Photovoltaic inverter ground impedance fault detection system and method

Abstract

The invention discloses a photovoltaic inverter ground impedance fault detection system and method. The system comprises a PID repair circuit and an acquisition circuit. The PID repair circuit is connected in parallel to two sides of the inverter, and the PID repair circuit is suitable for being equivalent to an LR circuit connected between the negative end of the direct current side of the inverter and the ground in a non-working state; and the acquisition circuit is suitable for detecting the inductive voltage of the LR circuit, so that when the inductive voltage abrupt change value of the LR circuit is detected to be greater than a set voltage threshold value, the inverter is affirmed to have a grounding fault. According to the method, the photovoltaic inverter ground impedance fault detection system is adopted to carry out ground fault judgment in an inverter grid-connected state. The method has the beneficial effects that under the condition that the direct current bus is stable, the ground fault of the inverter is identified on line by detecting the voltage change on the equivalent inductor of the secondary side of the PID power supply, the identification speed of the ground fault is increased, and the damage risk of a switch tube under the ground fault is reduced.

Description

Technical Field

[0001] The present application relates to the technical field of new energy power generation, and particularly relates to a photovoltaic inverter ground impedance fault detection system and method. Background Art

[0002] When the inverter in a photovoltaic system is connected to or disconnected from the grid, it is often necessary to detect its ground impedance; by detecting the ground impedance, problems in the grounding system, such as poor grounding and broken ground wires, can be discovered in a timely manner, so as to take measures for repair to ensure the safe and stable operation of the photovoltaic system.

[0003] In the case of inverter grid connection, the ground impedance detection is often completed by detecting the leakage current to the ground. The leakage current detection can cover most cases of sudden changes in grounding and insulation impedance during the grid-connected operation of the inverter. When the inverter insulation impedance drops to a few ohms, a few hundred ohms, or when a capacitor is suddenly connected to the machine, the detection can be completed. However, the above situation will fail when the ground impedance of the inverter changes from several hundred k ohms to several tens of k ohms during the operation of the inverter.

[0004] In the case of inverter off-grid, the ground impedance detection is often completed by detecting the PV or bus voltage to the ground. The ground impedance detection through the ground voltage is more accurate; however, during the operation of the inverter, due to the operation of the switching tubes, the capacitor will achieve dynamic voltage equalization, so the online detection during the grid-connected operation of the inverter cannot be realized; and it will also fail when the ground impedance of the inverter changes from several hundred k ohms to several tens of k ohms during the operation of the inverter. Summary of the Invention

[0005] One object of the present application is to provide a photovoltaic inverter ground impedance fault detection system that can solve at least one defect in the above background art.

[0006] Another object of the present application is to provide a photovoltaic inverter ground impedance fault detection method that can solve at least one defect in the above background art.

[0007] To achieve at least one of the above objects, the technical solution adopted in the present application is: a photovoltaic inverter ground impedance fault detection system, including a PID repair circuit and a collection circuit; the PID repair circuit is connected in parallel between the negative terminal of the DC side bus of the inverter and the AC side, and the PID repair circuit is adapted to be equivalent to an LR circuit connected between the negative terminal of the DC side bus of the inverter and the ground in a non-operating state; the collection circuit is adapted to detect the inductance voltage of the LR circuit, so that when the mutation value of the inductance voltage of the LR circuit is detected to be greater than a set voltage threshold, it is determined that the inverter has a grounding fault.

[0008] Preferably, the output terminal of the acquisition circuit is signal-connected to a controller for controlling the inverter, and the controller performs a wave blocking process on the inverter according to the grounding fault determination result of the acquisition circuit.

[0009] Preferably, the acquisition circuit includes a voltage sampling unit with the voltage threshold built therein; the voltage sampling unit is adapted to collect the inductor voltage of the LR circuit and calculate the mutation value, and the voltage sampling unit is adapted to send the grounding fault judgment signal indicated by the comparison result of the mutation value and the voltage threshold to the controller.

[0010] Preferably, the acquisition circuit includes a voltage sampling unit and a fault judgment unit connected by signal; the voltage sampling unit is adapted to collect the inductor voltage of the LR circuit, calculate the mutation value and then send it to the fault judgment unit; the fault judgment unit is signal-connected to the controller, and the fault judgment unit compares the set voltage threshold with the received mutation value, and then sends a grounding fault judgment signal to the controller.

