Combiner equipment, solar power generation system, and fault detection method

Abstract

The present application discloses a combiner device, a photovoltaic power generation system, and a fault detection method, the combiner device including at least two photovoltaic power generation strings connected in parallel, further including a current detection circuit for detecting the current of each photovoltaic power generation string, a voltage detection circuit for detecting the voltage of the photovoltaic power generation strings connected in parallel, an insulation impedance detection circuit for detecting the insulation impedance of the photovoltaic power generation strings connected in parallel, and a controller for determining whether a reverse connection fault occurs in the photovoltaic power generation string based on the current, voltage, and insulation impedance. When determining the photovoltaic power generation string, the three parameters of the current, voltage, and insulation impedance are comprehensively determined to accurately determine whether a reverse connection fault actually occurs in the photovoltaic power generation string, thereby reducing the impact of erroneous determination on the power generation amount, and the current alone cannot accurately determine whether a reverse connection fault occurs, and the current may be reversed due to other faults.

Description

Technical Field

[0001] This application claims the priority of a Chinese patent application filed with the China National Intellectual Property Administration on August 9, 2022, with an application number of 202210951810.X and an application title of "Combiner Equipment, Solar Power Generation System and Fault Detection Method", and all of its content is incorporated herein by reference.

[0002] This application relates to the technical field of solar power generation, specifically to combiner equipment, solar power generation systems and fault detection methods.

Background Art

[0003] With the continuous development of new energy, currently, the application of solar power generation is becoming increasingly widespread. A solar power generation system generally includes a combiner box, which can connect and merge multiple solar power generation strings in parallel and supply the merged power to a DC-AC circuit after merging. Each solar power generation string includes a plurality of solar power generation modules connected in series, and inside each solar power generation module, there are further a plurality of battery cells connected in series. Between the positive and negative outputs of the solar power generation module and the corresponding battery cell connection points, a plurality of diodes are connected in reverse parallel. For example, the number of diodes connected in reverse parallel may be three. The purpose of connecting the diodes in reverse parallel is to provide a bypass branch in case of an abnormality in the battery cell to avoid damage to the battery cell.

[0004] However, in actual application, it is difficult to completely avoid wiring errors during wiring work. For example, if a reverse connection occurs in one solar power string, all the current from other parallel-connected solar power strings will flow into that reverse-connected solar power string, causing an overcurrent in that string and damaging it. To solve the problem of solar power module damage due to reverse connection, generally, two solar power modules are connected in parallel and merged, and one current detection device is placed in each solar power string to detect whether the current is in the reverse direction, thereby determining whether a reverse connection has occurred.

[0005] However, when conventional solutions are actually applied, there are often problems with misjudgment. For example, when the open-circuit voltages of solar power strings do not match, there is a problem that the current will flow in the opposite direction when they are connected in parallel and merged. Also, when the wire cables of solar power strings are damaged and a ground short circuit occurs, a reverse current is generated, so even if the current of the solar power strings is detected, it is not possible to accurately determine whether or not a reverse connection fault has occurred. [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] Therefore, this application provides a combiner device, a solar power generation system, and a fault detection method that can accurately detect whether or not a reverse connection fault has occurred in a solar power generation string. [Means for solving the problem]

[0007] To solve the above technical problems, the technical solution provided in this application is as follows: This application provides a combiner device, and the combiner device is, Includes at least two solar power strings connected in parallel, A current detection circuit for detecting the current in each solar power generation string, A voltage detection circuit for detecting the voltage of a parallel-connected solar power generation string, An isolation impedance detection circuit for detecting the isolation impedance of a parallel-connected solar power generation string, The system further includes a controller for determining whether a reverse connection fault has occurred in a photovoltaic string based on current, voltage, and isolation impedance.

[0008] Preferably, the controller is used to determine that a reverse fault has occurred in the first photovoltaic string if the absolute value of the voltage is less than a preset voltage, the isolation impedance is greater than a preset impedance value, and the current in the first photovoltaic string is less than zero, and the first photovoltaic string is one of at least two photovoltaic strings connected in parallel.

[0009] Preferably, the controller is further used to determine that a voltage mismatch fault has occurred in a photovoltaic string if the voltage is greater than a preset voltage and the current in the first photovoltaic string is less than zero, and the first photovoltaic string is one of at least two photovoltaic strings connected in parallel.

