Photovoltaic system, direct current combiner box and fault isolation method

Abstract

The invention discloses a photovoltaic system, a DC combiner box and a fault isolation method. The photovoltaic system comprises a fault isolation circuit and a DC / DC conversion circuit. The first end of the fault isolation circuit is connected with N photovoltaic strings, and the second end of the fault isolation circuit is connected with the input end of the DC / DC conversion circuit; the fault isolation circuit comprises a multi-pole switch, and each group of photovoltaic group strings in the N photovoltaic group strings is connected with the input end of the power conversion circuit through the same-pole switch in the multi-pole switch; each group of photovoltaic group strings comprises at least two photovoltaic group strings; when a reverse connection fault exists in the N photovoltaic group strings, the linkage of the multi-pole switch is switched off, so that the complexity of a hardware structure is reduced, and the cost of the fault isolation circuit is reduced.

Description

[0001] This application is a divisional application. The application number of the original application is 202180065361.2, and the original application date is February 20, 2021. The entire contents of the original application are incorporated into this application by reference. Technical Field

[0002] The present application relates to the field of photovoltaic power generation technology, and in particular to a photovoltaic system, a DC combiner box and a fault isolation method. Background Art

[0003] At present, photovoltaic systems mainly include single-stage power conversion mode and two-stage power conversion mode. The single-stage power conversion mode refers to the direct current of the photovoltaic array being directly converted into alternating current through a direct current / alternating current (DC / AC) circuit, while the two-stage power conversion mode refers to the direct current of the photovoltaic array being first converted into alternating current through a direct current / direct current (DC / DC) conversion circuit, and then converted into alternating current through a second-stage DC / AC conversion circuit. Since the two-stage power conversion mode is more efficient than the single-stage power conversion mode, the two-stage power conversion mode is increasingly widely used in photovoltaic power generation systems.

[0004] Generally, the capacity of a single photovoltaic string is limited. In order to increase the capacity, multiple photovoltaic strings are connected in parallel at the input end of the DC / DC conversion circuit, that is, the positive poles of multiple photovoltaic strings are connected together, and the negative poles of multiple photovoltaic strings are connected together. However, when one of the photovoltaic strings is connected in reverse, the current of other photovoltaic strings will be fed back into the reversed photovoltaic string. Since the anti-parallel diodes of the solar panels in the photovoltaic string can withstand a limited current, when the current of multiple photovoltaic strings is fed back into one photovoltaic string, it will cause damage to the solar panels in the photovoltaic string. Summary of the invention

[0005] The present application provides a photovoltaic system, a DC combiner box and a fault isolation method, which can isolate the fault in time when reverse connection occurs in a photovoltaic string.

[0006] The embodiment of the present application provides a photovoltaic system, which can be 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 only include a DC / AC conversion circuit. The fault isolation circuit is connected between the photovoltaic string and the power conversion circuit, that is, N photovoltaic strings are connected to the power conversion circuit through the fault isolation circuit. In order to reduce the number of switches and at the same time to increase the input current of the power conversion circuit, the fault isolation circuit may include a multi-pole switch, N photovoltaic strings are divided into multiple groups, each photovoltaic string corresponds to a single-pole switch in the multi-pole switch, that is, all photovoltaic strings in each photovoltaic string share a single-pole switch to connect the input end of the power conversion circuit; each photovoltaic string includes at least two photovoltaic strings; as long as there is a reverse connection fault in the N photovoltaic strings, the multi-pole switch linkage is disconnected.

[0007] The fault isolation switch provided in the embodiment of the present application includes a multi-pole switch, and the multi-pole switch as a whole is a linkage switch, that is, a multi-P switch, and the multi-P switches are disconnected or turned on at the same time. When there is a reverse connection fault in N photovoltaic strings, the multi-pole switches are all disconnected, that is, as long as a reverse connection fault occurs in one of the photovoltaic strings, all pole switches in the fault isolation circuit are disconnected. Since at least two photovoltaic strings are divided into a group, each group corresponds to a pole switch, that is, each group of photovoltaic strings is connected in parallel to share a pole switch to connect the input end of the power conversion circuit. Therefore, the number of poles of the switch in the fault isolation circuit is reduced to a certain extent, thereby reducing the complexity of the hardware structure and reducing the cost of the fault isolation circuit.

[0008] In a possible implementation, N photovoltaic strings can be connected with a common positive pole or a common negative pole. For example, when the N photovoltaic strings are connected with a common positive pole, the positive poles of the N photovoltaic strings are connected together, and the positive poles of the N photovoltaic strings are connected to the input end of the power conversion circuit through a single-pole switch in a multi-pole switch; the N photovoltaic strings are grouped in pairs, and the negative pole of each photovoltaic string is connected to the input end of the power conversion circuit through a single-pole switch in a multi-pole switch; for example, when the N photovoltaic strings are connected with a common negative pole, the negative poles of the N photovoltaic strings are connected together, and the negative poles of the N photovoltaic strings are connected to the input end of the power conversion circuit through a single-pole switch in a multi-pole switch, and the N photovoltaic strings are grouped in pairs, and the positive pole of each photovoltaic string is connected to the input end of the power conversion circuit through a single-pole switch in a multi-pole switch.

[0009] Since N photovoltaic strings are grouped in pairs, that is, each photovoltaic string group includes two photovoltaic strings, and each photovoltaic string group corresponds to a one-pole switch, the number of switch poles is almost half of the number of photovoltaic strings, thereby greatly reducing the number of switches, simplifying the circuit connection, and saving the hardware cost of the fault isolation circuit. Since the multi-pole switches can be linked, when a reverse connection fault occurs in one or more photovoltaic strings, all of them can be reliably disconnected from the power conversion circuit, thereby protecting the photovoltaic strings and the power conversion circuit.

[0010] In a possible implementation, N photovoltaic strings are divided into M groups, when N is an even number, M=N / 2; when N is an odd number, M=(N+1) / 2; the fault isolation circuit includes M+1 pole switches, and the M+1 pole switches include the first pole switch and the remaining M pole switches; the M groups of photovoltaic strings correspond to the M pole switches one by one; the first ends of the N photovoltaic strings are connected to the input end of the power conversion circuit through the first pole switch; the M groups of photovoltaic strings are connected to the input end of the power conversion circuit through the M pole switches, and the first ends of the N photovoltaic strings are positive or negative. That is, M is approximately half of N, and the number of poles of the switch in the fault isolation circuit is less than the number of photovoltaic strings, so the number of poles of the switch is greatly reduced, and the hardware cost is reduced. In addition, since the N photovoltaic strings share a common positive pole or a common negative pole, the input current of the power conversion circuit is the sum of the currents of the N photovoltaic strings, so the input current of the power conversion circuit can be increased.

[0011] In a possible implementation, in order to reliably disconnect the switches in the fault isolation circuit when a reverse connection fault occurs in a photovoltaic string, the fault isolation circuit provided in the embodiment of the present application may also include a shunt trip device. The controller is used to send a disconnection instruction to the shunt trip device when there is a reverse connection fault in N photovoltaic strings. The shunt trip device operates according to the disconnection instruction and drives the M+1 pole switches to disconnect; before the shunt trip device is reset, the M+1 pole switches remain in the disconnected state. That is, before the shunt trip device is reset, the multi-pole switch remains in the disconnected state, thereby avoiding the multi-pole switch from malfunctioning and closing before the fault is cleared.

[0012] In a possible implementation, the presence of a reverse connection fault in a photovoltaic string can be determined by the current direction of the photovoltaic string. When the current direction of the photovoltaic string is reversed, it indicates that a reverse connection fault exists. That is, the photovoltaic system provided in this embodiment may also include: an input current detection circuit for detecting the current of each photovoltaic string in the N photovoltaic strings; when the controller determines that the current of any photovoltaic string in the N photovoltaic strings is reversed based on the current of each photovoltaic string, the M+1 pole switches are controlled to be disconnected.

[0013] In a possible implementation, it also includes: an input current detection circuit and an input voltage detection circuit; the input current detection circuit detects the current of each photovoltaic string in the N photovoltaic strings; the input voltage detection circuit detects the voltage between the first end of the first pole switch and the first end of each switch in the M pole switches to obtain M voltages; the controller is used to control the M+1 pole switches to be disconnected when at least one of the M voltages is less than the first voltage threshold and the current of at least one photovoltaic string in the N photovoltaic strings is greater than the first current threshold. As long as the voltage of a group of photovoltaic strings is low, some photovoltaic strings may have a short circuit fault. It should be understood that when a short circuit fault exists, the voltage of the photovoltaic string will drop and the current will rise. In order to accurately judge the short circuit fault, the voltage and current can be double judged. As long as there is a short circuit fault in the photovoltaic string, all switches in the fault isolation circuit are disconnected, thereby isolating the faulty photovoltaic string and protecting the subsequent circuit from the harm of the short circuit fault.

