Photovoltaic inverter

Abstract

The invention discloses a photovoltaic inverter. A power conversion circuit is correspondingly connected with a photovoltaic string; the controller obtains terminal voltage of each photovoltaic string before voltage disturbance, wherein the terminal voltage is positive voltage to ground or negative voltage to ground of the photovoltaic string; performing voltage disturbance on each photovoltaic string to obtain terminal voltage of each photovoltaic string after voltage disturbance; according to the terminal voltage of each photovoltaic string before voltage disturbance and the terminal voltage after voltage disturbance, determining a photovoltaic string with a ground fault; and for the photovoltaic group string with the ground fault, obtaining the photovoltaic cell panel with the ground fault by using the terminal voltage and the output voltage of the photovoltaic group string before voltage disturbance, or obtaining the photovoltaic cell panel with the ground fault by using the terminal voltage and the output voltage of the photovoltaic group string after voltage disturbance. The scheme is simple and easy to implement, no hardware needs to be added, manual one-by-one detection is not needed, the photovoltaic cell panel with the ground fault can be automatically determined, and the efficiency is high.

Description

Technical Field

[0001] This application relates to the field of photovoltaic power generation technology, and in particular to a photovoltaic inverter. Background Technology

[0002] Currently, photovoltaic power generation is receiving increasing attention. The direct current (DC) output from a photovoltaic array is converted into alternating current (AC) by an inverter and then fed back to the AC power grid. To improve power output, photovoltaic arrays typically consist of multiple photovoltaic modules connected in parallel.

[0003] In practical applications, photovoltaic (PV) arrays are prone to ground faults. Common causes of ground faults in PV arrays include: damaged cable insulation, internal short circuits to ground within the PV string, or short-term short circuits to ground caused by weather conditions. When a ground fault occurs in a PV array, it can cause significant leakage current, potentially leading to safety accidents.

[0004] IEC standard 62109-2 stipulates that the DC insulation impedance of the photovoltaic array to ground must be tested before the photovoltaic inverter is turned on. For non-isolated application scenarios, the inverter is not allowed to be turned on when the DC insulation impedance is low (cannot meet the leakage current requirements) until the DC insulation impedance returns to the normal value.

[0005] Currently, when photovoltaic power generation systems detect ground faults by detecting DC insulation impedance, they cannot pinpoint the specific location of the ground fault. This requires manual on-site inspection of each photovoltaic string, which is time-consuming and inefficient. Summary of the Invention

[0006] This application provides a photovoltaic inverter that can detect whether a photovoltaic string is faulty to ground and can automatically determine the specific location of the fault, and it is highly efficient.

[0007] This application provides a photovoltaic power generation system, including: a photovoltaic array, photovoltaic equipment, and a controller; the photovoltaic array includes m photovoltaic strings, where m is an integer greater than or equal to 1; the photovoltaic equipment includes m power conversion circuits; each power conversion circuit corresponds one-to-one with a photovoltaic string, and each photovoltaic string is connected to its corresponding power conversion circuit; the controller is used to obtain the terminal voltage of each photovoltaic string before voltage disturbance, the terminal voltage being the positive terminal voltage or negative terminal voltage of the photovoltaic string to ground, i.e., the voltage of PV+ or PV- to ground; voltage disturbance is performed on each photovoltaic string respectively, and the terminal voltage of each photovoltaic string after voltage disturbance is obtained respectively; when a ground fault occurs inside a photovoltaic string, the terminal voltage of the photovoltaic string will change significantly before and after voltage disturbance. The photovoltaic strings with ground faults are determined based on the terminal voltage before and after the voltage disturbance of each photovoltaic string; for the photovoltaic strings with ground faults, the photovoltaic panels with ground faults are obtained by using the terminal voltage and output voltage of the photovoltaic strings before the voltage disturbance, or by using the terminal voltage and output voltage of the photovoltaic strings after the voltage disturbance.

[0008] The photovoltaic (PV) equipment can be an inverter, comprising a DC / DC / DC conversion circuit and a DC / AC conversion circuit. The PV string is connected to the input of the DC / DC / DC conversion circuit, and the output of the DC / DC conversion circuit is used to connect to the inverter circuit. The DC / DC conversion circuit and the inverter circuit can be integrated within the inverter, using the inverter's controller to detect ground faults in the PV string. Alternatively, a separate controller can be used for this purpose. The inverter may not have a DC / DC circuit internally, only a DC / AC conversion circuit. The inverter can be a single-phase inverter or a three-phase inverter.

[0009] A significant change in the terminal voltage before and after a voltage disturbance indicates a ground fault in the photovoltaic (PV) string. Since all PV panels in the string are connected in series, when a short circuit to ground occurs at a point within the string, the potential at that location becomes the reference ground. Therefore, the reference potential of the string's terminal voltage is based on the ground potential at the fault location. By using the ratio of the terminal voltage to the total output voltage of the string, the specific location of the ground fault can be determined. This method is simple and easy to implement, requiring no additional hardware and eliminating the need for manual inspection of each of the N PV panels in the string. It automatically identifies the PV panel with the ground fault, resulting in high detection efficiency.

[0010] Preferably, it is not limited to subtracting the terminal voltage after the disturbance from the terminal voltage before the disturbance, or subtracting the terminal voltage before the disturbance from the terminal voltage after the disturbance; the main consideration is the absolute value of the voltage change. This is because a voltage disturbance may cause the terminal voltage to change in an increasing direction or in a decreasing direction. Specifically, the controller is used to determine that a photovoltaic string has a ground fault when the absolute value of the difference between the terminal voltage before and after the voltage disturbance of the photovoltaic string exceeds a preset threshold.

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

[0012] Preferably, since the open-circuit voltage is generally the maximum voltage, it does not need to be controlled and is the default open-circuit voltage. Specifically, the controller is used to control the output voltage of the photovoltaic string subjected to voltage disturbances from the open-circuit voltage before the disturbance to a first preset voltage after the disturbance, where the first preset voltage is less than the open-circuit voltage.

[0013] Preferably, under normal circumstances, when performing current and voltage scanning, the control changes from the open-circuit voltage to the short-circuit voltage, that is, from a large voltage to a smaller voltage. Specifically, the controller is used to control the output voltage of the photovoltaic string subjected to voltage disturbances from the open-circuit voltage before the disturbance to the short-circuit voltage after the disturbance.

[0014] Preferably, since the photovoltaic panels in the photovoltaic string are connected in series, each photovoltaic panel in series divides the voltage across the photovoltaic string. Therefore, the specific location of the ground fault can be obtained by using the ratio. Specifically, the controller is used to determine the photovoltaic panel with the ground fault by using the ratio of the terminal voltage before the voltage disturbance and the output voltage of the photovoltaic string, and including the number N of photovoltaic panels connected in series.

