Controllable turn-off converter valve for high voltage direct current (HVDC) system

Abstract

The invention relates to a controllable turn-off converter valve for a high voltage direct current (HVDC) system, each converter valve arm comprises a valve arm voltage-sharing device and a plurality of cascaded controllable turn-off converter modules, and each controllable turn-off converter module comprises an assembly voltage-sharing device and a plurality of cascaded controllable turn-off converter assemblies. Each controllable turn-off current conversion assembly is configured to comprise at least one voltage-sharing circuit and at least one controllable switching device, and two ends of each controllable switching device are provided with one voltage-sharing circuit in parallel. Therefore, the controllable turn-off converter valve can realize voltage sharing at each level, the requirement of the controllable turn-off converter valve on the consistency of controllable switching devices is reduced, a large number of controllable switching devices can be connected in series in the same converter valve arm, and reliable conversion of extra-high voltage direct current transmission at the voltage level of + / -800 kilovolts and above is realized. The problem of commutation failure of the extra-high-voltage direct-current type converter valve is solved, and safe and stable operation of a power system is ensured.

Description

Technical Field

[0001] The present application relates to the technical field of large-capacity commutation, and particularly to a controllable turn-off commutation valve for a high-voltage direct current (HVDC) system. Background Art

[0002] With the rapid development of science and technology, the ultra-high voltage (i.e., ±800 kV and above) direct current transmission method has been widely used in the occasions of asynchronous grid interconnection and long-distance high-power transmission. With the successive commissioning of ultra-high voltage direct current transmission projects, there has emerged a grid structure in which multiple DC lines are connected to the same area. The effective short-circuit ratios of multiple DC lines in each DC inverter station show a gradually decreasing trend, and the DC commutation valve system is extremely prone to commutation failure, affecting the safe and stable operation of the power system. Summary of the Invention

[0003] Based on this, it is necessary to provide a controllable turn-off commutation valve for a high-voltage direct current (HVDC) system to solve the problem of commutation failure of the commutation valve in the traditional high-voltage direct current system and ensure the safe and stable operation of the power system.

[0004] A controllable turn-off commutation valve for a high-voltage direct current (HVDC) system includes a plurality of commutation valve arms. Each commutation valve arm includes a valve arm voltage equalizer and a plurality of controllable turn-off commutation modules. The valve arm voltage equalizer is connected in parallel at both ends of a first structure formed by connecting the plurality of controllable turn-off commutation modules in series. Each controllable turn-off commutation module includes a component voltage equalizer and a plurality of controllable turn-off commutation components. The component voltage equalizer is connected in parallel at both ends of a second structure formed by connecting the plurality of controllable turn-off commutation components in series. Each controllable turn-off commutation component includes at least one voltage equalizing circuit and at least one controllable switching device, and one voltage equalizing circuit is connected in parallel at both ends of one controllable switching device.

[0005] In one embodiment, the component voltage equalizer is an equalizing capacitor. Each controllable turn-off commutation component includes one voltage equalizing circuit and one controllable switching device. The voltage equalizing circuit includes a device-level voltage equalizing circuit and a controllable voltage equalizing circuit, and the device-level voltage equalizing circuit and the controllable voltage equalizing circuit are respectively connected in parallel at both ends of the controllable switching device.

[0006] In one embodiment, the controllable voltage equalizing circuit includes a passive switching device and a first lightning arrester, and both ends formed after the passive switching device and the first lightning arrester are connected in series are respectively connected to both ends of the controllable switching device.

[0007] In one embodiment, the controllable voltage equalizing circuit includes an active switching device and a second lightning arrester, and both ends formed after the active switching device and the second lightning arrester are connected in series are respectively connected to both ends of the controllable switching device.

[0008] In one embodiment, the component voltage equalizing device is a third lightning arrester, the voltage equalizing circuit includes a device-level voltage equalizing circuit, and the device-level voltage equalizing circuit is arranged in parallel at both ends of the controllable switching device.

[0009] In one embodiment, the controllable turn-off commutation component includes a string voltage equalizing circuit and a plurality of controllable turn-off commutation strings. The string voltage equalizing circuit is arranged in parallel at both ends of a third structure formed by connecting the controllable turn-off commutation strings in series; each controllable turn-off commutation string includes a plurality of voltage equalizing circuits and a plurality of controllable switching devices connected in series, and one of the voltage equalizing circuits is arranged in parallel at both ends of each controllable switching device.

[0010] In one embodiment, the string voltage equalizing circuit includes a first capacitor and a first diode connected in series. Both ends formed after the first capacitor and the first diode are connected in series are respectively connected to both ends of the third structure formed by connecting the controllable turn-off commutation strings in series.

[0011] In one embodiment, the string voltage equalizing circuit further includes a first resistor, and the first resistor is connected in parallel with the first capacitor.

