Grid-supporting active converter, its control method and commutation system

Abstract

The present application discloses a grid-supporting active converter, its control method and a commutation system, belonging to the technical field of high-power power electronic conversion. The grid-supporting active converter includes an active commutation chain and a valve control system; the active commutation chain includes at least one active module, and the active module includes an energy storage unit, a power unit, a power control module and an energy storage control module; wherein, the power control module controls the operation of the power unit, the energy storage control module extracts energy from the energy storage element of the energy storage unit and controls the operation of the energy storage unit, and the valve control system communicates with the energy storage control module and the power control module. By arranging an energy storage control module that draws power from the energy storage element in the active module, it can be ensured that when the power grid loses power, the energy storage control module can still work normally and cooperate with the power control module to realize the black start function.

Description

Technical Field

[0001] The present application belongs to the technical field of high-power electronic power conversion, and specifically relates to a grid-supported active converter and a control method and a commutation system thereof. Background Art

[0002] In the field of large-capacity and high-power power electronic conversion technology, multilevel converters use modular cascade technology to integrate energy storage devices into sub-modules. They have the advantages of high modularity, good harmonic characteristics, and low equivalent switching frequency. They have become the standard topology in the field of high-voltage power electronics. By integrating the energy storage unit as a sub-module in the modular multilevel converter, such as integrating the energy storage unit in the static VAR generator to achieve high-voltage AC direct-mounted energy storage, or integrating the energy storage unit in the half-bridge module to achieve high-voltage DC direct-mounted energy storage, AC / DC power conversion and energy storage can be achieved simultaneously. The active converter thus born is a feasible solution that can effectively meet the access requirements of the energy storage system and play a role in supporting the power grid.

[0003] Multilevel converters with energy storage units need to be considered as black start power supplies for restarting regional power grids when power is lost, but existing technical solutions cannot meet the black start requirements. Summary of the invention

[0004] Purpose of the invention: The present application provides a grid-supported active converter, the purpose of which is to solve the technical problem in the prior art that the multi-level converter cannot be used as a black start power supply for restarting the regional power grid when the power grid loses power; the present application also provides a control method for the above-mentioned grid-supported active converter, the purpose of which is to provide a variety of selectable control modes for the grid-supported active converter; in addition, the present application also provides a commutation system, the purpose of which is to provide an application method of the grid-supported active converter.

[0005] Technical solution: A grid-supported active converter described in the present application includes an active commutation chain and a valve control system; wherein the active commutation chain includes at least one active module, and the active module includes:

[0006] An energy storage unit, comprising at least one energy storage element;

[0007] A power unit, comprising a DC capacitor and a power component connected in parallel, wherein the power component comprises a full-bridge circuit and / or a half-bridge circuit composed of power semiconductor devices, the DC capacitor is connected to the energy storage unit via a connecting switch, and a bypass switch is connected in parallel to the AC end of the power unit;

[0008] A power control module, controlling the operation of the power unit;

[0009] An energy storage control module, which takes energy from the energy storage element and controls the operation of the energy storage unit;

[0010] The valve control system communicates with the energy storage control module and the power control module.

[0011] Optionally, in some embodiments, the power control module communicates with the energy storage control module, or the power control module and the energy storage control module are integrated together.

[0012] Optionally, in some embodiments, the active commutation chain includes N active modules connected in series, where N is an integer greater than or equal to 2;

[0013] The connection mode between the active commutation chain and the valve control system includes point-to-point connection, group head-to-tail connection, series random connection, series head-to-tail connection or any combination thereof; wherein,

[0014] The point-to-point connection means that in the active commutation chain, all the active modules are connected to the valve control system through their respective power control modules and / or energy storage control modules;

[0015] The head-to-tail connection of the groups is: in the active commutation chain, P active modules form a group, 2≤P≤N; in the group, each active module is connected in series through the power control module and / or the energy storage control module, and the power control module and / or the energy storage control module of the active modules at the head and tail ends are connected to the valve control system;

[0016] The random series connection is: in the active commutation chain, all the active modules are connected in series through the power control module and / or the energy storage control module, and M active modules are selected, 2≤M≤N, and the power control module and / or the energy storage control module are connected to the valve control system through the M active modules;

[0017] The series head-to-tail connection is: in the active commutation chain, all the active modules are connected in series through the power control module and / or the energy storage control module, and the power control module and / or the energy storage control module of the active modules located at the head and tail ends are connected to the valve control system.

[0018] Optionally, in some embodiments, the valve control system includes at least one valve controller, and the power control module and the energy storage control module both communicate with the valve controller.