[0015] Preferably, the controller is specifically used to determine the photovoltaic panel with a ground fault when the terminal voltage is the positive voltage to ground using the following formula:

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

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

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

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

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

[0021] Preferably, the controller is specifically used to determine the photovoltaic panel with a ground fault when the terminal voltage is the positive voltage to ground using the following formula:

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

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

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

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

[0026] This application also provides a method for detecting ground faults in photovoltaic strings, comprising: obtaining the terminal voltage of each photovoltaic string before voltage disturbance, wherein the terminal voltage is the positive terminal voltage to ground or the negative terminal voltage to ground of the photovoltaic string; subjecting each photovoltaic string to voltage disturbance to obtain the terminal voltage of each photovoltaic string after voltage disturbance; determining the photovoltaic string with a ground fault based on the terminal voltage of each photovoltaic string before voltage disturbance and the terminal voltage after voltage disturbance; and for the photovoltaic string with a ground fault, obtaining the photovoltaic panel with the ground fault using the terminal voltage and output voltage of the photovoltaic string before voltage disturbance, or obtaining the photovoltaic panel with the ground fault using the terminal voltage and output voltage of the photovoltaic string after voltage disturbance.

[0027] A significant change in the terminal voltage before and after a voltage disturbance indicates a ground fault in the photovoltaic (PV) string. Since all PV panels in the string are connected in series, when a short circuit to ground occurs at a point within the string, the potential at that location becomes the reference ground. Therefore, the reference potential of the string's terminal voltage is based on the ground potential at the fault location. By using the ratio of the terminal voltage to the total output voltage of the string, the specific location of the ground fault can be determined. This method is simple and easy to implement, requiring no additional hardware and eliminating the need for manual inspection of each of the N PV panels in the string. It automatically identifies the PV panel with the ground fault, resulting in high detection efficiency.

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

[0029] Preferably, the step of performing voltage perturbation on each of the photovoltaic strings specifically includes: controlling the output voltage of the perturbed photovoltaic string to change along the direction of increasing voltage or along the direction of decreasing voltage.

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

[0031] Preferably, the voltage perturbation can be performed either from large to small or from small to large. When performing voltage perturbation on each of the photovoltaic strings, generally, during current-voltage scanning, the voltage is controlled from the open-circuit voltage to the short-circuit voltage, i.e., from a large voltage to a smaller voltage. Specifically, this includes controlling the output voltage of the perturbed photovoltaic string to change from the open-circuit voltage before the perturbation to the short-circuit voltage after the perturbation.

[0032] Preferably, since the photovoltaic panels in the photovoltaic string are all connected in series, each photovoltaic panel in series divides the voltage across the photovoltaic string. Therefore, the specific location of the ground fault can be obtained by using the ratio. The step of using the terminal voltage and output voltage of the photovoltaic string before voltage disturbance to determine the photovoltaic panel with the ground fault specifically includes: using the ratio of the terminal voltage and output voltage of the photovoltaic string before voltage disturbance to determine the photovoltaic panel with the ground fault, and including the number N of photovoltaic panels connected in series.

[0033] Preferably, the photovoltaic panels experiencing ground faults are obtained by using the ratio of the terminal voltage of the photovoltaic string before the voltage disturbance to the output voltage before the voltage disturbance, and the number N of photovoltaic panels connected in series. Specifically, when the terminal voltage is the positive voltage to ground, the photovoltaic panels experiencing ground faults are obtained using the following formula:

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

[0035] When the terminal voltage is the negative voltage to ground, the photovoltaic panel with a ground fault is obtained using the following formula:

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

[0037] Where Upv+ represents the positive terminal voltage to ground before the voltage disturbance, Upv- represents the negative terminal voltage to ground before the voltage disturbance, and Upv represents the output voltage before the voltage disturbance; N represents the number of photovoltaic panels connected in series in the photovoltaic string that has a ground fault, and x represents the x-th photovoltaic panel in the photovoltaic string that has a ground fault, starting from the positive terminal.

[0038] Preferably, the step of obtaining the photovoltaic panel with a ground fault by utilizing the terminal voltage of the photovoltaic string after voltage disturbance and the output voltage after voltage disturbance specifically includes: using the ratio of the terminal voltage of the photovoltaic string with a ground fault after voltage disturbance and the output voltage after voltage disturbance, and including the number N of photovoltaic panels connected in series to obtain the photovoltaic panel with a ground fault.

[0039] Preferably, the photovoltaic panel experiencing a ground fault is obtained by using the ratio of the terminal voltage after voltage disturbance of the photovoltaic string and the output voltage after voltage disturbance, and including the number N of photovoltaic panels connected in series. Specifically, this includes:

[0040] When the terminal voltage is the positive terminal voltage to ground, the photovoltaic panel with a ground fault is obtained using the following formula:

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

[0042] When the terminal voltage is the negative voltage to ground, the photovoltaic panel with a ground fault is obtained using the following formula:

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

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

[0045] This application embodiment also provides a photovoltaic device for detecting ground faults, including: a power conversion circuit, a controller, and a voltage detection circuit; the power conversion circuit corresponds one-to-one with a photovoltaic string, and each photovoltaic string is connected to a corresponding power conversion circuit; the voltage detection circuit is used to obtain the terminal voltage of each photovoltaic string before voltage disturbance, the terminal voltage being the positive terminal voltage to ground or the negative terminal voltage to ground of the photovoltaic string; the controller is used to perform voltage disturbance on each photovoltaic string respectively; the voltage detection circuit is also used to obtain the terminal voltage of each photovoltaic string after voltage disturbance respectively; the controller is also used to determine the photovoltaic string with a ground fault based on 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, the photovoltaic panel with the ground fault is obtained by using the terminal voltage and output voltage of the photovoltaic string before voltage disturbance, or by using the terminal voltage and output voltage of the photovoltaic string after voltage disturbance.

[0046] Preferably, the controller is specifically used 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 before the voltage disturbance and the terminal voltage after the voltage disturbance of the photovoltaic string exceeds a preset threshold.

[0047] Preferably, the embodiments of this application do not limit the direction of voltage disturbance. For example, the controller controls the output voltage of the photovoltaic string that is disturbed by voltage 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 disturbance to change from the open-circuit voltage before the voltage disturbance to a first preset voltage after the voltage disturbance, wherein the first preset voltage is less than the open-circuit voltage. That is, a preset voltage can be set, and the disturbance can be performed to this preset voltage.

[0049] Preferably, the controller uses the ratio of the terminal voltage and the output voltage of the photovoltaic string before the voltage disturbance of the ground fault to obtain the photovoltaic panel with the ground fault, and the number N of photovoltaic panels in series.

