Current source converter valve

Abstract

The invention relates to a current source converter valve, which is characterized in that controllable capacitor banks are respectively and correspondingly arranged between each phase alternating current end of a controllable turn-off converter module and each phase outlet end of a converter transformer, and the second ends of the controllable capacitor banks are respectively connected. Thus, in the operation process of the current source converter valve, commutation voltage can be provided for the controllable turn-off converter module through switching control over the full-bridge controllable capacitor sub-modules of the controllable capacitor bank, at the moment, leakage inductance of the converter transformer does not exist in a corresponding commutation loop, and active and reactive independent adjustment of the converter transformer can be achieved. According to the scheme, reactive power can be compensated by adopting the voltage source, the reactive power output range of the whole current source converter valve to an alternating current power grid is widened, and the operation flexibility and reliability of the converter valve are greatly improved.

Description

[0001] Cross-references

[0002] This application refers to Chinese Patent Application No. 202411484915.4, filed on October 23, 2024, entitled “Current Source Converter Valve”, which is incorporated herein by reference in its entirety. Technical Field

[0003] The present application relates to the field of commutation technology, and in particular to a current source commutation valve. Background Art

[0004] With the development of large-scale new energy bases and the continuous promotion of policies to send out high proportions of new energy, direct current transmission technology has developed rapidly. Conventional direct current transmission technology does not have the potential to access high proportions of new energy because it relies on grid phase switching, and the receiving-end converter valve has the problem of phase switching failure, and its power receiving reliability does not meet the development trend of future power grids; although flexible direct current transmission technology does not have the problem of phase switching failure, it has high equipment cost, large losses, and difficulty in increasing capacity. Therefore, controllable current source converter valves with advantages such as large capacity and strong shut-off capability have gradually been used.

[0005] However, in the related art, the operation flexibility and reliability of the controllable current source type converter valve are relatively low. Summary of the invention

[0006] Based on this, it is necessary to provide a current source converter valve to address the above problems.

[0007] The present application provides a current source converter valve, comprising: a DC side reactor, a controllable shutdown converter module, a converter transformer and a plurality of controllable capacitor groups, wherein the DC end of the controllable shutdown converter module is connected to a DC load via the DC side reactor; the converter transformer is used to connect to an AC power grid; a single-phase AC end of the controllable shutdown converter module is correspondingly connected to a first end of the controllable capacitor group and a single-phase outlet end of the converter transformer, and the second ends of the controllable capacitor groups are respectively connected; wherein the controllable capacitor group comprises a plurality of cascaded full-bridge controllable capacitor sub-modules, and the controllable capacitor group provides a commutation voltage for the controllable shutdown converter module by switching on and off different numbers of the full-bridge controllable capacitor sub-modules, so as to realize active and reactive power regulation of the current source converter valve.

[0008] In one embodiment, the full-bridge controllable capacitor submodule includes a capacitor, a first switch unit, a second switch unit, a fourth switch unit and a third switch unit, wherein the first end of the first switch unit is connected to the first end of the capacitor and the first end of the second switch unit, the second end of the second switch unit is connected to the first end of the fourth switch unit, the second end of the fourth switch unit is connected to the first end of the third switch unit and the second end of the capacitor, and the second end of the third switch unit is connected to the second end of the first switch unit; wherein the common end formed by the second switch unit and the fourth switch unit serves as the first end of the full-bridge controllable capacitor submodule, and the common end formed by the first switch unit and the third switch unit serves as the second end of the full-bridge controllable capacitor submodule.

[0009] In one embodiment, the capacitor is a DC capacitor.

[0010] In one embodiment, the controllable capacitor group includes a first controllable capacitor group, a second controllable capacitor group and a third controllable capacitor group; the controllable shutdown commutation module includes a first bridge arm unit, a second bridge arm unit, a third bridge arm unit, a fourth bridge arm unit, a fifth bridge arm unit and a sixth bridge arm unit, the first end of the first bridge arm unit, the first end of the third bridge arm and the first end of the fifth bridge arm are connected, and the common end formed is connected to the DC load through the DC side inductor; the second end of the first bridge arm unit is connected to the first end of the fourth bridge arm unit and the first end of the first controllable capacitor group, the second end of the third bridge arm unit is connected to the first end of the sixth bridge arm unit and the first end of the second controllable capacitor group, the second end of the fifth bridge arm unit is connected to the first end of the second bridge arm unit and the first end of the third controllable capacitor group, the second end of the fourth bridge arm unit, the second end of the sixth bridge arm unit and the second end of the second bridge arm unit are connected, and the common end formed is connected to the DC load.

[0011] In one embodiment, the first bridge arm unit, the second bridge arm unit, the third bridge arm unit, the fourth bridge arm unit, the fifth bridge arm unit and the sixth bridge arm unit have the same structure, and respectively include a protection circuit and a plurality of controllable switch devices connected in series, wherein the two ends of each of the controllable switch devices are respectively connected in parallel with a protection circuit.