[0010] Preferably, the controller is further used to determine that a short-circuit fault has occurred in the first photovoltaic string if the isolation impedance is less than a preset impedance value and the current in the first photovoltaic string is less than zero, and the first photovoltaic string is one of at least two photovoltaic strings connected in parallel.

[0011] Preferably, each photovoltaic module in the photovoltaic string includes an antiparallel connected diode, and the preset voltage is greater than the sum of the conduction voltage drops of the antiparallel connected diodes in the photovoltaic string and less than the open-circuit voltage of all the photovoltaic strings.

[0012] This application further provides a photovoltaic power generation system comprising a DC-AC circuit and at least one combiner device as described above. The output terminal of the combiner device is connected to the input terminal of the DC-AC circuit.

[0013] This application further provides a fault detection method applicable to a photovoltaic power generation system, the photovoltaic power generation system comprising a DCAC circuit and at least two photovoltaic power generation strings connected in parallel. This method is The steps include obtaining the current from each solar power string, The steps include obtaining the voltage of a parallel-connected solar power string, The steps include obtaining the isolation impedance of a parallel-connected solar power string, The method includes the step of determining whether a reverse connection fault has occurred in the photovoltaic string based on current, voltage, and isolation impedance.

[0014] Preferably, the step of determining whether a reverse connection fault has occurred in the photovoltaic string based on current, voltage, and isolation impedance is specifically: The process includes the step of determining that a reverse connection fault has occurred in the first photovoltaic string if the absolute value of the voltage is less than the preset voltage, the isolation impedance is greater than the preset impedance value, and the current in the first photovoltaic string is less than zero. The first solar power string is one of at least two solar power strings connected in parallel.

[0015] Preferably, the step further includes determining that a voltage mismatch fault has occurred in a photovoltaic string if the voltage is greater than a preset voltage and the current in the first photovoltaic string is less than zero, wherein the first photovoltaic string is one of at least two photovoltaic strings connected in parallel.

[0016] Preferably, the fault detection method further includes the step of determining that a short-circuit fault has occurred in the first photovoltaic string if the isolation impedance is less than a preset impedance value and the current in the first photovoltaic string is less than zero, wherein the first photovoltaic string is any one of at least two photovoltaic strings connected in parallel.

[0017] Preferably, each photovoltaic module in the photovoltaic string includes an antiparallel connected diode, and the preset voltage is greater than the sum of the conduction voltage drops of the antiparallel connected diodes in the photovoltaic string and less than the open-circuit voltage of all the photovoltaic strings. [Effects of the Invention]

[0018] As will be seen below, this application has the following beneficial effects. The combiner device provided in this application accurately determines whether a reverse connection fault has actually occurred in a photovoltaic string by comprehensively evaluating three parameters: current, voltage, and insulation impedance, thereby reducing the impact on power generation due to misjudgments. Current alone cannot accurately determine whether a reverse connection fault has occurred, as other faults can also cause the current to be reversed. For example, if the current in a photovoltaic string is reversed, but the insulation impedance is lower than the preset impedance value, it means that a short circuit fault has occurred, not a reverse connection fault. If the voltage is higher than the preset voltage and the current is reversed, it means that a voltage mismatch has occurred. A reverse connection fault is determined to have occurred only when the absolute value of the voltage is lower than the preset voltage, the insulation impedance is higher than the preset impedance value, and the current is reversed. Only when a reverse connection fault occurs does the maintenance worker need to remove and reconnect the reversed photovoltaic string and take appropriate measures if other faults occur. [Brief explanation of the drawing]

[0019] [Figure 1] Schematic diagram of m parallel-connected photovoltaic strings according to an embodiment of the present application [Figure 2] Schematic diagram of a photovoltaic module having anti-parallel-connected diodes according to the present application [Figure 3] Schematic diagram of two parallel-connected photovoltaic strings [Figure 4] Schematic diagram when reverse connection occurs in one of two parallel-connected photovoltaic strings [Figure 5] Schematic diagram when voltage mismatch occurs in parallel-connected photovoltaic strings [Figure 6] Schematic diagram when the positive and negative wire cables of a photovoltaic string are short-circuited to ground [Figure 7] Schematic diagram when the PV2 positive wire cable and the PV1 negative wire cable are short-circuited to ground [Figure 8] Schematic diagram of a combiner device according to an embodiment of the present application [Figure 9] Schematic diagram of another parallel-connected photovoltaic string according to an embodiment of the present application [Figure 10] Principle diagram of voltage mismatch according to an embodiment of the present application [Figure 11] Schematic diagram of the IV curve of parallel-connected photovoltaic strings according to an embodiment of the present application [Figure 12] Schematic diagram of a photovoltaic power generation system according to an embodiment of the present application [Figure 13] Flowchart of a fault detection method according to an embodiment of the present application

Embodiments for Carrying Out the Invention

[0020] Hereinafter, referring to the drawings of the embodiments of the present application, the technical solutions in the embodiments of the present application will be described.