[0011] A method for detecting the ground impedance fault of a photovoltaic inverter includes the following on-line monitoring process: sampling the DC bus voltage when the inverter is operating in the grid-connected state; if the DC bus voltage does not mutate, the grounding fault of the inverter is judged through the above photovoltaic inverter ground impedance fault detection system, otherwise the leakage current of the inverter is sampled to judge the leakage current fault.

[0012] Preferably, when a grounding fault is detected in the scenario where the DC bus voltage does not mutate, it is adapted to detect the leakage current on the AC side of the inverter to locate the specific position of the grounding fault.

[0013] Preferably, the location of the grounding fault includes the following process: detecting the leakage current on the AC side of the inverter, if the leakage current is greater than or equal to the set first current threshold, it is determined that the grounding fault occurs outside the inverter, otherwise it is determined that the grounding fault occurs inside the inverter.

[0014] Preferably, the leakage current fault judgment includes the following process: detecting the leakage current on the AC side of the inverter, if the leakage current is greater than or equal to the set second current threshold, it is determined that the inverter has a leakage current fault, otherwise it is determined that the inverter is operating normally.

[0015] Preferably, the grounding fault detection process before the inverter starts is as follows: detecting the operating state of the inverter, if the inverter is operating in the grid-connected state, perform on-line monitoring of the grounding fault, otherwise judge the grounding fault through the ground voltage detection.

[0016] Preferably, the process of the inverter judging the grounding fault through the ground voltage detection is as follows: Detect the ground voltage of the inverter. If the ground voltage is within the set range, it is determined that the inverter has no grounding fault and grid connection is performed, and the online monitoring of the grounding fault is carried out after the grid connection is completed; otherwise, it is determined that the inverter has a grounding fault and cannot be grid-connected.

[0017] Compared with the prior art, the beneficial effects of this application are as follows: (1) Under the condition of stable DC bus, by detecting the voltage change on the equivalent inductor of the secondary side of the PID power supply, the grounding fault of the inverter is identified online, the identification speed of the grounding fault is accelerated, and the damage risk of the switching tube under the grounding fault is reduced.

[0018] (2) According to the voltage on the equivalent inductor of the secondary side of the PID power supply and the magnitude of the leakage current, the type of grounding fault occurring in the system is judged, and the location of the fault is located, which is convenient for subsequent fault maintenance. Description of the Drawings

[0019] Figure 1 It is a schematic diagram of the architecture of an existing photovoltaic inverter system.

[0020] Figure 2 It is a schematic diagram of the architecture of the photovoltaic inverter ground impedance fault detection system in this application.

[0021] Figure 3 It is a schematic diagram of the equivalent circuit of the PID repair circuit in this application in the non-working state.

[0022] Figure 4 It is a schematic diagram of the structure of one example of the acquisition circuit in this application.

[0023] Figure 5 It is a schematic diagram of the structure of another example of the acquisition circuit in this application.

[0024] Figure 6 It is a schematic diagram of the waveform of the grounding fault detection in this application.

[0025] Figure 7 It is a schematic diagram of the architecture of the photovoltaic inverter system when an accidental grounding occurs in this application.

[0026] Figure 8 It is a schematic diagram of the working process of the photovoltaic inverter ground impedance detection method in this application.

[0027] Figure 9 It is a schematic diagram of the working process of starting the inverter in this application.

[0028] In the figure: PID repair circuit 100, LR circuit 110, acquisition circuit 200, voltage sampling unit 210, controller 220, fault judgment unit 230. Detailed implementation manners

[0029] Next, in combination with the detailed implementation manners, the present application will be further described. It should be noted that in the description of this specification, the descriptions with reference to terms such as "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" mean that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic descriptions of the above terms should not be understood as necessarily referring to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. In addition, those skilled in the art can combine and combine the different embodiments or examples described in this specification.

[0030] In the description of the present application, it should be noted that for orientation terms, if there are terms such as "center", "horizontal", "longitudinal", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", etc., indicating the orientation and position relationship is based on the orientation or position relationship shown in the drawings. This is only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and should not be understood as limiting the specific protection scope of the present application.

[0031] It should be noted that the terms "first", "second", etc. in the description and claims of the present application are used to distinguish similar objects and do not necessarily need to describe a specific order or sequence.