[0012] In one embodiment, the protection circuit includes a static voltage balancing circuit and a dynamic voltage balancing circuit connected in parallel.

[0013] In one embodiment, the static voltage balancing circuit includes a static voltage balancing resistor, which is arranged in parallel with the controllable switch device; and / or the dynamic voltage balancing circuit includes an RCD buffer circuit, which is arranged in parallel with the controllable switch device.

[0014] In one embodiment, each bridge arm unit further includes an energy consumption circuit, and two ends of each controllable switch device are respectively connected in parallel with one of the energy consumption circuits.

[0015] In one of the embodiments, each bridge arm unit further includes an energy consumption circuit, and the energy consumption circuit is arranged in parallel at two ends of at least two adjacent controllable switch devices.

[0016] In one embodiment, the controllable shutdown commutation module further includes a first saturated inductor, a second saturated inductor, a third saturated inductor, a fourth saturated inductor, a fifth saturated inductor and a sixth saturated inductor, the second end of the first bridge arm unit is connected to the first end of the fourth bridge arm unit through the first saturated inductor, the second end of the third bridge arm unit is connected to the first end of the sixth bridge arm unit through the second saturated inductor, the second end of the fifth bridge arm unit is connected to the first end of the second bridge arm unit through the third saturated inductor, the second end of the fourth bridge arm unit is connected to the DC load through the fourth saturated inductor, the second end of the sixth bridge arm unit is connected to the DC load through the fifth saturated inductor, and the second end of the second bridge arm unit is connected to the DC load through the sixth saturated inductor.

[0017] The above-mentioned current source converter valve is provided with a controllable capacitor group between each phase AC end of the controllable shutoff converter module and each phase outlet end of the converter transformer, and the second ends of each controllable capacitor group are connected respectively. In this way, during the operation of the current source converter valve, the switching control of the full-bridge controllable capacitor submodule of the controllable capacitor group can be performed to provide a commutation voltage for the controllable shutoff converter module. At this time, there is no leakage inductance of the converter transformer in the corresponding commutation circuit, and the active and reactive power of the converter transformer can be independently adjusted. Through the above scheme, the full-bridge controllable capacitor submodule can be used as a voltage source to compensate for reactive power, which broadens the reactive output range of the current source converter valve to the AC power grid as a whole, and greatly improves the operational flexibility and reliability of the converter valve. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the conventional technology, the drawings required for use in the embodiments or the conventional technology descriptions are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0019] Figure 1 This is a schematic diagram of the topological structure of a current source converter valve in an embodiment of the present application;

[0020] Figure 2 This is a schematic diagram of the structure of a controllable capacitor bank in one embodiment of the present application;

[0021] Figure 3 This is a schematic diagram of the structure of a full-bridge controllable capacitor submodule in an embodiment of the present application;

[0022] Figure 4 This is a schematic diagram of the capacitor charging of the full-bridge controllable capacitor submodule in one embodiment of the present application;

[0023] Figure 5 This is a schematic diagram of the capacitor discharge of the full-bridge controllable capacitor submodule in one embodiment of the present application;

[0024] Figure 6 This is a schematic diagram of the capacitor charging of the full-bridge controllable capacitor submodule in another embodiment of the present application;

[0025] Figure 7 This is a schematic diagram of the capacitor discharge of a full-bridge controllable capacitor submodule in another embodiment of the present application;

[0026] Figure 8 This is a timing diagram of charging and discharging of a full-bridge controllable capacitor submodule in an embodiment of the present application;

[0027] Fig. 9 This is a schematic diagram of the simulation of the charging and discharging process of the full-bridge controllable capacitor submodule in one embodiment of the present application;

[0028] Fig.10 This is a schematic diagram of the topological structure of a current source converter valve in another embodiment of the present application;

[0029] Fig.11 This is a schematic diagram of the structure of a bridge arm unit in one embodiment of the present application;

[0030] Fig.12 This is a schematic diagram of the structure of a bridge arm unit in another embodiment of the present application;

[0031] Fig.13 This is a schematic diagram of the structure of a bridge arm unit in another embodiment of the present application;

[0032] Fig.14 This is a schematic diagram of the structure of a bridge arm unit in another embodiment of the present application;

[0033] Fig.15 This is a schematic diagram of the topological structure of a current source converter valve in another embodiment of the present application;

[0034] Fig.16 Schematic diagram of the commutation process of the current source converter valve in one embodiment of the present application. DETAILED DESCRIPTION

[0035] In order to facilitate the understanding of the present application, the present application will be described more fully below with reference to the relevant drawings. The preferred embodiments of the present application are provided in the drawings. However, the present application can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure of the present application more thorough and comprehensive.

[0036] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application belongs. The terms used herein in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application.