[0014] In one possible implementation, the power conversion circuit includes: a DC / DC conversion circuit, that is, the photovoltaic string is connected to the input end of the DC / DC conversion circuit through a fault isolation circuit, and the output end of the DC / DC conversion circuit is connected to the input end of the DC / AC conversion circuit.

[0015] In a possible implementation, the embodiment of the present application can not only detect whether a short circuit fault occurs at the input end of the DC / DC conversion circuit, but also detect 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 avoid the expansion of the fault range and play a protective role, it is also necessary to control all pole switches in the fault isolation circuit to be disconnected to play a role in fault isolation. That is, the photovoltaic system provided by this embodiment also includes: an output current detection circuit for detecting the current at the second end of the first pole switch; an output voltage detection circuit for detecting the output voltage of the DC / DC conversion circuit; a controller for controlling the M+1 pole switches to be disconnected when the current at the second end of the first pole switch is greater than the second current threshold and the voltage at the output end of the DC / DC conversion circuit is less than the second preset voltage.

[0016] In a possible implementation, since any hardware may fail during operation, in order to ensure that the photovoltaic system operates safely and reliably, two controllers may be set in the photovoltaic system to form a backup, that is, to achieve redundant control, so that when one of the controllers fails, normal control operation is not affected. That is, the photovoltaic system provided in this embodiment includes a main controller and a backup controller; both the main controller and the backup controller are used to control the M+1 pole switches to be disconnected when there is a reverse connection fault in N photovoltaic strings.

[0017] In one possible implementation, in order to ensure the reliability of power supply, the embodiment of the present application provides two auxiliary sources to power the controller, that is, the photovoltaic system provided in this embodiment also includes: a main auxiliary source and a secondary auxiliary source; the main auxiliary source and the secondary auxiliary source are both used to power the main controller and the backup controller; the main 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.

[0018] In one possible implementation, in order to reliably power the controller under any circumstances, the photovoltaic system provided in the embodiment of the present application adopts a competitive power supply method, that is, it also includes: a first power supply circuit, which is used to obtain power from the group with the highest voltage among M groups of photovoltaic strings to provide power for the auxiliary auxiliary source.

[0019] In one possible implementation, the first power supply circuit includes: 2 (M+1) diodes and a first capacitor; each switch in the M+1-pole switches corresponds to two diodes in the 2 (M+1) diodes; the first end of each switch in the M+1-pole switches is respectively connected to the first end and the second end of the first capacitor through a forward-biased diode and a reverse-biased diode; the first end of each switch in the M+1-pole switches is connected to the corresponding photovoltaic string, and the second end of each switch in the M+1-pole switches is connected to the input end of the DC / DC conversion circuit.

[0020] In a possible implementation, the photovoltaic system provided in the embodiment of the present application also includes a second power supply circuit for supplying power to the main auxiliary source; the second power supply circuit includes: a first diode, a second diode, a third diode, a fourth diode and a second capacitor; the cathode and anode of the first diode are respectively connected to the positive output end of the DC / DC conversion circuit and the first end of the second capacitor; the anode and cathode of the second diode are respectively connected to the positive output end of the DC / DC conversion circuit and the second end of the second capacitor; the anode and cathode of the third diode are respectively connected to the first end of the second capacitor and the negative output end of the DC / DC conversion circuit, and the anode and cathode of the fourth diode are respectively connected to the negative output end of the DC / DC conversion circuit and the second end of the second capacitor; the main auxiliary source is connected to the positive output end of the DC / DC conversion circuit. Since the power supply of the main auxiliary source comes from the output end of the DC / DC conversion circuit, and the general photovoltaic system includes multiple DC / DC conversion circuits, and the output ends of the multiple DC / DC conversion circuits are connected in parallel, therefore, even if all the pole switches in the fault isolation circuit are disconnected and all the photovoltaic strings connected to the input end of the DC / DC conversion circuit are isolated, the output end of the DC / DC conversion circuit can also have power, that is, from other parallel DC / DC conversion circuits. This ensures the power supply of the main auxiliary source, thereby ensuring the power supply of the controller.

[0021] In a possible implementation, it includes: a plurality of fault isolation circuits and a plurality of DC / DC conversion circuits; the plurality of fault isolation circuits and the plurality of DC / DC conversion circuits correspond one to one.

[0022] In a possible implementation, the power conversion circuit includes: a DC / AC conversion circuit.

[0023] Based on a photovoltaic system provided in the above embodiment, an embodiment of the present application further provides a DC combiner box, including: multiple fault isolation circuits and multiple DC / DC conversion circuits; the multiple fault isolation circuits and the multiple DC / DC conversion circuits correspond one to one; the first end of each fault isolation circuit is connected to N photovoltaic strings, and the second end of each fault isolation circuit is connected to the input end of the 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 the input end of the corresponding power conversion circuit through the same pole switch in the multi-pole switch; each group of photovoltaic strings includes at least two photovoltaic strings; when there is a reverse connection fault in the N photovoltaic strings, the corresponding multi-pole switches are all disconnected.

[0024] In a possible implementation, each fault isolation circuit also includes a shunt trip device and a controller; the controller is used to send a disconnection instruction to the shunt trip device when there is a reverse connection fault in the N photovoltaic strings, and the shunt trip device is actuated according to the disconnection instruction and drives the multi-pole switches to disconnect; before the shunt trip device is reset, the multi-pole switches remain in the disconnected state.

[0025] Based on a photovoltaic system and a DC combiner box provided in the above embodiments, an embodiment of the present application further provides a fault isolation method, which is applied to a photovoltaic system, and the photovoltaic system includes: a fault isolation circuit and a power conversion circuit; the first end of the fault isolation circuit is used to connect N photovoltaic strings, and the 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 the input end of the power conversion circuit through the same pole switch in the multi-pole switch; each group of photovoltaic strings includes at least two photovoltaic strings; the method includes: judging whether there is a reverse connection fault in the N photovoltaic strings, and controlling the multi-pole switches to be disconnected.

[0026] In a possible implementation, determining whether a reverse connection fault exists in N photovoltaic strings specifically includes: obtaining the current of each photovoltaic string in the N photovoltaic strings; determining, based on the current of each photovoltaic string, whether the current of any photovoltaic string in the N photovoltaic strings is reversed, and determining whether a reverse connection fault exists in the N photovoltaic strings.

[0027] It can be seen from the above technical solutions that the embodiments of the present application have the following advantages:

[0028] The photovoltaic system includes a fault isolation circuit, wherein the fault isolation circuit is connected between the photovoltaic string and the power conversion circuit, that is, the photovoltaic string is connected to the power conversion circuit through the fault isolation circuit, and when there is a reverse connection fault in the photovoltaic string, the fault isolation circuit is activated to disconnect the connection between the photovoltaic string and the power conversion circuit. The fault isolation switch provided in the embodiment of the present application includes a multi-pole switch, and the multi-pole switch is a linkage switch as a whole, that is, a multi-P switch, and the multi-P switches are disconnected or turned on at the same time. When there is a reverse connection fault in N photovoltaic strings, the multi-pole switches are all disconnected, that is, as long as a reverse connection fault occurs in one of the photovoltaic strings, all the pole switches in the fault isolation circuit are disconnected. Since at least two photovoltaic strings are divided into a group, each group corresponds to a pole switch, that is, each group of photovoltaic strings is connected in parallel to share a pole switch to connect the input end of the power conversion circuit. Therefore, the number of poles of the switch in the fault isolation circuit is reduced to a certain extent, thereby reducing the complexity of the hardware structure and reducing the cost of the fault isolation circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1A A schematic diagram of a photovoltaic system provided in an embodiment of the present application;

[0030] Figure 1B A schematic diagram of another photovoltaic system provided in an embodiment of the present application;

[0031] Figure 2 A schematic diagram of another photovoltaic system provided in an embodiment of the present application;

[0032] Figure 3 A schematic diagram of a plurality of photovoltaic strings connected in parallel at the input end of a DC / DC conversion circuit;

[0033] Figure 4 A schematic diagram of a photovoltaic system with a fault isolation circuit provided in an embodiment of the present application;

[0034] Figure 5 For Figure 4 A corresponding circuit diagram;

[0035] Figure 6 A schematic diagram of a photovoltaic system corresponding to when N is an even number provided in an embodiment of the present application;

[0036] Figure 7 A schematic diagram of a photovoltaic system corresponding to when N is an odd number provided in an embodiment of the present application;

[0037] Figure 8 A schematic diagram of a photovoltaic system with a shunt trip device provided in an embodiment of the present application;

[0038] Fig. 9 A schematic diagram of another photovoltaic system provided in an embodiment of the present application;

[0039] Fig.10 A schematic diagram of another photovoltaic system provided in an embodiment of the present application;

[0040] Fig.11 A schematic diagram of another photovoltaic system provided in an embodiment of the present application;

[0041] Fig.12 A schematic diagram of a photovoltaic system including multiple DC / DC conversion circuits provided in the present application;

[0042] Fig.13 A schematic diagram of a DC combiner box provided in this application;

[0043] Fig.14 A schematic diagram of another photovoltaic system provided in an embodiment of the present application. DETAILED DESCRIPTION

[0044] The terms "first", "second", etc. in the following description are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, a feature defined as "first", "second", etc. may explicitly or implicitly include one or more of the features. In the description of this application, unless otherwise specified, "plurality" means two or more.