[0021] In the following description, terms such as “first,” “second,” etc., should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features described, but are for illustrative purposes only. Thus, features limited by “first,” “second,” etc., may explicitly or implicitly include one or more such features. Unless otherwise specified, “multiple” in the description of this application means two or more.

[0022] In this application, unless otherwise explicitly specified and limited, terms such as “connection” should be understood in a broad sense. For example, “connection” may be a fixed connection, a detachable connection, or an integrated connection, and may be a direct connection or an indirect connection via an intermediate medium. Also, “coupling connection” may be a method of electrical connection that realizes signal transmission. “Coupling connection” may be a direct electrical connection or an indirect electrical connection via an intermediate medium.

[0023] To make the above-mentioned objectives, features, and advantages of this application clearer and easier to understand, embodiments of this application will be described in more detail below, combining drawings and specific embodiments.

[0024] The combiner equipment provided by the embodiments of this application is applicable to photovoltaic power generation systems, i.e., the field of photovoltaic power generation. The combiner equipment may exist individually or be integrated inside an inverter, and the embodiments of this application do not specifically limit this. Furthermore, the embodiments of this application do not specifically limit the number of photovoltaic strings included inside the combiner equipment, and may include at least two photovoltaic strings connected in parallel.

[0025] Referring to Figure 1, the drawing is a schematic diagram of m parallel-connected photovoltaic strings provided by the embodiment of this application.

[0026] In Figure 1, m solar power generation strings, namely the first solar power generation string PV1 to the mth solar power generation string PVm, are shown as an example, and PV1 to PVm are connected in parallel. m is an integer greater than or equal to 2.

[0027] Each solar power string contains n solar power modules, i.e., the first solar power module B1 through the nth solar power module Bn, and B1, B2 through Bn are connected in series. n is an integer greater than or equal to 2.

[0028] Since the currents from multiple solar power strings merge together and enter a DC-AC circuit, it can also be called a combiner device.

[0029] Furthermore, multiple diodes are connected in antiparallel between the positive and negative outputs of the solar power generation module and the corresponding battery cell connection points. This provides a bypass branch in the event of a battery cell malfunction, thereby preventing damage to the battery cell. As shown in Figure 2, the diagram is a schematic representation of a solar power generation module provided by this application with diodes connected in antiparallel.

[0030] To address the problem of solar power module damage caused by reverse connection of solar power strings, conventional solutions have employed the integration of two solar power strings into one, i.e., two solar power strings connected in parallel. Refer to Figure 3, which is a schematic diagram of two solar power strings connected in parallel.

[0031] Two solar power strings, PV1 and PV2, are connected in parallel, and each solar power string includes B1, B2-Bn connected in series. Each solar power string is equipped with a current detection device 100 (e.g., a current sensor or shunt resistor) to detect whether or not a reverse current has occurred at the branch of the solar power string.

[0032] The following describes the current detection process when a reverse connection occurs in a solar power generation string, referring to Figure 4.

[0033] Referring to Figure 4, this diagram is a schematic representation of a situation where a reverse connection occurs in one of two parallel-connected solar power strings.

[0034] As can be seen by comparing Figure 3 and Figure 4, the wiring of PV1 in Figure 4 is normal, but a reverse connection of the positive and negative terminals has occurred in PV2, causing the current between PV1 and PV2 to form a loop, that is, the current in PV2 to flow in the reverse direction.

[0035] Another case where the current in PV2 is reversed is when the voltages of the photovoltaic strings are mismatched, meaning that among the photovoltaic strings connected in parallel, some have high voltages and others have low voltages.

[0036] Referring to Figure 5, this diagram is a schematic representation of a case where a voltage mismatch occurs in parallel-connected solar power generation strings.

