Power asymmetric converter, direct current transformer and control method thereof
By adopting the H-bridge topology of power asymmetric inverters in DC transformers, the problems of complex topology, high cost and small capacity in the prior art are solved, and the effects of simplifying the structure, reducing costs and increasing capacity are achieved.
Patent Information
- Application Number
- CN202411369307.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-09-29
- Publication Date
- 2025-02-18
Smart Images
Figure CN119483311A_ABST
Abstract
Description
Technical Field
[0001] The present application relates to the technical field of flexible direct current transmission, and in particular to a power asymmetric converter, a direct current transformer and a control method thereof. Background Art
[0002] Compared with traditional AC transmission, DC transmission technology has the advantages of long transmission distance and large transmission capacity. As the core equipment of flexible DC transmission system, voltage source converter has the advantages of flexibility, controllability and adaptability to weak power grid. Therefore, voltage source converter plays an important role in the grid-connected transmission of renewable energy.
[0003] In the scenario of large-scale renewable energy station aggregation and transmission, the flexible DC transmission system can transmit the electric energy of the renewable energy station to the power grid (i.e., forward power transmission). In scenarios where grid feeding is required for renewable energy station startup, load balancing, etc., the flexible DC transmission system can also transmit power from the grid to the renewable energy station (i.e., reverse power transmission). As a key power control device in the scenario of renewable energy station aggregation and transmission, the DC transformer has technical requirements for high-power forward transmission and low-power reverse transmission. However, in the DC transformer provided by the relevant technology, the commutation unit adopts a modular multi-level converter sub-module (which can be called an MMC sub-module). Due to the large number of fully controlled devices in the MMC sub-module, the entire converter topology is complex, the cost is high, and the capacity is small. Summary of the invention
[0004] In order to solve the problems of complex topology, high cost and small capacity in the prior art, the present application provides a power asymmetric converter, which may include a transformer module and a converter module.
[0005] The commutation module may include an A-phase commutation unit, a B-phase commutation unit and a C-phase commutation unit connected in series in sequence. Each phase commutation unit adopts an H-bridge topology structure.
[0006] Optionally, the first AC end of the transformer module serves as the input end or output end of the power asymmetric converter, the second AC end of the transformer module is connected to the AC end of the converter module, and the DC end of the converter module serves as the output end or input end of the power asymmetric converter.
[0007] In a possible implementation manner, each phase switching unit includes a first bridge arm, a second bridge arm, a third bridge arm, and a fourth bridge arm.
[0008] The first bridge arm and the second bridge arm are connected in series to form a first bridge arm branch, and the connection node between the first bridge arm and the second bridge arm serves as the first AC end of the phase-changing unit. The third bridge arm and the fourth bridge arm are connected in series to form a second bridge arm branch, and the connection node between the third bridge arm and the fourth bridge arm serves as the second AC end of the phase-changing unit. The first bridge arm branch and the second bridge arm branch are connected in parallel, and the first connection node between the first bridge arm branch and the second bridge arm branch serves as the first DC end of the phase-changing unit, and the second connection node between the first bridge arm branch and the second bridge arm branch serves as the second DC end of the phase-changing unit.
[0009] In one example, the first bridge arm, the second bridge arm, the third bridge arm and the fourth bridge arm each include a diode and a fully-controlled device, and the diode and the fully-controlled device are connected in reverse parallel.
[0010] In another example, the first bridge arm, the second bridge arm, the third bridge arm and the fourth bridge arm each include a plurality of diodes and a plurality of fully-controlled devices, and the plurality of diodes and the plurality of fully-controlled devices correspond one to one.
[0011] Multiple diodes are connected in series to form a diode branch, multiple fully-controlled devices are connected in series to form a fully-controlled device branch, and the diode branch and the fully-controlled device branch are connected in reverse parallel. Or. Multiple diodes and multiple fully-controlled devices are connected in reverse parallel one by one to form multiple power units, and multiple power units are connected in series.
[0012] Optionally, all fully-controlled devices in the first bridge arm and the fourth bridge arm in the phase-changing unit act according to the first control signal, and all fully-controlled devices in the second bridge arm and the third bridge arm in each phase-changing unit act according to the second control signal. The first control signal and the second control signal both use square wave signals with a duty cycle of 0.5, and the phase difference between the first control signal and the second control signal is 180°.