[0045] In addition, in the present application, directional terms such as "upper" and "lower" may be defined including but not limited to the orientation relative to the schematic placement of the components in the drawings. It should be understood that these directional terms may be relative concepts, which are used for relative description and clarification, and may change accordingly according to the change in the orientation of the components in the drawings.

[0046] In this application, unless otherwise clearly specified and limited, the term "connection" should be understood in a broad sense. For example, "connection" can be a fixed connection, a detachable connection, or an integral connection; it can be a direct connection or an indirect connection through an intermediate medium. In addition, the term "coupling" can be a way of achieving electrical connection for signal transmission. "Coupling" can be a direct electrical connection or an indirect electrical connection through an intermediate medium.

[0047] Photovoltaic system example

[0048] An embodiment of the present application relates to a photovoltaic system, which may include two-stage power conversion or single-stage power conversion. A photovoltaic system including a two-stage power conversion circuit is first introduced below. In order to enable those skilled in the art to better understand the technical solution provided by the embodiment of the present application, the photovoltaic system provided by the embodiment of the present application is introduced below in conjunction with the accompanying drawings.

[0049] See also Figure 1A, which is a schematic diagram of a photovoltaic system provided in an embodiment of the present application.

[0050] The photovoltaic system provided in the embodiment of the present application includes a DC / DC conversion circuit 200 and a DC / AC conversion circuit 300, wherein the input end of the DC / DC conversion circuit 200 is connected to a plurality of photovoltaic strings, and the input end of the DC / DC conversion circuit 200 is connected to a photovoltaic array 100, wherein the photovoltaic array 100 includes a plurality of photovoltaic strings. Figure 1A Four photovoltaic strings are used as an example for introduction, namely photovoltaic strings PV1 to PV4. Photovoltaic strings PV1 to PV4 can be connected in parallel to the input end of the DC / DC conversion circuit 200, thereby increasing the input current of the DC / DC conversion circuit 200. The output end of the DC / DC conversion circuit 200 is connected to the DC / AC conversion circuit 300.

[0051] The DC / DC conversion circuit 200 is used to complete the conversion from DC to DC, and the DC / AC conversion circuit 300 completes the conversion from DC to AC. The output end of the DC / AC conversion circuit 300 can be connected to a transformer, that is, connected to a power grid through a transformer.

[0052] in addition, Figure 1A What is shown is only a schematic diagram of one DC / DC conversion circuit 200 connected to a DC / AC conversion circuit 300. Generally, in order to increase the output power of the DC / AC conversion circuit 300, multiple DC / DC conversion circuits 200 can be connected to the input end of the DC / AC conversion circuit 300.

[0053] It should be understood that Figure 1A The power conversion circuit in the photovoltaic system shown includes a DC / DC conversion circuit 200 and a DC / AC conversion circuit 300. In addition, the photovoltaic system provided in the embodiment of the present application may also include a power conversion circuit that only includes a DC / AC conversion circuit, but does not include a DC / DC conversion circuit. Figure 1B As shown, this figure is a schematic diagram of another photovoltaic system provided in an embodiment of the present application.

[0054] Compare Figure 1A and Figure 1B It can be seen that Figure 1B The photovoltaic strings PV1 to PV4 are directly connected to the input end of the DC / AC conversion circuit 300. The technical solutions provided in the following embodiments of the present application do not limit the specific implementation form of the power conversion circuit, that is, Figure 1A The power conversion circuit shown includes a DC / DC conversion circuit 200 and a DC / AC conversion circuit 300, which can also be Figure 1B The power conversion circuit shown only includes a DC / AC conversion circuit 300. The following mainly describes the power conversion circuit including a DC / DC conversion circuit as an example.

[0055] See also Figure 2 , which is a schematic diagram of another photovoltaic system provided in an embodiment of the present application.

[0056] Figure 2 In the description, the output ends of the two DC / DC conversion circuits are connected to the DC / AC conversion circuit 300 as an example, that is, the output end of the first DC / DC conversion circuit 200a and the output end of the second DC / DC conversion circuit 200b are connected in parallel to the input end of the DC / AC conversion circuit 300. The first DC / DC conversion circuit 200a and the second DC / DC conversion circuit 200b can be integrated in a DC combiner box 1000, and the DC combiner box 1000 can have a maximum power point tracking function.

[0057] Figure 2 In the example, the input end of the first DC / DC conversion circuit 200a is connected to the photovoltaic string PV1 and the photovoltaic string PV2, and the input end of the second DC / DC conversion circuit 200b is connected to the photovoltaic string PV3 and the photovoltaic string PV4.

[0058] Figure 1A , Figure 1B or Figure 2 In the photovoltaic system shown, since the input end of the DC / DC conversion circuit is connected to multiple photovoltaic strings, generally multiple photovoltaic strings are connected in parallel. When one of the photovoltaic strings is reversely connected, that is, the positive and negative poles are reversed, the current of other photovoltaic strings will be fed back into the reversed photovoltaic string. Since the anti-parallel diodes in the photovoltaic strings can withstand a limited current, when the current of multiple photovoltaic strings is fed back into one photovoltaic string, it will cause damage to the batteries in the photovoltaic string.

[0059] See also Figure 3 , which is a schematic diagram of a plurality of photovoltaic strings connected in parallel at the input end of a DC / DC conversion circuit.

[0060] Let's continue with the example of four photovoltaic strings. Figure 3 The photovoltaic string is equivalent to a battery. Traditionally, the positive poles PV1+-PV4+ of the four photovoltaic strings are connected together to the positive input terminal of the DC / DC conversion circuit 200, and the negative poles PV1--PV4- of the four photovoltaic strings are connected together to the negative input terminal of the DC / DC conversion circuit 200. For example, when PV4 is reversely connected, that is, the positive and negative poles are reversed, it can be seen that the positive poles of PV1-PV3 are connected to the positive input terminal of the DC / DC conversion circuit 200, and the positive pole of PV4 is connected to the negative input terminal of the DC / DC conversion circuit 200. Figure 3 The picture shows the reverse connection of PV string PV4. Figure 3It can be seen that the current of PV1-PV3 is represented by a dotted line with an arrow, and the current of PV4 is represented by a solid line with an arrow, that is, the current of PV1-PV3 will be reversed into PV4, and PV4 will be damaged because of the large current. Figure 3 In the process, fuses are added to each photovoltaic string, that is, fuses F1-F4 are connected in series to four photovoltaic strings. Fuses will increase circuit losses. On the other hand, the disconnection of fuses requires twice the input current, and the reliability is relatively low.

[0061] In order to solve the problem caused by the reverse connection of the above photovoltaic strings, an embodiment of the present application provides a photovoltaic system, which includes a fault isolation circuit, wherein the fault isolation circuit includes a multi-pole switch, and the number of poles of the switch depends on the number of photovoltaic strings. For example, N photovoltaic strings are divided into multiple groups, and each group of photovoltaic strings includes at least two photovoltaic strings; each group of photovoltaic strings is connected to the input end of the power conversion circuit through the same pole switch in the multi-pole switch; when there is a reverse connection fault in the N photovoltaic strings, that is, as long as there is a reverse connection fault in one photovoltaic string, all photovoltaic strings connected to the same power conversion circuit are disconnected from the power conversion circuit, that is, the multi-pole switch linkage is disconnected, that is, the connection between the N photovoltaic strings and the power conversion circuit is disconnected.

[0062] The photovoltaic system provided by the embodiment of the present application, wherein the fault isolation circuit includes a multi-pole switch, that is, the multi-pole switch includes multiple Ps, and the multiple P switches can be linked and operated simultaneously. As long as one of the photovoltaic strings or multiple photovoltaic strings connected to the multi-pole switch has a reverse connection fault, all poles of the multi-pole switch are disconnected. Since each group of photovoltaic strings corresponds to a one-pole switch, and each group of photovoltaic strings includes at least two photovoltaic strings, the number of poles of the switch is almost half of the number of photovoltaic strings, thereby greatly reducing the number of switches, simplifying the circuit connection, and saving the hardware cost of the fault isolation circuit. Since the multi-pole switch can be linked, when a reverse connection fault occurs in one or more photovoltaic strings, all the connections with the power conversion circuit can be reliably disconnected, thereby protecting the photovoltaic strings and the power conversion circuit.