[0019] Optionally, in some embodiments, the valve control system includes two valve controllers, namely a first valve controller and a second valve controller, the power control module communicates with the first valve controller, and the energy storage control module communicates with the second valve controller.

[0020] Optionally, in some embodiments, the first valve controller and the second valve controller communicate; and / or

[0021] The first valve controller and the second valve controller are different plug-ins arranged in the same device, or the first valve controller and the second valve controller are arranged in different devices; and / or

[0022] The first valve controller is configured with a dual system for online switching; and / or

[0023] The second valve controller is configured with a dual system for online switching.

[0024] Optionally, in some embodiments, the connection switch is controlled by the power control module and / or the energy storage control module; and / or

[0025] The connection switch is connected in parallel with a charging circuit, and the charging circuit includes a charging switch and a resistor connected in series. The charging switch is controlled by the power control module and / or the energy storage control module.

[0026] Optionally, in some embodiments, the energy storage element includes a battery, a supercapacitor, a flywheel energy storage, a gas compression energy storage or any combination thereof; and / or

[0027] The energy storage unit further comprises a DC / DC converter, wherein the DC / DC converter is arranged between the energy storage element and an input end of the energy storage unit; and / or

[0028] comprising an undervoltage protection unit, which causes the energy storage control module to stop taking energy from the energy storage element when the bypass switch is closed and the voltage of the energy storage element is lower than a threshold value; and / or

[0029] The energy storage control module samples the position node of the bypass switch.

[0030] Accordingly, the control method provided in the present application for the above-mentioned grid-supported active converter includes an offline self-test mode, an active start mode, a black start mode or any combination thereof; wherein,

[0031] The offline self-test mode includes: relying on the energy storage unit to supply energy, realizing the active module self-test, and determining whether the startup conditions are met;

[0032] The active startup mode includes: when the AC power grid is normal, the grid-supported active converter is first connected to the power grid and then starts to operate;

[0033] The black start mode includes: when the grid-supported active converter is not connected to the grid or the grid loses power, the energy storage unit provides startup energy to enable the converter to operate and output independent active and / or reactive power to support the grid.

[0034] Optionally, in some embodiments, when there are an offline self-test mode, an active start mode and a black start mode at the same time, the offline self-test mode also includes judging whether to enter the active start mode or the black start mode according to the grid voltage condition.

[0035] Optionally, in some embodiments, the steps of the offline self-check mode include:

[0036] Obtaining, through the energy storage control module, the position information of the bypass switches of all the power units and the state of charge value of the energy storage element;

[0037] Entering the first stage: judging whether the number of bypass submodules exceeds the allowed redundancy number, if not, entering the second stage, if exceeded, the self-check fails and is not allowed to enter the second stage; wherein the bypass submodule is an active module with a closed bypass switch;

[0038] The second step: determine whether the number of active modules whose state of charge values ​​are lower than the allowed value for operation exceeds the allowed number. If so, it is considered that the black start self-test has failed and entry into the black start mode is not allowed.

[0039] Optionally, in some embodiments, the steps of the active startup mode include:

[0040] The DC capacitor is charged by the AC power grid, and the power control module obtains energy from the DC capacitor;

[0041] All non-bypassed submodules establish communication with the valve control system; wherein the non-bypassed submodules are active modules with bypass switches disconnected;

[0042] When the state of charge value of the energy storage element is less than a threshold value, the power unit corresponding to the energy storage element is controlled to output a zero level, or the power unit is limited to operate in a charging state or in a power limiting state;

[0043] Controlling the power semiconductor device in the power unit to unlock, the grid-supported active converter to connect to the grid and unlock for operation, and provide active and / or reactive support to the grid;

[0044] The state of charge value of the energy storage element is controlled to be increased, and when the state of charge value is greater than a threshold value, the restriction on the power unit is released.

[0045] Optionally, in some embodiments, the steps of the black start mode include:

[0046] Closing the connection switch to charge the DC capacitor through the energy storage unit;

[0047] The power control module obtains energy from the DC capacitor;

[0048] All non-bypassed submodules establish communication with the valve control system; wherein the non-bypassed submodules are active modules with bypass switches disconnected;

[0049] When the state of charge value of the energy storage element is less than a threshold value, controlling the power unit corresponding to the energy storage element to output a zero level state;

[0050] The power semiconductor devices in the power unit are controlled to unlock, and the converter outputs a given voltage to realize grid-connected or island power supply.

[0051] Accordingly, the present application provides a commutation system, comprising at least one commutation arm, wherein the commutation arm comprises at least one grid-supported active converter.

