WO2023045373A1 - 一种光伏发电系统及其控制方法和功率变换器 - Google Patents

一种光伏发电系统及其控制方法和功率变换器 Download PDF

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Publication number
WO2023045373A1
WO2023045373A1 PCT/CN2022/094855 CN2022094855W WO2023045373A1 WO 2023045373 A1 WO2023045373 A1 WO 2023045373A1 CN 2022094855 W CN2022094855 W CN 2022094855W WO 2023045373 A1 WO2023045373 A1 WO 2023045373A1
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Prior art keywords
photovoltaic
mlpe
state
string
photovoltaic string
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PCT/CN2022/094855
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English (en)
French (fr)
Inventor
俞雁飞
王新宇
李晓迅
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阳光电源股份有限公司
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Priority to EP22871434.1A priority Critical patent/EP4412024A1/en
Priority to AU2022350456A priority patent/AU2022350456A1/en
Publication of WO2023045373A1 publication Critical patent/WO2023045373A1/zh

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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
    • 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
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/0067—Converter structures employing plural converter units, other than for parallel operation of the units on a single load
    • H02M1/0077—Plural converter units whose outputs are connected in series
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/32—Means for protecting converters other than automatic disconnection
    • H02M1/325—Means for protecting converters other than automatic disconnection with means for allowing continuous operation despite a fault, i.e. fault tolerant converters
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/02—Conversion of dc power input into dc power output without intermediate conversion into ac
    • H02M3/04—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters
    • H02M3/10—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M3/145—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M3/155—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M3/156—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/02—Conversion of dc power input into dc power output without intermediate conversion into ac
    • H02M3/04—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters
    • H02M3/10—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M3/145—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M3/155—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M3/156—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators
    • H02M3/158—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators including plural semiconductor devices as final control devices for a single load
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/02—Conversion of dc power input into dc power output without intermediate conversion into ac
    • H02M3/04—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters
    • H02M3/10—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M3/145—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M3/155—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M3/156—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators
    • H02M3/158—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators including plural semiconductor devices as final control devices for a single load
    • H02M3/1582—Buck-boost converters
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
    • H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
    • H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • 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
    • H02S50/00—Monitoring or testing of PV systems, e.g. load balancing or fault identification
    • H02S50/10—Testing of PV devices, e.g. of PV modules or single PV cells
    • 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
    • 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

Definitions

  • the present application relates to the technical field of power electronics, in particular to a photovoltaic power generation system, a control method thereof, and a power converter.
  • each MLPE equipment In the existing photovoltaic power generation system with MLPE (Module Level Power Electronics, component-level power electronics) equipment, the input end of each MLPE equipment is connected to the corresponding photovoltaic module, and the output terminals of multiple MLPE equipment are connected in series to form a photovoltaic string.
  • MLPE Module Level Power Electronics, component-level power electronics
  • the MLPE equipment such as a component disconnector or a power optimizer, has a power semiconductor device inside it, which is used to control the electric energy flowing through it in the normal output state; and, it also has a bypass diode inside it, used for In the bypass operation state, the photovoltaic modules connected to itself are bypassed from the corresponding photovoltaic strings, and a flow path is provided for the photovoltaic strings.
  • the conduction voltage drop of the bypass diode is significantly higher than that of the power semiconductor device, the loss and heat generation of the MLPE device in the bypass operation state are much higher than those in the normal output state; therefore, the The bypass diode of the MLPE device usually needs to select a diode with a large power capacity, and the heat dissipation of the MLPE device should also be designed according to the heat generation in the bypass operation state; therefore, the system cost is high.
  • This application provides a photovoltaic power generation system and its control method and power converter to reduce the power consumption of MLPE equipment in bypass operation, so that diodes with lower power capacity and heat dissipation designs with lower heat dissipation requirements can be selected, saving system cost.
  • the first aspect of the present application provides a method for controlling a photovoltaic power generation system.
  • the photovoltaic power generation system includes: at least one photovoltaic string and its downstream power converter, and the photovoltaic string includes at least two output terminals connected in series Component-level power electronic MLPE equipment, the input ends of each of the MLPE equipment are respectively connected to corresponding photovoltaic modules; the control method includes:
  • the MLPE state characterization information it is judged whether at least one of the MLPE devices in the photovoltaic string is not in a normal output state
  • obtain the MLPE state characterization information of the photovoltaic string including:
  • the operating data of each of the MLPE devices in the photovoltaic string is respectively obtained as the MLPE state characterization information.
  • judging whether at least one of the MLPE devices in the photovoltaic string is not in a normal output state includes:
  • judging whether at least one of the MLPE devices in the photovoltaic string is not in a normal output state includes:
  • At least one of the MLPE devices in the photovoltaic string is in the fault state, it is determined that it is not in the normal output state.
  • judging whether at least one of the MLPE devices in the photovoltaic string is not in a normal output state includes:
  • the operating data of each of the MLPE devices in the photovoltaic string if there is at least one of the MLPE devices that has not obtained the temperature data corresponding to the operating data, it also includes:
  • judging whether at least one of the MLPE devices in the photovoltaic string is not in a normal output state includes:
  • obtain the MLPE state characterization information of the photovoltaic string including:
  • the operating parameters of the photovoltaic string are obtained as the MLPE state characterization information.
  • the operating parameters include: at least one of voltage, current and power.
  • the photovoltaic string before obtaining the MLPE state characterization information of the photovoltaic string, it also includes: changing the operating state of the photovoltaic string;
  • Judging whether at least one of the MLPE devices in the photovoltaic string is not in a normal output state includes: judging whether the variation of the operating parameters of the photovoltaic string before and after its operating state changes exceeds a preset variation; if the If the variation of the operating parameter exceeds the preset variation, it is determined that at least one of the MLPE devices is not in the normal output state.
  • judging whether at least one of the MLPE devices in the photovoltaic strings is not in a normal output state includes:
  • controlling the corresponding string current to be less than a preset threshold includes:
  • the corresponding string current is made smaller than the preset threshold.
  • the action of the power converter includes: disturbing the operating voltage or current of the photovoltaic string.
  • controlling the corresponding string current to be less than a preset threshold includes:
  • the current of the corresponding string is lower than the preset threshold.
  • the mode of changing the operating state of the corresponding MLPE equipment in the photovoltaic string is any one of the following: opening, closing, power derating, canceling power derating, increasing output current, and reducing output current.
  • the second aspect of the present application provides a power converter, including: a main circuit and a control unit; wherein:
  • the input end of the main circuit is connected to at least one photovoltaic string;
  • the photovoltaic string includes at least two MLPE devices whose output ends are connected in series, and the input ends of each of the MLPE devices are respectively connected to corresponding photovoltaic modules;
  • the main circuit is controlled by the control unit;
  • the control unit is further configured to execute the control method of the photovoltaic power generation system as described in any paragraph of the first aspect above.
  • the main circuit includes: a DC/AC conversion circuit, or, a DC/DC conversion circuit, or, a DC/AC conversion circuit and at least one DC/DC conversion circuit arranged in front of it.
