CN113629771B - Photovoltaic system and photovoltaic turn-off method - Google Patents
Photovoltaic system and photovoltaic turn-off method Download PDFInfo
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- CN113629771B CN113629771B CN202111037363.9A CN202111037363A CN113629771B CN 113629771 B CN113629771 B CN 113629771B CN 202111037363 A CN202111037363 A CN 202111037363A CN 113629771 B CN113629771 B CN 113629771B
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- 238000006243 chemical reaction Methods 0.000 claims description 62
- 230000000737 periodic effect Effects 0.000 claims description 11
- 230000000295 complement effect Effects 0.000 claims description 4
- 238000010248 power generation Methods 0.000 claims description 3
- 238000010586 diagram Methods 0.000 description 7
- 230000004048 modification Effects 0.000 description 4
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Classifications
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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
- H02J3/381—Dispersed generators
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02S—GENERATION OF ELECTRIC POWER BY CONVERSION OF INFRARED RADIATION, VISIBLE LIGHT OR ULTRAVIOLET LIGHT, e.g. USING PHOTOVOLTAIC [PV] MODULES
- H02S40/00—Components or accessories in combination with PV modules, not provided for in groups H02S10/00 - H02S30/00
- H02S40/30—Electrical components
- H02S40/32—Electrical components comprising DC/AC inverter means associated with the PV module itself, e.g. AC modules
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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
- H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
- H02J2300/20—The dispersed energy generation being of renewable origin
- H02J2300/22—The renewable source being solar energy
- H02J2300/24—The renewable source being solar energy of photovoltaic origin
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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
- Y02E10/50—Photovoltaic [PV] energy
-
- 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
- Y02E10/50—Photovoltaic [PV] energy
- Y02E10/56—Power conversion systems, e.g. maximum power point trackers
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- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Inverter Devices (AREA)
Abstract
The application provides a photovoltaic system and a shutdown control method. In the photovoltaic turn-off method, if the inverter enters a safe state, the input voltage of each turn-off device at the front stage of the inverter is reduced, so that each turn-off device enters a shutdown state or an under-voltage protection state, namely, the turn-off device is turned off; when each shutoff device of the front stage of the inverter is turned off, each path of photovoltaic string can enter a safe state, so that the photovoltaic shutoff method provided by the application can ensure that the photovoltaic string enters the safe state when the inverter enters the safe state.
Description
Technical Field
The invention relates to the technical field of photovoltaic power generation, in particular to a photovoltaic system and a turn-off control method.
Background
In any photovoltaic string 10 of the photovoltaic system shown in fig. 1, the output end of each photovoltaic module 11 is connected with the output end of one shutoff device 12, and the output ends of the shutoff devices 12 are cascaded with the output ends of the corresponding photovoltaic strings 10; the specific structure of the shutdown device 12 is shown in fig. 2, where the processor 01 of the shutdown device 12 collects an output current through the current collection unit 02, and shuts itself off when the output current is small, so as to cut off the connection between the corresponding photovoltaic module 11 and the inverter 20, and when all shutdown devices 12 in the photovoltaic string 10 are shut down, the photovoltaic string 10 enters a safe state.
However, when the number of the photovoltaic modules 11 included in each path of the photovoltaic string 10 connected to the inverter 20 is not completely the same, the mismatch phenomenon exists in the photovoltaic system, so that the shutdown device 12 in the photovoltaic string 10 cannot be timely turned off, and the photovoltaic string 10 cannot enter a safe state.