[0037] As can be seen from Figure 5, although the wiring of PV1 and PV2 is both normal and there is no reverse connection, the current in PV2 is in the reverse direction, which indicates that the voltage of PV1 is higher than the voltage of PV2.

[0038] Furthermore, there is yet another case where the current in a solar power string may be reversed. For example, if the wire cable of a solar power string is damaged due to mounting wear or insulation failure occurs, a short circuit to ground may occur in the wire cable of the solar power string. In this case, the current detection device may be able to detect a reverse current and report that a reverse connection fault has occurred in the solar power string, even though the solar power string is not actually reverse-connected.

[0039] Referring to Figure 6, this diagram is a schematic representation of a case where the positive and negative wire cables of a solar power generation string are short-circuited to ground.

[0040] The positive and negative wire cables of the photovoltaic string PV2 are short-circuited to ground, and in this case, the current detection device 100 can detect the occurrence of a reverse current in the photovoltaic string PV2.

[0041] Referring to Figure 7, this drawing is a schematic diagram of the case where the PV2 positive electrode and PV1 negative electrode wire cables are short-circuited to ground.

[0042] In this case, the current detection device 100 can also detect when a reverse current is generated in the solar power generation string PV2.

[0043] As described above, if a reverse connection, voltage mismatch, or ground short circuit occurs in a solar power generation string, a reverse current may be generated in any of these cases. Therefore, simply detecting the current does not accurately determine whether a reverse connection has occurred in the solar power generation string. Below, we introduce a combiner device provided by the embodiment of this application that can accurately detect whether a reverse connection has occurred in a solar power generation string.

[0044] Referring to Figure 8, the drawing is a schematic diagram of a combiner device provided by the embodiment of this application.

[0045] The combiner equipment provided by this embodiment includes at least two photovoltaic strings connected in parallel, and further includes a current detection circuit 801, a voltage detection circuit 803, an isolation impedance detection circuit 802, and a controller (not shown). The current detection circuit 801 is used to detect the current in each solar power generation string. In Figure 8, two solar power strings connected in parallel, namely the first solar power string PV1 and the second solar power string PV2 connected in parallel, are introduced as an example, but more solar power strings may be connected in parallel. The current detection circuit 801 can detect the current in PV1 and PV2, and here it can detect not only the magnitude of the current but also the direction of the current. For example, the direction in which the current flows from the solar power string to point A connected in parallel is defined as the forward direction. The voltage detection circuit 803 is used to detect the voltage of the parallel-connected solar power strings. Since multiple solar power strings are connected in parallel, when they stabilize, the voltages of all the solar power strings become approximately balanced, i.e., equal. The isolation impedance detection circuit 802 detects the isolation impedance to ground of the parallel-connected photovoltaic strings, and the isolation impedance is the total isolation impedance of the parallel-connected strings. The controller determines whether a reverse connection fault has occurred in the solar power string based on the current, voltage, and isolation impedance.

[0046] In the combiner equipment provided by the embodiment of this application, when determining a photovoltaic string, it is possible to accurately determine whether or not a reverse connection fault has actually occurred in the photovoltaic string by comprehensively determining three parameters: current, voltage, and insulation impedance. Current alone cannot accurately determine whether or not a reverse connection fault has occurred, as other faults can also cause the current to be reversed. For example, if the current in the photovoltaic string is reversed, but the insulation impedance is less than the preset impedance value, it means that a short circuit fault has occurred, not a reverse connection fault. If the voltage is greater than the preset voltage and the current is reversed, it means that a voltage mismatch has occurred. A reverse connection fault is determined to have occurred only when the absolute value of the voltage is less than the preset voltage, the insulation impedance is greater than the preset impedance value, and the current is reversed. Only when a reverse connection fault occurs does the maintenance worker need to remove and reconnect the reversed photovoltaic string and take appropriate measures if other faults occur.

[0047] Specifically, the combiner equipment provided by the embodiment of this application can not only determine whether a reverse connection fault has occurred in the solar power generation string, but also whether a voltage mismatch or a wire cable grounding short circuit fault has occurred in the solar power generation string, which will be described in detail below.

[0048] The controller is specifically used to determine that a reverse fault has occurred in the first solar power string if the absolute value of the voltage is less than the preset voltage, the isolation impedance is greater than the preset impedance value, and the current in the first solar power string is less than zero, and the first solar power string is one of at least two solar power strings connected in parallel.

