A photovoltaic system, a DC combiner box, and a fault isolation method

Abstract

This application discloses a photovoltaic system, a DC combiner box, and a fault isolation method, including: a fault isolation circuit and a DC / DC 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 input end of the DC / DC 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; when a reverse connection fault exists in the N photovoltaic strings, the multi-pole switches are all disconnected in a coordinated manner, thereby reducing the complexity of the hardware structure and reducing the cost of the fault isolation circuit.

Description

[0001] This application is a divisional application, the original application number is 202180065361.2, the original application date is February 20, 2021, and the entire contents of the original application are incorporated herein by reference. TECHNICAL FIELD

[0002] The present application relates to the technical field of photovoltaic power generation, in particular to a photovoltaic system, a direct current junction box and a fault isolation method. BACKGROUND

[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 that the direct current of a photovoltaic array is directly converted into alternating current through a direct current / alternating current (DC / AC) circuit, and the two-stage power conversion mode refers to that the direct current of a photovoltaic array is first converted through a direct current / direct current (DC / DC) conversion circuit for a first-stage direct current / direct current conversion, and then converted through a second-stage DC / AC conversion circuit for a second-stage direct current / alternating current conversion, and finally converted into alternating current. 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 improve 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 the multiple photovoltaic strings are connected together, and the negative poles of the multiple photovoltaic strings are connected together. However, when one of the photovoltaic strings is connected reversely, the currents of the other photovoltaic strings will be backfed into the reversely connected photovoltaic string. Since the diodes reversely connected in parallel in the photovoltaic string can only withstand limited current, when the currents of multiple photovoltaic strings are backfed into one photovoltaic string, the photovoltaic string will be damaged. SUMMARY

[0005] The present application provides a photovoltaic system, a direct current junction box and a fault isolation method, which can isolate the fault in time when the photovoltaic string is reversely connected.

[0006] This 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; the power conversion circuit may include a DC / DC conversion circuit and a DC / AC conversion circuit, or only a DC / AC conversion circuit. The fault isolation circuit is connected between the photovoltaic strings and the power conversion circuit, meaning N photovoltaic strings are connected to the power conversion circuit through the fault isolation circuit. To reduce the number of switches and simultaneously increase the input current of the power conversion circuit, the fault isolation circuit may include a multi-pole switch. The N photovoltaic strings are divided into multiple groups, with each group corresponding to one pole of the multi-pole switch; that is, all photovoltaic strings in each group share one pole to connect to the input terminal of the power conversion circuit. Each group of photovoltaic strings includes at least two photovoltaic strings; if a reverse connection fault occurs in any of the N photovoltaic strings, the multi-pole switch will trip.

[0007] The fault isolation switch provided in this application includes a multi-pole switch, which is a single, interconnected switch, i.e., a multi-P switch. These multi-P switches can be simultaneously open or closed. When a reverse connection fault exists in any of the N photovoltaic strings, all multi-pole switches are open. That is, if a reverse connection fault occurs in any one of the photovoltaic strings, all pole switches in the fault isolation circuit are open. Since the photovoltaic strings are grouped into at least two groups, each group corresponds to one pole switch, meaning each group of photovoltaic strings is connected in parallel and shares a single pole switch to connect to the input terminal of the power conversion circuit, the number of poles in the fault isolation circuit is reduced to a certain extent, thereby reducing the complexity of the hardware structure and the cost of the fault isolation circuit.

[0008] In one possible implementation, the N photovoltaic strings can be connected with a common positive terminal or a common negative terminal. For example, when the N photovoltaic strings are connected with a common positive terminal, their positive terminals are connected together, and the positive terminals of the N photovoltaic strings are connected to the input terminal 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 terminals of each group of photovoltaic strings are connected to the input terminal 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 terminal, their negative terminals are connected together, and the negative terminals of the N photovoltaic strings are connected to the input terminal 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 positive terminals of each group of photovoltaic strings are connected to the input terminal of the power conversion circuit through a single-pole switch in a multi-pole switch.

[0009] Since the N photovoltaic strings are grouped in pairs, with each group consisting of two photovoltaic strings and each group corresponding to a single-pole switch, the number of poles in the switch is almost half the number of photovoltaic strings. This significantly reduces the number of switches, simplifies the circuit connection, and saves on the hardware cost of the fault isolation circuit. Because the multi-pole switches can be linked, they can reliably disconnect all photovoltaic strings from the power conversion circuit when a reverse connection fault occurs, thus protecting both the photovoltaic strings and the power conversion circuit.

[0010] In one possible implementation, N photovoltaic strings are divided into M groups. When N is even, M = N / 2; when N is odd, M = (N+1) / 2. The fault isolation circuit includes an M+1 pole switch, which consists of a first pole switch and the remaining M pole switches. There is a one-to-one correspondence between the M groups of photovoltaic strings and the M pole switches. The first terminals of all N photovoltaic strings are connected to the input terminal of the power conversion circuit through the first pole switch. The M groups of photovoltaic strings are each connected to the input terminal of the power conversion circuit through M pole switches, and the first terminals of the N photovoltaic strings are either positive or negative. That is, M is approximately half of N. The number of poles in the fault isolation circuit is less than the number of photovoltaic strings, thus significantly reducing the number of poles and lowering hardware costs. Furthermore, since the N photovoltaic strings share a common positive or negative terminal, the input current of the power conversion circuit is the sum of the currents of the N photovoltaic strings, thereby increasing the input current of the power conversion circuit.

[0011] In one possible implementation, to ensure reliable disconnection of the switches in the fault isolation circuit when a reverse connection fault occurs in the photovoltaic strings, the fault isolation circuit provided in this application embodiment may further include a shunt trip device. A controller, when a reverse connection fault exists in any of the N photovoltaic strings, sends a disconnection command to the shunt trip device. The shunt trip device operates according to the disconnection command, causing all M+1 pole switches to disconnect. Before the shunt trip device resets, all M+1 pole switches remain open. That is, before the shunt trip device resets, the multi-pole switches remain open, thereby preventing accidental closing of the multi-pole switches before the fault is cleared.

[0012] In one possible implementation, a reverse connection fault in a photovoltaic string can be determined by the direction of the current in 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 of the N photovoltaic strings; when the controller determines that the current of any one of the N photovoltaic strings is reversed based on the current of each photovoltaic string, it controls the M+1 pole switch to be disconnected.

[0013] One possible implementation includes: an input current detection circuit and an input voltage detection circuit; the input current detection circuit detects the current of each of the N photovoltaic strings; the input voltage detection circuit detects the voltage between the first terminal of the first pole switch and the first terminal of each of the M pole switches, obtaining M voltages; the controller, 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, controls all M+1 pole switches to open. If the voltage of any one set 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. To accurately determine the short-circuit fault, both voltage and current can be used for judgment. If a photovoltaic string has a short-circuit fault, all switches in the fault isolation circuit will open, thereby isolating the faulty photovoltaic string and protecting the downstream circuit from the harm of the short-circuit fault.

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

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

[0016] In one possible implementation, since any hardware may malfunction during operation, two controllers can be set up in the photovoltaic system to form a backup, i.e., to achieve redundant control, so that if one controller fails, normal control operation is not affected. That is, in the photovoltaic system provided in this embodiment, the controllers include: a main controller and a backup controller; both the main controller and the backup controller are used to control the M+1 pole switch to disconnect when a reverse connection fault exists in N photovoltaic strings.

