Direct current transmission receiving end and direct current transmission system

Abstract

This application discloses a DC transmission receiving end and a DC transmission system. The DC transmission receiving end includes an inverter circuit and a receiving-end transformer. The inverter circuit includes a hybrid commutator converter and a modular multilevel converter. The first DC terminal of the hybrid commutator converter is connected to the DC transmission line, and the second DC terminal of the hybrid commutator converter is connected to the first DC terminal of the modular multilevel converter. The AC terminal of the hybrid commutator converter is connected to the receiving-end AC bus through a corresponding receiving-end transformer. The second DC terminal of the modular multilevel converter is grounded, and the AC terminal of the modular multilevel converter is connected to the receiving-end AC bus through a corresponding receiving-end transformer. In the embodiments of this application, a hybrid commutator converter and a modular multilevel converter connected in series are used at the DC transmission receiving end, enabling the DC transmission receiving end to have both DC-side fault ride-through capability and AC-side fault ride-through capability.

Description

Technical Field

[0001] This application relates to the field of DC power transmission technology, and in particular to a DC power transmission receiving end and a DC power transmission system. Background Technology

[0002] The core equipment of DC transmission technology is the converter. Currently, the mainstream converters are divided into current source converters (CSC) and voltage source converters (VSC).

[0003] Among them, the reactive power regulation capability of CSC has certain limitations. When a fault occurs on the AC side, it needs to rely on the AC grid to balance the reactive power, which makes it difficult to meet the rapid active support requirements of high voltage DC transmission. Due to its voltage source characteristics, VSC cannot effectively block the fault current loop when a fault occurs on the DC side. Summary of the Invention

[0004] This application relates to the field of DC power transmission technology, and in particular to a DC power transmission receiving end and a DC power transmission system, which have DC-side fault ride-through capability and AC-side fault ride-through capability.

[0005] In a first aspect, embodiments of this application provide a DC power transmission receiving end, including: an inverter circuit and a receiving end transformer;

[0006] The inverter circuit includes a hybrid commutation converter and a modular multilevel converter;

[0007] The DC first terminal of the hybrid commutator is used to connect to the DC transmission line.

[0008] The second DC terminal of the hybrid phase converter is connected to the first DC terminal of the modular multilevel converter, and the AC terminal of the hybrid phase converter is connected to the receiving-end AC bus through the corresponding receiving-end transformer.

[0009] The DC second terminal of the modular multilevel converter is grounded, and the AC terminal of the modular multilevel converter is connected to the receiving-end AC bus through the corresponding receiving-end transformer.

[0010] In one possible implementation, the DC transmission receiving end is a unipolar receiving end, which includes an inverter circuit; the DC transmission line is a DC positive bus.

[0011] In one possible implementation, the DC transmission receiving end is a bipolar receiving end, which includes two inverter circuits, namely a first inverter circuit and a second inverter circuit; the DC transmission line includes a DC positive bus and a DC negative bus.

[0012] The DC first terminal of the hybrid commutation converter in the first inverter circuit is used to connect to the DC positive bus.

[0013] The DC first terminal of the hybrid commutation converter in the second inverter circuit is used to connect to the DC negative bus.

[0014] In one possible implementation, the DC transmission receiving end also includes: a controller;

[0015] The controller is used to obtain the reactive power demand of the AC system when the AC voltage drops; based on the reactive power demand and the reactive power distribution coefficient of the hybrid commutation converter, it obtains the first reactive power command value; and controls the delay firing angle of the hybrid commutation converter based on the first reactive power command value to reduce the reactive power consumed by the hybrid commutation converter or to make the hybrid commutation converter generate reactive power.

[0016] Based on the reactive power demand and the reactive power distribution coefficient of the modular multilevel converter, the second reactive power command value is obtained; the three-phase AC voltage of the modular multilevel converter is controlled according to the second reactive power command value, so that the modular multilevel converter can output reactive power.

[0017] Secondly, embodiments of this application provide a DC power transmission system, including: a DC power transmission sending end and a DC power transmission receiving end as described in the first aspect embodiment; wherein, the DC power transmission sending end includes a rectifier circuit and a sending-end transformer;

[0018] The first DC terminal of the rectifier circuit is used to connect to the DC transmission line, the second DC terminal of the rectifier circuit is grounded, and the AC terminal of the rectifier circuit is connected to the sending-end AC bus through the corresponding sending-end transformer.

[0019] In one possible implementation, the DC transmission end is a unipolar end, which includes a rectifier circuit, specifically a first rectifier circuit; the DC transmission line is a DC positive bus.

[0020] In one possible implementation, the DC transmission end is a bipolar end, which includes two rectifier circuits, namely a first rectifier circuit and a second rectifier circuit; the DC transmission line includes a positive DC bus and a negative DC bus.

[0021] The first DC terminal of the first rectifier circuit is used to connect to the DC positive bus.

[0022] The first DC terminal of the second rectifier circuit is used to connect to the DC negative bus.

[0023] In one possible implementation, the first rectifier circuit includes a hybrid commutation converter and a modular multilevel converter;

[0024] The first DC terminal of the hybrid phase-commutation converter is used to connect to the DC transmission line, the second DC terminal of the hybrid phase-commutation converter is connected to the first DC terminal of the modular multilevel converter, and the AC terminal of the hybrid phase-commutation converter is connected to the sending-end AC bus through the corresponding sending-end transformer.

[0025] The DC second terminal of the modular multilevel converter is grounded, and the AC terminal of the modular multilevel converter is connected to the sending-end AC bus through the corresponding sending-end transformer.

