Photovoltaic system, DC combiner box and fault isolation circuit

Abstract

A photovoltaic system comprising a fault isolation circuit (400), a power conversion circuit and a controller (600), wherein a first end of the fault isolation circuit (400) is configured to be connected to N photovoltaic strings forming M groups of the photovoltaic strings, a second end of the fault isolation circuit (400) is connected to an input end of the power conversion circuit, and N is an integer greater than or equal to 3 and odd, and M is an integer greater than or equal to 2; the fault isolation circuit (400) comprises a multi-pole switch, the input end of the power conversion circuit is configured to be connected to negative or positive ends of each group of photovoltaic strings in the N photovoltaic strings through a different pole of switches in the multi-pole switch, and each of M-1 groups of photovoltaic strings consists of two photovoltaic strings, one of the M groups of photovoltaic strings consists of one photovoltaic string; and the controller (600) is configured to control the entire multi-pole switch to be switched off in conjunction when a reverse connection fault occurs in any of the N photovoltaic strings.

Description

TECHNICAL FIELD

[0001] This application relates to the field of photovoltaic power generation technologies and, more particularly, to a photovoltaic system, a DC combiner box and a fault isolation circuit. BACKGROUND

[0002] Currently, a photovoltaic system mainly includes a single-stage power conversion mode and a two-stage power conversion mode. In the single-stage power conversion mode, a direct current from a photovoltaic array is directly converted into an alternating current by a direct current / alternating current (DC / AC) circuit. In the two-stage power conversion mode, a direct current from a photovoltaic array is first subjected to a first-stage DC / DC conversion by a direct current / direct current (DC / DC) conversion circuit, and then subjected to a second-stage DC / AC conversion by a second-stage DC / AC conversion circuit, to finally be converted into an alternating current. The two-stage power conversion mode is more efficient than the single-stage power conversion mode.Therefore, the two-stage power conversion mode is increasingly used in a photovoltaic power generation system.

[0003] Typically, a single photovoltaic string has a limited capacity. To increase capacity, a plurality of photovoltaic strings are connected in parallel to an input end of a DC / DC conversion circuit. Specifically, positive electrodes of the plurality of photovoltaic strings are connected together, and negative electrodes of the plurality of photovoltaic strings are connected together. However, if one of the photovoltaic strings is reversely connected, currents from other photovoltaic strings flow back to the reversely connected photovoltaic string. Since an anti-parallel diode of a photovoltaic module in a photovoltaic string can carry a limited current, if currents from a plurality of photovoltaic strings flow back to one photovoltaic string, a photovoltaic module in the photovoltaic string will be damaged. SUMMARY

[0004] This application provides a photovoltaic system, a DC combiner box, and a fault isolation method for isolating a fault in a timely manner when a photovoltaic string is reversely connected.

[0005] An embodiment of this application provides a photovoltaic system. The photovoltaic system may be in a single-stage power conversion mode or a two-stage power conversion mode. The photovoltaic system includes a fault isolation circuit and a power conversion circuit, wherein the power conversion circuit may include a DC / DC conversion circuit and a DC / AC conversion circuit, or may include only a DC / AC conversion circuit. The fault isolation circuit is connected between a photovoltaic string and the power conversion circuit, i.e., N photovoltaic strings are connected to the power conversion circuit through the fault isolation circuit. To reduce the number of switches and increase the input current of the power conversion circuit, the fault isolation circuit may include a multi-pole switch.The N photovoltaic strings are divided into a plurality of groups, and each group of photovoltaic strings corresponds to a pole of a switch in the multi-pole switch. That is, all photovoltaic strings in each group of photovoltaic strings are connected to an input end of the power conversion circuit through a pole of a switch. Each group of photovoltaic strings includes at least two photovoltaic strings. Provided that a reverse connection fault occurs in the N photovoltaic strings, the entire multi-pole switch is switched off in conjunction.

[0006] The fault isolation switch provided in this embodiment of this application includes the multi-pole switch. The multi-pole switch is a link switch as a whole, namely a multi-P switch. The multi-P switch is turned off or turned on as a whole. When a reverse connection fault occurs in the N photovoltaic strings, the entire multi-pole switch is turned off. Specifically, provided that a reverse connection fault occurs in one of the photovoltaic strings, all poles of switches in the fault isolation circuit are turned off. At least two photovoltaic strings form a group, and each group corresponds to one pole of a switch. Specifically, each group of photovoltaic strings is connected in parallel and is connected to the input end of the power conversion circuit through one pole of a switch.Therefore, a number of poles of switches in the fault isolation circuit is reduced to a certain extent, so that the complexity of a hardware structure is reduced and the cost of the fault isolation circuit is reduced.

[0007] In one possible implementation, the positive electrodes or negative electrodes of the N photovoltaic strings can be connected. For example, when the positive electrodes of the N photovoltaic strings are connected, the positive electrodes of the N photovoltaic strings are connected to each other, the positive electrodes of the N photovoltaic strings are connected to the input end of the power conversion circuit through one pole of switches in the multi-pole switch, every two of the N photovoltaic strings form a group, and the negative electrodes of each group of photovoltaic strings are connected to the input end of the power conversion circuit through one pole of switches in the multi-pole switch.For example, when the negative electrodes of the N photovoltaic strings are connected, the negative electrodes of the N photovoltaic strings are connected to each other, the negative electrodes of the N photovoltaic strings are connected to the input end of the power conversion circuit through one pole of switches in the multi-pole switch, every two of the N photovoltaic strings form a group, and positive electrodes of each group of photovoltaic strings are connected to the input end of the power conversion circuit through one pole of switches in the multi-pole switch.

[0008] Every two of the N photovoltaic strings form a group. Specifically, each group of photovoltaic strings comprises two photovoltaic strings, and each group of photovoltaic strings corresponds to one pole of a switch. Therefore, the number of poles of switches is almost half of the number of photovoltaic strings. This significantly reduces the number of switches, simplifies circuit connections, and reduces the hardware cost of the fault isolation circuit. Because the multi-pole switch can operate in conjunction, when a reverse connection fault occurs in one or more photovoltaic strings, all photovoltaic strings can be reliably disconnected from the power conversion circuit, thus protecting the photovoltaic strings and the power conversion circuit.

[0009] In one possible implementation, the N photovoltaic strings are divided into M groups. If N is an even number, M = N / 2; or if N is an odd number, M = (N + 1) / 2. The fault isolation circuit includes an (M + 1)-pole switch. The (M + 1)-pole switch includes a first pole of a switch and other M poles of switches. The M groups of photovoltaic strings have a one-to-one correspondence with the M poles of switches. First ends of the N photovoltaic strings are all connected to the input end of the power conversion circuit through the first pole of a switch. The M groups of photovoltaic strings are each connected to the input end of the power conversion circuit through the M poles of switches. The first ends of the N photovoltaic strings are the positive electrodes or the negative electrodes.That is, M is approximately half of N, and the number of switch poles in the fault isolation circuit is smaller than the number of photovoltaic strings. Therefore, the number of switch poles is significantly reduced, and hardware costs are reduced. In addition, since the positive or negative electrodes of the N photovoltaic strings are connected, the input current of the power conversion circuit is the sum of the currents of the N photovoltaic strings. Therefore, the input current of the power conversion circuit can be increased.

[0010] In one possible implementation to reliably turn off the switch in the fault isolation circuit when a reverse connection fault occurs in a photovoltaic string, the fault isolation circuit provided in this embodiment of this application may further comprise: a shunt trip device; a controller configured to: send a disconnection instruction to the shunt trip device when a reverse connection fault occurs in the N photovoltaic strings. The shunt trip device acts according to the disconnection instruction and controls the entire (M+1)-pole switch to be turned off. The entire (M+1)-pole switch remains in an off state before the shunt trip device is reset.In particular, before the shunt trip device is reset, the multi-pole breaker remains in the off state to prevent the multi-pole breaker from being closed due to a malfunction before the fault is cleared.

[0011] In one possible implementation, it may be determined whether a reverse connection fault occurs in a photovoltaic string based on a current direction of the photovoltaic string. If the current direction of the photovoltaic string is reversed, it indicates that a reverse connection fault occurs. In particular, the photovoltaic system provided in this embodiment may further include an input current detection circuit configured to detect a current from each of the N photovoltaic strings. If it is determined that a current of any of the N photovoltaic strings is reversed based on the current of each photovoltaic string, the controller controls the entire (M+1)-pole switch to be turned off.

[0012] In one possible implementation, the photovoltaic system further includes an input current detection circuit and an input voltage detection circuit. The input current detection circuit detects a current from each of the N photovoltaic strings. The input voltage detection circuit detects a voltage between a first end of the first pole of the switch and a first end of each of the M poles of the switches to obtain M voltages. The controller is configured to: if at least one of the M voltages is less than a first voltage threshold and a current of at least one of the N photovoltaic strings is greater than a first current threshold, control the entire (M+1)-pole switch to be turned off. Provided that a voltage of a group of photovoltaic strings is low, a short-circuit fault may have occurred in a photovoltaic string.It is understood that when a short-circuit fault occurs, the voltage of the photovoltaic string decreases and the current increases. To accurately identify a short-circuit fault, the detection can be performed based on both voltage and current. Assuming that a short-circuit fault occurs in a photovoltaic string, all switches in the fault isolation circuit are turned off to isolate the faulty photovoltaic string and prevent damage to the next-stage circuit due to the short-circuit fault.

[0013] In one possible implementation, the power conversion circuit includes a DC / DC conversion circuit. Specifically, the photovoltaic strings are connected to an input end of the DC / DC conversion circuit through the fault isolation circuit, and an output end of the DC / DC conversion circuit is connected to an input end of a DC / AC conversion circuit.