[0017] In one possible implementation, to ensure the reliability of power supply, this application embodiment 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; both the main auxiliary source and the secondary auxiliary source are used to power the main controller and the backup controller; the main auxiliary source is connected to the output terminal of the DC / DC conversion circuit; and the secondary auxiliary source is connected to the first terminal 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 this application embodiment adopts a competitive power supply method, that is, it further includes: a first power supply circuit, used to draw power from the group with the highest voltage among the M groups of photovoltaic strings to supply power to the 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 switch corresponds to two of the 2 (M+1) diodes; the first terminal of each switch in the M+1 pole switch is connected to the first terminal and the second terminal of the first capacitor through a forward bias diode and a reverse bias diode, respectively; the first terminal of each switch in the M+1 pole switch is connected to the corresponding photovoltaic string, and the second terminal of each switch in the M+1 pole switch is connected to the input terminal of the DC / DC conversion circuit.

[0020] In one possible implementation, the photovoltaic system provided in this application embodiment further includes a second power supply circuit for powering 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 terminal of the DC / DC converter circuit and the first terminal of the second capacitor. The anode and cathode of the second diode are respectively connected to the positive output terminal of the DC / DC converter circuit and the second terminal of the second capacitor. The anode and cathode of the third diode are respectively connected to the first terminal of the second capacitor and the negative output terminal of the DC / DC converter circuit. The anode and cathode of the fourth diode are respectively connected to the negative output terminal of the DC / DC converter circuit and the second terminal of the second capacitor. The main auxiliary source is connected to the positive output terminal of the DC / DC converter circuit. Since the power source of the main auxiliary source comes from the output terminal of the DC / DC converter circuit, and since a typical photovoltaic system includes multiple DC / DC converter circuits with their output terminals connected in parallel, even if all pole switches in the fault isolation circuit are disconnected, isolating all photovoltaic strings connected to the input terminals of the DC / DC converter circuit, the output terminal of the DC / DC converter circuit can still be powered, i.e., it comes from other parallel DC / DC converter circuits. This ensures the power supply to both the main and auxiliary power sources, thereby guaranteeing the power supply to the controller.

[0021] One possible implementation includes: multiple fault isolation circuits and multiple DC / DC conversion circuits; the multiple fault isolation circuits and multiple DC / DC conversion circuits correspond one-to-one.

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

[0023] Based on the photovoltaic system provided in the above embodiments, this application also provides a DC combiner box, including: multiple fault isolation circuits and multiple DC / DC conversion circuits; the multiple fault isolation circuits and 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 in linkage.

[0024] In one possible implementation, each fault isolation circuit also includes a shunt trip device and a controller; the controller, when a reverse connection fault exists in N photovoltaic strings, sends a disconnect command to the shunt trip device, the shunt trip device operates according to the disconnect command and drives all multi-pole switches to disconnect; before the shunt trip device resets, all multi-pole switches remain in the open state.

[0025] Based on the photovoltaic system and DC combiner box provided in the above embodiments, this application also provides a fault isolation method applied to a photovoltaic system. The photovoltaic system includes: a fault isolation circuit and a power conversion circuit; a first terminal of the fault isolation circuit is used to connect N photovoltaic strings, and a second terminal 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 terminal 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: determining that there is a reverse connection fault in the N photovoltaic strings, and controlling the multi-pole switches to disconnect in a coordinated manner.

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

[0027] As can be seen from the above technical solutions, the embodiments of this application have the following advantages: The photovoltaic system includes a fault isolation circuit connected between the photovoltaic strings and the power conversion circuit. Specifically, the photovoltaic strings are connected to the power conversion circuit via the fault isolation circuit. When a reverse connection fault occurs in a photovoltaic string, the fault isolation circuit activates, disconnecting the photovoltaic strings from the power conversion circuit. The fault isolation switch provided in this embodiment includes a multi-pole switch, which is a single, interconnected switch (multi-P switch). These multi-P switches can be simultaneously open or closed. When a reverse connection fault occurs in any of the N photovoltaic strings, all multi-pole switches are open; that is, if a reverse connection fault occurs in any one photovoltaic string, all pole switches in the fault isolation circuit are open. Since the photovoltaic strings are grouped into at least two groups, each group corresponds to one pole switch, meaning each group of photovoltaic strings is connected in parallel and shares a single pole switch to connect to the input of the power conversion circuit, the number of poles in the fault isolation circuit is reduced to some extent, thereby reducing the complexity of the hardware structure and the cost of the fault isolation circuit. Attached Figure Description

[0028] Figure 1A A schematic diagram of a photovoltaic system provided in an embodiment of this application; Figure 1B A schematic diagram of yet another photovoltaic system provided in this application embodiment; Figure 2 A schematic diagram of another photovoltaic system provided in the embodiments of this application; Figure 3 This is a schematic diagram of multiple photovoltaic modules connected in series and parallel at the input of a DC / DC converter circuit. Figure 4 A schematic diagram of a photovoltaic system with a fault isolation circuit provided for an embodiment of this application; Figure 5 To and Figure 4 A corresponding circuit diagram; Figure 6 This application provides a schematic diagram of a photovoltaic system when N is an even number. Figure 7 This application provides a schematic diagram of a photovoltaic system when N is an odd number, as shown in the embodiments of the present application. Figure 8 A schematic diagram of a photovoltaic system with a shunt trip device provided in an embodiment of this application; Figure 9 A schematic diagram of yet another photovoltaic system provided in this application embodiment; Figure 10 A schematic diagram of another photovoltaic system provided in the embodiments of this application; Figure 11 A schematic diagram of another photovoltaic system provided in the embodiments of this application; Figure 12A schematic diagram of a photovoltaic system including multiple DC / DC conversion circuits provided in this application; Figure 13 A schematic diagram of a DC combiner box provided in this application; Figure 14 This is a schematic diagram of another photovoltaic system provided in an embodiment of this application. Detailed Implementation

[0029] The terms "first," "second," etc., used in the following description are for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature specified with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this application, unless otherwise stated, "multiple" means two or more.

[0030] Furthermore, in this application, directional terms such as "upper" and "lower" may be defined relative to the orientation in which the components are schematically placed in the accompanying drawings. It should be understood that these directional terms can be relative concepts, used for relative description and clarification, and can change accordingly depending on the orientation in which the components are placed in the accompanying drawings.

[0031] In this application, unless otherwise expressly specified and limited, the term "connection" should be interpreted broadly. For example, "connection" can be a fixed connection, a detachable connection, or an integral part; it can be a direct connection or an indirect connection through an intermediate medium. Furthermore, the term "coupled" can refer to a method of electrical connection for signal transmission. "Coupled" can be a direct electrical connection or an indirect electrical connection through an intermediate medium.

[0032] Photovoltaic system embodiment This application relates to a photovoltaic system, which may include a two-stage power conversion or a single-stage power conversion. The photovoltaic system including a two-stage power conversion circuit is described first. In order to enable those skilled in the art to better understand the technical solution provided by the embodiments of this application, the photovoltaic system provided by the embodiments of this application is described below with reference to the accompanying drawings.

[0033] See Figure 1A The figure is a schematic diagram of a photovoltaic system provided in an embodiment of this application.