For example, assuming that the first photovoltaic string and the second photovoltaic string are both connected to the inverter 20, and each of the first photovoltaic string and the second photovoltaic string includes N photovoltaic modules 11 and M photovoltaic modules 11, where N > M, when the inverter 20 is stopped, that is, when the inverter 20 enters a safe state, a reverse current occurs between the two photovoltaic strings 10, and the reverse current flows from the output end of the first photovoltaic string to the output end of the second photovoltaic string; as shown in fig. 3, when the inverter 20 enters the safety state, the parallel voltage of the first photovoltaic string and the second photovoltaic string is Upv, and as can be seen from the figure, upv is higher than the open circuit voltage Uoc2 of the second photovoltaic string and lower than the open circuit voltage Uoc1 of the first photovoltaic string, the output current of the first photovoltaic string is Ib, and the input current of the second photovoltaic string is Ib, and at this time, the magnitude of the backward current is Ib.
Therefore, how to ensure that the photovoltaic string enters the safe state when the inverter enters the safe state is a technical problem to be solved.
Disclosure of Invention
In view of the above, the present invention provides a photovoltaic system and a shutdown control method to ensure that a photovoltaic string is in a safe state when an inverter is in the safe state.
In order to achieve the above object, the embodiment of the present invention provides the following technical solutions:
In one aspect, the present application provides a photovoltaic shutdown method, including:
Judging whether the inverter enters a safe state;
And if the inverter enters a safe state, reducing the input voltage of each shutoff device of the front stage of the inverter, so that each shutoff device enters a shutdown state or an under-voltage protection state.
Optionally, before the step of reducing the input voltage of each of the shutdown devices of the previous stage of the inverter to make each of the shutdown devices enter the shutdown state or the under-voltage protection state, the method further includes:
Detecting whether a backward current occurs between each path of photovoltaic group strings of the front stage of the inverter;
and if the backward current occurs between the photovoltaic strings, returning to execute the step of reducing the input voltage of each shutoff device of the front stage of the inverter so that each shutoff device enters a shutdown state or an under-voltage protection state.
Optionally, reducing the input voltage of each of the shutdown devices of the front stage of the inverter to make each of the shutdown devices enter a shutdown state or an under-voltage protection state, including:
And controlling the direct-current side input voltage of the inverter to be smaller than the minimum value of the output voltages of the photovoltaic modules when each of the turnoff devices enters a shutdown state or an under-voltage protection state.
Optionally, the specific manner of controlling the dc side input voltage of the inverter to be smaller than the minimum value in the output voltages of the photovoltaic modules when each of the shutdown devices enters the shutdown state or the under-voltage protection state is as follows:
And controlling the direct-current side two-pole short circuit of the inverter.
Optionally, when the dc conversion circuit in the inverter is a non-isolated conversion circuit, the specific manner of controlling the shorting of the two poles on the dc side of the inverter is:
all switching tubes connected in parallel between the direct current buses in the direct current conversion circuit are controlled to be continuously conducted;
Or alternatively
And in a first preset time, controlling all switching tubes connected in parallel between the direct current buses in the direct current conversion circuit to be continuously conducted.
Optionally, when the dc conversion circuit in the inverter is an isolated conversion circuit, the specific manner of controlling the short circuit of the two poles on the dc side of the inverter is:
any bridge arm connected in parallel between the direct current buses in the direct current conversion circuit is controlled to be continuously conducted;
Or alternatively
And in a second preset time, controlling any bridge arm connected in parallel between the direct current buses in the direct current conversion circuit to conduct continuously.
Optionally, the specific manner of controlling the dc side input voltage of the inverter to be smaller than the minimum value in the output voltages of the photovoltaic modules when each of the shutdown devices enters the shutdown state or the under-voltage protection state is as follows:
controlling the periodic short circuit of the two poles of the direct current side of the inverter;
In a period, the ratio of the short-circuit time of the two poles at the direct current side of the inverter to the short-circuit releasing time is larger than a preset duty ratio; and the preset duty ratio represents the minimum value in the output voltage of each path of photovoltaic module when each shutoff device enters a shutdown state or an under-voltage protection state.