[0014] In one possible implementation, in this embodiment of this application, it is also possible to detect whether a short-circuit fault occurs at the input end of the DC / DC conversion circuit and whether a short-circuit fault occurs at the output end of the DC / DC conversion circuit. When a short-circuit fault occurs at the output end of the DC / DC conversion circuit, in order to prevent an expansion of a fault range and implement protection, all poles of switches in the fault isolation circuit must also be controlled to be turned off to implement fault isolation. Specifically, the photovoltaic system provided in this embodiment further includes: an output current detection circuit configured to detect a current at a second end of the first pole of the switch; and an output voltage detection circuit configured to detect an output voltage of the DC / DC conversion circuit.The controller is configured to: when the current at the second end of the first pole of the switch is greater than a second current threshold and a voltage at the output end of the DC / DC conversion circuit is lower than a second preset voltage, control the entire (M + 1) pole switch to be turned off.

[0015] In one possible implementation, since any hardware may fail during operation, to ensure safe and reliable operation of the photovoltaic system, two controllers may be arranged in the photovoltaic system to provide backup, that is, to implement redundancy control. If one of the controllers fails, normal control operation is not affected. Specifically, the controller in the photovoltaic system provided in this embodiment includes a primary controller and a secondary controller. Both the primary controller and the secondary controller are configured to: when a reverse connection fault occurs in the N photovoltaic strings, control the entire (M+1)-pole switch to be turned off.

[0016] In one possible implementation, to ensure power supply reliability, this embodiment of this application provides two auxiliary sources to supply power to the controller. Specifically, the photovoltaic system provided in this embodiment further includes a primary auxiliary source and a secondary auxiliary source. Both the primary auxiliary source and the secondary auxiliary source are configured to supply power to the primary controller and the secondary controller, respectively. The primary auxiliary source is connected to the output end of the DC / DC conversion circuit. The secondary auxiliary source is connected to the first end of the fault isolation circuit.

[0017] In one possible implementation, in order to reliably supply power to the controller in any case, the photovoltaic system provided in this embodiment of this application obtains power by contention, in particular, it further includes a first power conservation circuit configured to obtain power from a group of photovoltaic strings having a highest voltage in the M groups of photovoltaic strings to supply power to the secondary auxiliary source.

[0018] In one possible implementation, the first power conservation circuit includes 2 x (M + 1) diodes and a first capacitor. Each pole of the switch in the (M + 1)-pole switch corresponds to two of the 2 x (M + 1) diodes. The first end of each pole of the switch in the (M + 1)-pole switch is connected to a first end and a second end of the first capacitor through a forward bias diode and a reverse bias diode, respectively. The first end of each pole of the switch in the (M + 1)-pole switch is connected to a corresponding photovoltaic string. A second end of each pole of the switch in the (M + 1)-pole switch is connected to the input end of the DC / DC conversion circuit.

[0019] In one possible implementation, the photovoltaic system provided in this embodiment of this application further includes a second power conservation circuit for supplying power to the primary auxiliary source. The second power conservation circuit includes a first diode, a second diode, a third diode, a fourth diode, and a second capacitor. A cathode and an anode of the first diode are connected to a positive output end of the DC / DC conversion circuit and a first end of the second capacitor, respectively. An anode and a cathode of the second diode are connected to the positive output end of the DC / DC conversion circuit and a second end of the second capacitor, respectively. An anode and a cathode of the third diode are connected to the first end of the second capacitor and a negative output end of the DC / DC conversion circuit, respectively.An anode and a cathode of the fourth diode are connected to the negative output end of the DC / DC conversion circuit and the second end of the second capacitor, respectively. The primary auxiliary source is connected to the positive output end of the DC / DC conversion circuit. The primary auxiliary source receives power from the output end of the DC / DC conversion circuit. In addition, the photovoltaic system typically includes a plurality of DC / DC conversion circuits, and the output ends of the plurality of DC / DC conversion circuits are connected in parallel. Therefore, even if all poles of switches in the fault isolation circuit are turned off to isolate all photovoltaic strings connected to the input end of the DC / DC conversion circuit, the output end of the DC / DC conversion circuit can still supply power coming from another DC / DC conversion circuit connected in parallel with the DC / DC conversion circuit.This can ensure the power supply for the primary auxiliary source and therefore ensure the power supply for the controller.

[0020] In one possible implementation, the photovoltaic system includes a plurality of fault isolation circuits and a plurality of DC / DC conversion circuits, and the plurality of fault isolation circuits correspond one-to-one to the plurality of DC / DC conversion circuits.

[0021] In one possible implementation, the power conversion circuit includes a DC / AC conversion circuit.

[0022] Based on the photovoltaic system provided in the above embodiment, an embodiment of this application further provides a DC combiner box including a plurality of fault isolation circuits and a plurality of DC / DC conversion circuits. The plurality of fault isolation circuits correspond one-to-one to the plurality of DC / DC conversion circuits. A first end of each fault isolation circuit is connected to N photovoltaic strings, and a second end of each fault isolation circuit is connected to an input end of a DC / DC conversion circuit. Each fault isolation circuit includes a multi-pole switch, and each group of photovoltaic strings in the N photovoltaic strings is connected to an input end of a corresponding power conversion circuit through a pole of switches in the multi-pole switch.Each group of photovoltaic strings comprises at least two photovoltaic strings. If a reverse connection fault occurs in the N photovoltaic strings, the entire multi-pole switch in the link is switched off.

[0023] In one possible implementation, each fault isolation circuit further includes a shunt trip device and a controller. The controller is configured to: when a reverse connection fault occurs in the N photovoltaic strings, send a disconnection command to the shunt trip device. The shunt trip device acts according to the disconnection command and controls the multi-pole switch to be turned off. The multi-pole switch remains in an off state before the shunt trip device is reset.

[0024] Based on the photovoltaic system and the DC combiner box provided in the above embodiments, one embodiment of this application further provides a fault isolation method applied to the photovoltaic system. The photovoltaic system includes a fault isolation circuit and a power conversion circuit. A first end of the fault isolation circuit is configured to be connected to N photovoltaic strings, and a second end of the fault isolation circuit is connected to the power conversion circuit. The fault isolation circuit includes a multi-pole switch, and each group of photovoltaic strings in the N photovoltaic strings is connected to an input end of the power conversion circuit through a pole of switches in the multi-pole switch. Each group of photovoltaic strings includes at least two photovoltaic strings.The method includes: determining that a reverse connection fault occurs in the N photovoltaic strings, and controlling the entire multi-pole switch to be switched off in conjunction.

[0025] In one possible implementation, determining that a reverse connection fault occurs in the N photovoltaic strings comprises, in particular, obtaining a current of each of the N photovoltaic strings; and determining, based on the current of each photovoltaic string, that a current of any of the N photovoltaic strings is reversed, and determining that a reverse connection fault occurs in the N photovoltaic strings.

[0026] From the above technical solutions, it can be learned that embodiments of this application have the following advantages: The photovoltaic system includes the fault isolation circuit, and the fault isolation circuit is connected between the photovoltaic strings and the power conversion circuit. That is, the photovoltaic strings are connected to the power conversion circuit through the fault isolation circuit. When a reverse connection fault occurs in the photovoltaic strings, the fault isolation circuit acts to disconnect the photovoltaic strings from the power conversion circuit. The fault isolation switch provided in embodiments of this application includes the multi-pole switch. The multi-pole switch is a link switch as a whole, namely a multi-P switch. The multi-P switch is turned off or on as a whole. When a reverse connection fault occurs in the N photovoltaic strings, the entire multi-pole switch is turned off.Specifically, assuming a reverse connection fault occurs in one of the photovoltaic strings, all poles of switches in the fault isolation circuit are turned off. At least two photovoltaic strings form a group, and each group corresponds to a pole of a switch. Specifically, each group of photovoltaic strings is connected in parallel and is connected to the input end of the power conversion circuit through a pole of a switch. Therefore, the number of poles of switches in the fault isolation circuit is reduced to a certain extent, thus reducing the complexity of a hardware structure and reducing the cost of the fault isolation circuit. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1A is a schematic diagram of a photovoltaic system according to an embodiment of this application; Fig. 1B is a schematic diagram of another photovoltaic system according to an embodiment of this application; Fig. 2 is a schematic diagram of yet another photovoltaic system according to an embodiment of this application; Fig. 3 is a schematic diagram of a plurality of photovoltaic strings connected in parallel to an input end of a DC / DC conversion circuit; Fig. 4 is a schematic diagram of a photovoltaic system with a fault isolation circuit according to an embodiment of this application; Fig. 5 is a circuit diagram corresponding to Fig. 4; Fig. 6 is a schematic diagram of a photovoltaic system corresponding to a case where N is an even number according to an embodiment of this application; Fig. 7 is a schematic diagram of a photovoltaic system corresponding to a case where N is an odd number, according to an embodiment of this application; Fig. 8 is a schematic diagram of a photovoltaic system having a shunt trip device according to an embodiment of this application; Fig. 9 is a schematic diagram of yet another photovoltaic system according to an embodiment of this application; Fig. 10 is a schematic diagram of yet another photovoltaic system according to an embodiment of this application; Fig. 11 is a schematic diagram of another photovoltaic system according to an embodiment of this application; Fig. 12 is a schematic diagram of a photovoltaic system having a plurality of DC / DC conversion circuits according to this application; Fig. 13 is a schematic diagram of a DC combiner box according to this application; and Fig. 14 is a schematic diagram of yet another photovoltaic system according to an embodiment of this application. DESCRIPTION OF THE EMBODIMENTS

[0027] In the following descriptions, terms such as "first" and "second" are intended for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly indicating a set of specified technical features. Therefore, a feature limited by "first," "second," or the like may explicitly or implicitly encompass one or more features. In the descriptions of this application, "a plurality of," unless otherwise specified, means two or more than two.

