A photovoltaic power generation system, a photovoltaic inverter, and a method for detecting a ground fault of a photovoltaic string

Abstract

The present application discloses a photovoltaic power generation system, a method and a device for detecting the ground fault of a photovoltaic string. The power conversion circuits in the system correspond to the photovoltaic strings one by one. The controller obtains the terminal voltages of each photovoltaic string before voltage perturbation, and the terminal voltage is the positive-pole-to-ground voltage or the negative-pole-to-ground voltage of the photovoltaic string. Voltage perturbation is respectively performed on each photovoltaic string, and the terminal voltages of each photovoltaic string after voltage perturbation are respectively obtained. The photovoltaic string with a ground fault is determined according to the terminal voltage of each photovoltaic string before voltage perturbation and the terminal voltage after voltage perturbation. For the photovoltaic string with a ground fault, the photovoltaic panel with a ground fault is obtained by using the terminal voltage and the output voltage of the photovoltaic string before voltage perturbation, or the photovoltaic panel with a ground fault is obtained by using the terminal voltage and the output voltage of the photovoltaic string after voltage perturbation. This solution is simple and easy to implement, does not require adding any hardware, does not require manual detection one by one, can automatically determine the photovoltaic panel with a ground fault, and has high efficiency.

Description

Technical Field

[0001] This application relates to the technical field of photovoltaic power generation, and particularly to a photovoltaic power generation system, a method and a device for detecting the ground fault of a photovoltaic string. Background Art

[0002] At present, photovoltaic power generation has been paid more and more attention. The direct current output by a photovoltaic array is converted into alternating current by an inverter and then can be fed back to the alternating current power grid. In order to improve the power output, a photovoltaic array generally includes a plurality of photovoltaic strings connected in parallel.

[0003] In practical applications, the photovoltaic array is prone to ground faults, that is, ground faults. Common causes of ground faults in the photovoltaic array include: insulation damage of the cables of the photovoltaic array, internal short circuit to ground of the photovoltaic string, or short-term short circuit to ground of the photovoltaic array due to weather and other reasons. When a ground fault occurs in the photovoltaic array, it will cause a large leakage current, which may trigger a safety accident.

[0004] The IEC standard 62109-2 stipulates that before the photovoltaic inverter is turned on, it is necessary to detect the DC insulation impedance between the photovoltaic array and the ground. For non-isolated application scenarios, when the DC insulation impedance is low (the leakage current requirement cannot be met), the inverter is not allowed to be turned on until the DC insulation impedance returns to the normal value.

[0005] At present, when the photovoltaic power generation system detects a ground fault by detecting the DC insulation impedance, it cannot determine the specific location of the ground fault, and it is necessary to manually check each photovoltaic string on site, which takes a long time and has low efficiency. Summary of the Invention

[0006] This application provides a photovoltaic power generation system, a method and a device for detecting the ground fault of a photovoltaic string, which can detect whether the photovoltaic string has a ground fault, can automatically judge the specific fault location, and has high efficiency.

[0007] An embodiment of the present application provides a photovoltaic power generation system, including: a photovoltaic array, a photovoltaic device, and a controller; the photovoltaic array includes m photovoltaic strings, where m is an integer greater than or equal to 1; the photovoltaic device includes m power conversion circuits; the power conversion circuits correspond to the photovoltaic strings one by one, and each photovoltaic string is connected to the corresponding power conversion circuit; the controller is configured to obtain the terminal voltage of each photovoltaic string before voltage disturbance, the terminal voltage being the voltage of the positive electrode of the photovoltaic string to the ground or the voltage of the negative electrode of the photovoltaic string to the ground, that is, the voltage of PV+ or PV- to the ground; perform voltage disturbance on each photovoltaic string respectively, and obtain the terminal voltage of each photovoltaic string after voltage disturbance respectively; when a ground fault occurs inside the photovoltaic string, there will be an obvious change in the terminal voltage of the photovoltaic string before and after voltage disturbance. Determine the photovoltaic string with a ground fault according to the terminal voltage of each photovoltaic string before voltage disturbance and the terminal voltage after voltage disturbance; for the photovoltaic string with a ground fault, obtain the photovoltaic panel with a ground fault by using the terminal voltage of the photovoltaic string before voltage disturbance and the output voltage, or obtain the photovoltaic panel with a ground fault by using the terminal voltage of the photovoltaic string after voltage disturbance and the output voltage.

[0008] Among them, the photovoltaic device can be an inverter. The photovoltaic device includes a DC / DC (direct current / direct current) conversion circuit and a DC / AC (direct current / alternating current) conversion circuit. The photovoltaic string is connected to the input end of the DC / DC conversion circuit, and the output end of the DC / DC conversion circuit is used to connect to the inverter circuit. Among them, the DC / DC conversion circuit and the inverter circuit can be integrated inside the inverter, and the controller of the inverter is used to detect the ground fault of the photovoltaic string. Of course, a separate controller can also be set up to detect the ground fault of the photovoltaic string. Among them, there may be no DC / DC circuit inside the inverter, and only a DC / AC conversion circuit. Among them, the inverter can be a single-phase inverter or a three-phase inverter.

[0009] When there is an obvious change in the terminal voltage before voltage disturbance and the terminal voltage after voltage disturbance, it indicates that a ground fault has occurred in the photovoltaic string. Since all the photovoltaic panels in the photovoltaic string are connected in series, when a ground short circuit occurs at a certain place in the photovoltaic string, the potential at the position where the ground fault occurs is the reference ground. Therefore, the reference potential of the terminal voltage of the photovoltaic string is the ground potential at the ground fault location. The specific position where the ground fault occurs can be determined by using the ratio of the terminal voltage to the output voltage of the whole string. This method is simple and easy to implement, does not require any additional hardware equipment, and does not require manual detection of the N photovoltaic panels in the photovoltaic string one by one, and can automatically determine the photovoltaic panel with a ground fault, and the detection efficiency is relatively high.

[0010] Preferably, regardless of whether it is the terminal voltage before the disturbance minus the terminal voltage after the disturbance or the terminal voltage after the disturbance minus the terminal voltage before the disturbance, it mainly depends on the absolute value of the voltage change. Because the voltage disturbance may control the terminal voltage to change in the increasing direction or may control the terminal voltage to change in the decreasing direction. The controller is specifically configured to determine that the photovoltaic string with a ground fault when the absolute value of the difference between the terminal voltage of the photovoltaic string before the voltage disturbance and the terminal voltage after the voltage disturbance exceeds a preset threshold.

[0011] Preferably, the controller is specifically configured to control the output voltage of the photovoltaic string disturbed by the voltage to change along the direction of increasing voltage or along the direction of decreasing voltage.

[0012] Preferably, because the open-circuit voltage is generally the maximum voltage, that is, it does not need to be controlled and is the open-circuit voltage in the default state. The controller is specifically configured to control the output voltage of the photovoltaic string disturbed by the voltage to change from the open-circuit voltage before the voltage disturbance to the first preset voltage after the voltage disturbance, and the first preset voltage is less than the open-circuit voltage.

[0013] Preferably, generally, when performing current-voltage scanning, it is controlled from the open-circuit voltage to the short-circuit voltage, that is, from a large voltage to a smaller voltage. The controller is specifically configured to control the output voltage of the photovoltaic string disturbed by the voltage to change from the open-circuit voltage before the voltage disturbance to the short-circuit voltage after the voltage disturbance.

[0014] Preferably, since the photovoltaic panels in the photovoltaic string are in series, and the series-connected photovoltaic panels divide the voltage across the photovoltaic string, therefore, the specific ground fault location can be obtained by proportion. The controller is specifically configured to use the ratio of the terminal voltage and the output voltage of the photovoltaic string with the ground fault before the voltage disturbance and the number N of series-connected photovoltaic panels to obtain the photovoltaic panel with the ground fault.

[0015] Preferably, when the terminal voltage is the positive electrode to ground voltage, the photovoltaic panel with the ground fault is obtained by the following formula:

[0016] x = N * (Upv+ / Upv);

[0017] When the terminal voltage is the negative electrode to ground voltage, the photovoltaic panel with the ground fault is obtained by the following formula:

[0018] x = N * (1 - |Upv-| / Upv);

[0019] Among them, Upv+ represents the positive pole-to-ground voltage before voltage disturbance, Upv- represents the negative pole-to-ground voltage before voltage disturbance, and Upv represents the output voltage before voltage disturbance; N represents the number of series-connected photovoltaic panels included in the photovoltaic string with a ground fault, and x represents the x-th photovoltaic panel starting from the positive pole of the photovoltaic string with the ground fault.

[0020] Preferably, the controller is specifically configured to obtain the photovoltaic panel with a ground fault by using the ratio of the terminal voltage after voltage disturbance of the photovoltaic string with a ground fault and the output voltage after voltage disturbance, and the number N of series-connected photovoltaic panels.

[0021] Preferably, when the terminal voltage is the positive pole-to-ground voltage, the controller is specifically configured to obtain the photovoltaic panel with a ground fault through the following formula:

[0022] x = N*(Uv+ / Uv);

[0023] When the terminal voltage is the negative pole-to-ground voltage, the photovoltaic panel with a ground fault is obtained through the following formula:

[0024] x = N*(1 - |Uv-| / Uv);

[0025] Among them, Uv+ represents the positive pole-to-ground voltage after voltage disturbance, Uv- represents the negative pole-to-ground voltage after voltage disturbance, and Uv represents the output voltage after voltage disturbance; N represents the number of series-connected photovoltaic panels included in the photovoltaic string with a ground fault, and x represents the x-th photovoltaic panel starting from the positive pole of the photovoltaic string with the ground fault.

[0026] The embodiment of the present application also provides a method for detecting a ground fault of a photovoltaic string, including: obtaining the terminal voltage of each photovoltaic string before voltage disturbance, where the terminal voltage is the positive pole-to-ground voltage or the negative pole-to-ground voltage of the photovoltaic string; performing voltage disturbance on each of the photovoltaic strings respectively to obtain the terminal voltage of each photovoltaic string after voltage disturbance; determining the photovoltaic string with a ground fault according to the terminal voltage of each photovoltaic string before voltage disturbance and the terminal voltage after voltage disturbance; for the photovoltaic string with a ground fault, obtaining the photovoltaic panel with a ground fault by using the terminal voltage and the output voltage of the photovoltaic string before voltage disturbance, or obtaining the photovoltaic panel with a ground fault by using the terminal voltage and the output voltage of the photovoltaic string after voltage disturbance.

[0027] When there are obvious changes in the terminal voltage before voltage disturbance and the terminal voltage after voltage disturbance, it indicates that the photovoltaic string has a ground fault. Since all the photovoltaic panels in the photovoltaic string are connected in series, when there is a ground short circuit at a certain point in the photovoltaic string, the potential at the position where the ground fault occurs is the reference ground. Therefore, the reference potential of the terminal voltage of the photovoltaic string is the ground potential at the ground fault location. The specific location of the ground fault can be determined by using the ratio of the terminal voltage to the output voltage of the whole string. This method is simple and easy to implement, does not require additional hardware equipment, and does not require manual inspection of the N photovoltaic panels in the photovoltaic string one by one, and can automatically determine the photovoltaic panel with a ground fault, with relatively high detection efficiency.