[0034] The photovoltaic system provided in this application embodiment includes a DC / DC converter circuit 200 and a DC / AC converter circuit 300. The input terminal of the DC / DC converter circuit 200 is connected to multiple photovoltaic strings, and the input terminal of the DC / DC converter circuit 200 is connected to a photovoltaic array 100, wherein the photovoltaic array 100 includes multiple photovoltaic strings. Figure 1AThis example uses four photovoltaic strings, PV1 to PV4. PV1 to PV4 can be connected in parallel to the input of the DC / DC converter 200, thereby increasing the input current of the DC / DC converter 200. The output of the DC / DC converter 200 is connected to the DC / AC converter 300.

[0035] The DC / DC converter circuit 200 performs DC-DC conversion, and the DC / AC converter circuit 300 performs DC-AC conversion. The output of the DC / AC converter circuit 300 can be connected to a transformer, i.e., connected to the power grid through the transformer.

[0036] in addition, Figure 1A The diagram shown is only a schematic of one DC / DC converter circuit 200 connected to a DC / AC converter circuit 300. Generally, in order to increase the output power of the DC / AC converter circuit 300, multiple DC / DC converter circuits 200 can be connected to the input terminal of the DC / AC converter circuit 300.

[0037] 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. Alternatively, the photovoltaic system provided in this embodiment may also include only a DC / AC conversion circuit, excluding the DC / DC conversion circuit. See also... Figure 1B As shown in the figure, this figure is a schematic diagram of another photovoltaic system provided in the embodiment of this application.

[0038] Compare Figure 1A and Figure 1B It can be seen that, Figure 1B The photovoltaic strings PV1-PV4 are directly connected to the input terminal of the DC / AC conversion circuit 300. The technical solutions provided in the following embodiments of this application do not limit the specific implementation of the power conversion circuit; that is, they can be... Figure 1A The power conversion circuit shown includes a DC / DC converter 200 and a DC / AC converter 300, and can also be... Figure 1B The power conversion circuit shown only includes the DC / AC conversion circuit 300. The following description primarily uses a power conversion circuit that includes a DC / DC conversion circuit as an example.

[0039] See Figure 2 This figure is a schematic diagram of another photovoltaic system provided in an embodiment of this application.

[0040] Figure 2The example described uses two DC / DC converter circuits, both with their outputs connected to a DC / AC converter circuit 300. Specifically, the outputs of the first DC / DC converter circuit 200a and the second DC / DC converter circuit 200b are connected in parallel to the input of the DC / AC converter circuit 300. The first DC / DC converter circuit 200a and the second DC / DC converter circuit 200b can be integrated into a DC combiner box 1000, which provides maximum power point tracking (MPPT) functionality.

[0041] Figure 2 Taking the input terminal of the first DC / DC converter circuit 200a connected to photovoltaic strings PV1 and PV2 as an example, the input terminal of the second DC / DC converter circuit 200b is connected to photovoltaic strings PV3 and PV4.

[0042] Figure 1 or Figure 2 In the photovoltaic system shown, since the input terminal of the DC / DC converter circuit is connected to multiple photovoltaic strings, which are usually connected in parallel, when one of the photovoltaic strings is reversed (i.e., the positive and negative terminals are reversed), the current from the other photovoltaic strings will flow back into the reversed photovoltaic string. Since the diodes connected in anti-parallel in the photovoltaic string can only withstand a limited amount of current, when the current from multiple photovoltaic strings flows back into one photovoltaic string, it will cause damage to the batteries in that photovoltaic string.

[0043] See Figure 3 The figure shows a schematic diagram of multiple photovoltaic modules connected in series and parallel at the input of a DC / DC converter circuit.

[0044] Continuing with the example of four photovoltaic strings, Figure 3 In this circuit, a photovoltaic (PV) string is considered equivalent to a single battery. Traditionally, the positive terminals PV1+ through PV4+ of the four PV strings are connected together to the positive input terminal of the DC / DC converter circuit 200, and the negative terminals PV1- through PV4- of the four PV strings are connected together to the negative input terminal of the DC / DC converter circuit 200. For example, when PV4 is reversed (i.e., the positive and negative terminals are reversed), it can be seen that the positive terminals of PV1-PV3 are connected to the positive input terminal of the DC / DC converter circuit 200, while the positive terminal of PV4 is connected to the negative input terminal of the DC / DC converter circuit 200. Figure 3 This shows the reverse connection of one photovoltaic string PV4. Figure 3 As can be seen, the currents of PV1-PV3 are represented by dashed lines with arrows, while the current of PV4 is represented by solid lines with arrows. This means that the currents of PV1-PV3 will flow back into PV4, potentially damaging PV4 due to excessive current. On the other hand, Figure 3A fuse is added to each photovoltaic string, that is, the four photovoltaic strings are connected in series with fuses F1-F4 respectively. The fuse will increase the circuit loss. On the other hand, the fuse requires twice the input current to break and the reliability is relatively low.

[0045] To address the problem caused by reverse connection of photovoltaic (PV) strings, this application provides a PV system including a fault isolation circuit. This fault isolation circuit includes a multi-pole switch, the number of poles of which depends on the number of PV strings. For example, N PV strings are divided into multiple groups, each group containing at least two PV strings. Each group of PV strings is connected to the input terminal of a power conversion circuit via a switch on the same pole of the multi-pole switch. When a reverse connection fault exists among the N PV strings—that is, if even one PV string has a reverse connection fault—all PV strings connected to the same power conversion circuit are disconnected from the power conversion circuit. In other words, all multi-pole switches are simultaneously disconnected, effectively breaking the connection between the N PV strings and the power conversion circuit.

[0046] The photovoltaic system provided in this application embodiment includes a fault isolation circuit comprising a multi-pole switch, specifically a multi-P switch. These multi-P switches can operate in tandem, meaning that if a reverse connection fault occurs in one or more photovoltaic strings connected to the multi-pole switch, all poles of the multi-pole switch will disconnect. Since each photovoltaic string corresponds to one pole switch, and each photovoltaic string group includes at least two photovoltaic strings, the number of poles in the switch is almost half the number of photovoltaic strings, significantly reducing the number of switches, simplifying the circuit connection, and saving on the hardware cost of the fault isolation circuit. Because the multi-pole switches can operate in tandem, they can reliably disconnect all photovoltaic strings from the power conversion circuit when a reverse connection fault occurs, thereby protecting both the photovoltaic strings and the power conversion circuit.

[0047] One possible implementation is that when N photovoltaic strings share a common positive terminal, the positive terminals of the N photovoltaic strings are connected together, and the positive terminals of the N photovoltaic strings are connected to the input terminal 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, so that when one is reverse-connected, the other photovoltaic strings connected in parallel will be damaged by too much current, one possible implementation is to divide the N photovoltaic strings into pairs. Since the N photovoltaic strings share a common positive terminal, the negative terminals of the N photovoltaic strings are divided into pairs, and the negative terminals of each pair of photovoltaic strings are connected to the input terminal of the power conversion circuit through a single-pole switch in a multi-pole switch.

[0048] The above describes the case of N photovoltaic strings sharing a common positive electrode. In addition, N photovoltaic strings can also share a common negative electrode. The connection method of sharing a common negative electrode is described in detail below.