[0032] In the present application, unless otherwise clearly defined and limited, terms such as "installed", "connected", "connected", "fixed", etc. should be understood in a broad sense. For example, it can be a connection, a detachable connection, or integrated; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two elements or the interaction relationship between two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0033] In the present application, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may include that the first and second features are in direct contact, or may include that the first and second features are not in direct contact but are in contact through another feature between them. Moreover, a first feature being "above", "above" and "above" a second feature includes that the first feature is directly above and obliquely above the second feature, or simply indicates that the first feature is higher in level than the second feature. A first feature being "below", "below" and "below" a second feature includes that the first feature is directly below and obliquely below the second feature, or simply indicates that the first feature is lower in level than the second feature.

[0034] The terms "including" and "having" and any variations thereof in the specification and claims of the present application are intended to cover non-exclusive inclusions. For example, a process, method, system, product or apparatus comprising a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to these processes, methods, products or apparatuses.

[0035] One aspect of the present application provides a photovoltaic inverter to ground impedance fault detection system, such as Figure 2 As shown, one preferred embodiment includes a PID repair circuit 100 and a collection circuit 200. The PID repair circuit 100 is connected in parallel to the negative end of the DC bus and the AC side of the inverter. The PID repair circuit 100 can be equivalent to an LR circuit 110 connected between the negative end of the DC bus of the inverter and the ground in a non-working state. The collection circuit 200 can detect the inductance voltage of the LR circuit 110, so that when it is detected that the inductance voltage mutation value of the LR circuit 110 is greater than the set voltage threshold, it is determined that a ground fault occurs in the inverter.

[0036] For ease of understanding, the specific architecture of the traditional photovoltaic inverter system can be briefly described below. Figure 1 As shown, the photovoltaic inverter system mainly includes photovoltaic modules PV, DC / DC circuit and DC / AC circuit; the output end of the photovoltaic module PV is connected to the input end of the DC / DC circuit, the output end of the DC / DC circuit is connected to the DC side input end of the DC / AC circuit through the DC bus, and the AC side output end of the DC / AC circuit is connected to the power grid through the filter inductor, control switch and leakage current sensor. Among them, the filter inductor includes the inductor L set in the three phases a , L b and L c The control switch includes a switch K arranged on the three phases. a , K b and K c The corresponding three-phase grid voltages are v ga 、vgb and v gc 。

[0037] The leakage current i of the photovoltaic inverter system cm is caused by the existence of parasitic capacitance between the photovoltaic inverter system and the ground. Thus, during the operation of the inverter, a loop of parasitic capacitance - photovoltaic inverter system - power grid will be formed, and the common-mode voltage will generate a common-mode current on the parasitic capacitance. Figure 1 The capacitance C in pv is the parasitic capacitance between the photovoltaic module PV and the ground; the capacitance C ac is the parasitic capacitance between the output end of the inverter and the ground.

[0038] When the grounding impedance of the photovoltaic inverter system decreases, the leakage current i cm will increase accordingly. Therefore, by detecting the leakage current i cm the detection of the grounding impedance can be completed when the inverter is connected to the grid. However, the leakage current sampling is completed by a leakage current sensor. The leakage current sensor obtains the magnitude of the system leakage current by detecting the sum of the three-phase currents. Ideally, the sum of the three-phase currents should be 0. Due to the existence of the parasitic capacitances C pv and C ac there will be current flowing from the power grid to the ground, making the sum of the three-phase currents not 0. At this time, the sum of the three-phase currents is the magnitude of the leakage current.

[0039] There is a certain delay from the change of the leakage current to the completion of sampling by the leakage current sensor. Since the time that the switching devices in the inverter can withstand the short-circuit current is very short, when using the method of detecting the leakage current to judge whether the system has a grounding fault, the switching devices of the inverter may have been damaged before the fault is recognized and protection measures are taken.

[0040] At the same time, when an incomplete grounding fault occurs in the photovoltaic inverter system, the grounding impedance is not reduced to one hundred Ω or below. For example, when the grounding impedance of the photovoltaic inverter system decreases from 500 kΩ to 50 kΩ, the change of the leakage current is not obvious, and the photovoltaic inverter system cannot recognize the grounding fault.

