Combiner device, photovoltaic 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 was filed with the State Intellectual Property Office of the People's Republic of China on August 9, 2022, bearing application number 202210951810.X, and claims priority to a Chinese patent application entitled "Combiner Equipment, Photovoltaic Power Generation System and Fault Detection Method", the entire contents of which are incorporated herein by reference.

[0002] The present application relates to the technical field of photovoltaic power generation, and in particular to a combiner device, a photovoltaic power generation system, and a fault detection method. [Background technology]

[0003] With the continuous development of new energy, the application of photovoltaic power generation is becoming more and more widespread at present, and a photovoltaic power generation system generally includes a combiner box, which can connect multiple photovoltaic power generation strings in parallel to be combined, and then supply them to a DCAC circuit after combination. Each photovoltaic power generation string includes multiple photovoltaic power generation modules connected in series, and each photovoltaic power generation module further includes multiple battery cells connected in series. A number of diodes are connected in anti-parallel between the positive and negative poles of the output of the photovoltaic power generation module and the corresponding battery cell connection points, for example, the number of diodes connected in anti-parallel can be three. The purpose of connecting the diodes in anti-parallel is to provide a bypass branch when the battery cell is abnormal, to avoid damage to the battery cell.

[0004] However, in practical applications, it is difficult to completely avoid wiring errors in wiring work. For example, if a photovoltaic power string is reversely connected, all the currents of the other photovoltaic power strings connected in parallel will flow into the reversely connected photovoltaic power string, causing overcurrent in the reversely connected photovoltaic power string and resulting in damage. In order to solve the damage to photovoltaic power modules caused by reverse connection, generally, two photovoltaic power modules are connected in parallel to merge, and a current detection device is arranged in each photovoltaic power string to detect whether the current is reversed, thereby determining whether reverse connection has occurred.

[0005] However, when the conventional solutions are actually applied, there are often problems of misjudgment. For example, when the open circuit voltages of the photovoltaic power strings are not consistent, the current will be reversed when they are connected in parallel and merged. In addition, when the wire cable of the photovoltaic power string is damaged and a ground short circuit occurs, a reverse current will also occur, so even if the current of the photovoltaic power string is detected, it is not possible to accurately judge whether a reverse connection fault has occurred. Summary of the Invention [Problem to be solved by the invention]

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

[0007] In order to solve the above technical problems, the technical solutions provided in this application are as follows: The present application provides a combiner device, the combiner device comprising: at least two photovoltaic strings connected in parallel; a current detection circuit for detecting a current of each photovoltaic string; a voltage detection circuit for detecting a 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 has occurred in the photovoltaic power generation string based on the current, the voltage and the insulation impedance.

[0008] Preferably, the controller is specifically used for determining that a reverse connection fault has occurred in a first solar power generation string when the absolute value of the voltage is smaller than a preset voltage, the insulation impedance is greater than a preset impedance value, and the current of the first solar power generation string is smaller than zero, and the first solar power generation string is any one of the at least two solar power generation strings connected in parallel.

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

[0010] Preferably, the controller is further used to determine that a short circuit fault has occurred in a first solar power generation string when the insulation impedance is smaller than a preset impedance value and the current of the first solar power generation string is smaller than zero, and the first solar power generation string is any one of the at least two solar power generation strings connected in parallel.

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

[0012] The present application further provides a photovoltaic power generation system, the photovoltaic power generation system including a DCAC circuit and at least one combiner device as described above; The output of the combiner device is connected to the input of the DCAC circuit.

[0013] The present application further provides a fault detection method applied to a photovoltaic power generation system, the photovoltaic power generation system including: a DCAC circuit; and at least two photovoltaic power generation strings connected in parallel; The method comprises: obtaining a current of each solar power string; obtaining voltages of photovoltaic strings connected in parallel; Obtaining an insulation impedance of a photovoltaic power string connected in parallel; and determining whether a reverse connection fault has occurred in the solar power generation string based on the current, the voltage and the insulation impedance.

[0014] Preferably, the step of determining whether a reverse connection fault has occurred in the photovoltaic power generation string based on the current, the voltage, and the insulation impedance specifically includes: determining that a reverse connection fault occurs in the first photovoltaic power string when the absolute value of the voltage is smaller than the preset voltage, the insulation impedance is greater than the preset impedance value, and the current of the first photovoltaic power string is smaller than zero; The first photovoltaic power generation string is any one of the at least two photovoltaic power generation strings connected in parallel.