[0050] As can be seen from the above technical solutions, the embodiments of this application have the following advantages:

[0051] By perturbing the output voltage of a photovoltaic (PV) string—that is, controlling the output voltage of the PV string to change—and using the terminal voltage of the PV string before and after the change, it is possible to determine whether a ground fault has occurred in the PV string. The terminal voltage of the PV string refers to the voltage between the positive terminal and ground, or the voltage between the negative terminal and ground. When a ground fault occurs inside the PV string, the terminal voltage of the PV string will show a significant change before and after the voltage perturbation. When there is a significant change between the terminal voltage before and after the voltage perturbation, it indicates that a ground fault has occurred in the PV string. Since all the PV panels in the PV string are connected in series, when a short circuit to ground occurs at a certain point in the PV string, the potential at the location of the ground fault becomes the reference ground. Therefore, the reference potential of the PV string's terminal voltage is based on the ground potential at the location of the ground fault. By using the ratio of the terminal voltage to the total output voltage of the string, the specific location of the ground fault can be determined. This method is simple and easy to implement, requires no additional hardware, and does not require manual inspection of each of the N photovoltaic panels in the photovoltaic string. It can automatically identify the photovoltaic panel with a ground fault, resulting in high detection efficiency. Attached Figure Description

[0052] Figure 1 A schematic diagram illustrating a single photovoltaic string ground fault provided in an embodiment of this application;

[0053] Figure 2 for Figure 1 The corresponding impedance model diagram;

[0054] Figure 3 A schematic diagram of two photovoltaic strings provided in an embodiment of this application;

[0055] Figure 4 This is a schematic diagram of a photovoltaic power generation system corresponding to a single photovoltaic string provided in an embodiment of this application;

[0056] Figure 5 A flowchart illustrating a method for detecting ground faults in a photovoltaic string, as provided in this application embodiment;

[0057] Figure 6 This is a schematic diagram of a photovoltaic power generation system corresponding to a multi-channel photovoltaic string provided in the embodiments of this application;

[0058] Figure 7 A flowchart illustrating another method for detecting photovoltaic string-to-ground faults provided in this application embodiment;

[0059] Figure 8 A flowchart illustrating another method for detecting ground faults in photovoltaic strings provided in this application embodiment;

[0060] Figure 9 A schematic diagram of a universal photovoltaic system provided in the embodiments of this application;

[0061] Figure 10 This is a schematic diagram of a photovoltaic power generation system corresponding to another multi-channel photovoltaic string provided in an embodiment of this application;

[0062] Figure 11 A flowchart illustrating another method for detecting ground faults in photovoltaic strings provided in this application embodiment;

[0063] Figure 12 A schematic diagram of a photovoltaic device provided in an embodiment of this application;

[0064] Figure 13 A schematic diagram of another photovoltaic device provided in the embodiments of this application;

[0065] Figure 14 This is a schematic diagram of a photovoltaic power generation system provided in an embodiment of this application. Detailed Implementation

[0066] To enable those skilled in the art to better understand the technical solutions provided in the embodiments of this application, the following describes the working condition under ground fault using a single photovoltaic string as an example, and analyzes the working principle on which the technical solutions provided in the embodiments of this application are based in conjunction with the analysis of ground faults.

[0067] First, let's discuss ground faults. Standards require that inverters not be powered on when the DC insulation impedance is too low (unable to meet leakage current requirements). In this application's embodiment, a ground fault refers to a DC insulation impedance lower than the standard-permitted impedance for inverter power-on. For example, a short-circuit fault to ground is a special case of a ground fault.

[0068] Method Example 1:

[0069] See Figure 1 The figure is a schematic diagram of a single photovoltaic string ground fault provided in an embodiment of this application.

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

[0071] Figure 1 The corresponding impedance model can be found in [reference needed]. Figure 2 As shown.

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

[0073] When a photovoltaic panel in a photovoltaic string experiences a ground fault (mostly a low ground insulation impedance fault), the ground impedance Rg of that photovoltaic panel becomes a small impedance close to 0. At this time, the PV+ ground voltage Upv+ and PV- ground voltage Upv- are proportional to the voltage Upv between the positive and negative terminals of the photovoltaic string, where Upv+-Upv-=Upv.

[0074] Since N photovoltaic panels are connected in series, if one panel experiences a ground fault, meaning the potential of the faulty panel is approximately zero, the panel number at the fault location can be calculated using 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 in the embodiments of this application, the following description takes the occurrence of a ground fault in one of two photovoltaic strings as an example.

[0077] See Figure 3 The figure is a schematic diagram of two photovoltaic strings provided in an embodiment of this application.

[0078] Each photovoltaic string consists of 6 photovoltaic panels connected in series, such as... Figure 3 As 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 terminals 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] In the first photovoltaic string 100, the fourth photovoltaic panel 4 experienced a ground fault. The second photovoltaic string 200 did not experience a ground fault.

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

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

[0082] Therefore, in order to accurately determine the photovoltaic panel with a ground fault in a photovoltaic string, the technical solution adopted in this application embodiment is to disturb the voltage of the photovoltaic string in the photovoltaic power generation system, sample the voltage of the photovoltaic string to ground (i.e., the terminal voltage), and compare the terminal voltage before and after the disturbance to determine whether the photovoltaic string has a ground fault. When it is determined that the photovoltaic string has a ground fault, the specific fault location is further obtained from the ratio of PV+ to ground voltage or PV- to ground voltage to PV voltage.

[0083] For ease of understanding, the following section first describes the detection of a ground fault in a single photovoltaic (PV) string. The PV string is connected to the input of a DC / DC / DC converter circuit, and the output of the DC / DC converter circuit is used to connect to the inverter circuit. The DC / DC converter circuit and the inverter circuit can be integrated inside the inverter, and the inverter's controller can be used to detect ground faults in the PV string. Alternatively, a separate controller can be used for this purpose. The inverter may not have a DC / DC circuit internally, only a DC / AC converter circuit. The inverter can be a single-phase inverter or a three-phase inverter; this embodiment does not specify a particular type.

[0084] The following description uses a three-phase inverter as an example, where the inverter outputs three-phase AC power, namely L1, L2 and L3.

[0085] See Figure 4 The figure is a schematic diagram of a photovoltaic power generation system corresponding to a single photovoltaic string provided in an embodiment of this application.

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

[0087] A photovoltaic string consists of N photovoltaic panels connected in series. Figure 4 This example only uses N=5 as an example, assuming the second of five photovoltaic panels experiences a ground fault. The photovoltaic panels are numbered starting from the positive terminal PV+ closest to the photovoltaic string 100; that is, the photovoltaic panel connected to PV+ is the first photovoltaic panel, and the one connected to PV- is the fifth photovoltaic panel. Generally, N is greater than or equal to 2, meaning a photovoltaic string consists of at least two photovoltaic panels connected in series. A ground fault can occur at any point in the photovoltaic string; this embodiment only describes an example where a ground fault occurs at only one point in a single photovoltaic string.

[0088] This embodiment does not specifically limit the implementation of the DC / DC converter circuit 301 and the inverter circuit 302. For example, the DC / DC converter circuit 301 can be a boost circuit, a buck circuit, or a buck-boost circuit, or there may be no DC / DC circuit, with the photovoltaic module directly connected to the DC / AC circuit. Similarly, this embodiment does not specifically limit the specific topology of the inverter circuit 302.

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

[0090] See Figure 5 The figure is a flowchart of a method for detecting a photovoltaic string to ground fault provided in an embodiment of this application.

[0091] The method includes:

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

[0093] for Figure 4 The photovoltaic string shown obtains the terminal voltage before the voltage disturbance, that is, the PV+ voltage to ground or the PV- voltage to ground before the disturbance.

[0094] In practice, the simplest control method before voltage disturbance is to not control the photovoltaic string at all. When the output voltage of the photovoltaic string is not controlled, the output voltage of the photovoltaic string is generally its open-circuit voltage.

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

[0096] Figure 4 The diagram shows only one photovoltaic string. That is, controlling the input voltage of the DC / DC converter circuit 301 can realize the control of the output voltage of the photovoltaic string 100. Specifically, it can be realized by the controller of the inverter 300 or by other control devices. This embodiment does not make specific limitations.