[0041] Compared with the traditional current detection method for grounding faults, this embodiment adopts voltage detection. Voltage detection only requires a resistor to complete the detection of voltage changes. Since the resistor itself can complete the detection without processes such as induction like a sensor, the detection time required is shorter than that of current detection. Since the voltage across the inductor in the circuit changes ahead of the current, this embodiment can identify the inductor voltage to judge the grounding fault, thereby improving the fault recognition speed and increasing the recognition range at the same time.

[0042] It can be understood that there are multiple ways to collect the inductance voltage for grounding fault identification. It can be based on the inductance components of the PV inverter system itself for voltage collection, or additional inductance components can be set for voltage collection. Considering that setting additional inductance components will increase costs and may affect the architecture of the PV inverter system itself, in this embodiment, it is preferably to collect the voltage of the inductance components of the PV inverter system itself to implement grounding fault judgment.

[0043] It should be known that there are multiple types of inductance components in the PV inverter system itself. It can be the filter inductance on the AC side of the inverter, or the inductance in the functional circuits additionally configured in the PV inverter system, such as the PID repair circuit 100, etc. The PID phenomenon is that when the inverter is operating in parallel with the grid, a relatively high potential difference is formed between the inside and the frame of the crystalline silicon module, which then generates leakage current, causing positive or negative ions to accumulate on the surface of the battery cells, forming an electrode effect. Or positively charged Na ions enter the battery interior, forming defect centers, which reduces the number of photo-generated carriers. To eliminate the influence of the PID phenomenon on the PV module PV, according to the principle of ionization reversibility, the PID repair circuit 100 can add a DC voltage between the negative terminal of the inverter DC bus and the ground at night, thereby repairing the ionization phenomenon of the PV module PV caused by the PID phenomenon.

[0044] That is, the PID repair circuit 100 is in a non-operating state during the day, and the grounding fault detection of the PV inverter system is generally carried out during the day. Therefore, to reduce the impact of grounding fault identification on the PV inverter system, in this embodiment, it is preferably to collect the voltage of the inductance in the PID repair circuit 100 to implement the judgment of the grounding fault.

[0045] Specifically, as Figure 2 shown, the PID repair circuit 110 can draw power from the AC side of the inverter, output a DC voltage through the PID power supply, with the positive output terminal connected to the negative terminal of the DC bus; the negative output terminal is connected to the ground. When the inverter is operating normally in parallel with the grid during the day, the PID repair circuit 100 is not working. At this time, the switch K 1 is disconnected, and the secondary side of the PID power supply can be equivalent to an LR circuit 110 formed by the series connection of an inductor L PID and a grounding resistance R PID .

[0046] As Figure 2 shown, Z PV+ and Z PV- respectively represent the positive terminal to ground impedance and the negative terminal to ground impedance of the PV module PV. Taking the DC bus negative terminal to ground loop as an example for analysis, the grounding equivalent circuit of the PV inverter system is as Figure 3 shown. Among them, U equis the equivalent voltage of the DC bus negative terminal to the ground loop, and Z equ is the corresponding equivalent internal resistance, and L PID is the equivalent inductance of the secondary side of the PID power supply, and R PID is the grounding resistance of the PID power supply.

[0047] When a negative terminal grounding fault occurs in the inverter, the equivalent impedance Z equ of the DC bus negative terminal to the ground decreases, causing the voltage of the DC bus negative terminal to the ground to decrease. At this time, due to the effect of the equivalent inductance L PID of the secondary side of the PID power supply, the current flowing through the grounding resistance R PID of the PID power supply cannot change suddenly, and the voltage across the inductor L PID changes suddenly. Therefore, it is possible to determine whether a grounding fault has occurred in the inverter by detecting the sudden change voltage across the equivalent inductance L PID of the secondary side of the PID power supply. That is, a voltage threshold V th is set. When the sudden change value V PID of the voltage across the equivalent inductance L L of the secondary side of the PID power supply is greater than the voltage threshold V th , it is determined that a grounding fault has occurred in the inverter.

[0048] It should be noted that during the operation of the inverter, the upper and lower bus capacitors C 1 and C 2 may be unevenly pressurized. Therefore, when specifically determining the value of the voltage threshold V th , those skilled in the art can make a reasonable setting according to the actual working conditions.