[0063] One possible implementation is that when N photovoltaic strings share a common positive pole, the positive poles of the N photovoltaic strings are connected together, and the positive poles of the N photovoltaic strings are connected to the input end of the power conversion circuit through a single-pole switch in a multi-pole switch; in order to better protect each photovoltaic string and avoid too many photovoltaic strings being connected in parallel, when one of them is reversely connected, other photovoltaic strings connected in parallel are damaged by too much current. Therefore, one possible implementation is to group the N photovoltaic strings in pairs. Since the N photovoltaic strings share a common positive pole, the negative poles of the N photovoltaic strings are grouped in pairs, and the negative pole of each photovoltaic string is connected to the input end of the power conversion circuit through a single-pole switch in a multi-pole switch.

[0064] The above describes the situation where N photovoltaic strings share a common positive pole. In addition, N photovoltaic strings can also share a common negative pole. The following specifically describes the connection method of the common negative pole.

[0065] When N photovoltaic strings share a common negative pole, the negative poles of the N photovoltaic strings are connected together, and the negative poles of the N photovoltaic strings are connected to the input end of the power conversion circuit through a single-pole switch in the multi-pole switch. Similar to the common positive pole, the N photovoltaic strings are grouped in pairs, that is, the positive poles of the N photovoltaic strings are grouped in pairs and share a single-pole switch, and the positive pole of each group of photovoltaic strings is connected to the input end of the power conversion circuit through a single-pole switch in the multi-pole switch.

[0066] For example, N photovoltaic strings are divided into M groups, and each photovoltaic string group needs a pole switch to connect to the power conversion circuit, that is, M pole switches are required, and one end of the common positive pole or common negative pole of the N photovoltaic strings is connected to the power conversion circuit through a pole switch, so the fault isolation circuit includes M+1 pole switches. The relationship between M and N is divided into the following two cases according to whether N is an odd number or an even number. When N is an even number, M=N / 2; when N is an odd number, M=(N+1) / 2. The first ends of the N photovoltaic strings are all connected to the input end of the power conversion circuit through the first pole switch in the M+1 pole switch; the M groups of photovoltaic strings are respectively connected to the input end of the power conversion circuit through the M pole switches in the M+1 pole switch; when there is a reverse connection fault in the N photovoltaic strings, the M+1 pole switches are all disconnected, that is, as long as one of the photovoltaic strings has a reverse connection fault, all pole switches in the fault isolation circuit are disconnected. Since the photovoltaic strings are grouped in pairs, two photovoltaic strings are connected in parallel and share a common switch to connect the input end of the power conversion circuit; when N is an odd number, the remaining photovoltaic string in the group is a separate group. When one of the photovoltaic strings is reversely connected, only one photovoltaic string will be reversely connected, and the current is relatively small, so the reversely connected photovoltaic string will not be damaged.

[0067] In the embodiments of the present application, it is not limited whether the first end of the photovoltaic string is the positive pole or the negative pole, that is, N photovoltaic strings can be connected to a common positive pole or a common negative pole. For the convenience of description, the following embodiments are introduced by taking N photovoltaic strings connected to a common positive pole as an example. When N photovoltaic strings are connected to a common positive pole, the positive poles of the N photovoltaic strings are connected together and connected to the positive input end of the power conversion circuit through a pole switch. The negative poles of the N photovoltaic strings are connected in pairs to the negative input end of the power conversion circuit through corresponding pole switches. Since the positive poles of the N photovoltaic strings are connected together, the input current of the power conversion circuit can be increased. In addition, since the negative poles of the N photovoltaic strings are connected in pairs, the number of poles of the switch in the fault isolation circuit is reduced to a certain extent, thereby reducing the complexity of the hardware structure and reducing costs.

[0068] For ease of understanding, the following embodiments of the present application are first introduced by taking N as an even number as an example, taking a power conversion circuit including a DC / DC conversion circuit as an example, Figure 4 and Figure 5 , we will continue to introduce the example of connecting the input end of a DC / DC conversion circuit to four photovoltaic strings.

[0069] See also Figure 4 , which is a schematic diagram of a photovoltaic system with a fault isolation circuit provided in an embodiment of the present application.

[0070] See also Figure 5 , the figure is Figure 4 A corresponding circuit diagram.

[0071] from Figure 4 It can be seen that the four photovoltaic strings are connected to the first end of the fault isolation circuit 400, the second end of the fault isolation circuit 400 is connected to the input end of the DC / DC conversion circuit 200, and the output end of the DC / DC conversion circuit 200 is connected to the input end of the DC / AC conversion circuit 300. The positive poles of the four photovoltaic strings are connected together, that is, the positive poles of PV1+-PV4+ are connected together, and the four photovoltaic strings are divided into two groups, two photovoltaic strings in one group, that is, the negative poles of every two photovoltaic strings are connected together, PV1- and PV2- are connected together, and PV3- and PV4- are connected together.

[0072] When a reverse connection fault occurs in only one of the four photovoltaic strings, all switches in the fault isolation circuit 400 are disconnected, that is, the connection between all photovoltaic strings and the input end of the DC / DC conversion circuit 200 is disconnected to prevent the fault from spreading to other circuits.

[0073] Continuing with the example of PV4 reverse connection, since PV1- and PV2- are not connected to PV4-, when PV4 is reversely connected, only the current of PV3 is fed back to PV4. Therefore, the current fed back to PV4 is small and will not consume PV4. This is different from Figure 3 .

[0074] In order to more clearly describe the connection relationship between the photovoltaic string and the switch in the fault isolation circuit 400, Figure 5 Continue to introduce the working principle.

[0075] Since N is 4, which is an even number, M=4 / 2, that is, the photovoltaic strings are divided into 2 groups. Correspondingly, the fault isolation circuit 400 includes M+1 pole switches, that is, 2+1=3 pole switches, which are the first pole switch S1, the second pole switch S2 and the third pole switch S3.

[0076] Among them, the positive poles of PV1+-PV4+ are connected together to connect the first end of the first pole switch S1, and the second end of the first pole switch S1 is connected to the input end of the DC / DC conversion circuit 200. PV1- and PV2- are connected together to connect the first end of the second pole switch S2, and the second end of the second pole switch S2 is connected to the input end of the DC / DC conversion circuit 200. PV3- and PV4- are connected together to connect the first end of the third pole switch S3, and the second end of the third pole switch S3 is connected to the input end of the DC / DC conversion circuit 200.

[0077] When PV4 is reversely connected, the first pole switch S1, the second pole switch S2 and the third pole switch S3 are all disconnected.

[0078] Obviously, the photovoltaic system provided in the embodiment of the present application can disconnect all switches in the fault isolation circuit when the photovoltaic string is reversely connected, thereby disconnecting the photovoltaic string from the subsequent DC / DC conversion circuit to avoid other more serious faults caused by the reverse connection fault. In addition, since the fault isolation circuit provided in the embodiment of the present application can realize the connection of photovoltaic strings in groups of two, that is, at most two photovoltaic strings are connected to a single pole switch, thereby avoiding more photovoltaic strings from being connected together, when one of the photovoltaic strings has a reverse connection fault, the current of all other photovoltaic strings connected together will be reversed, causing damage to the photovoltaic string. In the embodiment of the present application, two photovoltaic strings are connected in parallel. Even if a reverse connection fault occurs, the reverse current is relatively small and will not damage the photovoltaic string. It should be understood that the reverse connection fault of the photovoltaic strings in all the embodiments of the present application means that at least one photovoltaic string is reversely connected, that is, as long as one photovoltaic string is reversely connected, it is necessary to disconnect the connection of N photovoltaic strings from the power conversion circuit.

[0079] The photovoltaic system provided in the embodiment of the present application, in order to protect the photovoltaic strings, divides every two photovoltaic strings into a group and connects a pole switch, rather than dividing a larger number of photovoltaic strings into a group. If a larger number of photovoltaic strings are connected in parallel, when reverse connection occurs, the magnitude of the reverse current cannot be guaranteed. Since there are many photovoltaic strings connected in parallel, the reverse current will increase and damage the photovoltaic strings. The embodiment of the present application is to ensure the safety of the photovoltaic strings when reverse connection occurs and to minimize the number of switches in the fault isolation circuit, so that the two are better balanced.

[0080] The above embodiment introduces an implementation including four photovoltaic strings. The technical solution provided in the embodiment of the present application is applicable to the case where N is an even number and has a larger value. For example, the following introduces an implementation of N=6, that is, six photovoltaic strings.

[0081] See also Figure 6 , this figure is a schematic diagram of a photovoltaic system corresponding to when N is an even number provided in an embodiment of the present application.

[0082] Since N=6, the photovoltaic strings are divided into M=6 / 2=3 groups, and the fault isolation circuit 400 includes M+1=4 pole switches, namely the first pole switch S1, the second pole switch S2, the third pole switch S3 and the fourth pole switch S4.