[0028] Additionally, in this application, orientation terms such as "top" and "bottom" may include, but are not limited to, being defined relative to component placement orientations shown in the accompanying drawings. It is understood that these directional terms may be relative concepts and are used for relative description and clarification, and may vary accordingly based on changes in the component placement orientations in the accompanying drawings.

[0029] In this application, the term "connection" is to be understood in a broad sense unless otherwise specified and limited. For example, the "connection" can be a fixed connection, a detachable connection, an integration, a direct connection, or an indirect connection through an intermediate medium. Additionally, a term "coupling" can refer to a way of implementing an electrical connection for signal transmission. The "coupling" can be a direct electrical connection or an indirect electrical connection through an intermediate medium. Design of a photovoltaic system

[0030] Embodiments of this application relate to a photovoltaic system. The photovoltaic system may include two-stage power conversion or single-stage power conversion. A photovoltaic system including two stages of power conversion circuits will first be described below. To enable those skilled in the art to better understand the technical solutions provided in embodiments of this application, the photovoltaic system provided in embodiments of this application will be described below with reference to the accompanying drawings.

[0031] Fig. 1A is a schematic diagram of a photovoltaic system according to an embodiment of this application.

[0032] The photovoltaic system provided in this embodiment of this application includes a DC / DC conversion circuit 200 and a DC / AC conversion circuit 300, wherein a plurality of photovoltaic strings are connected to an input end of the DC / DC conversion circuit 200. A photovoltaic array 100 is connected to the input end of the DC / DC conversion circuit 200, and the photovoltaic array 100 includes a plurality of photovoltaic strings. Fig. 1A, four photovoltaic strings are used as an example for the description: one photovoltaic string PV1 to one photovoltaic string PV4. The photovoltaic string PV1 to the photovoltaic string PV4 can be connected in parallel to the input end of the DC / DC conversion circuit 200 to increase an input current of the DC / DC conversion circuit 200. An output end of the DC / DC conversion circuit 200 is connected to the DC / AC conversion circuit 300.

[0033] The DC / DC conversion circuit 200 is configured to perform DC-to-DC conversion, and the DC / AC conversion circuit 300 performs DC-to-AC conversion. An output end of the DC / AC conversion circuit 300 may be connected to a transformer, that is, connected to a power grid through the transformer.

[0034] In addition, Fig. 1A is merely a schematic diagram of a DC / DC conversion circuit 200 connected to the DC / AC conversion circuit 300. Typically, to increase the output power of the DC / AC conversion circuit 300, a plurality of DC / DC conversion circuits 200 may be connected to an input end of the DC / AC conversion circuit 300.

[0035] It is understood that a power conversion circuit in the Fig. 1A includes the DC / DC conversion circuit 200 and the DC / AC conversion circuit 300. Alternatively, a power conversion circuit in a photovoltaic system provided in an embodiment of this application may include only a DC / AC conversion circuit and may not include a DC / DC conversion circuit. Fig. 1B is a schematic diagram of another photovoltaic system according to an embodiment of this application.

[0036] By comparing Fig. 1A and Fig. 1B it can be learned that a photovoltaic string PV1 to a photovoltaic string PV4 in Fig. 1B are directly connected to an input end of a DC / AC conversion circuit 300. A specific implementation form of the power conversion circuit is not limited to the technical solutions provided in the following embodiments of this application. In particular, the power conversion circuit may include the DC / DC conversion circuit 200 and the DC / AC conversion circuit 300, as shown in Fig. 1A; or the power conversion circuit may include only the DC / AC conversion circuit 300, as shown in Fig. 1B. An example in which the power conversion circuit includes a DC / DC conversion circuit will be used primarily for description below. Fig. 2 is a schematic diagram of yet another photovoltaic system according to an embodiment of this application.

[0037] In Fig. 2, an example is used for description in which the output ends of two DC / DC conversion circuits are both connected to a DC / AC conversion circuit 300. Specifically, an output end of a first DC / DC conversion circuit 200a and an output end of a second DC / DC conversion circuit 200b are connected in parallel and are connected to an input end of the DC / AC conversion circuit 300. The first DC / DC conversion circuit 200a and the second DC / DC conversion circuit 200b may be integrated into a DC combiner box 1000. The DC combiner box 1000 may have a maximum power point tracking function.

[0038] In Fig. 2, for example, an input end of the first DC / DC conversion circuit 200a is connected to a photovoltaic string PV1 and a photovoltaic string PV2, and an input end of the second DC / DC conversion circuit 200b is connected to a photovoltaic string PV3 and a photovoltaic string PV4.

[0039] In the Fig. 1 or Fig. In the photovoltaic system shown in Figure 2, a plurality of photovoltaic strings are connected to the input end of the DC / DC conversion circuit. The plurality of photovoltaic strings are typically connected in parallel. When one of the photovoltaic strings is reversely connected, that is, a positive electrode and a negative electrode are reversed, currents from other photovoltaic strings flow back to the reversely connected photovoltaic string. Since an antiparallel diode in the photovoltaic string can carry a limited current, if currents from a plurality of photovoltaic strings flow back to one photovoltaic string, a battery in the photovoltaic string will be damaged.

[0040] Fig. 3 is a schematic diagram of a plurality of photovoltaic arrays connected in parallel to an input end of a DC / DC conversion circuit.

[0041] Four photovoltaic strings are used as an example for the description. In Fig. 3, the photovoltaic strings are equivalent to a battery. Conventionally, a positive electrode PV1+ of the four photovoltaic strings is connected to a positive electrode PV4+ and then connected to a positive input end of a DC / DC conversion circuit 200, and a negative electrode PV1- of the four photovoltaic strings is connected to a negative electrode PV4- and then connected to a negative input end of the DC / DC conversion circuit 200. For example, if a PV4 is reversely connected, that is, a positive electrode and a negative electrode are reversed, it can be learned that the positive electrodes of a PV1 to a PV3 are connected to the positive input end of the DC / DC conversion circuit 200, and a positive electrode of the PV4 is connected to the negative input end of the DC / DC conversion circuit 200. Fig. Figure 3 shows a case where the photovoltaic string PV4 is connected in reverse. Fig. 3, it can be learned that currents from PV1 to PV3 are represented by dashed lines with arrows, and a current from PV4 is represented by solid lines with arrows, meaning that the currents from PV1 to PV3 flow back to PV4. The PV4 is damaged due to an excessively large current. In addition, in Fig. 3, a fuse is added to each photovoltaic string. Specifically, fuses F1 to F4 are connected in series to the four photovoltaic strings, respectively. The fuses increase the circuit loss. In addition, to break a fuse, an input current must be twice the input current, and reliability is low. To solve the above problems caused by the reverse connection of a photovoltaic string, an embodiment of this application provides a photovoltaic system. The photovoltaic system includes a fault isolation circuit. The fault isolation circuit includes a multi-pole switch.

[0042] The number of switch poles depends on the number of photovoltaic strings. For example, N photovoltaic strings are divided into a plurality of groups. Each group of photovoltaic strings includes at least two photovoltaic strings, and each group of photovoltaic strings is connected to an input end of a power conversion circuit through a switch pole in the multi-pole switch. If a reverse connection fault occurs in the N photovoltaic strings, that is, assuming a reverse connection fault occurs in one photovoltaic string, all photovoltaic strings connected to the same power conversion circuit are disconnected from the power conversion circuit. That is, the entire multi-pole switch is switched off in conjunction, and the N photovoltaic strings are disconnected from the power conversion circuit.

[0043] In the photovoltaic system provided in this embodiment of this application, the fault isolation circuit includes a multi-pole switch, that is, the multi-pole switch includes a plurality of Ps. The multi-P switch can operate in conjunction. Provided that a reverse connection fault occurs in one or more photovoltaic strings connected to the multi-pole switch, all poles of the multi-pole switch are turned off. Each group of photovoltaic strings corresponds to one pole of a switch, and each group of photovoltaic strings includes at least two photovoltaic strings. Therefore, the number of poles of switches is almost half of the number of photovoltaic strings. This significantly reduces the number of switches, simplifies circuit connections, and reduces the hardware cost of the fault isolation circuit.Because the multi-pole switch can operate in conjunction when a reverse connection fault occurs in one or more photovoltaic strings, all photovoltaic strings can be reliably disconnected from the power conversion circuit to protect the photovoltaic strings and the power conversion circuit. In one possible implementation, when the positive electrodes of the N photovoltaic strings are connected, the positive electrodes of the N photovoltaic strings are connected to each other, and the positive electrodes of the N photovoltaic strings are connected to the input end of the power conversion circuit through one pole of switches in the multi-pole switch.In one possible implementation, any two of the N photovoltaic strings can form a group to better protect each photovoltaic string and avoid a situation where an excessive number of photovoltaic strings are connected in parallel. If one photovoltaic string is reversed, other parallel-connected photovoltaic strings will be damaged due to excessive current. Since the positive electrodes of the N photovoltaic strings are connected, any two of the negative electrodes of the N photovoltaic strings form a group. The negative electrodes of each group of photovoltaic strings are connected to the input end of the power conversion circuit through one pole of switches in the multi-pole switch.

[0044] The above describes a case where the positive electrodes of the N photovoltaic strings are connected. Alternatively, the negative electrodes of the N photovoltaic strings may be connected. Specifically, the following describes a connection mode where the negative electrodes of the N photovoltaic strings are connected.