Optionally, when the dc conversion circuit in the inverter is a non-isolated two-level conversion circuit, the specific manner of controlling the periodic shorting of the two poles on the dc side of the inverter is as follows:
all switching tubes connected in parallel between the direct current buses in the direct current conversion circuit are controlled to be periodically conducted, or all switching tubes connected in parallel between the direct current buses in the direct current conversion circuit are controlled to be periodically conducted within a third preset time;
at this time, in a period, the ratio of the time of shorting the two poles at the dc side of the inverter to the time of releasing the shorting is greater than a preset duty ratio, specifically:
In one period, the ratio of the on time to the off time of all the switching tubes connected in parallel between the direct current buses in the direct current conversion circuit is larger than the preset duty ratio.
Optionally, when the dc conversion circuit in the inverter is a non-isolated three-level conversion circuit, the specific manner of controlling the periodic shorting of the two poles on the dc side of the inverter is as follows:
The upper half switching tube and the lower half switching tube which are connected in parallel between the direct current buses in the direct current conversion circuit are controlled to be periodically and complementarily conducted;
at this time, in a period, the ratio of the time of shorting the two poles at the dc side of the inverter to the time of releasing the shorting is greater than a preset duty ratio, specifically:
in one period, the ratio of the on time to the off time of the upper half switching tube and the ratio of the on time to the off time of the lower half switching tube are both larger than the preset duty ratio.
Optionally, when the dc conversion circuit in the inverter is an isolated conversion circuit, the specific manner of controlling the periodic shorting of the two poles on the dc side of the inverter is:
Controlling the periodical complementary conduction of an upper bridge arm and a lower bridge arm which are connected in parallel on any bridge arm between direct current buses in the direct current conversion circuit;
at this time, in a period, the ratio of the time of shorting the two poles at the dc side of the inverter to the time of releasing the shorting is greater than a preset duty ratio, specifically:
In one period, the ratio of the on time to the off time of the upper bridge arm and the ratio of the on time to the off time of the lower bridge arm are both larger than the preset duty ratio.
Another aspect of the application provides a photovoltaic system comprising: the photovoltaic power generation system comprises a photovoltaic turn-off controller, an inverter and at least one path of photovoltaic group string; each path of photovoltaic group string comprises: at least N photovoltaic modules and N shut-off devices; n is a positive integer; wherein:
in each path of photovoltaic group string, the output end of each photovoltaic module is connected with the input end of the corresponding shutoff device, and the two poles of the output end of all the shutoff devices are cascaded with the two poles of the output end of the corresponding photovoltaic group string;
the output ends of the photovoltaic group strings are connected in parallel with the direct current side of the inverter, and the alternating current side of the inverter is connected with a power grid or a load;
the photovoltaic shutdown controller is connected to the inverter for performing the photovoltaic shutdown method according to any of the further aspects of the application.
Optionally, the photovoltaic shutdown controller is integrated in the inverter.
According to the technical scheme, the application provides a photovoltaic turn-off method. In the photovoltaic turn-off method, if the inverter enters a safe state, the input voltage of each turn-off device at the front stage of the inverter is reduced, so that each turn-off device enters a shutdown state or an under-voltage protection state, namely, the turn-off device is turned off; when each shutoff device of the front stage of the inverter is turned off, each path of photovoltaic string can enter a safe state, so that the photovoltaic shutoff method provided by the application can ensure that the photovoltaic string enters the safe state when the inverter enters the safe state.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are required to be used in the embodiments or the description of the prior art will be briefly described below, and it is obvious that the drawings in the following description are only embodiments of the present invention, and that other drawings can be obtained according to the provided drawings without inventive effort for a person skilled in the art.