  • the third aspect of the present application provides a photovoltaic power generation system, including: the power converter as described in any paragraph of the second aspect above and at least one photovoltaic string arranged in its preceding stage;
  • the photovoltaic string includes at least two MLPE devices with output terminals connected in series;
  • each of the MLPE devices are respectively connected to corresponding photovoltaic modules.
  • the control method of the photovoltaic power generation system first obtains the MLPE state representation information of the photovoltaic string, and then judges whether there is at least one MLPE device in the photovoltaic string that is not in the normal output state according to the MLPE state representation information; if the photovoltaic string If there is at least one MLPE device in the string that is not in the normal output state, the current of the corresponding string is controlled to be less than the preset threshold; thereby reducing the power consumption of the corresponding MLPE device in the bypass operation state, so that the MLPE device can be designed with a smaller Bypass diodes for power capacity and heat dissipation measures with lower heat dissipation requirements save system cost.
  • FIG. 1 is a schematic structural diagram of a component disconnector provided by the prior art
  • FIG. 1 and Figure 2b are two structural schematic diagrams of power optimizers provided by the prior art
  • FIG. 3 is a schematic structural diagram of a photovoltaic power generation system provided in an embodiment of the present application.
  • Fig. 4 is a flowchart of a control method for a photovoltaic power generation system provided by an embodiment of the present application.
  • the term "comprises”, “comprises” or any other variation thereof is intended to cover a non-exclusive inclusion such that a process, method, article, or apparatus comprising a set of elements includes not only those elements, but also includes none. other elements specifically listed, or also include elements inherent in such a process, method, article, or apparatus.
  • an element defined by the phrase “comprising a " does not exclude the presence of additional identical elements in the process, method, article or apparatus comprising said element.
  • MLPE devices can be module disconnectors or power optimizers.
  • FIG. 1 shows the common structure of the module switch.
  • the conduction state that is, the normal output state
  • the power semiconductor device S is closed, the bypass diode D is cut off, and the photovoltaic module outputs electric energy to the outside.
  • the off state that is, in the bypass operation state
  • the power semiconductor device S is disconnected, the photovoltaic module at the input end no longer outputs electric energy, and the current of the photovoltaic string will pass through the bypass diode D to form a path.
  • the turn-on voltage drop of the bypass diode D is significantly higher than the turn-on voltage drop of its power semiconductor device S, resulting in the loss and heat generation of the component switch in the off state, which is much higher than that in the on state. Therefore, the bypass diode D of the component switch should be selected with a larger power capacity, and the heat dissipation of the component switch should be designed according to the heat generation in the off state.
  • the power optimizer uses a high-frequency switching tube to perform MPPT (Maximum Power Point Tracking, maximum power point tracking), and outputs the maximum power of the module. If the MPPT function of a single power optimizer fails, the string current will pass through the output terminal of the power optimizer ( The bypass diodes of String Side as shown in Figure 2a and Figure 2b) form the path. For example, the disconnection of the input terminal (PV Side as shown in Figure 2a and Figure 2b) from the photovoltaic module causes the power optimizer to lose power supply, or the MPPT function fails due to damage to the internal control circuit. For example, in the Buck-type optimizer shown in Figure 2a, after the MPPT function fails, its bypass diode D provides a flow path for the photovoltaic string.
  • MPPT Maximum Power Point Tracking, maximum power point tracking
  • the power optimizer will enter the bypass operation state after the MPPT function fails, and the heat generation is greater than that in the MPPT operation mode. It is necessary to select a diode with a larger power capacity, and the heat dissipation capacity of the whole machine needs to be in accordance with the diode heat generation in the bypass operation state. situation to design.
  • the present application provides a control method for a photovoltaic power generation system to reduce the power consumption of MLPE equipment in bypass operation, so that diodes with lower power capacity and heat dissipation designs with lower heat dissipation requirements can be selected to save system costs.
  • the photovoltaic power generation system includes: at least one photovoltaic string 101 (two are shown as an example in FIG. 3 ) and a subsequent power converter 102 . That is, the power converter 102 belongs to a power converter at the string level.
  • the photovoltaic string 101 includes at least two MLPE devices whose output ends are connected in series, and the input ends of each MLPE device are respectively connected to corresponding photovoltaic modules; in practical applications, each MLPE device can be connected to a photovoltaic module (as shown in Figure 3 ), or two or more photovoltaic modules can be connected, depending on the specific application environment.
  • Each MLPE device in the photovoltaic string 101 can be a power optimizer that performs a power regulation function, or a module disconnector that only performs a shutdown function, or a mixture of a power optimizer and a module disconnector Installation is not limited here, all within the scope of protection of the present application.
  • the control method may be implemented by the control unit in the power converter 102, the system controller of the photovoltaic power generation system, or an additional controller, etc., depending on the specific application environment. All are within the protection scope of the present application; the following uses the control unit in the power converter 102 as an example for illustration.
  • control method includes:
  • the MLPE state representation information is information that can characterize the state of the MLPE equipment in the photovoltaic string. Specifically, it can be the operating data of each MLPE equipment obtained by the control unit of the power converter through communication. The operating data can directly represent each MLPE The state of the equipment; or, the MLPE state representation information can also be the operating parameters of the photovoltaic string detected by the control unit, through which the output of the photovoltaic string can be represented, and then reflect whether there is at least one MLPE inside it The state of the equipment changes; the specific selection of the MLPE state representation information may depend on its specific application environment, and all are within the scope of protection of this application.
  • step S101 may be performed in real time or periodically, depending on the specific application environment.
  • the MLPE state characterization information determine whether there is at least one MLPE device in the photovoltaic string that is not in a normal output state.
  • the corresponding photovoltaic module performs normal power output through the MLPE equipment, and the conduction voltage drop of the power semiconductor device inside the MLPE equipment is small, so the power consumption and temperature of the MLPE equipment are within the normal range.
  • any at least one MLPE device when any at least one MLPE device is not in the normal output state, such as in the bypass operation state, the MLPE device will flow the string current through its internal bypass diode; due to the high conduction voltage drop of the bypass diode , at this time, if the cost is not sacrificed, the selection specifications and heat dissipation specifications of the bypass diode are improved, and it is allowed to work according to the traditional scheme, the power consumption and/or temperature of the MLPE equipment will exceed the corresponding normal range, which will easily lead to The device is damaged or a safety accident; therefore step S103 needs to be executed.
  • the control unit After the control unit recognizes that at least one MLPE device is not in the normal output state, it controls the current of the corresponding photovoltaic string not to exceed the preset threshold, thereby reducing the heating power of the MLPE device and making the entire system in a state of reliable operation. state. For example, under normal conditions, the maximum current of the photovoltaic string is 15A. After the control unit recognizes that at least one MLPE device is not in the normal output state, it can control the current of the corresponding photovoltaic string to not exceed 11A.