[0026] In one possible implementation, the first rectifier circuit includes a first modular multilevel converter and a second modular multilevel converter;

[0027] The first DC terminal of the first modular multilevel converter is used to connect to the DC transmission line. The second DC terminal of the first modular multilevel converter is connected to the first DC terminal of the second modular multilevel converter. The AC terminal of the first modular multilevel converter is connected to the sending-end AC bus through the corresponding sending-end transformer.

[0028] The second DC terminal of the second modular multilevel converter is grounded, and the AC terminal of the second modular multilevel converter is connected to the sending-end AC bus through the corresponding sending-end transformer.

[0029] In one possible implementation, the first rectifier circuit includes a first grid-commutated converter and a second grid-commutated converter;

[0030] The first DC terminal of the first grid phase converter is used to connect to the DC transmission line. The second DC terminal of the first grid phase converter is connected to the first DC terminal of the second grid phase converter. The AC terminal of the first grid phase converter is connected to the sending AC bus through the corresponding sending transformer.

[0031] The DC second terminal of the second grid phase converter is grounded, and the AC terminal of the second grid phase converter is connected to the sending-end AC bus through the corresponding sending-end transformer.

[0032] The DC transmission receiving end provided in this application embodiment includes two different types of inverter modules: a hybrid commutation converter and a modular multilevel converter. Because the hybrid grid commutation converter has unidirectional conductivity, it can quickly interrupt the fault current loop in the event of a DC-side fault. Furthermore, the modular multilevel converter can provide dynamic reactive power support in the event of an AC-side fault, supporting rapid recovery from AC-side faults. Therefore, the DC transmission receiving end provided in this application embodiment possesses both DC-side fault ride-through capability and AC fault ride-through capability. In addition, since neither the hybrid commutation converter nor the modular multilevel converter has a commutation failure problem, the DC transmission receiving end provided in this application embodiment does not have a commutation failure problem. Attached Figure Description

[0033] Figure 1 A schematic diagram of a DC power transmission receiving end provided in an embodiment of this application;

[0034] Figure 2An equivalent circuit diagram of a DC-side fault provided in an embodiment of this application;

[0035] Figure 3 A schematic diagram illustrating the coordinated control of reactive power of HCC and reactive power of MMC, provided in an embodiment of this application;

[0036] Figure 4 A schematic diagram of a control loop for an HCC provided in an embodiment of this application;

[0037] Figure 5 This application provides a schematic diagram of a control loop for an MMC.

[0038] Figure 6 A schematic diagram of a bipolar DC power transmission receiving end provided in an embodiment of this application;

[0039] Figure 7 A schematic diagram of an HCC provided for an embodiment of this application;

[0040] Figure 8 A schematic diagram of an MMC provided for an embodiment of this application;

[0041] Figure 9 This is a schematic diagram of a DC power transmission system provided in an embodiment of this application;

[0042] Figure 10 A schematic diagram of an LCC provided for an embodiment of this application;

[0043] Figure 11 This is a schematic diagram of another DC transmission system provided in an embodiment of this application;

[0044] Figure 12 A schematic diagram of yet another DC power transmission system provided in the embodiments of this application;

[0045] Figure 13 A schematic diagram of another DC transmission system provided in the embodiments of this application;

[0046] Figure 14 This is a schematic diagram of a DC power transmission system provided in an embodiment of this application;

[0047] Figure 15 This is a schematic diagram of another DC transmission system provided in an embodiment of this application;

[0048] Figure 16 This is a schematic diagram of a control device provided in an embodiment of this application. Detailed Implementation

[0049] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present application, and not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present application.

[0050] The terms "first" and "second," etc., used in the specification and claims of this application are used to distinguish different objects, not to describe a specific order of objects. For example, "first submodule" and "second submodule," etc., are used to distinguish different submodules, not to describe a specific order of submodules.

[0051] In the embodiments of this application, the terms "exemplary" or "for example" are used to indicate that something is an example, illustration, or description. Any embodiment or design that is described as "exemplary" or "for example" in the embodiments of this application should not be construed as being more preferred or advantageous than other embodiments or design. Specifically, the use of the terms "exemplary" or "for example" is intended to present the relevant concepts in a specific manner.

[0052] In the description of the embodiments of this application, unless otherwise stated, "multiple" means two or more, for example, multiple processing units means two or more processing units, multiple elements means two or more elements, etc.

[0053] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, the embodiments of this application will be further described in detail below with reference to the accompanying drawings and specific implementation methods.

[0054] See Figure 1 The figure is a schematic diagram of a DC power transmission receiving end provided in an embodiment of this application.

[0055] The DC power transmission receiving end provided in this application embodiment includes: an inverter circuit 1000 and receiving-end transformers (first transformer T1 and second transformer T2); the inverter circuit includes a hybrid commutated converter (HCC) and a modular multilevel converter (MMC); the first DC terminal of the hybrid commutated converter HCC is used to connect to the DC transmission line DC Line, the second DC terminal of the hybrid commutated converter HCC is connected to the first DC terminal of the modular multilevel converter MMC, and the AC terminal of the hybrid commutated converter HCC is connected to the receiving-end AC bus through the corresponding first transformer T1; the second DC terminal of the modular multilevel converter MMC is grounded, and the AC terminal of the modular multilevel converter MMC is connected to the receiving-end AC bus through the corresponding second transformer T2, and the receiving-end AC bus is connected to the power grid AC1.

[0056] In this embodiment, the DC transmission receiving end includes two different types of inverter modules: HCC and MMC, utilizing the advantages of each. The HCC includes an integrated gate-commutated thyristor (IGCT). Because the IGCT has unidirectional conductivity, the DC transmission receiving end can block the fault current loop, enabling DC-side fault ride-through. In the event of an AC-side fault, the MMC can provide dynamic reactive power support to the AC side, thereby supporting rapid recovery from AC-side faults. Therefore, the DC transmission receiving end provided in this embodiment possesses both DC-side and AC-side fault ride-through capabilities.