[0052] Optionally, in some embodiments, a commutation arm is included, and the commutation arm is connected across two poles of the DC bus;

[0053] Or it comprises three said commutation arms, each of said commutation arms is connected in a triangle, and the lead-out end is connected to the AC bus;

[0054] Or it comprises three commutation arms, each of which is connected in a star shape, and the lead-out end is connected to an AC bus;

[0055] Or it includes six said commutation arms, every two said commutation arms are connected in series to form a group, the terminals between two said commutation arms in each group are connected to the AC bus, the groups are connected in parallel, and the parallel terminals are connected to the two poles of the DC bus.

[0056] Beneficial effect: Compared with the prior art, the grid-supported active converter of the present application is provided with an energy storage control module, which stably draws energy from the energy storage element, controls the operation of the energy storage unit, and communicates with the valve control system, which can ensure that when the grid loses power, the energy storage control module of the active module can still work normally, and cooperates with the power control module to realize the black start function: that is, the process of closing the charging contactor, charging the DC capacitor, and then unlocking and starting; when the active module exits operation, the communication will not be interrupted. The control method of the grid-supported active converter includes an offline self-test mode, an active start mode, a black start mode or any combination thereof. By providing a variety of selectable modes, different usage requirements are fully guaranteed. The commutation system provides guidance for the practical application of the grid-supported active converter. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] The technical solution and other beneficial effects of the present application will be made apparent by describing in detail the specific implementation methods of the present application in conjunction with the accompanying drawings.

[0058] Figure 1 A schematic diagram of the structure of a grid-supported active converter provided in an embodiment of the present application;

[0059] Figure 2 A schematic diagram of the structure of another grid-supported active converter provided in an embodiment of the present application;

[0060] Figure 3 This is a schematic diagram of a point-to-point connection between an active commutation chain and a valve control system in an embodiment of the present application;

[0061] Figure 4 This is a schematic diagram of the end-to-end connection of the active commutation chain and the valve control system in the embodiment of the present application;

[0062] Figure 5 This is a schematic diagram of random series connection of active commutation chain and valve control system in an embodiment of the present application;

[0063] Figure 6 This is a schematic diagram of the end-to-end connection of the active commutation chain and the valve control system in series in an embodiment of the present application;

[0064] Figure 7 It is a structural schematic diagram of a combined connection mode of an active commutation chain and a valve control system in an embodiment of the present application;

[0065] Figure 8 This is a schematic diagram of a connection switch connected in parallel with a charging circuit in an embodiment of the present application;

[0066] Fig. 9 A structural schematic diagram of an application mode of a commutation arm composed of a grid-supported active converter provided in an embodiment of the present application;

[0067] Fig.10 A structural schematic diagram of an application mode of three converter arms composed of a grid-supported active converter provided in an embodiment of the present application;

[0068] Fig.11 A schematic structural diagram of another application mode of three converter arms composed of a grid-supported active converter provided in an embodiment of the present application;

[0069] Fig.12 A structural schematic diagram of an application mode of six converter arms composed of a grid-supported active converter provided in an embodiment of the present application;

[0070] Fig.13 This is a flow chart of a control method for a grid-supported active converter provided in an embodiment of the present application. DETAILED DESCRIPTION

[0071] The technical solutions in the embodiments of the present application will be described clearly and completely below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present application.

[0072] In the description of the present application, it should be noted that, unless otherwise clearly specified and limited, the terms "connected" and "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection, an electrical connection, or can communicate with each other; it can be directly connected, or indirectly connected through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to the specific circumstances. In the description of the present application, the meaning of "multiple" is two or more, unless otherwise clearly and specifically defined. In addition, the terms "first" and "second" are used for descriptive purposes only, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the said features.

[0073] The disclosure below provides many different embodiments or examples to realize the different structures of the present application. In order to simplify the disclosure of the present application, the parts and settings of specific examples are described below. Of course, they are only examples, and the purpose is not to limit the present application.

[0074] The applicant found that for the traditional active converter, when the system is started, the closing of the charging contactor needs to be controlled by the submodule control unit, but the submodule control unit draws energy from the submodule DC capacitor, and the DC capacitor in the submodule needs to draw energy from the grid side. The power cannot be drawn when the grid loses power; therefore, the traditional method can only be completed by connecting to the grid first, charging the DC capacitor, and then closing the charging contactor to connect the DC capacitor and the energy storage unit to complete the normal startup. In order to meet the needs of black start, the applicant has made improvements to the traditional solution and obtained the technical solution of this application.

