CN108832659B - Combined converter and control method - Google Patents
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- CN108832659B CN108832659B CN201810672674.4A CN201810672674A CN108832659B CN 108832659 B CN108832659 B CN 108832659B CN 201810672674 A CN201810672674 A CN 201810672674A CN 108832659 B CN108832659 B CN 108832659B
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- 238000010248 power generation Methods 0.000 description 6
- 238000010586 diagram Methods 0.000 description 4
- 239000004065 semiconductor Substances 0.000 description 4
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- 230000008569 process Effects 0.000 description 3
- 230000009471 action Effects 0.000 description 2
- 230000010363 phase shift Effects 0.000 description 2
- 230000009286 beneficial effect Effects 0.000 description 1
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E10/00—Energy generation through renewable energy sources
- Y02E10/70—Wind energy
- Y02E10/76—Power conversion electric or electronic aspects
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Abstract
The embodiment of the invention provides a combined current transformer and a control method, wherein the combined current transformer comprises a frame circuit breaker and at least two current transformers, wherein each current transformer comprises an alternating current network side, a direct current side, an alternating current motor side, a first contactor and a second contactor. The combined converter provided by the scheme controls the switching states of the first contactor, the second contactor and the third contactor, and independently controls the access state of each converter, so that the redundancy of the system is improved. Meanwhile, the frame circuit breaker can be always in a closed state, so that the breaking times of the frame circuit breaker are reduced, and the service life of the frame circuit breaker can be prolonged. Besides, the converter of a plurality of access systems are connected in parallel through the third contactor, so that the circulating current between the converters is reduced.
Description
Technical Field
The invention relates to the technical field of new energy motor control, in particular to a combined converter and a control method.
Background
The converter is a device which is commonly used in a power generation system and converts alternating current on a power grid side into direct current and then converts the direct current into alternating current on a motor side, and comprises a plurality of semiconductor switches which are connected in parallel, and the conversion of the alternating current and the direct current is realized through the switch combination state of the semiconductor switches. Specifically, the semiconductor switch may be a device having a switching function, such as an IGBT, an IGCT, and an IEGT.
As the power requirements of power generation systems become higher, the ac sides of multiple converters are often connected in parallel to meet the higher power requirements. However, since the ac sides of the plurality of converters are directly connected in parallel and the dc sides are not connected in parallel, in order to provide a redundant characteristic to the system, a frame breaker is provided on the ac side of each converter for independent control, which results in a large cost investment. In addition, the frequent breaking of the frame breakers of the plurality of converters causes the shortening of the service life, and the problem of the circulation among the plurality of converters is relatively prominent.
In order to reduce the circulating current existing between the plurality of converters, the alternating current side and the direct current side of the plurality of converters are generally connected in parallel, and synchronous control and circulating current restraining control algorithms are arranged on software to reduce the circulating current between the plurality of converters to the maximum extent.
However, the inventors have found that the mechanical and electrical life of the frame circuit breaker is limited, and it is necessary to reduce the number of times of disconnection of the converter, that is, the number of times of operation of the frame circuit breaker in the actual grid-connected operation.
Therefore, how to provide a combined converter which can solve the problem of circulating current between converters and prolong the service life of a frame circuit breaker is a great technical problem to be solved urgently by technical personnel in the field.
Disclosure of Invention
In view of this, the embodiment of the present invention provides a combined converter, which can not only meet the requirement of redundancy function, but also better solve the problem of circulating current between converters, and effectively prolong the service life of a frame circuit breaker.
In order to achieve the above purpose, the embodiments of the present invention provide the following technical solutions:
a combined current transformer comprises a frame breaker and at least two current transformers, wherein each current transformer comprises an alternating current network side, a direct current side, an alternating current motor side, a first contactor and a second contactor;
the alternating current network side of each converter is connected with one end of the frame circuit breaker through the first contactor, and the other end of the frame circuit breaker is connected with a power grid;
the alternating current motor side of each converter is electrically connected with a generator through the second contactor;
the direct current sides of the converters are connected in parallel through a third contactor.