[0013] For example, the rated power of the diode may be greater than the rated power of the fully controlled device. Then, the diode may be called a large-capacity diode, and the fully controlled device may be called a small-capacity device.
[0014] Optionally, fully controlled devices use integrated gate-commutated thyristors.
[0015] In a second aspect, the present application provides a DC transformer, comprising a voltage source converter and the above-mentioned power asymmetric converter.
[0016] The DC end of the voltage source converter serves as the input end or output end of the DC transformer, the AC end of the voltage source converter is connected to the first AC end of the transformer module, and the DC end of the converter module serves as the output end or input end of the DC transformer.
[0017] In one possible implementation, when the DC end of the voltage source converter serves as the input end of the DC transformer and the DC end of the converter module serves as the output end of the DC transformer, the voltage source converter adopts a fixed DC voltage control method and a fixed AC frequency control method, and the power asymmetric converter operates in an uncontrolled rectification state.
[0018] In another possible implementation, when the DC end of the voltage source converter is used as the output end of the DC transformer and the DC end of the converter module is used as the input end of the DC transformer, the following two situations are included:
[0019] (1) If the active power at the DC end of the converter module is less than or equal to the preset power limit, the voltage source converter adopts a fixed DC voltage control method and a fixed AC frequency control method, and all fully controlled devices in each bridge arm of the commutation unit operate according to the control signal.
[0020] (2) If the active power at the DC end of the converter module is greater than the preset power limit, the voltage source converter adopts a fixed DC power control method and a fixed AC frequency control method, and all fully controlled devices in each bridge arm of the commutation unit operate according to the control signal.
[0021] In a third aspect, the present application further provides a control method for a DC transformer, comprising:
[0022] When the DC end of the voltage source converter serves as the input end of the DC transformer and the DC end of the converter module serves as the output end of the DC transformer, the voltage source converter is controlled by a fixed DC voltage control method and a fixed AC frequency control method.
[0023] When the DC end of the voltage source converter is used as the output end of the DC transformer and the DC end of the converter module is used as the input end of the DC transformer, there are two cases:
[0024] (1) If the active power at the DC end of the converter module is less than or equal to the preset power limit, the voltage source converter is controlled by a constant DC voltage control method and a constant AC frequency control method, and all fully controlled devices in the power asymmetric converter are controlled by control signals.
[0025] (2) If the active power at the DC end of the converter module is greater than the preset power limit, the voltage source converter is controlled by a fixed DC power control method and a fixed AC frequency control method, and the operation of all fully controlled devices in the power asymmetric converter is controlled by a control signal.
[0026] Optionally, the control signal is used to control the actions of all fully controlled devices in the power asymmetric converter, including:
[0027] The first control signal is used to control the actions of all fully controlled devices in the first bridge arm and the fourth bridge arm in the phase switching unit, and the second control signal is used to control the actions of all fully controlled devices in the second bridge arm and the third bridge arm in each phase switching unit. The first control signal and the second control signal are both square wave signals with a duty cycle of 0.5, and the phase difference between the first control signal and the second control signal is 180°.
[0028] Compared with the prior art, the beneficial effects of this application are:
[0029] The power asymmetric converter provided by the present application may include a transformer module and a commutation module. The commutation module may include an A-phase commutation unit, a B-phase commutation unit, and a C-phase commutation unit connected in series in sequence. Each phase commutation unit adopts an H-bridge topology structure. Compared with the use of MMC submodules, the H-bridge topology structure in the power asymmetric converter provided by the present application includes a small number of fully controlled devices, which not only simplifies the topology of the entire power asymmetric converter, but also reduces the cost of the entire power asymmetric converter and increases the capacity of the power asymmetric converter.
[0030] The bridge arm of the converter module in the present application adopts a hybrid bridge arm, which can realize asymmetric power transmission and further reduce the cost of the entire asymmetric power converter.
[0031] The DC transformer provided in this application can be used in the high voltage field, and is particularly suitable for renewable energy site aggregation and transmission scenarios. BRIEF DESCRIPTION OF THE DRAWINGS
[0032] In order to more clearly illustrate the technical solutions in the present application or the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.