[0012] In one embodiment, the device-level voltage equalizing circuit includes a static voltage equalizing circuit and a reverse recovery voltage equalizing circuit, and the static voltage equalizing circuit and the reverse recovery voltage equalizing circuit are respectively connected in parallel with the controllable switching device.

[0013] In one embodiment, the static voltage equalizing circuit includes a second resistor, and the second resistor is arranged in parallel at both ends of the controllable switching device;

[0014] And / or, in one embodiment, the reverse recovery voltage equalizing circuit includes a third resistor and a second capacitor connected in series, and both ends formed after being connected in series are respectively connected to both ends of the controllable switching device.

[0015] In one embodiment, the controllable turn-off commutation valve arm further includes a saturable reactor, and the structure formed by connecting the controllable turn-off commutation modules in series is connected in series with the saturable reactor.

[0016] The above-mentioned controllable turn-off commutation valve for a high-voltage direct current (HVDC) system. Each commutation valve arm includes a valve arm voltage equalizer device and a plurality of cascaded controllable turn-off commutation modules. A single controllable turn-off commutation module includes a component voltage equalizer device and a plurality of cascaded controllable turn-off commutation components. A single controllable turn-off commutation component is configured to include at least one voltage equalizing circuit and at least one controllable switching device, and a voltage equalizing circuit is connected in parallel at both ends of a controllable switching device. In this way, through the hierarchical voltage equalization settings of the voltage equalizing circuit, the component voltage equalizer device, and the valve arm voltage equalizer device, the controllable turn-off commutation valve can achieve voltage equalization at each level, reducing the consistency requirements for the controllable switching devices of the controllable turn-off commutation valve. A large number of controllable switching devices can be connected in series in the same commutation valve arm, realizing reliable conversion of ultra-high voltage direct current transmission with a voltage level of ±800 kV and above, solving the problem of commutation failure of the commutation valve of the ultra-high voltage direct current type, and ensuring the safe and stable operation of the power system. Brief Description of the Drawings

[0017] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0018] Figure 1 Schematic diagram of the converter structure in some embodiments of the present application;

[0019] Figure 2 Schematic diagram of the commutation valve arm structure in some embodiments of the present application;

[0020] Figure 3 Schematic diagram of the converter structure in some other embodiments of the present application;

[0021] Figure 4 Schematic diagram of the controllable turn-off commutation module structure in some embodiments of the present application;

[0022] Figure 5 Schematic diagram of the controllable voltage equalizing circuit structure in some embodiments of the present application;

[0023] Figure 6 Schematic diagram of the commutation valve arm structure in some other embodiments of the present application;

[0024] Figure 7 Schematic diagram of the controllable turn-off commutation module structure in some other embodiments of the present application;

[0025] Figure 8 Schematic diagram of the commutation valve arm structure in some other embodiments of the present application;

[0026] Figure 9 Schematic diagram of the converter valve arm structure in some other embodiments of the present application;

[0027] Figure 10 Schematic diagram of the converter valve arm structure in some other embodiments of the present application. Detailed implementation manners

[0028] To facilitate the understanding of the present application, the present application will be described more comprehensively below with reference to the relevant drawings. Preferred embodiments of the present application are shown 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, these embodiments are provided to make the understanding of the disclosure of the present application more thorough and comprehensive.

[0029] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present application belongs. The terms used in the description of the present application herein are only for the purpose of describing specific embodiments and are not intended to limit the present application.

[0030] It can be understood that the terms "first", "second", etc. used in the present 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 one element from another. For example, without departing from the scope of the present application, the first resistor may be referred to as the second resistor, and similarly, the second resistor may be referred to as the first resistor. Both the first resistor and the second resistor are resistors, but they are not the same resistor.

[0031] It can be understood that "connection" in the following embodiments should be understood as "electrical connection", "communication connection", etc. if there is an electrical signal or data transmission between the connected circuits, modules, units, etc.

[0032] It can be understood that "at least one" means one or more, and "a plurality" means two or more. "At least part of an element" means part or all of the element.

[0033] As used herein, the singular forms "a", "an" and "the" may also include the plural forms unless the context clearly dictates otherwise. It should also be understood that the terms "comprises / include" or "has" etc. specify the presence of the stated features, wholes, steps, operations, components, parts or combinations thereof, but do not preclude 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 related listed items.

[0034] At present, with the change of market demand, the high-voltage direct current (HVDC) transmission method has been widely used in the interconnection of asynchronous power grids and long-distance high-power transmission occasions. Building large-scale wind power and photovoltaic bases in desert, gobi, and desert areas is an important measure for building a new power system and achieving the "dual carbon" goal. The tens of millions of kilowatt-level "desert, gobi, and desert" large-scale renewable energy bases are large in scale and wide in area, and the economically developed areas are far from the energy areas. The use of ultra-high voltage direct current technology can solve the problem of large-scale new energy transmission.

