Compensation device of a power converter and power conversion system

Abstract

The application discloses a compensation device of a converter and a power conversion system, and relates to the technical field of power electronics. In the compensation device, a first side of a first switch module is used for being connected with a grid-side equal potential cable of the converter, and a second side of the first switch module is connected with a first capacitor module; the first capacitor module comprises capacitors arranged between each phase in pairs, and the first capacitor module is connected with the grid-side equal potential cable in a closed state of the first switch module, which is equivalent to improving the capacity of the converter, so that the converter can be reasonably configured with the capacity, and thus the cost, volume and weight are not increased. Moreover, by controlling the on-off of the first switch module, the equivalent capacity of the converter can be changed, the control margin of the converter is improved, and the stable operation of a wind turbine generator system is ensured.

Description

Technical Field

[0001] This application relates to the field of power electronics technology, and in particular to a compensation device for a converter and a power conversion system. Background Technology

[0002] Currently, there are many shortcomings in the reactive power control methods of converters. For example, when the grid voltage fluctuates or the wind speed changes, the control margin of the converter is limited, and problems such as overcurrent and overvoltage are likely to occur, which in turn affect the stable operation of the power generation equipment. At the same time, in order to cope with the large reactive power demand, the capacity configuration of the converter will be too large, which will increase the cost, equipment size and weight. Utility Model Content

[0003] In view of the above problems, this application provides a compensation device and power conversion system for a converter to improve the control margin of the converter and reduce the capacity configuration of the converter. The specific solution is as follows:

[0004] A first aspect of this application provides a compensation device for a converter, comprising: a first switching module and a first capacitor module; wherein...

[0005] The first side of the first switch module is used to connect the grid-side equipotential cable of the converter;

[0006] The second side of the first switch module is connected to the first capacitor module;

[0007] The first capacitor module includes capacitors that are respectively set between each pair of phases.

[0008] In one possible implementation, the compensation device further includes: a second switching module and a second capacitor module;

[0009] The second capacitor module is connected to the second side of the first switch module via the second switch module.

[0010] In one possible implementation, the number of the second switch module and the number of the second capacitor module are the same and both are greater than 1;

[0011] Each of the second capacitor modules is connected to the second side of the first switch module via a corresponding second switch module.

[0012] In one possible implementation, the compensation device further includes: a third switch module;

[0013] The first capacitor module is connected to the second side of the first switch module through the third switch module.

[0014] In one possible implementation, the converter is a doubly fed wind power converter, and the grid-side equipotential cable is: a cable connecting the grid side of the doubly fed wind power converter to the grid connection point, or a cable connecting the stator of the generator connected to the doubly fed wind power converter to the grid connection point.

[0015] Alternatively, the converter is a full-power wind power converter, and the grid-side equipotential cable is the cable connecting the grid side of the full-power wind power converter to the grid connection point.

[0016] In one possible implementation, the switch module includes switches respectively installed on each phase transmission cable;

[0017] And / or,

[0018] The capacitor module includes three capacitors; the capacitors are connected in a star or delta configuration.

[0019] In one possible implementation, the compensation device further includes: a controller;

[0020] The control terminal of the switch module is connected to the corresponding output terminal of the controller.

[0021] A second aspect of this application provides a power conversion system, comprising: a converter, and a compensation device for the converter as described in the first aspect or any implementation thereof; wherein...

[0022] The compensation device is connected to the grid-side equipotential cable of the converter;

[0023] The converter's machine side is used to connect to the generator;

[0024] The grid side of the converter is used to connect to the grid connection point.

[0025] In one possible implementation, the converter is a doubly fed wind power converter, and the stator of the generator is connected to the grid connection point;

[0026] Alternatively, the converter may be a full-power wind power converter.

[0027] In one possible implementation, where there is no controller in the compensation device, the switching module in the compensation device is controlled by the internal controller of the converter.

[0028] The switching module in the compensation device is controlled by the controller, which is communicatively connected to the internal controller of the converter.

[0029] By employing the above technical solution, the converter compensation device provided in this application has a first side of the first switching module for connecting to the grid-side equipotential cable of the converter, and a second side of the first switching module for connecting to the first capacitor module. The first capacitor module includes capacitors respectively disposed between each pair of phases. When the first switching module is in the closed state, the first capacitor module is connected to the grid-side equipotential cable, effectively increasing the converter's capacity. This allows the converter to be configured with appropriate capacity without increasing cost, size, or weight. Furthermore, by controlling the on / off state of the first switching module, the equivalent capacity of the converter can be changed, improving the converter's control margin and ensuring the stable operation of the wind turbine. Attached Figure Description

[0030] The above and other features, advantages, and aspects of the embodiments of this disclosure will become more apparent from the accompanying drawings and the following detailed description. Throughout the drawings, the same or similar reference numerals denote the same or similar elements. It should be understood that the drawings are schematic, and the originals and elements are not necessarily drawn to scale.