[0028] Preferably, the determining the photovoltaic string with a ground fault according to the terminal voltage before voltage disturbance and the terminal voltage after voltage disturbance of each photovoltaic string specifically includes: when the absolute value of the difference between the terminal voltage before voltage disturbance and the terminal voltage after voltage disturbance of the photovoltaic string exceeds a preset threshold, determining that this path of photovoltaic string is the photovoltaic string with a ground fault.

[0029] Preferably, the separately performing voltage disturbance on each photovoltaic string specifically includes: controlling the output voltage of the photovoltaic string to be voltage-disturbed to change along the direction of increasing voltage or along the direction of decreasing voltage.

[0030] Preferably, the controlling the output voltage of the photovoltaic string to be voltage-disturbed to change along the direction of decreasing voltage specifically includes: controlling the output voltage of the photovoltaic string to be voltage-disturbed to change from the open-circuit voltage before voltage disturbance to a first preset voltage after voltage disturbance, and the first preset voltage is less than the open-circuit voltage.

[0031] Preferably, the voltage disturbance can change the voltage either from large to small or from small to large. When separately performing voltage disturbance on each photovoltaic string, generally, when performing current-voltage scanning, it is always controlled from the open-circuit voltage to the short-circuit voltage, that is, from a large voltage to a smaller voltage. Specifically, it includes: controlling the output voltage of the photovoltaic string to be voltage-disturbed to change from the open-circuit voltage before voltage disturbance to the short-circuit voltage after voltage disturbance.

[0032] Preferably, since the photovoltaic panels in the photovoltaic string are all in a series relationship, and the series-connected photovoltaic panels divide the voltage at both ends of the photovoltaic string, therefore, the specific ground fault location can be obtained by proportion. The obtaining the photovoltaic panel with a ground fault by using the terminal voltage and output voltage of the photovoltaic string before voltage disturbance specifically includes: using the ratio of the terminal voltage and output voltage of the photovoltaic string with a ground fault before voltage disturbance, and including the number N of series-connected photovoltaic panels to obtain the photovoltaic panel with a ground fault.

[0033] Preferably, the photovoltaic panels with ground faults are obtained by using the ratio of the terminal voltage before the voltage disturbance of the photovoltaic string with the ground fault and the output voltage before the voltage disturbance, and the number N of the series-connected photovoltaic panels, which specifically includes: when the terminal voltage is the positive-pole-to-ground voltage, the photovoltaic panels with ground faults are obtained by the following formula:

[0034] x = N * (Upv+ / Upv);

[0035] When the terminal voltage is the negative-pole-to-ground voltage, the photovoltaic panels with ground faults are obtained by the following formula:

[0036] x = N * (1 - |Upv-| / Upv);

[0037] Wherein, Upv+ represents the positive-pole-to-ground voltage before the voltage disturbance, Upv- represents the negative-pole-to-ground voltage before the voltage disturbance, Upv represents the output voltage before the voltage disturbance; N represents the number of the series-connected photovoltaic panels included in the photovoltaic string with the ground fault, and x represents the x-th photovoltaic panel starting from the positive pole of the photovoltaic string with the ground fault.

[0038] Preferably, the photovoltaic panels with ground faults are obtained by using the ratio of the terminal voltage of the photovoltaic string after the voltage disturbance and the output voltage after the voltage disturbance, which specifically includes: the photovoltaic panels with ground faults are obtained by using the ratio of the terminal voltage of the photovoltaic string with the ground fault after the voltage disturbance and the output voltage after the voltage disturbance, and the number N of the series-connected photovoltaic panels.

[0039] Preferably, the photovoltaic panels with ground faults are obtained by using the ratio of the terminal voltage of the photovoltaic string with the ground fault after the voltage disturbance and the output voltage after the voltage disturbance, and the number N of the series-connected photovoltaic panels, which specifically includes:

[0040] When the terminal voltage is the positive-pole-to-ground voltage, the photovoltaic panels with ground faults are obtained by the following formula:

[0041] x = N * (Uv+ / Uv);

[0042] When the terminal voltage is the negative-pole-to-ground voltage, the photovoltaic panels with ground faults are obtained by the following formula:

[0043] x = N * (1 - |Uv-| / Uv);

[0044] Wherein, Uv+ represents the positive-pole-to-ground voltage after the voltage disturbance, Uv- represents the negative-pole-to-ground voltage after the voltage disturbance, Uv represents the output voltage after the voltage disturbance; N represents the number of the series-connected photovoltaic panels included in the photovoltaic string with the ground fault, and x represents the x-th photovoltaic panel starting from the positive pole of the photovoltaic string with the ground fault.

[0045] The embodiment of the present application further provides a photovoltaic device for detecting a ground fault, including: a power conversion circuit, a controller, and a voltage detection circuit; the power conversion circuit corresponds to each photovoltaic string one by one, and each photovoltaic string is connected to the corresponding power conversion circuit; the voltage detection circuit is configured to obtain the terminal voltage of each photovoltaic string before voltage perturbation, and the terminal voltage is the positive electrode to ground voltage or the negative electrode to ground voltage of the photovoltaic string; the controller is configured to perform voltage perturbation on each photovoltaic string respectively; the voltage detection circuit is further configured to obtain the terminal voltage of each photovoltaic string after voltage perturbation respectively; the controller is further configured to determine the photovoltaic string with a ground fault according to the terminal voltage of each photovoltaic string before voltage perturbation and the terminal voltage after voltage perturbation; for the photovoltaic string with a ground fault, the photovoltaic panel with a ground fault is obtained by using the terminal voltage and the output voltage of the photovoltaic string before voltage perturbation, or the photovoltaic panel with a ground fault is obtained by using the terminal voltage and the output voltage of the photovoltaic string after voltage perturbation.

[0046] Preferably, the controller is specifically configured to determine that the photovoltaic string is a photovoltaic string with a ground fault when the absolute value of the difference between the terminal voltage of the photovoltaic string before voltage perturbation and the terminal voltage after voltage perturbation exceeds a preset threshold.

[0047] Preferably, the embodiment of the present application does not limit the direction of voltage perturbation. For example, the controller controls the output voltage of the photovoltaic string subjected to voltage perturbation to change along the direction of increasing voltage or along the direction of decreasing voltage.

[0048] Preferably, the controller controls the output voltage of the photovoltaic string subjected to voltage perturbation to change from the open-circuit voltage before voltage perturbation to a first preset voltage after voltage perturbation, and the first preset voltage is less than the open-circuit voltage. That is, a preset voltage can be set and perturbed to this preset voltage.

[0049] Preferably, the controller obtains the photovoltaic panel with a ground fault by using the ratio of the terminal voltage and the output voltage of the photovoltaic string with a ground fault before voltage perturbation and the number N of photovoltaic panels connected in series.

[0050] It can be seen from the above technical solutions that the embodiment of the present application has the following advantages:

[0051] By disturbing the output voltage of the photovoltaic string, that is, controlling the output voltage of the photovoltaic string to change, and using the terminal voltage of the photovoltaic string before the change and the terminal voltage of the photovoltaic string after the change to determine whether the photovoltaic string has a ground fault. The terminal voltage of the photovoltaic string refers to the positive electrode voltage to ground or the negative electrode voltage to ground. When a ground fault occurs inside the photovoltaic string, there will be an obvious change in the terminal voltage of the photovoltaic string before and after the voltage disturbance. When there is an obvious change between the terminal voltage before the voltage disturbance and the terminal voltage after the voltage disturbance, it indicates that the photovoltaic string has a ground fault. Since all the photovoltaic panels in the photovoltaic string are connected in series, when a ground short circuit occurs at a certain place in the photovoltaic string, the potential at the position where the ground fault occurs is the reference ground. Therefore, the reference potential of the terminal voltage of the photovoltaic string is the ground potential at the ground fault location. The specific location of the ground fault can be determined by using the ratio of the terminal voltage to the output voltage of the whole string. This method is simple and easy to implement, does not require any additional hardware equipment, and does not require manual detection of each of the N photovoltaic panels in the photovoltaic string one by one, and can automatically determine the photovoltaic panel with a ground fault, and the detection efficiency is relatively high. Brief Description of the Drawings

[0052] Figure 1 Schematic diagram of a single photovoltaic string ground fault provided by an embodiment of the present application;

[0053] Figure 2 is Figure 1 Corresponding impedance model schematic diagram;

[0054] Figure 3 Schematic diagram of two series photovoltaic strings provided by an embodiment of the present application;

[0055] Figure 4 Schematic diagram of a photovoltaic power generation system corresponding to a single photovoltaic string provided by an embodiment of the present application;

[0056] Figure 5 Flowchart of a method for detecting a ground fault of a photovoltaic string provided by an embodiment of the present application;

[0057] Figure 6 Schematic diagram of a photovoltaic power generation system corresponding to multiple photovoltaic strings provided by an embodiment of the present application;

[0058] Figure 7 Flowchart of another method for detecting a ground fault of a photovoltaic string provided by an embodiment of the present application;

[0059] Figure 8 Flowchart of yet another method for detecting a ground fault of a photovoltaic string provided by an embodiment of the present application;

[0060] Figure 9 Schematic diagram of a general photovoltaic system provided by an embodiment of the present application;

[0061] Figure 10 Schematic diagram of another photovoltaic power generation system corresponding to a multi-channel photovoltaic string provided by an embodiment of the present application;

[0062] Figure 11 Flowchart of another method for detecting the ground fault of a photovoltaic string provided by an embodiment of the present application;

[0063] Figure 12 Schematic diagram of a photovoltaic device provided by an embodiment of the present application;

[0064] Figure 13 Schematic diagram of another photovoltaic device provided by an embodiment of the present application;

[0065] Figure 14 Schematic diagram of a photovoltaic power generation system provided by an embodiment of the present application. Detailed implementation manners

[0066] To enable those skilled in the art to better understand the technical solutions provided by the embodiments of the present application, the working conditions during ground fault are introduced below taking a single photovoltaic string as an example, and the working principle based on which the technical solutions provided by the embodiments of the present application are analyzed in combination with the ground fault.

[0067] First, the ground fault is introduced. When the standard requires that the DC insulation impedance is low (the leakage current requirement cannot be met), the inverter is not allowed to start up. The ground fault in the embodiment of the present application refers to the impedance corresponding to the DC insulation impedance being lower than the standard allowed for the inverter to start up. For example, the ground short - circuit fault is a special case of the ground fault.

[0068] Method Embodiment 1:

[0069] Refer to Figure 1 , which is a schematic diagram of the ground fault of a single photovoltaic string provided by an embodiment of the present application.

[0070] Figure 1 The photovoltaic string shown includes N photovoltaic panels connected in series, including photovoltaic panels 1, 2... x,... N - 1, N. The positive pole of the photovoltaic string is PV +, and the negative pole of the photovoltaic string is PV -. N is an integer greater than or equal to 2.

[0071] Figure 1 The corresponding impedance model can be referred to Figure 2 as shown.

[0072] When there is no ground fault in the photovoltaic string, the resistance value of the internal resistance R0 of the photovoltaic panel is much smaller than the ground resistance Rg of the photovoltaic panel.

