Patent ID: 12199522

DESCRIPTION OF EMBODIMENTS

FIG.1is a schematic diagram of an application scenario of this application. As shown inFIG.1, this application may be applied to a photovoltaic power generation system in the field of photovoltaic power generation technologies. The photovoltaic power generation system may include at least one photovoltaic string11, an inverter12, and a grid13. In the system shown inFIG.1, N photovoltaic strings11are used as an example. All the N photovoltaic strings are separately connected to the inverter12, and the inverter12is further connected to the grid13.

Specifically, each photovoltaic string11in the N photovoltaic strings11may be obtained after a plurality of photovoltaic modules are connected in series and/or connected in parallel. The photovoltaic module may be a solar panel. Each photovoltaic module may be configured to: collect solar energy, and convert the solar energy into electric energy. Each photovoltaic string11may jointly transmit, to the inverter12, electric energy generated by all the photovoltaic modules. The inverter12may jointly transmit, to the grid13, electric energy transmitted by all the photovoltaic strings11. In an application scenario such as a large-sized photovoltaic station, the photovoltaic power generation system in which a plurality of photovoltaic strings11are connected to the grid13by using a same inverter12can improve transmission efficiency. In addition, the electric energy generated by the photovoltaic module is represented in a form of a direct current, and electric energy transmitted by the grid is represented in a form of a high-voltage alternating current. Therefore, the inverter12needs to convert, into alternating currents, direct currents generated by the N photovoltaic strings11, and then transmit the alternating currents to the grid13.

Further, a voltage of the direct current generated by the photovoltaic string is low, according to Joule's law, a loss is lower when electric energy is transmitted at a higher voltage. Therefore, to increase a grid-connected voltage of the inverter to improve power generation efficiency of the photovoltaic power generation system, for inverters in some photovoltaic power generation systems, a corresponding boost circuit is disposed for a photovoltaic string connected to each inverter, so that the inverter can further perform boost processing on a direct current that has a low voltage and that is generated by the photovoltaic string. For example,FIG.2is a schematic diagram of an internal structure of an inverter. On a basis of the photovoltaic power generation system shown inFIG.1, N boost circuits that are in a one-to-one correspondence with the N photovoltaic strings11are further disposed in the inverter12. After a boost circuit121connected to each photovoltaic string11performs boost processing on a direct current generated by the photovoltaic string11, a direct current/alternating current (DC/AC) inverter module122in the inverter converts the direct current into an alternating current, and further transmits the alternating current to the grid13. In addition, in some specific photovoltaic power generation systems, the inverter12shown inFIG.1andFIG.2may further be a photovoltaic maximum power point tracking (MPPT) module. The photovoltaic MPPT module may also be configured to: perform boost, and convert a direct current into an alternating current.

More specifically,FIG.3is a schematic diagram of a circuit structure of an inverter.FIG.3shows a specific circuit structure of the boost circuit shown inFIG.2. An example in which the boost circuit is a boost chopper circuit (BOOST chopper) is used to specifically describe a boost circuit1211in the inverter12. The boost circuit1211includes a boost input capacitor101, a boost inductor102, a boost switching transistor103, a boost diode104, and a bypass diode105. The boost circuit1211may control, through high-frequency on/off of the boost switching transistor103between an opened state and a closed state, the boost inductor102to be continuously switched between a charging state and a discharging state, to transmit energy by absorbing energy when the boost inductor102is charged and releasing energy when the boost inductor102is discharged, so that a voltage of an output side on the right of the boost circuit1211is higher than a voltage of an input side on the left of the boost circuit1211. It should be noted that, on a basis of a basic circuit of the boost circuit shown inFIG.3, another possible implementation of the boost circuit is not limited in this application.

In this case, based on the circuit structure shown inFIG.3, each boost circuit has a unidirectionally conducted boost diode and a unidirectionally conducted bypass diode, so that each photovoltaic string can unidirectionally transmit electric energy to a common bus124by using a boost circuit connected to the photovoltaic string. Finally, the common bus124transmits electric energy of all the photovoltaic strings to the DC/AC inverter module122. All the boost circuits are connected in parallel with the common bus124. Therefore, in this case, a voltage of the common bus124is equal to a highest voltage in output voltages of all the boost circuits. An input voltage of a photovoltaic string connected to an input side on the left of a boost circuit with a low output voltage is less than the voltage of the bus connected to an output side on the right. If no boost diode is disposed in the boost circuit, due to a voltage difference between the input side and the output side of the boost circuit, a backflow current from the output side to the input side of the boost circuit is generated. When the backflow current flows into the photovoltaic string connected to the input side of the boost circuit, a photovoltaic module in the photovoltaic string is damaged, or even a fire is caused. Consequently, a serious safety accident is caused, and an economic loss is caused.

Therefore, when either the boost diode or the bypass diode in the boost circuit is short-circuited, damage is caused to the photovoltaic string connected to the boost circuit. To avoid a serious consequence caused when the diode is short-circuited, in another implementation of the inverter, when the inverter is connected to the photovoltaic string by using the boost circuit, a fuse with a specified current melting threshold is further additionally disposed between the boost circuit and the photovoltaic string, to protect the photovoltaic string when the diode is short-circuited. For example,FIG.4is a schematic diagram of an internal structure of another inverter. In the photovoltaic power generation system shown inFIG.4, N fuses123that are in a one-to-one correspondence with the N photovoltaic strings11are further disposed in the inverter12, and each of the N photovoltaic strings11is connected to the boost circuit121by using one fuse123.