  • the control method provided by this embodiment can reduce the power consumption of the corresponding MLPE equipment in the bypass operation state through the above principles, so that the bypass diode with smaller power capacity can be used in the design of the MLPE equipment, and it can also use heat dissipation Lower heat dissipation measures are required, which avoids the problem of sacrificing cost in exchange for reliable operation of the system in the prior art.
  • control unit and each MLPE device have a communication mechanism, that is, the control unit and each MLPE device can communicate with each other as an example, and the control method is described in detail illustrate:
  • the communication between the control unit and each MLPE device can specifically be PLC (Power Line Carrier Communication) communication, ZigBee communication, etc.; it is not limited here, it depends on the application environment, and it is all described in this application within the scope of protection.
  • PLC Power Line Carrier Communication
  • ZigBee communication etc.; it is not limited here, it depends on the application environment, and it is all described in this application within the scope of protection.
  • Step S101 may specifically be: through communication, obtain the operation data of each MLPE device in the photovoltaic string as MLPE state characterization information.
  • Step S102 judging whether there is at least one MLPE device in the photovoltaic string that is not in a normal output state, which can be implemented in the following multiple forms:
  • the operation data can reflect the state of the corresponding MLPE equipment, such as normal output state or bypass operation state.
  • Step S102 may specifically include: judging whether there is at least one MLPE device in a bypass operation state in the photovoltaic string.
  • step S103 can be executed, thereby reducing the power consumption of the MLPE device in the bypass operation state, so that the MLPE device can Bypass diodes with smaller power capacity and heat dissipation measures can be used.
  • step S102 further includes: judging whether there is at least one MLPE device in a fault state in the photovoltaic string.
  • step S103 can be executed, so as to avoid the expansion of the fault caused by the large current of the MLPE device.
  • step S102 further includes: judging whether at least one MLPE device in the photovoltaic string is in an overtemperature state.
  • step S103 can be executed, thereby reducing the power consumption of the MLPE device in the bypass operation state, avoiding further deterioration of the over-temperature, and making the MLPE equipment can be designed with smaller power capacity bypass diodes and heat dissipation measures.
  • control method further includes: calculating the temperature data of other MLPE devices within a preset distance for the MLPE device that has not obtained the temperature data , get its temperature data. For example, select the temperature data of several adjacent MLPE devices, and calculate the temperature of the target MLPE device after weighted average.
  • the state of the MLPE equipment that can be identified also includes a communication disconnection state.
  • the communication loss of the MLPE equipment is likely to be caused by damage or abnormality of the MLPE equipment, such as damage to the power circuit, disconnection of the connection with the photovoltaic module at the input end, etc.
  • the MLPE equipment may run in the bypass operation state.
  • step S102 further includes: judging whether at least one MLPE device in the photovoltaic string is in a communication disconnected state.
  • step S103 can be executed, thereby reducing the power consumption of the MLPE device in bypass operation and preventing the target MLPE device from being in the bypass state Overheating and fault expansion during operation.
  • control unit can also obtain the operating parameters of the photovoltaic string through detection, as MLPE state representation information, to implement step S101; this situation is applicable to scenarios without a communication system, or the The scenario where the control unit can only send commands to the MLPE device in one direction.
  • the operating parameters include: at least one of voltage, current and power; it depends on the specific application environment, and all of them are within the protection scope of the present application.
  • step S102 may specifically be: detecting whether the open circuit voltage of the photovoltaic string is significantly lower than the prestored open circuit voltage value, and if so, determining that at least one MLPE device is in a fault or abnormal state, and then performing step S103.
  • step S102 may also be: detecting whether the current of the photovoltaic string exceeds a preset current value, and if so, performing step S103 to prevent overheating of the MLPE equipment.
  • different preset current values can also be set at different temperatures; because usually, the settings for MLPE equipment will allow it to withstand higher current at low temperatures, even if the temperature rise is higher Dangerous over-temperature values are also not reached; therefore, a higher preset current value can be set at lower temperatures, and a lower preset current value can be set at higher temperatures to give full play to the MLPE equipment and Power generation performance of photovoltaic strings.
  • the temperature used here can be collected by using the temperature sensor set by the power converter itself. Of course, it does not rule out the temperature collected by the MLPE equipment; it depends on the specific application environment. Yes, all within the protection scope of this application.
  • step S101 it is first performed: changing the operating state of the photovoltaic string.
  • step S102 includes: judging whether the variation of the operating parameters of the photovoltaic string before and after the change of its operating state exceeds the preset variation; normal output state.
  • control unit controls the photovoltaic string to be in a certain state, and then detects the operating parameters of the photovoltaic string at this time to determine whether at least one MLPE device is not in a normal output state. For example, the control unit first issues instructions to control all MLPE equipment photovoltaic strings to stop external output, and then detects the voltage of the photovoltaic strings. If the voltage of the photovoltaic strings is found to be significantly high, it is judged that at least one MLPE equipment is faulty or abnormal. state.
  • step S102 includes: judging whether the difference between the same operating parameters of each photovoltaic string is greater than the corresponding preset difference; if each If the difference between the same operating parameters of the photovoltaic strings is greater than the corresponding preset difference, it is determined that at least one MLPE device in at least one photovoltaic string is not in a normal output state.
  • the initial open-circuit voltage of the two photovoltaic strings is 800V, and the open-circuit voltage of one photovoltaic string suddenly drops to 750V, it is judged that there may be a MLPE equipment is in an abnormal state.
  • the power converter can be a single-stage inverter implemented by a DC/AC conversion circuit, or it can be a DC/AC conversion circuit and its preceding stage at least A DC/DC conversion circuit constitutes a two-level inverter, and only one integrated control unit is set in the two-level inverter to realize the control of the conversion circuits at all levels; in addition, the power converter can also be a separate A DC/DC converter, for example, a Boost converter in the front stage of a photovoltaic inverter, or a Boost converter with an independent control unit inside a two-stage inverter.
  • the power converter has at least one power conversion unit, the power conversion unit is a DC/DC converter and/or DC/AC converter, and the control unit can control the power conversion unit To change the current of the photovoltaic string connected to it. That is, step S103 may be implemented by the power converter itself, and the step S103 specifically includes: making the corresponding group string current less than a preset threshold through actions of the power converter.
  • the actions of the power converter include: disturbing the operating voltage or current of the photovoltaic string, thereby changing the current of the photovoltaic string to be less than a preset threshold.
  • step S103 may also include: making the current of the corresponding string less than a preset threshold by changing the operating state of the corresponding MLPE equipment in the photovoltaic string. That is, the control unit can change the operating state of the MLPE equipment by sending instructions to the MLPE equipment, so as to change the current of the photovoltaic string at the input end.
  • the mode of changing the operating state of the corresponding MLPE equipment in the photovoltaic string can be any of the following: opening, closing, power derating, canceling power derating, increasing output current, and reducing output current.
  • control unit can issue commands to turn on and off the MLPE device to at least one MLPE device, so that the photovoltaic module at the input end can be connected to the photovoltaic string or disconnected from the photovoltaic string, so as to change the current of the photovoltaic string Effect.