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

[0016] Preferably, the fault detection method further includes a step of determining that a short-circuit fault has occurred in a first solar power generation string when the insulation impedance is smaller than a preset impedance value and the current of the first solar power generation string is smaller than zero, and the first solar power generation string is any one of the at least two solar power generation strings connected in parallel.

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

[0018] As can be seen, the present application has the following beneficial effects: The combiner device provided by the present application can comprehensively determine whether a reverse connection fault has actually occurred in the photovoltaic power string by judging the photovoltaic power string based on three parameters, i.e., current, voltage, and insulation impedance, to accurately determine whether a reverse connection fault has actually occurred in the photovoltaic power string and reduce the impact of erroneous judgment on the power generation amount. Whether a reverse connection fault has occurred cannot be accurately determined by the current alone, and the current may also be reversed due to other faults. For example, if the current of the photovoltaic power string is reversed but the insulation impedance is smaller 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. Only when the absolute value of the voltage is smaller than the preset voltage, the insulation impedance is greater than the preset impedance value, and the current is reversed, it is determined that a reverse connection fault has occurred. Only when a reverse connection fault occurs, the maintenance personnel need to disconnect and reconnect the reverse-connected photovoltaic power string, and take corresponding measures when other faults occur. [Brief description of the drawings]

[0019] [Figure 1] FIG. 1 is a schematic diagram of m photovoltaic strings connected in parallel according to an embodiment of the present application; [Diagram 2] FIG. 1 is a schematic diagram of a photovoltaic module having anti-parallel connected diodes according to the present application; [Diagram 3] Schematic diagram of two photovoltaic strings connected in parallel [Figure 4] Schematic diagram of what happens when a reverse connection occurs in one of two solar power strings connected in parallel [Diagram 5] Schematic diagram of voltage mismatch in parallel-connected photovoltaic strings [Figure 6] Schematic diagram of a photovoltaic string with positive and negative wire cables shorted to ground [Figure 7] Schematic diagram of PV2 positive wire cable and PV1 negative wire cable shorted to ground [Figure 8] 1 is a schematic diagram of a combiner device according to an embodiment of the present application; [Figure 9] FIG. 1 is a 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] 1 is a schematic diagram of an IV curve of a photovoltaic string connected in parallel according to an embodiment of the present application; [Figure 12] 1 is a schematic diagram of a photovoltaic power generation system according to an embodiment of the present application; [Figure 13] 1 is a flowchart of a fault detection method according to an embodiment of the present application; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

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

[0021] The terms "first", "second", etc. in the following description cannot be understood as indicating or implying a relative importance or implying a number of the technical features indicated, but are merely for explanatory purposes. Thus, a feature qualified by "first" or "second" can explicitly or implicitly include one or more of the said features. Unless otherwise specified, in the description of this application, "plurality" means two or more than two.

[0022] In this application, unless otherwise expressly specified or limited, terms such as "connection" should be understood in a broad sense, for example, "connection" may be a fixed connection, a removable connection, or an integral connection, and may be a direct connection or an indirect connection via an intermediate medium. In addition, "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] In order to make the above objectives, features and advantages of the present application more clear and understandable, the following examples of the present application are further described in detail in combination with drawings and specific embodiments.

[0024] The combiner device provided by the embodiment of the present application is applied to a photovoltaic power generation system, i.e., the field of photovoltaic power generation, and the combiner device may be present separately or integrated inside an inverter, which is not specifically limited in the embodiment of the present application. In addition, the embodiment of the present application does not specifically limit the number of photovoltaic power generation strings included inside the combiner device, and may include at least two photovoltaic power generation strings connected in parallel.

[0025] Please refer to FIG. 1, which is a schematic diagram of m photovoltaic strings connected in parallel provided by an embodiment of the present application.

[0026] 1, m photovoltaic power generation strings, that is, a first photovoltaic power generation string PV1 to an m-th photovoltaic power generation string PVm, are shown as an example, and PV1 to PVm are connected in parallel, where m is an integer of 2 or more.

[0027] Each photovoltaic power generation string includes n photovoltaic power generation modules, ie, a first photovoltaic power generation module B1 to an n-th photovoltaic power generation module Bn, where B1, B2 to Bn are connected in series, where n is an integer of 2 or more.