[0049] When N photovoltaic strings share a common negative terminal, the negative terminals of the N photovoltaic strings are connected together. The negative terminals of the N photovoltaic strings are connected to the input terminal of the power conversion circuit through a single-pole switch in a multi-pole switch. Similar to the common positive terminal, the N photovoltaic strings are grouped in pairs, that is, the positive terminals of the N photovoltaic strings are grouped in pairs and share a single-pole switch. The positive terminal of each group of photovoltaic strings is connected to the input terminal of the power conversion circuit through a single-pole switch in a multi-pole switch.

[0050] For example, N photovoltaic strings are divided into M groups. Each group of photovoltaic strings requires a single-pole switch to connect to the power conversion circuit, i.e., M pole switches are needed. Furthermore, the ends of the N photovoltaic strings that share a common positive or negative terminal are connected to the power conversion circuit through a single-pole switch. Therefore, the fault isolation circuit includes M+1 pole switches. The relationship between M and N depends on whether N is odd or even, and falls into two cases: when N is even, M = N / 2; when N is odd, M = (N+1) / 2. The first terminals of all N photovoltaic strings are connected to the input terminal of the power conversion circuit through the first pole switch in the M+1 pole switch. The M groups of photovoltaic strings are each connected to the input terminal of the power conversion circuit through the M pole switches in the M+1 pole switch. When a reverse connection fault exists in any of the N photovoltaic strings, all M+1 pole switches are disconnected. That is, if a reverse connection fault occurs in any one of the photovoltaic strings, all pole switches in the fault isolation circuit are disconnected. Because the photovoltaic strings are grouped in pairs, two photovoltaic strings are connected in parallel and share a single-pole switch to connect to the input terminal of the power conversion circuit. When N is an odd number, the remaining photovoltaic string in each group forms a separate group. When one of the photovoltaic strings is reverse-connected, only one photovoltaic string's current flows back in, and the current is relatively small, so it will not damage the reverse-connected photovoltaic string.

[0051] In this embodiment, the first terminal of the photovoltaic string is not limited to whether it is positive or negative. That is, N photovoltaic strings can be connected with a common positive terminal or a common negative terminal. For ease of description, the following embodiments use the example of N photovoltaic strings connected with a common positive terminal. When N photovoltaic strings are connected with a common positive terminal, the positive terminals of the N photovoltaic strings are connected together and connected to the positive input terminal of the power conversion circuit via a single-pole switch. The negative terminals of the N photovoltaic strings are paired up and connected to the negative input terminal of the power conversion circuit via corresponding pole switches. Since the positive terminals of the N photovoltaic strings are connected together, the input current of the power conversion circuit can be increased. Furthermore, since the negative terminals of the N photovoltaic strings are paired up, the number of poles of the switches in the fault isolation circuit is reduced to some extent, thereby reducing the complexity of the hardware structure and lowering costs.

[0052] For ease of understanding, the following embodiments of this application will first be described using an even number of N as an example, taking a power conversion circuit including a DC / DC conversion circuit as an example, combined with... Figure 4 and Figure 5 We will continue with the example of connecting four photovoltaic strings to the input of a single DC / DC converter circuit.

[0053] See Figure 4 The figure is a schematic diagram of a photovoltaic system with a fault isolation circuit provided in an embodiment of this application.

[0054] See Figure 5 The image is related to Figure 4 A corresponding circuit diagram.

[0055] from Figure 4 As can be seen, the four photovoltaic strings are connected to the first terminal of the fault isolation circuit 400, the second terminal of the fault isolation circuit 400 is connected to the input terminal of the DC / DC converter circuit 200, and the output terminal of the DC / DC converter circuit 200 is connected to the input terminal of the DC / AC converter circuit 300. The four photovoltaic strings are divided into two groups, with two strings forming one group. Specifically, the negative terminals of every two photovoltaic strings are connected together: PV1- and PV2- are connected together, and PV3- and PV4- are connected together.

[0056] When any one of the four photovoltaic strings has a reverse connection fault, all switches in the fault isolation circuit 400 will be disconnected, that is, the connection between all photovoltaic strings and the input terminal of the DC / DC converter circuit 200 will be disconnected, thus preventing the fault from affecting other circuits.

[0057] Continuing with the example of reverse connection of PV4 in a photovoltaic string, since PV1- and PV2- are not connected to PV4-, when PV4 is reverse connected, only the current from PV3 flows back into PV4. Therefore, the current flowing back into PV4 is small and will not cause any loss to PV4. This is different from... Figure 3 .

[0058] To more clearly describe the connection relationship between the photovoltaic string and the switches in the fault isolation circuit 300, the following section combines... Figure 5 Let's continue with the explanation of how it works.

[0059] Since N is 4, which is an even number, M = 4 / 2, meaning the photovoltaic string is divided into 2 groups. Correspondingly, the fault isolation circuit 300 includes M+1 pole switches, which is 2+1=3 pole switches, namely the first pole switch S1, the second pole switch S2, and the third pole switch S3.

[0060] The positive terminals of PV1+ through PV4+ are connected together to the first terminal of the first-pole switch S1, and the second terminal of the first-pole switch S1 is connected to the input terminal of the DC / DC converter circuit 200. PV1- and PV2- are connected together to the first terminal of the second-pole switch S2, and the second terminal of the second-pole switch S2 is connected to the input terminal of the DC / DC converter circuit 200. PV3- and PV4- are connected together to the first terminal of the third-pole switch S3, and the second terminal of the third-pole switch S3 is connected to the input terminal of the DC / DC converter circuit 200.

[0061] When PV4 is reversed, the first pole switch S1, the second pole switch S2, and the third pole switch S3 are all disconnected.

[0062] Obviously, the photovoltaic system provided in this application embodiment can disconnect all switches in the fault isolation circuit when the photovoltaic strings are reverse-connected, thereby disconnecting the photovoltaic strings from the subsequent DC / DC conversion circuit and preventing the reverse connection fault from causing other more serious faults. Furthermore, since the fault isolation circuit provided in this application embodiment can achieve pairwise grouping of photovoltaic strings, that is, at most two photovoltaic strings are connected to a single-pole switch, it avoids more photovoltaic strings being connected together. In this case, if one photovoltaic string experiences a reverse connection fault, the current from all the other connected photovoltaic strings will flow back in, causing damage to the photovoltaic strings. In this application embodiment, two photovoltaic strings are connected in parallel, so even if a reverse connection fault occurs, the backflow current is relatively small and will not damage the photovoltaic strings. It should be understood that the existence of a reverse connection fault in all embodiments of this application refers to at least one photovoltaic string being reverse-connected; that is, if even one photovoltaic string is reverse-connected, the connection between N photovoltaic strings and the power conversion circuit needs to be disconnected.

[0063] The photovoltaic system provided in this application, in order to protect the photovoltaic strings, groups every two photovoltaic strings together and connects them to a single-pole switch, rather than grouping more photovoltaic strings together. If more photovoltaic strings are connected in parallel, the magnitude of the reverse current cannot be guaranteed when reverse connection occurs. Because there are more photovoltaic strings connected in parallel, the reverse current will increase, damaging the photovoltaic strings. This application embodiment achieves a better balance between ensuring the safety of the photovoltaic strings in the event of reverse connection and minimizing the number of switches in the fault isolation circuit.

[0064] The above embodiments describe the implementation of four photovoltaic strings. The technical solutions provided in this application are applicable to cases where N is an even number and takes a larger value. For example, the implementation of N=6, i.e., six photovoltaic strings, is described below.