[0035] Through in-depth research, it is found that in order to achieve ultra-high voltage direct current transmission, more than a hundred levels of IGCT (Integrated Gate-Commutated Thyristor) devices need to be connected in series in the converter valve arm of the converter valve, and the converter valve has relatively high requirements for the consistency of IGCT devices. However, in related technologies, there are inconsistencies in the turn-on and turn-off parameters of IGCT devices, and due to comprehensive factors such as the delay of the drive circuit of IGCT, it is very easy to cause a large voltage distribution difference between each IGCT during the turn-on and turn-off processes of IGCT devices. In the case of the active turn-off of the converter valve due to commutation failure, the turn-off of IGCT devices will cause the devices to undergo avalanche breakdown.

[0036] To solve the above problems, multi-level voltage equalization of IGCT devices can be considered to ensure voltage consistency in each level of the converter valve, with a view to realizing a converter valve arm with more than a hundred levels or even more IGCT devices in cascade, and ensuring uniform voltage distribution of IGCT devices during the active turn-off process of the converter valve. To solve the problem of controllable turn-off of IGCT, this application proposes relevant voltage equalization technical solutions, which can further solve the technical problem of converter valve commutation failure.

[0037] Based on the above considerations, this application provides a controllable turn-off converter valve for a high-voltage direct current HVDC system. Each converter valve arm includes a valve arm voltage equalizer device and multiple cascaded controllable turn-off converter modules. A single controllable turn-off converter module includes a component voltage equalizer device and multiple cascaded controllable turn-off converter components. A single controllable turn-off converter component is configured to include at least one voltage equalization circuit and at least one controllable switch device, and a voltage equalization circuit is connected in parallel at both ends of a controllable switch device.

[0038] Through the settings of the voltage equalization circuit, the component voltage equalizer device, and the valve arm voltage equalizer device in the above solution, voltage equalization can be achieved at each level of the controllable turn-off converter valve, reducing the requirements for the consistency of controllable switch devices in the controllable turn-off converter valve, enabling a large number of controllable switch devices to be connected in series in the same converter valve arm, realizing reliable conversion of ultra-high voltage direct current transmission with a voltage level of ±800 kV and above, solving the problem of converter valve commutation failure of ultra-high voltage direct current type converter valves, and ensuring the safe and stable operation of the power system.

[0039] The controllable turn-off converter valve provided by the embodiments of the present application is applied to the field of high-voltage direct current (HVDC) transmission. In particular, in some embodiments, the controllable turn-off converter valve can be applied to the field of ultra-high voltage (i.e., the voltage level is greater than or equal to ±800 kV) HVDC transmission. For the controllable turn-off converter valve of the embodiments of the present application, the controllable switching device used in the converter valve arm is an IGCT device. In one embodiment, it can be a reverse-blocking IGCT device, or a switching device with a reverse-blocking function formed by an asymmetric IGCT device and a diode, and the specific form is not limited.

[0040] Please refer to Figure 1 and Figure 2 , the present application provides a controllable turn-off converter valve for a high-voltage direct current (HVDC) system (i.e., the structure shown as 10 in the figure), which includes a plurality of converter valve arms 11. The converter valve arm 11 includes a valve arm voltage equalizer 300 and a plurality of controllable turn-off converter modules 200. The valve arm voltage equalizer 300 is connected in parallel at both ends of a first structure formed by connecting the controllable turn-off converter modules 200 in series; the controllable turn-off converter module 200 includes a component voltage equalizer 220 and a plurality of controllable turn-off converter components 210. The component voltage equalizer 220 is connected in parallel at both ends of a second structure formed by connecting the controllable turn-off converter components 210 in series; the controllable turn-off converter component 210 includes at least one voltage equalizing circuit 211 and at least one controllable switching device G. A voltage equalizing circuit 211 is connected in parallel at both ends of one controllable switching device G.

[0041] Specifically, the controllable turn-off converter valve of the present application can be combined with a converter transformer 20 to form a converter. The AC terminal of the controllable turn-off converter valve can be connected to an AC load through the converter transformer 20, while the DC terminal of the controllable turn-off converter valve is used to connect to a DC load. The parameter design of the converter transformer 20 is determined in combination with the operation mode and operation characteristics of the controllable turn-off converter valve. The controllable switching device G is a switching device that can realize on and off control under the action of a controllable signal. The converter transformer 20 is a device in the converter used to realize the transformation of the voltage level of the AC voltage. The converter valve arm 11 is a valve arm device in the controllable turn-off converter valve, which is arranged between the AC load and the DC load, has the ability of unidirectional conduction, and realizes the AC-DC conversion through conduction and turn-off. For the convenience of understanding the technical solution of the present application, the following embodiments will be explained by taking the controllable switching device G as an IGCT device as an example.

[0042] The controllable turn-off converter valve is formed by connecting the converter valve arms 11 in series and / or in parallel. The specific connection method is not unique, and the structure of the controllable turn-off converter valve obtained will be different according to different actual requirements.