[0037] It is understood that the terms "first", "second", etc. used in this application may be used herein to describe various elements, but these elements are not limited by these terms. These terms are only used to distinguish a first element from another element. For example, without departing from the scope of this application, a first resistor may be referred to as a second resistor, and similarly, a second resistor may be referred to as a first resistor. Both the first resistor and the second resistor are resistors, but they are not the same resistor.

[0038] It can be understood that the “connection” in the following embodiments should be understood as “electrical connection”, “communication connection”, etc. if the connected circuits, modules, units, etc. have electrical signals or data transmission between each other.

[0039] It can be understood that “at least one” means one or more, “plurality” means two or more, and “at least a portion of an element” means a part or all of an element.

[0040] When used herein, the singular forms "a", "an", and "said / the" may also include plural forms, unless the context clearly indicates otherwise. It should also be understood that the terms "include / comprise" or "have" and the like specify the presence of stated features, wholes, steps, operations, components, parts, or combinations thereof, but do not exclude the possibility of the presence or addition of one or more other features, wholes, steps, operations, components, parts, or combinations thereof. At the same time, the term "and / or" used in this specification includes any and all combinations of the relevant listed items.

[0041] With the development of high-voltage direct current transmission technology, controllable current source type converter valves have gradually become an indispensable component in high-voltage direct current transmission technology. With the application of controllable current source type converter valves, problems such as low operating flexibility and reliability have gradually been exposed.

[0042] Through research, it is found that the existing converter valve outlet generally uses a passive AC capacitor group. During normal operation, the capacitor current is large, and the capacitor polarity is frequently reversed, which can easily cause accelerated aging, thereby reducing the service life of the capacitor. On the other hand, the general dry capacitor has a small capacitance. In order to meet the demand for large capacitance, more capacitor combinations are required, which greatly increases the size of the equipment; although the oil capacitor has a large capacitance, there is a possibility of fire and combustion, which poses a great threat to the entire converter station equipment. That is, the low operating flexibility and reliability of the converter valve are caused by the passive AC capacitor group.

[0043] Based on this, the applicant has found through in-depth research that the polarity of DC capacitors will not be reversed during use, the service life is long, and special materials can easily increase the capacitance value, which is suitable for flexible DC transmission systems and has explosion-proof and fire-proof properties. Therefore, in order to enhance the operational flexibility of the converter valve, semiconductors can be combined with DC capacitors to form a controllable capacitor bank, and the capacitor voltage and current can be flexibly adjusted through switching control, greatly improving the operational flexibility and reliability of the converter valve.

[0044] Based on the above considerations, please refer to Figure 1 The present application provides a current source converter valve, comprising: a DC side reactor Ldc, a controllable shutdown converter module 11, a converter transformer 12 and a plurality of controllable capacitor groups 13, wherein the DC end of the controllable shutdown converter module 11 is connected to a DC load (shown as Ud) through the DC side reactor Ldc; the converter transformer 12 is used to connect to an AC power grid; a single-phase AC end of the controllable shutdown converter module 11 is correspondingly connected to a first end of a controllable capacitor group 13 and a single-phase outlet end of the converter transformer 12, and the second ends of each controllable capacitor group 13 are respectively connected; wherein the controllable capacitor group 13 provides a switching voltage for the controllable shutdown converter module 11 through switching, so as to realize active and reactive power regulation of the current source converter valve.

[0045] Please continue reading Figure 2 In one embodiment, the controllable capacitor bank 13 includes a plurality of cascaded full-bridge controllable capacitor submodules 130, wherein the first end of the first-stage full-bridge controllable capacitor submodule 130 serves as the first end of the controllable capacitor bank 13, the second end of the first-stage full-bridge controllable capacitor submodule 130 is connected to the next-stage full-bridge controllable capacitor submodule 130, the first end of the last-stage full-bridge controllable capacitor submodule 130 is connected to the previous-stage full-bridge controllable capacitor submodule 130, and the second end of the last-stage full-bridge controllable capacitor submodule 130 serves as the second end of the controllable capacitor bank 13. In this way, only the switching of different numbers of full-bridge controllable capacitor submodules 130 is required to provide a commutation voltage for the controllable shutdown commutation module 11.

[0046] Specifically, the cascade, that is, multiple full-bridge controllable capacitor submodules 130 are connected end to end in sequence to form a structure similar to a series connection, and the control end of each full-bridge controllable capacitor submodule 130 is connected to the valve controller. In this embodiment, each full-bridge controllable capacitor submodule 130 includes at least one capacitor, and each full-bridge controllable capacitor submodule 130 can be individually switched on and off, that is, according to actual needs, the number of full-bridge controllable capacitor submodules 130 put into operation in a controllable capacitor group 13 can be controlled. In this way, the phase and amplitude of the output AC voltage can be changed, and then the amount of reactive power generated can be changed, which broadens the reactive power output range of the current source converter valve to the power grid as a whole. Through this solution, each controllable capacitor group 13 includes multiple cascaded full-bridge controllable capacitor submodules 130, and the capacitors are arranged in a distributed manner, which greatly reduces the insulation difficulty and manufacturing difficulty of the current source converter valve.