  • the control unit can issue a power derating or cancel power derating command to at least one MLPE device to adjust the output power, so as to realize the change of the photovoltaic group The effect of the series current.
  • the control unit can issue a current regulation command, such as an command to increase the output current or a command to reduce the output current, to at least one MLPE device to adjust Output current, so as to achieve the effect of changing the current of the photovoltaic string.
  • a current regulation command such as an command to increase the output current or a command to reduce the output current
  • FIG. 1 Another embodiment of the present application also provides a power converter, including: a main circuit and a control unit; wherein:
  • the main circuit may only include a DC/AC conversion circuit, or may only include a DC/DC conversion circuit, or may also include a DC/AC conversion circuit and at least one DC/DC conversion circuit provided in its preceding stage.
  • the input end of the main circuit is connected to at least one photovoltaic string;
  • the photovoltaic string includes at least two MLPE devices whose output ends are connected in series, and the input ends of each MLPE device are respectively connected to corresponding photovoltaic modules.
  • the main circuit is controlled by the control unit; moreover, the control unit is also used to execute the control method described in any of the above-mentioned embodiments; the specific process and principle of the control method can refer to the above-mentioned embodiment, and will not be repeated here Let me repeat them one by one.
  • FIG. 3 Another embodiment of the present application also provides a photovoltaic power generation system, as shown in FIG. 3 , including: a power converter 102 and at least one photovoltaic string 101 arranged in front of it.
  • the photovoltaic string includes at least two MLPE devices whose output ends are connected in series; the input ends of each MLPE device are respectively connected to corresponding photovoltaic modules.
  • the structure and working principle of the power converter 102 can be referred to the above-mentioned embodiments, and will not be repeated here.
  • the DC side of the DC/AC conversion circuit is used as the input terminal, connected to a photovoltaic string, or at least two parallel connected photovoltaic strings; in the power converter
  • the input ends of each DC/DC conversion circuit are respectively connected to a photovoltaic string, or are respectively connected to at least two parallel connected photovoltaic strings; depending on the specific application environment.
  • the power converter 102 can specifically be an inverter.
  • this photovoltaic power generation system is linked with the MLPE equipment through the inverter, avoiding the scenario where the MLPE equipment bypasses a large current, and makes the MLPE equipment Compared with the prior art, the cost is lower, which is favorable for popularization and application.
  • each embodiment in this specification is described in a progressive manner, the same and similar parts of each embodiment can be referred to each other, and each embodiment focuses on the differences from other embodiments.
  • the description is relatively simple, and for related parts, please refer to the part of the description of the method embodiment.