[0049] Each solar module in a solar power string includes diodes connected in antiparallel, and the preset voltage is greater than the sum of the conduction voltage drops of the antiparallel diodes in the solar power string, and less than the open-circuit voltage of all solar power strings, i.e., less than the minimum open-circuit voltage of each solar power string.

[0050] Referring to Figure 9, the drawing is a schematic diagram of another parallel-connected photovoltaic string provided by an embodiment of the present application.

[0051] As can be seen in Figure 9, each photovoltaic module in each photovoltaic string includes diodes connected in antiparallel. Figure 9 illustrates an example where three diodes are connected in antiparallel to each photovoltaic module. Figure 9 also illustrates an example of reverse connection of PV2. A reverse current flows through PV2.

[0052] Because of the presence of antiparallel connected diodes, the reverse current in PV2 flows through the battery cells inside the solar module or through the antiparallel connected diodes. Therefore, the voltage Ubus at the parallel connection point (also called the confluence point) is limited to the sum of the maximum conduction voltage drops of the antiparallel connected diodes of each solar module connected in series in the solar string. As an example, if three diodes are antiparallel connected to each module, one solar string contains n solar modules connected in series, i.e., the maximum conduction voltage drop of the antiparallel connected diodes is n*3Ud, where Ud is the conduction voltage drop of the diodes, and generally Ud < 0.7V. Since the voltage Ubus between the positive and negative terminals of the parallel connection point can be positive or negative, it is necessary to determine the absolute value of Ubus, i.e., |Ubus| ≤ n*3Ud.

[0053] The following introduces the situation of voltage inconsistency while referring to FIGS. 10 and 11. Referring to FIG. 10, this drawing is a schematic diagram of the principle of voltage inconsistency provided by an embodiment of the present application. Referring to FIG. 11, this drawing is a schematic diagram of the IV curve of a parallel-connected solar power generation string provided by an embodiment of the present application.

[0054] In FIG. 11, PV1 represents the IV curve of the solar power generation string PV1, and PV2 represents the IV curve of the solar power generation string PV2. The horizontal coordinate of the IV curve is the voltage U, and the vertical coordinate is the current I. PV11 represents the mirror image curve of the IV curve of the solar power generation string PV1 with respect to the horizontal axis.

[0055] The voltage of PV1 is greater than the voltage of PV2. When the voltages of the solar power generation strings are inconsistent, the solar power generation string PV1 with a high open-circuit voltage Uoc_PV1 introduces current in the reverse direction to the solar power generation string PV2 with a low open-circuit voltage Uoc_PV2, that is, Uoc_PV2 < Uoc_PV1. For example, at this time, PV1 operates in the first quadrant (Ubus, I1) of the I-V curve. PV2 operates in the fourth quadrant (Ubus, -I1) of the I-V curve. The confluence point voltage Ubus is limited between the open-circuit voltage points of the two strings, that is, Uoc_PV2 < Ubus < Uoc_PV1.

[0056] Therefore, the preset voltage provided by the embodiment of the present application is smaller than the open-circuit voltages of all solar power generation strings, that is, smaller than the minimum open-circuit voltage. Since the open-circuit voltage of the solar power generation string is greater than the total maximum conduction voltage drop of the anti-parallel-connected diodes of the solar power generation module, the confluence point voltage Ubus is used as the determination basis for distinguishing between the reverse connection of the solar power generation string and the voltage inconsistency of the solar power generation string.

[0057] The controller is further used to determine that a voltage mismatch fault has occurred in a solar power string if the voltage is greater than a preset voltage and the current in the first solar power string is less than zero, and the first solar power string is one of at least two solar power strings connected in parallel.

[0058] The controller is further used to determine if a short-circuit fault has occurred in the first photovoltaic string if the isolation impedance is less than a preset impedance value and the current in the first photovoltaic string is less than zero, and the first photovoltaic string is one of at least two photovoltaic strings connected in parallel.

[0059] The combiner equipment provided by the embodiments of this application can accurately detect not only whether a reverse connection has occurred in the photovoltaic string, but also whether a voltage mismatch, i.e., imbalance, has occurred in the photovoltaic string, or whether a ground short circuit has occurred in the photovoltaic string, thereby enabling accurate determination of various faults and facilitating subsequent accurate maintenance.

[0060] Based on the combiner equipment provided in the above embodiments, the embodiments of this application further provide a photovoltaic power generation system, which will be described in detail below with reference to the drawings.