[0043] In one embodiment, the number of commutation valve arms 11 is six. After each pair of the commutation valve arms 11 is connected in series, three groups of commutation valve arms 11 are formed. Then, these three groups of commutation valve arms 11 are connected in parallel to form a six-pulse commutation device. Among them, the two ends formed by connecting the three groups of commutation valve arms 11 in parallel serve as the DC terminals, and the three common terminals formed by connecting the commutation valve arms 11 in series in pairs serve as the three-phase AC terminals.

[0044] In other embodiments, the number of commutation valve arms 11 can be twelve. In a similar manner to the above six-pulse commutation device, two six-pulse commutation valves are built, and then the two six-pulse commutation devices are connected in series to obtain a 12-pulse commutation device.

[0045] Taking a converter of the UHV type as an example, its controllable turn-off commutation valve can include a 12-pulse commutation device, or is formed by connecting two 12-pulse commutation devices in series to meet the requirements of UHV DC transmission. For the convenience of understanding the technical solution of this application, the following embodiments will take the controllable turn-off commutation valve formed by connecting two 12-pulse commutation devices in series as an example for explanation, and specific reference can be made to Figure 3 .

[0046] The controllable turn-off commutation valve in the figure includes a total of 24 commutation valve arms 11. The common terminal of the commutation valve arms 11 connected in series in pairs serves as one-phase AC terminal and is connected to the commutation transformer to achieve the UHV voltage level of 800 kV (kilovolts). Considering that the rated voltage level of a single IGCT device is currently 6.5 kV - 8 kV, in order to build a voltage level that meets 800 kV, each commutation valve arm 11 requires 80 - 100 IGCT devices connected in series.

[0047] The valve arm voltage equalizing device 300 is also a device used to equalize the voltage of the valve arm. Through the valve arm voltage equalizing device 300, the voltage equalization of multiple series-connected controllable turn-off commutation modules 200 can be achieved, ensuring the voltage consistency between the series-connected controllable turn-off commutation modules 200.

[0048] It should be noted that the type of the valve arm voltage equalizing device 300 is not unique, and any device that can achieve the voltage equalization function between the controllable turn-off commutation modules 200 can be used. For example, in one embodiment, the valve arm voltage equalizing device 300 is a lightning arrester. More specifically, in one embodiment, the valve arm voltage equalizing device 300 is a MOV (Metal Oxide Varistors) lightning arrester.

[0049] The component voltage equalizing device 220 is also a device used to equalize the voltage of each controllable turn-off commutation component 210 to ensure the voltage consistency between the controllable turn-off commutation components 210. The voltage equalizing circuit 211 is also a circuit used to equalize the voltage of the controllable switch device G to ensure the safe operation of the controllable turn-off device.

[0050] It can be understood that the type of the controllable switch device G is not unique, and any switch device that can be controlled to achieve the on and off functions can be used. For example, in one embodiment, the controllable switch device G is an IGCT. Further, in one embodiment, the controllable switch device G is a reverse-blocking IGCT device. In other embodiments, the controllable switch device G can also be constructed by an asymmetric IGCT and a diode, and no specific limitation is made. It can be selected according to actual needs.

[0051] For the above-mentioned controllable turn-off commutation valve used in the high-voltage DC HVDC system, each commutation valve arm 11 includes a valve arm voltage equalizer device 300 and a plurality of cascaded controllable turn-off commutation modules 200. A single controllable turn-off commutation module 200 includes a component voltage equalizer device 220 and a plurality of cascaded controllable turn-off commutation components 210. A single controllable turn-off commutation component 210 is configured to include at least one voltage equalizing circuit 211 and at least one controllable switch device G. A voltage equalizing circuit 211 is connected in parallel at both ends of a controllable switch device G. In this way, through the settings of the voltage equalizing circuit 211, the component voltage equalizer device 220, and the valve arm voltage equalizer device 300, the controllable turn-off commutation valve can achieve voltage equalization at each level, reduce the consistency requirement of the controllable switch device G for the controllable turn-off commutation valve, enable a large number of controllable switch devices G to be connected in series in the same commutation valve arm 11, realize the reliable conversion of ultra-high voltage DC power transmission with a voltage level of ±800 kV and above, solve the problem of commutation failure of the commutation valve of the ultra-high voltage DC type, and ensure the safe and stable operation of the power system.

[0052] Please refer to Figure 4 , in one embodiment, the component voltage equalizer device 220 is a voltage equalizing capacitor. The controllable turn-off commutation component 210 includes a voltage equalizing circuit 211 and a controllable switch device G (both are explained by taking the IGCT as an example). The voltage equalizing circuit 211 includes a device-level voltage equalizing circuit 413 and a controllable voltage equalizing circuit 412. The device-level voltage equalizing circuit 413 and the controllable voltage equalizing circuit 412 are respectively connected in parallel at both ends of the controllable switch device G.