  • the systems and system embodiments described above are only illustrative, and the units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is It can be located in one place, or it can be distributed to multiple network elements. Part or all of the modules can be selected according to actual needs to achieve the purpose of the solution of this embodiment. It can be understood and implemented by those skilled in the art without creative effort.

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Abstract

本申请提供一种光伏发电系统及其控制方法和功率变换器，其控制方法中首先获取光伏组串的MLPE状态表征信息，然后根据MLPE状态表征信息，判断光伏组串中是否存在至少一个MLPE设备未处于正常输出状态；若光伏组串中存在至少一个MLPE设备未处于正常输出状态，则控制相应的组串电流小于预设阈值；从而降低相应MLPE设备在旁路运行状态下的功耗，使MLPE设备在设计时可以采用更小功率容量的旁路二极管以及散热要求较低的散热措施，节省系统成本。

Description

一种光伏发电系统及其控制方法和功率变换器
本申请要求于2021年09月27日提交中国专利局、申请号为202111134707.8、发明名称为“一种光伏发电系统及其控制方法和功率变换器”的中国专利申请的优先权，其全部内容通过引用结合在本申请中。
技术领域
本申请涉及电力电子技术领域，特别涉及一种光伏发电系统及其控制方法和功率变换器。
背景技术
在现有的带MLPE(Module Level Power Electronics，组件级电力电子)设备的光伏发电系统中，各MLPE设备的输入端连接相应的光伏组件，多个MLPE设备的输出端依次串联形成光伏组串。
该MLPE设备，比如组件关断器或者功率优化器，其内部均具有功率半导体器件，用于在正常输出状态下对流过其中的电能进行控制；并且，其内部还均具有旁路二极管，用于在旁路运行状态下将自身所接的光伏组件从相应光伏组串中旁路掉，并为该光伏组串提供通流路径。
由于其中旁路二极管的导通压降要显著高于功率半导体器件的导通压降，导致该MLPE设备在旁路运行状态下的损耗和发热，均比正常输出状态下高很多；所以，该MLPE设备的旁路二极管通常需要选择功率容量较大的二极管，并且，该MLPE设备的散热，也要以旁路运行状态下的发热情况来进行设计；因此，系统成本高。
发明内容
本申请提供一种光伏发电系统及其控制方法和功率变换器，以降低MLPE设备在旁路运行状态下的功耗，从而可以选择功率容量较低的二极管以及散热要求较低的散热设计，节省系统成本。
为实现上述目的，本申请提供如下技术方案：
本申请第一方面提供了一种光伏发电系统的控制方法，所述光伏发电系统包括：至少一个光伏组串及其后级的功率变换器，所述光伏组串包括至少两个输出端串联连接的组件级电力电子MLPE设备，各所述MLPE设备的输入端分别连接相应的光伏组件；所述控制方法包括：
获取所述光伏组串的MLPE状态表征信息；
根据所述MLPE状态表征信息，判断所述光伏组串中是否存在至少一个所述MLPE设备未处于正常输出状态；
若所述光伏组串中存在至少一个所述MLPE设备未处于所述正常输出状态，则控制相应的组串电流小于预设阈值。
可选的，获取所述光伏组串的MLPE状态表征信息，包括：
通过通信，分别获取所述光伏组串中各所述MLPE设备的运行数据，作为所述MLPE状态表征信息。
可选的，判断所述光伏组串中是否存在至少一个所述MLPE设备未处于正常输出状态，包括：
判断所述光伏组串中是否存在至少一个所述MLPE设备处于旁路运行状态；
若所述光伏组串中存在至少一个所述MLPE设备处于所述旁路运行状态，则判定其未处于所述正常输出状态。
可选的，判断所述光伏组串中是否存在至少一个所述MLPE设备未处于正常输出状态，包括：
判断所述光伏组串中是否存在至少一个所述MLPE设备处于故障状态；
若所述光伏组串中存在至少一个所述MLPE设备处于所述故障状态，则判定其未处于所述正常输出状态。
可选的，判断所述光伏组串中是否存在至少一个所述MLPE设备未处于正常输出状态，包括：
判断所述光伏组串中是否存在至少一个所述MLPE设备处于过温状态；
若所述光伏组串中存在至少一个所述MLPE设备处于所述过温状态，则判定其未处于所述正常输出状态。
可选的，在分别获取所述光伏组串中各所述MLPE设备的运行数据之后，若存在至少一个所述MLPE设备未获取到其对应所述运行数据中的温度数据，则还包括：
对未获取到所述温度数据的所述MLPE设备，以其预设距离内的其他所述MLPE设备的所述温度数据进行计算，得到其所述温度数据。
可选的，判断所述光伏组串中是否存在至少一个所述MLPE设备未处于正常输出状态，包括：
判断所述光伏组串中是否存在至少一个所述MLPE设备处于通信失联状态；
若所述光伏组串中存在至少一个所述MLPE设备处于所述通信失联状态，则判定其未处于所述正常输出状态。
可选的，获取所述光伏组串的MLPE状态表征信息，包括：
通过检测，获取所述光伏组串的运行参数，作为所述MLPE状态表征信息。
可选的，所述运行参数包括：电压、电流和功率中的至少一种。
可选的，在获取所述光伏组串的MLPE状态表征信息之前，还包括：改变所述光伏组串的运行状态；
判断所述光伏组串中是否存在至少一个所述MLPE设备未处于正常输出状态，包括：判断所述光伏组串在其运行状态改变前后的运行参数变化量是否超过预设变化量；若所述运行参数变化量超过所述预设变化量，则判定其中存在至少一个所述MLPE设备未处于所述正常输出状态。
可选的，所述光伏组串的数量大于1时，判断所述光伏组串中是否存在至少一个所述MLPE设备未处于正常输出状态，包括：
判断各所述光伏组串的同一种所述运行参数之差是否大于相应预设差值；
若各所述光伏组串的同一种所述运行参数之差大于相应预设差值，则判定至少一个所述光伏组串中存在至少一个所述MLPE设备未处于正常输出状态。
可选的，控制相应的组串电流小于预设阈值，包括：
通过所述功率变换器的动作，使相应的组串电流小于所述预设阈值。
可选的，所述功率变换器的动作包括：对所述光伏组串的运行电压或者电流进行扰动。
可选的，控制相应的组串电流小于预设阈值，包括：
通过改变所述光伏组串中相应所述MLPE设备的运行状态，使相应的组串电流小于所述预设阈值。
可选的，对所述光伏组串中相应所述MLPE设备运行状态的改变方式， 为以下任意一种：开启、关闭、功率降额、取消功率降额、提高输出电流和降低输出电流。
本申请第二方面提供了一种功率变换器，包括：主电路和控制单元；其中：
所述主电路的输入端连接至少一个光伏组串；所述光伏组串包括至少两个输出端串联连接的MLPE设备，各所述MLPE设备的输入端分别连接相应的光伏组件；
所述主电路受控于所述控制单元；
所述控制单元还用于执行如上述第一方面任一段落所述的光伏发电系统的控制方法。
可选的，所述主电路包括：DC/AC变换电路，或者，DC/DC变换电路，又或者，DC/AC变换电路及设置于其前级的至少一个DC/DC变换电路。
本申请第三方面提供了一种光伏发电系统，包括：如上述第二方面任一段落所述的功率变换器及设置于其前级的至少一个光伏组串；
所述光伏组串包括至少两个输出端串联连接的MLPE设备；