[0083] The positive poles PV1+-PV6+ of the six photovoltaic strings are connected together to the first end of the first pole switch S1, and each two photovoltaic strings form a group. The negative poles of each two photovoltaic strings correspond to one pole switch, PV1- and PV2- are connected to the first end of the second pole switch S2, PV3- and PV4- are connected to the first end of the third pole switch S3, and PV5- and PV6- are connected to the first end of the fourth pole switch S4. The second end of the first pole switch S1, the second end of the second pole switch S2, the second end of the third pole switch S3, and the second end of the fourth pole switch S4 are all connected to the DC / DC conversion circuit 200.

[0084] The above describes the implementation when N is an even number. The following describes the implementation when N is an odd number in conjunction with the accompanying drawings.

[0085] See also Figure 7 , this figure is a schematic diagram of a photovoltaic system corresponding to when N is an odd number provided in an embodiment of the present application.

[0086] For the convenience of description, N=5 is taken as an example for introduction. Therefore, the 5 photovoltaic strings are divided into M=(N+1 / )2=3 groups, and the fault isolation circuit 400 includes M+1=4 pole switches, namely the first pole switch S1, the second pole switch S2, the third pole switch S3 and the fourth pole switch S4, that is, the number of poles of the switch is the same as when N is 6.

[0087] Since every two photovoltaic strings are grouped together, N is an odd number, and there is one photovoltaic string left that cannot be paired, the remaining photovoltaic string is a separate group and corresponds to a single-pole switch in the fault isolation circuit 400 .

[0088] The positive poles PV1+-PV5+ of the five photovoltaic strings are connected together to the first end of the first pole switch S1, and each two photovoltaic strings form a group. The negative poles of each two photovoltaic strings correspond to one pole switch, PV1- and PV2- are connected to the first end of the second pole switch S2, PV3- and PV4- are connected to the first end of the third pole switch S3, and PV5- is a group connected to the first end of the fourth pole switch S4. The second end of the first pole switch S1, the second end of the second pole switch S2, the second end of the third pole switch S3, and the second end of the fourth pole switch S4 are all connected to the DC / DC conversion circuit 200.

[0089] In the above, examples are respectively given with N being an even number and N being an odd number. The following will continue to take N being an even number, that is, N being 4, as an example to introduce other implementation methods.

[0090] In order to reliably disconnect the switch in the fault isolation circuit when a reverse connection fault occurs in a photovoltaic string, the fault isolation circuit provided in the embodiment of the present application may further include a shunt tripping device, which is described below in conjunction with the accompanying drawings.

[0091] See also Figure 8 , which is a schematic diagram of a photovoltaic system with a shunt trip device provided in an embodiment of the present application.

[0092] In the photovoltaic system provided in this embodiment, the fault isolation circuit further includes: a shunt trip device and a controller 600;

[0093] The controller 600 is used for sending a disconnection instruction to the shunt trip device when there is a reverse connection fault in N photovoltaic strings. The shunt trip device acts according to the disconnection instruction and drives the M+1 pole switches to disconnect. Before the shunt trip device is reset, the M+1 pole switches remain in the disconnected state.

[0094] For example, continuing with the example of a reverse connection fault of PV4, the controller 600 sends a disconnection command to the shunt trip device, and the shunt trip device is activated, thereby driving the three-pole switches S1-S3 to be disconnected. If the shunt trip device is not actively reset, the three-pole switches S1-S3 remain disconnected, avoiding the three-pole switches S1-S3 from closing when the fault of the photovoltaic string has not been resolved, thereby better protecting the photovoltaic string.

[0095] In addition, the controller 600 provided in the embodiment of the present application requires a power supply, and therefore, may include a first power supply circuit 500. The first power supply circuit 500 provided in the embodiment of the present application adopts a competitive power supply method, that is, the first power supply circuit 500 is used to supply power to the controller 600 from the group with the highest voltage among the M groups of photovoltaic strings, and does not need to supply power from each group of photovoltaic strings.

[0096] Figure 8 A method for implementing competitive power extraction is provided, that is, an implementation circuit of a first power extraction circuit, the first power extraction circuit includes 2 (M+1) diodes and a first capacitor; since N is 4, M is 2, and the first power extraction circuit 500 includes 6 diodes and one capacitor.

[0097] Each pole switch in the M+1 pole switches corresponds to two diodes among the 2 (M+1) diodes; the first end of each pole switch in the M+1 pole switches is respectively connected to the first end and the second end of the first capacitor through a forward biased diode and a reverse biased diode; the first end of each pole switch in the M+1 pole switches is connected to the corresponding photovoltaic string, and the second end of each pole switch in the M+1 pole switches is connected to the input end of the DC / DC conversion circuit.

[0098] from Figure 8It can be seen that the fault isolation circuit includes three-pole switches S1-S3, and each pole switch corresponds to two diodes, that is, the first end of the first pole switch S1 is connected to the two ends of the first capacitor C1 through the corresponding forward biased diode D2 and the reverse biased diode D1, the first end of the second pole switch S2 is connected to the two ends of the first capacitor C1 through the corresponding forward biased diode D4 and the reverse biased diode D3, and the first end of the third pole switch S3 is connected to the two ends of the first capacitor C1 through the corresponding forward biased diode D6 and the reverse biased diode D5. PV1+—PV4+ are connected together, that is, point A, the cathode of D1 is connected to point A, and similarly, the anode of D2 is connected to point A. PV1- and PV2- are connected together, that is, point B, the cathode of D3 is connected to point B, and similarly, the anode of D4 is connected to point B. PV3- and PV4- are connected together, that is, point C, the cathode of D5 is connected to point C, and similarly, the anode of D6 is connected to point C.

[0099] The specific working principle of competitive power supply is described below with examples in conjunction with the accompanying drawings.

[0100] For example, when the voltage of PV1 and PV2 connected in parallel is higher than the voltage of PV3 and PV4 connected in parallel, the voltage at point B is lower than the voltage at point C, and the current flows back to PV1 and PV2 through point B. Conversely, when the voltage of PV1 and PV2 connected in parallel is lower than the voltage of PV3 and PV4 connected in parallel, the voltage at point B is higher than the voltage at point C, and the current flows back to PV3 and PV4.

[0101] When PV1-PV4 are all reversed, the voltage of PV1 / PV2 connected in parallel is greater than the voltage of PV3 and PV4 connected in parallel, then the voltage at point B is higher than the voltage at point C, and the current flows out from PV1 and PV2, and vice versa from PV3 and PV4.

[0102] The following introduces a specific implementation method for determining whether a PV string is reversely connected.

[0103] See also Fig. 9 , which is a schematic diagram of another photovoltaic system provided in an embodiment of the present application.

[0104] The photovoltaic system provided in this embodiment may further include: an input current detection circuit 700;

[0105] The input current detection circuit 700 is used to detect the current of each photovoltaic string in the N photovoltaic strings; it should be understood that each photovoltaic string can be connected in series with a current sensor to detect the current of each photovoltaic string. Since the directions of the currents of the photovoltaic strings are the same under normal circumstances, if there is reverse connection, the current direction of the reversed photovoltaic string will be opposite to the direction of other normal photovoltaic strings. Therefore, it is possible to judge whether the connection is reversed by the current direction. For example, the current is positive under normal circumstances, and when reversed, the detected current is negative, thereby judging the reverse connection.

[0106] The controller 600 is used to control the M+1 pole switches in the fault isolation circuit 400 to disconnect when the current of any photovoltaic string among the N photovoltaic strings is reversed according to the current of each photovoltaic string. That is, the controller 600 sends a disconnection instruction to the shunt trip device, and the shunt trip device drives the three-pole switches S1-S3 to disconnect. As long as there is a reverse connection fault in all photovoltaic strings, it is necessary to disconnect all photovoltaic strings from the DC / DC conversion circuit 200.

[0107] The fault isolation circuit 400 provided in the embodiment of the present application can not only be disconnected when a reverse connection fault occurs in the photovoltaic string to play a protective role, but can also be disconnected when a short circuit fault occurs in the photovoltaic string to play a protective role, which is described in detail below.

[0108] The photovoltaic system provided in this embodiment may include not only the input current detection circuit 700 , but also an input voltage detection circuit 800 .

[0109] The input voltage detection circuit 800 is used to detect the voltage between the first end of the first pole switch S1 and the first end of each pole switch in the M pole switches (S2 and S3) to obtain M voltages; that is, the voltage detected by the input voltage detection circuit 800 is the voltage of each group in the M photovoltaic strings. As long as the voltage of one photovoltaic string is low, there may be a short circuit fault in some photovoltaic strings. It should be understood that when a short circuit fault exists, the voltage of the photovoltaic string will drop and the current will rise. In order to accurately judge the short circuit fault, both voltage and current can be judged. Fig. 9 In the embodiment, the input voltage detection circuit 800 needs to detect the voltage between point A where PV1+-PV4+ are connected together and point B where PV1- and PV2- are connected together. The input voltage detection circuit 800 also needs to detect the voltage between point A where PV1+-PV4+ are connected together and point C where PV3- and PV4- are connected together.

