A photovoltaic inverter ground impedance fault detection system and method

Abstract

The application discloses a photovoltaic inverter ground impedance fault detection system and method. The system comprises a PID repair circuit and a collection circuit. The PID repair circuit is connected in parallel on both sides of the inverter. The PID repair circuit is equivalent to an LR circuit connected between the negative terminal of the DC side of the inverter and the ground in the non-working state. The collection circuit is adapted to detect the inductance voltage of the LR circuit, so that when the inductance voltage mutation value of the LR circuit is greater than the set voltage threshold, it is determined that the inverter has a ground fault. The method uses the above-mentioned photovoltaic inverter ground impedance fault detection system to judge the ground fault of the inverter in the grid-connected state. The application has the beneficial effects that under the condition of stable DC bus, the voltage change on the equivalent inductance of the secondary side of the PID power supply is detected, the inverter ground fault is identified online, the identification speed of the ground fault is accelerated, and the damage risk of the switch tube under the ground fault is reduced.

Description

Technical Field

[0001] This application relates to the field of new energy power generation technology, and in particular to a system and method for detecting ground impedance faults in photovoltaic inverters. Background Technology

[0002] When the inverter of a photovoltaic system is connected to or off-grid, it is often necessary to test its ground impedance. By testing the ground impedance, problems in the grounding system can be detected in time, such as poor grounding or broken grounding wires, so that measures can be taken to repair them and ensure the safe and stable operation of the photovoltaic system.

[0003] In grid-connected inverter operation, grounding impedance is often measured by detecting leakage current to ground. Leakage current detection can cover most situations where grounding and insulation impedance changes suddenly occur during grid-connected inverter operation. It can be used to detect situations where the inverter's insulation impedance drops to a few ohms or hundreds of ohms, or when a capacitor is suddenly connected to the unit. However, it fails to detect situations where the inverter's grounding impedance changes from hundreds of kΩ to tens of kΩ during operation.

[0004] When the inverter is off-grid, grounding impedance is often detected by measuring the voltage of the PV or bus to ground. Grounding impedance detection by ground voltage has high accuracy; however, during inverter operation, due to the operation of the switching transistors, the capacitors will perform dynamic voltage equalization, so online detection cannot be achieved during the grid-connected operation of the inverter; and it will also fail when the grounding impedance changes from hundreds of k ohms to tens of k ohms during inverter operation. Summary of the Invention

[0005] One objective of this application is to provide a photovoltaic inverter ground impedance fault detection system that can solve at least one of the defects in the above-mentioned background art.

[0006] Another objective of this application is to provide a method for detecting ground impedance faults in photovoltaic inverters that can solve at least one of the defects in the aforementioned background art.

[0007] To achieve at least one of the above objectives, the technical solution adopted in this application is as follows: a photovoltaic inverter ground impedance fault detection system, comprising a PID repair circuit and a data acquisition circuit; the PID repair circuit is connected in parallel to the negative terminal of the DC bus and the AC side of the inverter, and the PID repair circuit is adapted to be equivalent to an LR circuit connected between the negative terminal of the DC bus and ground in the non-operating state; the data acquisition circuit is adapted to detect the inductor voltage of the LR circuit, so that when the detected inductor voltage mutation value of the LR circuit is greater than a set voltage threshold, the inverter is identified as having a ground fault.

[0008] Preferably, the output signal of the acquisition circuit is connected to a controller for controlling the inverter, and the controller performs waveform blocking processing on the inverter based on the ground fault identification result of the acquisition circuit.

[0009] Preferably, the acquisition circuit includes a voltage sampling unit with the voltage threshold built in; the voltage sampling unit is adapted to acquire the inductor voltage of the LR circuit and calculate the abrupt change value, and the voltage sampling unit is adapted to send the ground fault judgment signal indicated by the comparison result of the abrupt change 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 a signal connection; the voltage sampling unit is adapted to acquire the inductor voltage of the LR circuit and calculate the sudden change value before sending it to the fault judgment unit; the fault judgment unit is connected to the controller by a signal connection, and the fault judgment unit compares the received sudden change value with the set voltage threshold, and then sends a ground fault judgment signal to the controller.