[0033] Figure 1 A schematic structural diagram of a power asymmetric converter in an embodiment of the present application;
[0034] Figure 2a A schematic diagram of a connection relationship between multiple diodes and multiple fully-controlled devices in an embodiment of the present application;
[0035] Figure 2b A schematic diagram of another connection relationship between multiple diodes and multiple fully-controlled devices in an embodiment of the present application;
[0036] Figure 3 A schematic diagram of a first control signal and a second control signal in an embodiment of the present application;
[0037] Figure 4 A schematic structural diagram of a DC transformer in an embodiment of the present application;
[0038] Figure 5 A schematic flowchart of a control method for a DC transformer in an embodiment of the present application. DETAILED DESCRIPTION
[0039] The technical solution in this application will be described below in conjunction with the accompanying drawings.
[0040] The terms "first", "second", etc. in the specification embodiments, claims, and drawings of the present application are only used for the purpose of distinguishing descriptions, and cannot be understood as indicating or implying relative importance, nor can they be understood as indicating or implying order. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, including a series of steps or units. The method, system, product, or device is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products, or devices.
[0041] It should be understood that in the present application, "at least one (item)" means one or more, and "plurality" means two or more. "And / or" is used to describe the association relationship of associated objects, indicating that three relationships may exist. For example, "A and / or B" can mean: only A exists, only B exists, and A and B exist at the same time, where A and B can be singular or plural. The character " / " generally indicates that the objects associated before and after are in an "or" relationship. "At least one of the following" or similar expressions refers to any combination of these items, including any combination of single or plural items. For example, at least one of a, b or c can mean: a, b, c, "a and b", "a and c", "b and c", or "a and b and c", where a, b, c can be single or multiple.
[0042] The present application embodiment provides a power asymmetric converter, such as Figure 1 The power asymmetric converter 100 may include a transformer module 10 and a converter module 20 .
[0043] The commutation module 20 may include an A-phase commutation unit 1, a B-phase commutation unit 2 and a C-phase commutation unit 3 connected in series. Each phase commutation unit adopts an H-bridge topology structure.
[0044] Optionally, the first AC end of the transformer module 10 serves as the input end or output end of the power asymmetric converter 100, the second AC end of the transformer module 10 is connected to the AC end of the converter module 20, and the DC end of the converter module 20 serves as the output end or input end of the power asymmetric converter 100. In the case where the first AC end of the transformer module 10 serves as the input end of the power asymmetric converter 100 and the DC end of the converter module 20 serves as the output end of the power asymmetric converter 100, power flows from the transformer module 10 to the converter module 20, and the converter module 20 plays a rectifying role. In the case where the first AC end of the transformer module 10 serves as the output end of the power asymmetric converter 100 and the DC end of the converter module 20 serves as the input end of the power asymmetric converter 100, power flows from the converter module 20 to the transformer module 10, and the converter module 20 plays an inverting role. That is to say, the power asymmetric converter 100 provided in the embodiment of the present application can be a bidirectional converter.
[0045] In one possible implementation, reference Figure 1 Each switching unit includes a first bridge arm, a second bridge arm, a third bridge arm and a fourth bridge arm.
[0046] The first bridge arm and the second bridge arm are connected in series to form a first bridge arm branch, and the connection node between the first bridge arm and the second bridge arm serves as the first AC terminal AC1 of the phase-changing unit (which can be used as the positive AC terminal of the phase-changing unit). The third bridge arm and the fourth bridge arm are connected in series to form a second bridge arm branch, and the connection node between the third bridge arm and the fourth bridge arm serves as the second AC terminal AC2 of the phase-changing unit (which can be used as the negative AC terminal of the phase-changing unit). The first bridge arm branch and the second bridge arm branch are connected in parallel, and the first connection node between the first bridge arm branch and the second bridge arm branch serves as the first DC terminal DC1 of the phase-changing unit (which can be used as the positive DC terminal of the phase-changing unit), and the second connection node between the first bridge arm branch and the second bridge arm branch serves as the second DC terminal DC2 of the phase-changing unit (which can be used as the negative DC terminal of the phase-changing unit).
[0047] In one example, the first bridge arm, the second bridge arm, the third bridge arm and the fourth bridge arm each include a diode and a fully-controlled device. The diode and the fully-controlled device are connected in reverse parallel. Optionally, the fully-controlled device uses an integrated gate-commutated thyristor (IGCT) or the like.
[0048] In another example, the first bridge arm, the second bridge arm, the third bridge arm and the fourth bridge arm all include a plurality of diodes and a plurality of fully-controlled devices. The embodiment of the present application is described by taking IGCT as an example.