[0045] When the negative electrodes of the N photovoltaic strings are connected, the negative electrodes of the N photovoltaic strings are connected to each other, and the negative electrodes of the N photovoltaic strings are connected to the input end of the power conversion circuit through one pole of switches in the multi-pole switch. Similar to the case where the positive electrodes of the N photovoltaic strings are connected, any two of the N photovoltaic strings form a group. Specifically, any two of the positive electrodes of the N photovoltaic strings form a group and share one pole of a switch, and the positive electrodes of each group of photovoltaic strings are connected to the input end of the power conversion circuit through one pole of a switch in the multi-pole switch.

[0046] For example, the N photovoltaic strings are divided into M groups, and one pole of a switch is required to connect each group of photovoltaic strings to the power conversion circuit, that is, M poles of switches are required. In addition, one end where the positive electrodes or the negative electrodes of the N photovoltaic strings are connected is connected to the power conversion circuit through one pole of a switch. Therefore, the fault isolation circuit includes an (M + 1)-pole switch. A relationship between M and N includes two cases depending on whether N is an odd number or an even number: When N is an even number, M = N / 2; or when N is an odd number, M = (N + 1) / 2. First ends of the N photovoltaic strings are all connected to the input end of the power conversion circuit through a first pole of a switch in the (M + 1)-pole switch.The M groups of photovoltaic strings are each connected to the input end of the power conversion circuit through the M poles of switches in the (M+1)-pole switch. If a reverse connection fault occurs in the N photovoltaic strings, the entire (M+1)-pole switch is turned off. In particular, assuming that a reverse connection fault occurs in any of the photovoltaic strings, all poles of switches in the fault isolation circuit are turned off. Since any two photovoltaic strings form a group, two photovoltaic strings are connected in parallel and are connected to the input end of the power conversion circuit through one pole of a switch. If N is an odd number, a photovoltaic string remaining after grouping alone forms a group. If one of the photovoltaic strings is reversely connected, a current flows back from only one photovoltaic string.The current is small and therefore does not damage the reversely connected photovoltaic string.

[0047] In this embodiment of this application, it is not limited whether the first ends of the photovoltaic strings are the positive electrodes or the negative electrodes. Specifically, either the positive electrodes or the negative electrodes of the N photovoltaic strings can be connected. For convenience of description, an example in which the positive electrodes of the N photovoltaic strings are connected will be used for description in the following embodiments. When the positive electrodes of the N photovoltaic strings are connected, the positive electrodes of the N photovoltaic strings are connected to each other and are connected to a positive input end of the power conversion circuit through one pole of switches.Every two of the negative electrodes of the N photovoltaic strings form a group, and each group is connected to a negative input end of the power conversion circuit through a corresponding pole of switches. Since the positive electrodes of the N photovoltaic strings are connected together, the input current of the power conversion circuit can be increased. Furthermore, since every two of the negative electrodes of the N photovoltaic strings form a group, the number of poles of switches in the fault isolation circuit is reduced to a certain extent, thus reducing the complexity of the hardware structure and reducing costs.

[0048] For better understanding, an example in which N is an even number will first be used for description in the following embodiments of this application. An example in which the power conversion circuit includes a DC / DC conversion circuit will be used. Referring to Fig. 4 and Fig. 5, an example is further used for description in which four photovoltaic strings are connected to one input end of a DC / DC conversion circuit.

[0049] Fig. 4 is a schematic diagram of a photovoltaic system with a fault isolation circuit according to an embodiment of this application.

[0050] Fig. 5 is a circuit diagram corresponding to Fig. 4.

[0051] Out of Fig. 4, it can be learned that four photovoltaic strings are connected to a first end of a fault isolation circuit 400, a second end of the fault isolation circuit 400 is connected to an input end of a DC / DC conversion circuit 200, and an output end of the DC / DC conversion circuit 200 is connected to an input end of a DC / AC conversion circuit 300. Positive electrodes of the four photovoltaic strings are connected to each other, that is, positive electrodes PV1+ to PV4+ are connected to each other. The four photovoltaic strings are divided into two groups, and two photovoltaic strings form one group. Specifically, negative electrodes of each two photovoltaic strings are connected to each other, one PV1- and one PV2- are connected to each other, and one PV3- and one PV4- are connected to each other.

[0052] Provided that a reverse connection fault occurs in one of the four photovoltaic strings, all switches in the fault isolation circuit 400 are turned off, specifically, all photovoltaic strings are disconnected from the input end of the DC / DC conversion circuit 200 to prevent the fault from affecting another circuit.

[0053] An example in which a photovoltaic string PV4 is reversely connected will be used. Since PV1 and PV2 are not connected to PV4, when PV4 is reversely connected, only a current from PV3 flows back to PV4. Therefore, the current flowing back to PV4 is small and does not damage PV4. This is different from the case in Fig. 3.

[0054] In order to more clearly describe a connection relationship between the photovoltaic strings and the switches in the fault isolation circuit 300, an operation principle will be further described below with reference to Fig. 5 described.

[0055] Since N is 4 and N is an even number, M = 4 / 2. Specifically, the photovoltaic strings are divided into two groups. Accordingly, the fault isolation circuit 300 includes an (M + 1)-pole switch, namely 2 + 1 = 3 poles of switches: a first pole of switch S1, a second pole of switch S2, and a third pole of switch S3.

[0056] Positive electrodes PV1+ to PV4+ are connected to each other and are connected to a first end of the first pole of the switch S1, and a second end of the first pole of the switch S1 is connected to an input end of a DC / DC conversion circuit 200. A PV1- and a PV2- are connected to each other and are connected to a first end of the second pole of the switch S2, and a second end of the second pole of the switch S2 is connected to the input end of the DC / DC conversion circuit 200. A PV3- and a PV4- are connected to each other and are connected to a first end of the third pole of the switch S3, and a second end of the third pole of the switch S3 is connected to the input end of the DC / DC conversion circuit 200.

[0057] When a PV4 is connected backward, the first pole of switch S1, the second pole of switch S2 and the third pole of switch S3 are all turned off.

[0058] Of course, in the photovoltaic system provided in this embodiment of this application, when a photovoltaic string is reverse connected, all switches in the fault isolation circuit can be turned off to isolate the photovoltaic string from a next-stage DC / DC conversion circuit and prevent the reverse connection fault from causing another, more serious fault. Additionally, in the fault isolation circuit provided in this embodiment of this application, every two photovoltaic strings can form a group for connection. In particular, a maximum of two photovoltaic strings are connected to a separate pole of a switch.This prevents more photovoltaic strings from being connected together and avoids the following problem: When a reverse connection fault occurs in one photovoltaic string, currents from all other photovoltaic strings connected together flow back to that photovoltaic string, causing damage to the photovoltaic string. In this embodiment of this application, two photovoltaic strings are connected in parallel. Even if a reverse connection fault occurs, a reverse flow current is small and does not damage the photovoltaic strings. It should be understood that when a reverse connection fault occurs in a photovoltaic string in all embodiments of this application, it means that at least one photovoltaic string is reverse connected.In particular, assuming that one photovoltaic string is reversely connected, the N photovoltaic strings must be disconnected from the power conversion circuit.

[0059] In the photovoltaic system provided in this embodiment of this application, to protect photovoltaic strings, two photovoltaic strings each form a group instead of multiple photovoltaic strings and are connected to one pole of a switch. When multiple photovoltaic strings are connected in parallel, the magnitude of a reverse current cannot be ensured when a reverse connection occurs. Since many photovoltaic strings are connected in parallel, the reverse current increases and damages the photovoltaic strings. In this embodiment of this application, when a reverse connection occurs, the safety of photovoltaic strings is ensured while reducing the number of switches in the fault isolation circuit as much as possible to achieve a balance between safety and the number of switches.In the above embodiment, an implementation including four photovoltaic strings is described. The technical solutions provided in embodiments of this application are applicable to a case where N is an even number and has a larger value. For example, an implementation including N = 6, specifically six photovoltaic strings, is described below.

[0060] Fig. 6 is a schematic diagram of a photovoltaic system corresponding to a case where N is an even number according to an embodiment of this application.

[0061] Since N = 6, the photovoltaic strings are divided into M = 6 / 2 = 3 groups, and a fault isolation circuit 300 includes M + 1 = 4 poles of switches: a first pole of switch S1, a second pole of switch S2, a third pole of switch S3, and a fourth pole of switch S4.

[0062] Positive electrodes PV1+ to PV6+ of the six photovoltaic strings are connected to each other and are connected to a first end of the first pole of switch S1. Two photovoltaic strings each form a group. Negative electrodes of two photovoltaic strings each correspond to a pole of switch. A PV1- and a PV2- are connected to a first end of the second pole of switch S2. A PV3- and a PV4- are connected to a first end of the third pole of switch S3. A PV5- and a PV6- are connected to a first end of the fourth pole of switch S4. A second end of the first pole of switch S1, a second end of the second pole of switch S2, a second end of the third pole of switch S3, and a second end of the fourth pole of switch S4 are all connected to a DC / DC conversion circuit 200.

[0063] The above describes an implementation where N is an even number. The following describes an implementation where N is an odd number, with reference to the accompanying drawings.

[0064] Fig. 7 is a schematic diagram of a photovoltaic system corresponding to a case where N is an odd number, according to an embodiment of this application.

[0065] For simplicity of description, an example where N = 5 is used for the description. Therefore, five photovoltaic strings are divided into M = (N + 1 / ) 2 = 3 groups, and a fault isolation circuit 300 includes M + 1 = 4 poles of switches: a first pole of switch S1, a second pole of switch S2, a third pole of switch S3, and a fourth pole of switch S4. That is, the number of poles of switches is the same as that in the case where N is 6.