[0011] A method for detecting ground impedance faults in a photovoltaic inverter includes the following online monitoring process: sampling the DC bus voltage when the inverter is operating in grid-connected mode; if the DC bus voltage does not change abruptly, the ground fault of the inverter is determined by the aforementioned photovoltaic inverter ground impedance fault detection system; otherwise, the leakage current of the inverter is sampled to determine the leakage current fault.

[0012] Preferably, when a ground fault is detected in a scenario where the DC bus voltage does not change abruptly, it is suitable to locate the specific location of the ground fault by detecting the leakage current on the AC side of the inverter.

[0013] Preferably, the location of a 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 a set first current threshold, the ground fault is determined to occur outside the inverter; otherwise, the ground fault is determined to occur inside the inverter.

[0014] Preferably, the leakage current fault judgment includes the following process: the leakage current on the AC side of the inverter is detected. If the leakage current is greater than or equal to the set second current threshold, the inverter is identified as having a leakage current fault; otherwise, the inverter is identified as operating normally.

[0015] Preferably, the ground fault detection process before the inverter starts up is as follows: the operating status of the inverter is detected. If the inverter is operating in grid-connected mode, online monitoring of ground faults is performed; otherwise, ground faults are determined by detecting the ground voltage.

[0016] Preferably, the process of the inverter judging ground fault by detecting the ground voltage is as follows: the inverter's ground voltage is detected. If the ground voltage is within the set range, the inverter is determined to have no ground fault and is connected to the grid. After the grid connection is completed, online monitoring of ground fault is performed; otherwise, the inverter is determined to have a ground fault and cannot be connected to the grid.

[0017] Compared with the prior art, the beneficial effects of this application are as follows:

[0018] (1) Under the condition of stable DC bus, the inverter ground fault can be identified online by detecting the voltage change on the equivalent inductance of the secondary side of the PID power supply, thereby accelerating the identification speed of ground fault and reducing the risk of damage to the switching transistor under ground fault.

[0019] (2) Based on the voltage and leakage current on the equivalent inductance of the secondary side of the PID power supply, determine the type of grounding fault in the system and locate the fault location to facilitate subsequent fault repair. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the architecture of an existing photovoltaic inverter system.

[0021] Figure 2 This is a schematic diagram of the architecture of the photovoltaic inverter ground impedance fault detection system in this application.

[0022] Figure 3 This is a schematic diagram of the equivalent circuit of the PID repair circuit in the non-operating state in this application.

[0023] Figure 4 This is a schematic diagram of one example of the acquisition circuit in this application.

[0024] Figure 5 This is a schematic diagram of another example of the acquisition circuit in this application.

[0025] Figure 6 This is a waveform diagram of ground fault detection in this application.

[0026] Figure 7 This is a schematic diagram of the architecture of the photovoltaic inverter system in this application when it is accidentally grounded.

[0027] Figure 8 This is a schematic diagram of the working process of the photovoltaic inverter-to-ground impedance detection method in this application.

[0028] Figure 9 This is a schematic diagram illustrating the inverter startup process for this application.

[0029] In the diagram: PID repair circuit 100, LR circuit 110, acquisition circuit 200, voltage sampling unit 210, controller 220, fault judgment unit 230. Detailed Implementation

[0030] The present application will now be further described in conjunction with specific embodiments. It should be noted that, in the description of this specification, the use of terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicates that the specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms should not be construed as necessarily referring to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. In addition, those skilled in the art can combine and integrate the different embodiments or examples described in this specification.

[0031] In the description of this application, it should be noted that the terms "center", "lateral", "longitudinal", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", etc., which indicate the orientation and positional relationship based on the orientation or positional relationship shown in the accompanying drawings, are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and should not be construed as limiting the specific protection scope of this application.

[0032] It should be noted that the terms "first," "second," etc., in the specification and claims of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence.

[0033] In this application, unless otherwise expressly specified and limited, the terms "installation," "connection," "joining," and "fixing," etc., should be interpreted broadly. For example, they can refer to a connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0034] In this application, unless otherwise expressly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature being directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature being directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0035] The terms “comprising” and “having”, and any variations thereof, in the specification and claims of this application are intended to cover non-exclusive inclusion, for example, a process, method, system, product, or device that includes a series of steps or units is not necessarily limited to those steps or units that are explicitly listed, but may include other steps or units that are not explicitly listed or that are inherent to such process, method, product, or device.