[0031] Figure 1 A schematic diagram of a compensation device for a converter provided in an embodiment of this application;

[0032] Figure 2 Another schematic diagram of the compensation device for the converter provided in the embodiments of this application;

[0033] Figure 3 Another schematic diagram of the compensation device for the converter provided in the embodiments of this application;

[0034] Figure 4 Another schematic diagram of the compensation device for the converter provided in the embodiments of this application;

[0035] Figure 5 Another schematic diagram of the compensation device for the converter provided in the embodiments of this application;

[0036] Figure 6 A schematic diagram of a power conversion system provided in an embodiment of this application;

[0037] Figure 7 This is another schematic diagram of the power conversion system provided in the embodiments of this application;

[0038] Figure 8 This is another schematic diagram of the power conversion system provided in the embodiments of this application;

[0039] Figure 9 This is another schematic diagram of the power conversion system provided in the embodiments of this application. Detailed Implementation

[0040] The embodiments of this application are described below with reference to the accompanying drawings. The terminology used in the implementation section of this application is for explaining specific embodiments only and is not intended to limit the scope of this application.

[0041] The embodiments of this application are described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application. Those skilled in the art will understand that with the development of technology and the emergence of new scenarios, the technical solutions provided by the embodiments of this application are also applicable to similar technical problems.

[0042] The terms "first," "second," etc., used in the specification, claims, and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such terms are interchangeable where appropriate; this is merely a way of distinguishing objects with the same attributes in the embodiments of this application. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion, so that a process, method, system, product, or apparatus that comprises a series of elements is not necessarily limited to those elements, but may include other elements not explicitly listed or inherent to those processes, methods, products, or apparatuses.

[0043] This application provides a compensation device for a converter to improve the control margin of the converter and reduce the capacity configuration of the converter. The specific solution is as follows:

[0044] like Figure 1 As shown, the compensation device of the converter includes: a first switching module 101 and a first capacitor module 102; wherein:

[0045] The first side of the first switch module 101 is used to connect the grid-side equipotential cable of the converter. One side of the converter is used to connect to the power generation equipment, and the other side is used to connect to the power grid. As an example, the converter can be a wind power converter used in the field of wind power generation, in which case the power generation equipment specifically refers to a wind turbine generator. The converter can also be a converter used in other fields, as long as it is a device connected between the power generation equipment and the power grid and requires reactive power control, all of which are within the protection scope of this application. The grid-side equipotential cable refers to a cable with the same grid-side potential as the converter, and can be selected according to the specific implementation of the converter, as detailed below, and will not be repeated here.

[0046] The second side of the first switch module 101 is connected to the first capacitor module 102; when the first switch module 101 is in the closed state, the first capacitor module 102 is connected to the network-side equipotential cable; when the first switch module 101 is in the open state, the first capacitor module 102 is disconnected from the network-side equipotential cable.

[0047] In practical applications, to avoid causing imbalances in the power grid, the first switch module 101 may include: switches separately installed on each phase transmission cable; such as... Figure 1 As shown, the first switch module 101 includes: a switch K disposed on the A-phase transmission cable. A Switch K is installed on phase B transmission cable. B And, switch K installed on the C-phase transmission cable. C Each switch in the first switch module 101 can be set independently or integrated into the same switchgear, depending on the specific application environment, and all are within the protection scope of this application.

[0048] The first capacitor module 102 includes capacitors respectively disposed between each pair of phases. In practical applications, the first capacitor module 102 only needs to be configured such that there is at least one capacitor between any two phases; for example, the first capacitor module 102 may include three capacitors; and the connection method between these capacitors can be... Figure 1 Each capacitor C A C B and C C The star connection shown between them, or the connection method between these capacitors, can also be... Figure 2 Each capacitor C AB C BC and C AC The triangular connections shown between them; the specific application environment may vary, and all are within the scope of protection of this application.