More specifically,FIG.5is a schematic diagram of a circuit structure of another inverter.FIG.5shows a specific circuit structure of the boost circuit shown inFIG.4. Any two photovoltaic strings111and112in the N photovoltaic strings11are used as an example. Positive and negative poles of the photovoltaic string111are respectively connected to positive and negative poles of a corresponding boost circuit1211in the inverter12, and positive and negative poles of the photovoltaic string112are respectively connected to positive and negative poles of a corresponding boost circuit1212in the inverter12. In this case, the fuse123may be disposed on a positive pole line shown by the photovoltaic string111, and may also be disposed on a negative pole line shown by the photovoltaic string112. After a fuse is connected between each photovoltaic string and boost circuit, when a diode in any boost circuit is short-circuited, if a backflow current flowing to a photovoltaic string is generated because a voltage of an output side of the boost circuit is greater than a voltage of an input side, and when the backflow current is greater than the melting threshold of the fuse, the fuse melts, and the backflow current is not input into the photovoltaic string, to protect the photovoltaic string.

However, in the inverter shown inFIG.5, although the photovoltaic strings connected to all the boost circuits can be protected by disposing the fuses between the boost circuits and the photovoltaic strings to protect, in this solution, only when the fuse melts, it can be determined whether the diode in the boost circuit is short-circuited. Costs of disposing the fuse in the inverter are increased, and workload of maintaining the inverter and the fuse is increased.

Therefore, this application provides a method and an apparatus for detecting a short circuit of an inverter, and an inverter, to resolve a problem that a current flows back when a diode in a boost circuit in the inverter is short-circuited.

With reference to the accompanying drawings, the following describes the method and the apparatus for detecting a short circuit of an inverter, and the inverter provided in this application.

FIG.6is a schematic diagram of a structure of an embodiment of an inverter according to this application. The inverter provided in this embodiment may be applied to the photovoltaic power generation scenario shown inFIG.1. Direct currents generated by a plurality of photovoltaic strings11may be further transmitted to a grid13after an inverter12performs boost and conversion processing on the direct currents. In the example shown inFIG.6, that the inverter12is connected to a total of two photovoltaic strings, namely, a photovoltaic string111and a photovoltaic string112is used as an example for description, and the inverter12includes a plurality of boost circuits, a common bus124, and a direct current/alternating current (DC/AC) inverter module122. A quantity of boost circuits may be greater than or equal to a quantity of photovoltaic strings connected to the inverter. In this case, in the example shown inFIG.6, the inverter12may be connected to the photovoltaic string111by using an input side of a boost circuit1211in the inverter12, and connected to the photovoltaic string112by using an input side of a boost circuit1212in the inverter12. In addition, an output side of each boost circuit is connected in parallel with the common bus124. After performing boost processing on a direct current generated by the photovoltaic string111on the input side, the boost circuit1211may send, to the DC/AC inverter module122by using the common bus124, the direct current on which boost processing is performed. After performing boost processing on a direct current generated by the photovoltaic string112on the input side, the boost circuit1212may send, to the DC/AC inverter module122by using the common bus124, the direct current on which boost processing is performed. The DC/AC inverter module122converts the direct current into an alternating current, and then outputs the alternating current to the grid13.

Further, in the example shown inFIG.6, the boost circuit1211and the boost circuit1212each may be a boost circuit. Because the boost circuit1211is connected in parallel with the common bus124, and the boost circuit1212is also connected in parallel with the common bus124, a voltage of the common bus124is the same as a highest voltage of output sides of the boost circuit1211and the boost circuit1212. For example, a voltage of the output side of the boost circuit1211is 1000 V, a voltage of the output side of the boost circuit1212is 1200 V, and the voltage of the common bus124is 1200 V. In this case, an input voltage of the photovoltaic string111connected to the input side on the left of the boost circuit1211is less than the voltage of the common bus124connected to the output side on the right, and a boost diode104and a bypass diode105that are disposed in the boost circuit1211may be used to prevent a backflow current, generated due to a voltage difference between the input side and the output side of the boost circuit1211, from flowing into the photovoltaic string111.

More specifically, in this embodiment, to prevent a diode in each boost circuit in the inverter from being short-circuited, a processing module125in the inverter12may be configured to detect whether the diode in each boost circuit in the inverter is short-circuited. A scenario in which a detected diode is short-circuited includes the following: A boost diode in the boost circuit is short-circuited, or a bypass diode in the boost circuit is short-circuited, or both a boost diode and a bypass diode in the boost circuit are short-circuited.

Optionally, the processing module125may be an apparatus that is disposed in the inverter12and that is specially configured to detect whether a diode is short-circuited, or the processing module125may be an existing apparatus or module in the inverter12, for example, a central processing unit (CPU) or a hardware circuit. In addition, the processing module125may determine a circuit parameter by using a connection relationship between the processing module125and both each boost circuit and the common bus in the inverter. The connection relationship between the processing module125and both the boost circuit and the common bus is not shown inFIG.6. For example, the processing module125may be connected to an input side a-b and an output side a′-b′ of the boost circuit1211. In this case, the processing module may determine a voltage of the input side and a voltage of the output side of the boost circuit1211. Alternatively, the processing module125may be connected to a positive pole e and a negative pole f of the common bus124, and determine a voltage between e and f of the common bus124. In addition, in another possible implementation, the processing module125may be disposed outside the inverter12, and is used as a module independent of the inverter12.

FIG.7is a schematic flowchart of an embodiment of a method for detecting a short circuit of an inverter according to this application. The method for detecting a short circuit of an inverter shown inFIG.7may be performed by the processing module125shown inFIG.6, and may be used to detect whether the diode in each boost circuit inFIG.6is short-circuited. The method includes the following steps:S101. When the plurality of boost circuits are all in a non-working state, increase the voltage of the common bus from a first voltage to a second voltage.S102. Detect a circuit parameter of an input side of each boost circuit in the plurality of boost circuits.S103. Determine a short-circuited boost circuit in the plurality of boost circuits based on the circuit parameter.