[0057] In this embodiment, the HCC includes an IGCT, which has autonomous turn-off capability, enabling it to quickly turn off the current when needed to avoid commutation failure. The MMC includes submodules such as controllable switching transistors, like IGBTs / IGCTs. Because IGBTs / IGCTs have autonomous turn-off capability, they can also quickly turn off the current when needed to avoid commutation failure. Therefore, the DC transmission receiving end provided in this embodiment does not have the problem of commutation failure.

[0058] In this embodiment, the MMC can realize grid control and provide active and reactive power support. Therefore, when the HCC adopts phase control mode, the MMC can be used to realize reactive power support and thus effectively regulate the AC bus voltage at the receiving end. Since the HCC and MMC can simultaneously perform rapid adjustment of active power to realize frequency support, the DC bus receiving end provided in this embodiment has grid control capability, thereby improving the stability of the DC transmission system, enhancing the adaptability of the DC transmission system, and promoting the consumption of new energy.

[0059] It should be understood that the phase-controlled mode of the HCC mentioned in the embodiments of this application refers to the regulation of the HCC output voltage and power by controlling the firing angle of the IGCT. The phase-controlled mode of the HCC can be applied to large-scale energy base power transmission projects, such as long-distance power transmission from large hydropower stations and thermal power plants.

[0060] The following section will introduce the DC-side fault ride-through capability and AC-side fault ride-through capability of the DC transmission receiving end.

[0061] In this embodiment of the application, in the event of a fault on the DC side of the DC transmission receiving end, the MMC adopts a fixed DC voltage control strategy, i.e., constant voltage control, and the DC voltage U of the MMC is... dc_MMC If it can be stabilized within a certain range, the MMC can be approximated as a voltage source, and the DC voltage U of the HCC... dc_HCC It will change, and HCC can be approximately equivalent to an IGCT series variable voltage source.

[0062] An exemplary equivalent circuit diagram of the DC transmission terminal in this application embodiment when a fault occurs on the DC side is shown below. Figure 2 As shown; where, Figure 2 The DC voltage of the HCC in the circuit can be obtained using the following formula:

[0063] (1)

[0064] Where, α i For delayed trigger angle, T i For the converter transformer turns ratio, U aci N represents the converter bus line voltage, and N is the number of 6-pulse converters.

[0065] Furthermore, according to Kirchhoff's voltage law, the voltage u across the IGCT valve can be obtained using the following formula (2). IGCT :

[0066] (2)

[0067] According to the above formula (2), when a fault occurs on the DC side of the DC transmission receiving end, the voltage u across the IGCT valve is... IGCT Reverse.

[0068] In this embodiment of the application, due to the unidirectional conductivity of the IGCT in the HCC, when the voltage u of the IGCT... IGCT When reversed, the IGCT can prevent the current from flowing in the opposite direction, thereby quickly blocking the fault current.

[0069] When a voltage drop occurs due to an AC side fault, since the HCC uses a fully controlled IGCT as the commutation device, there is no need to increase the turn-off margin after the fault to avoid commutation failure. At the same time, as shown in the following formula (3), the HCC can increase the delayed firing angle α. i In this way, the reactive power consumed by the HCC can be reduced or even made to generate reactive power, so the HCC can provide a certain amount of reactive power support under transient conditions.

[0070] (3)

[0071] Where μ is the commutation time, P is the active power, and Q is the active power. coni The reactive power consumed by HCC.

[0072] In this embodiment of the application, for HCC, the firing angle α can be delayed. i Reduce the reactive power consumed by HCC or generate reactive power to provide some reactive power support for the AC system.

[0073] Furthermore, due to the rapid and flexible control of the MMC, in the event of an AC-side fault, the MMC can quickly adjust the reactive power output when the AC voltage drops, providing dynamic reactive power compensation. This compensates for the insufficient reactive power regulation capability of the HCC during AC faults, thereby improving the voltage support capability of the AC power grid. The embodiments of this application can support rapid recovery from AC-side faults at the receiving end of the DC transmission line by coordinating the reactive power of the HCC and the reactive power of the MMC.

[0074] For ease of understanding, this application provides a schematic diagram of the reactive power of the HCC and the reactive power of the MMC under coordinated control. See [link to schematic diagram]. Figure 3 .

[0075] like Figure 3 As shown, the first DC terminal of the hybrid phase-commutation converter HCC is used to connect to the DC transmission line, and the second DC terminal of the hybrid phase-commutation converter HCC is connected to the first DC terminal of the modular multilevel converter MMC. The AC terminal of the hybrid phase-commutation converter HCC is connected to the receiving-end AC bus through the corresponding first transformer T1. The second DC terminal of the modular multilevel converter MMC is grounded, and the AC terminal of the modular multilevel converter MMC is connected to the receiving-end AC bus through the corresponding second transformer T2. The receiving-end AC bus is connected to the power grid AC1.

[0076] First, by fully utilizing the reactive power regulation capabilities of each converter and comprehensively considering multi-dimensional constraints such as device, equipment, and system operation modes, the maximum reactive power regulation ΔQm_HCC and the maximum reactive power regulation ΔQm_MMC of the HCC and MMC converters are obtained. The maximum reactive power regulation ΔQm_HCC of the HCC and the maximum reactive power regulation ΔQm_MMC of the MMC converter represent the maximum ranges of reactive power regulated by the HCC and MMC, respectively.