[0053] Specifically, in the solution of this embodiment, a single controllable turn-off commutation component 210 is built by a single controllable switch device G, and equalizing capacitors are used to achieve the equalizing function between the controllable turn-off commutation components 210. Correspondingly, the equalizing circuit 211 connected in parallel at both ends of the controllable switch device G can be built in the form of parallel connection of a device-level equalizing circuit 413 and a controllable equalizing circuit 412. In this way, during the operation of the controllable turn-off commutation valve, through the equalizing capacitors, the component voltage distribution can be made uniform under high-frequency impact voltages. Through the design of the equalizing circuit 211 at both ends of the controllable switch device G, on the one hand, through the equalizing effect of the device-level equalizing circuit 413, the reverse recovery overvoltage can be suppressed and the static voltage can be equalized to ensure the safe operation of the controllable switch device G. On the other hand, when abnormal current conduction occurs in the controllable turn-off commutation valve, etc., by cutting off the controllable equalizing circuit 412, the pressure release caused by abnormal current conduction in the controllable equalizing circuit 412 can be avoided, and the operation reliability of the controllable turn-off commutation valve can be improved.

[0054] It should be noted that the type of the equalizing capacitor is not unique. It can be a single capacitor or a capacitor bank formed by multiple capacitors in series and / or parallel, and no specific limitation is made. The size of the equalizing capacitor is not unique. Specifically, it can be determined according to the size of the stray capacitance in the commutation valve arm 11, combined with the broadband equivalent model of the commutation valve arm 11 and the overall parameter calculation, as long as the equalizing requirement is met under high-frequency impact voltages such as steep waves.

[0055] In one embodiment, the controllable equalizing circuit 412 includes a passive switch device and a first lightning arrester. The two ends formed after the series connection of the passive switch device and the first lightning arrester are respectively connected to both ends of the controllable switch device G.

[0056] Specifically, a passive switch device is a switch that does not require an external power source as a driving force to control the switch state. In the solution of this embodiment, the series structure of the passive switch device and the first lightning arrester is used as the controllable equalizing circuit 412. In the normal state, the passive switch device is in the conducting state, and overvoltage suppression can be achieved through the first lightning arrester, so as to ensure voltage consistency; in the case of abnormal current conduction, etc., the passive switch device is turned off, and the first lightning arrester is cut out of operation to avoid pressure release caused by abnormal current conduction of the first lightning arrester.

[0057] This solution uses a passive switch device and a first lightning arrester to build the controllable equalizing circuit 412, which has high operation stability and safety, and does not require external power supply, with the advantage of low maintenance cost.

[0058] It should be noted that the specific type of the passive switch device is not unique. In one embodiment, please refer to Figure 5, the passive switching device can be a TVS (Transient Voltage Suppressor), a gap switch, etc., which is not specifically limited.

[0059] Similarly, the type of the first lightning arrester is not unique either. Any device that can achieve overvoltage suppression can be used. For example, in one embodiment, the first lightning arrester is a MOV lightning arrester.

[0060] In one embodiment, the controllable voltage equalizing circuit 412 includes an active switching device and a second lightning arrester. The two ends formed after the series connection of the active switching device and the second lightning arrester are respectively connected to the two ends of the controllable switching device G.

[0061] Specifically, the active switching device is a switch that requires an external power source as a driving force to control its switching state. In the solution of this embodiment, a series structure of an active switching device and a second lightning arrester is used as the controllable voltage equalizing circuit 412. In the normal state, the active switching device is in the on state, and overvoltage suppression can be achieved through the second lightning arrester, thereby ensuring voltage consistency. In the case of abnormal current flow, etc., the active switching device is turned off, and the second lightning arrester is cut out of operation to avoid pressure release caused by abnormal current flow in the second lightning arrester. This solution uses an active switching device and a second lightning arrester to build the controllable voltage equalizing circuit 412, which has the advantage of high response speed.

[0062] It should be noted that the specific type of the active switching device is not unique. In one embodiment, it can be a silicon controlled rectifier (SCR), an insulated-gate bipolar transistor (IGBT), etc., which is not specifically limited.

[0063] Similarly, the type of the second lightning arrester is not unique either. Any device that can achieve overvoltage suppression can be used. For example, in one embodiment, the second lightning arrester is a MOV lightning arrester.

[0064] Please refer to Figure 6 , in one embodiment, the component voltage equalizing device 220 is a third lightning arrester, and the voltage equalizing circuit 211 includes a device-level voltage equalizing circuit 413. The device-level voltage equalizing circuit 413 is arranged in parallel at both ends of the controllable switching device G.

[0065] Specifically, a third lightning arrester is used to achieve the voltage equalization function between the controllable turn-off commutation components 210. Correspondingly, the voltage equalization circuit 211 connected in parallel across the controllable switch device G can adopt the device-level voltage equalization circuit 413. In this way, during the operation of the controllable turn-off commutation valve, through the voltage equalization effect of the device-level voltage equalization circuit 413, the reverse recovery overvoltage can be suppressed, and the voltage equalization of the static voltage can be achieved to ensure the safe operation of the controllable switch device G. When the voltages between the controllable turn-off commutation components 210 are inconsistent, voltage equalization and voltage limitation can be performed through the third lightning arrester.