[0065] See Figure 6 The figure is a schematic diagram of a photovoltaic system when N is an even number, provided in an embodiment of this application.

[0066] Since N=6, the photovoltaic strings are divided into M=6 / 2=3 groups. The fault isolation circuit 300 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.

[0067] The positive terminals PV1+ through PV6+ of the six photovoltaic strings are connected together to the first terminal of the first switch S1. Each pair of photovoltaic strings forms a group, and the negative terminals of each pair of photovoltaic strings correspond to a single switch. PV1- and PV2- are connected to the first terminal of the second switch S2, PV3- and PV4- are connected to the first terminal of the third switch S3, and PV5- and PV6- are connected to the first terminal of the fourth switch S4. The second terminals of the first switch S1, the second switch S2, the third switch S3, and the fourth switch S4 are all connected to the DC / DC converter circuit 200.

[0068] The above describes the implementation when N is even. The following section, with reference to the attached diagram, describes the implementation when N is odd.

[0069] See Figure 7 The figure is a schematic diagram of a photovoltaic system provided in an embodiment of this application when N is an odd number.

[0070] For ease of description, we will take N=5 as an example. Therefore, the 5 photovoltaic strings are divided into M=(N+1 / )2=3 groups. The fault isolation circuit 300 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 switches is the same as when N is 6.

[0071] Since each pair of photovoltaic strings is grouped together, and N is an odd number, the last remaining photovoltaic string cannot be paired. Therefore, the remaining photovoltaic string is grouped separately and corresponds to a single-pole switch in the fault isolation circuit 300.

[0072] The positive terminals PV1+ through PV5+ of the five photovoltaic strings are connected together to the first terminal of the first switch S1. Each pair of photovoltaic strings forms a group, and the negative terminals of each pair of photovoltaic strings correspond to a single switch. PV1- and PV2- are connected to the first terminal of the second switch S2, PV3- and PV4- are connected to the first terminal of the third switch S3, and PV5- is connected separately to the first terminal of the fourth switch S4. The second terminals of the first switch S1, the second switch S2, the third switch S3, and the fourth switch S4 are all connected to the DC / DC converter circuit 200.

[0073] The above examples illustrate N as both even and odd. Below, we will continue with N as an even number, specifically N = 4, to introduce other implementation methods.

[0074] In order to reliably disconnect the switch in the fault isolation circuit when a reverse connection fault occurs in the photovoltaic string, the fault isolation circuit provided in this application embodiment may also include a shunt trip device, which will be described below with reference to the accompanying drawings.

[0075] See Figure 8 The figure is a schematic diagram of a photovoltaic system with a shunt trip device provided in an embodiment of this application.

[0076] In the photovoltaic system provided in this embodiment, the fault isolation circuit also includes: a shunt trip device and a controller 600; The controller 600 is used to send a disconnect command to the shunt trip device when there is a reverse connection fault in N photovoltaic strings. The shunt trip device will act according to the disconnect command and drive all M+1 pole switches to disconnect. Before the shunt trip device is reset, all M+1 pole switches will remain in the open state.

[0077] For example, continuing with the case of a reverse connection fault in PV4, the controller 600 sends a disconnect command to the shunt trip device. The shunt trip device activates, thereby causing all three switches S1-S3 to disconnect. If the shunt trip device is not actively reset, the three switches S1-S3 will remain open, preventing the three switches S1-S3 from closing before the fault in the photovoltaic string is resolved, thus better protecting the photovoltaic string.

[0078] Furthermore, the controller 600 provided in this application embodiment requires a power supply, therefore, it may include a first power-harvesting circuit 500. The first power-harvesting circuit 500 provided in this application embodiment adopts a competitive power-harvesting method, that is, the first power-harvesting circuit 500 is used to draw power from the group with the highest voltage among the M groups of photovoltaic strings to power the controller 500, and does not need to draw power from each group of photovoltaic strings.

[0079] Figure 8 A competitive power supply implementation method is given, namely, a first power supply circuit, which includes 2 (M+1) diodes and a first capacitor; since N is 4, M is 2, and the first power supply circuit includes 6 diodes and one capacitor.

[0080] Each pole of the M+1 pole switch corresponds to two of the two (M+1) diodes; the first terminal of each pole of the M+1 pole switch is connected to the first and second terminals of the first capacitor through a forward bias diode and a reverse bias diode, respectively; the first terminal of each pole of the M+1 pole switch is connected to the corresponding photovoltaic string, and the second terminal of each pole of the M+1 pole switch is connected to the input terminal of the DC / DC conversion circuit.

[0081] from Figure 8As can be seen, the fault isolation circuit includes three-pole switches S1-S3, each corresponding to two diodes. Specifically, the first terminal of the first switch S1 is connected to the two ends of the first capacitor C1 via the corresponding forward-biased diode D2 and reverse-biased diode D1. The first terminal of the second switch S2 is connected to the two ends of the first capacitor C1 via the corresponding forward-biased diode D4 and reverse-biased diode D3. The first terminal of the third switch S3 is connected to the two ends of the first capacitor C1 via the corresponding forward-biased diode D6 and reverse-biased diode D5. PV1+—PV4+ are connected together, i.e., 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, i.e., 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, i.e., point C. The cathode of D5 is connected to point C, and similarly, the anode of D6 is connected to point C.

[0082] The following example, with reference to the accompanying diagram, illustrates the specific working principle of competitive power supply.

[0083] 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 less 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 less 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.

[0084] When all PV1-PV4 are reversed, the voltage of PV1 / PV2 connected in parallel is greater than the voltage of PV3 and PV4 connected in parallel. Therefore, the voltage at point B is higher than the voltage at point C, and the current flows out from PV1 and PV2. Conversely, the current flows out from PV3 and PV4.

[0085] The following describes a specific method for determining reverse connection of photovoltaic strings.

[0086] See Figure 9 This figure is a schematic diagram of another photovoltaic system provided in an embodiment of this application.

[0087] The photovoltaic system provided in this embodiment may further include: an input current detection circuit 700; The input current detection circuit 700 is used to detect the current in each of 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 in each string. Normally, the current in each photovoltaic string flows in the same direction. If there is a reverse connection, the current in the reversed photovoltaic string will flow in the opposite direction to the other normal photovoltaic strings. Therefore, the current direction can be used to determine if there is a reverse connection. For example, the current is positive under normal conditions, but negative under reverse connection, thus indicating a reverse connection.

[0088] The controller 600 determines, based on the current of each of the N photovoltaic strings, that if the current in any one of the photovoltaic strings is reversed, all M+1 pole switches in the fault isolation circuit 300 should be disconnected. Specifically, the controller 600 sends a disconnect command to the shunt trip device, which then activates, causing all three pole switches S1-S3 to disconnect. If even one photovoltaic string has a reverse connection fault, all photovoltaic strings must be disconnected from the DC / DC converter circuit 200.

[0089] The fault isolation circuit 300 provided in this application embodiment can not only disconnect when there is a reverse connection fault in the photovoltaic string, thus playing a protective role, but also disconnect when there is a short circuit fault in the photovoltaic string, thus playing a protective role. It will be described in detail below.

[0090] The photovoltaic system provided in this embodiment includes not only an input current detection circuit 700, but may also include an input voltage detection circuit 800.