[0066] Since every two photovoltaic strings form a group and N is an odd number, a last remaining photovoltaic string cannot be paired. Therefore, the remaining photovoltaic string forms a group by itself and corresponds to one pole of switches in the fault isolation circuit 300.

[0067] Positive electrodes PV1+ to PV5+ of the five photovoltaic strings are connected to each other and are connected to a first end of the first pole of switch S1. Two photovoltaic strings each form a group. Negative electrodes of two photovoltaic strings each correspond to a pole of the switch. A PV1- and a PV2- are connected to a first end of the second pole of switch S2. A PV3- and a PV4- are connected to a first end of the third pole of switch S3. A PV5- forms a group alone and is connected to a first end of the fourth pole of switch S4. A second end of the first pole of switch S1, a second end of the second pole of switch S2, a second end of the third pole of switch S3, and a second end of the fourth pole of switch S4 are all connected to a DC / DC conversion circuit 200.

[0068] An example where N is an even number and an example where N is an odd number are used above for description. An example where N is an even number, i.e., N is 4, is used below to describe other implementations.

[0069] To reliably turn off a switch in a fault isolation circuit when a reverse link fault occurs in a photovoltaic string, the fault isolation circuit provided in this embodiment of this application may further include a shunt trip device. Descriptions are provided below with reference to the accompanying drawings.

[0070] Fig. 8 is a schematic diagram of a photovoltaic system with a shunt trip device according to an embodiment of this application.

[0071] In the photovoltaic system provided in this embodiment, a fault isolation circuit further includes a shunt trip device and a controller 600. The controller 600 is configured to: when a reverse connection fault occurs in N photovoltaic strings, send a disconnection command to the shunt trip device. The shunt trip device acts according to the disconnection command and drives an entire (M+1)-pole switch to be turned off. The entire (M+1)-pole switch remains in an off state before the shunt trip device is reset.

[0072] An example in which a reverse connection fault occurs in a PV4 will be used further. The controller 600 sends a disconnection command to the shunt trip device. The shunt trip device acts to control all three poles of switches S1 to S3 to be turned off. If the shunt trip device is not actively reset, the three poles of switches S1 to S3 remain in off states. This prevents the three poles of switches S1 to S3 from being turned on before the photovoltaic string fault is cleared, allowing the photovoltaic string to be better protected.

[0073] Additionally, the controller 600 provided in this embodiment of this application must receive power from a power supply and may therefore include a first power conservation circuit 500. The first power conservation circuit 500 provided in this embodiment of this application receives power through contention.

[0074] In particular, the first power sustaining circuit 500 is configured to receive power from a group of photovoltaic strings having a highest voltage in M ​​groups of photovoltaic strings to supply power to the controller 500 without receiving power from each group of photovoltaic strings.

[0075] Fig. Figure 8 shows an implementation of power conservation through contention, i.e., a circuit implementation of a first power conservation circuit. The first power conservation circuit includes 2 x (M + 1) diodes and a first capacitor. Since N is 4, M is 2, and the first power conservation circuit includes six diodes and one capacitor.

[0076] Each pole of the switch in the (M + 1)-pole switch corresponds to two of the 2 x (M + 1) diodes. A first end of each pole of the switch in the (M + 1)-pole switch is connected to a first end and a second end of the first capacitor through a forward bias diode and a reverse bias diode, respectively. The first end of each pole of the switch in the (M + 1)-pole switch is connected to a corresponding photovoltaic string. A second end of each pole of the switch in the (M + 1)-pole switch is connected to an input end of a DC / DC conversion circuit.

[0077] Out of Fig. 8, it can be learned that the fault isolation circuit includes the three poles of the switches S1 to S3, and each pole of the switch corresponds to two diodes. Specifically, a first end of the first pole of the switch S1 is connected to two ends of the first capacitor C1 through a corresponding forward bias diode D2 and a corresponding reverse bias diode D1, respectively; a first end of the second pole of the switch S2 is connected to two ends of the first capacitor C1 through a corresponding forward bias diode D4 and a corresponding reverse bias diode D3, respectively; and a first end of the third pole of the switch S3 is connected to two ends of the first capacitor C1 through a corresponding forward bias diode D6 and a corresponding reverse bias diode D5, respectively. A PV1+ to a PV4+ are connected to each other at a point A. A cathode of D1 is connected to the point A.Similarly, an anode of D2 is connected to point A. A PV1 and a PV2 are connected together at point B. A cathode of D3 is connected to point B. Similarly, an anode of D4 is connected to point B. A PV3 and a PV4 are connected together at point C. A cathode of D5 is connected to point C. Similarly, an anode of D6 is connected to point C.

[0078] The following describes a specific operating principle of a contention-based power supply using an example with reference to the accompanying drawing.

[0079] For example, when a voltage of a PV1 and a PV2 connected in parallel is higher than a voltage of a PV3 and a PV4 connected in parallel, a voltage at the point B is lower than a voltage at the point C, and a current flows back to the PV1 and the PV2 through the point B. On the contrary, when a voltage of the PV1 and the PV2 connected in parallel is lower than a voltage of the PV3 and the PV4 connected in parallel, a voltage at the point B is higher than a voltage at the point C, and a current flows back to the PV3 and the PV4.

[0080] When PV1 to PV4 are all connected in reverse, if a voltage of PV1 and PV2 connected in parallel is higher than a voltage of PV3 and PV4 connected in parallel, a voltage at point B is higher than a voltage at point C, and a current flows out of PV1 and PV2; otherwise, a current flows out of PV3 and PV4.

[0081] The following describes a specific implementation of determining whether a photovoltaic string is reverse connected.

[0082] Fig. 9 is a schematic diagram of yet another photovoltaic system according to an embodiment of this application.

[0083] The photovoltaic system provided in this embodiment may further include an input current detection circuit 700.

[0084] The input current detection circuit 700 is configured to detect a current from each of the N photovoltaic strings. It should be understood that a current sensor may be connected in series to each photovoltaic string to detect a current of the photovoltaic string. In normal cases, the current directions of all photovoltaic strings are the same. When reverse connection occurs, a current direction of a reverse-connected photovoltaic string is opposite to that of another normal photovoltaic string. Therefore, it can be determined based on a current direction whether reverse connection occurs. For example, in normal cases, a current is a positive value, and when reverse connection occurs, a detected current is a negative value, and therefore, it is determined that reverse connection occurs.

[0085] A controller 600 is configured to: when it is determined, based on the current of each photovoltaic string, that a current of any of the N photovoltaic strings is reversed, control an entire (M+1)-pole switch in a fault isolation circuit 300 to be turned off. Specifically, the controller 600 sends a disconnection instruction to a shunt trip device, and the shunt trip device controls all three poles of switches S1 to S3 to be turned off. Assuming that a reverse connection fault occurs in one of all the photovoltaic strings, all photovoltaic strings must be disconnected from a DC / DC conversion circuit 200.

[0086] The fault isolation circuit 300 provided in this embodiment of this application can be disconnected not only for protection when a reverse connection fault occurs in a photovoltaic string, but also for protection when a short circuit fault occurs in a photovoltaic string. Details will be described below.

[0087] In addition to the input current detection circuit 700, the photovoltaic system provided in this embodiment may further include an input voltage detection circuit 800.

[0088] The input voltage detection circuit 800 is configured to detect a voltage between a first end of the first pole of the switch S1 and a first end of each of the M poles of the switches (S2 and S3) to obtain M voltages. Specifically, a voltage detected by the input voltage detection circuit 800 is a voltage of each group of photovoltaic strings in the M groups of photovoltaic strings. Assuming that a voltage of a group of photovoltaic strings is low, a short-circuit fault may have occurred in a photovoltaic string. It is understood that when the short-circuit fault occurs, a voltage of the photovoltaic string decreases and a current increases. To accurately identify a short-circuit fault, the determination may be performed based on both a voltage and a current. As shown in Fig. 9, the input voltage detection circuit 800 needs to detect a voltage between a point A where a PV1+ to a PV4+ are connected together and a point B where a PV1- and a PV2- are connected together, and the input voltage detection circuit 800 needs to further detect a voltage between the point A where the PV1+ to the PV4+ are connected and a point C where a PV3- and a PV4- are connected together.

[0089] In a specific implementation, the controller 600 is configured to: if at least one of the M voltages is less than a first voltage threshold and a current of at least one of the N photovoltaic strings is greater than a first current threshold, control the entire (M+1)-pole switch to be turned off. Specifically, assuming a short-circuit fault occurs in a photovoltaic string, all switches in the fault isolation circuit 300 are turned off to isolate the faulty photovoltaic string and prevent a next-stage circuit from being damaged due to the short-circuit fault.

[0090] The above embodiment describes how to detect a short-circuit fault at an input end of a DC / DC conversion circuit. The following describes a short-circuit fault at an output end of a DC / DC conversion circuit.

[0091] Fig. 10 is a schematic diagram of yet another photovoltaic system according to an embodiment of this application.

[0092] In this embodiment of this application, it is also possible to detect whether a short-circuit fault occurs at an input end of a DC / DC conversion circuit and whether a short-circuit fault occurs at an output end of the DC / DC conversion circuit. When a short-circuit fault occurs at the output end of the DC / DC conversion circuit, in order to prevent the expansion of a fault range and implement protection, all poles of switches in a fault isolation circuit must also be controlled to be turned off to implement fault isolation.

[0093] The photovoltaic system provided in this embodiment further includes an output voltage detection circuit 901 and an output current detection circuit 902. The output voltage detection circuit 901 is configured to detect an output voltage of the DC / DC conversion circuit 200.