Optionally, the alternating current motor side of the converter is connected to the same winding end of the generator through the second contactor.
Optionally, the ac motor sides of the plurality of converters are connected to different winding ends of the generator through the second contactor, respectively.
Optionally, the converter further includes: a grid-side sub-converter and a machine-side sub-converter,
the power grid side sub-converter comprises a first three-phase power unit, a direct-current crowbar unit and a grid-connected filtering unit;
the motor side sub-converter comprises a second three-phase power unit and a filter;
the first three-phase power unit, the direct-current crowbar unit and the second three-phase power unit are connected in parallel;
two ends of the direct current crowbar unit are used as direct current sides of the converter;
the middle point of the first three-phase power unit is connected with the input end of the grid-connected filtering unit, and the output end of the grid-connected filtering unit is used as the alternating current network side of the converter;
the middle point of the second three-phase power unit is connected with the input end of the filter, and the output end of the filter is used as the alternating current motor side of the converter.
Optionally, the converter further includes:
a first fuse in series with the first contactor;
and/or the presence of a gas in the gas,
a second fuse in series with the second contactor;
and/or the presence of a gas in the gas,
a third fuse in series with the third contactor.
A control method applied to any one of the above combined converters, the control method comprising:
the first working mode is used for controlling the frame circuit breaker to be closed, controlling the first contactor to be closed, controlling the second contactor to be opened and controlling the third contactor to be closed so as to enable the converter to be in a grid-connected standby state;
the second working mode is used for controlling the frame circuit breaker to be closed, controlling the first contactor to be closed, controlling the second contactor to be closed and controlling the third contactor to be closed so as to enable the converter to be in a grid-connected running state;
the third working mode is used for controlling the frame circuit breaker to be closed, the first contactor to be opened, the second contactor to be opened and the third contactor to be opened so as to enable the converter to be in a shutdown state;
and in a fourth working mode, the frame circuit breaker is controlled to be closed, the first contactor and the second contactor of the converter are controlled to be opened, the first contactor and the second contactor of the converter are controlled to be closed, and the third contactor is controlled to be closed, so that the converter is in a redundant running state.
Optionally, the method further includes:
and acquiring the temperature of the converter with the first contactor closed, and controlling the corresponding converter to be in the third working mode when the temperature is greater than a first preset value.
Optionally, the method further includes:
and when the temperature is lower than a second preset value, controlling the corresponding converter to be in a second working mode.
Optionally, the method further includes:
acquiring a given value of generating power to be tracked;
determining the target access number of the converters in the combined converter according to the given value of the generating power and the rated generating power of each converter;
and controlling the converter with the target access quantity to be in the second working mode, and controlling other converters to be in the third working mode.
Optionally, the method further includes:
acquiring a fault state of a converter in the combined converter;
and controlling the converter with the fault to be in the third working mode and sending an alarm.
A wind turbine converter comprising any one of the above described combined converters.
Based on the technical scheme, the embodiment of the invention provides a combined current transformer which comprises a frame circuit breaker and at least two current transformers, wherein each current transformer comprises an alternating current power grid side, a direct current side, an alternating current motor side, a first contactor and a second contactor. Specifically, the alternating current network side of each converter is connected with one end of the frame circuit breaker through the first contactor, and the other end of the frame circuit breaker is connected with the power grid. And the alternating current motor side of each converter is electrically connected with a generator through the second contactor. The direct current sides of the converters are connected in parallel through a third contactor. Therefore, in the combined converter provided by the scheme, the switching-in state of each converter is independently controlled by controlling the switching states of the first contactor, the second contactor and the third contactor, so that the redundancy of the system is improved. At the moment, the frame circuit breaker can be always in a closed state, namely, the breaking times of the frame circuit breaker are reduced, and the service life of the frame circuit breaker can be further prolonged. Besides, the converter of a plurality of access systems are connected in parallel through the third contactor, so that the circulating current between the converters is reduced.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the provided drawings without creative efforts.