[0077] Secondly, based on the maximum reactive power regulation ΔQm_HCC of HCC and the maximum reactive power regulation ΔQm_MMC of MMC, the reactive power distribution coefficient K of HCC is obtained. HCC And the reactive power distribution factor K of MMC MMC Among them, the reactive power distribution coefficients of HCC are K. HCC The reactive power distribution factor K of MMC MMC The expressions are shown in formulas (4) and (5) below:

[0078] (4)

[0079] (5)

[0080] Then, in the event of an AC side fault, the AC voltage drops from U to U. f The reactive power demand of the AC system is obtained as ΔQ. f Fully consider the reactive power coordinated control capability of HCC and MMC on ΔQ f The reactive power distribution ΔQ of the HCC under AC side fault can be obtained by the following formula (6). HCC_ref The reactive power distribution of MMC, ΔQ, can be obtained through the following formula (7). MMC_ref .

[0081] (6)

[0082] (7)

[0083] Finally, the reactive power distribution ΔQ of HCC is... HCC_ref Reactive power distribution ΔQ with MMC HCC_ref The reactive power of HCC and MMC are respectively used as command values ​​to control the reactive power of HCC and MMC, thereby enabling coordinated regulation of reactive power of HCC and MMC, supporting rapid recovery of AC side faults at the receiving end of DC transmission.

[0084] For example, this application provides a schematic diagram of the control loop of an HCC, see [link to relevant documentation]. Figure 4 .

[0085] like Figure 4As shown, based on the reactive power distribution ΔQ of HCC HCC_ref Initial reactive power instruction Q HCC_ref and system reactive power Q HCC The reactive power difference ΔQ is obtained; the reactive power difference ΔQ is used as the input of the HCC control loop, and the output of the HCC control loop is delayed firing angle α. i By controlling the delayed firing angle α i The reactive power consumed by the HCC (High-Voltage Control Cell) can be reduced, or even partially generated, to provide some reactive power support. It should be understood that the HCC control mechanism in this embodiment is a mature technology in the field and will not be described in detail here.

[0086] For example, this application provides a schematic diagram of the control loop of an MMC, see [link to relevant documentation]. Figure 5 .

[0087] like Figure 5 As shown, according to the initial active power command P MMC_ref and system active power P HCC The active power difference ΔP is obtained; the active power difference ΔP is used as the input of the active power control loop, and the phase θ of the AC voltage output by the active power loop is... * According to the reactive power distribution ΔQ of MMC MMC_ref Initial reactive power instruction Q MMC_ref and system reactive power Q MMC The reactive power difference ΔQ is obtained; the reactive power difference ΔQ is used as the input of the reactive power control loop, and the output AC voltage amplitude V of the reactive power control loop is obtained. * Phase θ of AC voltage * And the amplitude V of AC voltage * As the input to the MMC inner loop control, the MMC inner loop control outputs a three-phase AC voltage reference value u. ca_ref u cb_ref and u cc_ref By controlling the three-phase AC voltage, the MMC generates some reactive power to provide reactive power support. It should be understood that the active power control loop, reactive power control loop, and MMC inner loop control in the embodiments of this application are all mature technologies in the field, and will not be described in detail here.

[0088] In this embodiment of the application, by coordinating the reactive power of the HCC and the reactive power of the MMC, rapid recovery from AC side faults can be supported.

[0089] The above embodiments have described a unipolar DC transmission receiving end. In order to improve the transmission efficiency of DC transmission, this application embodiment also provides a bipolar DC transmission receiving end, which will be described in detail below with reference to the accompanying drawings.

[0090] See Figure 6The figure is a schematic diagram of a bipolar DC power transmission receiving end provided in an embodiment of this application.

[0091] like Figure 6 As shown, the bipolar DC transmission receiving end includes two inverter circuits, namely the first inverter circuit 1000 and the second inverter circuit 2000.

[0092] The first inverter circuit 1000 includes HCC1 and MMC1. The first DC terminal of HCC1 is connected to the positive DC bus, and the second DC terminal of HCC1 is connected to the first DC terminal of MMC1. The AC terminal of HCC1 is connected to the receiving-end AC bus DC Line1 through receiving-end transformer T1. The second DC terminal of MMC1 is grounded, and the AC terminal of MMC1 is connected to the receiving-end AC bus through receiving-end transformer T2. The second inverter circuit 2000 includes HCC2 and MMC2. The first DC terminal of HCC2 is connected to the negative DC bus DC Line2, and the second DC terminal of HCC2 is connected to the first DC terminal of MMC2. The AC terminal of HCC2 is connected to the receiving-end AC bus through receiving-end transformer T3. The second DC terminal of MMC2 is grounded, and the AC terminal of MMC2 is connected to the receiving-end AC bus through receiving-end transformer T4.

[0093] For example, the current of the DC positive bus DC Line1 is +800kV, and the current of the DC negative bus DC Line2 is -800kV.

[0094] For example, this application provides a schematic diagram of HCC, see [link to schematic diagram]. Figure 7 .

[0095] like Figure 7 As shown, the HCC includes a three-phase full-bridge circuit. Each phase includes an upper half-bridge arm and a lower half-bridge arm, with the midpoint of the upper and lower half-bridge arms connected to AC power. Specifically, the first terminal of the first switch Q1 is connected to the positive DC terminal, the second terminal of the first switch Q1 is connected to the first terminal of the fourth switch Q4, the second terminal of the fourth switch Q4 is connected to the negative DC terminal, and the second terminal of the first switch Q1 is connected to ua; the first terminal of the third switch Q3 is connected to the positive DC terminal, the second terminal of the third switch Q3 is connected to the first terminal of the sixth switch Q6, the second terminal of the sixth switch Q6 is connected to the negative DC terminal, and the second terminal of the third switch Q3 is connected to ub; the first terminal of the fifth switch Q5 is connected to the positive DC terminal, the second terminal of the fifth switch Q5 is connected to the first terminal of the second switch Q2, the second terminal of the second switch Q2 is connected to the negative DC terminal, and the second terminal of the fifth switch Q5 is connected to uc.