[0073] When a ground fault occurs in a certain photovoltaic panel in a photovoltaic string (mostly a low ground insulation impedance fault), the ground impedance Rg of this photovoltaic panel becomes a small impedance close to 0. At this time, there is a proportional relationship between the ground voltage Upv+ of PV+ and the ground voltage Upv- of PV- and the voltage Upv between the positive and negative poles of the photovoltaic string. Among them, Upv+ - Upv- = Upv.

[0074] Because N photovoltaic panels are connected in series and a ground fault occurs in one photovoltaic panel, that is, the potential of the photovoltaic panel with the ground fault is approximately the reference zero potential. Therefore, the number of the photovoltaic panel at the fault location can be calculated through the following formula:

[0075] x = N * (1 - |Upv-| / Upv) or x = N * (Upv+ / Upv)

[0076] To enable those skilled in the art to more fully understand the technical solutions provided by the embodiments of the present application, the following takes a ground fault occurring at a location in one of two photovoltaic strings as an example for introduction.

[0077] See Figure 3 , this figure is a schematic diagram of two strings of photovoltaic strings provided by the embodiments of the present application.

[0078] Each photovoltaic string includes 6 photovoltaic panels connected in series. As Figure 3 shown, the first photovoltaic string 100 includes photovoltaic panels 1 - 6, and the second photovoltaic string 200 includes photovoltaic panels 1 - 6. The first photovoltaic string 100 and the second photovoltaic string 200 are in the same photovoltaic power generation system and have the same reference ground, but the positive and negative poles of the first photovoltaic string 100 and the second photovoltaic string 200 are independent of each other, that is, PV1+ and PV2+ are not connected together, and PV1- and PV2- are not connected together.

[0079] Among them, the fourth photovoltaic panel 4 of the first photovoltaic string 100 has a ground fault. The second photovoltaic string 200 has no ground fault.

[0080] At this time, the ground voltage of PV1- is obtained by voltage division of the battery internal resistance R0, that is, |Upv1-| / Upv1 = 2 / 6 = 1 / 3.

[0081] Since the ground voltage of the second photovoltaic string 200 is still determined by its ground impedance Rg. At this time, if Upv2 remains unchanged and the voltage value of Upv1 is changed, the ground voltage of the first photovoltaic string 100 will change accordingly, and its magnitude Upv1- = -1 / 3Upv1. For example, when Upv1 = 0, the ground voltage of the first photovoltaic string 100 also becomes 0V. If Upv1 remains unchanged and Upv2 is changed, the voltage of Upv1- still maintains a proportional relationship with Upv1.

[0082] Therefore, in order to accurately determine the photovoltaic panel with a ground fault in a certain photovoltaic string, the technical solution adopted in the embodiments of the present application is to perturb the voltage of the photovoltaic string in the photovoltaic power generation system, sample the voltage of the photovoltaic string to the ground (i.e., the terminal voltage), and compare the terminal voltages before and after the perturbation, so as to determine whether there is a ground fault in this photovoltaic string. When it is determined that there is a ground fault in this photovoltaic string, the specific fault location can be further obtained from the proportional relationship between the PV+ voltage to the ground or the PV- voltage to the ground and the PV voltage.

[0083] For ease of understanding, the judgment of a ground fault for a single photovoltaic string will be introduced first. The photovoltaic string is connected to the input end of a DC / DC conversion circuit, and the output end of the DC / DC conversion circuit is used to connect to an inverter circuit. Among them, the DC / DC conversion circuit and the inverter circuit can be integrated inside the inverter, and the controller of the inverter is used to implement the detection of the ground fault of the photovoltaic string. Of course, a separate controller can also be set up to implement the detection of the ground fault of the photovoltaic string. Among them, there may be no DC / DC circuit inside the inverter, and only a DC / AC conversion circuit. Among them, the inverter can be a single-phase inverter or a three-phase inverter, which is not specifically limited in the embodiments of the present application.

[0084] The following will be introduced by taking a three-phase inverter as an example, that is, the output end of the inverter outputs three-phase alternating current, namely L1, L2, and L3.

[0085] See Figure 4 , this figure is a schematic diagram of a photovoltaic power generation system corresponding to a single photovoltaic string provided by the embodiments of the present application.

[0086] This embodiment is introduced by taking a single photovoltaic string as an example. The photovoltaic string 100 is connected to the input end of the inverter 300. Specifically, PV+ is connected to the positive input end of the DC / DC conversion circuit 301, and PV- is connected to the negative input end of the DC / DC conversion circuit 301. The DC / DC conversion circuit 301 is connected to the input end of the inverter circuit 302, and the output end of the inverter circuit 302 can be connected to the AC grid.

[0087] The photovoltaic string includes N photovoltaic panels connected in series. Figure 4 Only N = 5 is taken as an example for introduction here, and taking the second of the five photovoltaic panels as an example of having a ground fault. The photovoltaic panels are numbered starting from the positive electrode PV+ of the photovoltaic string 100, that is, the photovoltaic panel connected to PV+ is the first photovoltaic panel, and the photovoltaic panel connected to PV- is the fifth photovoltaic panel. Generally, N is greater than or equal to 2, that is, a single photovoltaic string includes at least 2 photovoltaic panels connected in series. A ground fault may occur at any position in the photovoltaic string. Only one ground fault in a single photovoltaic string is taken as an example for introduction in the embodiments of the present application.

[0088] In the embodiments of the present application, the specific implementation manners of the DC / DC conversion circuit 301 and the inverter circuit 302 are not specifically limited. For example, the DC / DC conversion circuit 301 can be a boost circuit, a buck circuit, or a buck-boost circuit, or there can be no DC / DC circuit, and the photovoltaic module is directly connected to the DC / AC circuit. Similarly, the specific topological form of the inverter circuit 302 is not specifically limited in this embodiment.

[0089] The method for detecting the ground fault of the photovoltaic string provided in this embodiment can be applied to the controller of the inverter 300, or can be applied to other controllers, such as the controller of a photovoltaic power station.

[0090] See Figure 5 , which is a flowchart of a method for detecting the ground fault of a photovoltaic string provided in the embodiments of the present application.

[0091] The method includes:

[0092] S501: Obtain the terminal voltage of each photovoltaic string before the voltage perturbation. The terminal voltage is the voltage of the positive pole of the photovoltaic string to the ground or the voltage of the negative pole to the ground;

[0093] For Figure 4 the photovoltaic string shown, obtain the terminal voltage before the voltage perturbation, that is, the voltage of PV+ to the ground or the voltage of PV- to the ground before the perturbation.

[0094] In specific implementation, the simplest control manner before the voltage perturbation is to not perform any control on the photovoltaic string. When not controlling the output voltage of the photovoltaic string, the output voltage of the photovoltaic string is generally its open-circuit voltage..

[0095] S502: Perform voltage perturbation on each photovoltaic string respectively, and obtain the terminal voltage of each photovoltaic string after the voltage perturbation respectively;

[0096] Figure 4 shown includes only one photovoltaic string, that is, controlling the input voltage of the DC / DC conversion circuit 301 can realize the control of the output voltage of the photovoltaic string 100, which can be specifically realized by the controller of the inverter 300 or by other control devices, and is not specifically limited in this embodiment.

[0097] Specific voltage perturbation methods include many kinds. For example, control the output voltage of the photovoltaic string 100 to change from large to small, or control the output voltage of the photovoltaic string 100 to change from small to large, or control from the open-circuit voltage to the short-circuit voltage. Generally, it can be scanned and controlled along the current-voltage IV curve of the photovoltaic module to make the photovoltaic string 100 work at a certain point on the curve.

[0098] For example, when controlling the output voltage of the photovoltaic string subjected to voltage perturbation to change along the direction of decreasing voltage, specifically including:

[0099] Control the output voltage of the photovoltaic string disturbed by voltage to change from the open-circuit voltage before the voltage disturbance to a first preset voltage after the voltage disturbance, where the first preset voltage is less than the open-circuit voltage.

[0100] The first preset voltage can be the voltage corresponding to any operating point less than the open-circuit voltage.

[0101] S503: Determine the photovoltaic string with a ground fault according to the terminal voltage of each photovoltaic string before the voltage disturbance and the terminal voltage after the voltage disturbance;

[0102] When a certain photovoltaic panel in the photovoltaic string 100 has a ground fault, the positive pole PV+ of the photovoltaic string 100 has a significantly different voltage to the ground Upv+ from the voltage to the ground before the disturbance. Similarly, the negative pole PV- of the photovoltaic string 100 also has a significantly different voltage to the ground Upv- before and after the disturbance.

[0103] For whether the photovoltaic string 100 has a ground fault, it can be judged whether a short-circuit fault occurs according to the difference between Upv+ before and after the voltage disturbance, or it can also be judged whether a short-circuit fault occurs through the difference between Upv- before and after the voltage disturbance.

[0104] For example, when the absolute value of the difference between the terminal voltage of the photovoltaic string before the voltage disturbance and the terminal voltage after the voltage disturbance exceeds a preset threshold, it is determined that this path of the photovoltaic string is a photovoltaic string with a ground fault.

[0105] The preset threshold can be set according to the actual application scenario, and the specific value is not specifically limited in this embodiment.

[0106] The following will give specific examples for illustration, taking three examples respectively;

[0107] The first: Control the output voltage of the photovoltaic string to change from large to small.

[0108] Perform voltage disturbance between the open-circuit voltage and the short-circuit voltage, control the output voltage of the photovoltaic string to jump to the short-circuit voltage point by 300V, and then judge the jump of the terminal voltage. For example, first control the output voltage of the photovoltaic string to be 600V, sample the terminal voltage as Upv1, perform voltage disturbance, control the output voltage of the photovoltaic string to be 300V, that is, the voltage is reduced by 300V, sample the terminal voltage as Upv2, obtain the difference between Upv2 and Upv1. Since the output voltage of the photovoltaic string changes from large to small, therefore, Upv2 is less than Upv1. Therefore, Upv2 - Upv1 is a negative value. Therefore, when the absolute value of the difference between Upv2 and Upv1 is greater than the preset threshold, it is determined that this path of the photovoltaic string has a ground fault.

[0109] It should be noted that Upv1 and Upv2 can be the voltage of the positive pole to the ground or the voltage of the negative pole to the ground.

[0110] The second method: control the output voltage of the photovoltaic string to change from small to large.

[0111] Control the output voltage of the photovoltaic string to jump to the open-circuit voltage. For example, first control the output voltage of the photovoltaic string to be 600V, sample the terminal voltage Upv1, perform voltage perturbation, control the output voltage of the photovoltaic string to be 900V, that is, the voltage increases by 300V, sample the terminal voltage as Upv2, and obtain the difference between Upv2 and Upv1. Since the output voltage of the photovoltaic string changes from small to large, therefore, Upv2 is greater than Upv1. Therefore, Upv2 - Upv1 is a positive value. When the difference between Upv2 and Upv1 is greater than the preset threshold, it is determined that there is a ground fault in this photovoltaic string.

[0112] The third method: control the output voltage of the photovoltaic string to change from the open-circuit voltage to the short-circuit voltage.