[0075] like Figure 1 As shown, an embodiment of the present application provides a grid-supported active converter, including an active commutation chain and a valve control system. The active commutation chain is mainly composed of active modules 1, and the number of active modules 1 is at least 1, that is, the active commutation chain includes N active modules 1, where N is an integer greater than or equal to 1. In some embodiments, when N is greater than or equal to 2, the active modules 1 are connected in series.

[0076] The active module 1 includes an energy storage unit, a power unit, a power control module (Sub-module controller, referred to as SMC) and an energy storage control module (Battery control module, referred to as BCM).

[0077] Among them, the main components of the energy storage unit include energy storage elements, and the number of energy storage elements is at least one, that is, in some embodiments, only one energy storage element may be provided in the energy storage unit, while in some other embodiments, multiple energy storage elements may be provided in the energy storage unit. Optionally, the energy storage element may have a variety of forms, including batteries, supercapacitors, flywheel energy storage, gas compression energy storage, or any combination thereof. In addition, other devices known in the art that can store electrical energy may also be selected, and those skilled in the art may make a choice from these devices according to the different requirements of different embodiments.

[0078] The power unit includes a DC capacitor and a power component connected in parallel, wherein the power component includes a full-bridge circuit and / or a half-bridge circuit composed of power semiconductor devices, that is, the power component can be Figure 1 The full-bridge circuit shown may also be a half-bridge circuit or a full-bridge half-bridge hybrid circuit known in the art, and those skilled in the art may select the circuit form of the power component according to different requirements of different embodiments. The DC capacitor is connected to the energy storage unit via a connecting switch KM, and a bypass switch is connected in parallel to the AC end of the power unit.

[0079] The power control module controls the operation of the power unit, and the power control module communicates with the valve control system.

[0080] The energy storage control module takes energy from the energy storage element of the energy storage unit and controls the operation of the energy storage unit. The energy storage control module communicates with the valve control system. Specifically, in some embodiments, the energy storage control module has a built-in energy storage communication unit, and the energy storage control module communicates with the valve control system through its built-in energy storage communication unit.

[0081] In addition, the applicant also found that the submodule control unit and the valve control unit in the traditional solution are one-to-one communication, and do not have communication redundancy. Once the optical fiber communication is interrupted, the module will be forced to bypass, and the corresponding energy storage unit will also be out of operation. The energy storage unit is of high value and easy to damage. After the exit from operation, it will affect the operating income of the equipment, and at the same time, it will cause the state of charge (SOC) of the energy storage units of each submodule of the commutation chain to be uneven. Therefore, the applicant further improved the solution of this application to achieve communication redundancy.

[0082] Specifically, in order to achieve mutual communication redundancy between the power control module and the energy storage control module, in some embodiments, the power control module communicates with the energy storage control module, and the communication method can be implemented in the form of light and / or electricity. Through the communication between the two, the communication resources are shared, thereby improving the communication redundancy capability of the system. Or in some embodiments, the power control module and the energy storage control module are integrated together to form a module, which has all the functions of the power control module and all the functions of the energy storage control module, so that the effect of mutual communication redundancy can be achieved without mutual communication. At the same time, the power control module and the energy storage control module both communicate with the valve control system, and combined with the communication method of the dual-ring network, dual communication redundancy is achieved. The interruption of any node or communication link in the communication network will not cause the interruption of data transmission between systems, which has the advantage of high reliability.

[0083] The power control module receives control instructions from the valve control system and / or the energy storage control module. It can be understood that in some embodiments, the power control module receives control instructions from the valve control system; in some embodiments, the power control module can be configured to receive control instructions from the energy storage control module; in some embodiments, the power control module can be configured to receive control instructions from the energy storage control module and the valve control system.

[0084] The energy storage control module receives control instructions from the valve control system and / or the power control module. It can be understood that in some embodiments, the energy storage control module can be configured to receive control instructions from the valve control system; in some embodiments, the energy storage control module can be configured to receive control instructions from the power control module; in some embodiments, the energy storage control module can be configured to receive control instructions from the power control module and the valve control system.

[0085] The valve control system includes at least one valve base controller (VBC), and both the power control module and the energy storage control module establish communication with the valve controller.

[0086] See also Figure 1 As shown, in some embodiments, the valve control system is provided with two valve controllers, namely a first valve controller VBC1 and a second valve controller VBC2, the power control module communicates with the first valve controller VBC1, and the energy storage control module communicates with the second valve controller VBC2.

[0087] See also Figure 2 As shown, in some embodiments, only one valve controller is provided in the valve control system, and the power control module and the energy storage control module both communicate with the same valve controller.