[0047] The DC side reactor Ldc is a reactor arranged on the DC side of the current source converter valve and used to connect to the DC load on the DC side. By setting the DC side reactor Ldc, a certain current limiting effect can be achieved, thereby improving the operating safety of the current source converter valve. The controllable shut-off converter module 11 is a device in the current source converter valve that is constructed by controllable shut-off and conduction type switching devices and is used to perform the commutation function. The controllable capacitor group 13 is a device composed of capacitors and controllable units that can realize AC voltage output through switching control, thereby participating in phase change.

[0048] It can be understood that in one embodiment, in order to realize the operation control of the controllable shutdown converter module 11 and the controllable capacitor group 13, the current source converter valve also includes a valve controller, wherein the control end of the controllable shutdown converter module 11 and the control end of each controllable capacitor group 13 are respectively connected to the valve controller. In this way, when there is a need for phase switching, the switching of the controllable capacitor group 13 and the switching of each bridge arm in the controllable shutdown converter module 11 can be controlled by the valve controller to realize the phase switching function.

[0049] The solution of the embodiment of the present application utilizes the AC voltage provided by the controllable capacitor group 13 as the commutation voltage of the converter valve to perform commutation. The leakage inductance of the converter transformer 12 does not participate in the commutation. The commutation process of the controllable shutdown commutation module 11 is faster, and no external circuit is required to provide the commutation voltage.

[0050] The controllable capacitor bank 13 has two control degrees of freedom: voltage amplitude and phase, while active and reactive decoupling only requires two control degrees of freedom. Therefore, through the solution of the embodiment of the present application, through the joint action of the controllable capacitor bank 13 and the controllable shutdown converter module 11, independent decoupling control of active and reactive power can be achieved. The current source converter valve can realize modulation control of DC current, indirectly control the capacitor voltage and phase in the controllable capacitor bank 13, and then realize active and reactive exchange with the AC power grid.

[0051] It should be noted that in the scheme of this embodiment, by controlling the opening time of the controllable shutdown commutation module 11 and the injected current, the voltage of the controllable capacitor group 13 is indirectly controlled, thereby realizing reactive power compensation and transmission. The main function of the controllable capacitor group 13 is to be equivalent to an AC capacitor through the control of the full-bridge switch. At this time, the controllable shutdown commutation module 11 serves as the main body of power control and voltage control, and the controllable capacitor group 13 mainly plays an auxiliary role. That is, in this scheme, the DC side voltage is only generated by the controllable shutdown commutation module 11, and the control of the DC voltage can be realized by the controllable shutdown commutation module 11. The controllable capacitor group 13 is only used for AC active regulation and reactive power compensation.

[0052] The above-mentioned current source converter valve is provided with a controllable capacitor group 13 between each phase AC end of the controllable shut-off converter module 11 and each phase outlet end of the converter transformer 12, and the second ends of each controllable capacitor group 13 are connected respectively. In this way, during the operation of the current source converter valve, the switching control of the full-bridge controllable capacitor submodule 130 of the controllable capacitor group 13 can be used to provide a commutation voltage for the controllable shut-off converter module 11. At this time, there is no leakage inductance of the converter transformer in the corresponding commutation loop, and the active and reactive power of the converter transformer 12 can be independently adjusted. Through the above scheme, the full-bridge controllable capacitor submodule 130 can be used as a voltage source to compensate for reactive power, which broadens the reactive output range of the current source converter valve to the AC power grid as a whole, and greatly improves the operational flexibility and reliability of the converter valve.

[0053] Furthermore, through the technical solution of the present application, the controllable shutdown commutation module 11 can realize active shutdown control. Therefore, under working conditions such as AC fault, the current can be directly shut down by the controllable shutdown commutation module 11, thereby forcing commutation, and having the ability to completely resist commutation failure.

[0054] See also Figure 3In one embodiment, the full-bridge controllable capacitor submodule 130 includes a capacitor C, a first switch unit T1, a second switch unit T2, a fourth switch unit T4 and a third switch unit T3, a first end of the first switch unit T1 is connected to a first end of the capacitor C and a first end of the second switch unit T2, a second end of the second switch unit T2 is connected to a first end of the fourth switch unit T4, a second end of the fourth switch unit T4 is connected to a first end of the third switch unit T3 and a second end of the capacitor C, and a second end of the third switch unit T3 is connected to a second end of the first switch unit T1; wherein a common end formed by the second switch unit T2 and the fourth switch unit T4 serves as a first end of the full-bridge controllable capacitor submodule 130, and a common end formed by the first switch unit T1 and the third switch unit T3 serves as a second end of the full-bridge controllable capacitor submodule 130.