[0028] Since the currents of multiple solar power strings are combined together and enter the DCAC circuit, it may also be called a combiner device.

[0029] In addition, a number of diodes are connected in anti-parallel between the positive and negative poles of the output of the photovoltaic power generation module and the corresponding battery cell connection points, thereby providing a bypass branch to avoid damage to the battery cell when an abnormality occurs in the battery cell. As shown in Figure 2, this figure is a schematic diagram of a photovoltaic power generation module provided by the present application with diodes connected in anti-parallel.

[0030] In order to solve the damage of the photovoltaic module caused by reverse connection of the photovoltaic strings, the conventional solution is to integrate two photovoltaic strings into one, that is, the two photovoltaic strings are connected in parallel. Refer to Figure 3, which is a schematic diagram of two photovoltaic strings connected in parallel.

[0031] Two photovoltaic power generation strings PV1 and PV2 are connected in parallel, and each photovoltaic power generation string includes B1, B2 to Bn connected in series. Each photovoltaic power generation string is provided with a current detection device 100 (e.g., a current sensor or a shunt resistor) for detecting whether a reverse current occurs in a branch of the photovoltaic power generation string.

[0032] Below, we will introduce the current detection process when reverse connection occurs in a solar power string, with reference to Figure 4.

[0033] Please refer to FIG. 4, which is a schematic diagram of a case where reverse connection occurs in one of two photovoltaic power generation strings connected in parallel.

[0034] As can be seen by comparing Figures 3 and 4, the wiring of PV1 in Figure 4 is normal, but because the positive and negative poles of PV2 are reversed, the current between PV1 and PV2 forms a loop, that is, the current of PV2 flows in the reverse direction.

[0035] There is another case where the current in PV2 may be reversed, namely when the voltages of the photovoltaic strings are mismatched, i.e., among the photovoltaic strings connected in parallel, some have a higher voltage and some have a lower voltage.

[0036] Please refer to FIG. 5, which is a schematic diagram of a voltage mismatch occurring in photovoltaic power generation strings connected in parallel.

[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 of PV2 is in the reverse direction, which indicates that the voltage of PV1 is higher than the voltage of PV2.

[0038] There is another case where the current of the photovoltaic string is reversed, for example, when the wire cable of the photovoltaic string is damaged in its coating or has an insulation failure due to installation wear, the wire cable of the photovoltaic string may have a ground short circuit. In this case, the current detection device can detect the reverse current, so that it will report that the photovoltaic string has a reverse connection fault, but the photovoltaic string is not actually reverse connected.

[0039] Please refer to FIG. 6, which is a schematic diagram of a case where the positive and negative wire cables of a photovoltaic power string are shorted to ground.

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

[0041] Please refer to FIG. 7, which is a schematic diagram of the PV2 positive and PV1 negative wire cables being shorted to ground.

[0042] At this time, the current detection device 100 can also detect the occurrence of a reverse current in the photovoltaic power generation string PV2.

[0043] As described above, when reverse connection, voltage mismatch, or ground short circuit of a wire cable occurs in a photovoltaic power string, a reverse current may occur, so that it is not possible to accurately determine whether a reverse connection occurs in a photovoltaic power string by simply detecting a current. Hereinafter, a combiner device provided by an embodiment of the present application that can accurately detect whether a reverse connection occurs in a photovoltaic power string will be introduced.

[0044] Please refer to FIG. 8, which is a schematic diagram of a combiner device provided by an embodiment of the present application.

[0045] The combiner equipment provided by this embodiment includes at least two solar power generation strings connected in parallel, and further includes a current detection circuit 801, a voltage detection circuit 803, an insulation impedance detection circuit 802, and a controller (not shown). The current detection circuit 801 is used to detect the current of each photovoltaic power generation string. 8, two photovoltaic power strings connected in parallel, i.e., a first photovoltaic power string PV1 and a second photovoltaic power string PV2 connected in parallel, are still taken as an example, and more photovoltaic power strings may be connected in parallel. A current detection circuit 801 can detect the currents of PV1 and PV2, and can detect not only the magnitude of the current but also the direction of the current, for example, the direction flowing from the photovoltaic power string to point A connected in parallel is the forward direction. The voltage detection circuit 803 is used to detect the voltages of the photovoltaic power strings connected in parallel, and since multiple photovoltaic power strings are connected in parallel, when stable, the voltages of all the photovoltaic power strings are approximately balanced, i.e., equal. The insulation impedance detection circuit 802 detects the insulation impedance to ground of the photovoltaic power generation strings connected in parallel, and the insulation impedance is the total insulation impedance of the photovoltaic power generation strings connected in parallel; The controller determines whether a reverse connection fault occurs in the photovoltaic power generation string based on the current, the voltage, and the insulation impedance.