[0088] In some embodiments, all valve controllers in the valve control system communicate with each other, and the specific communication method can be implemented using optical and / or electrical communication methods. That is to say, in an embodiment where two valve controllers are set up, there is communication between the first valve controller and the second valve controller, thereby further enhancing the communication redundancy effect.

[0089] The valve controller in the valve control system can be integrated into the same device or different devices can be used. Specifically, in some embodiments, the first valve controller and the second valve controller are different plug-ins arranged in the same device, or in some embodiments, the first valve controller and the second valve controller are arranged in different devices. In addition, the first valve controller is configured with A and B dual systems that can be switched online and / or the second valve controller is configured with A and B dual systems that can be switched online, thereby further improving the reliability of the system.

[0090] Furthermore, for some embodiments in which the active commutation chain includes multiple active modules connected in series (i.e., when N is greater than or equal to 2), in order to enhance the effect of dual communication redundancy, the connection method between the active commutation chain and the valve control system can be selectively configured, and the selectable connection methods mainly include point-to-point connection, group head-to-tail connection, series random connection, series head-to-tail connection, or any combination thereof.

[0091] Specifically, Figure 3 As shown, the point-to-point connection is: in the active commutation chain, all active modules are connected to the valve control system through their own power control modules and / or energy storage control modules. In this connection mode, each active module is independently connected to the valve control system. In the embodiment of this connection mode, the power control module and the energy storage control module are mutually redundant in communication. Even if the link connection between any one of them and the valve control system is interrupted, the communication can be maintained through the other one to ensure the stability of the communication.

[0092] like Figure 4 As shown, the head-to-tail connection of the group is: in the active commutation chain, P active modules are grouped as one, 2≤P≤N; in each group, each active module is connected in series through a power control module and / or an energy storage control module, and the power control module and / or energy storage control module of the active modules at the head and tail ends are connected to the valve control system. In this connection mode, each active module in each group has at least two links to maintain communication with the valve control system, and even if one of the links is interrupted, the other link can continue to maintain smooth communication. Figure 4 In the embodiment shown, N=6, P=2.

[0093] like Figure 5 As shown, the series random connection is: in the active commutation chain, all active modules are connected in series through the power control module and / or the energy storage control module, and M active modules are selected, 2≤M≤N, and connected to the valve control system through their power control modules and / or energy storage control modules. In this connection mode, each active module has at least two links to maintain communication with the valve control system, and some active modules selected to be connected to the valve control system even have at least three communication links to maintain communication with the valve control system, so even if one of the nodes is interrupted, other links can still maintain communication. Figure 5 In the embodiment shown, N=6, M=6.

[0094] like Figure 6 As shown, the series head-to-tail connection is: in the active commutation chain, all active modules are connected in series through the power control module and / or the energy storage control module, and the power control module and / or the energy storage control module of the active modules at the head and tail ends are connected to the valve control system. In this connection mode, each active module has at least two links to maintain communication with the valve control system, and even if one of the links is interrupted, the other link can continue to maintain smooth communication.

[0095] It should be noted that when N=2, N=P=M=2, and the three connection modes of group head-to-tail connection, series random connection, and series head-to-tail connection have the same final results.

[0096] In addition, in any of the above methods, the power control module and the energy storage control module can be configured to communicate with each other, so that the two have mutual communication redundancy. It can be foreseen that the possibility of communication interruption is further compressed to an extremely low level, which can ensure the stability of data transmission.

[0097] In some embodiments, the active commutation chain and the valve control system can be connected in a combined manner, for example, a combined connection of group head-to-tail connection and series head-to-tail connection can be selected. For details, please refer to Figure 7The grid-supported active converter shown in the figure selects K active modules' power control modules to be connected in series, and the head and tail communicate with the valve control system respectively, 2≤K≤N; the power control module inside the active module communicates with the energy storage communication unit; the energy storage communication units of L active modules are connected in series, and the head and tail communicate with the valve control system respectively, 2≤L≤N. Figure 7 This is an embodiment when K=3 and L=6. The power control module and the energy storage communication unit form a dual-loop network connection mode, which fully guarantees the stability of data transmission. Of course, according to the number of active modules, K and L can choose other values, such as K=2, L=3; or, other connection combinations can also be used.

[0098] The connecting switch KM is connected between the DC capacitor and the energy storage unit and can be controlled by the power control module and / or the energy storage control module. Figure 8 As shown, in some embodiments, the connection switch is connected in parallel with a charging circuit, the charging circuit includes a charging switch and a resistor connected in series, and the charging switch is controlled by a power control module and / or an energy storage control module. By setting up the charging circuit, when the energy storage unit and the DC capacitor are connected, the impact current is reduced.