[0066] Through this solution, the third lightning arrester is used to achieve voltage equalization between components, and lightning arresters do not need to be set at both ends of each controllable switch device G, reducing the number of lightning arresters used. At the same time, the volume of the component voltage equalization device 220 can also be reduced, thereby reducing the volume of the commutation valve arm 11.

[0067] It can be understood that the type of the third lightning arrester is not unique. For the convenience of understanding the technical solution of this application, in the following embodiments, the third lightning arrester can be understood as a MOV lightning arrester.

[0068] Please refer to Figure 7 , in one embodiment, the controllable turn-off commutation component 210 includes a string voltage equalization circuit 520 and multiple controllable turn-off commutation strings 510. The string voltage equalization circuit 520 is connected in parallel across both ends of the third structure formed by the series connection of each controllable turn-off commutation string 510; the controllable turn-off commutation string 510 includes multiple voltage equalization circuits 211 (specifically, the device-level voltage equalization circuit 413 in the figure) and multiple series-connected controllable switch devices G, and a voltage equalization circuit 211 is connected in parallel across both ends of each controllable switch device G.

[0069] Specifically, when the component voltage equalization device 220 is a third lightning arrester, the controllable switch devices G in the controllable turn-off commutation component 210 are also hierarchically divided. The same controllable turn-off commutation component 210 includes a string voltage equalization circuit 520 and multiple controllable turn-off commutation strings 510. After the multiple controllable turn-off commutation strings 510 are connected in series, they are then connected in parallel with the string voltage equalization circuit 520. In this way, through the string voltage equalization circuit 520, the active turn-off voltage equalization of a single controllable turn-off commutation component 210 can be achieved, improving the operation reliability of the controllable turn-off commutation component 210.

[0070] It should be noted that the type of the string voltage equalization circuit 520 is not unique, as long as it can achieve active turn-off voltage equalization. For example, please continue to refer to Figure 7 , in one embodiment, the string voltage equalization circuit 520 includes a first capacitor C and a first diode D connected in series. The two ends formed after the series connection of the first capacitor C and the first diode D are respectively connected to both ends of the third structure formed by the series connection of each controllable turn-off commutation string 510.

[0071] Specifically, in the solution of this embodiment, the string equalizing circuit 520 is specifically a CD-type equalizing circuit, which can effectively suppress overvoltage through the first capacitor C during the operation of the controllable turn-off thyristor valve, thereby protecting the controllable turn-off thyristor valve. It can also absorb and release energy to stabilize the voltage output of the controllable turn-off thyristor valve and ensure that it fluctuates within the normal range. Further, by setting the first diode D, RC oscillation between the first capacitor C and other structures can be avoided, and the operation reliability of the string equalizing circuit 520 can be improved.

[0072] In one embodiment, the string equalizing circuit 520 further includes a voltage discharging circuit. The voltage discharging circuit is connected to the first capacitor C to accelerate the voltage discharging speed of the first capacitor C, so as to ensure that the first capacitor C has sufficient capacity for energy absorption during the next turn-off, thereby ensuring the CD equalizing effect.

[0073] It should be noted that the specific type of the voltage discharging circuit is not unique, and any device or circuit that can quickly consume electrical energy can be used, and no specific limitation is made. For example, in one embodiment, please continue to refer to Figure 7 , the voltage discharging circuit can be a resistor, that is, the string equalizing circuit 520 further includes a first resistor R, and the first resistor R is connected in parallel with the first capacitor C.

[0074] It can be understood that in one embodiment, to ensure that the CD equalizing circuit can reliably achieve the equalizing effect during the operation of the controllable turn-off thyristor valve, the cathode of the first diode D should be connected to the cathode of the controllable switch device G in the controllable turn-off thyristor string 510, and the anode of the first diode D can be directly or indirectly connected to the anode of the controllable switch device G. In this way, the first diode D can also prevent current backflow and further improve the operation reliability of the string equalizing circuit 520.

[0075] In one of the embodiments, the device-level equalizing circuit 413 includes a static equalizing circuit and a reverse recovery equalizing circuit, and the static equalizing circuit and the reverse recovery equalizing circuit are respectively connected in parallel with the controllable switch device G.

[0076] Specifically, in the solution of this embodiment, the device-level equalizing circuit 413 connected in parallel across a single controllable switch device G includes a static equalizing circuit and a reverse recovery equalizing circuit, and the static equalizing circuit and the reverse recovery equalizing circuit are respectively connected in parallel across the controllable switch device G. In this way, during the operation of the controllable turn-off thyristor valve, it can equalize the static voltage to ensure the safe operation of the controllable switch device G, and can also suppress the reverse recovery overvoltage, further improving the operation safety of the controllable switch device G.