Fig. 1 is a schematic diagram of a prior art inverter;
FIG. 2 is a schematic diagram of a prior art shutoff;
Fig. 3 is an IV curve of a first photovoltaic string and a second photovoltaic string connected to an inverter 20;
Fig. 4a, fig. 4b, and fig. 4c are three flow diagrams of the shutdown control method provided in the present disclosure;
FIG. 5 is a schematic diagram showing the variation of the input voltage and the output voltage of the shutoff device after the shutoff device enters under-voltage protection or stops;
Fig. 6 a-6 d are schematic diagrams of four variations of the control signal of the first switching tube K1 and the dc side input voltage of the inverter 20 in fig. 1, respectively;
FIG. 7 is a schematic diagram of a non-isolated three-level DC conversion circuit;
fig. 8 a-8 c are three variations of the dc side input voltage of the inverter and the control signals of the second switching tube K2 and the third switching tube K3 in fig. 7, respectively;
Fig. 9 is a schematic structural diagram of the photovoltaic system provided by the present application.
Detailed Description
The following description of the embodiments of the present application will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present application, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the application without making any inventive effort, are intended to be within the scope of the application.
In the present application, relational terms such as first and second, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one … …" does not exclude the presence of other like elements in a process, method, article, or apparatus that comprises the element.
In order to ensure that the photovoltaic string enters a safe state when the inverter is stopped, the embodiment of the application provides a photovoltaic shutdown method, the specific flow of which is shown in fig. 4a, which specifically comprises the following steps:
s110, judging whether the inverter enters a safe state.
If the inverter enters a safe state, executing step S120; and if the inverter does not enter the safe state, stopping executing the photovoltaic turn-off method provided by the application.
It should be noted that, when the inverter works normally, even if the number of the photovoltaic group strings connected to the inverter is different, no backward current will occur between the photovoltaic group strings, so that the photovoltaic turn-off method provided by the application does not need to be executed when the inverter works normally.
S120, reducing the input voltage of each shutoff device of the front stage of the inverter, so that each shutoff device enters a shutdown state or an under-voltage protection state.
Wherein, in general, the shutoff device is turned off when the output current of the shutoff device is smaller than a certain value; but in addition, when the input voltage of the shutoff device is smaller than a certain value, the shutoff device can enter a shutdown state or an under-voltage protection state, and the shutoff device can be turned off at the moment.
Therefore, after step S120, each of the shutters of the inverter front stage is turned off; when each shutoff device of the front stage of the inverter is turned off, each path of photovoltaic string enters a safe state, so that the photovoltaic turning-off method provided by the application can ensure that the photovoltaic string enters the safe state when the inverter enters the safe state.
In another embodiment of the present application, as shown in fig. 4b, the photovoltaic shutdown method further comprises the following steps before step S120:
s210, detecting whether backward current occurs between each path of photovoltaic group strings of the front stage of the inverter.
If the backward current occurs between the photovoltaic strings, executing step S120; and if no backward current exists among the photovoltaic group strings, stopping executing the photovoltaic turn-off method provided by the application.
It should be noted that, according to the background art, when there is a mismatch phenomenon between the photovoltaic strings, a reverse current will occur between the photovoltaic strings, in other words, if a reverse current occurs between the photovoltaic strings, it is indicated that there is a mismatch phenomenon between the photovoltaic strings at this time, so by executing step S210, it can be determined whether there is a mismatch phenomenon between the photovoltaic strings; in addition, when no backward current occurs between the photovoltaic strings, no mismatch phenomenon exists between the photovoltaic strings, so that when the inverter enters a safe state, the shutoff device can detect that the output current of the shutoff device is too small, thereby cutting off the connection between the photovoltaic module and the inverter, and therefore, when no backward current occurs between the photovoltaic strings, the photovoltaic shutoff method provided by the application does not need to be executed.
Another embodiment of the present application provides a specific implementation of step S120, whose specific flow is shown in fig. 4c, including the following steps:
And S310, controlling the direct-current side input voltage of the inverter to be smaller than the minimum value of the output voltages of the photovoltaic modules when the turnoff devices enter the shutdown state or the under-voltage protection state.
After step S310, the input voltage at the dc side of the inverter can ensure that each of the shutdown devices enters a shutdown state or an under-voltage protection state, so that each path of photovoltaic strings can be ensured to enter a safe state when the inverter enters the safe state.