[0097] There are many specific voltage disturbance methods. For example, controlling the output voltage of the photovoltaic string 100 to change from large to small, or controlling the output voltage of the photovoltaic string 100 to change from small to large, or controlling it from open circuit voltage to short circuit voltage. Generally, scanning control can be performed along the current-voltage IV curve of the photovoltaic module to make the photovoltaic string 100 operate at a certain point on the curve.

[0098] For example, when the output voltage of a photovoltaic string controlled by a voltage disturbance changes in the direction of decreasing voltage, specifically including:

[0099] The output voltage of the photovoltaic string subjected to voltage disturbance is controlled to change from the open-circuit voltage before the voltage disturbance to a first preset voltage after the voltage disturbance, wherein the first preset voltage is less than the open-circuit voltage.

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

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

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

[0103] To determine whether a ground fault has occurred in the photovoltaic string 100, the difference between Upv+ and Upv- before and after the voltage disturbance can be used to determine whether a short circuit fault has occurred.

[0104] For example, when the absolute value of the difference between the terminal voltage before the voltage disturbance and the terminal voltage after the voltage disturbance of the photovoltaic string exceeds a preset threshold, the photovoltaic string is determined to be 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 examples illustrate this point, using three different examples each;

[0107] The first method involves controlling the output voltage of the photovoltaic string to change from high to low.

[0108] Voltage perturbation is applied between the open-circuit voltage and the short-circuit voltage to control the output voltage of the photovoltaic string to jump 300V towards the short-circuit voltage point, thereby determining the voltage jump. For example, the output voltage of the photovoltaic string is initially controlled at 600V, and the sampling terminal voltage is Upv1. Voltage perturbation is then applied to control the output voltage of the photovoltaic string to 300V, i.e., the voltage drops by 300V. The sampling terminal voltage is Upv2, and the difference between Upv2 and Upv1 is obtained. Since the output voltage of the photovoltaic string changes from high to low, Upv2 is less than Upv1. Therefore, Upv2 - Upv1 is a negative value. Thus, when the absolute value of the difference between Upv2 and Upv1 is greater than a preset threshold, it is determined that a ground fault has occurred in that photovoltaic string.

[0109] It should be noted that Upv1 and Upv2 can be either positive or negative voltages to ground.

[0110] The second method involves controlling the output voltage of the photovoltaic string to gradually increase.

[0111] The output voltage of the photovoltaic (PV) string is controlled to transition towards an open-circuit voltage. For example, the output voltage of the PV string is initially controlled at 600V, and the sampling terminal voltage Upv1 is used. The voltage is then perturbed, and the output voltage of the PV string is controlled at 900V, which is an increase of 300V. The sampling terminal voltage is then Upv2, and the difference between Upv2 and Upv1 is obtained. Since the output voltage of the PV string increases from a small value to an large value, Upv2 is greater than Upv1. Therefore, Upv2 - Upv1 is a positive value. When the difference between Upv2 and Upv1 is greater than a preset threshold, it is determined that a ground fault has occurred in that PV string.

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

[0113] When the voltage disturbance control photovoltaic string changes the output voltage from open circuit voltage to short circuit voltage, that is, the short circuit voltage after voltage disturbance is 0, that is, the output voltage changes from large to 0, and the sampling terminal voltage is also close to 0, then it is confirmed that there is a ground fault in the photovoltaic string.

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

[0115] For a single photovoltaic (PV) string, when only one point experiences a ground fault, the terminal voltage of the PV string is proportional to its output voltage. Therefore, the location of the PV panel experiencing the ground fault can be determined by using this proportional relationship.

[0116] The ratio of the terminal voltage to the output voltage of the photovoltaic string can be determined by either the ratio of the terminal voltage before the voltage disturbance to the output voltage of the photovoltaic string, or by the ratio of the terminal voltage after the disturbance to the output voltage of the photovoltaic string.

[0117] by Figure 4For example, since five photovoltaic (PV) panels are connected in series between PV+ and PV-, when the second PV panel experiences a ground fault, whether before or after a voltage disturbance, if 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 PV panel has experienced a ground fault. It should be noted that the second PV panel here refers to the second PV panel counting from the PV+ end. Additionally, when the number of PV panels in each PV string is unknown, N and x represent percentages, i.e., N represents 100%, and x represents the percentage of the PV string from PV+ where the fault occurred. For example, x = 20% indicates a ground fault occurred at approximately 20%. To more accurately locate ground faults, voltage sampling near short-circuit points can be avoided as much as possible.

[0118] For example, the ratio of Upv+ before voltage disturbance to Upv before voltage disturbance can be used to obtain the photovoltaic panel that has experienced a ground fault.

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

[0120] It should be noted that a ground fault in a photovoltaic panel can refer not only to a short circuit to ground caused by the photovoltaic panel itself, but also to a short circuit to ground caused by insulation damage in the series cables connected to it.

[0121] The method provided in this embodiment perturbs the output voltage of a photovoltaic (PV) string, i.e., controls the output voltage of the PV string to change, and uses the terminal voltage of the PV string before and after the change to determine whether a ground fault has occurred in the PV string. A significant change in the terminal voltage before and after the voltage perturbation indicates that a ground fault has occurred in the PV string. All PV panels in the PV string are connected in series. When a ground fault occurs at a certain location in the PV string, the potential at the ground fault point is approximately equal to the reference ground. At this time, the voltage received by all PV panels from one end of the PV string to the fault point 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 total output voltage of the string. This method is simple and easy to implement, requires no additional hardware, and does not require manual inspection of each of the N PV panels in the PV string; it can automatically identify the PV panel with a ground fault, resulting in high efficiency.

[0122] Method Example 2:

[0123] The above embodiments use an inverter corresponding to one photovoltaic (PV) string as an example. The following describes an inverter with multiple PV strings, each corresponding to its own DC / DC conversion circuit. That is, there is a one-to-one correspondence between PV strings and DC / DC conversion circuits, and each DC / DC conversion circuit is independent; their positive or negative input terminals are not shorted together. Because each PV string is independent and connected to its corresponding DC / DC conversion circuit, the input control and sampling of each PV string do not affect each other. Each PV string can undergo voltage perturbation independently, either simultaneously or in a time-sharing manner. No specific limitations are made in the embodiments of this application.

[0124] See Figure 6 The figure is a schematic diagram of a photovoltaic power generation system corresponding to multiple photovoltaic strings provided in the embodiments of this application.

[0125] This embodiment uses three photovoltaic strings as an example: a first photovoltaic string 100a, a second photovoltaic string 100b, and a third photovoltaic string 100c. Both the first photovoltaic string 100a and the second photovoltaic string 100b experience ground faults. Each of the three photovoltaic strings consists of five photovoltaic panels connected in series, numbered from PV+ to PV- as the 1st to the 5th photovoltaic panels.

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

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

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

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

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

[0131] Among them, the fourth photovoltaic panel in the first photovoltaic string 100a experienced a ground fault, and the first photovoltaic panel in the second photovoltaic string 100b experienced a ground fault.