[0049] The plurality of diodes correspond to the plurality of fully-controlled devices one by one. The plurality of diodes may include diode D1, diode D2, ..., diode Dn. The plurality of fully-controlled devices may include IGCT1, IGCT2, ..., IGCTn.
[0050] like Figure 2a , diode D1, diode D2, ..., diode Dn are connected in series in sequence to form a diode branch. IGCT1, IGCT2, ..., IGCTn are connected in series in sequence to form a fully controlled device branch. The diode branch and the fully controlled device branch are connected in reverse parallel.
[0051] like Figure 2b , diode D1, diode D2, ..., diode Dn and IGCT1, IGCT2, ..., IGCTn are connected in reverse parallel one by one to form a plurality of power units, and the plurality of power units are connected in series. That is, each power unit may include a diode and an IGCT connected in reverse parallel. That is, the anode of the diode is in the same direction as the cathode of the IGCT, and the cathode of the diode is in the same direction as the anode of the IGCT.
[0052] It can be seen that in the embodiment of the present application, each bridge arm includes a diode and an IGCT. Therefore, the first bridge arm, the second bridge arm, the third bridge arm and the fourth bridge arm can all be called mixed bridge arms.
[0053] Exemplarily, the transformer module 10 may be a three-phase AC transformer. The first AC end of the three-phase AC transformer may be a low-voltage side, and the three low-voltage side windings may be connected in a star structure. The second AC end of the three-phase AC transformer may be a high-voltage side, and the three high-voltage side windings are respectively connected to the three phase-changing units.
[0054] Optionally, all IGCTs of the first bridge arm and the fourth bridge arm in the switching unit operate according to the first control signal CS1. That is, the first bridge arm and the fourth bridge arm share the first control signal CS1. All IGCTs of the second bridge arm and the third bridge arm in each phase switching unit operate according to the second control signal CS2. The second bridge arm and the third bridge arm share the second control signal CS2. Both the first control signal CS1 and the second control signal CS2 use square wave signals with a duty cycle of 0.5, and the phase difference between the first control signal CS1 and the second control signal CS2 is 180°, such as Figure 3 shown. Figure 3 Medium, CS1 A CS2 represents the first control signal for controlling the first bridge arm in the A phase switching unit. A CS3 represents the second control signal for controlling the second bridge arm in the A phase switching unit. A CS4 represents the second control signal for controlling the third bridge arm in the A phase switching unit. ACS1 represents the first control signal for controlling the fourth bridge arm in the A-phase switching unit. B CS2 represents the control signal for controlling the first bridge arm in the B phase switching unit. B CS3 represents the second control signal for controlling the second bridge arm in the B phase switching unit. B CS4 represents the second control signal for controlling the third bridge arm in the B phase switching unit. B CS1 represents the first control signal for controlling the fourth bridge arm in the B phase switching unit. C CS2 represents the first control signal for controlling the first bridge arm in the C phase switching unit. C CS3 represents the second control signal for controlling the second bridge arm in the C phase switching unit. C CS4 represents the second control signal for controlling the third bridge arm in the C phase switching unit. C Represents a first control signal for controlling the fourth bridge arm in the C-phase commutation unit.
[0055] The present application also provides a DC transformer, such as Figure 4 The DC transformer 1000 includes a voltage source converter (Voltage Source Converter, VSC) 200 and the above-mentioned power asymmetric converter 100 .
[0056] The DC end of the voltage source converter 200 serves as the input end or output end of the DC transformer 100 , the AC end of the voltage source converter 200 is connected to the first AC end of the transformer module 10 , and the DC end of the converter module 20 serves as the output end or input end of the DC transformer 1000 .
[0057] The voltage source converter 200 may include multiple active bridge arms. The specific topology structure may refer to Figure 4 , the embodiments of this application will not be described in detail.
[0058] Apart from Figure 4 The voltage source converter 200 shown in the embodiment of the present application can also be a three-phase bridge arm alternating conduction type modular multi-level converter, a three-phase thyristor type two-level converter, a three-phase IGCT type two-level converter, a three-phase three-level converter, etc., which is not limited in the embodiment of the present application.