It should be noted that, after the shutdown device enters the shutdown state or the under-voltage protection state, the input voltage and the output voltage of the shutdown device change as shown in fig. 5, before the shutdown device does not enter the shutdown state or the under-voltage protection state, the input voltage and the output voltage of the shutdown device gradually decrease over time, after the shutdown device enters the shutdown state or the under-voltage protection state, the input voltage of the shutdown device gradually rises to the open-circuit voltage of the corresponding photovoltaic module and is maintained, and the output voltage of the shutdown device drops to zero, that is, the shutdown device is turned off.
The above is only one specific embodiment in step S120, and in practical applications, including but not limited to the above embodiment, the present application is not limited thereto, and may be within the scope of the present application as the case may be.
In another embodiment of the present application, one embodiment of step S310 is as follows: and controlling the direct-current side two-pole short circuit of the inverter.
When the direct current conversion circuit in the inverter is a non-isolated conversion circuit, a specific way for controlling the direct current side two-pole short circuit of the inverter can be as follows: all switching tubes connected in parallel between the direct current buses in the direct current conversion circuit are controlled to be continuously conducted; the method can also be as follows: and in a first preset time, controlling all switching tubes connected in parallel between the direct current buses in the direct current conversion circuit to be continuously conducted.
Taking the non-isolated two-level dc conversion circuit 21 in fig. 1 as an example, the first switching tube K1 is controlled to be continuously turned on, so that two poles on the dc side of the inverter 20 can be shorted, and at this time, a control signal of the first switching tube K1 and a dc side input voltage of the inverter 20 are shown in fig. 6 a; or during the first preset time, the first switching tube K1 is controlled to be continuously turned on, or the two poles of the dc side of the inverter 20 may be shorted, at this time, the control signal of the first switching tube K1 and the dc side input voltage of the inverter 20 are as shown in fig. 6 b.
Taking the non-isolated three-level direct current conversion circuit shown in fig. 7 as an example, the second switching tube K2 and the third switching tube K3 are controlled to be continuously conducted, so that two poles of the direct current side of the inverter can be short-circuited, and at the moment, control signals of the second switching tube K2 and the third switching tube K3 and the direct current side input voltage of the inverter are shown in fig. 8 a; or in the first preset time, the second switching tube K2 and the third switching tube K3 are controlled to be continuously conducted, so that the two poles of the direct current side of the inverter can be short-circuited, and at the moment, the control signals of the second switching tube K2 and the third switching tube K3 and the direct current side input voltage of the inverter are shown in fig. 8 b.
The first preset time is a preset time, and is not specifically limited herein, and may be determined according to practical situations, which are all within the protection scope of the present application.
When the direct current conversion circuit in the inverter is an isolated conversion circuit, the specific mode for controlling the direct current side two-pole short circuit of the inverter is as follows: any bridge arm connected in parallel between the direct current buses in the direct current conversion circuit is controlled to be continuously conducted; or in a second preset time, any bridge arm connected in parallel between the direct current buses in the direct current conversion circuit is controlled to be continuously conducted.
The second preset time is a preset time, which is not specifically limited herein, and may be determined according to practical situations, and all the second preset time is within the protection scope of the present application.
The above-mentioned four embodiments are only four embodiments for controlling the direct-current side two-pole short circuit of the inverter, and in practical applications, including but not limited to the above-mentioned embodiments, the embodiments are not specifically limited herein, and the embodiments are all within the protection scope of the present application as the case may be.
In another embodiment of the present application, one embodiment of step S310 is as follows: and controlling the periodic short circuit of the two poles of the direct current side of the inverter.
In one period, the ratio of the short-circuit time of the two poles at the DC side of the inverter to the short-circuit releasing time is larger than a preset duty ratio; in addition, the preset duty ratio represents the minimum value in the output voltage of each path of photovoltaic module when each shutoff device enters a shutdown state or an under-voltage protection state.