[0091] The input voltage detection circuit 800 detects the voltage between the first terminal of the first-pole switch S1 and the first terminal of each of the M-pole switches (S2 and S3), obtaining M voltages. That is, the input voltage detection circuit 800 detects the voltage of each of the M photovoltaic strings. If the voltage of any one photovoltaic string is low, there may be a short circuit fault in some of the 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 increase. To accurately determine a short circuit fault, both voltage and current can be used for judgment. Figure 9 In the input voltage detection circuit 800, it 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.

[0092] One specific implementation involves a controller 600 that, 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, controls all switches on pole M+1 to open. In other words, if a short-circuit fault exists in a photovoltaic string, all switches in the fault isolation circuit 300 will open, thereby isolating the faulty photovoltaic string and protecting the downstream circuitry from the short-circuit fault.

[0093] The above-described embodiments are for detecting short-circuit faults at the input terminal of a DC / DC converter circuit. The following describes short-circuit faults at the output terminal of a DC / DC converter circuit.

[0094] See Figure 10This figure is a schematic diagram of another photovoltaic system provided in an embodiment of this application.

[0095] This application embodiment can detect not only whether a short circuit fault occurs at the input terminal of the DC / DC converter circuit, but also whether a short circuit fault occurs at the output terminal of the DC / DC converter circuit. When a short circuit fault occurs at the output terminal of the DC / DC converter circuit, in order to prevent the fault range from expanding and to play a protective role, it is also necessary to control all pole switches in the fault isolation circuit to be disconnected, so as to play a fault isolation role.

[0096] The photovoltaic system provided in this embodiment also includes: an output voltage detection circuit 901 and an output current detection circuit 902; The output voltage detection circuit 901 is used to detect the output voltage of the DC / DC converter circuit 200. The output current detection circuit 902 is used to detect the current at the second terminal of the first pole switch S1; that is, to detect the input current of the DC / DC converter circuit 200.

[0097] To accurately determine whether a short circuit fault has occurred at the output of the DC / DC converter circuit 200, both voltage and current conditions need to be considered. A short circuit fault is determined to have occurred when both conditions are met. Specifically, the controller 600 controls all M+1 pole switches to open when the current at the second terminal of the first pole switch S1 is greater than a second current threshold and the voltage at the output of the DC / DC converter circuit 200 is less than a second preset voltage. Since the first pole switch S1 connects to all photovoltaic strings, the output current detection circuit 902 only needs to detect the current flowing through the first pole switch S1.

[0098] It should be understood that both the input current detection circuit and the output current detection circuit can be implemented using current sensors. When there is a reverse connection in the photovoltaic string, the current in the photovoltaic string is in the opposite direction to the current in the normal photovoltaic string. Therefore, the presence of a reverse connection fault can be determined by detecting the direction of the current. For example, if the current in the normal photovoltaic string is positive, then the current in the reverse-connected photovoltaic string will be negative, i.e., less than zero, indicating a current reversal. Alternatively, the current may be less than a preset threshold, also indicating a reverse connection fault. A current sensor can be installed in each photovoltaic string to detect its current. Furthermore, for example, with four photovoltaic strings, current sensors can be installed in three of them, and a current sensor can be used for the output current. The current in the remaining photovoltaic string can then be obtained by subtracting the sum of the currents in the three photovoltaic strings from the output current, thus reducing the need for one current sensor.

[0099] The photovoltaic system provided in this application embodiment, in order to more comprehensively protect the safe and reliable operation of the photovoltaic system, can 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 also disconnect all pole switches in the fault isolation circuit 400 when a short circuit fault occurs at the output terminal of the DC / DC converter circuit 200, so as to prevent the short circuit fault at the output terminal of the DC / DC converter circuit 200 from causing damage to the photovoltaic string.

[0100] The above embodiments describe the scenario where power is drawn from the photovoltaic string to supply power to the controller. To ensure that the controller continues to operate when the photovoltaic string is disconnected or has no power output, this application embodiment also includes another power drawing method, which can serve as the main power supply method for the controller. A detailed description is provided below with reference to the accompanying drawings.

[0101] See Figure 11 This figure is a schematic diagram of another photovoltaic system provided in an embodiment of this application.

[0102] Since any hardware may malfunction during operation, to ensure the safe and reliable operation of the photovoltaic system, two controllers can be set up in the photovoltaic system to form a backup, that is, to achieve redundant control. When one controller 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; Both the main controller 600a and the backup controller 600b are used to control the M+1 pole switches to open when a reverse connection fault exists in N photovoltaic strings. That is, in this embodiment, the main controller 600a and the backup controller 600b operate simultaneously. Both controllers can simultaneously receive detection signals from the input voltage detection circuit 800, the input current detection circuit 700, the output voltage detection circuit 901, and the output current detection circuit 902. In other words, both controllers can simultaneously receive input voltage, input current, output current, and output voltage, and can use the received signals to determine whether it is necessary to control the opening of all pole switches in the fault isolation circuit 400. This ensures that if one controller fails and cannot accurately send a disconnect command to the fault isolation circuit, the other normal controller can accurately and reliably control the opening of all pole switches.

[0103] In addition, to ensure the reliability of power supply, this application embodiment provides two auxiliary sources, namely: a main auxiliary source 903 and a secondary auxiliary source 904; Both the main auxiliary power source 903 and the secondary auxiliary power source 904 are used to power the main controller 600a and the backup controller 600b. The main auxiliary power source 903 is connected to the output terminal of the DC / DC converter circuit 200; that is, the power supply of the main auxiliary power source 903 comes from the output terminal of the DC / DC converter circuit 200.

[0104] The auxiliary power source 904 is connected to the first terminal of the fault isolation circuit 400, meaning that the power supply of the auxiliary power source 904 comes from the photovoltaic string.

[0105] Since the photovoltaic system provided in this application embodiment includes two auxiliary sources, when one auxiliary source fails, the other normal auxiliary source can still supply power to the controller, ensuring the normal operation of the controller.

[0106] The second power supply circuit that provides power to the main auxiliary power source 903 is described below.

[0107] 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; The cathode and anode of the first diode D7 are connected to the positive output terminal of the DC / DC converter circuit 200 and the first terminal of the second capacitor C2, respectively; the anode and cathode of the second diode D8 are connected to the positive output terminal of the DC / DC converter circuit 200 and the second terminal of the second capacitor C2, respectively. The anode and cathode of the third diode D9 are connected to the first terminal of the second capacitor C2 and the negative output terminal of the DC / DC converter circuit 200, respectively. The anode and cathode of the fourth diode D10 are connected to the negative output terminal of the DC / DC converter circuit 200 and the second terminal of the second capacitor C2, respectively. The main auxiliary power source 903 is connected to the positive output terminal of the DC / DC converter circuit 200 via a second power supply circuit. Since the main auxiliary power source 903 is powered by the output terminal of the DC / DC converter circuit 200, and since a typical photovoltaic system includes multiple DC / DC converter circuits with their output terminals connected in parallel, even if all pole switches in the fault isolation circuit 400 are disconnected, isolating all photovoltaic strings connected to the input terminal of the DC / DC converter circuit 200, the output terminal of the DC / DC converter circuit 200 can still be powered, i.e., by the other parallel-connected DC / DC converter circuits. This ensures the power supply to the main auxiliary power source 903, thereby ensuring the power supply to the controller.