[0055] Specifically, the full-bridge controllable capacitor submodule 130 adopts a full-bridge structure, and each switch unit includes a controllable switch device and a diode connected in reverse parallel with the controllable switch device. The controllable switch device used in each switch unit can be an IGCT (Integrated Gate Commutated Thyristor) or an IGBT (Insulated Gate Bipolar Transistor), which is not specifically limited.

[0056] It should be noted that in order to avoid the polarity reversal of the capacitor during use, which affects the service life of the full-bridge controllable capacitor submodule 130, in one embodiment, the capacitor of the full-bridge controllable capacitor submodule 130 is a DC capacitor.

[0057] In order to facilitate understanding of the operating principle of the controllable capacitor bank 13, a more detailed embodiment is provided below for explanation. Figure 4 , Figure 5 , Figure 6 and Figure 7 The full-bridge controllable capacitor module 130 can be divided into four working modes, which are represented by serial numbers (a), (b), (c), and (d) respectively; Figure 8 As shown, it is a timing diagram of charging and discharging of the full-bridge controllable capacitor module 130, such as Fig. 9 As shown, it is a simulation analysis of the charging and discharging process of the full-bridge controllable capacitor submodule 130.

[0058] in, Figure 4 As shown, in stage (a), the port voltage of the full-bridge controllable capacitor submodule 130 is positive, and the current charges the capacitor through the diodes of T1 and T4; Figure 5As shown, in stage (b), the port voltage of the full-bridge controllable capacitor submodule 130 is positive, and the current discharges the capacitor through the controllable switch device branches of T4 and T1; Figure 6 As shown, in stage (c), the port voltage of the full-bridge controllable capacitor submodule 130 is negative, and the current charges the capacitor through the diode branches of T2 and T3; Figure 7 As shown, in stage (d), the port voltage of the full-bridge controllable capacitor submodule 130 is negative, and the current discharges the capacitor through the controllable switch device branches of T3 and T2. During the charging and discharging process, the polarity of the capacitor voltage remains unchanged, and the controllable capacitor group 13 can eventually generate an ideal voltage by modulating the controllable switch device.

[0059] like Fig. 9 As shown, Tb1 and Tb2 represent the controllable switch devices of T1 and T2 respectively, and Td1 and Td2 represent the reverse parallel diodes in T1 and T2 respectively. It can be seen from the simulation results that the voltage of the full-bridge controllable capacitor submodule 130 always maintains forward charging and discharging, and each device is subjected to a half-cycle capacitor voltage at both ends. The conduction sequence and working principle between the devices in the four stages within a cycle are consistent with those described above. This simulation model verifies the feasibility of the full-bridge controllable capacitor submodule 130.

[0060] Please refer to Fig.10 In one embodiment, the controllable capacitor group 13 includes a first controllable capacitor group 131, a second controllable capacitor group 132 and a third controllable capacitor group 133; the controllable shutdown commutation module 11 includes a first bridge arm unit S1, a second bridge arm unit S2, a third bridge arm unit S3, a fourth bridge arm unit S4, a fifth bridge arm unit S5 and a sixth bridge arm unit S6, the first end of the first bridge arm unit S1, the first end of the third bridge arm and the first end of the fifth bridge arm are connected, and the common end formed is connected to the DC load through the DC side reactor Ldc; the The second end of the first bridge arm unit S1 is connected to the first end of the fourth bridge arm unit S4 and the first end of the first controllable capacitor group 131, the second end of the third bridge arm unit S3 is connected to the first end of the sixth bridge arm unit S6 and the first end of the second controllable capacitor group 132, the second end of the fifth bridge arm unit S5 is connected to the first end of the second bridge arm unit S2 and the first end of the third controllable capacitor group 133, the second end of the fourth bridge arm unit S4, the second end of the sixth bridge arm unit S6 and the second end of the second bridge arm unit S2 are connected, and the common end formed is connected to a DC load.

[0061] Specifically, the diagram Lt represents the leakage inductance of the converter transformer, and the controllable shutdown converter module 11 adopts a switchable six-pulse converter bridge topology structure, which includes six bridge arms, a common end formed by connecting the first bridge arm unit S1 and the fourth bridge arm unit S4, a common end formed by connecting the third bridge arm unit S3 and the sixth bridge arm unit S6, and a common end formed by connecting the fifth bridge arm unit S5 and the second bridge arm unit S2, which together serve as the three-phase outlet of the controllable shutdown converter module 11, and each phase outlet is respectively connected to a controllable capacitor group 13 and a phase outlet end of the converter transformer 12, so as to form a controllable shutdown converter module 11. Through the solution of this embodiment, the controllable shutdown converter module 11 can realize three-phase AC power regulation, which has a wide range of application scenarios.