When the direct current conversion circuit in the inverter is a non-isolated two-level conversion circuit, a specific mode of controlling the periodic short circuit of the two poles at the direct current side of the inverter can be as follows: all switching tubes connected in parallel between the direct current buses in the direct current conversion circuit are controlled to be periodically conducted; the method can also be as follows: and in a third preset time, controlling all switching tubes connected in parallel between the direct current buses in the direct current conversion circuit to conduct periodically.
At this time, in one period, the ratio of the short-circuit time of the two poles at the dc side of the inverter to the time of releasing the short-circuit is greater than a preset duty ratio, specifically: in one period, the ratio of the on time to the off time of all the switching tubes connected in parallel between the direct current buses in the direct current conversion circuit is larger than a preset duty ratio.
Taking the non-isolated two-level dc conversion circuit 21 in fig. 1 as an example, the first switching tube K1 is controlled to be periodically turned on, and at this time, as shown in fig. 6c, the ratio of the time when the control signal of the first switching tube K1 is at the high level to the time when the control signal is at the low level is greater than the preset duty ratio; or in a third preset time, the first switching tube K1 is controlled to be periodically turned on, and the ratio of the time when the control signal of the first switching tube K1 is at the high level to the time when the control signal is at the low level in one period is greater than the preset duty ratio as shown in fig. 6d, and the dc side input voltage of the inverter 20.
The third preset time is a preset time, and is not specifically limited herein, and may be determined according to practical situations, which are all within the protection scope of the present application.
When the direct current conversion circuit in the inverter is a non-isolated three-level conversion circuit, the specific mode of periodically shorting the two poles on the direct current side of the inverter is as follows: and controlling the periodic complementary conduction of an upper half switching tube and a lower half switching tube which are connected in parallel between the direct current buses in the direct current conversion circuit.
At this time, in one period, the ratio of the short-circuit time of the two poles at the dc side of the inverter to the time of releasing the short-circuit is greater than a preset duty ratio, specifically: in one period, the ratio of the on time to the off time of the upper half switching tube and the ratio of the on time to the off time of the lower half switching tube are larger than the preset duty ratio.
Taking the non-isolated three-level direct current conversion circuit shown in fig. 7 as an example, the second switching tube K2 and the third switching tube K3 are controlled to be periodically and complementarily turned on, at this time, the control signals of the second switching tube K2 and the third switching tube K3 and the direct current side input voltage of the inverter are controlled, and as shown in fig. 8c, in one period, the ratio of the on time to the off time of the second switching tube K2 and the ratio of the on time to the off time of the third switching tube K3 are both greater than the preset duty ratio.
When the direct current conversion circuit in the inverter is an isolated conversion circuit, the specific mode of periodically shorting the two poles on the direct current side of the inverter is as follows: and controlling the periodical complementary conduction of an upper bridge arm and a lower bridge arm which are connected in parallel on any bridge arm between the direct current buses in the direct current conversion circuit.
At this time, in one period, the ratio of the short-circuit time of the two poles at the dc side of the inverter to the time of releasing the short-circuit is greater than a preset duty ratio, specifically: the ratio of the on time to the off time of the upper bridge arm and the ratio of the on time to the off time of the lower bridge arm are both larger than the preset duty ratio.
The above-mentioned four embodiments, which are merely embodiments for shorting the periods of the two poles on the dc side of the inverter, are not limited to the above-mentioned embodiments, but are not specifically limited thereto, and they are all within the scope of the present application as the case may be.
In addition, the above embodiments are only two embodiments of step S120, and in practical applications, including but not limited to the above embodiments, the present application is not limited to the above embodiments, and the present application is applicable to any particular embodiment; however, the first embodiment can lower the dc side input voltage of the inverter more quickly, so that the photovoltaic string can enter a safe state in a shorter time, which is beneficial to system protection.
Another embodiment of the present application provides a photovoltaic system, whose specific structure is shown in fig. 9, specifically including: a photovoltaic shutdown controller 30, an inverter 20, and at least one photovoltaic string 10; each path of the photovoltaic string 10 includes: at least N photovoltaic modules 11 and N switches 12.