[0049] In this embodiment, as Figure 4 and Figure 5 show, the output signal of the acquisition circuit 200 is connected to a controller 220 for controlling the inverter. The controller 220 performs a wave blocking process on the inverter according to the grounding fault determination result of the acquisition circuit 200. That is, when the acquisition circuit 200 determines that a grounding fault has occurred in the inverter, the controller 220 will perform a wave blocking process on the inverter; when the acquisition circuit 200 determines that the inverter is operating normally, the controller 220 controls the inverter to maintain normal operation.

[0050] It can be understood that the specific structure and working principle of the controller 220 are well-known technologies to those skilled in the art, so they will not be elaborated in detail here. The controller 220 can use an independent control device to separately implement the determination of grounding faults, such as a CPLD, etc.; of course, the control function of the inverter can also be integrated into the main controller of the photovoltaic inverter system.

[0051] It should be noted that there are various specific structures of the acquisition circuit 200 that can realize the acquisition and judgment of the inductance voltage of the LR circuit 110. For the convenience of understanding, the following will be described in detail through two specific examples.

[0052] Example 1: As Figure 4 shown, the acquisition circuit 200 includes a voltage sampling unit 210 with a built-in voltage threshold. The acquisition end of the voltage sampling unit 210 is connected in parallel to both ends of the equivalent inductor L in the LR circuit 110 PID . The output end of the voltage sampling unit 210 is directly connected to the input end of the controller 220. The voltage sampling unit 210 can acquire the inductance voltage of the LR circuit 110 and calculate the mutation value. The voltage sampling unit 210 can send the grounding fault judgment signal error indicated by the comparison result of the mutation value and the voltage threshold to the controller 220, and then the controller 220 can send a corresponding control signal Lock to the inverter.

[0053] Example 2: As Figure 5 shown, the acquisition circuit 200 includes a voltage sampling unit 210 and a fault judgment unit 230 that are signal-connected. The acquisition end of the voltage sampling unit 210 is connected in parallel to both ends of the equivalent inductor L in the LR circuit 110 PID . The output end of the voltage sampling unit 210 is connected to the input end of the fault judgment unit 230. The voltage sampling unit 210 can acquire the inductance voltage of the LR circuit 110, calculate the mutation value, and then send it to the fault judgment unit 230; the fault judgment unit 230 is signal-connected to the controller 220. The fault judgment unit 230 compares the set voltage threshold with the received mutation value, and then sends a grounding fault judgment signal error to the controller 220. Subsequently, the controller 220 can send a corresponding control signal Lock to the inverter.

[0054] It can be understood that the above two examples can both meet the requirements of this application, and can be specifically selected according to the actual needs of those skilled in the art. The specific structure and working principle of the voltage sampling unit 210 are both well-known technologies to those skilled in the art. A common voltage sampling unit 210 can select a voltage sensor. The specific structure and working principle of the fault judgment unit 230 are also well-known technologies to those skilled in the art. A common fault judgment unit 230 can select a comparator or a logic gate circuit, etc.

[0055] For the convenience of understanding, the following will briefly describe its working process by taking the fault judgment unit 230 as a comparator. One input end of the comparator is connected to the output end of the voltage sampling unit 210, and the voltage threshold V thAs the input to the other input terminal of the comparator, the output terminal of the comparator is connected to the input terminal of the controller 220. When the voltage sampling unit 210 sends the mutation value V L of the inductor voltage it has collected to the comparator, the comparator compares the mutation value V L with the voltage threshold V th and sends the comparison result error to the controller 220.

[0056] For further understanding, the above-mentioned grounding fault detection process will be briefly described from the perspective of voltage waveforms. As Figure 6 shown, the bus voltage V bus always needs to be kept stable. At time t 1 , the voltage V PV- of the negative terminal of the DC bus to the ground decreases, causing a mutation value V L in the voltage across the equivalent inductor on the secondary side of the PID power supply. And if V L is greater than the voltage threshold V th , the blocking signal Lock output by the controller 220 is set to a high level, and the system recognizes a grounding fault and performs blocking processing on the inverter.