[0062] It should be pointed out that the structure of each bridge arm unit in the controllable shut-off commutation module 11 is not unique. It can be a structure formed by connecting the turnable devices in series, or a structure formed by connecting the turnable devices in series with the commutation topology (including full bridge or half bridge), without specific limitation.

[0063] In one embodiment, a structure formed by connecting the turnable devices in series is taken as an example. Fig.11 The first bridge arm unit S1, the second bridge arm unit S2, the third bridge arm unit S3, the fourth bridge arm unit S4, the fifth bridge arm unit S5 and the sixth bridge arm unit S6 have the same structure, and respectively include a protection circuit 111 and a plurality of controllable switch devices G connected in series, wherein a protection circuit 111 is connected in parallel at both ends of each controllable switch device G.

[0064] Specifically, the type of controllable switch device G in the bridge arm unit is not unique, and it can be a fully controlled device with bidirectional blocking capability, or a series combination of a fully controlled device with forward voltage withstand capability and a fast recovery diode. In more detail, it can be a fully controlled reverse resistance type IGCT, a fully controlled reverse resistance type IGBT, an asymmetric IGCT in series with a fast recovery diode, a fully controlled reverse resistance type GTO (Gate-Turn-Off Thyristor), an asymmetric GTO in series with a fast recovery diode, etc., without specific limitation. Similarly, the structure of the protection circuit 111 is not unique, as long as it is a device that can improve the operating safety of the controllable switch device G during commutation operation. In this solution, the bridge arm unit includes a controllable switch device G connected in series, which can meet the requirements of large current and overload operation.

[0065] In more detail, in one embodiment, since the current source converter valve is generally used in high voltage and large capacity applications and needs to withstand surge current, the controllable switch device G can use the most technically and economically efficient fully controlled reverse resistance IGCT. When a fault occurs on the AC side and causes the grid voltage to drop, the controllable switch device G will have a situation where the device that should be turned off cannot be turned off normally but is turned on. At this time, the upper and lower bridge arms are directly connected, and a commutation failure occurs. The solution of the embodiment of the present application, after using a fully controlled IGCT device, can set a delay time to make the device actively shut down to ensure that the device successfully commutates, that is, to achieve active commutation, and thus have the ability to completely reduce commutation failure.

[0066] It should be noted that see Fig.12 In a more detailed embodiment, the protection circuit 111 includes a static voltage balancing circuit 1111 and a dynamic voltage balancing circuit 1112 connected in parallel.

[0067] Specifically, the static voltage balancing circuit 1111 is a circuit that realizes voltage balancing under static (non-dynamically changing) conditions, which can make the equivalent resistance of each controllable switch device G similar when the controllable switch device G is turned off, thereby realizing voltage balancing and preventing a single controllable switch device G from being subjected to excessive voltage. The dynamic voltage balancing circuit 1112 is a circuit that absorbs instantaneous overvoltage and overcurrent under dynamic conditions and protects the controllable switch device G from voltage fluctuations.

[0068] Through the solution of this implementation, a static voltage equalizing circuit 1111 and a dynamic voltage equalizing circuit 1112 are respectively configured for the same controllable switch device G, which can ensure that the controllable switch device G has high operating safety both statically and dynamically.

[0069] It is understood that the specific types of the static voltage balancing circuit 1111 and the dynamic voltage balancing circuit 1112 are not unique. Fig.12 In one embodiment, the static voltage balancing circuit 1111 includes a static voltage balancing resistor, and the static voltage balancing resistor is connected in parallel with the controllable switch device G.

[0070] And / or, in one embodiment, the dynamic voltage balancing circuit 1112 includes an RCD buffer circuit, and the RCD buffer circuit is arranged in parallel with the controllable switch device G.

[0071] Specifically, this embodiment uses a static voltage-equalizing resistor as the static voltage-equalizing circuit 1111, which is connected in parallel at both ends of the controllable switch device G to achieve static voltage equalization of the controllable switch device G. The circuit structure is simple and the circuit cost is effectively saved. In other embodiments, a Zener diode clamping circuit or the like can also be used as the static voltage-equalizing circuit 1111, which is not specifically limited.

[0072] The RCD snubber circuit is composed of three basic components: resistor (R), capacitor (C) and diode (D), and through a specific connection method, it forms a circuit structure that can absorb instantaneous overvoltage and overcurrent. The working principle of the RCD circuit is based on the synergy of capacitors and resistors. When there is an instantaneous overvoltage or overcurrent in the circuit, the capacitor will quickly absorb the energy and gradually dissipate the energy through the resistor. At the same time, the diode plays a unidirectional conductive role in the circuit, ensuring that energy can only flow in a predetermined direction. In this solution, the dynamic voltage balancing circuit 1112 adopts an RCD snubber circuit to suppress the rate of change of the off-state voltage of each device, thereby achieving the voltage balancing effect of connecting the devices in series.