[0077] It should be noted that the specific types of the static voltage equalization circuit and the reverse recovery voltage equalization circuit are not unique. Please refer to Figure 4 or Figure 7 , in one embodiment, the static voltage equalization circuit includes a second resistor Rd, and the second resistor Rd is arranged in parallel across both ends of the controllable switching device G.

[0078] Specifically, the solution of this embodiment realizes static voltage equalization in the form of a static voltage equalization resistor, and has high voltage equalization reliability. In other embodiments, other voltage equalization methods may also be adopted, such as capacitor voltage equalization, etc., which are not specifically limited.

[0079] And / or, please refer to Figure 4 or Figure 7 , in one embodiment, the reverse recovery voltage equalization circuit includes a third resistor Rs and a second capacitor Cs connected in series, and both ends formed after series connection are respectively connected to both ends of the controllable switching device G.

[0080] Specifically, in this embodiment, the reverse recovery voltage equalization is realized in the form of a series RC damping circuit, and the circuit structure is simple and the voltage equalization reliability is high.

[0081] Please refer to Figure 8 , in one embodiment, the commutation valve arm 11 further includes a saturable reactor Ls, and the structure formed by series connection of each controllable turn-off commutation module 200 is connected in series with the saturable reactor Ls.

[0082] Specifically, the saturable reactor Ls is a reactor that can act as a non-linear inductor, and it is mainly used to suppress the rate of change of the current in the commutation valve arm 11. By respectively arranging a saturable reactor Ls in each commutation valve arm 11, when the commutation valve arm 11 bears a steep wave impact, the voltage stress generated on the controllable switching device G can be limited, and the turn-on current flowing through the controllable switching device G can be limited, so that the voltage distribution inside the commutation valve arm 11 is uniform.

[0083] It can be understood that in the above embodiment, the saturable reactor Ls is centrally arranged at one end of the commutation valve arm 11. In other embodiments, the saturable reactor Ls can also be dispersedly arranged in each controllable turn-off commutation module 200, that is, in each controllable turn-off commutation module 200, a saturable reactor Ls is connected in series with the controllable switching device G. Further, the saturable reactor Ls can also be dispersedly arranged in each controllable turn-off commutation component 210.

[0084] It should be noted that in one embodiment, if the current rate of change tolerance of the controllable switching device G is relatively high, the saturable reactor Ls may not be set, and it can be specifically selected according to actual requirements.

[0085] For the convenience of understanding the technical solution of the present application, the present application will be explained below in conjunction with relatively detailed embodiments.

[0086] Please refer to Figure 9 , taking any one of the converter valve arms 11 as an example, based on the IGCT devices with a rated voltage of 6.5 kV - 7.2 kV, a voltage-sharing capacitor can be used as the component voltage-sharing device 220 to build the converter valve arm 11. At the component level, a turn-off thyristor converter component 210 includes an IGCT and a voltage-sharing circuit 211 connected in parallel at both ends thereof. At this time, the voltage-sharing circuit 211 is a three-stage voltage-sharing structure. The first-stage voltage sharing is a reverse recovery voltage-sharing circuit formed by RC in series; the second-stage voltage sharing is a static voltage-sharing resistor; the third-stage voltage sharing is a controllable voltage-sharing circuit 412, which includes an active switching device and a second lightning arrester connected in series, or includes a passive switching device and a first lightning arrester connected in series. At the module level, 15 turn-off thyristor converter components 210 and voltage-sharing capacitors are used to build a turn-off thyristor converter module 200. Specifically, after 15 turn-off thyristor converter components 210 are connected in series, a voltage-sharing capacitor is connected at both ends to achieve component-level voltage sharing with the voltage-sharing capacitor. Finally, 6 turn-off thyristor converter modules 200 are connected in series, and a valve arm voltage-sharing device 300 (specifically a MOV lightning arrester) is connected in parallel at both ends of the series structure to build a converter valve arm 11 including 90 IGCTs connected in series, that is, a 90-stage IGCT valve arm structure.

[0087] Please refer to Figure 10 , based on the IGCT devices with a rated voltage of 8 kV and above, a lightning arrester can be used as the component voltage-sharing device 220 to build the converter valve arm 11. At the string level, a turn-off thyristor converter string 510 includes an IGCT and a voltage-sharing circuit 211 connected in parallel at both ends thereof. At this time, the voltage-sharing circuit 211 is a two-stage voltage-sharing structure. The first-stage voltage sharing is a static voltage-sharing resistor; the second-stage voltage sharing is a reverse recovery voltage-sharing circuit formed by RC in series. At the component level, a turn-off thyristor converter component 210 includes 4 turn-off thyristor converter strings 510 connected in series, and a string voltage-sharing circuit 520 connected in parallel at both ends of the series structure. The string voltage-sharing circuit 520 is a CD voltage-sharing circuit (a resistor is connected in parallel at the capacitor to discharge the voltage). At the module level, 4 turn-off thyristor converter components 210 and a lightning arrester are used to build a turn-off thyristor converter module 200. Specifically, after 4 turn-off thyristor converter components 210 are connected in series, a lightning arrester is connected at both ends to achieve component-level voltage sharing with the lightning arrester. Finally, 5 turn-off thyristor converter modules 200 are connected in series, and a valve arm voltage-sharing device 300 is connected in parallel at both ends of the series structure to build a converter valve arm 11 including 80 IGCTs connected in series, that is, an 80-stage IGCT valve arm structure.