[0099] In some embodiments, the energy storage unit further includes a DC / DC converter, which is disposed between the energy storage element and the input end of the energy storage unit to perform isolation and voltage conversion functions.

[0100] In some embodiments, the grid-supported active converter further includes an undervoltage protection unit. When the bypass switch is closed and the voltage of the energy storage element is lower than a threshold, the undervoltage protection unit causes the energy storage control module to stop drawing energy from the energy storage element.

[0101] In some embodiments, the position node of the bypass switch may be sampled by the energy storage control module.

[0102] Accordingly, the embodiment of the present application further provides a commutation system, in which the above-mentioned grid-supported active converter is applied. Specifically, the commutation system includes at least one commutation arm, each commutation arm includes i grid-supported active converters, and i is an integer greater than or equal to 1. Without departing from the inventive concept of the present application, the structure of the grid-supported active converter is set as required. Figure 7 Taking the converter in as an example, the power control modules of K active modules are connected in series, and the head and the tail communicate with the valve control system respectively, 2≤K≤i*N; the power control module inside the active module communicates with the energy storage communication unit; the energy storage communication units of L active modules are connected in series, and the head and the tail communicate with the valve control system respectively, 2≤L≤i*N.

[0103] like Fig. 9As shown, in some embodiments, when one of the above-mentioned converter arms is provided, the converter arm is connected across the two poles of the DC bus. This structural method is suitable for a high-voltage DC direct-hung energy storage system.

[0104] like Fig.10 As shown, in some embodiments, when three commutation arms are provided, each commutation arm may be connected in a triangle shape, and the lead-out end may be connected to the AC bus; or Fig.11 As shown, the three commutation arms can be connected in star shape, and the lead-out ends can be connected to the AC bus. This structural method is often used in static VAR generators.

[0105] like Fig.12 As shown, six of the above-mentioned commutation arms can also be set, and every two commutation arms are connected in series to form a group. The terminals between the two commutation arms in each group are connected to the AC bus, and the groups are connected in parallel with each other, and the parallel terminals are connected to the two poles of the DC bus.

[0106] Correspondingly, an embodiment of the present application further provides a control method applicable to the above-mentioned grid-supported active converter, the method comprising an offline self-test mode, an active start mode, a black start mode or any combination thereof.

[0107] Among them, the offline self-test mode includes: relying on the energy storage unit to supply energy, realizing active module self-test, and judging whether the startup conditions are met.

[0108] Among them, the active startup mode includes: when the AC power grid is normal, the grid-supported active converter is first connected to the power grid and then starts running.

[0109] Among them, the black start mode includes: when the grid-supported active converter is not connected to the grid or the grid loses power, the energy storage unit provides starting energy to realize the operation of the converter and output independent active and reactive power to support the grid.

[0110] In some embodiments, when there are an offline self-test mode, an active start mode and a black start mode at the same time, the offline self-test mode also includes judging whether to enter the active start mode or the black start mode according to the grid voltage condition.

[0111] Specifically, Fig.13 As shown, in some embodiments, the control method includes the step of first executing an offline self-test mode, wherein the step of the offline self-test mode includes:

[0112] Obtain the position information of the bypass switches of all power units and the state of charge value of the energy storage element through the energy storage control module;

[0113] Entering the first stage: judging whether the number of bypass submodules exceeds the allowed redundancy number, if not, entering the second stage, if exceeded, the self-check fails and is not allowed to enter the second stage; wherein the bypass submodule is an active module with the bypass switch closed;

[0114] The second step: determine whether the number of active modules whose state of charge values ​​are lower than the allowed value for operation exceeds the allowed number. If so, it is considered that the black start self-test has failed and entry into the black start mode is not allowed.

[0115] When the self-test passes, it is determined whether there is AC power. When there is AC power, the AC power grid is in a normal state and enters the active start mode. The steps of the active start mode include:

[0116] The DC capacitor is charged by the AC grid, and the power control module draws energy from the DC capacitor;

[0117] All non-bypassed submodules establish communication with the valve control system; wherein the non-bypassed submodules are active modules with the bypass switches disconnected;

[0118] When the state of charge value of the energy storage element is less than a threshold value, the power unit connected to the energy storage element is controlled to output a zero level, or the power unit is limited to operate in a charging state or a power limiting state;

[0119] Control the unlocking of power semiconductor devices in the power unit, and the grid-supported active converter is unlocked and operated in grid connection to provide active and / or reactive support to the grid;

[0120] The control increases the state of charge value of the energy storage element, and when the state of charge value is greater than a threshold value, the restriction on the power unit is released.