[0094] The output current detection circuit 902 is configured to detect a current at a second end of a first pole of the switch S1, that is, to detect an input current of the DC / DC conversion circuit 200.

[0095] To accurately determine whether a short-circuit fault occurs at the output end of the DC / DC conversion circuit 200, the determination must also be made based on both a voltage and a current. If both the voltage and current meet corresponding determination conditions, it is determined that a short-circuit fault occurs. Specifically, a controller 600 is configured to: when the current at the second end of the first pole of the switch S1 is greater than a second current threshold and a voltage at the output end of the DC / DC conversion circuit 200 is lower than a second preset voltage, control an entire (M+1)-pole switch to be turned off. Since the first pole of the switch S1 is connected to all photovoltaic strings, the output current detection circuit 902 only needs to detect a current flowing through the first pole of the switch S1.

[0096] It should be understood that both the input current detection circuit and the output current detection circuit can be implemented using current sensors. When a photovoltaic string is reversely connected, a current direction of the photovoltaic string is opposite to that of a normal photovoltaic string. Therefore, by detecting a current direction, it can be determined whether a reverse connection fault occurs. For example, if a current of the normal photovoltaic string is positive, a current of the reversely connected photovoltaic string is negative, that is, less than zero. In this case, it is determined that the current is reversed. Alternatively, if the current is less than a preset threshold, it can be considered that the current is reversed and a reverse connection fault occurs.A current sensor can be arranged in each photovoltaic string to detect a current of the photovoltaic string. Additionally, if four photovoltaic strings are included, for example, current sensors can be arranged in three of the photovoltaic strings, and one current sensor is arranged for an output current. In this case, a current of another photovoltaic string can be obtained by subtracting a sum of the currents of the three photovoltaic strings from the output current. In this way, one current sensor can be omitted.

[0097] In the photovoltaic system provided in this embodiment of this application, in order to comprehensively ensure safer and more reliable operation of the photovoltaic system, all poles of switches in the fault isolation circuit 400 can be turned off when a reverse connection fault occurs in a photovoltaic string, all poles of switches in the fault isolation circuit 400 can be turned off when a short-circuit fault occurs in a photovoltaic string, and all poles of switches in the fault isolation circuit 400 can be turned off when a short-circuit fault occurs at the output end of the DC / DC conversion circuit 200 to prevent the short-circuit fault at the output end of the DC / DC conversion circuit 200 from causing damage to the photovoltaic strings.

[0098] In the above embodiment, a case is described where power is obtained from the photovoltaic string to supply power to the controller. To ensure that the controller can continue to operate when the photovoltaic string is disconnected or the photovoltaic string has no power output, an embodiment of this application further includes another power obtaining method that can serve as a main power supply method for the controller. The following provides detailed descriptions with reference to the accompanying drawings.

[0099] Fig. 11 is a schematic diagram of another photovoltaic system according to an embodiment of this application.

[0100] Since any hardware may fail during operation, to ensure safe and reliable operation of the photovoltaic system, two controllers may be arranged in the photovoltaic system to provide backup, i.e., implement redundancy control. If one of the controllers fails, normal control operation is not affected. Specifically, a controller 600 in the photovoltaic system provided in this embodiment includes a primary controller 600a and a secondary controller 600b.

[0101] Both the primary controller 600a and the secondary controller 600b are configured to: when a reverse connection fault occurs in N photovoltaic strings, control an entire (M + 1) pole switch to be turned off.Specifically, in this embodiment of this application, the primary controller 600a and the secondary controller 600b operate simultaneously, and the primary controller 600a and the secondary controller 600b can simultaneously receive detection signals sent from an input voltage detection circuit 800, an input current detection circuit 700, an output voltage detection circuit 901, and an output current detection circuit 902, that is, the two controllers can simultaneously receive an input voltage, an input current, an output current, and an output voltage, and can determine whether all poles of switches in a fault isolation circuit 400 should be controlled to be turned off based on the received signals.In this way, it can be ensured that when one controller is faulty and cannot accurately send a disconnection instruction to the fault isolation circuit, the other normal controller can accurately and reliably control all poles of switches to be turned off.

[0102] In addition, to ensure the reliability of the power supply, this embodiment of this application provides two auxiliary sources: a primary auxiliary source 903 and a secondary auxiliary source 904.

[0103] Both the primary auxiliary source 903 and the secondary auxiliary source 904 are configured to supply power to the primary controller 600a and the secondary controller 600b.

[0104] The primary auxiliary source 903 is connected to an output end of a DC / DC conversion circuit 200, that is, the primary auxiliary source 903 receives power from the output end of the DC / DC conversion circuit 200.

[0105] The secondary auxiliary source 904 is connected to a first end of the fault isolation circuit 400, that is, the secondary auxiliary source 904 receives power from the photovoltaic strings.

[0106] The photovoltaic system provided in this embodiment of this application includes two auxiliary sources. Therefore, if one of the auxiliary sources fails, the other normal auxiliary source can normally supply power to the controller to ensure normal operation of the controller.

[0107] A second power maintenance circuit that provides a power source for the primary auxiliary source 903 is described below.

[0108] The second power conservation circuit includes a first diode D7, a second diode D8, a third diode D9, a fourth diode D10 and a second capacitor C2.

[0109] A cathode and an anode of the first diode D7 are connected to a positive output end of the DC / DC conversion circuit 200 and a first end of the second capacitor C2, respectively. An anode and a cathode of the second diode D8 are connected to the positive output end of the DC / DC conversion circuit 200 and a second end of the second capacitor C2, respectively.

[0110] An anode and a cathode of the third diode D9 are connected to the first end of the second capacitor C2 and a negative output end of the DC / DC conversion circuit 200, respectively. An anode and a cathode of the fourth diode D10 are connected to the negative output end of the DC / DC conversion circuit 200 and the second end of the second capacitor C2, respectively.

[0111] The primary auxiliary source 903 is connected to the positive output end of the DC / DC conversion circuit 200 through the second power sustaining circuit. The primary auxiliary source 903 receives power from the output end of the DC / DC conversion circuit 200. In addition, the photovoltaic system typically includes a plurality of DC / DC conversion circuits, and the output ends of the plurality of DC / DC conversion circuits are connected in parallel. Therefore, even if all poles of switches in the fault isolation circuit 400 are turned off to isolate all photovoltaic strings connected to an input end of the DC / DC conversion circuit 200, the output end of the DC / DC conversion circuit 200 can still supply power from another DC / DC conversion circuit connected in parallel with the DC / DC conversion circuit 200.This can ensure the power supply for the primary auxiliary source 903 and therefore ensure the power supply for the controller.

[0112] In this embodiment of this application, the specific implementation form of the DC / DC conversion circuit in the above photovoltaic systems is not limited. For example, the DC / DC conversion circuit may be a boost circuit, namely a boost circuit that includes a bypass relay. When the bypass relay is turned on, the boost circuit can be bypassed, meaning that a voltage boost is not required, and a photovoltaic string is directly connected to a next-stage DC / AC conversion circuit through the bypass relay.

[0113] Usually, in order to increase the output power of an inverter, a plurality of DC / DC conversion circuits are connected to one input end of the DC / AC conversion circuit.

[0114] Fig. 12 is a schematic diagram of a photovoltaic system having a plurality of DC / DC conversion circuits according to an embodiment of this application.

[0115] The photovoltaic system provided in this embodiment includes a plurality of fault isolation circuits and a plurality of DC / DC conversion circuits.

[0116] The plurality of fault isolation circuits correspond one-to-one to the plurality of DC / DC conversion circuits. Specifically, an input end of each DC / DC conversion circuit is connected to a corresponding fault isolation circuit. Output ends of the plurality of DC / DC conversion circuits are all connected to an input end of a DC / AC conversion circuit 300.

[0117] In the following descriptions, for example, at least two DC / DC conversion circuits, such as a first DC / DC conversion circuit 200a and a second DC / DC conversion circuit 200b, are connected to the input end of the DC / AC conversion circuit. Input ends of the first DC / DC conversion circuit 200a and the second DC / DC conversion circuit 200b are respectively connected to corresponding photovoltaic arrays. Specifically, the first DC / DC conversion circuit 200a corresponds to a photovoltaic array 100a, and the second DC / DC conversion circuit 200b corresponds to a photovoltaic array 100b. The photovoltaic array 100a and the photovoltaic array 100b each include a plurality of photovoltaic strings. For details, reference is made to the descriptions in the above embodiments.Photovoltaic strings in the photovoltaic array are not described in detail in this embodiment. In this embodiment, a first fault isolation circuit 400a is connected between the photovoltaic array 100a and an input end of the first DC / DC conversion circuit 200a, and a second fault isolation circuit 400b is connected between the photovoltaic array 100b and an input end of the second DC / DC conversion circuit 200b. The functions of the first fault isolation circuit 400a and the second fault isolation circuit 400b are the same as those of the fault isolation circuit in the photovoltaic system described in the previous embodiments. Details will not be described again here.

[0118] For example, if a reverse connection fault occurs in a photovoltaic string in the photovoltaic array 100a, all switches in the first fault isolation circuit 400a are turned off, that is, the photovoltaic array 100a stops operating, and no power is supplied to the input end of the first DC / DC conversion circuit 200a. However, since the photovoltaic strings in the photovoltaic array 100b are normal, the operation of the DC / AC conversion circuit 300 is not affected, and the DC / AC conversion circuit 300 can normally output electrical power. DC combiner box design

[0119] Additionally, a photovoltaic system provided in embodiments of this application may include a combiner box, namely a DC combiner box. A plurality of fault isolation circuits and a plurality of DC / DC conversion circuits are integrated into the DC combiner box.