[0096] It should be noted that the first switch Q1, the second switch Q2, the third switch Q3, the fourth switch Q4, the fifth switch Q5 and the sixth switch Q6 in the embodiments of this application are all IGCTs.

[0097] For example, this application provides a schematic diagram of an MMC, see [link to schematic diagram]. Figure 8 .

[0098] like Figure 8 As shown, the MMC includes a three-phase power conversion circuit. Each phase includes an upper half-bridge arm and a lower half-bridge arm, with AC power connected at the midpoint between the upper and lower half-bridge arms. The upper half-bridge arm comprises n sub-modules connected in series, and the lower half-bridge arm comprises n sub-modules connected in series, where n is an integer greater than or equal to 2.

[0099] It should be understood that the types of the first submodule SM1, the second submodule SM2, ... and the Nth submodule are not specifically limited in the embodiments of this application. For example, the first submodule SM1, the second submodule SM2, ... and the Nth submodule can be a half-bridge submodule or a full-bridge submodule.

[0100] In addition, the embodiments of this application do not specifically limit the type of controllable switching transistor in the first submodule SM1, the second submodule SM2, ... and the Nth submodule. For example, the controllable switching transistor in the first submodule SM1, the second submodule SM2, ... and the Nth submodule can be an insulated-gate bipolar transistor (IGBT) or an IGCT.

[0101] Based on the DC power transmission receiving end described in the foregoing embodiments, this application also provides a DC power transmission system, which will be described in detail below with reference to the accompanying drawings.

[0102] See Figure 9 The figure is a schematic diagram of a DC power transmission system provided in an embodiment of this application.

[0103] like Figure 9 As shown, the DC transmission system includes a DC transmission sending end and a DC transmission receiving end. The DC transmission sending end includes a rectifier circuit 3000 and sending-end transformers (third transformer T3 and fourth transformer T4), and the DC transmission receiving end includes an inverter circuit 1000 and receiving-end transformers (first transformer T1 and second transformer T2).

[0104] The rectifier circuit 3000 includes a first line-commutated converter (LCC) and an LCC2. The first DC terminal of LCC1 is connected to the DC transmission line DC Line, the second DC terminal of LCC1 is connected to the first DC terminal of LCC2, the AC terminal of LCC1 is connected to the sending-end AC bus through the third transformer T3, and the sending-end AC bus is connected to the second power grid AC2. The second DC terminal of LCC2 is grounded, and the AC terminal of LCC2 is connected to the sending-end AC bus through the fourth transformer T4, and the sending-end AC bus is connected to the second power grid AC2.

[0105] The inverter circuit 1000 includes HCC and MMC. The first DC terminal of HCC is connected to the DC transmission line DC Line, and the second DC terminal of HCC is connected to the first DC terminal of MMC. The AC terminal of HCC is connected to the receiving-end AC bus through the first transformer T1, and the receiving-end AC bus is connected to the first power grid AC1. The second DC terminal of MMC is grounded, and the AC terminal of MMC is connected to the receiving-end AC bus through the second transformer T2, and the receiving-end AC bus is connected to the first power grid AC1.

[0106] The use of an LCC as the rectifier circuit at the DC transmission end in this embodiment has the following advantages: First, the LCC mainly uses thyristors as power switching devices, and thyristors have the characteristics of mature manufacturing process and low production cost; Second, the LCC can withstand high voltage and current, and has strong power transmission capability, thus enabling large-capacity power transmission in high-voltage DC transmission systems to meet the needs of long-distance, high-power transmission; Third, the LCC relies on the AC system to provide commutation voltage, and has good operating performance when connected to a strong AC system.

[0107] For example, a schematic diagram of an LCC is shown below. Figure 10 As shown.

[0108] like Figure 10 As shown, the LCC includes a three-phase full-bridge circuit. Each phase includes an upper half-bridge arm and a lower half-bridge arm, with the midpoint of the upper and lower half-bridge arms connected to AC power. Specifically, the first terminal of the first switch Q1 is connected to the positive DC terminal, the second terminal of the first switch Q1 is connected to the first terminal of the fourth switch Q4, the second terminal of the fourth switch Q4 is connected to the negative DC terminal, and the second terminal of the first switch Q1 is connected to ua; the first terminal of the third switch Q3 is connected to the positive DC terminal, the second terminal of the third switch Q3 is connected to the first terminal of the sixth switch Q6, the second terminal of the sixth switch Q6 is connected to the negative DC terminal, and the second terminal of the third switch Q3 is connected to ub; the first terminal of the fifth switch Q5 is connected to the positive DC terminal, the second terminal of the fifth switch Q5 is connected to the first terminal of the second switch Q2, the second terminal of the second switch Q2 is connected to the negative DC terminal, and the second terminal of the fifth switch Q5 is connected to uc.

[0109] It should be noted that the first switch Q1, the second switch Q2, the third switch Q3, the fourth switch Q4, the fifth switch Q5 and the sixth switch Q6 in the embodiments of this application are all thyristors.

[0110] Furthermore, in order to improve the transmission efficiency of the DC transmission system, this application provides another DC transmission system, the schematic diagram of which is shown below. Figure 11 .

[0111] like Figure 11As shown, the DC transmission system includes a DC transmission sending end and a DC transmission receiving end. The DC transmission sending end includes a first rectifier circuit 3000, a second rectifier circuit 4000, and sending-end transformers (fifth transformer T5, sixth transformer T6, seventh transformer T7, and eighth transformer T8); the DC transmission receiving end includes a first inverter circuit 1000, a second inverter circuit 2000, and receiving-end transformers (first transformer T1, second transformer T2, third transformer T3, and fourth transformer T4).