[0132] The specific implementation method for determining the first photovoltaic string 100a and the second photovoltaic string 100b can be the same as described in Method Implementation Example 1, and will not be repeated here. For example, Upv+ before and after the voltage disturbance can be detected to determine whether a ground fault has occurred, or Upv- before and after the voltage disturbance can be detected to determine whether a ground fault has occurred.

[0133] The photovoltaic panels experiencing ground faults are obtained by utilizing the terminal voltage and output voltage of the photovoltaic string before voltage disturbance, specifically including:

[0134] The photovoltaic panels experiencing ground faults are obtained by using the ratio of the terminal voltage to the output voltage before the voltage disturbance of the photovoltaic string under the ground fault, and the number N of photovoltaic panels connected in series.

[0135] That is, when a ground fault is determined to occur in the first photovoltaic string 100a and the second photovoltaic string 100b, the location of the ground fault is determined by the ratio of the terminal voltage of the first photovoltaic string 100a before the disturbance to its output voltage before the disturbance, N=5. Similarly, the location of the ground fault is determined by the ratio of the terminal voltage of the second photovoltaic string 100b before the disturbance to its output voltage before the voltage disturbance, N=5.

[0136] See Figure 7 The figure is a flowchart of another method for detecting photovoltaic string ground faults provided in an embodiment of this application.

[0137] S701-S703 are the same as S501-S503, and will not be described again here.

[0138] S704: For a photovoltaic string that has experienced a ground fault, the photovoltaic panel experiencing the ground fault is obtained by using the ratio of the terminal voltage of the photovoltaic string before the voltage disturbance to the output voltage before the voltage disturbance, and including the number N of photovoltaic panels connected in series.

[0139] Specifically, it includes:

[0140] When the terminal voltage is the voltage between the positive terminal and ground, the photovoltaic panel with a ground fault is obtained using the following formula:

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

[0142] When the terminal voltage is the voltage of the negative terminal to ground, the photovoltaic panel with a ground fault is obtained using the following formula:

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

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

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

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

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

[0148] The number of photovoltaic panels in the first photovoltaic string 100a that experience a ground fault is x2 = (1 - |U2 - | / U2) * N.

[0149] Figure 7 The first method describes using the ratio of the terminal voltage before the disturbance to the output voltage before the disturbance to determine the location of a ground fault. The second method describes using the ratio of the terminal voltage after the disturbance to the output voltage after the disturbance to determine the location of a ground fault.

[0150] See Figure 8 The figure is a flowchart of another method for detecting photovoltaic string ground faults provided in an embodiment of this application.

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

[0152] S804: For a photovoltaic string that has experienced a ground fault, the photovoltaic panel experiencing the ground fault is obtained by using the ratio of the terminal voltage and the output voltage after the voltage disturbance of the photovoltaic string with the ground fault, and the number N of photovoltaic panels connected in series.

[0153] Specifically, it includes:

[0154] When the terminal voltage is the voltage between the positive terminal and ground, the photovoltaic panel with a ground fault is obtained using the following formula:

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

[0156] When the terminal voltage is the voltage of the negative terminal to ground, the photovoltaic panel with a ground fault is obtained using the following formula:

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

[0158] Wherein, Uv+ represents the voltage of the positive terminal to ground after the voltage disturbance, Uv- represents the voltage of the negative terminal to ground after the voltage disturbance, and Uv represents the output voltage after the voltage disturbance; N represents the number of photovoltaic panels connected in series in the photovoltaic string that has a ground fault, and x represents the x-th photovoltaic panel in the photovoltaic string that has a ground fault, starting from the positive terminal.

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

[0160] The following example illustrates this: before a voltage disturbance, the photovoltaic string operates at the operating point corresponding to the open-circuit voltage without any control. During a voltage disturbance, the output voltage of the photovoltaic string is reduced from the open-circuit voltage.

[0161] Figure 6 This example only uses three photovoltaic strings corresponding to three DC / DC conversion circuits, with each string including five photovoltaic panels. The technical solution provided in this embodiment does not limit the specific number of photovoltaic strings or the number of photovoltaic panels. Figure 9 The diagram shown is a schematic of a universal photovoltaic system provided in an embodiment of this application.

[0162] The photovoltaic system comprises m photovoltaic strings, where m is an integer greater than or equal to 2. Each photovoltaic string corresponds to a DC / DC or DC / AC conversion circuit. Each photovoltaic string includes n photovoltaic panels connected in series, where n is an integer greater than or equal to 2. Furthermore, the number of photovoltaic strings experiencing ground faults is not limited; as long as only one ground fault occurs in each photovoltaic string, the method provided in this embodiment can accurately locate the fault.

[0163] The method provided in this embodiment is applicable to the detection of ground faults in inverters with multiple photovoltaic (PV) strings. These PV strings share neither a common positive nor a common negative terminal, and each is independently connected to its corresponding DC / DC or DC / AC conversion circuit. When a ground fault occurs in one or more strings, the change in terminal voltage before and after the voltage disturbance can accurately determine whether a ground fault has occurred in that PV string. Furthermore, when only one ground fault exists in a PV string, the PV panel with the ground fault can be identified by the ratio of the terminal voltage to the output voltage. This method is simple and easy to implement, requiring no additional hardware and eliminating the need for manual inspection of each of the N PV panels in the PV string. It can automatically identify the PV panel with the ground fault, resulting in high efficiency.

[0164] Method Example 3:

[0165] This embodiment describes a multi-channel photovoltaic string, each photovoltaic string corresponding 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 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 This figure is a schematic diagram of another photovoltaic power generation system corresponding to multiple photovoltaic strings provided in an embodiment of this application.

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

[0168] This embodiment uses three photovoltaic strings as an example: a first photovoltaic string 100a, a second photovoltaic string 100b, and a third photovoltaic string 100c. Both the first photovoltaic string 100a and the second photovoltaic string 100b experience ground faults. Each of the three photovoltaic strings consists of five photovoltaic panels connected in series, numbered from PV+ to PV- as the 1st to the 5th photovoltaic panels.

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

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

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

[0172] The negative input terminals of the first DC / DC converter circuit 301a, the second DC / DC converter circuit 301b, and the third DC / DC converter circuit 301c are all connected together, meaning that PV- is shorted together. Therefore, the Upv- values ​​of the three photovoltaic strings are equal.

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

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

[0175] Since the PV-phase of all photovoltaic strings is shorted together, voltage perturbation cannot be applied to two or more photovoltaic strings simultaneously. Instead, voltage perturbation must be applied to each photovoltaic string separately and sequentially.

[0176] See Figure 11 The figure is a flowchart of another method for detecting photovoltaic string ground faults provided in an embodiment of this application.

[0177] S1101: Collects the voltage Upv- to ground of PV- that is shorted together before the voltage disturbance;

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

[0179] For specific voltage perturbation methods, please refer to the description in the above embodiments. No control needs to be performed on the other photovoltaic strings. For example, voltage perturbation can be performed on the first photovoltaic string 100a first.

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

[0181] Each photovoltaic string can be perturbed one by one. In this embodiment, it is not limited to starting from the first photovoltaic string, that is, the order of the photovoltaic strings being perturbed is not limited.

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

[0183] Since the PV- terminals of all photovoltaic strings are shorted together, Upv- is the overall voltage of the negative terminal of the photovoltaic array relative 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 there is a ground fault in the first photovoltaic string.