[0113] Voltage perturbation controls the output voltage of the photovoltaic string to change from the open-circuit voltage to the short-circuit voltage, that is, the short-circuit voltage after voltage perturbation is 0, that is, the output voltage changes from large to 0, and the sampled terminal voltage is also close to 0, then it is confirmed that there is a ground fault in this photovoltaic string.

[0114] S504: For the photovoltaic string with a ground fault, obtain the photovoltaic panel with the ground fault by using the terminal voltage and output voltage of the photovoltaic string before voltage perturbation, or obtain the photovoltaic panel with the ground fault by using the terminal voltage and output voltage of the photovoltaic string after voltage perturbation.

[0115] For a photovoltaic string, when there is only one ground fault, there is a proportional relationship between the terminal voltage of the photovoltaic string and the output voltage of the photovoltaic string. Therefore, the position of the photovoltaic panel with the ground fault in the photovoltaic string can be obtained by using the proportional relationship between the terminal voltage and the output voltage of the photovoltaic string.

[0116] Among them, the ratio of the terminal voltage to the output voltage of the photovoltaic string can use the ratio of the terminal voltage and the output voltage of the photovoltaic string before voltage perturbation, or can also use the ratio of the terminal voltage and the output voltage of the photovoltaic string after perturbation.

[0117] Take Figure 4For example, since five photovoltaic panels are connected in series between PV+ and PV-. When the second photovoltaic panel has a ground fault, whether before or after the voltage disturbance, when the ratio of the absolute value of Upv+ to Upv is 2 / 5, or the ratio of the absolute value of Upv- to Upv is 3 / 5, it indicates that the second photovoltaic panel has a ground fault. It should be noted that: here, the second photovoltaic panel refers to the second photovoltaic panel counted from the PV+ end. In addition, when the number of photovoltaic panels included in each photovoltaic string of a photovoltaic array is unknown, N and x here represent percentages, that is, N represents 100%, and the percentage represented by x is the percentage of the fault occurring at the distance from PV+ in the photovoltaic string. For example, if x = 20%, it indicates that a ground fault occurs at about 20%. In order to locate the ground fault more accurately, the voltage sampling near the short-circuit point can be avoided as much as possible.

[0118] For example, the photovoltaic panel with a ground fault is obtained by using the ratio of Upv+ before the voltage disturbance to Upv before the voltage disturbance.

[0119] It should be noted that the above is only an introduction to a specific implementation method. As long as there is a certain proportional relationship between the terminal voltage and the output voltage of the whole string, the specific location of the ground fault can be determined. The above ratio is not necessarily exactly 2 / 5 because of differences in sampling or the actual working environment, resulting in a slight deviation. However, as long as it is within the preset deviation range, the corresponding photovoltaic panel with a ground fault can be determined.

[0120] It should be noted that a ground fault of a certain photovoltaic panel not only means that the photovoltaic panel itself is short-circuited to the ground, but also can be a ground short-circuit caused by insulation damage of the series cables before and after it.

[0121] The method provided in this embodiment determines whether a photovoltaic string has a ground fault by disturbing the output voltage of the photovoltaic string, that is, controlling the output voltage of the photovoltaic string to change, and using the terminal voltage of the photovoltaic string before the change and the terminal voltage of the photovoltaic string after the change. When there is a significant change between the terminal voltage before the voltage disturbance and the terminal voltage after the voltage disturbance, it indicates that the photovoltaic string has a ground fault. All the photovoltaic panels in the photovoltaic string are connected in series. When a ground fault occurs at a certain position in the photovoltaic string, the potential at the ground fault is approximately equal to the reference ground. At this time, the voltage divided by all the photovoltaic panels from one end of the photovoltaic string to the fault can be considered as the terminal voltage. Therefore, the specific location of the ground fault can be determined by using the ratio of the terminal voltage to the output voltage of the whole string. This method is simple and easy to implement, does not require any additional hardware equipment, and does not require manual detection of the N photovoltaic panels of the photovoltaic string one by one, and can automatically determine the photovoltaic panel with a ground fault, with high efficiency.

[0122] Method Embodiment Two:

[0123] The above embodiments are introduced by taking the inverter corresponding to one photovoltaic string as an example. The following introduces an inverter corresponding to multiple photovoltaic strings. Each photovoltaic string corresponds to its own DC / DC conversion circuit, that is, the photovoltaic string and the DC / DC conversion circuit are in a one-to-one correspondence, and each DC / DC conversion circuit is independent of each other, and the positive input terminal or the negative input terminal is not short-circuited together. Since each photovoltaic string is independent and connected to its corresponding DC / DC conversion circuit, the input control and sampling of each photovoltaic string do not affect each other, and each photovoltaic string can perform voltage disturbance independently, either simultaneously or in a time-sharing manner, which is not specifically limited in the embodiments of the present application.

[0124] See also Figure 6 , which is a schematic diagram of a photovoltaic power generation system corresponding to multiple photovoltaic strings provided in an embodiment of the present application.

[0125] In this embodiment, three photovoltaic strings are used as examples, namely the first photovoltaic string 100a, the second photovoltaic string 100b and the third photovoltaic string 100c, wherein the first photovoltaic string 100a and the second photovoltaic string 100b both have ground faults. And the three photovoltaic strings each include 5 photovoltaic panels connected in series, from PV+ to PV-, which are the 1st to the 5th photovoltaic panels.

[0126] The first photovoltaic string 100a is connected to the input end of the first DC / DC conversion circuit 301a;

[0127] The second photovoltaic string 100b is connected to the input end of the second DC / DC conversion circuit 301b;

[0128] The third photovoltaic string 100c is connected to the input end of the third DC / DC conversion circuit 301c.

[0129] The output ends of the first DC / DC conversion circuit 301a, the second DC / DC conversion circuit 301b and the third DC / DC conversion circuit 301c are all connected to the input end of the inverter circuit 302. The output ends of the first DC / DC conversion circuit 301a, the second DC / DC conversion circuit 301b and the third DC / DC conversion circuit 301c can be connected in parallel to the same bus.

[0130] The first DC / DC conversion circuit 301 a , the second DC / DC conversion circuit 301 b , the third DC / DC conversion circuit 301 c and the inverter circuit 302 may be integrated inside the inverter.

[0131] The fourth photovoltaic cell panel in the first photovoltaic string 100a has a ground fault, and the first photovoltaic cell panel in the second photovoltaic string 100b has a ground fault.

[0132] The specific implementation of determining the first photovoltaic string 100a and the second photovoltaic string 100b can utilize the method introduced in the first method embodiment, which will not be elaborated here. For example, it is possible to detect Upv+ before and after the voltage perturbation to determine whether a ground fault has occurred, or it is also possible to detect Upv- before and after the voltage perturbation to determine whether a ground fault has occurred.

[0133] Obtaining the photovoltaic panels with ground faults by using the terminal voltage and output voltage of the photovoltaic string before the voltage perturbation specifically includes:

[0134] Obtaining the photovoltaic panels with ground faults by using the ratio of the terminal voltage and output voltage of the photovoltaic string with ground faults before the voltage perturbation, and the number N of photovoltaic panels connected in series.

[0135] That is, when it is determined that the first photovoltaic string 100a and the second photovoltaic string 100b have ground faults, the position of the ground fault is determined by using the ratio of the terminal voltage before the perturbation to the output voltage before the perturbation of the first photovoltaic string 100a and N = 5. Similarly, the position of the ground fault is determined by using the ratio of the terminal voltage before the perturbation to the output voltage before the voltage perturbation of the second photovoltaic string 100b and N = 5.

[0136] See Figure 7 , which is a flowchart of another method for detecting ground faults of photovoltaic strings provided by the embodiment of the present application.

[0137] S701 - S703 are respectively the same as S501 - S503, which will not be elaborated here.

[0138] S704: For the photovoltaic string with a ground fault, obtain the photovoltaic panels with ground faults by using the ratio of the terminal voltage of the photovoltaic string with ground faults before the voltage perturbation and the output voltage before the voltage perturbation, and the number N of photovoltaic panels connected in series.

[0139] Specifically includes:

[0140] When the terminal voltage is the voltage of the positive pole to the ground, the photovoltaic panels with ground faults are obtained through the following formula:

[0141] x = N * (Upv+ / Upv);

[0142] When the terminal voltage is the voltage of the negative pole to the ground, the photovoltaic panels with ground faults are obtained through the following formula:

[0143] x = N * (1 - |Upv-| / Upv);

[0144] Among them, Upv+ represents the voltage of the positive electrode to the ground before voltage disturbance, Upv- represents the voltage of the negative electrode to the ground before voltage disturbance, and Upv represents the output voltage before voltage disturbance; N represents the number of series-connected photovoltaic panels included in the photovoltaic string with a ground fault, and x represents the x-th photovoltaic panel starting from the positive electrode of the photovoltaic string with the ground fault.

[0145] The principle on which the above formula is based is that N photovoltaic panels are connected in series. When the x-th photovoltaic panel is short-circuited to the ground, Upv+ / Upv of the photovoltaic string is x / N. Since both Upv+ and Upv can be obtained through the voltage detection circuit, and N is a known number, x can be obtained, and x is the photovoltaic panel with a ground fault. Similarly, the photovoltaic panel with a ground fault can also be determined through the voltage of the negative electrode of the photovoltaic string to the ground and the output voltage before disturbance, that is, when the x-th photovoltaic panel is short-circuited to the ground, (1 - |Upv-| / Upv) of the photovoltaic string is x / N. Since both Upv- and Upv can be obtained through the voltage detection circuit, and N is a known number, x can be obtained.

[0146] For example, the open-circuit voltage U1 when the first photovoltaic string 100a is open-circuited and the open-circuit voltage U2 when the second photovoltaic string 100b is open-circuited are collected before voltage disturbance respectively. The voltage U1- of PV- to the ground when the first photovoltaic string 100a is open-circuited and the voltage U2- of PV- to the ground when the second photovoltaic string 100b is open-circuited are collected before voltage disturbance respectively.

[0147] Then, the photovoltaic panel x1 with a ground fault in the first photovoltaic string 100a = (1 - |U1-| / U1) * N;

[0148] The photovoltaic panel x2 with a ground fault in the first photovoltaic string 100a = (1 - |U2-| / U2) * N.

[0149] Figure 7 What is introduced above is to determine the position of the ground fault by using the ratio of the terminal voltage before disturbance and the output voltage before disturbance. Next, the method of determining the position of the ground fault by using the ratio of the terminal voltage after disturbance and the output voltage after disturbance is introduced.

[0150] See Figure 8 , which is a flowchart of another method for detecting the ground fault of a photovoltaic string provided by an embodiment of the present application.

[0151] S801 - S703 are the same as S501 - S503 respectively, and will not be elaborated here.

[0152] S804: For a photovoltaic string with a ground fault, obtain the photovoltaic panel with the ground fault by using the ratio of the terminal voltage and the output voltage after voltage perturbation of the photovoltaic string with the ground fault, and the number N of series-connected photovoltaic panels.