[0049] The compensation device provided in this embodiment, when the first switch module 101 is in the closed state, connects the first capacitor module 102 to the grid-side equipotential cable, which is equivalent to increasing the capacity of the converter. This allows the converter to be configured with appropriate capacity without increasing cost, size, or weight. Furthermore, by controlling the on / off state of the first switch module 101, the equivalent capacity of the converter can be changed, improving the control margin of the converter and ensuring the stable operation of the power generation equipment.

[0050] Based on the previous embodiment, the compensation device may further include Figure 3 (in order to be in) Figure 1As shown in the example (based on which the example is presented): the second switch module 201 and the second capacitor module 202; the second capacitor module 202 is connected to the second side of the first switch module 101 through the second switch module 201.

[0051] Similar to the previous embodiment, the second switch module 201 may also include switches respectively installed on each phase transmission cable, and each switch inside can be installed independently or integrated, depending on the specific application environment, all of which are within the protection scope of this application.

[0052] In practical applications, the second capacitor module 202 may also include three capacitors; and the connection between these capacitors can be a star connection (e.g., Figure 3 (as shown in the diagram) or a triangular connection (not shown). Furthermore, the structure of the second capacitor module 202 can be the same as or different from the first capacitor module 102; the capacitance value of the second capacitor module 202 can be the same as or different from the first capacitor module 102, depending on the specific application environment, and all are within the scope of protection of this application.

[0053] for Figure 3 As shown in the structure, if only the first switch module 101 is in the closed state, then only the first capacitor module 102 is connected to the grid-side equipotential cable, thus increasing the equivalent capacity of the converter to a certain extent. If both the first switch module 101 and the second switch module 201 are in the closed state, then both the first capacitor module 102 and the second capacitor module 202 are connected to the grid-side equipotential cable, further increasing the equivalent capacity of the converter. In practical applications, the on / off state of each switch module can be determined according to the required equivalent capacity of the converter, and the required equivalent capacity can be determined according to the reactive power demand of the converter.

[0054] Furthermore, the compensation device can be configured such that the number of the second switch module 201 and the second capacitor module 202 is the same and both are greater than 1; for example... Figure 4 As shown, each of the second capacitor modules 202 is connected to the second side of the first switch module 101 through a corresponding second switch module 201.

[0055] At this point, the compensation device consists of multiple controllable capacitor modules and their corresponding fast-switching switch modules. All capacitor modules are connected to the grid point through a general switch module, namely the first switch module 101, to achieve connection with the external power grid. In the event of an emergency fault, the first switch module 101 can be disconnected to achieve rapid disconnection control. The first switch module 101 is directly connected to a set of capacitors, namely the first capacitor module 102. When the reactive power demand of the system exceeds the reactive current corresponding to the first capacitor module 102, the first switch module 101 can be closed, allowing the first capacitor module 102 to operate at its equivalent capacity. The remaining second capacitor modules 202 can be configured with different capacitance values ​​according to the system design requirements, and each can be combined with a matching second switch module 201. This allows the first switch module 101 and different second switch modules 201 to be closed in real time according to the required equivalent capacity, providing multiple compensation capacity options. By controlling the on / off state of each switch module, the connection and disconnection of the corresponding capacitor modules can be achieved in a short time, with a fast response speed.

[0056] In practical applications, it can also be like Figure 5 As shown, a third switch module 301 is provided in the compensation device; the first capacitor module 102 is connected to the second side of the first switch module 101 through the third switch module 301. At this time, each capacitor module is connected to the second side of the first switch module 101 through a corresponding switch module; when the first switch module 101 is closed, if any switch module among the second switch modules 201 and the third switch module 301 is closed, the capacitor module connected to it is put into the equivalent capacitance; when the capacitance of the first capacitor module 102 is at its maximum... Figure 5 The structure shown can reduce the granularity of capacity compensation.

[0057] This compensation device, through its unique circuit topology, enables precise control of the capacitive reactive power of the connected converter. In practical applications, it can dynamically adjust the reactive power compensation strategy based on the real-time grid status and the operating parameters of the generating equipment, effectively improving the control margin of the converter, ensuring the stable operation of the generating equipment, and simultaneously reducing the capacity configuration of the converter.

[0058] Based on the above embodiments, the position of the compensation device can be configured in various ways, such as:

[0059] If converter 20 is a doubly fed wind power converter, then as follows Figure 6 As shown, the compensation device 10 can be installed on the grid side of the doubly-fed wind turbine converter, that is, the grid-side equipotential cable can specifically refer to the cable connecting the grid side of the doubly-fed wind turbine converter to the grid connection point PCC; or, as shown... Figure 7As shown, the compensation device 10 can also be installed on the stator side of the corresponding generator DFIG, that is, the grid-side equivalent cable can also refer to the cable of the stator connection and grid connection point PCC of the generator DFIG connected to the doubly fed wind power converter.