[0121] When the self-test passes, it is determined whether there is AC power. If there is no AC power, the black start mode is entered. The steps of the black start mode include:

[0122] Close the connecting switch to charge the DC capacitor through the energy storage unit;

[0123] The power control module draws energy from the DC capacitor;

[0124] All non-bypassed submodules establish communication with the valve control system; wherein the non-bypassed submodules are active modules with bypass switches disconnected;

[0125] When the state of charge value of the energy storage element is less than a threshold value, the power unit connected to the energy storage element is controlled to output a zero level state;

[0126] The power semiconductor devices in the control power unit are unlocked, and the converter outputs a given voltage to achieve grid-connected or island power supply.

[0127] The above is a detailed introduction to a grid-supported active converter and its control method and commutation system provided in the embodiments of the present application. Specific examples are used in this article to illustrate the principles and implementation methods of the present application. The description of the above embodiments is only used to help understand the technical solutions and core ideas of the present application. Ordinary technicians in this field should understand that they can still modify the technical solutions recorded in the aforementioned embodiments, or replace some of the technical features therein with equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A grid-supporting active converter, characterized in that, it includes an active commutation chain and a valve control system; wherein, the active commutation chain includes at least one active module, and the active module includes: a energy storage unit, including at least one energy storage element; a power unit, including a DC capacitor and a power component connected in parallel, the power component includes a full-bridge circuit and / or a half-bridge circuit composed of power semiconductor devices, the DC capacitor is connected to the energy storage unit through a connection switch, and the AC terminal of the power unit is shunted by a bypass switch; a power control module, controlling the operation of the power unit; a energy storage control module, extracting energy from the energy storage element and controlling the operation of the energy storage unit; the valve control system communicates with the energy storage control module and the power control module; the power control module communicates with the energy storage control module, or the power control module and the energy storage control module are integrated together; the valve control system includes two valve controllers, namely a first valve controller and a second valve controller, the power control module communicates with the first valve controller, and the energy storage control module communicates with the second valve controller; wherein, the grid-supporting active converter is used to execute an off-line self-check mode, including: the energy storage control module is used to obtain the position information of the bypass switches of all the power units and the state of charge value of the energy storage elements; in the first step, judge whether the number of bypass sub-modules exceeds the allowable redundancy number. If not, enter the second step. If it exceeds, the self-check fails and the second step is not allowed to enter; wherein, the bypass sub-module is an active module with a closed bypass switch; in the second step, judge whether the number of active modules with a state of charge value lower than the operating allowable value exceeds the allowable number. If it exceeds, it is considered that the black start self-check fails and the black start mode is not allowed to enter; in the black start mode, the energy storage control module closes the connection switch, and charges the DC capacitor through the energy storage unit; the power control module is used to extract energy from the DC capacitor; all non-bypass sub-modules establish communication with the valve control system; wherein, the non-bypass sub-module is an active module with an open bypass switch; the power control module is used to control the power unit corresponding to the energy storage element to output a zero-level state when the state of charge value of the energy storage element is less than the threshold, control the power semiconductor devices in the power unit to unlock, and the converter outputs a given voltage to realize grid connection or island power supply.

2. The grid-supporting active converter according to claim 1, characterized in that, the active commutation chain includes N of the active modules connected in series, and N is an integer greater than or equal to 2; the connection mode between the active commutation chain and the valve control system includes point-to-point connection, grouped head-to-tail connection, series random connection, series head-to-tail connection or any combination thereof; wherein, the point-to-point connection is: in the active commutation chain, all the active modules are connected to the valve control system through their respective power control modules and / or energy storage control modules; The head-to-tail connection of the groups is as follows: in the active commutation chain, P active modules are grouped together, where 2 ≤ P ≤ N; within each group, the active modules are connected in series through the power control module and / or the energy storage control module, and the power control module and / or the energy storage control module of the active modules at both ends are connected to the valve control system; The series random connection is as follows: in the active commutation chain, all the active modules are connected in series through the power control module and / or the energy storage control module. Optionally, M active modules are selected, where 2 ≤ M ≤ N, and the power control module and / or the energy storage control module of these M active modules are connected to the valve control system; The series head-to-tail connection is as follows: in the active commutation chain, all the active modules are connected in series through the power control module and / or the energy storage control module, and the power control module and / or the energy storage control module of the active modules at both ends are connected to the valve control system.

3. The grid-supporting active converter according to claim 1, wherein, the first valve controller communicates with the second valve controller; and / or the first valve controller and the second valve controller are different plug-ins arranged in the same device, or the first valve controller and the second valve controller are arranged in different devices; and / or the first valve controller is configured with a dual-system for online switching; and / or the second valve controller is configured with a dual-system for online switching.