各所述MLPE设备的输入端分别连接相应的光伏组件。
本申请提供的光伏发电系统的控制方法，其首先获取光伏组串的MLPE状态表征信息，然后根据MLPE状态表征信息，判断光伏组串中是否存在至少一个MLPE设备未处于正常输出状态；若光伏组串中存在至少一个MLPE设备未处于正常输出状态，则控制相应的组串电流小于预设阈值；从而降低相应MLPE设备在旁路运行状态下的功耗，使MLPE设备在设计时可以采用更小功率容量的旁路二极管以及散热要求较低的散热措施，节省系统成本。
附图说明
为了更清楚地说明本申请实施例或现有技术中的技术方案，下面将对实施例或现有技术描述中所需要使用的附图作简单地介绍，显而易见地，下面描述中的附图仅仅是本申请的一些实施例，对于本领域普通技术人员来讲，在不付出创造性劳动的前提下，还可以根据这些附图示出的结构获得其他的附图。
图1为现有技术提供的组件关断器的结构示意图；
图2a和图2b为现有技术提供的功率优化器的两种结构示意图；
图3为本申请实施例提供的光伏发电系统的结构示意图；
图4为本申请实施例提供的光伏发电系统的控制方法的流程图。
具体实施方式
下面将结合本申请实施例中的附图，对本申请实施例中的技术方案进行清楚、完整地描述，显然，所描述的实施例仅仅是本申请一部分实施例，而不是全部的实施例。基于本申请中的实施例，本领域普通技术人员在没有做出创造性劳动前提下所获得的所有其他实施例，都属于本申请保护的范围。
在本申请中，术语“包括”、“包含”或者其任何其他变体意在涵盖非排他性的包含，从而使得包括一系列要素的过程、方法、物品或者设备不仅包括那些要素，而且还包括没有明确列出的其他要素，或者是还包括为这种过程、方法、物品或者设备所固有的要素。在没有更多限制的情况下，由语句“包括一个……”限定的要素，并不排除在包括所述要素的过程、方法、物品或者设备中还存在另外的相同要素。
实际应用中，MLPE设备可以是组件关断器或者功率优化器等。
图1所示为组件关断器的常用结构，在导通状态也即正常输出状态下，其功率半导体器件S闭合，旁路二极管D截止，光伏组件对外输出电能。在关断状态也即旁路运行状态下，其功率半导体器件S断开，输入端的光伏组件不再对外输出电能，光伏组串的电流将经过旁路二极管D形成通路。旁路二极管D的导通压降要显著高于其功率半导体器件S的导通压降，导致组件关断器在关断状态下的损耗和发热，比导通状态下高很多。因此，组件关断器的旁路二极管D要选择功率容量较大的二极管，并且组件关断器的散热要以关断状态下的发热情况来设计。
功率优化器采用高频开关管来执行MPPT(Maximum Power Point Tracking，最大功率点跟踪)，输出组件的最大功率，若单个功率优化器的MPPT功能失效，组串电流将经过功率优化器输出端(如图2a和图2b中所示的String Side)的旁路二极管形成通路。例如输入端(如图2a和图2b中所示的PV Side)与光伏组件的连接断开导致功率优化器失去供电、或者内部控制电路损坏而导致的MPPT功能失效。例如，图2a中所示的Buck型优化器，在MPPT功能失效后，其旁路二极管D为光伏组串提供通流路径。同理，图2b中所示的 BuckBoost型优化器，在MPPT功能失效后，旁路二极管D1和D2为光伏组串提供通流路径。因此，功率优化器在MPPT功能失效后会进入旁路运行状态，发热比MPPT工作模式下大，需要选择较大功率容量的二极管，并且整机的散热能力需要按照旁路运行状态下的二极管发热情况来设计。
本申请提供一种光伏发电系统的控制方法，以降低MLPE设备在旁路运行状态下的功耗，从而可以选择功率容量较低的二极管以及散热要求较低的散热设计，节省系统成本。
如图3所示，该光伏发电系统包括：至少一个光伏组串101(图3中以两个为例进行展示)及其后级的功率变换器102。也即，该功率变换器102属于组串级别的功率变换器。
光伏组串101包括至少两个输出端串联连接的MLPE设备，且各MLPE设备的输入端分别连接相应的光伏组件；实际应用中每个MLPE设备可以分别连接一个光伏组件(如图3中所示)，也可以连接两个或更多个光伏组件，视其具体应用环境而定即可。
该光伏组串101内的各个MLPE设备可以均是执行功率调节功能的功率优化器，也可以均是只做关断功能的组件关断器，还可以是功率优化器和组件关断器的混合安装，此处不做限定，均在本申请的保护范围内。
执行该控制方法的，可以是该功率变换器102中的控制单元，也可以是该光伏发电系统的系统控制器，还可以是额外增加的控制器等，视其具体应用环境而定即可，均在本申请的保护范围内；下面以功率变换器102中的控制单元为例进行说明。
参见图4，该控制方法包括：
S101、获取光伏组串的MLPE状态表征信息。
该MLPE状态表征信息，是一个能够表征光伏组串内MLPE设备状态的信息，其具体可以是该功率变换器的控制单元通过通信获取的各MLPE设备的运行数据，该运行数据能够直接表征各个MLPE设备的状态；或者，该MLPE状态表征信息也可以是该控制单元检测得到的光伏组串的运行参数，通过该运行参数能够表征该光伏组串的输出情况，进而体现其内部是否有至少一个MLPE设备出现状态变化；该MLPE状态表征信息的具体选择可以视其具体应用环境 而定，均在本申请的保护范围内。
实际应用中，可以实时或周期性执行步骤S101，视其具体应用环境而定即可。
S102、根据MLPE状态表征信息，判断光伏组串中是否存在至少一个MLPE设备未处于正常输出状态。
正常输出状态下，相应光伏组件通过该MLPE设备进行正常的电能输出，该MLPE设备内部的功率半导体器件的导通压降较小，所以该MLPE设备的功耗和温度均在正常范围内。
而当任意至少一个MLPE设备未处于正常输出状态，比如处于旁路运行状态下，该MLPE设备将会通过其内部的旁路二极管流通组串电流；由于该旁路二极管的导通压降较高，此时若不牺牲成本、提高旁路二极管的选型规格和散热措施规格，并任其按照传统方案进行工作，则该MLPE设备的功耗和/或温度会超过相应的正常范围，容易导致器件损坏或者安全事故；所以需要执行步骤S103。
S103、控制相应的组串电流小于预设阈值。
该控制单元在识别到至少有一个MLPE设备未处于正常输出状态后，就控制对应的光伏组串的电流不超过预设阈值，从而可以减少该MLPE设备的发热功率，使整个系统处于可靠运行的状态。例如，正常状态下，光伏组串的最大电流为15A，该控制单元在识别到至少有一个MLPE设备未处于正常输出状态后，可以控制对应的光伏组串电流不超过11A。
本实施例提供的该控制方法，通过上述原理，能够降低相应MLPE设备在旁路运行状态下的功耗，使MLPE设备在设计时可以采用更小功率容量的旁路二极管，而且还能够采用散热要求较低的散热措施，避免了现有技术中以牺牲成本来换取系统可靠运行的问题。
在上一实施例的基础之上，本实施例以控制单元与各个MLPE设备之间具有通信机制，也即该控制单元与各个MLPE设备之间可以进行相互通信为例，对该控制方法进行详细说明：
此时，该控制单元与各个MLPE设备之间的通信，具体可以是PLC(Power  Line Carrier Communication)通信、ZigBee通信等；此处不做限定，视其应用环境而定即可，均在本申请的保护范围内。
步骤S101具体可以是：通过通信，分别获取光伏组串中各MLPE设备的运行数据，作为MLPE状态表征信息。步骤S102、判断光伏组串中是否存在至少一个MLPE设备未处于正常输出状态，具体可以有以下多种实现形式：
(1)该运行数据能够体现相应MLPE设备的状态，比如正常输出状态或旁路运行状态等。
步骤S102具体可以包括：判断光伏组串中是否存在至少一个MLPE设备处于旁路运行状态。
若光伏组串中存在至少一个MLPE设备处于旁路运行状态，则判定其未处于正常输出状态，即可执行步骤S103，从而降低MLPE设备旁路运行状态下的功耗，使MLPE设备在设计时可以采用更小功率容量的旁路二极管以及散热措施。