[0110] In a specific implementation, the controller 600 is used to control all M+1 pole switches to be disconnected when at least one of the M voltages is less than the first voltage threshold and the current of at least one of the N photovoltaic strings is greater than the first current threshold. That is, as long as there is a short circuit fault in the photovoltaic string, all switches in the fault isolation circuit 400 are disconnected, thereby isolating the faulty photovoltaic string and protecting the subsequent circuit from the harm of the short circuit fault.

[0111] The above-described embodiment is for detecting a short-circuit fault at the input end of a DC / DC conversion circuit. The following describes a short-circuit fault at the output end of a DC / DC conversion circuit.

[0112] See also Fig.10 , which is a schematic diagram of another photovoltaic system provided in an embodiment of the present application.

[0113] The embodiment of the present application can not only detect whether a short circuit fault occurs at the input end of the DC / DC conversion circuit, but also detect 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 avoid the expansion of the fault range and play a protective role, it is also necessary to control all pole switches in the fault isolation circuit to be disconnected to play a role in fault isolation.

[0114] The photovoltaic system provided in this embodiment further includes: an output current detection circuit 901 and an output voltage detection circuit 902;

[0115] An output voltage detection circuit 902 is used to detect the output voltage of the DC / DC conversion circuit 200;

[0116] The output current detection circuit 901 is used to detect the current at the second end of the first pole switch S1 , that is, to detect the input current of the DC / DC conversion circuit 200 .

[0117] In order to accurately determine whether a short circuit fault occurs at the output end of the DC / DC conversion circuit 200, dual judgments of voltage and current are also required. When both meet the corresponding judgment conditions, a short circuit fault is determined to occur. That is, the controller 600 controls the M+1 pole switches to be disconnected when the current at the second end of the first pole switch S1 is greater than the second current threshold and the voltage at the output end of the DC / DC conversion circuit 200 is less than the second preset voltage. Since the first pole switch S1 is connected to all photovoltaic strings, the output current detection circuit 901 only detects the current flowing through the first pole switch S1.

[0118] It should be understood that both the input current detection circuit and the output current detection circuit can be implemented by a current sensor. When there is reverse connection in the photovoltaic string, the current of the photovoltaic string is opposite to the current direction of the normal photovoltaic string. Therefore, it is possible to determine whether there is a reverse connection fault by detecting the direction of the current. For example, when the current of the normal photovoltaic string is positive, the current of the reverse-connected photovoltaic string is negative, that is, less than zero, then it is judged that the current is reversed, or it can be less than a preset threshold, then it is considered to be reversed and a reverse connection fault occurs. A current sensor can be set in each photovoltaic string to detect the current of the photovoltaic string. In addition, for example, if four photovoltaic strings are included, three of the photovoltaic strings can be provided with current sensors, and a current sensor is provided for the output current. Then the current of another photovoltaic string can be obtained by subtracting the sum of the currents of the three photovoltaic strings from the output current, so that one less current sensor can be provided.

[0119] The photovoltaic system provided in the embodiment of the present application can, in order to more comprehensively protect the safe and reliable operation of the photovoltaic system, not only disconnect all pole switches in the fault isolation circuit 400 when a reverse connection fault occurs in the photovoltaic string, but also disconnect all pole switches in the fault isolation circuit 400 when a short circuit fault occurs in the photovoltaic string, and can also disconnect all pole switches in the fault isolation circuit 400 when a short circuit fault occurs at the output end of the DC / DC conversion circuit 200, so as to prevent the short circuit fault at the output end of the DC / DC conversion circuit 200 from causing damage to the photovoltaic string.

[0120] The above embodiment introduces the situation of taking power from the photovoltaic string to power the controller. In order to ensure that the controller can continue to work when the photovoltaic string is disconnected or the photovoltaic string has no power output, the embodiment of the present application also includes another power taking method, which can be used as the main power supply method of the controller. The following is a detailed introduction with reference to the accompanying drawings.

[0121] See also Fig.11 , which is a schematic diagram of another photovoltaic system provided in an embodiment of the present application.

[0122] Since any hardware may fail during operation, in order to ensure that the photovoltaic system operates safely and reliably, two controllers may be set in the photovoltaic system to form a backup, that is, to achieve redundant control. When one of the controllers fails, it does not affect the normal control operation. That is, in the photovoltaic system provided in this embodiment, the controller 600 includes: a main controller 600a and a backup controller 600b;

[0123] The main controller 600a and the backup controller 600b are both used to control the M+1 pole switches to be disconnected when there is a reverse connection fault in N photovoltaic strings. That is, in the embodiment of the present application, the main controller 600a and the backup controller 600b work simultaneously, and the main controller 600a and the backup controller 600b can simultaneously receive the detection signals sent by the input voltage detection circuit 800, the input current detection circuit 700, the output voltage detection circuit 902 and the output current detection circuit 901, that is, the two controllers can simultaneously receive the input voltage, input current, output current and output voltage, and can use the received signals to determine whether it is necessary to control all pole switches in the fault isolation circuit 400 to be disconnected. In this way, it can be ensured that when one of the controllers fails and cannot accurately send a disconnection instruction to the fault isolation circuit, the other normal controller can accurately and reliably control all pole switches to be disconnected.

[0124] In addition, in order to ensure the reliability of power supply, the embodiment of the present application provides two auxiliary sources, namely, including: a main auxiliary source 903 and a secondary auxiliary source 904;

[0125] The main auxiliary source 903 and the secondary auxiliary source 904 are both used to supply power to the main controller 600a and the standby controller 600b;

[0126] The main auxiliary source 903 is connected to the output end of the DC / DC conversion circuit 200 ; that is, the power supply of the main auxiliary source 903 comes from the output end of the DC / DC conversion circuit 200 .

[0127] The secondary auxiliary source 904 is connected to the first end of the fault isolation circuit 400 , that is, the power source of the secondary auxiliary source 904 comes from the photovoltaic string.

[0128] Since the photovoltaic system provided in the embodiment of the present application includes two auxiliary sources, when one of the auxiliary sources fails, the other normal auxiliary source can supply power to the controller as usual to ensure the normal operation of the controller.

[0129] The second power supply circuit that provides power source for the main auxiliary power source 903 is introduced below.

[0130] The second power supply circuit includes: a first diode D7, a second diode D8, a third diode D9, a fourth diode D10 and a second capacitor C2;

[0131] The cathode and anode of the first diode D7 are respectively connected to the positive output end of the DC / DC conversion circuit 200 and the first end of the second capacitor C2; the anode and cathode of the second diode D8 are respectively connected to the positive output end of the DC / DC conversion circuit 200 and the second end of the second capacitor C2;

[0132] The anode and cathode of the third diode D9 are respectively connected to the first end of the second capacitor C2 and the negative output end of the DC / DC conversion circuit 200, and the anode and cathode of the fourth diode D10 are respectively connected to the negative output end of the DC / DC conversion circuit 200 and the second end of the second capacitor C2;

[0133] The main auxiliary source 903 is connected to the positive output end of the DC / DC conversion circuit 200 through the second power extraction circuit. Since the power supply of the main auxiliary source 903 comes from the output end of the DC / DC conversion circuit 200, and the photovoltaic system generally includes multiple DC / DC conversion circuits, and the output ends of the multiple DC / DC conversion circuits are connected in parallel, even if all the pole switches in the fault isolation circuit 400 are disconnected and all the photovoltaic strings connected to the input end of the DC / DC conversion circuit 200 are isolated, the output end of the DC / DC conversion circuit 200 can also have electricity, that is, from other parallel DC / DC conversion circuits. In this way, the power supply of the main auxiliary source 903 can be guaranteed, thereby ensuring the power supply of the controller.

[0134] The specific implementation form of the DC / DC conversion circuit in each of the above photovoltaic systems is not limited in the embodiments of the present application, and can be, for example, a boost circuit with a bypass relay, i.e., a Boost circuit. When the bypass relay is closed, the Boost circuit can be bypassed, i.e., there is no need to boost the voltage, and the photovoltaic string is directly connected to the DC / AC conversion circuit of the subsequent stage through the bypass relay.

[0135] Generally, in order to increase the output power of the inverter, multiple DC / DC conversion circuits are connected to the input end of the DC / AC conversion circuit.

[0136] See also Fig.12 , which is a schematic diagram of a photovoltaic system including multiple DC / DC conversion circuits provided in an embodiment of the present application.

[0137] The photovoltaic system provided in this embodiment includes: a plurality of fault isolation circuits and a plurality of DC / DC conversion circuits;

[0138] The multiple fault isolation circuits correspond to the multiple DC / DC conversion circuits one by one, that is, the input end of each DC / DC conversion circuit is connected to a corresponding fault isolation circuit. The output ends of the multiple DC / DC conversion circuits are all connected to the input end of the DC / AC conversion circuit 300.