Fig. 1 is a schematic structural diagram of a combined converter according to an embodiment of the present invention;
fig. 2 is a schematic structural diagram of another combined converter according to an embodiment of the present invention;
fig. 3 is a schematic structural diagram of another combined converter according to an embodiment of the present invention;
fig. 4 is a schematic flowchart of a control method according to an embodiment of the present invention;
fig. 5 is a schematic flow chart of a control method according to an embodiment of the present invention;
fig. 6 is a schematic flow chart of a control method according to an embodiment of the present invention;
fig. 7 is a schematic flow chart of a control method according to an embodiment of the present invention;
fig. 8 is a schematic flowchart of a control method according to an embodiment of the present invention.
Detailed Description
Referring to fig. 1, fig. 1 is a schematic structural diagram of a combined converter according to an embodiment of the present invention, where the combined converter includes a frame breaker 11 and at least two converters 12. Wherein each of said converters 12 comprises an ac grid side 121, a dc side 122, an ac machine side 123, a first contactor 124 and a second contactor 125.
Specifically, the connection relationship of each device in the combined converter is as follows:
the grid side alternating current output end 121 of each converter 12 is connected with one end of the frame breaker 11 through the first contactor 124, and the other end of the frame breaker 11 is connected with a grid;
the ac motor side 123 of each of the converters 12 is electrically connected to the generator 13 via the second contactor 125;
the dc sides 122 of a plurality of said converters 12 are all connected in parallel to each other by means of a third contactor 126.
In combination with the connection relationship, the combined converter provided by this embodiment can be connected to the whole power generation system by controlling the first contactor and the second contactor to be closed. When the first contactor of the converter is controlled to be closed, the converter can be isolated from a power grid, and therefore the system redundancy of the combined converter provided by the embodiment is high. Moreover, the scheme realizes the connection and disconnection of the converter through the first contactor and the second contactor, and the action of the frame breaker is not required to be controlled, so that the use frequency of the frame breaker is reduced, and the service life of the frame breaker is prolonged.
It should be noted that in this embodiment, the contactor is adopted to share the function of the original frame circuit breaker for cutting off the converter, and the contactor does not cause the reduction of the service life of the device due to the switching times.
In addition, the combined converter provided by the embodiment connects the dc-side output terminals of each converter in parallel through the third contactor, so that the parallel-connected converters do not generate a circulating current between the converters.
On the basis of the above embodiments, in the combined converter provided in this embodiment, the ac side of the converter may be connected to the motor with a phase difference, or may be connected to the motor without a phase difference.
Specifically, as shown in fig. 2, the ac machine side of the converters may be connected to the motor with a phase difference, wherein the ac machine sides of the converters are connected to different winding ends of the generator through the second contactors.
As shown in fig. 3, the ac machine side of the converter may be connected to the machine without phase difference, wherein the ac machine side of the converter is connected to the same winding end of the generator via the second contactor.
Specifically, the current transformer provided in this embodiment may further include: a grid side sub-converter and a motor side sub-converter.
The power grid side sub-converter comprises a first three-phase power unit, a direct-current crowbar unit and a grid-connected filtering unit;
the motor side sub-converter comprises a second three-phase power unit and a filter;
the first three-phase power unit, the direct-current crowbar unit and the second three-phase power unit are connected in parallel;
two ends of the direct current crowbar unit are used as direct current sides of the converter;
the middle point of the first three-phase power unit is connected with the input end of the grid-connected filtering unit, and the output end of the grid-connected filtering unit is used as the alternating current network side of the converter;
the middle point of the second three-phase power unit is connected with the input end of the filter, and the output end of the filter is used as the alternating current motor side of the converter.
In addition, the converter in the combined converter provided by this embodiment further includes:
a first fuse in series with the first contactor;
and/or the presence of a gas in the gas,
a second fuse in series with the second contactor;
and/or the presence of a gas in the gas,
a third fuse in series with the third contactor.