[0088] In the description of this specification, the descriptions referring to terms such as "some embodiments", "other embodiments", etc. mean that the specific features, structures, materials, or characteristics described in connection 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.

[0089] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the various technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered to be within the scope described in this specification.

[0090] The above-described embodiments only express several implementation manners of the present application. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the patent application. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present application, several modifications and improvements can still be made, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be subject to the appended claims.

Claims

1. A controllable turn-off commutation valve for a high-voltage direct current (HVDC) system, characterized in that, It includes multiple commutation valve arms, each of the commutation valve arms includes a valve arm voltage equalizer device and multiple controllable turn-off commutation modules, and the valve arm voltage equalizer device is connected in parallel at both ends of a first structure formed by connecting the multiple controllable turn-off commutation modules in series; each of the controllable turn-off commutation modules includes a component voltage equalizer device and multiple controllable turn-off commutation components, and the component voltage equalizer device is connected in parallel at both ends of a second structure formed by connecting the multiple controllable turn-off commutation components in series; each of the controllable turn-off commutation components includes at least one voltage equalizing circuit and at least one controllable switching device, and one voltage equalizing circuit is connected in parallel at both ends of one controllable switching device.

2. The controllable turn-off commutation valve according to claim 1, wherein The component voltage equalizer device is an equalizing capacitor, each of the controllable turn-off commutation components includes one voltage equalizing circuit and one controllable switching device, the voltage equalizing circuit includes a device-level voltage equalizing circuit and a controllable voltage equalizing circuit, and the device-level voltage equalizing circuit and the controllable voltage equalizing circuit are respectively connected in parallel at both ends of the controllable switching device.

3. The controllable turn-off commutation valve according to claim 2, characterized in that, The controllable voltage equalizing circuit includes a passive switching device and a first lightning arrester, and both ends formed after the passive switching device and the first lightning arrester are connected in series are respectively connected to both ends of the controllable switching device.

4. The controllable turn-off commutation valve according to claim 2, characterized in that, The controllable voltage equalizing circuit includes an active switching device and a second lightning arrester, and both ends formed after the active switching device and the second lightning arrester are connected in series are respectively connected to both ends of the controllable switching device.

5. The controllable turn-off commutation valve according to claim 1, wherein The component voltage equalizer device is a third lightning arrester, the voltage equalizing circuit includes a device-level voltage equalizing circuit, and the device-level voltage equalizing circuit is connected in parallel at both ends of the controllable switching device.

6. The controllable turn-off commutation valve according to claim 5, characterized in that, Each of the controllable turn-off commutation components includes a string voltage equalizing circuit and multiple controllable turn-off commutation strings, and the string voltage equalizing circuit is connected in parallel at both ends of a third structure formed by connecting the multiple controllable turn-off commutation strings in series; each of the controllable turn-off commutation strings includes multiple voltage equalizing circuits and multiple controllable switching devices connected in series, and one voltage equalizing circuit is respectively connected in parallel at both ends of each controllable switching device.

7. The turn-off thyristor valve according to claim 6, characterized in that, The string voltage equalizing circuit includes a first capacitor and a first diode connected in series, and both ends formed after the first capacitor and the first diode are connected in series are respectively connected to both ends of the third structure formed by connecting the multiple controllable turn-off commutation strings in series.

8. The controllable turn-off commutation valve according to claim 7, wherein The string voltage equalizing circuit further includes a first resistor, and the first resistor is connected in parallel with the first capacitor.

9. The turn-off controllable commutation valve according to claim 2 or 5, characterized in that, The device-level voltage equalizing circuit includes a static voltage equalizing circuit and a reverse recovery voltage equalizing circuit, and the static voltage equalizing circuit and the reverse recovery voltage equalizing circuit are respectively connected in parallel with the controllable switching device.

10. The controllable turn-off commutation valve according to claim 9, wherein The static voltage equalizing circuit includes a second resistor, and the second resistor is connected in parallel at both ends of the controllable switching device; and / or, the reverse recovery voltage equalizing circuit includes a third resistor and a second capacitor connected in series, and both ends formed after being connected in series are respectively connected to both ends of the controllable switching device.

11. The controllable turn-off commutation valve according to any one of claims 1-8, characterized in that, The commutation valve arm further includes a saturable reactor, and the structure formed by connecting the multiple controllable turn-off commutation modules in series is connected in series with the saturable reactor.

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