[0153] Specifically, it includes:

[0154] When the terminal voltage is the voltage of the positive pole to the ground, obtain the photovoltaic panel with the ground fault through the following formula:

[0155] x = N * (Uv+ / Uv);

[0156] When the terminal voltage is the voltage of the negative pole to the ground, obtain the photovoltaic panel with the ground fault through the following formula:

[0157] x = N * (1 - |Uv-| / Uv);

[0158] Among them, Uv+ represents the voltage of the positive pole to the ground after voltage perturbation, Uv- represents the voltage of the negative pole to the ground after voltage perturbation, Uv represents the output voltage after voltage perturbation; N represents the number of series-connected photovoltaic panels included in the photovoltaic string with the ground fault, and x represents the x-th photovoltaic panel of the photovoltaic string with the ground fault starting from the positive pole.

[0159] The principle based on the above formula is that N photovoltaic panels are connected in series. When the x-th photovoltaic panel is short-circuited to the ground, the Uv+ / Uv of this photovoltaic string is x / N. Since both Uv+ and Uv can be obtained through the voltage detection circuit, and N is a known number, therefore, x can be obtained, and x is the photovoltaic panel with the ground fault. Similarly, the photovoltaic panel with the ground fault can also be obtained through the voltage of the negative pole of the photovoltaic string to the ground and the output voltage before perturbation, that is, when the x-th photovoltaic panel is short-circuited to the ground, the (1 - |Uv-| / Uv) of this photovoltaic string is x / N. Since both Uv- and Uv can be obtained through the voltage detection circuit, and N is a known number, therefore, x can be obtained.

[0160] The following is introduced in combination with a specific example. For example, before voltage perturbation, the photovoltaic string does not perform any control and works at the operating point corresponding to the open-circuit voltage. When voltage perturbation occurs, control the output voltage of the photovoltaic string to decrease from the open-circuit voltage.

[0161] Figure 6 Only three photovoltaic strings corresponding to three DC / DC conversion circuits are taken as an example for introduction, and each string includes 5 photovoltaic panels. The technical solution provided in this embodiment does not limit the specific number of paths of the photovoltaic string and the number of photovoltaic panels. As Figure 9 shown, it is a schematic diagram of a general photovoltaic system provided by an embodiment of the present application.

[0162] The photovoltaic system includes a total of m photovoltaic strings, where m is an integer greater than or equal to 2, and each photovoltaic string corresponds to a DC / DC or DC / AC conversion circuit. Each photovoltaic string includes n series-connected photovoltaic panels, where n is an integer greater than or equal to 2. And the number of photovoltaic strings with a ground fault is not limited. As long as there is only one ground fault in each photovoltaic string, the method provided in this embodiment can accurately locate the fault location.

[0163] The method provided in this embodiment can be applied to the detection of ground faults when the inverter corresponds to multiple photovoltaic strings. The multiple photovoltaic strings are neither common positive nor common negative, and are independently connected to the corresponding DC / DC or DC / AC conversion circuits. When one or more strings have a ground fault, it can be accurately determined whether the photovoltaic string has a ground fault through the change in the terminal voltage before and after voltage perturbation. Moreover, when there is only one ground fault in one photovoltaic string, the photovoltaic panel with the ground fault can be obtained through the proportional relationship between the terminal voltage and the output voltage. This method is simple and easy to implement, does not require additional hardware equipment, and does not require manual detection of the N photovoltaic panels of the photovoltaic string one by one, and can automatically determine the photovoltaic panel with the ground fault, with high efficiency.

[0164] Method Embodiment Three:

[0165] This embodiment introduces multiple photovoltaic strings, and each photovoltaic string corresponds to its own DC / DC or DC / AC conversion circuit, that is, one photovoltaic string corresponds to one DC / DC conversion circuit, but the positive input terminals or negative input terminals of each DC / DC conversion circuit are shorted together. For example, the positive input terminals of all conversion circuits are shorted together, or the negative input terminals of all conversion circuits are shorted together.

[0166] See Figure 10 , which is a schematic diagram of another photovoltaic power generation system corresponding to multiple photovoltaic strings provided in the embodiment of the present application.

[0167] In this embodiment, the negative input terminals of all DC / DC conversion circuits are shorted together, that is, the PV- of each photovoltaic string is shorted together, and the PV+ of each photovoltaic string is independently connected to the positive input terminal of its corresponding DC / DC conversion circuit.

[0168] In this embodiment, three photovoltaic strings are taken as an example for illustration, namely the first photovoltaic string 100a, the second photovoltaic string 100b, and the third photovoltaic string 100c, where both the first photovoltaic string 100a and the second photovoltaic string 100b have a ground fault. And each of the three photovoltaic strings includes 5 photovoltaic panels connected in series, and from PV+ to PV- are the first to the fifth photovoltaic panels in sequence.

[0169] The first photovoltaic string 100a is connected to the input end of the first DC / DC conversion circuit 301a;

[0170] The second photovoltaic string 100b is connected to the input end of the second DC / DC conversion circuit 301b;

[0171] The third photovoltaic string 100c is connected to the input end of the third DC / DC conversion circuit 301c.

[0172] The negative input ends of the first DC / DC conversion circuit 301a, the second DC / DC conversion circuit 301b, and the third DC / DC conversion circuit 301c are all connected together, that is, PV- are all short-circuited together. Therefore, the Upv- of the three photovoltaic strings are equal.

[0173] The negative input ends of the first DC / DC conversion circuit 301a, the second DC / DC conversion circuit 301b, and the third DC / DC conversion circuit 301c are all connected together. The output ends of the first DC / DC conversion circuit 301a, the second DC / DC conversion circuit 301b, and the third DC / DC conversion circuit 301c can be connected in parallel.

[0174] The first DC / DC conversion circuit 301a, the second DC / DC conversion circuit 301b, the third DC / DC conversion circuit 301c, and the inverter circuit 302 can be integrated inside the inverter.

[0175] Since the PV- of all photovoltaic strings are short-circuited together, voltage disturbances cannot be performed on two or more photovoltaic strings simultaneously. Voltage disturbances need to be performed on each photovoltaic string separately in sequence.

[0176] See Figure 11 , which is a flowchart of another method for detecting the ground fault of a photovoltaic string provided by an embodiment of the present application.

[0177] S1101: Collect the ground voltage Upv- of PV- that are short-circuited together before the voltage disturbance;

[0178] S1102: Perform a voltage disturbance on the first photovoltaic string;

[0179] For the specific voltage disturbance method, reference can be made to the introduction in the above embodiments, and no control is required for the other photovoltaic strings. For example, first perform a voltage disturbance on the first photovoltaic string 100a.

[0180] S1103: Collect the ground voltage Upv- of PV- after the voltage disturbance.

[0181] Voltage disturbances can be performed on each photovoltaic string one by one. In this embodiment, it is not limited to starting from the first photovoltaic string, that is, the sequence of the photovoltaic strings for voltage disturbance is not limited.

[0182] Since the PV- of each photovoltaic string is shorted together, only one voltage sampling circuit for PV- to ground needs to be set, saving hardware costs.

[0183] Since the PV- of all photovoltaic strings is shorted together, Upv- is the voltage of the negative pole of the entire photovoltaic array to ground.

[0184] S1104: When the absolute value of the difference between Upv- before voltage disturbance and Upv- after voltage disturbance is greater than a preset threshold, it is determined that the first photovoltaic string has a ground fault.

[0185] S1105: Perform S1102 - S1104 on other photovoltaic strings to determine whether a ground fault occurs.

[0186] Since the PV- is shorted together, voltage disturbances need to be performed on each photovoltaic string one by one to determine whether a ground fault occurs.

[0187] For example, when performing a voltage disturbance on the second photovoltaic string, no control is performed on other photovoltaic strings, and only the output voltage of the second photovoltaic string is controlled to change.

[0188] S1106: When the voltage disturbances on all photovoltaic strings are completed, if only one photovoltaic string has a ground fault, the photovoltaic panels with ground faults are obtained by using the ratio of Upv- before voltage disturbance to the output voltage of this photovoltaic string before voltage disturbance.

[0189] For example, when the voltage disturbances on all photovoltaic strings are completed and it is determined that only the first photovoltaic string has a ground fault, the photovoltaic panels with ground faults in the first photovoltaic string are obtained by using x = (1 - |Upv-| / U1) * N, where U1 is the output voltage of the first photovoltaic string.

[0190] In the method provided in this embodiment, since the positive or negative poles of each photovoltaic string are connected together, only when only one string has a ground fault can the position of the photovoltaic panel with the ground fault be accurately obtained. When multiple strings have ground faults, only the photovoltaic strings with ground faults can be accurately determined, and the specific position of the photovoltaic panel with the ground fault cannot be accurately obtained.

[0191] In this embodiment, only the case where the PV- of each photovoltaic string is shorted together is taken as an example for introduction. Similarly, the PV- of each photovoltaic string can also be independent of each other, and the PV+ of each photovoltaic string is shorted together.

[0192] For the method provided by the embodiments of the present application, when one end of multiple photovoltaic strings is short-circuited together, that is, the positive poles of multiple photovoltaic strings in the photovoltaic array are short-circuited together, or the negative poles are short-circuited together, voltage disturbances are sequentially applied to each photovoltaic string, and it can be accurately determined whether there is a ground fault in each photovoltaic string. When there is only one ground fault, using the ratio relationship between the terminal voltage and the output voltage, the position of the faulty photovoltaic panel can be accurately located.

[0193] Embodiment 1 of Photovoltaic Equipment

[0194] Based on the method for detecting the ground fault of a photovoltaic string provided in the above embodiments, the embodiments of the present application also provide a photovoltaic device, and its working principle will be introduced in detail below with reference to the drawings.

[0195] See Figure 12 , which is a schematic diagram of a photovoltaic device for detecting ground faults provided by the embodiments of the present application.

[0196] A photovoltaic device for detecting ground faults provided by the embodiments of the present application includes: a power conversion circuit, a controller 400, and a voltage detection circuit 500;

[0197] The power conversion circuits correspond to the photovoltaic strings one by one, and each photovoltaic string is connected to the corresponding power conversion circuit; that is, one power conversion circuit corresponds to one photovoltaic string. The power conversion circuit can be a DC / DC conversion circuit or a DC / AC conversion circuit. Since the photovoltaic strings and the power conversion circuits correspond to each other one by one, individual control of the photovoltaic strings can be achieved.

[0198] Figure 12 Two photovoltaic strings are taken as examples for introduction in

[0199] The first photovoltaic string 100a is connected to the corresponding first power conversion circuit 300a, and the second photovoltaic string 100b is connected to the corresponding second power conversion circuit 300b.

[0200] The voltage detection circuit 500 is used to obtain the terminal voltage of each photovoltaic string before voltage disturbance, and the terminal voltage is the voltage of the positive pole of the photovoltaic string to the ground or the voltage of the negative pole to the ground;

[0201] It should be noted that one voltage detection circuit can be set for each photovoltaic string, or multiple photovoltaic strings can share one voltage detection circuit, which is not specifically limited in this embodiment.