Schematically, the combined converter provided by the embodiment is formed by connecting converters 1 to n in parallel. The direct current sides of the converters 1 to n are connected through direct current FUSEs FUSE01 to FUSE0n and direct current contactors K01 to K0n respectively; the power grid sides of the converters 1-n are converged to a total grid-connected frame breaker QF through alternating current contactors K11-Kn 1 and alternating current FUSEs FUSE 11-FUSE 1n respectively, and are connected with a power grid through the alternating current FUSEs FUSE; the motor sides of the converters 1 to n are respectively connected to a total busbar output by 1 to n sets of windings of the generator through alternating current contactors K12 to Kn2 and alternating current FUSEs FUSE12 to FUSEn2, or respectively connected with 1 to n sets of windings of the generator.
In combination with the hardware structure of the combined converter, this embodiment further provides a control method applied to the combined converter, as shown in fig. 4, where the control method includes:
a first working mode, S41, controlling the frame circuit breaker to be closed, controlling the first contactor to be closed, controlling the second contactor to be opened, and controlling the third contactor to be closed, so that the converter is in a grid-connected standby state;
a second working mode, S42, controlling the frame circuit breaker to be closed, controlling the first contactor to be closed, controlling the second contactor to be closed, and controlling the third contactor to be closed, so that the converter is in a grid-connected operation state;
a third operating mode, S43, controlling the frame circuit breaker to be closed, the first contactor to be opened, the second contactor to be opened, and the third contactor to be opened, so as to enable the converter to be in a shutdown state;
and in a fourth working mode, S44, the frame circuit breaker is controlled to be closed, a part of the first contactor and the second contactor of the converter are controlled to be opened, a part of the first contactor and the second contactor of the converter are controlled to be closed, and the third contactor is controlled to be closed, so that the converter is in a redundant operation state.
Therefore, in the combined converter provided by the scheme, the switching-in state of each converter is independently controlled by controlling the switching states of the first contactor and the second contactor, so that the redundancy of the system is improved. At the moment, the frame circuit breaker can be always in a closed state, namely, the breaking times of the frame circuit breaker are reduced, and the service life of the frame circuit breaker can be further prolonged. And because the converters accessed into the system are connected in parallel through the third contactor, the circulating current among the converters is reduced.
In addition, as shown in fig. 5, the control method may further include:
and S51, acquiring the temperature of the converter with the first contactor closed, and controlling the corresponding converter to be in the third working mode when the temperature is greater than a first preset value.
On the basis of the above embodiment, as shown in fig. 6, the control method may further include:
and S61, when the temperature is lower than a second preset value, controlling the corresponding converter to be in a second working mode.
And, as shown in fig. 7, the control method may further include:
s71, acquiring a given value of the generated power to be tracked;
s72, determining the target access number of the converters in the combined converter according to the given power generation power value and the rated power generation power of each converter;
and S73, controlling the current transformer with the target access number to be in the second working mode, and controlling other current transformers to be in the third working mode.
In addition, as shown in fig. 8, the control method provided in this embodiment may further include:
s81, acquiring the fault state of a converter in the combined converter;
and S82, controlling the converter with the fault to be in the third working mode and sending an alarm.
In practical operation, the combined converter provided in this embodiment can switch in and out the converter i on the branch (i ═ 1,2, ·, n) by switching off the ac contactors K11, K21, and Kn1 while maintaining the power grid side breaker QF in a closed state.
Specifically, the combined converter provided by the embodiment can be applied to various technical fields, such as the wind power field. The working process of the combined converter will now be described by taking the above combined converter as an example for application in the field of wind power.
In the field of wind power, a main control system of a wind turbine generator set issues a given value of generated power to be tracked to a combined converter according to wind speed and generated power predicted by wind power, and a communication controller of the combined converter controls switching-in and switching-out of converters 1-n in the combined converter according to generated power data predicted by the wind power.