[0112] The first rectifier circuit 3000 includes LCC1 and LCC2. The first DC terminal of LCC1 is connected to the positive DC bus DCLine1, and the second DC terminal of LCC1 is connected to the first DC terminal of LCC2. The AC terminal of LCC1 is connected to the sending-end AC bus through the fifth transformer T5, and the sending-end AC bus is connected to the second power grid AC2. The second DC terminal of LCC2 is grounded, and the AC terminal of LCC2 is connected to the sending-end AC bus through the sixth transformer T6, and the sending-end AC bus is connected to the second power grid AC2.

[0113] The second rectifier circuit 4000 includes LCC3 and LCC4. The first DC terminal of LCC4 is connected to the positive DC bus DCLine2, and the second DC terminal of LCC4 is connected to the first DC terminal of LCC3. The AC terminal of LCC4 is connected to the sending-end AC bus through the seventh transformer T7, and the sending-end AC bus is connected to the second power grid AC2. The second DC terminal of LCC3 is grounded, and the AC terminal of LCC3 is connected to the sending-end AC bus through the eighth transformer T8, and the sending-end AC bus is connected to the second power grid AC2.

[0114] It should be understood that the connection of the DC transmission receiving end has been described in the foregoing embodiments, and will not be repeated here.

[0115] The embodiments of this application can improve the transmission efficiency of the DC transmission system by employing bipolar DC transmission sending end and bipolar DC transmission receiving end.

[0116] See Figure 12 This figure is a schematic diagram of another DC power transmission system provided in an embodiment of this application.

[0117] like Figure 12 As shown, the DC transmission system includes a DC transmission sending end and a DC transmission receiving end. The DC transmission sending end includes a rectifier circuit 3000 and sending-end transformers (third transformer T3 and fourth transformer T4); the DC transmission receiving end includes an inverter circuit 1000 and receiving-end transformers (first transformer T1 and second transformer T2).

[0118] The rectifier circuit includes MMC2 and MMC3. The first DC terminal of MMC2 is connected to the positive DC bus DC Line, and the second DC terminal of MMC2 is connected to the first DC terminal of MMC3. The AC terminal of MMC is connected to the sending-end AC bus through the third transformer T3, and the sending-end AC bus is connected to the second power grid AC2. The second DC terminal of MMC3 is grounded, and the AC terminal of MMC3 is connected to the sending-end AC bus through the fourth transformer T4, and the sending-end AC bus is connected to the second power grid AC2.

[0119] It should be understood that the connection of the DC transmission receiving end has been described in the foregoing embodiments, and will not be repeated here.

[0120] In this embodiment, using an MMC as the rectifier circuit at the DC transmission sending end has the following advantages: First, the MMC can quickly adjust the active power delivered to the DC line according to the actual situation, and at the same time, accurately control the reactive power output according to the voltage requirements of the AC bus at the sending end, maintain voltage stability, and improve system operating efficiency; Second, when a fault occurs in the AC system at the sending end (such as a short-circuit fault), the MMC has a certain fault ride-through capability, maintaining a certain operating state during the fault period and preventing the converter from being quickly blocked due to the fault; Third, compared with an LCC, the MMC does not need to rely on the AC system to provide commutation voltage. Even if the short-circuit capacity of the AC system at the sending end is small and the voltage support capability is weak, the MMC can still operate stably, expanding the application range of the DC transmission system in different grid environments.

[0121] Furthermore, to improve the transmission efficiency of DC power transmission, this application provides another DC power transmission system, the schematic diagram of which is shown below. Figure 13 .

[0122] like Figure 13 As shown, the DC transmission system includes a DC transmission sending end and a DC transmission receiving end. The DC transmission sending end includes a first rectifier circuit 3000, a second rectifier circuit 4000, and sending-end transformers (fifth transformer T5, sixth transformer T6, seventh transformer T7, and eighth transformer T8); the DC transmission receiving end includes a first inverter circuit 1000, a second inverter circuit 2000, and receiving-end transformers (first transformer T1, second transformer T2, third transformer T3, and fourth transformer T4).

[0123] The first rectifier circuit 3000 includes MMC3 and MMC4. The first DC terminal of MMC3 is connected to the positive DC bus DCLine1, and the second DC terminal of MMC3 is connected to the first DC terminal of MMC4. The AC terminal of MMC3 is connected to the sending-end AC bus through the fifth transformer T5, and the sending-end AC bus is connected to the second power grid AC2. The second DC terminal of MMC4 is grounded, and the AC terminal of MMC4 is connected to the sending-end AC bus through the sixth transformer T6, and the sending-end AC bus is connected to the second power grid AC2.

[0124] The second rectifier circuit 4000 includes MMC5 and MMC6. The first DC terminal of MMC6 is connected to the positive DC bus DCLine2, and the second DC terminal of MMC6 is connected to the first DC terminal of MMC5. The AC terminal of MMC6 is connected to the sending-end AC bus through the seventh transformer T7, and the sending-end AC bus is connected to the second power grid AC2. The second DC terminal of MMC5 is grounded, and the AC terminal of MMC5 is connected to the sending-end AC bus through the eighth transformer T8, and the sending-end AC bus is connected to the second power grid AC2.

[0125] It should be understood that the connection of the DC transmission receiving end has been described in the foregoing embodiments, and will not be repeated here.

[0126] The embodiments of this application can improve the transmission efficiency of the DC transmission system by employing bipolar DC transmission sending end and bipolar DC transmission receiving end.

[0127] See Figure 14 The figure is a schematic diagram of a DC power transmission system provided in an embodiment of this application.