[0059] In the embodiment of the present application, the DC end of the voltage source converter 200 is used as the input end of the DC transformer 1000 and the DC end of the converter module 20 is used as the output end of the DC transformer 1000, which can be understood as forward power transmission. The DC end of the voltage source converter 200 is used as the output end of the DC transformer 1000 and the DC end of the converter module 20 is used as the input end of the DC transformer 1000, which can be understood as reverse power transmission. The specific description is as follows:
[0060] In the case of forward power transmission, the voltage source converter 200 adopts a constant DC voltage control method and a constant AC frequency control method, and the power asymmetric converter 100 operates in an uncontrolled rectification state.
[0061] In the case of reverse power transfer, it can be divided into the following two cases:
[0062] (1) If the active power at the DC end of the commutation module 20 is less than or equal to the preset power limit, the voltage source converter 200 adopts a constant DC voltage control mode and a constant AC frequency control mode, and all IGCTs of each bridge arm in the commutation unit operate according to the control signal.
[0063] (2) If the active power at the DC end of the commutation module 20 is greater than the preset power limit, the voltage source converter 200 adopts a constant DC power control method and a constant AC frequency control method, and all IGCTs of each bridge arm in the commutation unit operate according to the control signal.
[0064] The present application embodiment provides a control method for a DC transformer, such as Figure 5 The control method 2000 comprises the following steps:
[0065] Step S1: When the DC end of the voltage source converter serves as the input end of the DC transformer and the DC end of the converter module serves as the output end of the DC transformer (i.e., the forward power transmission mentioned above), the voltage source converter is controlled by a fixed DC voltage control method and a fixed AC frequency control method.
[0066] Step S2: When the DC end of the voltage source converter is used as the output end of the DC transformer and the DC end of the converter module is used as the input end of the DC transformer (i.e., the reverse power transmission described above), there are two cases:
[0067] (1) If the active power at the DC end of the converter module is less than or equal to the preset power limit, the voltage source converter is controlled by a constant DC voltage control method and a constant AC frequency control method, and the operation of all IGCTs in the power asymmetric converter is controlled by a control signal.
[0068] (2) If the active power at the DC end of the converter module is greater than the preset power limit, the voltage source converter is controlled by a fixed DC power control method and a fixed AC frequency control method, and all IGCTs in the power asymmetric converter are controlled by a control signal. Specifically, controlling the actions of all fully controlled devices in the power asymmetric converter by a control signal may include:
[0069] The first control signal is used to control the actions of all IGCTs in the first bridge arm and the fourth bridge arm in the phase switching unit, and the second control signal is used to control the actions of all IGCTs in the second bridge arm and the third bridge arm in each phase switching unit. The first control signal and the second control signal both use square wave signals with a duty cycle of 0.5, and the phase difference between the first control signal and the second control signal is 180°. The control signals for controlling the IGCTs in the first bridge arm, the second bridge arm, the third bridge arm, and the fourth bridge arm can refer to Figure 3 .
[0070] During the start-up process of the DC transformer, first, the capacitor in the voltage source converter 200 can be charged through the power asymmetric converter 100. The voltage source converter 200 is unlocked and starts the control, and after the DC voltage is stabilized, all IGBTs of the power asymmetric converter 100 are locked to perform forward power transmission.
[0071] The above are merely embodiments of the application and are not intended to limit the application. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the application are included in the scope of the claims of the pending application.
Claims
1. A power asymmetric converter, characterized in that: It includes a transformer module and a converter module; The commutation module comprises an A-phase commutation unit, a B-phase commutation unit and a C-phase commutation unit connected in series in sequence; each phase commutation unit adopts an H-bridge topology structure; The first AC end of the transformer module serves as the input end or output end of the power asymmetric converter, the second AC end of the transformer module is connected to the AC end of the converter module, and the DC end of the converter module serves as the output end or input end of the power asymmetric converter.
2. The power asymmetric converter according to claim 1, characterized in that: Each of the phase switching units comprises a first bridge arm, a second bridge arm, a third bridge arm and a fourth bridge arm; The first bridge arm and the second bridge arm are connected in series to form a first bridge arm branch, and a connection node between the first bridge arm and the second bridge arm serves as a first AC end of the phase switching unit; the third bridge arm and the fourth bridge arm are connected in series to form a second bridge arm branch, and a connection node between the third bridge arm and the fourth bridge arm serves as a second AC end of the phase switching unit; the first bridge arm branch and the second bridge arm branch are connected in parallel, and a first connection node between the first bridge arm branch and the second bridge arm branch serves as a first DC end of the phase switching unit, and a second connection node between the first bridge arm branch and the second bridge arm branch serves as a second DC end of the phase switching unit.