[0120] The DC combiner box includes the plurality of fault isolation circuits and the plurality of DC / DC conversion circuits. The plurality of fault isolation circuits correspond one-to-one to the plurality of DC / DC conversion circuits. A first end of each fault isolation circuit is connected to N photovoltaic strings, and a second end of each fault isolation circuit is connected to an input end of a DC / DC conversion circuit. Each fault isolation circuit includes a multi-pole switch, and each group of photovoltaic strings in the N photovoltaic strings is connected to an input end of a corresponding power conversion circuit through a pole of switches in the multi-pole switch. Each group of photovoltaic strings includes at least two photovoltaic strings.If a reverse connection fault occurs in the N photovoltaic strings, the entire multi-pole switch in link is turned off.

[0121] Two power conversion circuits will be used as examples for description below. An example in which the power conversion circuit is a DC / DC conversion circuit will be used for description. The operating principles and advantages in the above embodiment of a photovoltaic system are also applicable to the DC combiner box provided in this embodiment, and similar parts will not be described in detail again herein.

[0122] Fig. 13 is a schematic diagram of a DC combiner box according to an embodiment of this application.

[0123] A first DC / DC conversion circuit 200a, a second DC / DC conversion circuit 200b, a first fault isolation circuit 400a, and a second fault isolation circuit 400b are all integrated into the DC combiner box 1000.

[0124] The DC combiner box provided in this embodiment of this application includes the fault isolation circuit. The fault isolation circuit includes a multi-pole switch, and the multi-pole switch operates in conjunction, that is, is turned on or off as a whole. The number of poles of the switches depends on the number of photovoltaic strings. When N photovoltaic strings are divided into M groups, the fault isolation circuit includes an (M + 1)-pole switch. The relationship between M and N includes two cases, depending on whether N is an odd number or an even number: when N is an even number, M = N / 2; or when N is an odd number, M = (N + 1) / 2. First ends of the N photovoltaic strings are all connected to an input end of the DC / DC conversion circuit through a first pole of a switch in the (M + 1)-pole switch.The M groups of photovoltaic strings are each connected to the input end of the DC / DC conversion circuit through M poles of switches in the (M+1)-pole switch. If a reverse connection fault occurs in the N photovoltaic strings, the entire (M+1)-pole switch is turned off. In particular, assuming a reverse connection fault occurs in any of the photovoltaic strings, all poles of switches in the fault isolation circuit are turned off. Since any two photovoltaic strings form a group, two photovoltaic strings are connected in parallel and are connected to the input end of the DC / DC conversion circuit through one pole of a switch. If N is an odd number, a photovoltaic string remaining after grouping alone forms a group. If one of the photovoltaic strings is reversely connected, a current flows back from only one photovoltaic string.The current is small and therefore does not damage the reversely connected photovoltaic string.

[0125] In this embodiment of this application, it is not limited whether the first ends of the photovoltaic strings are positive electrodes or negative electrodes. Specifically, either the positive electrodes or the negative electrodes of the N photovoltaic strings can be connected. For convenience of description, an example in which the positive electrodes of the N photovoltaic strings are connected will be used for description in the following embodiments. When the positive electrodes of the N photovoltaic strings are connected, the positive electrodes of the N photovoltaic strings are connected to each other and are connected to a positive input end of the DC / DC conversion circuit through one pole of switches. Every two of the negative electrodes of the N photovoltaic strings form a group, and each group is connected to a negative input end of the DC / DC conversion circuit through a corresponding pole of switches.Since the positive electrodes of the N photovoltaic strings are connected together, the input current of the DC / DC conversion circuit can be increased. Furthermore, since every two of the negative electrodes of the N photovoltaic strings form a group, the number of switch poles in the fault isolation circuit is reduced to a certain extent, thus reducing the complexity of the hardware structure and reducing costs.

[0126] In the above embodiments, an example in which a power conversion circuit includes a DC / DC conversion circuit and a DC / AC conversion circuit is used for description. The following describes an implementation in which a power conversion circuit includes only a DC / AC conversion circuit with reference to the accompanying drawings.

[0127] Fig.14 is a schematic diagram of yet another photovoltaic system according to an embodiment of this application.

[0128] The photovoltaic system provided in this embodiment includes a fault isolation circuit 400 and a DC / AC conversion circuit 300. For a specific implementation of the fault isolation circuit 400, reference is made to the descriptions in the preceding embodiments. A number of poles of switches included in the fault isolation circuit 400 refers to a number of photovoltaic strings in a photovoltaic array 100 connected to the fault isolation circuit 400. When a photovoltaic string is reversely connected, all poles of switches in the fault isolation circuit 400 are turned off, that is, switched off in conjunction, so that the photovoltaic array 100 is disconnected from the DC / AC conversion circuit 300.This can protect the photovoltaic strings while preventing the reverse connection fault from causing damage to the DC / AC conversion circuit 300. Additionally, the fault isolation circuit 400 can also isolate the photovoltaic array 100 from the DC / AC conversion circuit 300 when a short-circuit fault occurs in a photovoltaic string. Method embodiment

[0129] Based on the photovoltaic system and the DC combiner box provided in the above embodiments, an embodiment of this application further provides a fault isolation method.

[0130] The fault isolation method provided in this embodiment is applied to the photovoltaic system described in any of the preceding embodiments. The photovoltaic system includes a fault isolation circuit and a power conversion circuit. A first end of the fault isolation circuit is connected to N photovoltaic strings, and a second end of the fault isolation circuit is connected to the power conversion circuit. The fault isolation circuit includes a multi-pole switch, and each group of photovoltaic strings in the N photovoltaic strings is connected to an input end of the power conversion circuit through a pole of switches in the multi-pole switch. Each group of photovoltaic strings includes at least two photovoltaic strings.

[0131] The procedure includes: Determining that a reverse connection fault occurs in the N photovoltaic strings and controlling an entire (M + 1)-pole switch to be turned off. Determining that a reverse connection fault occurs in the N photovoltaic strings specifically includes: Obtaining a current from each of the N photovoltaic strings; and Determining, based on the current of each photovoltaic string, that a current of any of the N photovoltaic strings is reversed, and determining that a reverse connection fault occurs in the N photovoltaic strings.

[0132] When a photovoltaic string is reversely connected, the current direction of the photovoltaic string is opposite to that of a normal photovoltaic string. Therefore, by detecting the current direction, it can be determined whether a reverse connection fault occurs. For example, if the current of the normal photovoltaic string is positive, the current of the reversely connected photovoltaic string is negative, that is, less than zero. In this case, it is determined that the current is reversed. Alternatively, if the current is less than a preset threshold, it can be considered that the current is reversed and a reverse connection fault occurs. A current sensor can be arranged in each photovoltaic string to detect the current of the photovoltaic string.Additionally, for example, if four photovoltaic strings are included, current sensors may be arranged in three of the photovoltaic strings, and one current sensor is arranged for one output current. In this case, a current of another photovoltaic string can be obtained by subtracting a sum of currents of the three photovoltaic strings from the output current. In this way, one current sensor can be omitted. To better prevent a photovoltaic string from carrying an excessively large current when the photovoltaic string is reversely connected, two photovoltaic strings may form a group, and each group of photovoltaic strings has a one-to-one correspondence with one pole of a switch in the multi-pole switch.

[0133] An example in which two of the N photovoltaic strings form a group is used for the description.

[0134] positive electrodes of the N photovoltaic strings are connected, the positive electrodes of the N photovoltaic strings are connected to the input end of the power conversion circuit through one pole of switches in the multi-pole switch, every two of the N photovoltaic strings form a group, and negative electrodes of each group of photovoltaic strings are connected to the input end of the power conversion circuit through one pole of switches in the multi-pole switch.

[0135] Alternatively, negative electrodes of the N photovoltaic strings are connected, the negative electrodes of the N photovoltaic strings are connected to the input end of the power conversion circuit through one pole of switches in the multi-pole switch, every two of the N photovoltaic strings form a group, and positive electrodes of each group of photovoltaic strings are connected to the input end of the power conversion circuit through one pole of switches in the multi-pole switch.

[0136] The N photovoltaic strings are divided into M groups. If N is an even number, M = N / 2; or if N is an odd number, M = (N + 1) / 2. The fault isolation circuit includes an (M + 1)-pole switch. The (M + 1)-pole switch operates in conjunction, i.e., is turned on or off as a whole. First ends of the N photovoltaic strings are each connected to an input end of a DC / DC conversion circuit through a first pole of a switch in the (M + 1)-pole switch. The M groups of photovoltaic strings are each connected to the input end of the DC / DC conversion circuit through M poles of switches in the (M + 1)-pole switch.

[0137] It should be understood that in this application, "at least one (element)" means one or more, and "a plurality of" means two or more. The term "and / or" is used to describe an association relationship between associated objects and represents that three relationships can exist. For example, "A and / or B" can represent the following three cases: only A exists, only B exists, and both A and B exist, where A and B can be singular or plural. The character " / " usually indicates an "or" relationship between the associated objects. "At least one of the following" or a similar expression thereof indicates any combination of the elements, including any combination of one or more of the elements. For example, at least one of a, b, or c a can indicate b, c, a and b, a and c, b and c, or a, b and c, where a, b, and c can be singular or plural.

[0138] The above embodiments are intended merely to describe the technical solutions of this application without limiting this application. Although this application is described in detail with reference to the above embodiments, those skilled in the art should understand that they can still make modifications to the technical solutions described in the above embodiments or make equivalent substitutions for some technical features thereof without departing from the spirit and scope of the technical solutions of embodiments of this application.