Specifically, in this embodiment, when the processing module125in the inverter detects whether the diode in the boost circuit is short-circuited, all the boost circuits in the inverter need to be in a non-working state. The boost circuit includes at least a working state and a non-working state. The boost circuit1211is used as an example. When the boost circuit1211is in a working state, boost processing may be performed on a voltage Vabof the input side a-b, to obtain a voltage Va′b′of the output side a′-b′. In this case, Vab<Va′b′. When the boost circuit1211is in a non-working state, boost processing is not performed on a voltage Vabof the input side a-b. In this case, Vab=Va′b′.

Optionally, when all the boost circuits in the inverter are in a non-working state, the processing module125may actively perform the method for detecting a short circuit of an inverter shown inFIG.7, to detect whether the diode in each boost circuit is short-circuited. Alternatively, when the processing module125performs detection, if some or all of the boost circuits in the inverter are still in a working state, the processing module125first switches all the boost circuits in the inverters to a non-working state, and then performs S101shown inFIG.7.

In this case, when the plurality of boost circuits in the inverter are all in a non-working state, because each boost circuit is connected in parallel with the common bus in the inverter, the voltage of the common bus is equal to a highest voltage of output sides of all the boost circuits in the inverter, and is denoted as the first voltage in this embodiment. In S101, the processing module125increases, to the second voltage, the first voltage that is of the common bus and that exists when all the boost circuits are in a non-working state. The second voltage is greater than the first voltage, so that the second voltage of the common bus is higher than the first voltage of the output sides of all the boost circuits.

In this case, all the boost circuits are connected in parallel with the common bus124, and all the boost circuits in the inverter12are in a non-working state. After the processing module125increases the voltage of the common bus124to the second voltage, voltages of the output sides on the right of all the boost circuit are equal to the second voltage. Therefore, the voltages of the output sides of all the boost circuits in the inverter12are greater than the voltages of the input sides of the boost circuits, including a boost circuit corresponding to the first voltage that is the highest voltage of the output sides before the boost.

In this case, for each boost circuit, the boost circuit1211inFIG.6is used as an example. If the boost diode104and the bypass diode105in the boost circuit1211are not short-circuited, the voltage Va′b′of the output side a′-b′ of the boost circuit1211should be greater than the voltage Vabof the input side a-b, a positive pole current direction of the input side is a-a′, and a negative pole current direction of the input side is b′-b. However, if either or both of the boost diode104and the bypass diode105in the boost circuit1211are short-circuited, at least the following two cases occur: 1. The voltage Vabof the input side a-b on the left of the boost circuit1211is equal to the voltage Va′b′of the output side a′-b′ on the right. 2. A positive pole current direction of the input side of the boost circuit1211is a′-a, and a negative pole current direction of the input side is b-b′. Because a current direction existing after the short circuit is opposite to a current direction existing when the diode is not short-circuited, the current may also be referred to as a “backflow current”. Therefore, the processing module125may determine, by using a voltage or a current of the input side of each boost circuit, whether the diode in each boost circuit is short-circuited.

In a specific implementation of the embodiment shown inFIG.7, the processing module125may determine, by detecting the voltage of the input side of the boost circuit, whether the boost circuit is short-circuited. After increasing the voltage of the bus from the first voltage to the second voltage by using S101, the processing module125further detects the voltage of the input side of each boost circuit in the inverter12in S102. The boost circuit1211inFIG.6is used as an example. The processing module125may be connected to a positive pole a and a negative pole b on the input side of the boost circuit1211, and detect the voltage Vabbetween a and b by using a connection relationship. In this case, when detecting that the voltage Vabof the input side of the boost circuit1211is less than the second voltage, the processing module125determines that the boost diode104and the bypass diode105in the boost circuit1211are not short-circuited. When detecting that the voltage of the input side of the boost circuit1211is equal to the second voltage, the processing module125determines that the boost diode104and/or the bypass diode105in the boost circuit1211are/is short-circuited. Then, the processing module125detects, based on the foregoing method for detecting the boost circuit1211, whether all the boost circuits in the inverter12are short-circuited, and finally determines, by using S103, that a diode in a boost circuit whose input side has a voltage equal to the second voltage in the inverter is short-circuited. In addition, the processing module125performs boost processing on the common bus, and the voltage of the common bus is greater than the voltages of the input sides of all the boost circuits. Therefore, the processing module125may detect whether all the boost circuits are short-circuited.

In another specific implementation of the embodiment shown inFIG.7, the processing module125may determine, by detecting the current of the input side of the boost circuit, whether the diode in the boost circuit is short-circuited. After increasing the voltage of the bus from the first voltage to the second voltage by using S101, the processing module125further detects the current of the input side of each boost circuit in the inverter12in S102. The boost circuit1211inFIG.6is also used as an example. The processing module125may be connected to a positive pole a or a negative pole b on the input side of the boost circuit1211, and detect a current direction at the point a or b by using a connection relationship. When detecting that a positive pole current direction on the input side of the boost circuit1211is a-a′ or a negative pole current direction on the input side is b′-b, the processing module125determines that the boost diode104and the bypass diode105in the boost circuit1211are not short-circuited. When detecting that a positive pole current direction on the input side of the boost circuit1211is a′-a or a negative pole current direction on the input side is b-b′, the processing module125determines that the boost diode104and/or the bypass diode105in the boost circuit1211are/is short-circuited. Then, the processing module125detects, based on the foregoing method for detecting the boost circuit1211, whether all the boost circuits in the inverter12are short-circuited, and finally determines, by using S103, that a diode in a boost circuit whose input side has a backflow current in the inverter is short-circuited. In addition, the processing module125performs boost processing on the common bus, the voltage of the common bus is greater than the voltages of the input sides of all the boost circuits, and all short-circuited boost circuit have voltage differences and backflow currents may be generated. Therefore, the processing module125may detect whether all the boost circuits are short-circuited.