[0128] like Figure 14 As shown, the DC transmission system includes a DC transmission sending end and a DC transmission receiving end. The DC transmission sending end includes a rectifier circuit 3000 and sending-end transformers (third transformer T3 and fourth transformer T4); the DC transmission receiving end includes an inverter circuit 1000 and receiving-end transformers (first transformer T1 and second transformer T2).

[0129] The rectifier circuit includes HCC3 and MMC3. The first DC terminal of HCC3 is connected to the positive DC bus DC Line, and the second DC terminal of HCC3 is connected to the first DC terminal of MMC4. The AC terminal of HCC3 is connected to the sending-end AC bus through the third transformer T3, and the sending-end AC bus is connected to the second power grid AC2. The second DC terminal of MMC4 is grounded, and the AC terminal of MMC4 is connected to the sending-end AC bus through the fourth transformer T4, and the sending-end AC bus is connected to the second power grid AC2.

[0130] It should be understood that the connection of the DC transmission receiving end has been described in the foregoing embodiments, and will not be repeated here.

[0131] As described in the preceding embodiments regarding the DC transmission receiving end, by using HCC and MMC connected in series at the DC transmission receiving end, the DC transmission receiving end possesses both AC fault ride-through capability and DC fault ride-through capability. Similarly, by using HCC and MMC connected in series at the DC transmission sending end, the DC transmission sending end can also possess both AC fault ride-through capability and DC fault ride-through capability.

[0132] Furthermore, to improve the transmission efficiency of DC power transmission, this application provides another DC power transmission system, the schematic diagram of which is shown below. Figure 15 .

[0133] like Figure 15 As shown, the DC transmission system includes a DC transmission sending end and a DC transmission receiving end. The DC transmission sending end includes a first rectifier circuit 3000, a second rectifier circuit 4000, and sending-end transformers (fifth transformer T5, sixth transformer T6, seventh transformer T7, and eighth transformer T8); the DC transmission receiving end includes a first inverter circuit 1000, a second inverter circuit 2000, and receiving-end transformers (first transformer T1, second transformer T2, third transformer T3, and fourth transformer T4).

[0134] The first rectifier circuit 3000 includes HCC3 and MMC3. The first DC terminal of HCC3 is connected to the positive DC bus DCLine1, and the second DC terminal of HCC3 is connected to the first DC terminal of MMC3. The AC terminal of HCC3 is connected to the sending-end AC bus through the fifth transformer T5, and the sending-end AC bus is connected to the second power grid AC2. The second DC terminal of MMC3 is grounded, and the AC terminal of MMC3 is connected to the sending-end AC bus through the sixth transformer T6, and the sending-end AC bus is connected to the second power grid AC2.

[0135] The second rectifier circuit 4000 includes HCC4 and MMC4. The first DC terminal of HCC4 is connected to the positive DC bus DCLine2, and the second DC terminal of HCC4 is connected to the first DC terminal of MMC4. The AC terminal of HCC4 is connected to the sending-end AC bus through the seventh transformer T7, and the sending-end AC bus is connected to the second power grid AC2. The second DC terminal of MMC4 is grounded, and the AC terminal of MMC4 is connected to the sending-end AC bus through the eighth transformer T8, and the sending-end AC bus is connected to the second power grid AC2.

[0136] It should be understood that the connection of the DC transmission receiving end has been described in the foregoing embodiments, and will not be repeated here.

[0137] The embodiments of this application can improve the transmission efficiency of the DC transmission system by employing bipolar DC transmission sending end and bipolar DC transmission receiving end.

[0138] In one possible implementation, see Figure 16 The figure is a schematic diagram of a control device provided in an embodiment of this application.

[0139] The control device may include a memory 1011 and a processor 1012. The processor 1012 may be connected to the converter to control the switching actions of the controllable switching transistors in the converter. Figure 16 As shown, the memory can be random access memory (RAM), flash memory, read-only memory (ROM), EPROM, non-volatile read-only memory (Electronic Programmable ROM), registers, hard disks, removable disks, etc.

[0140] The memory 1011 can store computer instructions. When the computer instructions stored in the memory 1011 are executed by the processor 1012, the processor 1012 can use the executed detection method. The memory 1011 can also store data, such as preset ranges, preset thresholds, and other information involved in the above embodiments.

[0141] In the above embodiments, implementation can be achieved, in whole or in part, through software, hardware, firmware, or any combination thereof. When implemented in software, it can be implemented, in whole or in part, as a computer program product. A computer program product includes one or more computer instructions. When the computer program instructions are loaded and executed on a computer, all or part of the flow or function according to the embodiments of this application is generated. The computer can be a general-purpose computer, a special-purpose computer, a computer network, or other programmable device. The computer instructions can be stored in a computer-readable storage medium or transmitted from one computer-readable storage medium to another. For example, computer instructions can be transmitted from one website, computer, server, or data center to another website, computer, server, or data center via wired (e.g., coaxial cable, fiber optic, digital subscriber line (DSL)) or wireless (e.g., infrared, wireless, microwave, etc.) means. The computer-readable storage medium can be any available medium that a computer can access or a data storage device such as a server or data center that integrates one or more available media. The available medium can be a magnetic medium (e.g., floppy disk, hard disk, magnetic tape) or a semiconductor medium (e.g., solid-state disk (SSD)).

[0142] This application also provides a readable storage medium for storing the methods provided in the above embodiments. Examples include random access memory (RAM), flash memory, read-only memory (ROM), EPROM, non-volatile read-only memory (EPROM), registers, hard disks, removable disks, or any other form of storage medium in the art.

[0143] It should be noted that the various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. Regarding the methods disclosed in the embodiments, since they correspond to the product embodiments disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to in the description of the product embodiments.