[0061] Referring to Figure 12, which is a schematic diagram of a photovoltaic power generation system provided by an embodiment of this application.

[0062] The photovoltaic power generation system provided by this embodiment includes a DCAC circuit 1201 and a combiner device 1202 as described in the above embodiment. The output terminal of the combiner device 1202 is connected to the input terminal of the DC-AC circuit 1201.

[0063] The embodiments of this application do not specifically limit the number of combiner devices 1202 included in the photovoltaic power generation system, nor do they limit the number of photovoltaic power generation strings included in the combiner devices 1202. Furthermore, the combiner devices 1202 may be integrated inside the inverter, that is, the inverter may contain the combiner devices and DC-AC circuit 1201 internally, and the controller may be the controller of the inverter.

[0064] The photovoltaic power generation system provided by the embodiment of this application can accurately recognize whether or not a reverse connection fault has occurred in the photovoltaic power generation string. If a reverse connection fault is determined to have occurred, the reversed photovoltaic power generation string can be promptly removed and correctly reconnected. Therefore, operation and maintenance personnel can be accurately instructed to quickly locate and maintain the faulty area, effectively reducing the inconvenience caused by misdiagnosis of faults, thereby increasing the amount of solar power generated and improving the efficiency of the photovoltaic power generation system.

[0065] Based on the combiner equipment and photovoltaic power generation system provided in the above embodiments, the embodiments of this application further provide a fault detection method, which will be described in detail below with reference to the drawings. The specific principles introduced in the above embodiments of the combiner equipment will not be explained again in the method embodiments, but can be found in the description of the embodiments of the combiner equipment.

[0066] Referring to Figure 13, the drawing is a flowchart of the fault detection method provided by the embodiment of this application.

[0067] The fault detection method provided by this embodiment is applied to a photovoltaic power generation system, which includes a DC-AC circuit and at least two photovoltaic power generation strings connected in parallel. The method includes the following steps: In step S1301, the current of each solar power generation string is obtained. In step S1302, the voltage of the parallel-connected solar power generation strings is obtained. In step S1303, the ground-to-ground isolation impedance of the parallel-connected photovoltaic strings is obtained. Here, there is no order in which S1301 to S1303 are performed. In S1304, it is determined whether or not a reverse connection fault has occurred in the solar power generation string based on the current, voltage, and insulation impedance.

[0068] The step of determining whether a reverse connection fault has occurred in the photovoltaic string based on current, voltage, and isolation impedance is as follows: The process includes the step of determining that a reverse fault has occurred in the first photovoltaic string if the absolute value of the voltage is less than a preset voltage, the isolation impedance is greater than a preset impedance value, and the current in the first photovoltaic string is less than zero, wherein the first photovoltaic string is one of at least two photovoltaic strings connected in parallel.

[0069] Each solar module in a solar power string includes an antiparallel connected diode, and the preset voltage is greater than the sum of the conduction voltage drops of the antiparallel connected diodes in the solar power string, and less than the open-circuit voltage of all the solar power strings.

[0070] Furthermore, the fault detection method provided by the embodiments of this application further includes the step of determining that a voltage mismatch fault has occurred in a photovoltaic string if the voltage is greater than a preset voltage and the current in the first photovoltaic string is less than zero, wherein the first photovoltaic string is any one of at least two photovoltaic strings connected in parallel.

[0071] Here, the fact that the current in the photovoltaic string in the embodiment of this application is less than zero means that the current is in the reverse direction, and regarding the direction of the current, if it is in the forward direction, the current can be defined as positive.

[0072] Furthermore, the fault detection method provided by the embodiments of this application further includes the step of determining that a short-circuit fault has occurred in the first photovoltaic string if the isolation impedance is less than a preset impedance value and the current in the first photovoltaic string is less than zero, wherein the first photovoltaic string is any one of at least two photovoltaic strings connected in parallel.

[0073] In the combiner equipment provided by the embodiment of this application, when determining a photovoltaic string, it is possible to accurately determine whether or not a reverse connection fault has actually occurred in the photovoltaic string by comprehensively determining three parameters: current, voltage, and insulation impedance. Current alone cannot accurately determine whether or not a reverse connection fault has occurred, as other faults can also cause the current to be reversed. For example, if the current in the photovoltaic string is reversed, but the insulation impedance is less than the preset impedance value, it means that a short circuit fault has occurred, not a reverse connection fault. If the voltage is greater than the preset voltage and the current is reversed, it means that a voltage mismatch has occurred. A reverse connection fault is determined to have occurred only when the absolute value of the voltage is less than the preset voltage, the insulation impedance is greater than the preset impedance value, and the current is reversed. Only when a reverse connection fault occurs does the maintenance worker need to remove and reconnect the reversed photovoltaic string and take appropriate measures if other faults occur.