Optionally, the processing module125may perform detection in one or a combination of the foregoing two specific implementations of this embodiment. For example, the processing module125may determine, by detecting that a voltage of an input side of a boost circuit is equal to the second voltage, that the boost circuit is short-circuited, or may determine, by detecting that an input side of a boost circuit has a backflow current, that the boost circuit is short-circuited, or may determine, when determining that an input side of a boost circuit has a voltage equal to the second voltage and has a backflow current, that the boost circuit is short-circuited.

Optionally, after determining that the boost circuit in which the diode is short-circuited exists in the inverter, the processing module125may send prompt information, to indicate a short circuit in the inverter to maintenance personnel of the inverter, and indicate a specific short-circuited boost circuit. For example, the prompt information may be displayed by using a display screen, played by using a speaker, or the like. It may be understood that, in this embodiment, the processing module125may detect that none of the plurality of boost circuits is short-circuited, and send no prompt information.

In conclusion, in the method for detecting a short circuit of an inverter provided in this embodiment, the processing module increases the voltage of the common bus when the plurality of boost circuits in the inverter are all in a non-working state, then detects the circuit parameters of the input sides of all the plurality of boost circuits, and further determines the boost circuit in which the diode is short-circuited in the plurality of boost circuits based on the circuit parameters of the input sides of the boost circuits. Compared with a manner of disposing a fuse to detect whether a boost circuit is short-circuited in a conventional technology shown inFIG.5, because no additional fuse needs to be disposed in the inverter, circuit complexity of the inverter can be reduced, and circuit complexity of a photovoltaic power generation system including the inverter is reduced.

In addition, in this embodiment, the processing module can controllably increase the voltage of the bus from the first voltage to the second voltage, and the second voltage only needs to be slightly higher than the first voltage. In this way, even if the diode in the boost circuit is short-circuited, the second voltage of the bus does not cause an excessively large backflow current. Therefore, in a process of detecting whether the diode in the boost circuit is short-circuited, protection of the photovoltaic module connected to the boost circuit can be further ensured. Compared with the conventional technology in which the fuse melts by passively waiting for the voltage of the bus to be uncontrollably increased, protection of the photovoltaic module is improved, and it is further ensured that a serious consequence is not caused because the photovoltaic module is damaged by the backflow current.

Further, on a basis of the embodiment shown inFIG.7,FIG.8is a schematic flowchart of another embodiment of a method for detecting a short circuit of an inverter according to this application. As shown inFIG.8, after the processing module125determines the short-circuited boost circuit in the plurality of boost circuits by using S103, the method further includes S104of controlling, to be lower than a preset power, an output power of a photovoltaic string connected to a boost circuit that is not short-circuited, to protect a photovoltaic string connected to the short-circuited boost circuit.

Specifically, in this embodiment, when the processing module125determines, by using the foregoing embodiment, that there is a short circuit in the plurality of boost circuits, due to a characteristic that the boost circuit can further reduce the voltage of the output side thereof, if the processing module125detects the short-circuited boost circuit in the plurality of boost circuits, another boost circuit that is not short-circuited in the plurality of boost circuits may be enabled. In this way, after the another boost circuit that is not short-circuited is switched to a working state, a voltage of an output side is reduced by using the boost circuit that is not short-circuited, to reduce an output power of the photovoltaic string connected to the short-circuited boost circuit. When the short-circuited boost circuit does not work, a voltage of an output side of the boost circuit may be denoted as a third voltage. In this case, after the boost circuit that is not short-circuited is switched to a working state, the voltage of the output side of the boost circuit that is not short-circuited may be less than the third voltage, so that a power of the output side of the boost circuit that is not short-circuited is reduced. It may be understood that reducing a voltage of an output side of a boost circuit is also equivalent to reducing a voltage of an input side of the boost circuit and reducing a voltage of an output side of a photovoltaic string. Then, after output powers of all boost circuits that are not short-circuited in the plurality of boost circuits are reduced, a voltage of the photovoltaic string connected to the short-circuited boost circuit can also be reduced. Therefore, a voltage of an input side of the short-circuited boost circuit is reduced by reducing the output power of the photovoltaic string connected to the boost circuit that is not short-circuited, to protect the photovoltaic string connected to the short-circuited boost circuit.

For example, in the circuit shown inFIG.6, when it is detected that the diode in the boost circuit1211is short-circuited, the boost circuit1211has failed. In this case, the processing module125may switch the boost circuit1212to a working state, and reduce an output voltage of an output side c′-d′ by using the boost circuit1212, to reduce power of the input side of the boost circuit1211, that is, reduce an output power of a photovoltaic string111, so as to protect the photovoltaic string111connected to the short-circuited boost circuit1211.

In conclusion, in the method for detecting a short circuit of an inverter provided in this embodiment, after detecting the short-circuited boost circuit in the plurality of boost circuits, the processing module125can further reduce the voltage of the bus by enabling the boost circuit that is not short-circuited, to reduce the output power of the photovoltaic string connected to the short-circuited boost circuit, and protect the photovoltaic string connected to the short-circuited boost circuit. Therefore, the photovoltaic string can be automatically protected after the boost circuit is short-circuited, so that measures are taken before operation and maintenance personnel find and process the short-circuited boost circuit, to ensure that the photovoltaic string is not damaged. This further improves safety performance of the photovoltaic power generation system.