[0202] The controller 400 is used to apply voltage disturbances to each of the photovoltaic strings respectively;

[0203] When the positive input terminals and negative input terminals of the first power conversion circuit 300a and the second power conversion circuit 300b are independent and not connected together, the controller 400 can simultaneously perform voltage perturbation on the first photovoltaic string 100a and the second photovoltaic string 100b. When the positive input terminal or the negative input terminal of the first power conversion circuit 300a and the power conversion circuit 300b are connected together, the controller 400 needs to sequentially perform voltage perturbation on the first photovoltaic string 100a and the second photovoltaic string 100b.

[0204] Specific voltage perturbation methods include many types. For example, controlling the output voltage of the photovoltaic string to change from large to small, or controlling the output voltage of the photovoltaic string to change from small to large, or controlling from the open-circuit voltage to the short-circuit voltage. Generally, it is possible to perform scanning control along the current-voltage (IV) curve of the photovoltaic module, so that the photovoltaic string 100 operates at a certain point on the IV curve.

[0205] For example, when controlling the output voltage of the photovoltaic string being voltage perturbed to change along the direction of voltage decrease, specifically including:

[0206] Controlling the output voltage of the photovoltaic string being voltage perturbed to change from the open-circuit voltage before voltage perturbation to a first preset voltage after voltage perturbation, where the first preset voltage is less than the open-circuit voltage.

[0207] The first preset voltage can be the voltage corresponding to any operating point less than the open-circuit voltage.

[0208] The voltage detection circuit 500 is further configured to respectively obtain the terminal voltages of each photovoltaic string after voltage perturbation;

[0209] The controller 400 is further configured to determine the photovoltaic string with a ground fault according to the terminal voltage of each photovoltaic string before voltage perturbation and the terminal voltage after voltage perturbation; for the photovoltaic string with a ground fault, obtain the photovoltaic panel with a ground fault by using the terminal voltage and the output voltage of the photovoltaic string before voltage perturbation, or obtain the photovoltaic panel with a ground fault by using the terminal voltage and the output voltage of the photovoltaic string after voltage perturbation.

[0210] It should be noted that when positioning the ground fault location, when using the voltage parameters before voltage perturbation, the voltage detection circuit 500 can also obtain the output voltage of the photovoltaic string before voltage perturbation. When using the voltage parameters after voltage perturbation, the voltage detection circuit 500 can also obtain the output voltage of the photovoltaic string after voltage perturbation.

[0211] In this embodiment, the position of the controller 400 is not specifically limited. It can be the controller corresponding to the power conversion circuit, that is, each power conversion circuit corresponds to a controller. It can also be that the power conversion circuits share a controller, and the power conversion circuits can communicate with the controller with each other.

[0212] When a ground fault occurs in a certain photovoltaic panel in a photovoltaic string, the positive electrode PV+ of the photovoltaic string has a significantly different ground voltage Upv+ from that before the disturbance. Similarly, the negative electrode PV- of the photovoltaic string also has a significantly different ground voltage Upv- before and after the disturbance.

[0213] For whether a ground fault occurs in the photovoltaic string, it can be determined whether a short-circuit fault occurs according to the difference in Upv+ before and after the voltage disturbance, or it can also be determined whether a short-circuit fault occurs through the difference in Upv- before and after the voltage disturbance.

[0214] For example, when the absolute value of the difference between the terminal voltage of the photovoltaic string before the voltage disturbance and the terminal voltage after the voltage disturbance exceeds a preset threshold, it is determined that the photovoltaic string is a photovoltaic string with a ground fault.

[0215] For a photovoltaic string, when there is only one ground fault, there is a proportional relationship between the terminal voltage of the photovoltaic string and the output voltage of the photovoltaic string. Therefore, the position of the photovoltaic panel with a ground fault in the photovoltaic string can be obtained by using the proportional relationship between the terminal voltage and the output voltage of the photovoltaic string.

[0216] Among them, the ratio of the terminal voltage to the output voltage of the photovoltaic string can use the ratio of the terminal voltage before the voltage disturbance and the output voltage of the photovoltaic string, or it can also use the ratio of the terminal voltage after the disturbance and the output voltage of the photovoltaic string.

[0217] Continue to refer to Figure 4 , since 5 photovoltaic panels are connected in series between PV+ and PV-. When the second photovoltaic panel has a ground fault, whether it is before the voltage disturbance or after the voltage disturbance, when the ratio of the absolute value of Upv+ to Upv is 2 / 5, or the ratio of the absolute value of Upv- to Upv is 3 / 5, it indicates that the second photovoltaic panel has a ground fault. It should be noted that: the second photovoltaic panel here refers to the second photovoltaic panel counted from the PV+ end. In addition, when the number of photovoltaic panels included in each photovoltaic string in a certain photovoltaic array is unknown, N and x here represent percentages, that is, N represents 100%, and the percentage represented by x is the percentage of the position from PV+ where the fault occurs in the photovoltaic string. For example, if x = 20%, it indicates that a ground fault occurs at about 20%.

[0218] The photovoltaic device provided in this embodiment can be Figure 4 in the form shown, or can be Figure 6 in the form shown, or can also be in the form as Figure 10 shown, Figure 10 The negative input terminals of all DC / DC conversion circuits are connected together. In addition, it can also be that the positive input terminals of all DC / DC conversion circuits are connected together.

[0219] In addition, when the power conversion circuit can be a DC / AC conversion circuit, refer to Figure 13 As shown, this figure is a schematic diagram of another photovoltaic device for detecting ground faults provided by an embodiment of the present application.

[0220] Figure 13 The photovoltaic device shown does not include a DC / DC conversion circuit and only includes a DC / AC conversion circuit. That is, when the photovoltaic device is an inverter, the inverter is a single-stage inverter. Figure 6 and Figure 10 The inverter shown is a two-stage inverter, which includes both a DC / DC conversion circuit and a DC / AC conversion circuit.

[0221] The first photovoltaic string 100a is connected to the corresponding first DC / AC conversion circuit 300a, and the second photovoltaic string 100b is connected to the corresponding second DC / AC conversion circuit 300b.

[0222] The voltage detection circuit 500 is used to detect the terminal voltage and output voltage of the first photovoltaic string 100a and the second photovoltaic string 100b before voltage perturbation, and is also used to detect the terminal voltage and output voltage of the first photovoltaic string 100a and the second photovoltaic string 100b after voltage perturbation. The voltage detection circuit 500 sends both the detected terminal voltage and output voltage to the controller 400.

[0223] The controller 400 controls the output voltage of the first photovoltaic string 100a by controlling the input voltage of the first DC / AC conversion circuit 300a, and controls the output voltage of the second photovoltaic string 100b by controlling the input voltage of the second DC / AC conversion circuit 300b, so as to realize the voltage perturbation of the first photovoltaic string 100a and the second photovoltaic string 100b.

[0224] For example, the photovoltaic panel with a ground fault is obtained by using the ratio of Upv+ before voltage perturbation to Upv before voltage perturbation.

[0225] It should be noted that the above is only an introduction to a specific implementation method. As long as there is a certain proportional relationship between the terminal voltage and the output voltage of the whole string, the specific ground fault location can be determined. The above ratio is not necessarily exactly 2 / 5 because of differences in sampling or the actual working environment, resulting in a slight deviation. However, as long as it is within the preset deviation range, the corresponding photovoltaic panel with a ground fault can be determined.

[0226] It should be noted that a ground fault of a certain photovoltaic panel not only means that the photovoltaic panel itself is short-circuited to the ground, but also can be a ground short circuit caused by insulation damage of the series cables before and after it.

[0227] The photovoltaic device provided in this embodiment determines whether a ground fault occurs in a photovoltaic string by disturbing the output voltage of the photovoltaic string, that is, controlling the output voltage of the photovoltaic string to change, and using the terminal voltage of the photovoltaic string before voltage disturbance and the terminal voltage of the photovoltaic string after voltage disturbance. When there is an obvious change between the terminal voltage before voltage disturbance and the terminal voltage after voltage disturbance, it indicates that a ground fault has occurred in the photovoltaic string. All the photovoltaic panels in the photovoltaic string are connected in series. When a ground fault occurs at a certain position in the photovoltaic string, the potential at the ground fault is approximately equal to the reference ground. At this time, the voltage divided by all the photovoltaic panels from one end of the photovoltaic string to the fault can be regarded as the terminal voltage. Therefore, the specific position of the ground fault can be determined by using the ratio of the terminal voltage to the output voltage of the whole string. This method is simple and easy to implement, does not require additional hardware equipment, and does not require manual detection of the N photovoltaic panels in the photovoltaic string one by one, and can automatically determine the photovoltaic panel with a ground fault, with high efficiency.

[0228] The photovoltaic panel with a located fault can be obtained by the ratio of the terminal voltage before voltage disturbance to the output voltage of the photovoltaic string, or by the ratio of the terminal voltage after voltage disturbance to the output voltage of the photovoltaic string. The following is a specific introduction respectively.

[0229] First, use the terminal voltage before voltage disturbance and the output voltage of the whole string before voltage disturbance.

[0230] The controller is specifically configured to obtain the photovoltaic panel with a ground fault through the following formula when the terminal voltage is the positive pole-to-ground voltage:

[0231] x = N*(Upv+ / Upv);

[0232] When the terminal voltage is the negative pole-to-ground voltage, obtain the photovoltaic panel with a ground fault through the following formula:

[0233] x = N*(1 - |Upv-| / Upv);

[0234] Among them, Upv+ represents the positive pole-to-ground voltage before voltage disturbance, Upv- represents the negative pole-to-ground voltage before voltage disturbance, Upv represents the output voltage before voltage disturbance; N represents the number of series-connected photovoltaic panels included in the photovoltaic string with a ground fault, and x represents the xth photovoltaic panel from the positive pole of the photovoltaic string with a ground fault.

[0235] The principle on which the above formula is based is that N photovoltaic panels are connected in series. When the x-th photovoltaic panel is short-circuited to the ground, the ratio of Upv+ / Upv of the photovoltaic string is x / N. Since both Upv+ and Upv can be obtained through a voltage detection circuit, and N is a known number, x can be obtained. x is the photovoltaic panel with a ground fault. Similarly, the photovoltaic panel with a ground fault can also be determined by the negative terminal voltage to ground and the output voltage of the photovoltaic string before perturbation, that is, when the x-th photovoltaic panel is short-circuited to the ground, the ratio of (1 - |Upv-| / Upv) of the photovoltaic string is x / N. Since both Upv- and Upv can be obtained through a voltage detection circuit, and N is a known number, x can be obtained.

[0236] For example, collect the open-circuit voltage U1 when the first photovoltaic string 100a is open-circuited and the open-circuit voltage U2 when the second photovoltaic string 100b is open-circuited before voltage perturbation respectively. Collect the PV- to ground voltage U1- when the first photovoltaic string 100a is open-circuited and the PV- to ground voltage U2- when the second photovoltaic string 100b is open-circuited before voltage perturbation respectively.

[0237] Then, the photovoltaic panel x1 with a ground fault in the first photovoltaic string 100a = (1 - U1-| / U1) * N;

[0238] The photovoltaic panel x2 with a ground fault in the first photovoltaic string 100a = (1 - |U2-| / U2) * N.

[0239] The above describes determining the location of the ground fault using the ratio of the terminal voltage before perturbation and the output voltage before perturbation. Next, the location of the ground fault is determined using the ratio of the terminal voltage after perturbation and the output voltage after perturbation.