[0060] In practical applications, such as Figure 8 As shown, a grid connection cabinet 30 may also be installed between the stator of the generator and the grid connection point PCC. This grid connection cabinet 30 includes a stator contactor KM2 and a main circuit breaker Q1. The stator of the generator is connected to the grid connection point PCC via the stator contactor KM2 and the main circuit breaker Q1. The grid side of the doubly-fed wind power converter is also connected to the grid connection point PCC via the main circuit breaker Q1. In this case, the compensation device 10 can be installed between the stator of the generator and the grid connection cabinet 30 (e.g., ...). Figure 8 As shown in the figure, it can also be set between the grid side of the doubly fed wind power converter and the grid connection cabinet 30 (not shown), or between the grid connection cabinet 30 and the grid connection point PCC (not shown); or, the compensation device 10 can also be set in the grid connection cabinet 30, and it can be set at any position of any transmission cable in the grid connection cabinet 30, such as any transmission cable between the stator contactor KM2 and the main circuit breaker Q1, or any transmission cable on both sides of the stator contactor KM2 and the main circuit breaker Q1; it depends on the specific application environment, and all of them are within the protection scope of this application.

[0061] If converter 20 is a full-power wind power converter, then as follows Figure 9 As shown, the compensation device 10 can be installed on the grid side of the full-power wind power converter, that is, the grid-side equivalent cable is the cable connecting the grid side of the full-power wind power converter to the grid connection point PCC. Figure 9 In this context, G represents the generator connected to the full-power wind power converter.

[0062] In practical applications, the compensation device 10 can be set in a suitable location according to the unit space, depending on the specific application environment, and all of these are within the protection scope of this application.

[0063] Based on the above embodiments, each switching module in the compensation device 10 can be controlled by a separate controller or by the internal controller of the converter 20.

[0064] If a separate controller is used to control the on / off state of each switch module, then the compensation device 10, based on the above embodiment, further includes: a controller; in this case, Figures 1 to 5 The control terminals of each switch module shown are connected to the corresponding output terminals of the controller.

[0065] In this case, the controller is connected to the internal controller of the converter 20. Either one of them is responsible for determining the switching combination scheme of each capacitor module in the compensation device 10, and then the controller controls the corresponding switching module to close.

[0066] For example, the internal controller of converter 20 can be responsible for determining the switching combination scheme. Specifically, the internal controller of converter 20 collects voltage and current information from the grid-connected point PCC, and combines this with the dispatching instructions from the wind turbine main control and generator speed information. After algorithm analysis, it determines the appropriate switching combination scheme corresponding to the specific reactive power demand value under the dispatching instruction, and sends the capacitor switching control instruction to the controller. When the controller receives the capacitor switching control instruction, it determines the capacitor modules that need to be put into operation under the switching combination scheme, and controls the closing of the switch modules connected to the corresponding capacitor modules, thereby realizing the rapid switching of the corresponding capacitor modules. After the corresponding capacitor module is successfully switched, the switch module feeds back a signal to the controller. Furthermore, the controller can receive the capacitor switching control instructions sent by converter 20 in real time and dynamically adjust the switching control of the capacitor modules accordingly.

[0067] Alternatively, the controller can be responsible for determining the switching combination scheme. Specifically, the internal controller of the converter 20 first sends the voltage and current information of the grid connection point PCC, the specific value of reactive power demand under the dispatch command, and generator speed information to the controller via communication. Then, the controller performs algorithm analysis to determine a suitable switching combination scheme, and controls the corresponding switch module to close according to the switching combination scheme, thereby realizing the rapid switching of the corresponding capacitor module. After the corresponding capacitor module is successfully switched, the switch module also feeds back a signal to the controller. Furthermore, the controller receives the information sent by the converter 20 in real time and dynamically adjusts the switching combination scheme accordingly to realize the switching control of the corresponding capacitor module.

[0068] In this scenario, the compensation device 10 can achieve precise control of the capacitive reactive power of the connected converter 20. Moreover, based on the real-time status of the power grid and the operating parameters of the wind turbine, the reactive power compensation strategy can be dynamically adjusted, effectively improving the control margin of the converter 20, ensuring the stable operation of the wind turbine, and reducing the capacity configuration of the converter 20.