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

[0186] Since the PV strings are shorted together, it is necessary to perform voltage disturbances on each PV string individually to determine whether a ground fault has occurred.

[0187] For example, when the voltage of the second photovoltaic string is disturbed, the other photovoltaic strings are not controlled in any way; only the output voltage of the second photovoltaic string is changed.

[0188] S1106: When the voltage disturbance of all photovoltaic strings is completed, if only one photovoltaic string has a ground fault, the photovoltaic panel with the ground fault is obtained by using the ratio of Upv- before the voltage disturbance to the output voltage of that photovoltaic string before the voltage disturbance.

[0189] For example, after all photovoltaic strings have undergone voltage disturbance, and it is determined that only the first photovoltaic string has a ground fault, the photovoltaic panel with the ground fault in the first photovoltaic string can be obtained using x = (1 - |Upv-| / U1)*N. Here, U1 is the output voltage of the first photovoltaic string.

[0190] The method provided in this embodiment, since the positive or negative terminals of each photovoltaic string are connected together, can only accurately determine the location of the photovoltaic panel with a ground fault when only one string has a ground fault. When multiple strings have ground faults, it can only accurately determine the photovoltaic string with the ground fault, but cannot accurately determine the location of the specific photovoltaic panel with the ground fault.

[0191] In this embodiment, we only use the example of shorting the PV- of each photovoltaic string together. Similarly, the PV- of each photovoltaic string can also be independent of each other, while the PV+ of each photovoltaic string can be shorted together.

[0192] The method provided in this application, when one end of multiple photovoltaic strings is shorted together (i.e., the positive terminals or negative terminals of multiple photovoltaic strings in a photovoltaic array are shorted together), sequentially applies voltage perturbations to each photovoltaic string, which can accurately determine whether there is a ground fault in each photovoltaic string. When there is only one ground fault, the location of the faulty photovoltaic panel can be accurately located by using the ratio of the terminal voltage to the output voltage.

[0193] Photovoltaic Equipment Example 1

[0194] Based on the method for detecting photovoltaic string ground faults provided in the above embodiments, this application also provides a photovoltaic device, the working principle of which will be described in detail below with reference to the accompanying drawings.

[0195] See Figure 12 The figure is a schematic diagram of a photovoltaic device for detecting ground faults provided in an embodiment of this application.

[0196] This application provides a photovoltaic device for detecting ground faults, comprising: a power conversion circuit, a controller 400, and a voltage detection circuit 500;

[0197] The power conversion circuit corresponds one-to-one with each photovoltaic string, and each photovoltaic string is connected to its 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. Because there is a one-to-one correspondence between the photovoltaic strings and the power conversion circuits, individual control of the photovoltaic strings can be achieved.

[0198] Figure 12 The following section uses two photovoltaic strings as examples: the first photovoltaic string 100a and the second photovoltaic string 100b.

[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 the voltage disturbance, wherein the terminal voltage is the positive terminal voltage to ground or the negative terminal voltage to ground of the photovoltaic string.

[0201] It should be noted that each photovoltaic string can be equipped with a voltage detection circuit, or multiple photovoltaic strings can share a voltage detection circuit; this embodiment does not impose any specific limitations.

[0202] The controller 400 is used to perform voltage perturbation on each of the photovoltaic strings;

[0203] When the positive 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 apply voltage perturbations to the first photovoltaic string 100a and the second photovoltaic string 100b. When the positive or negative input terminals of the first power conversion circuit 300a and the power conversion circuit 300b are connected together, the controller 400 needs to apply voltage perturbations to the first photovoltaic string 100a and the second photovoltaic string 100b sequentially.

[0204] There are many specific voltage disturbance methods. 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 it from open circuit voltage to short circuit voltage. Generally, scanning control can be performed along the current-voltage (IV) curve of the photovoltaic module to make the photovoltaic string 100 operate at a certain point on the IV curve.

[0205] For example, when the output voltage of a photovoltaic string controlled by a voltage disturbance changes in the direction of decreasing voltage, specifically including:

[0206] The output voltage of the photovoltaic string subjected to voltage disturbance is controlled to change from the open-circuit voltage before the voltage disturbance to a first preset voltage after the voltage disturbance, wherein the first preset voltage is less than the open-circuit voltage.

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

[0208] The voltage detection circuit 500 is also used to obtain the terminal voltage of each photovoltaic string after voltage disturbance.

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

[0210] It should be noted that when locating a ground fault, the voltage detection circuit 500 can also obtain the output voltage of the photovoltaic string before the voltage disturbance when using the voltage parameters before the disturbance. Similarly, when using the voltage parameters after the disturbance, the voltage detection circuit 500 can also obtain the output voltage of the photovoltaic string after the disturbance.

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

[0212] When a photovoltaic panel in a photovoltaic string experiences a ground fault, the voltage Upv+ at the positive terminal of the photovoltaic string will be significantly different from the voltage before the disturbance. Similarly, the voltage Upv- at the negative terminal of the photovoltaic string will also be significantly different before and after the disturbance.

[0213] To determine whether a short-circuit fault has occurred in a photovoltaic string, the difference between Upv+ and Upv- before and after the voltage disturbance can be used to determine whether a short-circuit fault has occurred.

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

[0215] For a single photovoltaic (PV) string, when only one point experiences a ground fault, the terminal voltage of the PV string is proportional to its output voltage. Therefore, the location of the PV panel experiencing the ground fault can be determined by using this proportional relationship.

[0216] The ratio of the terminal voltage to the output voltage of the photovoltaic string can be determined by either the ratio of the terminal voltage before the voltage disturbance to the output voltage of the photovoltaic string, or by the ratio of the terminal voltage after the disturbance to the output voltage of the photovoltaic string.

[0217] See also Figure 4 Since five photovoltaic (PV) panels are connected in series between PV+ and PV-, when the second PV panel experiences a ground fault, whether before or after a voltage disturbance, if 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 PV panel has experienced a ground fault. It should be noted that the second PV panel here refers to the second PV panel counting from the PV+ end. Furthermore, when the number of PV panels in each PV string is unknown, N and x represent percentages, i.e., N represents 100%, and x represents the percentage of the PV string from PV+ where the fault occurred. For example, x = 20% indicates that a ground fault occurred at approximately 20% of the string.

[0218] The photovoltaic equipment provided in this embodiment can be Figure 4 The form shown can also be Figure 6 The form shown can also be as follows: Figure 10 The form shown, Figure 10 Alternatively, the negative input terminals of all DC / DC converter circuits can be connected together.

[0219] Additionally, when the power conversion circuit can be a DC / AC conversion circuit, see [link to relevant documentation]. Figure 13 As shown in the figure, this figure is a schematic diagram of another photovoltaic device for detecting ground faults provided in an embodiment of this application.

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

[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 the voltage disturbance, and also to detect the terminal voltage and output voltage of the first photovoltaic string 100a and the second photovoltaic string 100b after the voltage disturbance. The voltage detection circuit 500 sends 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, thereby achieving voltage disturbance of the first photovoltaic string 100a and the second photovoltaic string 100b.

[0224] For example, the ratio of Upv+ before voltage disturbance to Upv before voltage disturbance can be used to obtain the photovoltaic panel that has experienced a ground fault.