[0046] In the combiner device provided by the embodiment of the present application, when judging a photovoltaic power string, the three parameters of current, voltage and insulation impedance are judged comprehensively, so that it can accurately judge whether a reverse connection fault has actually occurred in the photovoltaic power string. Only the current cannot accurately judge whether a reverse connection fault has occurred, and other faults may also cause the current to reverse. For example, if the current of the photovoltaic power string reverses but the insulation impedance is smaller than the preset impedance value, it means that a short circuit fault occurs, not a reverse connection fault. If the voltage is greater than the preset voltage and the current reverses, it means that a voltage mismatch occurs. Only when the absolute value of the voltage is smaller than the preset voltage, the insulation impedance is greater than the preset impedance value, and the current reverses, it is determined that a reverse connection fault has occurred. Only when a reverse connection fault occurs, the maintenance personnel need to disconnect and reconnect the reverse-connected photovoltaic power string, and take corresponding measures when other faults occur.

[0047] Specifically, the combiner equipment provided in the embodiments of the present application can not only determine whether a reverse connection fault occurs in a photovoltaic power string, but also determine whether a voltage mismatch or a wire cable ground short circuit fault occurs in a photovoltaic power string, which will be introduced in detail below.

[0048] The controller is specifically used for determining that a reverse connection fault has occurred in a first solar power generation string when the absolute value of the voltage is smaller than a preset voltage, the insulation impedance is greater than a preset impedance value, and the current of the first solar power generation string is smaller than zero, and the first solar power generation string is any one of the at least two solar power generation strings connected in parallel.

[0049] Each photovoltaic power generation module in the photovoltaic power string includes an anti-parallel connected diode, and the preset voltage is greater than the sum of the conduction voltage drops of the anti-parallel connected diodes in the photovoltaic power generation string and less than the open circuit voltages of all the photovoltaic power generation strings, i.e., less than the minimum open circuit voltage of each photovoltaic power generation string.

[0050] Reference is made to FIG. 9, which is a schematic diagram of another parallel-connected photovoltaic power string provided by an embodiment of the present application.

[0051] As can be seen from Fig. 9, the photovoltaic modules in each photovoltaic string include diodes connected in anti-parallel, and Fig. 9 takes an example in which each photovoltaic module has three diodes connected in anti-parallel. Fig. 9 also takes an example in which PV2 is reverse-connected, and a reverse current flows in PV2.

[0052] Due to the existence of anti-parallel connected diodes, the reverse current in PV2 flows through the battery cells or anti-parallel connected diodes inside the photovoltaic module. Therefore, the voltage Ubus at the parallel connection point (also called the junction point) is limited to the sum of the maximum conduction voltage drops of the anti-parallel connected diodes of each photovoltaic module connected in series in the photovoltaic string. Taking three diodes connected in anti-parallel as an example, a photovoltaic string includes n photovoltaic modules connected in series, that is, the maximum conduction voltage drop of the anti-parallel connected diodes is n*3Ud, where Ud is the conduction voltage drop of the diode, and generally, Ud<0.7V. The voltage Ubus between the positive and negative poles of the parallel connection point may be positive or negative, so it is necessary to determine the absolute value of Ubus, i.e., |Ubus|≦n*3Ud.

[0053] The following describes the situation of voltage inconsistency with reference 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 abscissa of the IV curve is the voltage U, and the ordinate 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 abscissa axis.

[0055] The voltage of PV1 is higher 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 larger 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 the photovoltaic power string when the voltage is greater than a preset voltage and the current of the first photovoltaic power string is less than zero, the first photovoltaic power string being any one of the at least two photovoltaic power strings connected in parallel.

[0058] The controller is further used to determine that a short circuit fault has occurred in a first solar power generation string when the insulation impedance is smaller than a preset impedance value and the current of the first solar power generation string is smaller than zero, the first solar power generation string being any one of the at least two solar power generation strings connected in parallel.