[0108] This application does not limit the specific implementation of the DC / DC conversion circuit in the above photovoltaic systems. For example, it can be a boost circuit with a bypass relay. When the bypass relay is closed, the boost circuit can be bypassed, that is, the boost circuit does not need to be boosted, and the photovoltaic string is directly connected to the subsequent DC / AC conversion circuit through the bypass relay.

[0109] To increase the output power of the inverter, multiple DC / DC conversion circuits are typically connected to the input of the DC / AC conversion circuit.

[0110] See Figure 12 The figure is a schematic diagram of a photovoltaic system including multiple DC / DC conversion circuits provided in an embodiment of this application.

[0111] The photovoltaic system provided in this embodiment includes: multiple fault isolation circuits and multiple DC / DC conversion circuits; Multiple fault isolation circuits correspond one-to-one with multiple DC / DC conversion circuits, meaning that the input terminal of each DC / DC conversion circuit is connected to a corresponding fault isolation circuit. The output terminals of all multiple DC / DC conversion circuits are connected to the input terminals of the DC / AC conversion circuit 300.

[0112] The following example illustrates a DC / AC converter circuit whose input is connected to at least two DC / DC converter circuits: a first DC / DC converter circuit 200a and a second DC / DC converter circuit 200b. The inputs of the first DC / DC converter circuit 200a and the second DC / DC converter circuit 200b are connected to their respective photovoltaic arrays; that is, the first DC / DC converter circuit 200a corresponds to photovoltaic array 100a, and the second DC / DC converter circuit 200b corresponds to photovoltaic array 100b. Both photovoltaic arrays 100a and 100b include multiple photovoltaic strings, as detailed in the above embodiments. This embodiment does not provide a detailed illustration of the photovoltaic strings within the photovoltaic arrays. In this embodiment, a first fault isolation circuit 400a is connected between the inputs of photovoltaic array 100a and the first DC / DC converter circuit 200a, and a second fault isolation circuit 400b is connected between the inputs of photovoltaic array 100b and the second DC / DC converter 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 circuits in the photovoltaic system described in the above embodiments, and will not be repeated here.

[0113] For example, when there is a reverse connection fault 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 terminal 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.

[0114] DC combiner box example In addition, the photovoltaic system provided in this application embodiment may include a combiner box, i.e. a DC combiner box, in which multiple fault isolation circuits and multiple DC / DC conversion circuits are integrated.

[0115] The DC combiner box includes: multiple fault isolation circuits and multiple DC / DC conversion circuits; the multiple fault isolation circuits and 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 a reverse connection fault exists in the N photovoltaic strings, the corresponding multi-pole switches are all disconnected in a coordinated manner.

[0116] The following description uses two power conversion circuits as examples, with the DC / DC conversion circuit being used as an example. The working principle and advantages of the photovoltaic system embodiments described above are also applicable to the DC combiner box provided in this embodiment; the same parts will not be repeated here.

[0117] See Figure 13 The figure is a schematic diagram of a DC combiner box provided in an embodiment of this application.

[0118] The first DC / DC converter circuit 200a, the second DC / DC converter circuit 200b, the first fault isolation circuit 400a, and the second fault isolation circuit 400b are all integrated in the DC combiner box 1000.

[0119] The DC combiner box provided in this application includes a fault isolation circuit, which comprises a multi-pole switch. These multi-pole switches are linked, meaning they close or open simultaneously. The number of poles depends on the number of photovoltaic strings. If N photovoltaic strings are divided into M groups, the fault isolation circuit includes an M+1 pole switch. The relationship between M and N depends on whether N is odd or even, and can be categorized into two cases: when N is even, M = N / 2; when N is odd, M = (N+1) / 2. The first terminals of all N photovoltaic strings are connected to the input terminal of the DC / DC converter circuit via the first pole switch in the M+1 pole switch. The M groups of photovoltaic strings are each connected to the input terminal of the DC / DC converter circuit via the M pole switches in the M+1 pole switch. When a reverse connection fault exists among the N photovoltaic strings, all M+1 pole switches are open; that is, if a reverse connection fault occurs in any one of the photovoltaic strings, all pole switches in the fault isolation circuit are open. Because the photovoltaic strings are grouped in pairs, two photovoltaic strings are connected in parallel and share a single-pole switch to connect to the input terminal of the DC / DC converter circuit. When N is odd, the remaining photovoltaic string in each group forms a separate group. When one of the photovoltaic strings is reverse-connected, only one photovoltaic string's current flows back in, and the current is relatively small, so it will not damage the reverse-connected photovoltaic string.

[0120] In this embodiment, the first terminal of the photovoltaic string is not limited to whether it is positive or negative. That is, N photovoltaic strings can be connected with a common positive terminal or a common negative terminal. For ease of description, the following embodiments use the example of N photovoltaic strings connected with a common positive terminal. When N photovoltaic strings are connected with a common positive terminal, the positive terminals of the N photovoltaic strings are connected together and connected to the positive input terminal of the DC / DC converter circuit via a single-pole switch. The negative terminals of the N photovoltaic strings are paired up and connected to the negative input terminal of the DC / DC converter circuit via corresponding pole switches. Since the positive terminals of the N photovoltaic strings are connected together, the input current of the DC / DC converter circuit can be increased. Furthermore, since the negative terminals of the N photovoltaic strings are paired up, the number of poles of the switches in the fault isolation circuit is reduced to some extent, thereby reducing the complexity of the hardware structure and lowering costs.

[0121] The embodiments described above are all based on power conversion circuits including DC / DC conversion circuits and DC / AC conversion circuits. The following describes the implementation of a power conversion circuit that only includes a DC / AC conversion circuit, with reference to the accompanying drawings.

[0122] See Figure 14 This figure is a schematic diagram of another photovoltaic system provided in an embodiment of this application.

[0123] The photovoltaic system provided in this embodiment includes a fault isolation circuit 400 and a DC / AC conversion circuit 300. The implementation of the fault isolation circuit 400 can be found in the description of the above embodiment. The number of switching poles in the fault isolation circuit 400 is related to the number of photovoltaic strings in the connected photovoltaic array 100. When a photovoltaic string is reverse-connected, all poles of the fault isolation circuit 400 are disconnected, i.e., they are linked and disconnected together, thereby disconnecting the photovoltaic array 100 from the DC / AC conversion circuit 300. This protects the photovoltaic strings and prevents the reverse connection fault from damaging the DC / AC conversion circuit 300. Additionally, the fault isolation circuit 400 can also disconnect the photovoltaic array 100 from the DC / AC conversion circuit 300 when a short-circuit fault occurs in the photovoltaic string.

[0124] Method Implementation Examples Based on the photovoltaic system and DC combiner box provided in the above embodiments, this application also provides a fault isolation method.

[0125] The fault isolation method provided in this embodiment is applied to the photovoltaic system described in any of the above embodiments. 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 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: If a reverse connection fault is detected in any of the N photovoltaic strings, the M+1 pole switch will be disconnected.

[0126] Determining if a reverse connection fault exists in N photovoltaic strings specifically includes: Obtain the current of each of the N photovoltaic strings; If the current in any one of the N photovoltaic strings is reversed based on the current in each photovoltaic string, then a reverse connection fault is determined to exist in the N photovoltaic strings.