[0144] The above description of the disclosed embodiments enables those skilled in the art to make or use this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A DC power transmission receiving end, characterized in that, include: Inverter circuit, receiving-end transformer, and controller; the inverter circuit includes a hybrid commutation converter and a modular multilevel converter; The first DC terminal of the hybrid phase-commutation converter is used to connect to a DC transmission line. The second DC terminal of the hybrid phase-commutation converter is connected to the first DC terminal of the modular multilevel converter. The AC terminal of the hybrid phase-commutation converter is connected to the receiving-end AC bus through the corresponding receiving-end transformer. The second DC terminal of the modular multilevel converter is grounded. The AC terminal of the modular multilevel converter is connected to the receiving-end AC bus through the corresponding receiving-end transformer. The controller is configured to: acquire the reactive power demand of the AC system when the AC voltage drops; obtain a first reactive power command value based on the reactive power demand and the reactive power allocation coefficient of the hybrid commutation converter; control the delay firing angle of the hybrid commutation converter based on the first reactive power command value to reduce the reactive power consumed by the hybrid commutation converter or to enable the hybrid commutation converter to generate reactive power; obtain a second reactive power command value based on the reactive power demand and the reactive power allocation coefficient of the modular multilevel converter; and control the three-phase AC voltage of the modular multilevel converter based on the second reactive power command value to enable the modular multilevel converter to generate reactive power. The calculation methods for the reactive power allocation coefficient of the hybrid commutator and the modular multilevel converter are shown in the following formulas: ； ； Among them, K HCC K is the reactive power distribution coefficient of the hybrid commutator. MMC ΔQ is the reactive power distribution coefficient of the modular multilevel commutator. m_HCC ΔQ is the maximum reactive power regulation of the hybrid commutator. m_MMC This is the maximum reactive power regulation of the modular multilevel commutator. The calculation formulas for the first reactive power command value and the second reactive power command value are shown in the following formulas: ； ； Where, ΔQ HCC_ref The first reactive power command value, ΔQ MMC_ref The second reactive power command value, ΔQ f This represents the reactive power requirement of the AC system.

2. The DC transmission receiving end according to claim 1, characterized in that, The DC power receiving end is a unipolar receiving end, and the DC power receiving end includes one of the inverter circuits; the DC power transmission line is a DC positive bus.

3. The DC transmission receiving end according to claim 1, characterized in that, The DC power transmission receiving end is a bipolar receiving end, and the DC power transmission receiving end includes two inverter circuits, namely a first inverter circuit and a second inverter circuit; the DC power transmission line includes a DC positive bus and a DC negative bus; The DC first terminal of the hybrid commutation converter in the first inverter circuit is used to connect to the DC positive bus. The DC first terminal of the hybrid commutation converter in the second inverter circuit is used to connect to the DC negative bus.

4. A DC transmission system, characterized in that, include: A DC power transmission sending end and a DC power transmission receiving end as described in any one of claims 1-3; wherein the DC power transmission sending end includes a rectifier circuit and a sending-end transformer; The first DC terminal of the rectifier circuit is used to connect to the DC transmission line, the second DC terminal of the rectifier circuit is grounded, and the AC terminal of the rectifier circuit is connected to the sending-end AC bus through the corresponding sending-end transformer.

5. The DC transmission system according to claim 4, characterized in that, The DC power transmission terminal is a unipolar terminal, and the DC power transmission terminal includes a rectifier circuit, which is a first rectifier circuit; the DC power transmission line is a DC positive bus.

6. The DC transmission system according to claim 4, characterized in that, The DC power transmission terminal is a bipolar terminal, and the DC power transmission terminal includes two rectifier circuits, namely a first rectifier circuit and a second rectifier circuit; the DC power transmission line includes a DC positive bus and a DC negative bus. The first DC terminal of the first rectifier circuit is used to connect to the DC positive bus. The first DC terminal of the second rectifier circuit is used to connect to the DC negative bus.

7. The DC transmission system according to claim 5 or 6, characterized in that, The first rectifier circuit includes a hybrid commutation converter and a modular multilevel converter; The first DC terminal of the hybrid phase-commutation converter is used to connect to the DC transmission line, the second DC terminal of the hybrid phase-commutation converter is connected to the first DC terminal of the modular multilevel converter, and the AC terminal of the hybrid phase-commutation converter is connected to the sending-end AC bus through the corresponding sending-end transformer. The DC second terminal of the modular multilevel converter is grounded, and the AC terminal of the modular multilevel converter is connected to the sending-end AC bus through the corresponding sending-end transformer.

8. The DC transmission system according to claim 5 or 6, characterized in that, The first rectifier circuit includes a first modular multilevel converter and a second modular multilevel converter; The first DC terminal of the first modular multilevel converter is used to connect to the DC transmission line, the second DC terminal of the first modular multilevel converter is connected to the first DC terminal of the second modular multilevel converter, and the AC terminal of the first modular multilevel converter is connected to the sending-end AC bus through the corresponding sending-end transformer. The second DC terminal of the second modular multilevel converter is grounded, and the AC terminal of the second modular multilevel converter is connected to the sending-end AC bus through the corresponding sending-end transformer.

9. The DC transmission system according to claim 5 or 6, characterized in that, The first rectifier circuit includes a first grid-commutated converter and a second grid-commutated converter; The first DC terminal of the first grid phase-commutation converter is used to connect to the DC transmission line, the second DC terminal of the first grid phase-commutation converter is connected to the first DC terminal of the second grid phase-commutation converter, and the AC terminal of the first grid phase-commutation converter is connected to the sending-end AC bus through the corresponding sending-end transformer. The second DC terminal of the second grid phase converter is grounded, and the AC terminal of the second grid phase converter is connected to the sending-end AC bus through the corresponding sending-end transformer.

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