[0057] It should be noted that in the above-mentioned grounding fault detection process, if the DC bus voltage mutates, then a mutated voltage will also appear across the equivalent inductor on the secondary side of the PID power supply, which will cause the sampling result of the voltage sampling unit 210 to be inaccurate. Therefore, the photovoltaic inverter ground impedance fault detection system of the present application can only perform grounding fault detection when the DC bus voltage does not mutate, and when it is detected that the DC bus voltage mutates, the voltage across the equivalent inductor on the secondary side of the PID power supply is not used as the basis for judging grounding faults; at the same time, the ground impedance faults of the inverter include not only grounding faults but also leakage current faults. To ensure the normal operation of the ground impedance fault detection of the inverter, a photovoltaic inverter ground impedance fault detection method can be given below.

[0058] Another aspect of the present application provides a photovoltaic inverter ground impedance fault detection method. As Figure 8 shown, one preferred embodiment includes the following online monitoring process: sampling the DC bus voltage when the inverter is operating in the grid-connected state. If the DC bus voltage does not mutate, the grounding fault of the inverter is judged through the above-mentioned photovoltaic inverter ground impedance fault detection system; otherwise, the leakage current on the AC side of the inverter is sampled to judge the leakage current fault.

[0059] It can be understood that before performing ground fault detection, the DC bus voltage of the inverter can be sampled and detected first. If the DC bus voltage does not change suddenly, then the ground fault detection of the inverter can be judged by using the aforementioned mutation value of the equivalent inductance voltage on the secondary side of the PID power supply at this time. If the DC bus voltage changes suddenly, then the ground impedance fault condition of the inverter can be judged according to the change of the leakage current at this time.

[0060] It should be known that the occurrence of a ground fault in the inverter may be caused by the degradation of the internal insulation performance of the inverter, or may be caused by Figure 7 the leakage current i caused by the internal ground fault as shown in cm flowing to the ground accidentally through an accidental ground connection, and at this time the leakage current sensor cannot detect the increase of the leakage current. The occurrence of a ground fault in the inverter may also be caused by reasons such as the damage of the insulation layer of the external cable of the inverter. The external ground fault will cause an increase in the detected value of the inverter leakage current. Therefore, when a ground fault is detected in the scenario where the DC bus voltage does not change suddenly, the specific location of the ground fault can be located by detecting the leakage current on the AC side of the inverter. For the convenience of understanding, the specific location process of the ground fault will be described in detail below.

[0061] Specifically, as shown in Figure 8 the mutation value V of the equivalent inductance voltage on the secondary side of the PID power supply is sampled. If the detected mutation value V L is greater than or equal to the voltage threshold V L th , continue to detect the leakage current i on the AC side of the inverter. cm If the leakage current i cm th1 is greater than or equal to the set first current threshold I , it is determined that the ground fault occurs outside the inverter, otherwise it is determined that the ground fault occurs inside the inverter. It should be noted that the specific value of the first current threshold I th1 can be selected according to the actual needs of those skilled in the art.

[0062] In this embodiment, as shown in Figure 8 , the leakage current fault judgment includes the following process: detecting the leakage current on the AC side of the inverter. If the leakage current i cm is greater than or equal to the set second current threshold I th2 , it is determined that the inverter has a leakage current fault, otherwise it is determined that the inverter is operating normally. At the same time, when sampling the mutation value V of the equivalent inductance voltage on the secondary side of the PID power supply L , if the detected mutation value V L is less than the voltage threshold V th , it is also possible to continue to detect the leakage current i on the AC side of the inverter cm , and then judge whether it is a leakage current fault of the inverter by comparing it with the second current threshold I​th2 to determine whether a leakage current fault occurs in the inverter based on the comparison result. It should be noted that the specific value of the second current threshold I th2 can be selected by those skilled in the art according to their actual needs. The value of the second current threshold I th2 can be the same as the value of the first current threshold I th1 .

[0063] In this embodiment, to ensure the safe operation of the inverter, a ground fault detection is required before the inverter starts up; then the process of judging the ground fault based on the startup of the inverter is as follows: detect the operating state of the inverter. If the inverter is operating in the grid-connected state, perform online monitoring of the ground fault. Otherwise, judge the ground fault through the detection of the voltage to the ground.

[0064] Specifically, the process of the inverter judging the ground fault through the detection of the voltage to the ground is as follows: detect the voltage of the inverter to the ground. If the voltage to the ground is within the set range, it is determined that the inverter has no ground fault and grid connection is performed. After the grid connection is completed, online monitoring of the ground fault is performed; otherwise, it is determined that the inverter has a ground fault and cannot be grid-connected. It should be noted that for the normal range value of the voltage to the ground, those skilled in the art can select it according to the actual working conditions.