[0139] The following example takes the case where the input end of the DC / AC conversion circuit is connected to at least two of the following DC / DC conversion circuits: the first DC / DC conversion circuit 200a and the second DC / DC conversion circuit 200b. The input ends of the first DC / DC conversion circuit 200a and the second DC / DC conversion circuit 200b are connected to their respective corresponding photovoltaic arrays, that is, the first DC / DC conversion circuit 200a corresponds to the photovoltaic array 100a, and the second DC / DC conversion circuit 200b corresponds to the photovoltaic array 100b. The photovoltaic array 100a and the photovoltaic array 100b both include multiple photovoltaic strings. For details, please refer to the introduction of the above embodiments. The photovoltaic strings in the photovoltaic array are not illustrated in detail in this embodiment. In this embodiment, the first fault isolation circuit 400a is connected between the input end of the photovoltaic array 100a and the first DC / DC conversion circuit 200a, and the second fault isolation circuit 400b is connected between the input end of the photovoltaic array 100b and 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 above embodiments, and are not described in detail here.

[0140] For example, when a reverse connection fault occurs in the photovoltaic strings in the photovoltaic array 100a, all switches in the first fault isolation circuit 400a are disconnected, that is, the photovoltaic array 100a stops working, and there is no power supply 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 output electrical energy normally.

[0141] DC combiner box embodiment

[0142] In addition, the photovoltaic system provided in the embodiment of the present application may include a combiner box, that is, a DC combiner box, in which multiple fault isolation circuits and multiple DC / DC conversion circuits are integrated.

[0143] The DC combiner box includes: multiple fault isolation circuits and multiple DC / DC conversion circuits; the multiple fault isolation circuits correspond to the multiple DC / DC conversion circuits one by one; the first end of each fault isolation circuit is connected to N photovoltaic strings, and the second end of each fault isolation circuit is connected to the input end of the DC / DC conversion circuit; each fault isolation circuit includes a multi-pole switch, and each photovoltaic string in the N photovoltaic strings is connected to the input end of the corresponding power conversion circuit through the same pole switch in the multi-pole switch; each photovoltaic string includes at least two photovoltaic strings; when there is a reverse connection fault in the N photovoltaic strings, the corresponding multi-pole switches are all disconnected.

[0144] The following is an introduction using two power conversion circuits as examples, wherein the power conversion circuit is introduced using a DC / DC conversion circuit as an example. The working principles and advantages of the above photovoltaic system embodiments are also applicable to the DC combiner box provided in this embodiment, and the same parts are not repeated here.

[0145] See also Fig.13 , which is a schematic diagram of a DC combiner box provided in an embodiment of the present application.

[0146] The first DC / DC conversion circuit 200 a , the second DC / DC conversion circuit 200 b , the first fault isolation circuit 400 a , and the second fault isolation circuit 400 b are all integrated in the DC combiner box 1000 .

[0147] Since the DC combiner box provided in the embodiment of the present application includes a fault isolation circuit, wherein the fault isolation circuit includes a multi-pole switch, and the multi-pole switches are linked, that is, they are closed or disconnected at the same time. The number of poles of the switch depends on the number of photovoltaic strings. N photovoltaic strings are divided into M groups, and the fault isolation circuit includes M+1 pole switches. The relationship between M and N is divided into the following two cases according to whether N is an odd number or an even number. When N is an even number, M=N / 2; when N is an odd number, M=(N+1) / 2. The first ends of the N photovoltaic strings are connected to the input end of the DC / DC conversion circuit through the first pole switch in the M+1 pole switch; the M groups of photovoltaic strings are respectively connected to the input end of the DC / DC conversion circuit through the M pole switches in the M+1 pole switch; when there is a reverse connection fault in the N photovoltaic strings, the M+1 pole switches are all disconnected, that is, as long as a reverse connection fault occurs in one of the photovoltaic strings, all pole switches in the fault isolation circuit are disconnected. Since the photovoltaic strings are grouped in pairs, two photovoltaic strings are connected in parallel and share a common switch to connect the input end of the DC / DC conversion circuit; when N is an odd number, the remaining photovoltaic string in the group is a separate group. When one of the photovoltaic strings is reversely connected, only one photovoltaic string will be reversely fed back, and the current is relatively small, so the reversely connected photovoltaic string will not be damaged.

[0148] In the embodiments of the present application, it is not limited whether the first end of the photovoltaic string is the positive pole or the negative pole, that is, N photovoltaic strings can be connected to a common positive pole or a common negative pole. For the convenience of description, the following embodiments are introduced by taking N photovoltaic strings connected to a common positive pole as an example. When N photovoltaic strings are connected to a common positive pole, the positive poles of the N photovoltaic strings are connected together and connected to the positive input end of the DC / DC conversion circuit through a pole switch. The negative poles of the N photovoltaic strings are connected in pairs to the negative input end of the DC / DC conversion circuit through corresponding pole switches. Since the positive poles of the N photovoltaic strings are connected together, the input current of the DC / DC conversion circuit can be increased. In addition, since the negative poles of the N photovoltaic strings are connected in pairs, the number of poles of the switch in the fault isolation circuit is reduced to a certain extent, thereby reducing the complexity of the hardware structure and reducing costs.

[0149] The embodiments described above are all described by taking the example that the power conversion circuit includes a DC / DC conversion circuit and a DC / AC conversion circuit. The following describes the implementation of the power conversion circuit including only a DC / AC conversion circuit in conjunction with the accompanying drawings.

[0150] See also Fig.14 , which is a schematic diagram of another photovoltaic system provided in an embodiment of the present application.

[0151] The photovoltaic system provided in this embodiment includes a fault isolation circuit 400 and a DC / AC conversion circuit 300. The implementation method of the fault isolation circuit 400 can be specifically referred to the introduction of the above embodiment. The number of switch poles included in the fault isolation circuit 400 is related to the number of photovoltaic strings in the connected photovoltaic array 100. When the photovoltaic string is reversely connected, all the switches in the fault isolation circuit 400 are disconnected, that is, they are linked and disconnected together, thereby disconnecting the connection between the photovoltaic array 100 and the DC / AC conversion circuit 300, protecting the photovoltaic string while avoiding the damage caused by the reverse connection fault to the DC / AC conversion circuit 300. In addition, the fault isolation circuit 400 can also disconnect the connection between the photovoltaic array 100 and the DC / AC conversion circuit 300 when there is a short circuit fault in the photovoltaic string.

[0152] Method Embodiment

[0153] Based on a photovoltaic system and a DC combiner box provided in the above embodiments, an embodiment of the present application further provides a fault isolation method.

[0154] The fault isolation method provided in this embodiment is applied to the photovoltaic system introduced in any one of the above embodiments, and the photovoltaic system includes: a fault isolation circuit and a power conversion circuit; the first end of the fault isolation circuit is connected to N photovoltaic strings, and the 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 photovoltaic string in the N photovoltaic strings is connected to the input end of the power conversion circuit through the same pole switch in the multi-pole switch; each photovoltaic string includes at least two photovoltaic strings;

[0155] The method includes:

[0156] It is determined that there is a reverse connection fault in the N photovoltaic strings, and the switches of the M+1 poles are all controlled to be disconnected.

[0157] Determine whether there is a reverse connection fault in N photovoltaic strings, including:

[0158] Obtaining the current of each photovoltaic string among the N photovoltaic strings;

[0159] According to the current of each photovoltaic string, it is determined that the current of any photovoltaic string among the N photovoltaic strings is reversed, and it is determined that a reverse connection fault exists in the N photovoltaic strings.

[0160] When there is reverse connection in the photovoltaic string, the current of the photovoltaic string is opposite to the current direction of the normal photovoltaic string. Therefore, it is possible to determine whether there is a reverse connection fault by detecting the direction of the current. For example, when the current of the normal photovoltaic string is positive, the current of the reverse-connected photovoltaic string is negative, that is, less than zero, then it is determined that the current is reversed, or it can be less than a preset threshold, then it is considered to be reversed and a reverse connection fault occurs. A current sensor can be set in each photovoltaic string to detect the current of the photovoltaic string. In addition, for example, if four photovoltaic strings are included, three of the photovoltaic strings can be provided with current sensors, and a current sensor is provided for the output current. Then the current of another photovoltaic string can be obtained by subtracting the sum of the currents of the three photovoltaic strings from the output current, so that one less current sensor can be provided.

[0161] In order to better protect the photovoltaic strings from being subjected to too much current when reversely connected, every two photovoltaic strings can be divided into a group, and each group of photovoltaic strings corresponds one-to-one to one pole switch in the multi-pole switch.

[0162] The following is an example of N photovoltaic strings, where every two photovoltaic strings are grouped together.

[0163] N photovoltaic strings share a common positive pole, and the positive poles of the N photovoltaic strings are connected to the input end of the power conversion circuit through a single-pole switch in the multi-pole switch; N photovoltaic strings are grouped in pairs, and the negative pole of each photovoltaic string group is connected to the input end of the power conversion circuit through a single-pole switch in the multi-pole switch;

[0164] or,

[0165] N photovoltaic strings share a common negative pole, and the negative poles of the N photovoltaic strings are connected to the input end of the power conversion circuit through a single-pole switch in the multi-pole switch. The N photovoltaic strings are grouped in pairs, and the positive pole of each photovoltaic string is connected to the input end of the power conversion circuit through a single-pole switch in the multi-pole switch.

