converter) converts the first DC voltage U dc1 Converted into the port voltage U of the first converter 1 dc3 , is sent to the second converter 2 (as the receiving converter) through the transmission line, and the port voltage U dc4 , through real-time adjustment to ensure U dc3 with U dc4 There is a voltage difference between them. When power is transmitted, U dc3 Slightly larger, U dc3 Can be 301kV, U dc4 The port voltage U of the first converter 1 is about 300 kV. dc3 and the port voltage U of the second converter 2 dc4 They are all DC voltages containing AC bias voltages, wherein the peak value of the AC bias voltage is 50 kV. Figure 6 middle, I dcThe DC current of the transmission line is about 1kA. The port voltage U dc3 like Figure 7 As shown, the port voltage U of the second converter 2 dc4 The waveform diagram is as follows Figure 8 As shown, the DC current I dc The waveform diagram is as follows Fig. 9 shown.

[0105] pass Figures 6 to 9 It can be seen that, since the second converter 2 is an active load characteristic, the first converter 1 can adopt constant DC voltage control, and the second converter 2 can adopt constant power control. It can be seen that the first converter 1 and the second converter 2 can adapt to different DC control methods, and have good interactive adaptability with other DC systems in related technologies.

[0106] The above are merely embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention are included in the scope of the claims of the present invention to be approved.

Claims

1. A high voltage direct current transmission system, characterized in that: The invention comprises a first converter and a second converter; the first converter and the second converter each comprise at least two bridge arms; The first converter is used to: convert the first DC voltage into a port voltage; The second converter is used to: convert the port voltage into a second DC voltage; Wherein, the port voltage is a DC voltage containing an AC bias voltage.

2. The high voltage direct current transmission system according to claim 1, characterized in that: The first converter further includes a first DC port, a second DC port, a third DC port and a fourth DC port, and the second converter further includes a fifth DC port, a sixth DC port, a seventh DC port and an eighth DC port; Wherein, the first DC port and the second DC port constitute the first end of the first converter, and also serve as the first end of the high-voltage direct current transmission system; the third DC port and the fourth DC port constitute the second end of the first converter, the fifth DC port and the sixth DC port constitute the first end of the second converter, the third DC port is connected to the fifth DC port, and the fourth DC port is connected to the sixth DC port; the seventh DC port and the eighth DC port constitute the second end of the second converter, and also serve as the second end of the high-voltage direct current transmission system; The first end of the high-voltage direct current transmission system is an input end or an output end, and the second end of the high-voltage direct current transmission system is an output end or an input end.

3. The high voltage direct current transmission system according to claim 2, characterized in that: The first converter or the second converter comprises a first bridge arm, a second bridge arm and a passive branch; The first ends of the first bridge arm and the passive branch are respectively connected to serve as the third DC port or the fifth DC port; the second end of the first bridge arm is connected to the first end of the second bridge arm to serve as the first DC port or the seventh DC port; the second end of the second bridge arm and the passive branch are respectively connected to serve as the second DC port, the fourth DC port, the sixth DC port and the eighth DC port.

4. The high voltage direct current transmission system according to claim 3, characterized in that: The passive branch includes a capacitor and a first inductor connected in series.

5. The high voltage direct current transmission system according to claim 3, characterized in that: The first bridge arm and the second bridge arm both include a controlled voltage source; The first bridge arm and / or the second bridge arm comprises a second inductor connected in series with the controlled voltage source.

6. The high voltage direct current transmission system according to claim 2, characterized in that: The first converter or the second converter comprises a first bridge arm, a second bridge arm, a third bridge arm and a fourth bridge arm; The first ends of the first bridge arm and the third bridge arm are respectively connected to serve as the third DC port or the fifth DC port; The second end of the first bridge arm is connected to the first end of the second bridge arm to serve as the first DC port or the seventh DC port; or, the second end of the first bridge arm is connected to the first end of the second bridge arm to serve as the first DC port or the seventh DC port, and the second end of the third bridge arm is connected to the first end of the fourth bridge arm to serve as the thirteenth DC port of the first converter or the fourteenth DC port of the second converter; or, the second end of the first bridge arm, the first end of the second bridge arm, the second end of the first bridge arm and the first end of the fourth bridge arm are connected to serve as the first DC port or the seventh DC port; The second ends of the second bridge arm and the fourth bridge arm are respectively connected to serve as the second DC port, the fourth DC port, the sixth DC port and the eighth DC port.

7. The high voltage direct current transmission system according to claim 6, characterized in that: The first bridge arm, the second bridge arm, the third bridge arm and the fourth bridge arm all include a controlled voltage source; The first bridge arm and / or the second bridge arm comprises a second inductor connected in series with a corresponding controlled voltage source, and the third bridge arm and / or the fourth bridge arm comprises a third inductor connected in series with a corresponding controlled voltage source.

8. The high voltage direct current transmission system according to claim 2, characterized in that: The first converter or the second converter includes a first bridge arm, a second bridge arm, a third bridge arm, a fourth bridge arm, a fifth bridge arm and a sixth bridge arm; the first converter also includes a ninth DC port and a tenth DC port, and the second converter also includes an eleventh DC port and a twelfth DC port; The first ends of the first bridge arm, the third bridge arm and the fifth bridge arm are respectively connected to serve as the third DC port or the fifth DC port; The second end of the first bridge arm is connected to the first end of the second bridge arm to serve as the first DC port or the seventh DC port; the second end of the third bridge arm is connected to the first end of the fourth bridge arm to serve as the ninth DC port or the eleventh DC port; the second end of the fifth bridge arm is connected to the first end of the sixth bridge arm to serve as the tenth DC port or the twelfth DC port; or, the second end of the first bridge arm, the second end of the third bridge arm, the second end of the fifth bridge arm, the first end of the second bridge arm, the first end of the fourth bridge arm and the first end of the sixth bridge arm are connected to serve as the first DC port or the seventh DC port; The second ends of the second bridge arm, the fourth bridge arm and the sixth bridge arm are respectively connected to serve as the second DC port, the fourth DC port, the sixth DC port and the eighth DC port.

9. The high voltage direct current transmission system according to claim 8, characterized in that: The first bridge arm, the second bridge arm, the third bridge arm, the fourth bridge arm, the fifth bridge arm and the sixth bridge arm include a controlled voltage source; The first bridge arm and / or the second bridge arm also includes a second inductor connected in series with the corresponding controlled voltage source, the third bridge arm and / or the fourth bridge arm also includes a third inductor connected in series with the corresponding controlled voltage source, and the fifth bridge arm and / or the sixth bridge arm also includes a fourth inductor connected in series with the corresponding controlled voltage source.

10. The high voltage direct current transmission system according to claim 5, 7 or 9, characterized in that: The controlled voltage source comprises a half-bridge topology and / or a full-bridge topology.

11. The high voltage direct current transmission system according to claim 10, characterized in that: The half-bridge topology structure and the full-bridge topology structure are both one or more.

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