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

[0226] It should be noted that a ground fault in a photovoltaic panel can refer not only to a short circuit to ground caused by the photovoltaic panel itself, but also to a short circuit to ground caused by insulation damage in the series cables connected to it.

[0227] The photovoltaic device provided in this embodiment determines whether a ground fault has occurred in the photovoltaic string by perturbing the output voltage of the photovoltaic string, i.e., controlling the output voltage of the photovoltaic string to change. The terminal voltage of the photovoltaic string before and after the voltage perturbation is used to determine whether a ground fault has occurred. A significant change in the terminal voltage before and after the voltage perturbation indicates that a ground fault has occurred in the photovoltaic string. All photovoltaic panels in the photovoltaic string are connected in series. When a ground fault occurs at a certain location in the photovoltaic string, the potential at the ground fault point is approximately equal to the reference ground. At this time, the voltage received by all photovoltaic panels from one end of the photovoltaic string to the fault point 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 total output voltage of the string. This method is simple and easy to implement, requires no additional hardware, and does not require manual inspection of each of the N photovoltaic panels in the photovoltaic string. It can automatically identify the photovoltaic panel with a ground fault, resulting in high efficiency.

[0228] The location of faulty photovoltaic panels can be determined by the ratio of the terminal voltage before the voltage disturbance to the output voltage of the photovoltaic string, or by the ratio of the terminal voltage after the voltage disturbance to the output voltage of the photovoltaic string. These will be explained in detail below.

[0229] The first method utilizes the terminal voltage before the voltage disturbance and the output voltage of the entire series before the voltage disturbance.

[0230] The controller, specifically used to determine the photovoltaic panel with a ground fault when the terminal voltage is the positive-to-ground voltage, employs the following formula:

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

[0232] When the terminal voltage is the negative voltage to ground, the photovoltaic panel with a ground fault is obtained using the following formula:

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

[0234] Where Upv+ represents the positive terminal voltage to ground before the voltage disturbance, Upv- represents the negative terminal voltage to ground before the voltage disturbance, and Upv represents the output voltage before the voltage disturbance; N represents the number of photovoltaic panels connected in series in the photovoltaic string that has a ground fault, and x represents the x-th photovoltaic panel in the photovoltaic string that has a ground fault, starting from the positive terminal.

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

[0236] For example, the open-circuit voltage U1 of the first photovoltaic string 100a and the open-circuit voltage U2 of the second photovoltaic string 100b are collected before the voltage disturbance. The PV-to-ground voltage U1- of the first photovoltaic string 100a and the PV-to-ground voltage U2- of the second photovoltaic string 100b are also collected before the voltage disturbance.

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

[0238] The number of photovoltaic panels in the first photovoltaic string 100a that experience a ground fault is x2 = (1 - |U2 - | / U2) * N.

[0239] The above describes how to determine the location of a ground fault by using the ratio of the terminal voltage before the disturbance to the output voltage before the disturbance. The following describes how to determine the location of a ground fault by using the ratio of the terminal voltage after the disturbance to the output voltage after the disturbance.

[0240] The second method utilizes the terminal voltage after voltage disturbance and the output voltage of the entire series after voltage disturbance.

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

[0242] The controller, specifically used to determine the photovoltaic panel with a ground fault when the terminal voltage is the positive-to-ground voltage, employs the following formula:

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

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

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

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

[0247] For example, before a voltage disturbance, the photovoltaic string does not undergo any control and operates at the operating point corresponding to the open circuit voltage. When a 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 photovoltaic equipment and photovoltaic strings is as follows: Figure 4 , Figure 6 As shown, regardless of whether there is one or multiple photovoltaic strings, as long as a ground fault occurs in one string, the location of the fault can be accurately pinpointed. When the connection relationship between the photovoltaic equipment and the photovoltaic strings is as follows... Figure 10 As shown, because the PV-phase connections of all photovoltaic strings are shorted together, voltage perturbations cannot be applied to two or more photovoltaic strings simultaneously; each photovoltaic string must be perturbed sequentially. Furthermore... Figure 10 Because the positive or negative terminals of each photovoltaic string are connected together, the location of the photovoltaic panel with the ground fault can only be accurately determined when only one string has a ground fault. When multiple strings have ground faults, only the photovoltaic string with the ground fault can be accurately identified, but the specific location of the photovoltaic panel with the ground fault cannot be accurately determined.

[0249] for Figure 10 The photovoltaic equipment shown can accurately determine whether a ground fault exists in each photovoltaic string by sequentially perturbing the voltage of each string when one end of multiple photovoltaic strings is shorted together (i.e., the positive terminals or negative terminals of multiple photovoltaic strings in the photovoltaic array are shorted together). When only one ground fault exists, the location of the faulty photovoltaic panel can be accurately determined by using the ratio of the terminal voltage to the output voltage.

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

[0251] The photovoltaic equipment provided in the above embodiments can accurately locate the location of a ground fault in a photovoltaic string when there is only one photovoltaic string and only one ground fault occurs in that string. When there are multiple photovoltaic strings and the positive and negative terminals of the photovoltaic strings are not connected together, all photovoltaic strings with ground faults can be identified, and the fault location can be accurately located when there is only one ground fault in a photovoltaic string. When there are multiple photovoltaic strings and the positive or negative terminals of all photovoltaic strings are connected together, all photovoltaic strings with ground faults can be identified. When there is only one ground fault, the location of the faulty photovoltaic panel can be accurately located by using the ratio of the terminal voltage to the output voltage.

[0252] System Implementation Examples

[0253] Based on the above embodiments for detecting photovoltaic string ground faults and photovoltaic equipment, this application also provides a photovoltaic power generation system, which will be described in detail below with reference to the accompanying drawings.

[0254] See Figure 14 The figure is a schematic diagram of a photovoltaic power generation system provided in an embodiment of this application.

[0255] This application provides a photovoltaic power generation system, including: a photovoltaic array, photovoltaic equipment, and a controller;

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

[0257] The photovoltaic device includes m power conversion circuits; each power conversion circuit corresponds one-to-one with a photovoltaic string, 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 disturbance, wherein the terminal voltage is the positive terminal voltage to ground or the negative terminal voltage to ground of the photovoltaic string; to perform voltage disturbance on each of the photovoltaic strings respectively, and to obtain the terminal voltage of each photovoltaic string after voltage disturbance; to determine the photovoltaic string with ground fault based on the terminal voltage of each photovoltaic string before voltage disturbance and the terminal voltage after voltage disturbance; and to obtain the photovoltaic panel with ground fault using the terminal voltage and output voltage of the photovoltaic string before voltage disturbance, or using the terminal voltage and output voltage of the photovoltaic string after voltage disturbance.

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

[0260] The controller is specifically used to control the output voltage of the photovoltaic string that is disturbed by voltage to change in the direction of increasing voltage or in the direction of decreasing voltage.

[0261] The controller is specifically used to control the output voltage of the photovoltaic string subjected to voltage disturbance to change from the open-circuit voltage before the voltage disturbance to a first preset voltage after the voltage disturbance, wherein the first preset voltage is less than the open-circuit voltage.

[0262] The controller is specifically used to control the output voltage of the photovoltaic string that is subjected to voltage disturbance, from the open-circuit voltage before the voltage disturbance to the short-circuit voltage after the voltage disturbance.