Wherein, N is a positive integer, the value of N is not specifically limited, and the value is within the protection scope of the application according to the specific situation.
In each path of photovoltaic group string 10, the output end of each photovoltaic module 11 is connected with the input end of a corresponding shutoff device 12, and the two poles of the output end of all the shutoff devices 12 are cascaded with the two poles of the output end of the corresponding photovoltaic group string 10; the output ends of the photovoltaic strings 10 are connected in parallel with the direct current side of the inverter 20, and the alternating current side of the inverter 20 is connected with a power grid or a load; the photovoltaic shutdown controller 30 is connected to the inverter 20 for performing the photovoltaic shutdown method provided by the embodiments.
Alternatively, the photovoltaic shutdown controller 30 may be integrated into the inverter 20, which is not specifically limited herein, and may be within the scope of the present application as the case may be.
It should be noted that, the photovoltaic quick turn-off system and the photovoltaic system both adopt the photovoltaic turn-off method provided by the embodiments, so that when the self inverter 20 is stopped, the self photovoltaic string 10 can be brought into a safe state, thereby improving the self power safety and the turn-off reliability, and being beneficial to market popularization.
The features described in the various embodiments of the present disclosure may be interchanged or combined with one another in the description of the disclosed embodiments to enable those skilled in the art to make or use the application. The above description is only of the preferred embodiment of the present application, and is not intended to limit the present application in any way. While the application has been described with reference to preferred embodiments, it is not intended to be limiting. Any person skilled in the art can make many possible variations and modifications to the technical solution of the present application or modifications to equivalent embodiments using the methods and technical contents disclosed above, without departing from the scope of the technical solution of the present application. Therefore, any simple modification, equivalent variation and modification of the above embodiments according to the technical substance of the present application still fall within the scope of the technical solution of the present application.
Claims (11)
1. A method of photovoltaic shutdown, comprising:
Judging whether the inverter enters a safe state;
If the inverter enters a safe state, reducing the input voltage of each shutoff device of the front stage of the inverter to enable each shutoff device to enter a shutdown state or an under-voltage protection state;
wherein, reduce the input voltage of each turn-off device of the preceding stage of the said inverter, make each said turn-off device enter the state of stopping or undervoltage protection, include:
and controlling the direct-current side input voltage of the inverter to be smaller than the minimum value of the output voltages of all the paths of photovoltaic modules when all the turnoff devices enter the shutdown state or the undervoltage protection state.
2. The photovoltaic shutdown method according to claim 1, further comprising, before the step of reducing the input voltage of each of the shutdown devices of the inverter front stage to bring each of the shutdown devices into a shutdown state or an undervoltage protection state:
Detecting whether a backward current occurs between each path of photovoltaic group strings of the front stage of the inverter;
and if the backward current occurs between the photovoltaic strings, returning to execute the step of reducing the input voltage of each shutoff device of the front stage of the inverter so that each shutoff device enters a shutdown state or an under-voltage protection state.
3. The method according to claim 1, wherein the specific manner of controlling the dc side input voltage of the inverter to be smaller than the minimum value of the output voltages of the photovoltaic modules when each of the shutdown state or the undervoltage protection state is:
And controlling the direct-current side two-pole short circuit of the inverter.
4. A photovoltaic shutdown method according to claim 3, wherein when the dc conversion circuit in the inverter is a non-isolated conversion circuit, the specific manner of controlling the dc side two-pole shorting of the inverter is:
all switching tubes connected in parallel between the direct current buses in the direct current conversion circuit are controlled to be continuously conducted;
Or alternatively
And in a first preset time, controlling all switching tubes connected in parallel between the direct current buses in the direct current conversion circuit to be continuously conducted.