[0166] N photovoltaic strings are divided into M groups, when N is an even number, M=N / 2; when N is an odd number, M=(N+1) / 2; the fault isolation circuit includes M+1 pole switches, and the M+1 pole switches are linked, that is, closed or opened at the same time; the first ends of the N photovoltaic strings are connected to the input end of the DC / DC conversion circuit through the first pole switch in the M+1 pole switches; the M groups of photovoltaic strings are respectively connected to the input end of the DC / DC conversion circuit through the M pole switches in the M+1 pole switches.

[0167] It should be understood that in the present application, "at least one (item)" means one or more, and "plurality" means two or more. "And / or" is used to describe the association relationship of associated objects, indicating that three relationships may exist. For example, "A and / or B" can mean: only A exists, only B exists, and A and B exist at the same time, where A and B can be singular or plural. The character " / " generally indicates that the objects associated before and after are in an "or" relationship. "At least one of the following" or similar expressions refers to any combination of these items, including any combination of single or plural items. For example, at least one of a, b or c can mean: a, b, c, "a and b", "a and c", "b and c", or "a and b and c", where a, b, c can be single or multiple.

[0168] As described above, the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A photovoltaic system, characterized in that: include: A linkage switch, two DC / DC conversion circuits and a DC / AC conversion circuit; The input of the DC / DC conversion circuit is used to connect multiple photovoltaic strings through the linkage switch, and the outputs of the two DC / DC conversion circuits are connected in parallel to the input of the DC / AC conversion circuit; The first end of the linkage switch is used to connect N photovoltaic strings among the multiple photovoltaic strings, and the second end of the linkage switch is connected to the input end of the DC / DC conversion circuit, where N is an integer greater than or equal to 2; The linkage switch includes at least three pole switches that are disconnected or turned on at the same time, a tripping device and a controller, the N photovoltaic strings include multiple groups of photovoltaic strings, and the photovoltaic strings in each group are connected to the input end of the DC / DC conversion circuit through the same pole switch of the at least three pole switches, at least one photovoltaic string in the multiple groups of photovoltaic strings includes at least two photovoltaic strings and is connected to the same multi-pole switch, and the tripping device is used to drive the multiple pole switches in the linkage switch to disconnect simultaneously; The controller is used to control the trip device to drive the multiple pole switches to simultaneously disconnect from the DC / DC conversion circuit when a reverse connection fault occurs in the N photovoltaic strings.

2. The photovoltaic system according to claim 1, characterized in that: The N photovoltaic strings share a common positive pole, and the positive poles of the N photovoltaic strings are connected to the input end of the DC / DC conversion circuit through one pole switch in the multi-pole switch; the N photovoltaic strings are grouped in pairs, and the negative pole of each group of photovoltaic strings is connected to the input end of the DC / DC conversion circuit through one pole switch in the multi-pole switch; or, The N photovoltaic strings share a common negative pole, and the negative poles of the N photovoltaic strings are connected to the input end of the DC / DC conversion circuit through a pole switch in the multi-pole switch. The N photovoltaic strings are grouped in pairs, and the positive pole of each group of photovoltaic strings is connected to the input end of the DC / DC conversion circuit through a pole switch in the multi-pole switch.

3. The photovoltaic system according to claim 1 or 2, characterized in that: The N photovoltaic strings are divided into M groups, when N is an even number, M=N / 2; when N is an odd number, M=(N+1) / 2; The linkage switch includes an M+1 pole switch, and the M+1 pole switch includes a first pole switch and the remaining M pole switches; M groups of photovoltaic strings correspond to the M pole switches one by one; the first ends of the N photovoltaic strings are connected to the input end of the DC / DC conversion circuit through the first pole switch; the M groups of photovoltaic strings are connected to the input end of the DC / DC conversion circuit through the M pole switches respectively, and the first ends of the N photovoltaic strings are positive or negative.

4. The photovoltaic system according to claim 3, characterized in that: The controller is used for sending a disconnection instruction to the trip device when there is a reverse connection fault in the N photovoltaic strings. The trip device is actuated according to the disconnection instruction and drives the M+1 pole switches to disconnect. Before the trip device is reset, the M+1 pole switches remain in the disconnected state.

5. The photovoltaic system according to claim 4, characterized in that: Also includes: Input current detection circuit; The input current detection circuit is used to detect the current of each photovoltaic string in the N photovoltaic strings; The controller is used for controlling the M+1 pole switches to be disconnected when it is determined that the current of any one of the N photovoltaic strings is reversed according to the current of each photovoltaic string.

6. The photovoltaic system according to claim 4, characterized in that: Also includes: Input current detection circuit, input voltage detection circuit; The input current detection circuit is used to detect the current of each photovoltaic string in the N photovoltaic strings; The input voltage detection circuit is used to detect the voltage between the first end of the first pole switch and the first end of each switch in the M pole switches to obtain M voltages; The controller is used to control the M+1 pole switches to be disconnected when at least one of the M voltages is less than a first voltage threshold and the current of at least one of the N photovoltaic strings is greater than a first current threshold.

7. The photovoltaic system according to claim 3, characterized in that: Also includes: an output voltage detection circuit and an output current detection circuit; The output current detection circuit is used to detect the current at the second end of the first pole switch; The output voltage detection circuit is used to detect the output voltage of the DC / DC conversion circuit; The controller is used to control the M+1 pole switches to be disconnected when the current at the second end of the first pole switch is greater than a second current threshold and the voltage at the output end of the DC / DC conversion circuit is less than a second preset voltage.

8. The photovoltaic system according to claim 7, characterized in that: The controller comprises: a main controller and a standby controller; The main controller and the standby controller are both used to control the M+1 pole switches to be disconnected when a reverse connection fault occurs in the N photovoltaic strings.

9. The photovoltaic system according to claim 8, characterized in that: Also includes: A primary auxiliary source and a secondary auxiliary source; The main auxiliary source and the secondary auxiliary source are both used to supply power to the main controller and the standby controller; The main 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 linkage switch.

10. The photovoltaic system according to claim 9, characterized in that: Also includes: A first power supply circuit; The first power-taking circuit is used to take power from the group with the highest voltage among the M groups of photovoltaic strings to supply power to the secondary auxiliary source.

11. The photovoltaic system according to claim 10, characterized in that: The first power supply circuit includes 2 (M+1) diodes and a first capacitor; Each switch in the M+1-pole switches corresponds to two diodes in the 2(M+1) diodes; The first end of each switch in the M+1-pole switches is connected to the first end and the second end of the first capacitor respectively through a forward biased diode and a reverse biased diode; the first end of each switch in the M+1-pole switches is connected to the corresponding photovoltaic string, and the second end of each switch in the M+1-pole switches is connected to the input end of the DC / DC conversion circuit.

12. The photovoltaic system according to any one of claims 9 to 11, characterized in that: Also includes: A second power supply circuit; The second power supply circuit includes: a first diode, a second diode, a third diode, a fourth diode and a second capacitor; The cathode and anode of the first diode are connected to the positive output terminal of the DC / DC conversion circuit and the first end of the second capacitor respectively; the anode and cathode of the second diode are connected to the positive output terminal of the DC / DC conversion circuit and the second end of the second capacitor respectively; The anode and cathode of the third diode are respectively connected to the first end of the second capacitor and the negative output end of the DC / DC conversion circuit, and the anode and cathode of the fourth diode are respectively connected to the negative output end of the DC / DC conversion circuit and the second end of the second capacitor; The main auxiliary source is connected to the positive output terminal of the DC / DC conversion circuit.

13. A fault isolation method, characterized in that: Applied to a photovoltaic system, the photovoltaic system comprising: a linkage switch, two DC / DC conversion circuits and a DC / AC conversion circuit; The input of the DC / DC conversion circuit is used to connect multiple photovoltaic strings through a linkage switch, and the outputs of the two DC / DC conversion circuits are connected in parallel to the input of the DC / AC conversion circuit; The first end of the linkage switch is used to connect N photovoltaic strings among the multiple photovoltaic strings, and the second end of the linkage switch is connected to the input end of the DC / DC conversion circuit, where N is an integer greater than or equal to 2; The linkage switch includes a plurality of pole switches and tripping devices that are turned on or off at the same time, the N photovoltaic strings include a plurality of groups of photovoltaic strings, and the photovoltaic strings in each group are connected to the input end of the DC / DC conversion circuit through the same pole switch among the plurality of pole switches; at least one of the plurality of photovoltaic strings includes at least two photovoltaic strings connected to the same multi-pole switch; The method comprises: When a reverse connection fault occurs in the N photovoltaic strings, the tripping device is controlled to drive the plurality of pole switches to disconnect from the DC / DC conversion circuit simultaneously.

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