That is, the present embodiment may also provide a wind turbine converter including any one of the above-described combined converters.
In addition, the combined converter provided by the embodiment can also control the switching-in and switching-out of the converters 1 to n according to the detected working temperature of the converter itself, such as the temperature of core devices such as the IGBT, when the detected temperature is greater than the set temperature.
Furthermore, the combined converter provided by the embodiment can also detect whether the converter has a fault, and when the converter is detected to have the fault, the controller of the combined converter automatically switches out the converter on the corresponding fault branch without participating in operation, so that the multi-level derating operation of the converter is realized.
From the hardware architecture and the control flow of the combined converter provided by the embodiment of the invention, the combined converter can be easily obtained to have the following beneficial effects:
1. the parallel structure in the converter is fully utilized, the on-line adjustment of the single-machine capacity of the converter is realized, the relative operation time of the converter under low power is shortened, the self-power consumption is reduced, the integral power generation efficiency of a unit is improved, and meanwhile, when a branch converter fails, a derating operation mode can be switched in through simple software setting, so that the generating capacity of the unit is improved, and the wind abandoning rate is reduced;
2. when the generated current is small, the number of the converters which are put into operation can be reduced, so that the actual working current of the converters is raised, and the problem of large proportion of harmonic components at a low current stage is solved;
3. according to the predicted generating power, the average working temperature of the converter is predicted, the switching-in and switching-out of the converters 1-n are controlled, the working temperature of core devices such as IGBT (insulated gate bipolar translator) and the like is kept stable in a small range, and therefore the working life of a semiconductor device is prolonged;
4. in the operation process, the action times of the grid-connected end frame circuit breaker QF are greatly reduced, the cut-in and cut-out of the grid-side converters 1-n are controlled only by the contactors K11-Kn 1, and the electrical service life of the frame circuit breaker QF is guaranteed;
5. the method can be suitable for the access of a multi-winding generator, such as no electrical connection and electrical connection at the central point among multiple sets of windings, no phase shift and phase shift among the multiple sets of windings, and the like;
6. the parallel connection scheme of three-phase rectification and inversion as a unit is adopted, the direct current side commutation loop is simple and compact in design, and in the normal operation process, if two converters adopt the same hardware, theoretically, current stress is not borne on direct current contactors and direct current fuses which are connected in parallel among a plurality of groups of converters. Even if in fact because of the inconsistency of hardware circuit, the current that bears on direct current contactor and direct current fuse in this scheme is less.
To sum up, the embodiment of the present invention provides a combined current transformer, which includes a frame circuit breaker and at least two current transformers, wherein each of the current transformers includes an ac power grid side, a dc side, an ac motor side, a first contactor, and a second contactor. Specifically, the alternating current network side of each converter is connected with one end of the frame circuit breaker through the first contactor, and the other end of the frame circuit breaker is connected with the power grid. And the alternating current motor side of each converter is electrically connected with a generator through the second contactor. The direct current sides of the converters are connected in parallel through a third contactor. Therefore, in the combined converter provided by the scheme, the switching-in state of each converter is independently controlled by controlling the switching states of the first contactor and the second contactor, so that the redundancy of the system is improved. At the moment, the frame circuit breaker can be always in a closed state, namely, the breaking times of the frame circuit breaker are reduced, and the service life of the frame circuit breaker can be further prolonged. Besides, the converter of a plurality of access systems are connected in parallel through the third contactor, so that the circulating current between the converters is reduced.
The embodiments in the present description are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments are referred to each other. The device disclosed by the embodiment corresponds to the method disclosed by the embodiment, so that the description is simple, and the relevant points can be referred to the method part for description.
Those of skill would further appreciate that the various illustrative elements and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware, computer software, or combinations of both, and that the various illustrative components and steps have been described above generally in terms of their functionality in order to clearly illustrate this interchangeability of hardware and software. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the implementation. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present invention.