(2)通过该运行数据，能够识别的MLPE设备的状态还包括故障状态，该故障状态包括但不限于过流、过压、器件单体失效、接线错误等。此时步骤S102还包括：判断光伏组串中是否存在至少一个MLPE设备处于故障状态。
若光伏组串中存在至少一个MLPE设备处于故障状态，则判定其未处于正常输出状态，即可执行步骤S103，从而避免MLPE设备由于电流较大而导致故障扩大。
(3)该运行数据包括MLPE设备的温度数据，通过该运行数据，能够识别的MLPE设备的状态还包括过温状态。此时步骤S102还包括：判断光伏组串中是否存在至少一个MLPE设备处于过温状态。
若光伏组串中存在至少一个MLPE设备处于过温状态，则判定其未处于正常输出状态，即可执行步骤S103，从而降低MLPE设备旁路运行状态下的功耗，避免过温进一步恶化，使MLPE设备在设计时可以采用更小功率容量的旁路二极管以及散热措施。
特殊的，如果某个MLPE设备不具备相应的温度检测装置，或者其温度检测装置出现器件故障、传输故障等情况，也即在步骤S101之后分别获取光伏组串中各MLPE设备的运行数据之后，若存在至少一个MLPE设备未获取 到其对应运行数据中的温度数据，则该控制方法还包括：对未获取到温度数据的MLPE设备，以其预设距离内的其他MLPE设备的温度数据进行计算，得到其温度数据。例如选择临近的几个MLPE设备的温度数据，加权平局后推算目标MLPE设备的温度。
(4)通过该运行数据，能够识别的MLPE设备的状态还包括通信失联状态。MLPE设备通信失联，很可能是由于MLPE设备损坏或者异常导致，例如电源电路损坏、与输入端光伏组件的连接断开等，此时MLPE设备既有可能会运行在旁路运行状态。此时步骤S102还包括：判断光伏组串中是否存在至少一个MLPE设备处于通信失联状态。
若光伏组串中存在至少一个MLPE设备处于通信失联状态，则判定其未处于正常输出状态，即可执行步骤S103，从而降低MLPE设备旁路运行的功耗，防止目标MLPE设备可能处于旁路运行状态时的过热和故障扩大。
除了通过通信获取MLPE设备的运行数据外，该控制单元还可以通过检测，获取光伏组串的运行参数，作为MLPE状态表征信息，来实现步骤S101；该情况适用于无通信系统的场景，或者该控制单元只能单方向向MLPE设备发送指令的场景。
该运行参数包括：电压、电流和功率中的至少一种；视其具体的应用环境而定即可，均在本申请的保护范围内。
此时，步骤S102具体可以是：检测光伏组串的开路电压是否明显低于预存的开路电压值，若是，则判定至少有一个MLPE设备处于故障或异常状态，即可执行步骤S103。或者，该步骤S102也可以是：检测光伏组串的电流是否超过预设电流值，若超过则执行步骤S103，以防止MLPE设备过热。另外，在实际应用中，还可以在不同的温度下设置不同的预设电流值；因为通常情况下，对于MLPE设备的设置会使其在低温下可以承受较高的电流，即使温升较高也不会达到危险的过温值；因此，在温度较低时可以设置较高的预设电流值，而在温度较高时则可以设置较低的预设电流值，以充分发挥MLPE设备及光伏组串的发电性能。并且，此处所用到的温度，可以是使用功率变换器自身所设置的温度传感器来采集得到的，当然，也不排除是获取得到的MLPE 设备所采集的温度；视其具体应用环境而定即可，均在本申请的保护范围内。
作为一种优选方式，在步骤S101之前，先执行：改变光伏组串的运行状态。此时，步骤S102包括：判断光伏组串在其运行状态改变前后的运行参数变化量是否超过预设变化量；若运行参数变化量超过预设变化量，则判定其中存在至少一个MLPE设备未处于正常输出状态。
也即，控制单元控制光伏组串处于确定的某一状态，然后检测此时光伏组串的运行参数，来判断是否有至少一个MLPE设备未处于正常输出状态。例如，该控制单元先下发指令控制所有MLPE设备光伏组串停止对外输出，再检测光伏组串的电压，若发现光伏组串的电压明显偏高，则判断至少有一个MLPE设备处于故障或异常状态。
作为一种优选方式，该功率变换器前级所接光伏组串的数量大于1时，步骤S102，包括：判断各光伏组串的同一种运行参数之差是否大于相应预设差值；若各光伏组串的同一种运行参数之差大于相应预设差值，则判定至少一个光伏组串中存在至少一个MLPE设备未处于正常输出状态。
比如，该功率变换器的前级连接两个光伏组串，两个光伏组串的初始开路电压均为800V，后续忽然有一个光伏组串的开路电压降低到750V，则判断其内部可能有一个MLPE设备处于异常状态。
需要说明的是，在上述实施例的基础之上，实际应用中，该功率变换器可以是DC/AC变换电路实现的单级逆变器，也可以是DC/AC变换电路和其前级至少一个DC/DC变换电路构成的两级逆变器，其该两级逆变器内仅设置一个集成的控制单元来实现对于各级变换电路的控制；另外，该功率变换器还可以是单独的DC/DC变换器，例如，光伏逆变器前级的Boost变换器，或者，两级逆变器内部具有独立控制单元的Boost变换器。
不论该功率变换器的具体结构如何设置，该功率变换器具有至少一个功率变换单元，该功率变换单元为DC/DC变换器和/或DC/AC变换器，该控制单元可以通过控制功率变换单元来改变其所接光伏组串的电流。也即，可以通过功率变换器自身来实现步骤S103，该步骤S103具体包括：通过功率变换器的动作，使相应的组串电流小于预设阈值。该功率变换器的动作包括：对光伏组 串的运行电压或者电流进行扰动，从而改变光伏组串的电流，使其小于预设阈值。
另外，步骤S103也可以包括：通过改变光伏组串中相应MLPE设备的运行状态，使相应的组串电流小于预设阈值。也即，该控制单元可以通过发送指令给MLPE设备，改变MLPE设备的运行状态，来改变输入端的光伏组串的电流。
具体的，对光伏组串中相应MLPE设备运行状态的改变方式，可以为以下任意一种：开启、关闭、功率降额、取消功率降额、提高输出电流和降低输出电流。
作为优选方式，控制单元可以下发开启MLPE设备和关闭MLPE设备的指令给至少一个MLPE设备，使其输入端的光伏组件接入光伏组串或者从光伏组串中脱离，从而实现改变光伏组串电流的效果。
作为优选方式，若MLPE设备是可以进行功率调节的功率优化器，则控制单元可以下发功率降额或者取消功率降额的指令给至少一个MLPE设备，使其调整输出功率，从而实现改变光伏组串电流的效果。
作为优选方式，若MLPE设备是可以进行输出电流调节的功率优化器，控制单元可以下发电流调节的指令，比如提高输出电流的指令或降低输出电流的指令，给至少一个MLPE设备，使其调整输出电流，从而实现改变光伏组串电流的效果。
本申请另一实施例还提供了一种功率变换器，包括：主电路和控制单元；其中：
该主电路可以仅包括DC/AC变换电路，或者也可以仅包括DC/DC变换电路，又或者还可以同时包括DC/AC变换电路及设置于其前级的至少一个DC/DC变换电路。
主电路的输入端连接至少一个光伏组串；光伏组串包括至少两个输出端串联连接的MLPE设备，各MLPE设备的输入端分别连接相应的光伏组件。
该主电路受控于该控制单元；而且，该控制单元还用于执行如上述任一实施例所述的控制方法；该控制方法的具体过程及原理参见上述实施例即可，此 处不再一一赘述。
本申请另一实施例还提供了一种光伏发电系统，参见图3，包括：功率变换器102及设置于其前级的至少一个光伏组串101。
光伏组串包括至少两个输出端串联连接的MLPE设备；各MLPE设备的输入端分别连接相应的光伏组件。
该功率变换器102的结构及工作原理参见上述实施例即可，此处不再一一赘述。
该功率变换器中仅一级DC/AC变换电路时，该DC/AC变换电路的直流侧作为输入端，连接一个光伏组串，或者至少两个并联连接的光伏组串；该功率变换器中包括有DC/DC变换电路时，各DC/DC变换电路的输入端，分别连接一个光伏组串，或者分别连接至少两个并联连接的光伏组串；视其具体的应用环境而定即可。
该功率变换器102具体可以是逆变器，通过上述实施例所述的工作原理，本光伏发电系统通过逆变器与MLPE设备联动，规避了MLPE设备旁路大电流的场景，使MLPE设备的成本相比于现有技术更低，利于推广应用。