On a basis of the foregoing embodiments, this application further provides the following specific implementations, to implement S101of increasing the voltage of the common bus from a first voltage to a second voltage. The following is described with reference to the accompanying drawings.

In a first possible implementation, when the plurality of boost circuits are all in a non-working state, the processing module125may determine a boost circuit whose input side has a lowest voltage. Because the voltage of the common bus is equal to the highest voltage of the output sides of the plurality of boost circuits, it may be considered that a diode in the boost circuit whose input side has a lowest voltage is not short-circuited. Therefore, after the processing module125switches, to a working state, the boost circuit whose input side has a lowest voltage, the boost circuit performs boost processing on a direct current of a photovoltaic string on the input side, and then inputs the direct current to the common bus, to increase the voltage of the common bus.

More specifically,FIG.9is a schematic flowchart of an embodiment of increasing a voltage of a bus according to this application.FIG.9is a complete schematic flowchart in which the processing module125in the inverter shown inFIG.6increases the voltage of the bus in the foregoing implementation. The method includes the following steps.

S201. The processing module125determines voltages of input sides of all boost circuits in the plurality of boost circuits. Specifically, when the plurality of boost circuits are all in a non-working state, the processing module125needs to first determine the voltages of the input sides of all the boost circuits in the plurality of boost circuits by using S201. For example, the processing module125may determine that the voltage of the input side of the boost circuit1211is 1400 V, the voltage of the input side of the boost circuit1212is 1200 V, and the voltage of the common bus124is 1400 V.

S202. The processing module125determines, from the plurality of boost circuits in S201, a first boost circuit whose input side has a lowest voltage. Specifically, the processing module125may determine that the voltages of the input side and the output side of the boost circuit1212whose input side has a lowest voltage are different, where a diode in the boost circuit1212is not short-circuited, and determine, in S202, that the boost circuit1212is the first boost circuit.

S203. The processing module125switches the boost circuit1212to a working state.

S204. The boost circuit1212increases a voltage of the received direct current of the photovoltaic string112from 1200 V to a value greater than 1400 V, for example, increases the voltage to 1450 V. In this case, the voltage of the common bus124is also 1450 V, to boost the common bus124. It should be noted that a general boost circuit significantly increases a voltage. In S204, the boost circuit1212only needs to work at a small duty cycle to increase the voltage of the direct current generated by the photovoltaic string. Therefore, a duty cycle at which the boost circuit1212can work may be adjusted based on the voltage of the common bus, provided that the voltage of the output side of the boost circuit1212is greater than the voltage of the common bus in S201.

S205. The processing module125determines whether the voltages of the input sides of all the boost circuits are lower than the voltage of the bus. The voltage of the bus is the second voltage obtained after an increase.

S206. If the voltages of the input sides of all the boost circuits are lower than the second voltage obtained after an increase, it indicates that none of diodes in the boost circuits is short-circuited, and the procedure may end.

S207. If there is a boost circuit, in all the boost circuits, whose input side has a voltage equal to the second voltage obtained after an increase, determine that a diode in the boost circuit whose input side has a voltage equal to the second voltage obtained after an increase is short-circuited.

S208. After determining the short-circuited boost circuit, the processing module125further controls, to be lower than a preset power, an output power of a photovoltaic string connected to a boost circuit that is not short-circuited, to protect a photovoltaic string connected to the short-circuited boost circuit. Finally, the procedure ends.

In a second possible implementation, when the plurality of boost circuits are all in a non-working state, the processing module125may randomly determine a boost circuit from the plurality of boost circuits, so that the boost circuit performs boost processing on a direct current of a photovoltaic string on an input side based on a low duty cycle, and then inputs the direct current to the common bus, to increase the voltage of the common bus.

More specifically,FIG.10is a schematic flowchart of another embodiment of increasing a voltage of a bus according to this application.FIG.10is a complete schematic flowchart in which the processing module125in the inverter shown inFIG.6increases the voltage of the bus in the foregoing implementation. The method includes the following steps.

S301. The processing module125determines voltages of input sides of all boost circuits in the plurality of boost circuits. Specifically, when the plurality of boost circuits are all in a non-working state, the processing module125needs to first determine the voltages of the input sides of all the boost circuits in the plurality of boost circuits by using S301. For example, the processing module125may determine that the voltage of the input side of the boost circuit1211is 1000 V, the voltage of the input side of the boost circuit1212is 1000 V, and the voltage of the common bus124is 1000 V.

S302. The processing module125randomly determines a boost circuit from the plurality of boost circuits determined in S301, where the boost circuit is denoted as a second boost circuit. This embodiment may be applied to a case in which the voltages of the input sides of all the boost circuits are the same. In this case, a second boost circuit is randomly determined from the plurality of boost circuits.

S303. The processing module125switches, to a working state, the second boost circuit determined in S302.

S304. The second boost circuit increases a voltage of a received direct current of a photovoltaic string from the first voltage to the second voltage, for example, increases the voltage to 1050 V. In this case, the voltage of the common bus124is also increased from 1000 V to 1050 V, to boost the common bus124. It should be noted that a general boost circuit significantly increases a voltage. In S304, the second boost circuit only needs to work at a very small preset duty cycle to increase the voltage of the direct current generated by the photovoltaic string. Therefore, a duty cycle at which the second boost circuit can work may be adjusted based on the voltage of the common bus, provided that a voltage of an output side of the second boost circuit is greater than the voltage of the common bus in S301.