3. The power asymmetric converter according to claim 2, characterized in that: The first bridge arm, the second bridge arm, the third bridge arm and the fourth bridge arm each include a diode and a fully-controlled device; the diode and the fully-controlled device are connected in reverse parallel.
4. The power asymmetric converter according to claim 2, characterized in that: The first bridge arm, the second bridge arm, the third bridge arm and the fourth bridge arm each include a plurality of diodes and a plurality of fully-controlled devices; the plurality of diodes and the plurality of fully-controlled devices correspond one to one; The multiple diodes are connected in series in sequence to form a diode branch, the multiple fully-controlled devices are connected in series in sequence to form a fully-controlled device branch, the diode branch and the fully-controlled device branch are connected in reverse parallel; or; the multiple diodes and the multiple fully-controlled devices are connected in reverse parallel one by one to form a plurality of power units, and the multiple power units are connected in series.
5. The power asymmetric converter according to any one of claims 2 to 4, characterized in that: All the fully-controlled devices of the first bridge arm and the fourth bridge arm in each phase switching unit act according to the first control signal, and all the fully-controlled devices of the second bridge arm and the third bridge arm in each phase switching unit act according to the second control signal; The first control signal and the second control signal are both square wave signals with a duty cycle of 0.5, and the phase difference between the first control signal and the second control signal is 180°.
6. The power asymmetric converter according to claim 3 or 4, characterized in that: The fully controlled device adopts an integrated gate-commutated thyristor.
7. A DC transformer, characterized in that: A method comprising a voltage source converter and a power asymmetric converter according to any one of claims 1 to 6; The DC end of the voltage source converter serves as the input end or output end of the DC transformer, the AC end of the voltage source converter is connected to the first AC end of the transformer module, and the DC end of the converter module serves as the output end or input end of the DC transformer.
8. The DC transformer according to claim 7, characterized in that: In the case where the DC end of the voltage source converter serves as the input end of the DC transformer and the DC end of the converter module serves as the output end of the DC transformer, the voltage source converter adopts a fixed DC voltage control mode and a fixed AC frequency control mode, and the power asymmetric converter operates in an uncontrolled rectification state; In the case where the DC end of the voltage source converter serves as the output end of the DC transformer and the DC end of the converter module serves as the input end of the DC transformer, the following two cases are included: If the active power at the DC end of the commutation module is less than or equal to the preset power limit, the voltage source converter adopts the fixed DC voltage control mode and the fixed AC frequency control mode, and all fully controlled devices of each bridge arm in the commutation unit act according to the control signal; If the active power at the DC end of the commutation module is greater than the preset power limit, the voltage source converter adopts the fixed DC power control method and the fixed AC frequency control method, and all fully controlled devices in each bridge arm of the commutation unit act according to the control signal.
9. A control method for a DC transformer as claimed in claim 7 or 8, characterized in that: include: In the case where the DC end of the voltage source converter serves as the input end of the DC transformer and the DC end of the converter module serves as the output end of the DC transformer, the voltage source converter is controlled by a fixed DC voltage control method and a fixed AC frequency control method; When the DC end of the voltage source converter is used as the output end of the DC transformer and the DC end of the converter module is used as the input end of the DC transformer, there are two cases: If the active power at the DC end of the converter module is less than or equal to the preset power limit, the voltage source converter is controlled by the fixed DC voltage control method and the fixed AC frequency control method, and all fully controlled devices in the power asymmetric converter are controlled by control signals; If the active power at the DC end of the converter module is greater than the preset power limit, the voltage source converter is controlled by a fixed DC power control method and a fixed AC frequency control method, and the operation of all fully controlled devices in the power asymmetric converter is controlled by a control signal.
10. The control method according to claim 9, characterized in that: The controlling of the actions of all fully controlled devices in the power asymmetric converter by control signals includes: Control the actions of all fully-controlled devices in the first bridge arm and the fourth bridge arm in the phase switching unit through the first control signal, and control the actions of all fully-controlled devices in the second bridge arm and the third bridge arm in each phase switching unit through the second control signal; The first control signal and the second control signal are both square wave signals with a duty cycle of 0.5, and the phase difference between the first control signal and the second control signal is 180°.