[0240] Second, using the terminal voltage after voltage perturbation and the output voltage of the entire string after voltage perturbation.

[0241] The controller is specifically configured to obtain the photovoltaic panel with a ground fault using the ratio of the terminal voltage after perturbation of the photovoltaic string with a ground fault and the output voltage after perturbation, and the number N of photovoltaic panels connected in series.

[0242] The controller is specifically configured to, when the terminal voltage is the positive terminal voltage to ground, obtain the photovoltaic panel with a ground fault through the following formula:

[0243] x = N * (Uv+ / Uv);

[0244] When the terminal voltage is the negative terminal voltage to ground, obtain the photovoltaic panel with a ground fault through the following formula:

[0245] x = N * (1 - |Uv-| / Uv);

[0246] Among them, Uv+ represents the positive electrode-to-ground voltage after voltage disturbance, Uv- represents the negative electrode-to-ground voltage after voltage disturbance, and Uv represents the output voltage after voltage disturbance; N represents the number of series-connected photovoltaic panels included in the photovoltaic string with a ground fault, and x represents the x-th photovoltaic panel starting from the positive electrode of the photovoltaic string with the ground fault.

[0247] For example, before voltage disturbance, the photovoltaic string does not perform any control and operates at the operating point corresponding to the open-circuit voltage. When voltage disturbance occurs, the output voltage of the photovoltaic string is controlled to decrease from the open-circuit voltage.

[0248] It should be noted that when the connection relationship between the photovoltaic device and the photovoltaic string is as Figure 4 , Figure 6 shown, whether there is one or more photovoltaic strings, as long as there is a ground fault in one string, accurate positioning of the fault location can be achieved. When the connection relationship between the photovoltaic device and the photovoltaic string is as Figure 10 shown, since the PV- of all photovoltaic strings are shorted together, voltage disturbance cannot be performed on two or more photovoltaic strings simultaneously, and voltage disturbance needs to be performed on each photovoltaic string separately in sequence. And Figure 10 for the corresponding photovoltaic device, since the positive or negative electrodes of each photovoltaic string are connected together, only when there is a ground fault in only one string can the position of the photovoltaic panel with the ground fault be accurately obtained. When there are ground faults in multiple strings, only the photovoltaic strings with ground faults can be accurately judged, and the specific position of the photovoltaic panel with the ground fault cannot be accurately obtained.

[0249] For Figure 10 the photovoltaic device shown, when one end of multiple photovoltaic strings is shorted together, that is, the positive electrodes of multiple photovoltaic strings in the photovoltaic array are shorted together, or the negative electrodes are shorted together, voltage disturbance is performed on each photovoltaic string in sequence, and it can be accurately judged whether there is a ground fault in each photovoltaic string. When there is only one ground fault, the position of the faulty photovoltaic panel can be accurately located by using the ratio relationship between the terminal voltage and the output voltage.

[0250] Since the PV- of each photovoltaic string is shorted together, only one voltage sampling circuit for PV- to ground needs to be set, saving hardware costs.

[0251] For the photovoltaic device provided in the above embodiments, when there is only one photovoltaic string and there is only one ground fault in the photovoltaic string, the position of the ground fault in the photovoltaic string can be accurately located. When there are multiple photovoltaic strings and the positive and negative electrodes of the photovoltaic strings are not connected together, all the photovoltaic strings with ground faults can be identified, and when there is only one ground fault in a photovoltaic string, the fault position can be accurately located. When there are multiple photovoltaic strings and the positive or negative electrodes of all the photovoltaic strings are connected together, all the photovoltaic strings with ground faults can be identified. When there is only one ground fault, the position of the faulty photovoltaic panel can be accurately located by using the ratio relationship between the terminal voltage and the output voltage.

[0252] System embodiment

[0253] Based on the detection of ground faults of photovoltaic strings and photovoltaic devices provided in 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 accompanying drawings.

[0254] See Figure 14 , which is a schematic diagram of a photovoltaic power generation system provided by an embodiment of the present application.

[0255] An embodiment of the present application provides a photovoltaic power generation system, including: a photovoltaic array, a photovoltaic device, and a controller;

[0256] The photovoltaic array includes m photovoltaic strings, where m is an integer greater than or equal to 1;

[0257] The photovoltaic device includes m power conversion circuits; the power conversion circuits correspond to the photovoltaic strings one by one, and each photovoltaic string is connected to the corresponding power conversion circuit;

[0258] The controller is configured to obtain the terminal voltage of each photovoltaic string before voltage perturbation, where the terminal voltage is the voltage of the positive electrode of the photovoltaic string to the ground or the voltage of the negative electrode to the ground; perform voltage perturbation on each photovoltaic string respectively, and obtain the terminal voltage of each photovoltaic string after voltage perturbation; determine the photovoltaic string with a ground fault according to the terminal voltage of each photovoltaic string before voltage perturbation and the terminal voltage after voltage perturbation; for the photovoltaic string with a ground fault, obtain the faulty photovoltaic panel by using the terminal voltage and the output voltage of the photovoltaic string before voltage perturbation, or obtain the faulty photovoltaic panel by using the terminal voltage and the output voltage of the photovoltaic string after voltage perturbation.

[0259] The controller is specifically configured to determine that the photovoltaic string is a photovoltaic string with a ground fault when the absolute value of the difference between the terminal voltage of the photovoltaic string before voltage perturbation and the terminal voltage after voltage perturbation exceeds a preset threshold.

[0260] A controller, specifically configured to control the output voltage of a photovoltaic string disturbed by voltage to change in the direction of increasing voltage or in the direction of decreasing voltage.

[0261] A controller, specifically configured to control the output voltage of a photovoltaic string disturbed by voltage to change from the open-circuit voltage before voltage disturbance to a first preset voltage after voltage disturbance, where the first preset voltage is less than the open-circuit voltage.

[0262] A controller, specifically configured to control the output voltage of a photovoltaic string disturbed by voltage to change from the open-circuit voltage before voltage disturbance to the short-circuit voltage after voltage disturbance.

[0263] A controller, specifically configured to obtain a photovoltaic panel with a ground fault by using the ratio of the terminal voltage and the output voltage of the photovoltaic string with a ground fault before voltage disturbance, and the number N of photovoltaic panels connected in series.

[0264] A controller, specifically configured to obtain a photovoltaic panel with a ground fault through the following formula when the terminal voltage is the positive-pole-to-ground voltage:

[0265] x = N * (Upv+ / Upv);

[0266] When the terminal voltage is the negative-pole-to-ground voltage, a photovoltaic panel with a ground fault is obtained through the following formula:

[0267] x = N * (1 - |Upv-| / Upv);

[0268] Wherein, Upv+ represents the positive-pole-to-ground voltage before voltage disturbance, Upv- represents the negative-pole-to-ground voltage before voltage disturbance, Upv represents the output voltage before voltage disturbance; N represents the number of photovoltaic panels connected in series in the photovoltaic string with a ground fault, and x represents the xth photovoltaic panel starting from the positive pole of the photovoltaic string with a ground fault.

[0269] A controller, specifically configured to obtain a photovoltaic panel with a ground fault by using the ratio of the terminal voltage and the output voltage after voltage disturbance of the photovoltaic string with a ground fault, and the number N of photovoltaic panels connected in series.

[0270] A controller, specifically configured to obtain a photovoltaic panel with a ground fault through the following formula when the terminal voltage is the positive-pole-to-ground voltage:

[0271] x = N * (Uv+ / Uv);

[0272] When the terminal voltage is the negative-pole-to-ground voltage, a photovoltaic panel with a ground fault is obtained through the following formula:

[0273] x = N * (1 - |Uv-| / Uv);

[0274] Among them, Uv+ represents the positive electrode-to-ground voltage after voltage disturbance, Uv- represents the negative electrode-to-ground voltage after voltage disturbance, and Uv represents the output voltage after voltage disturbance; N represents the number of series-connected photovoltaic panels included in the photovoltaic string with a ground fault, and x represents the x-th photovoltaic panel starting from the positive electrode of the photovoltaic string with the ground fault.

[0275] The photovoltaic power generation system provided by this embodiment includes: a photovoltaic array 100 and the photovoltaic device 1000 introduced in the above embodiment;

[0276] The photovoltaic array 100 includes M photovoltaic strings, and M is an integer greater than or equal to 1;

[0277] The photovoltaic device 100 includes M of the power conversion circuits.

[0278] The M photovoltaic strings in the photovoltaic array 100 and the M power conversion circuits in the photovoltaic device 1000 are in a one-to-one relationship, that is, the input end of each power conversion circuit is connected to its corresponding photovoltaic string.

[0279] The photovoltaic device can be an inverter or a busbar box, and there is no specific limitation in the embodiments of this application.

[0280] When the photovoltaic device is an inverter, the inverter can be a two-stage inverter, such as Figure 6 shown, and can include a DC / DC conversion circuit and a DC / AC conversion circuit. The inverter can also be a single-stage inverter, that is, only includes a DC / AC conversion circuit, such as Figure 13 shown.

[0281] The specific implementation manner of the controller in the photovoltaic power generation system for the ground fault of the photovoltaic module can refer to the descriptions of the method embodiment and the photovoltaic device embodiment, and will not be elaborated here.

[0282] The photovoltaic power generation system provided by the embodiments of the present application includes the photovoltaic devices introduced in the above embodiments. When there is only one photovoltaic string and only one ground fault occurs in the photovoltaic string, the position of the ground fault in the photovoltaic string can be accurately located. When there are multiple photovoltaic strings and the positive and negative poles of the photovoltaic strings are not connected together, all the photovoltaic strings with ground faults can be identified, and when there is only one ground fault in a photovoltaic string, the fault position can be accurately located. When there are multiple photovoltaic strings and the positive or negative poles of all the photovoltaic strings are connected together, all the photovoltaic strings with ground faults can be identified. When there is only one ground fault, the position of the faulty photovoltaic panel can be accurately located by using the ratio relationship between the terminal voltage and the output voltage. This photovoltaic power generation system can monitor the ground fault of the photovoltaic array before the inverter is connected to the grid. When the DC insulation impedance is low, that is, when a ground fault occurs, the fault can be removed in time according to the located fault position, so that the photovoltaic power generation system can operate normally as soon as possible, be connected to the grid for power generation, and improve the working efficiency.

[0283] It should be understood that in the present application, "at least one (item)" means one or more, and "multiple" means two or more. "And / or" is used to describe the association relationship of associated objects and indicates that three relationships can exist. For example, "A and / or B" can mean: only A exists, only B exists, and both A and B exist at the same time. Among them, A and B can be singular or plural. The character " / " generally means that the associated objects before and after are in an "or" relationship. "At least one (one) of the following" or its similar expression refers to any combination of these items, including any combination of single item (one) or plural items (ones). For example, at least one (one) of a, b or c can mean: a, b, c, "a and b", "a and c", "b and c", or "a and b and c", where a, b, c can be single or multiple.