[0073] See also Fig.13 In one embodiment, each bridge arm unit further includes an energy consumption circuit 112, and two ends of each controllable switch device G are respectively connected in parallel with an energy consumption circuit 112.

[0074] Specifically, the energy consumption circuit 112 is a circuit that can consume electric energy. In the solution of this embodiment, each controllable switch device G is connected in parallel with an energy consumption branch. In this way, the controllable switch device G can be prevented from overvoltage during the operation of the current source converter valve.

[0075] It should be noted that the specific structure of the energy consumption circuit 112 is not unique. In one embodiment, the energy consumption circuit 112 includes a lightning arrester.

[0076] See also Fig.14 In one embodiment, each bridge arm unit further includes an energy consumption circuit 112, and an energy consumption circuit 112 is arranged in parallel at two ends of at least two adjacent controllable switch devices G.

[0077] Specifically, in this embodiment, a plurality of controllable switch devices G are connected in parallel to an energy consumption circuit 112 (such as a lightning arrester), and while overvoltage protection is provided to the controllable switch devices G, voltage balancing among the plurality of controllable switch devices G can also be achieved. In this solution, a plurality of controllable switch devices G share a lightning arrester, and the purpose is to reduce the number of lightning arresters in parallel and reduce circuit costs when the voltage balancing consistency of the devices is good. At the same time, the withstand voltage value of the lightning arrester can be increased, the residual voltage ratio can be increased, and the manufacturing difficulty can be reduced.

[0078] See also Fig.15In one embodiment, the controllable shutdown converter module 11 also includes a first saturated inductor L1, a second saturated inductor L2, a third saturated inductor L3, a fourth saturated inductor L4, a fifth saturated inductor L5 and a sixth saturated inductor L6, the second end of the first bridge arm unit S1 is connected to the first end of the fourth bridge arm unit S4 through the first saturated inductor L1, the second end of the third bridge arm unit S3 is connected to the first end of the sixth bridge arm unit S6 through the second saturated inductor L2, the second end of the fifth bridge arm unit S5 is connected to the first end of the second bridge arm unit S2 through the third saturated inductor L3, the second end of the fourth bridge arm unit S4 is connected to the DC load through the fourth saturated inductor L4, the second end of the sixth bridge arm unit S6 is connected to the DC load through the fifth saturated inductor L5, and the second end of the second bridge arm unit S2 is connected to the DC load through the sixth saturated inductor L6.

[0079] In the solution of this embodiment, each bridge arm unit is correspondingly configured with a saturated inductor, so that the current change rate tolerance of the bridge arm unit can be improved, the bridge arm current flowing into the bridge arm unit can be limited, and the bridge arm current is prevented from being too large to impact and damage the controllable switch device G, thereby improving the operating reliability of the current source converter valve. It can be understood that in one embodiment, in order to improve the overall structure of the current source converter valve and to save space, each saturated inductor can be set at the end of the valve assembly of the current source converter valve.

[0080] It should be pointed out that in other embodiments, if the bridge arm unit has a high tolerance to the current change rate, the saturation inductance may not be set, and the selection is made in combination with actual needs.

[0081] In order to facilitate the understanding of the commutation operation of the current source commutation valve, the following is an explanation in conjunction with a more detailed embodiment. Fig.16 , when the current is normally flowing, the current flows through the controllable switch device G (IGCT) of the S1 (first bridge arm unit) branch, carrying the rated current and overload current; when commutating, the S1 branch sends a drive signal to make the IGCT device actively shut down, establish a commutation voltage, and the current of the S1 main branch is commutated to the CD buffer circuit (part of the RCD buffer circuit). The diode of the RCD buffer circuit bypasses its resistance, so that the voltage balancing effect of its capacitor is improved. When the voltage of the RCD buffer circuit is charged to the action voltage of the lightning arrester, the voltage of the series IGCT devices is clamped, and the voltage balancing between the IGCT devices is achieved by voltage limiting. When the S3 (third bridge arm unit) branch device is subjected to positive pressure, it is triggered to open, the DC current is commutated to the S3 branch, and the current of the S1 branch drops to 0, completing the shutdown commutation process.

[0082] Through the solution of the present application, the influence of the leakage inductance of the converter transformer on the commutation process is completely eliminated, and there is no commutation angle in the working process of the current source converter valve, which greatly reduces the reactive power consumption of the system; the current source converter valve has the ability to completely resist commutation failure and has reactive voltage support capability, which is suitable for power supply to the weak AC power grid at the receiving end and also for the all-new energy transmission scenario at the sending end.

[0083] In the description of this specification, the description with reference to the terms "some embodiments", "other embodiments", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic description of the above terms does not necessarily refer to the same embodiment or example.

[0084] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0085] The above-described embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be construed as limiting the scope of the patent application. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent application shall be subject to the attached claims.