[0263] The controller is specifically used to obtain the photovoltaic panels with ground faults by utilizing the ratio of the terminal voltage and output voltage of the photovoltaic string before the voltage disturbance caused by the ground fault, and including the number N of photovoltaic panels connected in series.

[0264] The controller, specifically used to determine the photovoltaic panel with a ground fault when the terminal voltage is the positive-to-ground voltage, employs the following formula:

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

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

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

[0268] Where Upv+ represents the positive terminal voltage to ground before the voltage disturbance, Upv- represents the negative terminal voltage to ground before the voltage disturbance, and Upv represents the output voltage before the voltage disturbance; N represents the number of photovoltaic panels connected in series in the photovoltaic string that has a ground fault, and x represents the x-th photovoltaic panel in the photovoltaic string that has a ground fault, starting from the positive terminal.

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

[0270] The controller, specifically used to determine the photovoltaic panel with a ground fault when the terminal voltage is the positive-to-ground voltage, employs the following formula:

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

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

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

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

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

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

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

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

[0279] The photovoltaic equipment can be an inverter or a combiner box, as not specifically limited in the embodiments of this application.

[0280] When photovoltaic equipment is used as an inverter, the inverter can be a two-stage inverter, such as... Figure 6 As shown, it can include both DC / DC conversion circuits and DC / AC conversion circuits. The inverter can also be a single-stage inverter, i.e., it only includes a DC / AC conversion circuit, such as... Figure 13 As shown.

[0281] The specific method by which the controller in the photovoltaic power generation system implements the ground fault response of the photovoltaic module can be found in the descriptions of the method embodiments and photovoltaic equipment embodiments, and will not be repeated here.

[0282] The photovoltaic power generation system provided in this application includes the photovoltaic equipment described in the above embodiments. When there is only one photovoltaic string and only one ground fault occurs in the photovoltaic string, the location of the ground fault in the photovoltaic string can be accurately located. When there are multiple photovoltaic strings and the positive and negative terminals of the photovoltaic strings are not connected together, all photovoltaic strings with ground faults can be identified, and when there is only one ground fault in a photovoltaic string, the fault location can be accurately located. When there are multiple photovoltaic strings and the positive or negative terminals of all photovoltaic strings are connected together, all photovoltaic strings with ground faults can be identified. When there is only one ground fault, the location of the faulty photovoltaic panel can be accurately located by using the ratio of the terminal voltage to the output voltage. This photovoltaic power generation system can monitor ground faults in the photovoltaic array before the inverter is connected to the grid. When the DC insulation impedance is low, i.e., when a ground fault occurs, the fault can be promptly cleared according to the located fault location, so that the photovoltaic power generation system can operate normally and generate electricity through grid connection as soon as possible, improving working efficiency.

[0283] It should be understood that in this application, "at least one (item)" means one or more, and "more than" means two or more. "And / or" is used to describe the relationship between related objects, indicating that three relationships can exist. For example, "A and / or B" can represent three cases: only A exists, only B exists, and both A and B exist simultaneously, where A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects are in an "or" relationship. "At least one (item) of the following" or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, at least one (item) of a, b, or c can represent: a, b, c, "a and b", "a and c", "b and c", or "a and b and c", where a, b, and c can be single or multiple.

[0284] The above-described embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. A photovoltaic inverter, characterized in that, include: Multiple power conversion circuits, controllers, and voltage detection circuits; The multiple power conversion circuits are used to connect to multiple photovoltaic strings, wherein the input of the power circuit is connected to the output of the photovoltaic string and is used to adjust the input voltage of the power conversion circuit, which is the output voltage of the photovoltaic string; The voltage detection circuit is used to obtain the terminal voltage of each photovoltaic string before the voltage disturbance, wherein the terminal voltage is the positive terminal voltage to ground or the negative terminal voltage to ground of the photovoltaic string. The controller is used to perform voltage perturbation on each of the photovoltaic strings; The voltage detection circuit is also used to obtain the terminal voltage of each photovoltaic string after voltage disturbance. The controller is also configured to determine the photovoltaic string with a ground fault based on the terminal voltage of each photovoltaic string before the voltage disturbance and the terminal voltage after the voltage disturbance.

2. The photovoltaic inverter according to claim 1, characterized in that, The photovoltaic string includes multiple photovoltaic panels connected in series; The controller is used to identify the photovoltaic panels with ground faults by using the terminal voltage and output voltage of the photovoltaic string before the voltage disturbance, or by using the terminal voltage and output voltage of the photovoltaic string after the voltage disturbance.

3. The photovoltaic inverter according to claim 1 or 2, characterized in that, The controller is specifically used to determine that a photovoltaic string is a photovoltaic string with a ground fault when the absolute value of the difference between the terminal voltage before the voltage disturbance and the terminal voltage after the voltage disturbance of the photovoltaic string exceeds a preset threshold.

4. The photovoltaic inverter according to claim 1 or 2, characterized in that, The controller is specifically used to control the output voltage of the photovoltaic string that is disturbed by voltage to change in the direction of increasing voltage or in the direction of decreasing voltage.

5. The photovoltaic inverter according to claim 4, characterized in that, The controller is specifically used to control the output voltage of the photovoltaic string subjected to voltage disturbance to change from the open-circuit voltage before the voltage disturbance to a first preset voltage after the voltage disturbance, wherein the first preset voltage is less than the open-circuit voltage.

6. The photovoltaic inverter according to any one of claims 1 or 2, characterized in that, The controller is specifically used to obtain the photovoltaic panel with the ground fault by using the ratio of the terminal voltage and the output voltage before the voltage disturbance of the photovoltaic string under the ground fault, and including the number N of photovoltaic panels connected in series.

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

8. The photovoltaic inverter according to any one of claims 1 or 2, characterized in that, The controller is specifically used to obtain the photovoltaic panel with the ground fault by using the ratio of the terminal voltage after the voltage disturbance of the photovoltaic string and the output voltage after the voltage disturbance, and including the number N of photovoltaic panels connected in series.

9. The photovoltaic inverter according to claim 8, characterized in that, Specifically, the controller is used to determine the photovoltaic panel with a ground fault when the terminal voltage is the positive voltage to ground using the following formula: x = N*(Uv+ / Uv); When the terminal voltage is the negative voltage to ground, the photovoltaic panel with a ground fault is obtained using the following formula: x = N*(1-|Uv-| / Uv); Wherein, Uv+ represents the positive terminal voltage to ground after voltage disturbance, Uv- represents the negative terminal voltage to ground after voltage disturbance, and Uv represents the output voltage after voltage disturbance; N represents the number of photovoltaic panels connected in series in the photovoltaic string that has a ground fault, and x represents the x-th photovoltaic panel in the photovoltaic string that has a ground fault, starting from the positive terminal.

10. The photovoltaic inverter system according to claim 1 or 2, characterized in that, The power conversion circuit includes multiple DC / DC / DC conversion circuits and DC / AC conversion circuits. The photovoltaic string is connected to the input terminals of the multiple DC / DC / DC conversion circuits, and the output terminal of the DC / DC conversion circuit is used to connect to the inverter circuit.

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