[0065] The above describes the basic principle, main features and advantages of the present application. Those skilled in the art of this industry should understand that the present application is not limited by the above embodiments. What is described in the above embodiments and the specification is only the principle of the present application. Without departing from the spirit and scope of the present application, the present application will have various changes and improvements, and these changes and improvements all fall within the scope of the present application claimed. The scope of protection required by the present application is defined by the appended claims and their equivalents.

Claims

1. A photovoltaic inverter ground impedance fault detection system, characterized in that: include: PID repair circuit; The PID repair circuit is connected in parallel to the negative end of the DC busbar and the AC side of the inverter. The PID repair circuit is suitable for being equivalent to an LR circuit connected between the negative end of the DC busbar and the ground in a non-working state; as well as Acquisition circuit; The acquisition circuit is suitable for detecting the inductance voltage of the LR circuit, so that when it is detected that the sudden change value of the inductance voltage of the LR circuit is greater than a set voltage threshold, it is determined that a ground fault occurs in the inverter.

2. The photovoltaic inverter ground impedance fault detection system according to claim 1, characterized in that: The output end signal of the acquisition circuit is connected to a controller for controlling the inverter, and the controller performs wave sealing processing on the inverter according to the ground fault identification result of the acquisition circuit.

3. The photovoltaic inverter ground impedance fault detection system according to claim 2, characterized in that: The acquisition circuit includes a voltage sampling unit with the voltage threshold built in; The voltage sampling unit is suitable for collecting the inductance voltage of the LR circuit and calculating the mutation value, and the voltage sampling unit is suitable for sending a ground fault judgment signal indicated by a comparison result between the mutation value and the voltage threshold to the controller.

4. The photovoltaic inverter ground impedance fault detection system according to claim 2, characterized in that: The acquisition circuit includes a voltage sampling unit and a fault judgment unit connected to the signal; The voltage sampling unit is adapted to collect the inductance voltage of the LR circuit and calculate the mutation value and then send it to the fault judgment unit; The fault judgment unit is connected to the controller by signal. The fault judgment unit compares the set voltage threshold with the received mutation value, and then sends a ground fault judgment signal to the controller.

5. A method for detecting a photovoltaic inverter ground impedance fault, characterized in that: The online monitoring process includes the following: Sampling the DC bus voltage when the inverter is working in the grid-connected state; If the DC bus voltage does not suddenly change, the ground fault of the inverter is judged by the photovoltaic inverter ground impedance fault detection system described in any one of claims 1 to 4, otherwise the leakage current of the inverter is sampled to judge the leakage current fault.

6. The photovoltaic inverter ground impedance fault detection method according to claim 5, characterized in that: When a ground fault is detected in a scenario where the DC bus voltage does not suddenly change, it is suitable to locate the specific position of the ground fault by detecting the leakage current on the AC side of the inverter.

7. The photovoltaic inverter ground impedance fault detection method according to claim 6, characterized in that: The location of the ground fault includes the following process: detecting the leakage current on the AC side of the inverter, if the leakage current is greater than or equal to the set first current threshold, it is determined that the ground fault occurs outside the inverter, otherwise it is determined that the ground fault occurs inside the inverter.

8. The photovoltaic inverter ground impedance fault detection method according to claim 5, characterized in that: The leakage current fault judgment includes the following process: detecting the leakage current on the AC side of the inverter, if the leakage current is greater than or equal to the set second current threshold, it is determined that the inverter has a leakage current fault, otherwise it is determined that the inverter is operating normally.

9. The photovoltaic inverter ground impedance fault detection method according to claim 5, characterized in that: The ground fault detection process before the inverter is started is as follows: the operating status of the inverter is detected. If the inverter is working in the grid-connected state, the ground fault is monitored online. Otherwise, the ground fault is judged by ground voltage detection.

10. The photovoltaic inverter ground impedance fault detection method according to claim 9, characterized in that: The process of the inverter judging the ground fault by ground voltage detection is as follows: detect the inverter's ground voltage. If the ground voltage is within the set range, it is determined that the inverter has no ground fault and is connected to the grid. After the grid connection is completed, online monitoring of the ground fault is performed; otherwise, it is determined that the inverter has a ground fault and cannot be connected to the grid.

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