[0069] Furthermore, if there is sufficient resource margin in the internal controller of the converter 20, the internal controller of the converter 20 can also be used to control the on / off switching of each switching module. Specifically, it can combine the collected voltage and current information to directly control the switching of the capacitor modules according to its own control requirements; in this case, no additional controller is needed in the compensation device 10. The internal controller of the converter 20 includes... Figures 6 to 9In the diagram, the sub-controllers of the grid-side converter 22 and the machine-side converter 21 can be used to control the switching modules based on either the sub-controller of the grid-side converter 22 or the sub-controller of the machine-side converter 21, depending on their respective control resource margins. This is all within the scope of protection of this application.

[0070] Another embodiment of this application also provides a power conversion system, such as Figures 6 to 9 The diagram shows: a converter 20, and a compensation device 10 as described in any of the above embodiments; wherein the compensation device 10 is connected to the grid-side equipotential cable of the converter 20, and the generator side of the converter 20 is used to connect to a generator (such as...). Figures 6 to 8 The generator DFIG shown Figure 9 As shown in G), the grid side of the converter 20 is used to connect to the grid connection point PCC. The specific structure and working principle of the compensation device 10 can be found in the above embodiments, and will not be repeated here.

[0071] As described in the above embodiments, the converter 20 can be a doubly-fed wind power converter, in which case the generator side of the converter 20 is connected to a generator (e.g., Figures 6 to 8 The rotor of the generator DFIG shown is connected to the grid connection point PCC; or, the converter 20 can also be a full-power wind power converter, with the generator (such as...) connected to the generator side. Figure 9 The stator of G shown in the diagram is connected to the grid-side connection point PCC of the full-power wind power converter.

[0072] Regardless of the type of converter used in the converter 20, its internal components all include Figures 6 to 9 The generator-side converter 21 and grid-side converter 22 shown in the figure are connected to the generator via a corresponding filter module on the AC side of the generator-side converter 21 and the grid-side converter 22 via a corresponding filter module. The DC side of the generator-side converter 21 and the DC side of the grid-side converter 22 can be connected via a DC bus, and a corresponding bus capacitor is connected between the positive and negative poles of the DC bus.

[0073] Furthermore, in the absence of a controller in the compensation device 10, the switching module within it is controlled by the internal controller of the converter 20, such as a sub-controller of the grid-side converter 22 or a sub-controller of the generator-side converter 21. When the compensation device 10 includes a controller, the switching module within it is controlled by that controller, and the controller is communicatively connected to the internal controller of the converter 20. The precise switching control process for the capacitor module and the dynamic adjustment process for the reactive power compensation strategy can be found in the above embodiments and will not be repeated here.

[0074] In practical applications, the compensation device 10 can be used in various scenarios. For example, it can be applied to the capacitive reactive power dispatching mode of a doubly-fed generator unit. Under the capacitive reactive power dispatching mode of a doubly-fed generator unit, especially under large slip conditions, the large capacitive reactive current of the rotor can cause overvoltage on the rotor side. In extreme cases, the over-modulation of the converter 20 connected to the rotor side can lead to over-modulation and loss of control, resulting in turbine failure and shutdown. When the compensation device 10 is included in the power conversion system, when the converter 20 connected to the rotor side detects that its modulation or apparent current reaches the corresponding preset threshold under the capacitive reactive power compensation mode, it uploads the reactive power compensation switching command and various information described in the above embodiments to the controller of the compensation device 10. The controller combines various information to allocate the number of capacitor modules to be put into operation, that is, to determine the switching combination scheme, and quickly switches each capacitor module. At this time, the reactive power of the system can be dynamically compensated by the generator-side converter 21 to achieve dynamic balance of the unit's reactive power.