Claims

1. A current source converter valve, characterized in that: include: DC side reactor; A controllable shutdown commutation module, wherein the DC end of the controllable shutdown commutation module is connected to a DC load via the DC side reactor; Converter transformer, used to connect to the AC grid; A plurality of controllable capacitor groups, wherein one-phase AC end of the controllable shutdown converter module is correspondingly connected to the first end of the controllable capacitor group and one-phase output end of the converter transformer, and the second ends of the controllable capacitor groups are respectively connected; wherein the controllable capacitor group comprises a plurality of cascaded full-bridge controllable capacitor submodules, and the controllable capacitor group provides a switching voltage for the controllable shutdown converter module by switching on and off different numbers of the full-bridge controllable capacitor submodules, so as to realize active and reactive regulation of the current source converter valve.

2. The current source converter valve according to claim 1, characterized in that: The full-bridge controllable capacitor submodule includes a capacitor, a first switch unit, a second switch unit, a third switch unit and a fourth switch unit, wherein the first end of the first switch unit is connected to the first end of the capacitor and the first end of the second switch unit, the second end of the second switch unit is connected to the first end of the fourth switch unit, the second end of the fourth switch unit is connected to the first end of the third switch unit and the second end of the capacitor, and the second end of the third switch unit is connected to the second end of the first switch unit; wherein the common end formed by the second switch unit and the fourth switch unit serves as the first end of the full-bridge controllable capacitor submodule, and the common end formed by the first switch unit and the third switch unit serves as the second end of the full-bridge controllable capacitor submodule.

3. The current source converter valve according to claim 1, characterized in that: The capacitor is a DC capacitor.

4. The current source converter valve according to any one of claims 1 to 3, characterized in that: The controllable capacitor group includes a first controllable capacitor group, a second controllable capacitor group and a third controllable capacitor group; The controllable shutdown commutation module includes a first bridge arm unit, a second bridge arm unit, a third bridge arm unit, a fourth bridge arm unit, a fifth bridge arm unit and a sixth bridge arm unit, wherein the first end of the first bridge arm unit, the first end of the third bridge arm and the first end of the fifth bridge arm are connected, and the common end formed is connected to the DC load through the DC side reactor; the second end of the first bridge arm unit is connected to the first end of the fourth bridge arm unit and the first end of the first controllable capacitor group, the second end of the third bridge arm unit is connected to the first end of the sixth bridge arm unit and the first end of the second controllable capacitor group, the second end of the fifth bridge arm unit is connected to the first end of the second bridge arm unit and the first end of the third controllable capacitor group, the second end of the fourth bridge arm unit, the second end of the sixth bridge arm unit and the second end of the second bridge arm unit are connected, and the common end formed is connected to the DC load.

5. The current source converter valve according to claim 4, characterized in that: The structures of the first bridge arm unit, the second bridge arm unit, the third bridge arm unit, the fourth bridge arm unit, the fifth bridge arm unit and the sixth bridge arm unit are consistent, and respectively include a protection circuit and a plurality of controllable switch devices connected in series, wherein the two ends of each of the controllable switch devices are respectively connected in parallel with a protection circuit.

6. The current source converter valve according to claim 5, characterized in that: The protection circuit includes a static voltage balancing circuit and a dynamic voltage balancing circuit connected in parallel.

7. The current source converter valve according to claim 6, characterized in that: The static voltage balancing circuit includes a static voltage balancing resistor, and the static voltage balancing resistor is arranged in parallel with the controllable switch device; And / or, the dynamic voltage balancing circuit includes an RCD buffer circuit, and the RCD buffer circuit is arranged in parallel with the controllable switch device.

8. The current source converter valve according to claim 5, characterized in that: Each bridge arm unit also includes an energy consumption circuit, and two ends of each controllable switch device are respectively connected in parallel with an energy consumption circuit.

9. The current source converter valve according to claim 5, characterized in that: Each bridge arm unit also includes an energy consumption circuit, and the two ends of at least two adjacent controllable switch devices are provided with an energy consumption circuit in parallel.

10. The current source converter valve according to claim 4, characterized in that: The controllable shutdown commutation module also includes a first saturated inductor, a second saturated inductor, a third saturated inductor, a fourth saturated inductor, a fifth saturated inductor and a sixth saturated inductor. The second end of the first bridge arm unit is connected to the first end of the fourth bridge arm unit through the first saturated inductor, the second end of the third bridge arm unit is connected to the first end of the sixth bridge arm unit through the second saturated inductor, the second end of the fifth bridge arm unit is connected to the first end of the second bridge arm unit through the third saturated inductor, the second end of the fourth bridge arm unit is connected to the DC load through the fourth saturated inductor, the second end of the sixth bridge arm unit is connected to the DC load through the fifth saturated inductor, and the second end of the second bridge arm unit is connected to the DC load through the sixth saturated inductor.

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