[0074] Each example in this specification is described progressively, and each example primarily describes the differences from other examples. Similar or identical parts between examples can be referenced to one another. The descriptions of the systems or apparatus disclosed in the examples are relatively simple, as they correspond to the methods disclosed in the examples, and relevant parts should be referred to the description of the method.

[0075] The above description of the disclosed embodiments will enable those skilled in the art to implement or use the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Accordingly, the present application is not limited to these embodiments shown herein, but rather covers the broadest scope consistent with the principles and novel features disclosed herein.

Claims

1. It is a combiner, It includes at least two solar power strings connected in parallel, A current detection circuit for detecting the current in each of the aforementioned solar power generation strings, A voltage detection circuit for detecting the voltage of the solar power generation strings connected in parallel, An isolation impedance detection circuit for detecting the isolation impedance of the solar power generation strings connected in parallel, A controller for determining whether a reverse connection fault has occurred in the solar power generation string based on the current, voltage, and insulation impedance, It further includes, The combiner device is characterized in that the controller is used to determine that a reverse connection fault has occurred in the first photovoltaic string when the absolute value of the voltage is less than a preset voltage, the isolation impedance is greater than a preset impedance value, and the current in the first photovoltaic string is less than zero, and the first photovoltaic string is one of the at least two photovoltaic strings connected in parallel.

2. The controller is further used to determine that a voltage mismatch fault has occurred in the solar power string if the voltage is greater than the preset voltage and the current in the first solar power string is less than zero. The combiner device according to feature 1.

3. The controller is further used to determine that a short-circuit fault has occurred in the first photovoltaic string if the isolation impedance is less than a preset impedance value and the current in the first photovoltaic string is less than zero. The combiner device according to feature 1.

4. Each solar power module in the solar power string includes diodes connected in antiparallel, and the preset voltage is greater than the sum of the conduction voltage drops of the antiparallel diodes in the solar power string and less than the open-circuit voltage of all solar power strings. The combiner device according to feature 1.

5. It is a solar power generation system, A DCAC circuit and at least one combiner device as described in any one of claims 1 to 4, The output terminal of the combiner device is connected to the input terminal of the DC-AC circuit. A solar power generation system characterized by the following features.

6. A fault detection method applicable to a solar power generation system, The aforementioned photovoltaic power generation system includes a DCAC circuit and at least two photovoltaic power generation strings connected in parallel. This method is The steps include obtaining the current from each of the aforementioned solar power generation strings, The steps include obtaining the voltage of the solar power generation strings connected in parallel, The steps include obtaining the isolation impedance of the photovoltaic strings connected in parallel, A step of determining whether a reverse connection fault has occurred in the solar power generation string based on the current, the voltage, and the insulation impedance, Includes, The step of determining whether a reverse connection fault has occurred in the solar power generation string based on the current, the voltage, and the insulation impedance is as follows: The step includes determining that a reverse connection fault has occurred in the first photovoltaic string if the absolute value of the voltage is less than the preset voltage, the isolation impedance is greater than the preset impedance value, and the current in the first photovoltaic string is less than zero. A fault detection method characterized in that the first solar power generation string is one of the at least two solar power generation strings connected in parallel.

7. The further step includes determining that a voltage mismatch fault has occurred in the solar power string if the voltage is greater than a preset voltage and the current in the first solar power string is less than zero. The fault detection method according to claim 6, characterized by the features described above.

8. The further step includes determining that a short-circuit fault has occurred in the first photovoltaic string if the isolation impedance is less than a preset impedance value and the current in the first photovoltaic string is less than zero. The fault detection method according to claim 6, characterized by the features described above.

9. Each solar power module in the solar power string includes diodes connected in antiparallel, and the preset voltage is greater than the sum of the conduction voltage drops of the antiparallel diodes in the solar power string and less than the open-circuit voltage of all solar power strings. A fault detection method according to any one of claims 6 to 8, characterized by the features described herein.

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