5. A photovoltaic shutdown method according to claim 3, wherein when the dc conversion circuit in the inverter is an isolated conversion circuit, the specific manner of controlling the dc side two-pole shorting of the inverter is:
any bridge arm connected in parallel between the direct current buses in the direct current conversion circuit is controlled to be continuously conducted;
Or alternatively
And in a second preset time, controlling any bridge arm connected in parallel between the direct current buses in the direct current conversion circuit to conduct continuously.
6. The method according to claim 1, wherein the specific manner of controlling the dc side input voltage of the inverter to be smaller than the minimum value of the output voltages of the photovoltaic modules when each of the shutdown state or the undervoltage protection state is:
controlling the periodic short circuit of the two poles of the direct current side of the inverter;
In a period, the ratio of the short-circuit time of the two poles at the direct current side of the inverter to the short-circuit releasing time is larger than a preset duty ratio; and the preset duty ratio represents the minimum value in the output voltage of each path of photovoltaic module when each shutoff device enters a shutdown state or an under-voltage protection state.
7. The method according to claim 6, wherein when the dc conversion circuit in the inverter is a non-isolated two-level conversion circuit, the specific manner of controlling the periodic shorting of the two poles on the dc side of the inverter is:
all switching tubes connected in parallel between the direct current buses in the direct current conversion circuit are controlled to be periodically conducted, or all switching tubes connected in parallel between the direct current buses in the direct current conversion circuit are controlled to be periodically conducted within a third preset time;
at this time, in a period, the ratio of the time of shorting the two poles at the dc side of the inverter to the time of releasing the shorting is greater than a preset duty ratio, specifically:
In one period, the ratio of the on time to the off time of all the switching tubes connected in parallel between the direct current buses in the direct current conversion circuit is larger than the preset duty ratio.
8. The method according to claim 6, wherein when the dc conversion circuit in the inverter is a non-isolated three-level conversion circuit, the specific manner of controlling the periodic shorting of the two poles on the dc side of the inverter is:
The upper half switching tube and the lower half switching tube which are connected in parallel between the direct current buses in the direct current conversion circuit are controlled to be periodically and complementarily conducted;
at this time, in a period, the ratio of the time of shorting the two poles at the dc side of the inverter to the time of releasing the shorting is greater than a preset duty ratio, specifically:
in one period, the ratio of the on time to the off time of the upper half switching tube and the ratio of the on time to the off time of the lower half switching tube are both larger than the preset duty ratio.
9. The photovoltaic shutdown method according to claim 6, wherein when the dc conversion circuit in the inverter is an isolated conversion circuit, the specific manner of controlling the periodic shorting of the two poles on the dc side of the inverter is:
Controlling the periodical complementary conduction of an upper bridge arm and a lower bridge arm which are connected in parallel on any bridge arm between direct current buses in the direct current conversion circuit;
at this time, in a period, the ratio of the time of shorting the two poles at the dc side of the inverter to the time of releasing the shorting is greater than a preset duty ratio, specifically:
In one period, the ratio of the on time to the off time of the upper bridge arm and the ratio of the on time to the off time of the lower bridge arm are both larger than the preset duty ratio.
10. A photovoltaic system, comprising: the photovoltaic power generation system comprises a photovoltaic turn-off controller, an inverter and at least one path of photovoltaic group string; each path of photovoltaic group string comprises: at least N photovoltaic modules and N shut-off devices; n is a positive integer; wherein:
in each path of photovoltaic group string, the output end of each photovoltaic module is connected with the input end of the corresponding shutoff device, and the two poles of the output end of all the shutoff devices are cascaded with the two poles of the output end of the corresponding photovoltaic group string;
the output ends of the photovoltaic group strings are connected in parallel with the direct current side of the inverter, and the alternating current side of the inverter is connected with a power grid or a load;
The photovoltaic shutdown controller is connected to the inverter for performing the photovoltaic shutdown method of any of claims 1-9.
11. The photovoltaic system of claim 10, wherein the photovoltaic shutdown controller is integrated in the inverter.
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