[0284] As mentioned above, the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A photovoltaic power generation system, characterized in that, Comprising: A photovoltaic array, a photovoltaic device, and a controller; The photovoltaic array includes m photovoltaic strings, where m is an integer greater than or equal to 1; The photovoltaic device includes m power conversion circuits; the power conversion circuits are connected to the photovoltaic strings; The controller is configured to obtain the terminal voltage of each photovoltaic string before voltage perturbation, where the terminal voltage is the positive-pole-to-ground voltage or the negative-pole-to-ground voltage of the photovoltaic string; perform voltage perturbation on each of the photovoltaic strings respectively to obtain the terminal voltage of each photovoltaic string after voltage perturbation; determine the photovoltaic string with a ground fault based on the terminal voltage of each photovoltaic string before voltage perturbation and the terminal voltage after voltage perturbation; for the photovoltaic string with a ground fault, obtain the photovoltaic panel with a ground fault by using the terminal voltage and the output voltage of the photovoltaic string before voltage perturbation, or obtain the photovoltaic panel with a ground fault by using the terminal voltage and the output voltage of the photovoltaic string after voltage perturbation.

2. The system according to claim 1, wherein Specifically, the controller is configured to determine that the photovoltaic string is a photovoltaic string with a ground fault when the absolute value of the difference between the terminal voltage of the photovoltaic string before voltage perturbation and the terminal voltage after voltage perturbation exceeds a preset threshold.

3. The system according to claim 1, characterized in that, Specifically, the controller is configured to control the output voltage of the photovoltaic string subjected to voltage perturbation to change in the direction of increasing voltage or in the direction of decreasing voltage.

4. The system according to claim 3, wherein Specifically, the controller is configured to control the output voltage of the photovoltaic string subjected to voltage perturbation to change from the open-circuit voltage before voltage perturbation to a first preset voltage after voltage perturbation, where the first preset voltage is less than the open-circuit voltage.

5. The system according to claim 4, wherein Specifically, the controller is configured to control the output voltage of the photovoltaic string subjected to voltage perturbation to change from the open-circuit voltage before voltage perturbation to the short-circuit voltage after voltage perturbation.

6. The system according to any one of claims 2-4, characterized in that Specifically, the controller is configured to obtain the photovoltaic panel with a ground fault by using the ratio of the terminal voltage and the output voltage of the photovoltaic string with a ground fault before voltage perturbation and the number N of series-connected photovoltaic panels.

7. The system according to claim 6, characterized in that, Specifically, when the terminal voltage is the positive-pole-to-ground voltage, the controller obtains the photovoltaic panel with a ground fault through the following formula: x = N * (Upv+ / Upv); When the terminal voltage is the negative-pole-to-ground voltage, the controller obtains the photovoltaic panel with a ground fault through the following formula: x = N * (1 - |Upv-| / Upv); Where, Upv+ represents the positive-pole-to-ground voltage before voltage perturbation, Upv- represents the negative-pole-to-ground voltage before voltage perturbation, Upv represents the output voltage before voltage perturbation; N represents the number of series-connected photovoltaic panels included in the photovoltaic string with a ground fault, and x represents the x-th photovoltaic panel starting from the positive pole of the photovoltaic string with a ground fault.

8. The system according to any one of claims 2-4, characterized in that, Specifically, the controller is configured to obtain the photovoltaic panel with a ground fault by using the ratio of the terminal voltage and the output voltage after voltage perturbation of the photovoltaic string with a ground fault and the number N of series-connected photovoltaic panels.

9. The system according to claim 8, wherein Specifically, when the terminal voltage is the positive-pole-to-ground voltage, the controller obtains the photovoltaic panel with a ground fault through the following formula: x = N * (Uv+ / Uv); When the terminal voltage is the negative-pole-to-ground voltage, the controller obtains the photovoltaic panel with a ground fault through the following formula: x = N * (1 - |Uv-| / Uv); Where, Uv+ represents the positive electrode-to-ground voltage after voltage disturbance, Uv- represents the negative electrode-to-ground voltage after voltage disturbance, and Uv represents the output voltage after voltage disturbance; N represents the number of series-connected photovoltaic panels included in the photovoltaic string with a ground fault, and x represents the x-th photovoltaic panel starting from the positive electrode of the photovoltaic string with the ground fault.

10. A method for detecting the ground fault of a photovoltaic string, characterized in that, It includes: Obtaining the terminal voltage of each photovoltaic string before voltage disturbance, where the terminal voltage is the positive electrode-to-ground voltage or the negative electrode-to-ground voltage of the photovoltaic string; Performing voltage disturbance on each of the photovoltaic strings respectively to obtain the terminal voltage of each photovoltaic string after voltage disturbance; Determining the photovoltaic string with a ground fault according to the terminal voltage of each photovoltaic string before voltage disturbance and the terminal voltage after voltage disturbance; For the photovoltaic string with a ground fault, obtaining the photovoltaic panel with a ground fault by using the terminal voltage and the output voltage of the photovoltaic string before voltage disturbance, or obtaining the photovoltaic panel with a ground fault by using the terminal voltage and the output voltage of the photovoltaic string after voltage disturbance.

11. The method according to claim 10, wherein The determining the photovoltaic string with a ground fault according to the terminal voltage of each photovoltaic string before voltage disturbance and the terminal voltage after voltage disturbance specifically includes: When the absolute value of the difference between the terminal voltage of the photovoltaic string before voltage disturbance and the terminal voltage after voltage disturbance exceeds a preset threshold, determining that this path of photovoltaic string is the photovoltaic string with a ground fault.

12. The method according to claim 11, wherein The performing voltage disturbance on each of the photovoltaic strings respectively specifically includes: Controlling the output voltage of the photovoltaic string to be voltage-disturbed to change along the direction of increasing voltage or along the direction of decreasing voltage.

13. The method according to claim 12, characterized in that, The controlling the output voltage of the photovoltaic string to be voltage-disturbed to change along the direction of decreasing voltage specifically includes: Controlling the output voltage of the photovoltaic string to be voltage-disturbed to change from the open-circuit voltage before voltage disturbance to the first preset voltage after voltage disturbance, where the first preset voltage is less than the open-circuit voltage.

14. The method according to claim 13, wherein The performing voltage disturbance on each of the photovoltaic strings respectively specifically includes: Controlling the output voltage of the photovoltaic string to be voltage-disturbed to change from the open-circuit voltage before voltage disturbance to the short-circuit voltage after voltage disturbance.

15. The method according to any one of claims 11-13, characterized in that, The obtaining the photovoltaic panel with a ground fault by using the terminal voltage and the output voltage of the photovoltaic string before voltage disturbance specifically includes: Obtaining the photovoltaic panel with a ground fault by using the ratio of the terminal voltage and the output voltage of the photovoltaic string with the ground fault before voltage disturbance and the number N of series-connected photovoltaic panels.

16. The method according to claim 15, wherein The obtaining the photovoltaic panel with a ground fault by using the ratio of the terminal voltage of the photovoltaic string with the ground fault before voltage disturbance and the output voltage before voltage disturbance and the number N of series-connected photovoltaic panels specifically includes: When the terminal voltage is the positive electrode-to-ground voltage, obtaining the photovoltaic panel with a ground fault through the following formula: x = N * (Upv+ / Upv); When the terminal voltage is the negative electrode-to-ground voltage, obtaining the photovoltaic panel with a ground fault through the following formula: x = N * (1 - |Upv-| / Upv); Among them, Upv+ represents the positive electrode-to-ground voltage before voltage disturbance, Upv- represents the negative electrode-to-ground voltage before voltage disturbance, and Upv represents the output voltage before voltage disturbance; N represents the number of series-connected photovoltaic panels included in the photovoltaic string with a ground fault, and x represents the x-th photovoltaic panel starting from the positive electrode of the photovoltaic string with the ground fault.

17. The method according to any one of claims 11-13, characterized in that, Obtaining the photovoltaic panel with a ground fault by using the terminal voltage of the photovoltaic string after voltage disturbance and the output voltage after voltage disturbance specifically includes: Obtaining the photovoltaic panel with a ground fault by using the ratio of the terminal voltage of the photovoltaic string with the ground fault after voltage disturbance to the output voltage after voltage disturbance and the number N of series-connected photovoltaic panels included.

18. The method according to claim 17, wherein Obtaining the photovoltaic panel with a ground fault by using the ratio of the terminal voltage of the photovoltaic string with the ground fault after voltage disturbance to the output voltage after voltage disturbance and the number N of series-connected photovoltaic panels included specifically includes: When the terminal voltage is the positive electrode-to-ground voltage, the photovoltaic panel with a ground fault is obtained through the following formula: x = N * (Uv+ / Uv); When the terminal voltage is the negative electrode-to-ground voltage, the photovoltaic panel with a ground fault is obtained through the following formula: x = N * (1 - |Uv-| / Uv); Among them, Uv+ represents the positive electrode-to-ground voltage after voltage disturbance, Uv- represents the negative electrode-to-ground voltage after voltage disturbance, and Uv represents the output voltage after voltage disturbance; N represents the number of series-connected photovoltaic panels included in the photovoltaic string with a ground fault, and x represents the x-th photovoltaic panel starting from the positive electrode of the photovoltaic string with the ground fault.

19. A photovoltaic inverter, characterized in that, Including: A power conversion circuit, a controller, and a voltage detection circuit; The power conversion circuit is used to be connected to the photovoltaic string; The voltage detection circuit is used to obtain the terminal voltage of each photovoltaic string before voltage disturbance, and the terminal voltage is the positive electrode-to-ground voltage or the negative electrode-to-ground voltage of the photovoltaic string; The controller is used to perform voltage disturbance on each of the photovoltaic strings respectively; The voltage detection circuit is further used to obtain the terminal voltage of each photovoltaic string after voltage disturbance respectively; The controller is further used to determine the photovoltaic string with a ground fault according to the terminal voltage of each photovoltaic string before voltage disturbance and the terminal voltage after voltage disturbance; for the photovoltaic string with the ground fault, obtain the photovoltaic panel with the ground fault by using the terminal voltage and the output voltage of the photovoltaic string before voltage disturbance, or obtain the photovoltaic panel with the ground fault by using the terminal voltage and the output voltage of the photovoltaic string after voltage disturbance.

20. The photovoltaic inverter according to claim 19, characterized in that, Specifically, the controller is used to determine that the photovoltaic string is the photovoltaic string with a ground fault when the absolute value of the difference between the terminal voltage of the photovoltaic string before voltage disturbance and the terminal voltage after voltage disturbance exceeds a preset threshold.

21. The photovoltaic inverter according to claim 19, characterized in that, Specifically, the controller is used to control the output voltage of the photovoltaic string subjected to voltage disturbance to change in the direction of increasing voltage or in the direction of decreasing voltage.

22. The photovoltaic inverter according to claim 21, wherein, Specifically, the controller is used to control the output voltage of the photovoltaic string subjected to voltage disturbance to change from the open-circuit voltage before voltage disturbance to a first preset voltage after voltage disturbance, and the first preset voltage is less than the open-circuit voltage.

23. The photovoltaic inverter according to any one of claims 20-22, characterized in that, The controller is specifically configured to obtain the photovoltaic panels with ground faults by using the ratio of the terminal voltage before the voltage perturbation of the photovoltaic string with ground faults to the output voltage, and the number N of photovoltaic panels connected in series.

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