本说明书中的各个实施例均采用递进的方式描述，各个实施例之间相同相似的部分互相参见即可，每个实施例重点说明的都是与其他实施例的不同之处。尤其，对于系统或系统实施例而言，由于其基本相似于方法实施例，所以描述得比较简单，相关之处参见方法实施例的部分说明即可。以上所描述的系统及系统实施例仅仅是示意性的，其中所述作为分离部件说明的单元可以是或者也可以不是物理上分开的，作为单元显示的部件可以是或者也可以不是物理单元，即可以位于一个地方，或者也可以分布到多个网络单元上。可以根据实际的需要选择其中的部分或者全部模块来实现本实施例方案的目的。本领域普通技术人员在不付出创造性劳动的情况下，即可以理解并实施。
专业人员还可以进一步意识到，结合本文中所公开的实施例描述的各示例的单元及算法步骤，能够以电子硬件、计算机软件或者二者的结合来实现，为了清楚地说明硬件和软件的可互换性，在上述说明中已经按照功能一般性地描 述了各示例的组成及步骤。这些功能究竟以硬件还是软件方式来执行，取决于技术方案的特定应用和设计约束条件。专业技术人员可以对每个特定的应用来使用不同方法来实现所描述的功能，但是这种实现不应认为超出本申请的范围。
对所公开的实施例的上述说明，本说明书中各实施例中记载的特征可以相互替换或者组合，使本领域专业技术人员能够实现或使用本发明。对这些实施例的多种修改对本领域的专业技术人员来说将是显而易见的，本文中所定义的一般原理可以在不脱离本发明的精神或范围的情况下，在其它实施例中实现。因此，本发明将不会被限制于本文所示的这些实施例，而是要符合与本文所公开的原理和新颖特点相一致的最宽的范围。

Claims (18)

  1. 一种光伏发电系统的控制方法，其特征在于，所述光伏发电系统包括：至少一个光伏组串及其后级的功率变换器，所述光伏组串包括至少两个输出端串联连接的组件级电力电子MLPE设备，各所述MLPE设备的输入端分别连接相应的光伏组件；所述控制方法包括：
    获取所述光伏组串的MLPE状态表征信息；
    根据所述MLPE状态表征信息，判断所述光伏组串中是否存在至少一个所述MLPE设备未处于正常输出状态；
    若所述光伏组串中存在至少一个所述MLPE设备未处于所述正常输出状态，则控制相应的组串电流小于预设阈值。
  2. 根据权利要求1所述的光伏发电系统的控制方法，其特征在于，获取所述光伏组串的MLPE状态表征信息，包括：
    通过通信，分别获取所述光伏组串中各所述MLPE设备的运行数据，作为所述MLPE状态表征信息。
  3. 根据权利要求2所述的光伏发电系统的控制方法，其特征在于，判断所述光伏组串中是否存在至少一个所述MLPE设备未处于正常输出状态，包括：
    判断所述光伏组串中是否存在至少一个所述MLPE设备处于旁路运行状态；
    若所述光伏组串中存在至少一个所述MLPE设备处于所述旁路运行状态，则判定其未处于所述正常输出状态。
  4. 根据权利要求2所述的光伏发电系统的控制方法，其特征在于，判断所述光伏组串中是否存在至少一个所述MLPE设备未处于正常输出状态，包括：
    判断所述光伏组串中是否存在至少一个所述MLPE设备处于故障状态；
    若所述光伏组串中存在至少一个所述MLPE设备处于所述故障状态，则判定其未处于所述正常输出状态。
  5. 根据权利要求2所述的光伏发电系统的控制方法，其特征在于，判断 所述光伏组串中是否存在至少一个所述MLPE设备未处于正常输出状态，包括：
    判断所述光伏组串中是否存在至少一个所述MLPE设备处于过温状态；
    若所述光伏组串中存在至少一个所述MLPE设备处于所述过温状态，则判定其未处于所述正常输出状态。
  6. 根据权利要求5所述的光伏发电系统的控制方法，其特征在于，在分别获取所述光伏组串中各所述MLPE设备的运行数据之后，若存在至少一个所述MLPE设备未获取到其对应所述运行数据中的温度数据，则还包括：
    对未获取到所述温度数据的所述MLPE设备，以其预设距离内的其他所述MLPE设备的所述温度数据进行计算，得到其所述温度数据。
  7. 根据权利要求2所述的光伏发电系统的控制方法，其特征在于，判断所述光伏组串中是否存在至少一个所述MLPE设备未处于正常输出状态，包括：
    判断所述光伏组串中是否存在至少一个所述MLPE设备处于通信失联状态；
    若所述光伏组串中存在至少一个所述MLPE设备处于所述通信失联状态，则判定其未处于所述正常输出状态。
  8. 根据权利要求1所述的光伏发电系统的控制方法，其特征在于，获取所述光伏组串的MLPE状态表征信息，包括：
    通过检测，获取所述光伏组串的运行参数，作为所述MLPE状态表征信息。
  9. 根据权利要求8所述的光伏发电系统的控制方法，其特征在于，所述运行参数包括：电压、电流和功率中的至少一种。
  10. 根据权利要求9所述的光伏发电系统的控制方法，其特征在于，在获取所述光伏组串的MLPE状态表征信息之前，还包括：改变所述光伏组串的运行状态；
    判断所述光伏组串中是否存在至少一个所述MLPE设备未处于正常输出状态，包括：判断所述光伏组串在其运行状态改变前后的运行参数变化量是否超过预设变化量；若所述运行参数变化量超过所述预设变化量，则判定其中存 在至少一个所述MLPE设备未处于所述正常输出状态。
  11. 根据权利要求9所述的光伏发电系统的控制方法，其特征在于，所述光伏组串的数量大于1时，判断所述光伏组串中是否存在至少一个所述MLPE设备未处于正常输出状态，包括：
    判断各所述光伏组串的同一种所述运行参数之差是否大于相应预设差值；
    若各所述光伏组串的同一种所述运行参数之差大于相应预设差值，则判定至少一个所述光伏组串中存在至少一个所述MLPE设备未处于正常输出状态。
  12. 根据权利要求1-11中任一项所述的光伏发电系统的控制方法，其特征在于，控制相应的组串电流小于预设阈值，包括：
    通过所述功率变换器的动作，使相应的组串电流小于所述预设阈值。
  13. 根据权利要求12所述的光伏发电系统的控制方法，其特征在于，所述功率变换器的动作包括：对所述光伏组串的运行电压或者电流进行扰动。
  14. 根据权利要求1-11中任一项所述的光伏发电系统的控制方法，其特征在于，控制相应的组串电流小于预设阈值，包括：
    通过改变所述光伏组串中相应所述MLPE设备的运行状态，使相应的组串电流小于所述预设阈值。
  15. 根据权利要求14所述的光伏发电系统的控制方法，其特征在于，对所述光伏组串中相应所述MLPE设备运行状态的改变方式，为以下任意一种：开启、关闭、功率降额、取消功率降额、提高输出电流和降低输出电流。
  16. 一种功率变换器，其特征在于，包括：主电路和控制单元；其中：
    所述主电路的输入端连接至少一个光伏组串；所述光伏组串包括至少两个输出端串联连接的MLPE设备，各所述MLPE设备的输入端分别连接相应的光伏组件；
    所述主电路受控于所述控制单元；
    所述控制单元还用于执行如权利要求1-15任一项所述的光伏发电系统的控制方法。
  17. 根据权利要求16所述的功率变换器，其特征在于，所述主电路包括：DC/AC变换电路，或者，DC/DC变换电路，又或者，DC/AC变换电路及设置于其前级的至少一个DC/DC变换电路。
  18. 一种光伏发电系统，其特征在于，包括：如权利要求16或17所述的功率变换器及设置于其前级的至少一个光伏组串；
    所述光伏组串包括至少两个输出端串联连接的MLPE设备；
    各所述MLPE设备的输入端分别连接相应的光伏组件。
PCT/CN2022/094855 2021-09-27 2022-05-25 一种光伏发电系统及其控制方法和功率变换器 WO2023045373A1 (zh)

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