S305. The processing module125determines whether the voltages of the input sides of all the boost circuits are lower than the voltage of the bus. The voltage of the bus is the second voltage obtained after an increase.

S306. If the voltages of the input sides of all the boost circuits are lower than the second voltage obtained after an increase, it indicates that none of diodes in the boost circuits is short-circuited, and the procedure may end.

S307. If there is a boost circuit, in all the boost circuits, whose input side has a voltage equal to the second voltage obtained after an increase, determine that a diode in the boost circuit whose input side has a voltage equal to the second voltage obtained after an increase is short-circuited.

S308. After determining the short-circuited boost circuit, the processing module125further controls, to be lower than a preset power, an output power of a photovoltaic string of a boost circuit that is not short-circuited, to protect a photovoltaic string connected to the short-circuited boost circuit. Finally, the procedure ends.

In a third possible implementation, in the photovoltaic power generation system, the inverter is further connected to the grid by using the DC/AC module. Therefore, to increase the voltage of the common bus connected to one side of the DC/AC module, power may be obtained from the grid connected to the other side of the DC/AC module. An alternating current in the grid is converted into a direct current, and then the direct current is input into the common bus, to increase the voltage of the common bus. To implement the foregoing boost manner, an alternating current/direct current (AC/DC) rectifier module further needs to be disposed in the inverter. Specifically,FIG.11is a schematic diagram of a structure of another embodiment of an inverter according to this application. On a basis ofFIG.6, the inverter shown inFIG.11further includes an AC/DC module126. An input side of the AC/DC module126is connected to the grid13, and an output side of the AC/DC module126is connected to the common bus124.

More specifically,FIG.12is a schematic flowchart of still another embodiment of increasing a voltage of a bus according to this application.FIG.12is a complete schematic flowchart in which the processing module125in the inverter shown inFIG.11increases the voltage of the bus in the foregoing implementation. The method includes the following steps.

S401. The processing module125determines voltages of input sides of all boost circuits in the plurality of boost circuits. Specifically, when the plurality of boost circuits are all in a non-working state, the processing module125needs to first determine the voltages of the input sides of all the boost circuits in the plurality of boost circuits by using S401. For example, the processing module125may determine that the voltage of the input side of the boost circuit1211is 1400 V, the voltage of the input side of the boost circuit1212is 1200 V, and the voltage of the common bus124is 1400 V.

S402. After converting an alternating current in the grid13into a direct current by using the AC/DC module126, the processing module125inputs the direct current into the common bus124, to increase the voltage of the common bus124, for example, increase the voltage from 1400 V to 1450 V, so as to boost the common bus124.

S403. The processing module125determines whether the voltages of the input sides of all the boost circuits are lower than the voltage of the bus. The voltage of the bus is the second voltage obtained after an increase.

S404. If the voltages of the input sides of all the boost circuits are lower than the second voltage obtained after an increase, it indicates that none of diodes in the boost circuits is short-circuited, and the procedure may end.

S405. If there is a boost circuit, in all the boost circuits, whose input side has a voltage equal to the second voltage obtained after an increase, determine that a diode in the boost circuit whose input side has a voltage equal to the second voltage obtained after an increase is short-circuited.

S406. After determining the short-circuited boost circuit, the processing module125further controls, to be lower than a preset power, an output power of a photovoltaic string of a boost circuit that is not short-circuited, to protect a photovoltaic string connected to the short-circuited boost circuit. Finally, the procedure ends.

Further, this application further provides a method for detecting a short circuit of an inverter. The method may be applied to an inverter shown inFIG.13.FIG.13is a schematic diagram of a structure of still another embodiment of an inverter according to this application. On a basis ofFIG.6, each boost circuit in the inverter shown inFIG.13includes an overcurrent protector106connected in series with a boost switching transistor103. The overcurrent protector106is configured to be disconnected when a current flowing through the boost switching transistor103is excessively large, to perform overcurrent protection. The overcurrent protector106may be a current transformer.

More specifically,FIG.14is a schematic flowchart of still another embodiment of a method for detecting a short circuit of an inverter according to this application.FIG.14shows a procedure in which the processing module125in the inverter shown inFIG.13detects, in the foregoing implementation, whether a plurality of boost circuits are short-circuited. The method includes the following steps.

S501. The processing module125determines voltages of input sides of all boost circuits in the plurality of boost circuits. Specifically, when the plurality of boost circuits are all in a non-working state, the processing module125needs to first determine the voltages of the input sides of all the boost circuits in the plurality of boost circuits by using S501. For example, the processing module125may determine that the voltage of the input side of the boost circuit1211is 1000 V, the voltage of the input side of the boost circuit1212is 1000 V, and the voltage of the common bus124is 1000 V.

S502. The processing module125randomly determines a boost circuit from the plurality of boost circuits determined in S501, where the boost circuit is denoted as a third boost circuit. This embodiment may be applied to a case in which the voltages of the input sides of all the boost circuits are the same. In this case, a third boost circuit is randomly determined from the plurality of boost circuits.

S503. The processing module125switches, to a working state, the third boost circuit determined in S502.

S504. The third boost circuit increases a voltage of a received direct current of a photovoltaic string from the first voltage to the second voltage, for example, increases the voltage to 1050 V. In this case, the voltage of the common bus124is also increased from 1000 V to 1050 V, to boost the common bus124.

S505. The processing module125determines whether an overcurrent protector in the third boost circuit performs protection. The boost circuit1211is used as an example. When a current flowing through the boost switching transistor103is greater than a preset threshold, it indicates that the diode in the boost circuit1211is short-circuited. In this case, the overcurrent protector106turns off a drive of the boost switching transistor103, to protect the boost switching transistor103.