[0059] The combiner device provided by the embodiments of the present application can not only accurately detect whether a reverse connection occurs in a photovoltaic power string, but also accurately detect whether a voltage mismatch, i.e., an unbalance, occurs in the photovoltaic power string, or whether a ground short circuit occurs in the photovoltaic power string, and can accurately determine various faults, facilitating accurate maintenance afterwards.

[0060] Based on the combiner device provided by the above embodiments, an embodiment of the present application further provides a photovoltaic power generation system, which will be introduced in detail below with reference to the drawings.

[0061] Please refer to FIG. 12, which is a schematic diagram of a solar power generation system provided by an embodiment of the present application.

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

[0063] The embodiments of the present application do not specifically limit the number of combiner devices 1202 included in the photovoltaic power generation system, nor limit the number of photovoltaic power generation strings included in the combiner device 1202. In addition, the combiner device 1202 may be integrated into the inverter, that is, the inverter includes the combiner device and the DCAC circuit 1201 therein, and the controller may be the controller of the inverter.

[0064] The photovoltaic power generation system provided by the embodiments of the present application can accurately recognize whether a reverse connection fault has occurred in a photovoltaic power generation string. If it is determined that a reverse connection fault has occurred, the reverse-connected photovoltaic power generation string can be promptly disconnected and accurately connected. Therefore, operation and maintenance personnel can be accurately instructed to quickly locate the fault location and perform maintenance, and the inconvenience caused by erroneous fault determination can be effectively reduced, thereby increasing the amount of photovoltaic power generation and improving the photovoltaic power generation efficiency.

[0065] Based on the combiner device and the photovoltaic power generation system provided by the above embodiments, the embodiments of the present 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 device are not described again in the method embodiments, but can be referred to the description of the embodiments of the combiner device.

[0066] Please refer to FIG. 13, which is a flowchart of a fault detection method provided by an embodiment of the present application.

[0067] The fault detection method provided by this embodiment is applied to a solar power generation system, and the solar power generation system includes a DCAC circuit and at least two solar power generation strings connected in parallel; The method includes the following steps. In step S1301, the current of each photovoltaic power generation string is obtained. In step S1302, the voltages of the photovoltaic power generation strings connected in parallel are obtained. In step S1303, the insulation impedance to ground of the photovoltaic power generation strings connected in parallel is obtained. Here, S1301 to S1303 have no order. In S1304, it is determined whether a reverse connection fault occurs in the photovoltaic power generation string based on the current, the voltage and the insulation impedance.

[0068] The step of determining whether a reverse connection fault occurs in the photovoltaic power generation string based on the current, the voltage, and the insulation impedance is specifically described as follows: The method includes a step of determining that a reverse connection fault has occurred in a first solar power generation string when the absolute value of the voltage is smaller than a preset voltage, the insulation impedance is greater than a preset impedance value, and the current of the first solar power generation string is smaller than zero, and the first solar power generation string is any one of the at least two solar power generation strings connected in parallel.

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

[0070] In addition, the fault detection method provided by the embodiments of the present application further includes a step of determining that a voltage mismatch fault has occurred in the solar power string when the voltage is greater than a preset voltage and the current of the first solar power string is less than zero, and the first solar power string is any one of the at least two solar power strings connected in parallel.

[0071] Here, the current of the photovoltaic power generation string in the embodiment of the present application being less than zero means that the current has reversed direction, and when the current direction is forward, the current can be defined as positive.

[0072] In addition, the fault detection method provided by the embodiments of the present application further includes a step of determining that a short-circuit fault has occurred in the first solar power generation string when the insulation impedance is smaller than a preset impedance value and the current of the first solar power generation string is smaller than zero, and the first solar power generation string is any one of the at least two solar power generation strings connected in parallel.

[0073] In the combiner device provided by the embodiment of the present application, when judging a photovoltaic power string, the three parameters of current, voltage and insulation impedance are judged comprehensively, so that it can accurately judge whether a reverse connection fault has actually occurred in the photovoltaic power string. Only the current cannot accurately judge whether a reverse connection fault has occurred, and other faults may also cause the current to reverse. For example, if the current of the photovoltaic power string reverses but the insulation impedance is smaller than the preset impedance value, it means that a short circuit fault occurs, not a reverse connection fault. If the voltage is greater than the preset voltage and the current reverses, it means that a voltage mismatch occurs. Only when the absolute value of the voltage is smaller than the preset voltage, the insulation impedance is greater than the preset impedance value, and the current reverses, it is determined that a reverse connection fault has occurred. Only when a reverse connection fault occurs, the maintenance personnel need to disconnect and reconnect the reverse-connected photovoltaic power string, and take corresponding measures when other faults occur.