The steps of a method or algorithm described in connection with the embodiments disclosed herein may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. A software module may reside in Random Access Memory (RAM), memory, Read Only Memory (ROM), electrically programmable ROM, electrically erasable programmable ROM, registers, hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art.
The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended 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 (11)
1. A combined current transformer is characterized by comprising a frame breaker, at least two current transformers and at least one third contactor, wherein each current transformer comprises an alternating current network side, a direct current side, an alternating current motor side, a first contactor and a second contactor;
the alternating current network side of each converter is connected with one end of the frame circuit breaker through the first contactor, the other end of the frame circuit breaker is connected with a power grid, and the frame circuit breaker is in a closed state;
the alternating current motor side of each converter is electrically connected with a generator through the second contactor;
the direct current sides of the converters are connected in parallel through the third contactor; wherein the third contactors are closed except when the converters are in a shutdown state to reduce circulating currents between the converters.
2. The combined converter according to claim 1, characterized in that the ac machine side of the converter is connected to the same winding end of the generator through the second contactor.
3. The combined converter according to claim 1, wherein a plurality of the converter ac machine sides are connected to different winding ends of the generator via the second contactor, respectively.
4. The combined converter according to claim 1, wherein the converter further comprises: a grid-side sub-converter and a machine-side sub-converter,
the power grid side sub-converter comprises a first three-phase power unit, a direct-current crowbar unit and a grid-connected filtering unit;
the motor side sub-converter comprises a second three-phase power unit and a filter;
the first three-phase power unit, the direct-current crowbar unit and the second three-phase power unit are connected in parallel;
two ends of the direct current crowbar unit are used as direct current sides of the converter;
the middle point of the first three-phase power unit is connected with the input end of the grid-connected filtering unit, and the output end of the grid-connected filtering unit is used as the alternating current network side of the converter;
the middle point of the second three-phase power unit is connected with the input end of the filter, and the output end of the filter is used as the alternating current motor side of the converter.
5. The combined converter according to claim 1, wherein the converter further comprises:
a first fuse in series with the first contactor;
and/or the presence of a gas in the gas,
a second fuse in series with the second contactor;
and/or the presence of a gas in the gas,
a third fuse in series with the third contactor.
6. A control method for a combined converter according to any of claims 1-5, said control method comprising:
the first working mode is used for controlling the frame circuit breaker to be closed, controlling the first contactor to be closed, controlling the second contactor to be opened and controlling the third contactor to be closed so as to enable the converter to be in a grid-connected standby state;
the second working mode is used for controlling the frame circuit breaker to be closed, controlling the first contactor to be closed, controlling the second contactor to be closed and controlling the third contactor to be closed so as to enable the converter to be in a grid-connected running state;
the third working mode is used for controlling the frame circuit breaker to be closed, the first contactor to be opened, the second contactor to be opened and the third contactor to be opened so as to enable the converter to be in a shutdown state;
and in a fourth working mode, the frame circuit breaker is controlled to be closed, the first contactor and the second contactor of the converter are controlled to be opened, the first contactor and the second contactor of the converter are controlled to be closed, and the third contactor is controlled to be closed, so that the converter is in a redundant running state.
7. The control method according to claim 6, characterized by further comprising:
and acquiring the temperature of the converter with the first contactor closed, and controlling the corresponding converter to be in the third working mode when the temperature is greater than a first preset value.
8. The control method according to claim 7, characterized by further comprising:
and when the temperature is lower than a second preset value, controlling the corresponding converter to be in a second working mode.
9. The control method according to claim 6, characterized by further comprising:
acquiring a given value of generating power to be tracked;
determining the target access number of the converters in the combined converter according to the given value of the generating power and the rated generating power of each converter;
and controlling the converter with the target access quantity to be in the second working mode, and controlling other converters to be in the third working mode.
10. The control method according to claim 6, characterized by further comprising:
acquiring a fault state of a converter in the combined converter;
and controlling the converter with the fault to be in the third working mode and sending an alarm.
11. Wind turbine converter, characterized in that it comprises a combined converter according to any of claims 1-5.
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