S506. If it is determined that the overcurrent protector in the third boost circuit does not perform overcurrent protection, it indicates that a diode in the third boost circuit is not short-circuited, and the procedure may end.

S507. If it is determined that the overcurrent protector in the third boost circuit performs overcurrent protection, it indicates that a diode in the third boost circuit is short-circuited.

Then, after detection is separately performed by sequentially using the plurality of boost circuits in the inverter as the foregoing third boost circuit by using steps S502to S505, all short-circuited boost circuits in the plurality of boost circuits may be finally determined.

S508. After determining all the short-circuited boost circuits in the plurality of boost circuits, the processing module125further controls, to be lower than a preset power, an output power of a photovoltaic string of a boost circuit that is not short-circuited, to protect a photovoltaic string connected to the short-circuited boost circuit. Finally, the procedure ends.

In the foregoing embodiments provided in this application, the method for detecting a short circuit of an inverter provided in embodiments of this application is described from a perspective of the processor in the inverter. To implement functions in the foregoing methods provided in embodiments of this application, the processor used as an execution body may further include a hardware structure and/or a software module, and implement the foregoing functions in a form of the hardware structure, the software module, or the hardware structure plus the software module. Whether a function in the foregoing functions is performed by the hardware structure, the software module, or the combination of the hardware structure and the software module depends on particular applications and design constraints of the technical solutions.

For example,FIG.15is a schematic diagram of a structure of an embodiment of an inverter detection apparatus according to this application. The apparatus shown inFIG.15may be configured to perform the method described in any one ofFIG.7toFIG.10andFIG.12, and is configured to detect whether an inverter is short-circuited. The apparatus includes a boost module1501, a detection module1502, and a determining module1503. The boost module1501is configured to: when a plurality of boost circuits are all in a non-working state, increase a voltage of a common bus from a first voltage to a second voltage. The first voltage is equal to a highest voltage in voltages of input sides of the plurality of boost circuits. The detection module1502is configured to detect a circuit parameter of the input side of each boost circuit in the plurality of boost circuits. The determining module1503is configured to determine a short-circuited boost circuit in the plurality of boost circuits based on the circuit parameters of the plurality of boost circuits.

Optionally, if the circuit parameter is a voltage, the determining module1503is specifically configured to determine, based on voltages of the plurality of boost circuits, that a boost circuit whose input side has a voltage equal to the second voltage in the plurality of boost circuits is short-circuited.

Optionally, if the circuit parameter is a current, the determining module1503is specifically configured to determine, based on currents of the plurality of boost circuits, that a boost circuit whose input side has a backflow current in the plurality of boost circuits is short-circuited.

Optionally, the input sides of the plurality of boost circuits are connected to a plurality of photovoltaic strings in a one-to-one correspondence manner. A direct current/alternating current inverter module is specifically configured to: convert a direct current into an alternating current, and then output the alternating current to a grid.

FIG.16is a schematic diagram of a structure of another embodiment of an inverter detection apparatus according to this application. On a basis of the embodiment shown inFIG.15, the apparatus shown inFIG.16further includes a switching module1601and a control module1602. The switching module1601is configured to switch, to a working state, a boost circuit that is not short-circuited in the plurality of boost circuits. The control module1602is configured to control, to be lower than a preset power, an output power of a photovoltaic string connected to the boost circuit that is not short-circuited, to protect a photovoltaic string connected to the short-circuited boost circuit.

Optionally, the control module1602is specifically configured to control, to be less than a third voltage, a voltage of an output side of the boost circuit that is not short-circuited, so that the output power of the photovoltaic string connected to the boost circuit that is not short-circuited is lower than the preset power, where the third voltage is a voltage that is of an output side of the short-circuited boost circuit and that exists when the plurality of boost circuits are all in a non-working state.

Optionally, the switching module1601may be further configured to switch the plurality of boost circuits to a non-working state.

Optionally, in the foregoing embodiments, the boost module1501is specifically configured to: determine a first boost circuit whose input side has a lowest voltage in the plurality of boost circuits; and switch the first boost circuit to a working state, where a direct current that is output by the first boost circuit to the common bus in a working state is used to increase the voltage of the common bus from the first voltage to the second voltage.

Optionally, in the foregoing embodiments, the boost module1501is specifically configured to: determine a second boost circuit from the plurality of boost circuits; and switch the second boost circuit to a working state, and control the second boost circuit to boost a direct current of an input side based on a duty cycle less than a preset threshold, and then output the direct current to the common bus, where the direct current is used to increase the voltage of the common bus from the first voltage to the second voltage.

Optionally, in the foregoing embodiments, the inverter detected by the apparatus further includes an alternating current/direct current rectifier module, an input side of the alternating current/direct current rectifier module is connected to an output side of the direct current/alternating current rectifier module, and an output side of the alternating current/direct current rectifier module is connected to the common bus. In this case, the boost module1501is specifically configured to: convert an alternating current into a direct current by using the alternating current/direct current rectifier module, and output the direct current to the common bus, where the direct current that is output by the alternating current/direct current rectifier module is used to increase the voltage of the common bus from the first voltage to the second voltage.

FIG.17is a schematic diagram of a structure of still another embodiment of an inverter detection apparatus according to this application. The apparatus shown inFIG.17may be configured to perform the method described inFIG.12, and is configured to detect whether an inverter is short-circuited. The apparatus includes a boost module1701and a determining module1702. The boost module1701is configured to: when a plurality of boost circuits are all in a non-working state, increase a voltage of a common bus from a first voltage to a second voltage. The second voltage is greater than the first voltage, and the first voltage is equal to a highest voltage in voltages of input sides of the plurality of boost circuits. The determining module1702is configured to detect a short-circuited boost circuit in the plurality of boost circuits based on a state of an overcurrent protector in each boost circuit in the plurality of boost circuits.