[0127] When a photovoltaic (PV) string is reverse-connected, the current in that PV string flows in the opposite direction to the current in a normal PV string. Therefore, the presence of a reverse-connection fault can be determined by detecting the direction of the current. For example, if the current in a normal PV string is positive, the current in the reverse-connected PV string will be negative (less than zero), indicating a reverse current. The current may also be less than a preset threshold, indicating a reverse connection fault. A current sensor can be installed in each PV string to detect the current. Alternatively, for example, with four PV strings, current sensors can be installed in three of them, and a current sensor can be installed in the output current. The current in the remaining PV string can then be obtained by subtracting the sum of the currents in the three PV strings from the output current, thus reducing the need for a separate current sensor.

[0128] To better protect the photovoltaic strings from excessive current during reverse connection, two photovoltaic strings can be grouped together, with each group corresponding to a single-pole switch in a multi-pole switch.

[0129] The following example uses N photovoltaic strings, with each pair of photovoltaic strings forming a group.

[0130] N photovoltaic strings share a common positive terminal, and the positive terminals of the N photovoltaic strings are connected to the input terminal of the power conversion circuit through a single-pole switch in a multi-pole switch; the N photovoltaic strings are paired up, and the negative terminals of each pair of photovoltaic strings are connected to the input terminal of the power conversion circuit through a single-pole switch in a multi-pole switch. or, N photovoltaic strings share a common negative terminal. The negative terminals of the N photovoltaic strings are connected to the input terminal of the power conversion circuit through one of the multi-pole switches. The N photovoltaic strings are paired up, and the positive terminals of each pair of photovoltaic strings are connected to the input terminal of the power conversion circuit through one of the multi-pole switches.

[0131] N photovoltaic strings are divided into M groups. When N is even, M = N / 2; when N is odd, M = (N+1) / 2. The fault isolation circuit includes an M+1 pole switch, which is linked, meaning they close or open simultaneously. The first terminal of each of the N photovoltaic strings is connected to the input terminal of the DC / DC converter circuit through the first pole switch of the M+1 pole switch. The M groups of photovoltaic strings are connected to the input terminal of the DC / DC converter circuit through the M pole switches of the M+1 pole switch.

[0132] It should be understood that in this application, "at least one (item)" means one or more, and "more than" means two or more. "And / or" is used to describe the relationship between related objects, indicating that three relationships can exist. For example, "A and / or B" can represent three cases: only A exists, only B exists, and both A and B exist simultaneously, where A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects are in an "or" relationship. "At least one (item) of the following" or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, at least one (item) of a, b, or c can represent: a, b, c, "a and b", "a and c", "b and c", or "a and b and c", where a, b, and c can be single or multiple.

[0133] The above-described embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. A photovoltaic system, characterized in that, include: Fault isolation circuit, power conversion circuit, and controller; The first terminal of the fault isolation circuit is used to connect N photovoltaic strings, and the second terminal of the fault isolation circuit is connected to the input terminal of the power conversion circuit; N is an integer greater than or equal to 2. The fault isolation circuit includes a multi-pole switch, which includes an M-pole switch. The M-pole switch divides the N photovoltaic strings into M groups of photovoltaic strings. Each of the M groups of photovoltaic strings is connected to the input terminal of the power conversion circuit through the same pole switch in the M-pole switch. At least one of the M groups of photovoltaic strings includes at least two photovoltaic strings, and M is an integer greater than or equal to 2. The controller is used to control all the multi-pole switches to disconnect 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, and when there is a reverse connection fault in the N photovoltaic strings. The M voltages are the voltages between the end of the first pole switch connected to the photovoltaic string and the end of each of the M pole switches connected to the photovoltaic string.

2. The photovoltaic system according to claim 1, characterized in that, The N photovoltaic strings share a common positive terminal, and the positive terminals of the N photovoltaic strings are connected to the input terminal of the power conversion circuit through one of the multi-pole switches; the N photovoltaic strings are paired up, and the negative terminal of each pair of photovoltaic strings is connected to the input terminal of the power conversion circuit through one of the multi-pole switches. or, The N photovoltaic strings share a common negative terminal, and the negative terminals of the N photovoltaic strings are connected to the input terminal of the power conversion circuit through one of the multi-pole switches. The N photovoltaic strings are grouped in pairs, and the positive terminal of each group of photovoltaic strings is connected to the input terminal of the power conversion circuit through one of the multi-pole switches.

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 fault isolation circuit includes an M+1 pole switch, which includes a first pole switch and the remaining M pole switches; M sets of photovoltaic strings correspond one-to-one with the M pole switches; the first terminals of the N photovoltaic strings are all connected to the input terminal of the power conversion circuit through the first pole switch; the M sets of photovoltaic strings are respectively connected to the input terminal of the power conversion circuit through the M pole switches, and the first terminals of the N photovoltaic strings are either positive or negative.

4. The photovoltaic system according to any one of claims 1-3, characterized in that, Also includes: Controller; The fault isolation circuit also includes: a shunt trip device; The controller is used to send a disconnect command to the shunt trip device when a reverse connection fault occurs in any of the N photovoltaic strings. The shunt trip device operates according to the disconnect command and causes all M+1 pole switches to disconnect. Before the shunt trip device is reset, all M+1 pole switches remain in the open 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 of the N photovoltaic strings; The controller is configured to control all M+1 pole switches to open when the current of any one of the N photovoltaic strings is reversed based on 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 of the N photovoltaic strings; The input voltage detection circuit is used to detect the voltage between the first terminal of the first pole switch and the first terminal of each of the M pole switches to obtain M voltages. The controller is configured to open all M+1 pole switches 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 any one of claims 4-6, characterized in that, The power conversion circuit includes a DC / DC conversion circuit.

8. The photovoltaic system according to claim 7, characterized in that, It 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 terminal of the first pole switch; The output voltage detection circuit is used to detect the output voltage of the DC / DC converter circuit; The controller is configured to open all M+1 pole switches when the current at the second terminal of the first pole switch is greater than a second current threshold and the voltage at the output terminal of the DC / DC converter circuit is less than a second preset voltage.

9. The photovoltaic system according to claim 7 or 8, characterized in that, The controller includes: a main controller and a backup controller; Both the main controller and the backup controller are used to control the M+1 pole switch to disconnect when there is a reverse connection fault in the N photovoltaic strings.

10. The photovoltaic system according to claim 9, characterized in that, Also includes: Primary auxiliary source and secondary auxiliary source; Both the main auxiliary power source and the secondary auxiliary power source are used to power the main controller and the backup controller; The main auxiliary source is connected to the output terminal of the DC / DC converter circuit; The auxiliary source is connected to the first terminal of the fault isolation circuit.

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

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

13. The photovoltaic system according to any one of claims 10-12, characterized in that, Also includes: 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 respectively connected to the positive output terminal of the DC / DC converter circuit and the first terminal of the second capacitor; the anode and cathode of the second diode are respectively connected to the positive output terminal of the DC / DC converter circuit and the second terminal of the second capacitor. The anode and cathode of the third diode are respectively connected to the first terminal of the second capacitor and the negative output terminal of the DC / DC converter circuit; the anode and cathode of the fourth diode are respectively connected to the negative output terminal of the DC / DC converter circuit and the second terminal of the second capacitor. The main auxiliary source is connected to the positive output terminal of the DC / DC converter circuit.

14. The photovoltaic system according to any one of claims 7-13, characterized in that, include: 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.

15. The photovoltaic system according to any one of claims 3-6, characterized in that, The power conversion circuit includes a DC / AC conversion circuit.

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