4. The grid-supporting active converter according to claim 1, wherein, the connection switch is controlled by the power control module and / or the energy storage control module; and / or a charging circuit is connected in parallel to the connection switch, the charging circuit includes a charging switch and a resistor connected in series, and the charging switch is controlled by the power control module and / or the energy storage control module.

5. The grid-supporting active converter according to claim 1, wherein, the energy storage element includes a battery, a super capacitor, a flywheel energy storage, a gas compression energy storage, or any combination thereof; and / or the energy storage unit further includes a DC / DC converter, and the DC / DC converter is arranged between the energy storage element and the input end of the energy storage unit; and / or it includes an undervoltage protection unit. When the bypass switch is closed and the voltage of the energy storage element is lower than the threshold, the undervoltage protection unit causes the energy storage control module to stop extracting energy from the energy storage element; and / or the energy storage control module samples the position node of the bypass switch.

6. A control method for the grid-supporting active converter according to any one of claims 1-5, wherein, it includes an offline self-check mode, an active start mode, a black start mode, or any combination thereof; wherein, the offline self-check mode includes: relying on the energy supply of the energy storage unit to realize the self-check of the active modules and determine whether the start-up conditions are met; the active start mode includes: when the AC power grid is normal, the grid-supporting active converter first connects to the power grid and then realizes start-up operation; The black start mode includes: when the grid-supporting active converter is not connected to the grid or the grid loses power, the energy storage unit provides startup energy to enable the converter to operate and output independent active power and / or reactive power to support the grid.

7. The control method of the grid-supporting active converter according to claim 6, wherein, when there are an off-line self-check mode, an active startup mode, and a black start mode at the same time, the off-line self-check mode further includes judging whether to enter the active startup mode or the black start mode according to the grid voltage condition.

8. The control method of the grid-supporting active converter according to claim 6, wherein, the steps of the off-line self-check mode include: obtaining the position information of the bypass switches of all the power units and the state of charge value of the energy storage element through the energy storage control module; entering the first step: judging whether the number of bypass sub-modules exceeds the allowable redundancy number. If it does not exceed, enter the second step. If it exceeds, the self-check fails and it is not allowed to enter the second step; wherein, the bypass sub-module is an active module with the bypass switch closed; the second step: judging whether the number of active modules with the state of charge value lower than the allowable operating value exceeds the allowable number. If it exceeds, it is considered that the black start self-check fails and it is not allowed to enter the black start mode.

9. The control method of the grid-supporting active converter according to claim 6, wherein, the steps of the active startup mode include: charging the DC capacitor from the AC grid, and the power control module obtaining energy from the DC capacitor; establishing communication between all non-bypass sub-modules and the valve control system; wherein, the non-bypass sub-module is an active module with the bypass switch open; when the state of charge value of the energy storage element is less than the threshold value, controlling the power unit corresponding to the energy storage element to output a zero level, or restricting the power unit to operate in the charging state or in the limited power state; controlling the power semiconductor devices in the power unit to unlock, and the grid-supporting active converter being connected to the grid and unlocked to operate, providing active power and / or reactive power support to the grid; controlling to increase the state of charge value of the energy storage element, and when the state of charge value is greater than the threshold value, lifting the restriction on the power unit.

10. The control method of the grid-supporting active converter according to claim 6, wherein, the steps of the black start mode include: closing the connection switch and charging the DC capacitor through the energy storage unit; the power control module obtaining energy from the DC capacitor; establishing communication between all non-bypass sub-modules and the valve control system; wherein, the non-bypass sub-module is an active module with the bypass switch open; when the state of charge value of the energy storage element is less than the threshold value, controlling the power unit corresponding to the energy storage element to output a zero level state; controlling the power semiconductor devices in the power unit to unlock, and the converter outputting a given voltage to achieve grid connection or island power supply.

11. A commutation system, wherein, it includes at least one commutation arm, and the commutation arm includes at least one grid-supporting active converter according to claims 1-5.

12. The commutation system according to claim 11, characterized in that, it includes one of the commutation arms, and the commutation arm is connected across the two poles of the DC bus; or it includes three of the commutation arms, and the commutation arms are connected in a triangle and the leads are connected to the AC bus; or it includes three of the commutation arms, and the commutation arms are connected in a star and the leads are connected to the AC bus; or it includes six of the commutation arms, every two of the commutation arms are connected in series to form a group, leads are drawn between the two commutation arms in each group and connected to the AC bus, the groups are connected in parallel with each other, and the leads of the parallel connection are drawn out and connected to the two poles of the DC bus.

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