Claims

[1] A photovoltaic system comprising a fault isolation circuit (400), a power conversion circuit and a controller (600), wherein a first end of the fault isolation circuit (400) is configured to be connected to N photovoltaic strings forming M groups of the photovoltaic strings, a second end of the fault isolation circuit (400) is connected to an input end of the power conversion circuit, and N is an integer greater than or equal to 3 and odd, and M is an integer greater than or equal to 2; the fault isolation circuit (400) comprises a multi-pole switch, the input end of the power conversion circuit is configured to be connected to negative or positive ends of each group of photovoltaic strings in the N photovoltaic strings through a different pole of switches in the multi-pole switch, and each of M-1 groups of photovoltaic strings consists of two photovoltaic strings, one of the M groups of photovoltaic strings consists of one photovoltaic string; and the controller (600) is configured to control the entire multi-pole switch to be switched off in conjunction when a reverse connection fault occurs in any of the N photovoltaic strings. [2] A photovoltaic system comprising a fault isolation circuit (400), a power conversion circuit and a controller (600), wherein a first end of the fault isolation circuit (400) is configured to be connected to N photovoltaic strings forming M groups of the photovoltaic strings, a second end of the fault isolation circuit (400) is connected to an input end of the power conversion circuit, and M is an integer greater than or equal to 2; the fault isolation circuit (400) comprises a multi-pole switch, the input end of the power conversion circuit is configured to be connected to negative or positive ends of each group of photovoltaic strings in the N photovoltaic strings through a different pole of switches in the multi-pole switch, and the group of photovoltaic strings comprises at least two photovoltaic strings; and the controller (600) is configured to control the entire multi-pole switch to be switched off in conjunction when a reverse connection fault occurs in any of the N photovoltaic strings. [3] The photovoltaic system according to claim 1 or 2, wherein the input end of the power conversion circuit is configured to be connected to negative electrodes of each group of photovoltaic strings through a different pole of switches in the multi-pole switch; or the input end of the power conversion circuit is configured to be connected to positive electrodes of each group of photovoltaic strings through a different pole of switches in the multi-pole switch. [4] A photovoltaic system according to claim 1 or 2, wherein the N photovoltaic strings are divided into M groups, and when N is an even number, M = N / 2, or when N is an odd number, M = (N + 1) / 2; and the fault isolation circuit (400) comprises an (M + 1)-pole switch, the (M + 1)-pole switch comprises a first pole of switches and other M poles of switches, the M groups of photovoltaic strings are in one-to-one correspondence with the M poles of switches, the input end of the power conversion circuit is configured to be connected to all first ends of the N photovoltaic strings through the first pole of switches, the input end of the power conversion circuit is configured to be connected to the M groups of photovoltaic strings respectively through the M poles of switches, and the first ends of the N photovoltaic strings are the positive electrodes or the negative electrodes. [5] The photovoltaic system of claim 4, wherein the fault isolation circuit (400) further comprises a shunt trip device; and the controller (600) is configured to: when a reverse connection fault occurs in the N photovoltaic strings, send a disconnection instruction to the shunt trip device, the shunt trip device acts according to the disconnection instruction and controls the entire (M + 1)-pole switch to be turned off, and the entire (M + 1)-pole switch remains in an off state before the shunt trip device is reset. [6] The photovoltaic system of claim 5, further comprising an input current detection circuit (700), wherein the input current detection circuit (700) is configured to detect a current from each of the N photovoltaic strings; and the controller (600) is configured to: when it is determined based on the current of each photovoltaic string that a current of any of the N photovoltaic strings is reversed, control the entire (M + 1)-pole switch to be turned off. [7] The photovoltaic system of claim 5, further comprising an input current detection circuit (700) and an input voltage detection circuit (800), wherein the input current detection circuit (700) is configured to detect a current from each of the N photovoltaic strings; the input voltage detection circuit (800) is configured to detect a voltage between a first end of the first pole of the switch and a first end of each of the M poles of the switches to obtain M voltages; and the controller (600) is configured to: if at least one of the M voltages is less than a first voltage threshold and a current of at least one of the N photovoltaic strings is greater than a first current threshold, control the entire (M + 1)-pole switch to be turned off. [8] Photovoltaic system according to one of claims 5 to 7, wherein the power conversion circuit comprises a DC / DC conversion circuit (200) and an output voltage detection circuit (901) and an output current detection circuit (902), wherein the output current detection circuit (902) is configured to detect a current at a second end of the first pole of the switch; the output voltage detection circuit (901) is configured to detect an output voltage of the DC / DC conversion circuit (200); and the controller (600) is configured to: when the current at the second end of the first pole of the switch is greater than a second current threshold and a voltage at an output end of the DC / DC conversion circuit (200) is lower than a second preset voltage, control the entire (M + 1)-pole switch to be turned off. [9] The photovoltaic system of claim 8, wherein the controller (600) comprises a primary controller (600a) and a secondary controller (600b); and both the primary controller (600a) and the secondary controller (600b) are configured to: when a reverse connection fault occurs in the N photovoltaic strings, control the entire (M + 1)-pole switch to be turned off. [10] A photovoltaic system according to claim 8, further comprising a primary auxiliary source (903) and a secondary auxiliary source (904), wherein both the primary auxiliary source (903) and the secondary auxiliary source (904) are configured to supply power to the primary controller (600a) and the secondary controller (600b); the primary auxiliary source (903) is connected to the output end of the DC / DC conversion circuit (200); and the secondary auxiliary source (904) is connected to the first end of the fault isolation circuit (400). [11] The photovoltaic system of claim 10, further comprising a first power maintenance circuit (500), wherein the first power maintenance circuit (500) is configured to receive power from a group of photovoltaic strings having a highest voltage in the M groups of photovoltaic strings to supply power to the secondary auxiliary source (904), and the first power conservation circuit (500) comprises 2 x (M + 1) diodes and a first capacitor (C1); each pole of the switch in the (M + 1)-pole switch corresponds to two of the 2 x (M + 1) diodes; and the first end of each pole of the switch in the (M + 1)-pole switch is connected to a first end and a second end of the first capacitor (C1) through a forward bias diode and a reverse bias diode, respectively, the first end of each pole of the switch in the (M + 1)-pole switch is connected to a corresponding photovoltaic string, and a second end of each pole of the switch in the (M + 1)-pole switch is connected to an input end of the DC / DC conversion circuit (200). [12] Photovoltaic system according to one of claims 10 to 11, further comprising a second power maintenance circuit, wherein the second power conservation circuit comprises a first diode (D7), a second diode (D8), a third diode (D9), a fourth diode (D10) and a second capacitor (C2); a cathode and an anode of the first diode (D7) are connected to a positive output end of the DC / DC conversion circuit (200) and a first end of the second capacitor (C2), respectively, and an anode and a cathode of the second diode (D8) are connected to the positive output end of the DC / DC conversion circuit (200) and a second end of the second capacitor (C2), respectively; an anode and a cathode of the third diode (D9) are connected to the first end of the second capacitor (C2) and a negative output end of the DC / DC conversion circuit (200), respectively, and an anode and a cathode of the fourth diode (D10) are connected to the negative output end of the DC / DC conversion circuit (200) and the second end of the second capacitor (C2), respectively; and the primary auxiliary source (903) is connected to the positive output end of the DC / DC conversion circuit (200), and a plurality of fault isolation circuits (400) and a plurality of DC / DC conversion circuits (200), wherein the plurality of fault isolation circuits (400) are in one-to-one correspondence with the plurality of DC / DC conversion circuits (200). [13] A power system comprising a plurality of photovoltaic systems according to claim 1 or 2, wherein the power conversion circuit (200) in each of the photovoltaic systems is a DC / DC conversion circuit and output ends of the plurality of DC / DC conversion circuits are connected in parallel, and the input end of the DC / DC conversion circuit in the respective photovoltaic system is configured to be connected to all the positive or negative ends of the strings of all the groups in each of the photovoltaic systems which are connected by a different pole of switches in the multi-pole switch of the fault isolation circuit (400) of the respective photovoltaic system. [14] A photovoltaic inverter comprising a fault isolation circuit (400), a power conversion circuit and a controller (600), wherein a first end of the fault isolation circuit (400) is configured to be connected to a plurality of photovoltaic strings comprising N photovoltaic strings forming M groups of the photovoltaic strings, a second end of the fault isolation circuit (400) is connected to an input end of the power conversion circuit, and; the fault isolation circuit (400) comprises a multi-pole switch having at least four or three poles of switches, the input end of the power conversion circuit being configured to be connected to negative or positive ends of each group of photovoltaic strings in the N photovoltaic strings through a different pole of switches in the multi-pole switch, where M is an integer greater than or equal to 2, N is an integer greater than or equal to 4, and each group of photovoltaic strings comprises two or three photovoltaic strings; or N is an integer greater than or equal to 3 and odd, M is an integer greater than or equal to 2, and each of M-1 groups of photovoltaic strings consists of two photovoltaic strings, one of the M groups of photovoltaic strings consists of one photovoltaic string; and the controller (600) is configured to control the entire multi-pole switch to be switched off in conjunction when a reverse connection fault occurs in any of the N photovoltaic strings. [15] The photovoltaic inverter according to claim 14, wherein the input end of the power conversion circuit is configured to be connected to positive electrodes of the N photovoltaic strings through one pole of switches in the multi-pole switch, and the input end of the power conversion circuit is configured to be connected to negative electrodes of each group of the N photovoltaic strings through a different pole of switches in the multi-pole switch; or the input end of the power conversion circuit is configured to be connected to negative electrodes of the N photovoltaic strings through one pole of switches in the multi-pole switch, and the input end of the power conversion circuit is configured to be connected to positive electrodes of each group of the N photovoltaic strings through a different pole of switches in the multi-pole switch.

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