[0074] In addition, each embodiment in this specification will be described step by step, and each embodiment will mainly describe the differences from other embodiments, and the same or similar parts between each embodiment may be referred to each other. Since the system or device disclosed in the embodiment corresponds to the method disclosed in the embodiment, the description thereof is relatively simple, and the relevant parts may be referred to the description of the method part.

[0075] The above description of the disclosed embodiments enables one skilled in the art to realize 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 may be implemented in other embodiments without departing from the spirit or scope of the present application. Thus, the present application is not intended to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A combiner device, comprising: at least two photovoltaic strings connected in parallel; a current detection circuit for detecting a current in each of the photovoltaic strings; a voltage detection circuit for detecting a 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; a controller for determining whether a reverse connection fault has occurred in the solar power generation string based on the current, the voltage, and the insulation impedance; 4. The combiner device according to claim 3, further comprising:

2. The controller is used to determine that a reverse connection fault occurs in a first photovoltaic power generation string when the absolute value of the voltage is smaller than a preset voltage, the insulation impedance is larger than a preset impedance value, and a current of a first photovoltaic power generation string is smaller than zero, and the first photovoltaic power generation string is any one of the at least two photovoltaic power generation strings connected in parallel.

2. A combiner device according to claim 1.

3. The controller is further used to determine that a voltage mismatch fault occurs in the photovoltaic power string when the voltage is greater than a preset voltage and a current of the first photovoltaic power string is less than zero, the first photovoltaic power string being any one of the at least two photovoltaic power strings connected in parallel. A combiner device according to claim 1 or 2.

4. The controller is further used to determine that a short circuit fault occurs in a first photovoltaic power string when the insulation impedance is smaller than a preset impedance value and a current of the first photovoltaic power string is smaller than zero, the first photovoltaic power string being any one of the at least two photovoltaic power strings connected in parallel. A combiner device according to claim 1 or 2.

5. Each photovoltaic power generation module in the photovoltaic power generation string includes an anti-parallel connected diode, and the preset voltage is greater than a sum of the conduction voltage drops of the anti-parallel connected diodes in the photovoltaic power generation string and less than the open circuit voltages of all the photovoltaic power generation strings; A combiner device according to claim 2 or 3.

6. A solar power generation system, comprising: A DCAC circuit and at least one combiner device according to any one of claims 1 to 5, The output end of the combiner device is connected to the input end of the DCAC circuit. A solar power generation system comprising:

7. A fault detection method applied to a solar power generation system, comprising: The solar power generation system includes a DCAC circuit and at least two solar power generation strings connected in parallel; The method comprises: obtaining a current of each of the photovoltaic strings; obtaining a voltage of the photovoltaic power strings connected in parallel; obtaining an insulation impedance of the photovoltaic power strings connected in parallel; determining whether a reverse connection fault occurs in the solar power generation string based on the current, the voltage, and the insulation impedance; A fault detection method comprising:

8. The step of determining whether a reverse connection fault occurs in the solar power generation string based on the current, the voltage, and the insulation impedance includes: determining that a reverse connection fault occurs in the first photovoltaic power string when the absolute value of the voltage is smaller than a preset voltage, the insulation impedance is greater than a preset impedance value, and a current of the first photovoltaic power string is smaller than zero; The first solar power string is any one of the at least two solar power strings connected in parallel.

8. The fault detection method according to claim 7.

9. If the voltage is greater than a preset voltage and the current of the first solar power string is less than zero, determining that a voltage mismatch fault occurs in the solar power string; The first solar power string is any one of the at least two solar power strings connected in parallel.

8. The fault detection method according to claim 7.

10. If the insulation impedance is less than a preset impedance value and a current of the first photovoltaic power string is less than zero, determining that a short circuit fault occurs in the first photovoltaic power string; The first solar power string is any one of the at least two solar power strings connected in parallel.

8. The fault detection method according to claim 7.

11. Each photovoltaic power generation module in the photovoltaic power generation string includes an anti-parallel connected diode, and the preset voltage is greater than a sum of the conduction voltage drops of the anti-parallel connected diodes in the photovoltaic power generation string and less than the open circuit voltages of all the photovoltaic power generation strings; The fault detection method according to any one of claims 7 to 10.

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