[0075] Alternatively, the compensation device 10 can also be applied to doubly-fed low-slip conditions, that is, conditions where the speed difference between the rotor speed and the synchronous speed of the doubly-fed generator is small. Specifically, for doubly-fed low-slip conditions, especially synchronous speed conditions, the long-term high-current heat accumulation due to the rotor's low-frequency three-phase current maintaining operation in one direction can severely affect the reliability of the power devices in the converter 20, and in extreme cases, even module failure may occur. Considering that the magnitude of the rotor-side excitation current affects the heat generation and energy loss of the generator and converter 20, the rotor-side excitation current can be removed to reduce the apparent rotor current, thereby ensuring the stability and reliability of the equipment operation. Under normal circumstances, the generator excitation current is provided by the converter 20 connected to the rotor side. In grid-connected mode, after the capacitor module in the compensation device 10 is put into operation, the generator excitation current is provided by the capacitor module, and the rotor-side excitation current can be removed synchronously; therefore, the step size of the removal of the rotor-side excitation current can be configured according to the reactive power corresponding to a single capacitor module in the compensation device 10. When the controller in the compensation device 10 receives the cancellation flag bit uploaded in real time by the internal controller of the converter 20, it can quickly and accurately disconnect the corresponding capacitor module in real time according to the magnitude of reactive current or reactive power. Considering that the capacitance value of the disconnected capacitor module may not be perfectly matched with the reactive current to be disconnected, the small reactive deviation can be combined with the dynamic compensation of the grid-side converter 22 to achieve dynamic balance of the unit's reactive power.

[0076] The power conversion system provided in this embodiment, by employing the compensation device 10, can rationally configure the capacity of the converter 20, thereby reducing the cost, size, and weight of the converter 20. Furthermore, it can effectively reduce the current of the machine-side converter 21, improve the control margin of the converter 20, and enhance system reliability.

[0077] Similar or identical parts between the various embodiments in this specification can be referred to mutually. Each embodiment focuses on describing the differences from other embodiments. In particular, for system or system embodiments, since they are basically similar to method embodiments, the description is relatively simple, and relevant parts can be referred to the description of the method embodiments. The systems and system embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units, that is, they may be located in one place or distributed across multiple network units. Some or all of the modules can be selected to achieve the purpose of this embodiment according to actual needs. Those skilled in the art can understand and implement this without creative effort.

[0078] The features described above regarding the disclosed embodiments can be substituted for or combined with each other to enable those skilled in the art to implement or use this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A compensation device for a converter, characterized in that, include: The first switch module and the first capacitor module; wherein... The first side of the first switch module is used to connect the grid-side equipotential cable of the converter; The second side of the first switch module is connected to the first capacitor module; The first capacitor module includes capacitors respectively disposed between each pair of phases; The first switch module includes: switches respectively installed on each phase transmission cable; And / or, The first capacitor module includes at least three capacitors; the capacitors are connected in a star or delta configuration.

2. The compensation device for the converter according to claim 1, characterized in that, The compensation device further includes: a second switch module and a second capacitor module; The second capacitor module is connected to the second side of the first switch module via the second switch module.

3. The compensation device for the converter according to claim 2, characterized in that, The number of the second switch module and the second capacitor module are the same and both are greater than 1; Each of the second capacitor modules is connected to the second side of the first switch module via a corresponding second switch module.

4. The compensation device for the converter according to claim 2, characterized in that, The compensation device further includes: a third switch module; The first capacitor module is connected to the second side of the first switch module through the third switch module.

5. The compensation device for the converter according to any one of claims 1 to 4, characterized in that, The converter is a doubly fed wind power converter, and the grid-side equipotential cable is: the cable connecting the grid side of the doubly fed wind power converter to the grid connection point, or the cable connecting the stator of the generator connected to the doubly fed wind power converter to the grid connection point. Alternatively, the converter is a full-power wind power converter, and the grid-side equipotential cable is the cable connecting the grid side of the full-power wind power converter to the grid connection point.

6. The compensation device for a converter according to any one of claims 1 to 4, characterized in that, Other switch modules include switches installed on each phase transmission cable; And / or, Other capacitor modules include at least three capacitors; the capacitors are connected in a star or delta configuration.

7. The compensation device for a converter according to any one of claims 1 to 4, characterized in that, The compensation device further includes: a controller; The control terminal of the switch module is connected to the corresponding output terminal of the controller; The controller is communicatively connected to the internal controller of the converter.

8. A power conversion system, characterized in that, include: A converter, and a compensation device for the converter as described in any one of claims 1 to 7; wherein... The compensation device is connected to the grid-side equipotential cable of the converter. The converter's machine side is used to connect to the generator; The grid side of the converter is used to connect to the grid connection point.

9. The power conversion system according to claim 8, characterized in that, The converter is a doubly fed wind power converter, and the stator of the generator is connected to the grid connection point; Alternatively, the converter may be a full-power wind power converter.

10. The power conversion system according to claim 8 or 9, characterized in that, In the absence of a controller in the compensation device, the switching module in the compensation device is controlled by the internal controller of the converter; When the compensation device includes a controller, the switching module in the compensation device is controlled by the controller, and the controller is communicatively connected to the internal controller of the converter.

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