Division into the modules in embodiments of this application is an example, is merely division into logical functions, and may be other division during actual implementation. In addition, functional modules in embodiments of this application may be integrated into one processor, or each of the modules may exist alone physically, or two or more modules may be integrated into one module. The integrated module may be implemented in a form of hardware, or may be implemented in a form of a software functional module.

FIG.18is a schematic diagram of a structure of an apparatus according to an embodiment of this application. The apparatus may be configured to perform the method for detecting a short circuit of an inverter in the foregoing embodiments of this application, and may be an apparatus for detecting a short circuit of an inverter. As shown inFIG.18, the apparatus1800may include a processor1801(for example, a CPU) and a memory1802. The memory1802may include a high-speed random access memory (RAM), and may further include a non-volatile memory (NVM), for example, at least one magnetic disk storage. The memory1802may store various instructions, to complete various processing functions and implement method steps of this application. Optionally, the apparatus1800in this application may further include a communication bus1803. The communications bus1803is configured to implement a communication connection between components.

In this embodiment, the memory1802is configured to store computer executable program code. The program code includes instructions. When the processor1801executes the instructions, the instructions enable the processor1801of the apparatus to perform a processing action of the processor in any one of the foregoing embodiments or the optional embodiments of this application. Implementation principles and technical effects thereof are similar, and details are not described herein again.

The term “a plurality of” in this specification refers to two or more than two. The term “and/or” in this specification describes only an association relationship for describing associated objects and indicates that there may be any one of three relationships. For example, A and/or B may represent any one of the following three cases: Only A exists, both A and B exist, or only B exists. In addition, the character “/” in this specification usually indicates an “or” relationship between the associated objects. In the formula, the character “/” indicates a “division” relationship between the associated objects.

It may be understood that various numerals in embodiments of this application are merely used for differentiation for ease of description, and are not intended to limit the scope of embodiments of this application.

It may be understood that in embodiments of this application, sequence numbers of the foregoing processes do not mean execution sequences. The execution sequences of the processes should be determined based on functions and internal logic of the processes, and should not be construed as any limitation on the implementation processes of embodiments of this application.

It may be understood that, in embodiments of this application, the memory may be a non-volatile memory, such as a hard disk drive (HDD) or a solid-state drive (SSD), or may be a volatile memory, such as a random access memory (RAM). The memory is any other medium that can be configured to carry or store expected program code in a form of instructions or a data structure and that can be accessed by a computer, but is not limited thereto. The memory in embodiments of this application may alternatively be a circuit or any other apparatus that can implement a storage function, and is configured to store the program instructions and/or the data.

Based on the foregoing descriptions of the implementations, a person skilled in the art may clearly understand that for the purpose of convenient and brief descriptions, division into the foregoing functional modules is merely used as an example for illustration. In actual application, the foregoing functions can be allocated to different functional modules for implementation based on a requirement, that is, an inner structure of an apparatus is divided into different functional modules to implement all or some of the functions described above.

In the several embodiments provided in this application, it should be understood that the disclosed apparatus and method may be implemented in another manner. For example, the described apparatus embodiment is merely an example. For example, the division into the modules or units is merely logical function division, and may be other division in actual implementation. For example, a plurality of units or components may be combined, or may be integrated into another apparatus, or some features may be ignored or not performed. In addition, the displayed or discussed mutual couplings or direct couplings or communication connections may be implemented through some interfaces. The indirect couplings or communication connections between the apparatuses or units may be implemented in electrical, mechanical, or other forms.

The units described as separate components may or may not be physically separate, and components displayed as units may be one or more physical units, that is, may be located in one place, or may be distributed on a plurality of different places. Some or all of the units may be selected depending on actual requirements to achieve the objectives of the solutions in the embodiments.

In addition, functional units in embodiments of this application may be integrated into one processing unit, or each of the units may exist alone physically, or two or more units are integrated into one unit. The integrated unit may be implemented in a form of hardware, or may be implemented in a form of a software functional unit.

A method provided in embodiments of this application may be completely or partially implemented by using software, hardware, firmware, or any combination thereof. When software is used to implement the embodiments, the embodiments may be implemented completely or partially in a form of a computer program product. The computer program product includes one or more computer instructions. When the computer program instructions are loaded and executed on a computer, all or some of the procedures or functions according to embodiments of this application are generated. The computer may be a general-purpose computer, a dedicated computer, a computer network, a network device, a terminal, or another programmable apparatus. The computer instructions may be stored in a computer-readable storage medium or may be transmitted from a computer-readable storage medium to another computer-readable storage medium. For example, the computer instructions may be transmitted from a website, computer, server, or data center to another website, computer, server, or data center in a wired (for example, a coaxial cable, an optical fiber, or a digital subscriber line (DSL)) or wireless (for example, infrared, radio, or microwave) manner. The computer-readable storage medium may be any usable medium accessible by a computer, or a data storage device, such as a server or a data center, integrating one or more usable media. The usable medium may be a magnetic medium (for example, a floppy disk, a hard disk, or a magnetic tape), an optical medium (for example, a digital video disc (DVD)), a semiconductor medium (for example, an SSD), or the like.

The foregoing descriptions are merely specific implementations of this application, but are not intended to limit the protection scope of this application. Any variation or replacement within the technical scope disclosed in this application shall fall within the protection scope of this application. Therefore, the protection scope of this application shall be subject to the protection scope of the claims.