[0036] One aspect of this application provides a photovoltaic inverter ground impedance fault detection system, such as Figure 2 As shown, one preferred embodiment includes a PID repair circuit 100 and a data acquisition circuit 200. The PID repair circuit 100 is connected in parallel to the negative terminal of the DC bus and the AC side of the inverter. In its non-operating state, the PID repair circuit 100 can be equivalent to an LR circuit 110 connected between the negative terminal of the DC bus and ground. The data acquisition circuit 200 can detect the inductor voltage of the LR circuit 110, so that when a sudden change in the inductor voltage of the LR circuit 110 is detected to be greater than a set voltage threshold, a ground fault is identified in the inverter.

[0037] To facilitate understanding, a simple description of the specific architecture of a traditional photovoltaic inverter system will be provided below. For example... Figure 1 As shown, the photovoltaic inverter system mainly includes photovoltaic modules (PV), a DC / DC circuit, and a DC / AC circuit. The output of the photovoltaic modules (PV) is connected to the input of the DC / DC circuit. The output of the DC / DC circuit is connected to the DC input of the DC / AC circuit via a DC bus. The AC output of the DC / AC circuit is connected to the power grid via a filter inductor, a control switch, and a leakage current sensor. The filter inductor includes inductors L1 and L2 installed in the three phases. a L b and L c The control switches include switches K installed on the three phases. a K b and K c The corresponding three-phase grid voltages are v ga vgb and v gc .

[0038] Leakage current i of photovoltaic inverter system cm The cause of this is the existence of parasitic capacitance between the photovoltaic inverter system and the ground. As a result, during the operation of the inverter, a loop is formed between the parasitic capacitance, the photovoltaic inverter system, and the power grid, and the common-mode voltage will generate a common-mode current on the parasitic capacitance. Figure 1 Medium capacitor C pv The parasitic capacitance between the photovoltaic module (PV) and the ground; capacitance C ac This is the parasitic capacitance between the inverter output and ground.

[0039] When the grounding impedance of the photovoltaic inverter system decreases, the leakage current i cm The leakage current i will increase accordingly. cm Grounding impedance can be detected during inverter grid-connected operation. However, leakage current sampling is performed using a leakage current sensor. The leakage current sensor obtains 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 parasitic capacitance C. pv With C ac The presence of leakage current will cause current to flow through the power grid to the ground, making the sum of the three-phase currents non-zero. At this time, the sum of the three-phase currents is the magnitude of the leakage current.

[0040] Leakage current sensors require a certain delay from the change in leakage current to the completion of sampling. Since the switching devices in the inverter can only withstand short-circuit current for a very short time, using leakage current detection to determine whether a ground fault has occurred in the system may result in damage to the inverter's switching devices before the fault is detected and protective measures are taken.

[0041] Meanwhile, when a partial grounding fault occurs in the photovoltaic inverter system, the grounding impedance does not decrease to 100 kΩ or below. For example, if the grounding impedance of the photovoltaic inverter system decreases from 500 kΩ to 50 kΩ, the leakage current does not change significantly, and the photovoltaic inverter system cannot detect the grounding fault.

[0042] Compared to traditional current detection methods for ground faults, this embodiment uses voltage detection. Voltage detection only requires a resistor to detect voltage changes. Since a resistor does not require sensing or other processes like a sensor to complete the detection, its detection time is shorter than that of current detection. Because the voltage across the inductor in the circuit changes ahead of the current, this embodiment can identify the inductor voltage to determine the ground fault, thereby improving the speed of fault identification and increasing the identification range.

[0043] It is understandable that there are multiple ways to collect inductor voltage for ground fault identification. It can be based on the inductor element of the photovoltaic inverter system itself, or it can be based on additional inductor elements. Considering that additional inductor elements will increase costs and may affect the architecture of the photovoltaic inverter system itself, this embodiment prefers to collect voltage from the inductor element of the photovoltaic inverter system itself to achieve ground fault judgment.

[0044] It should be understood that photovoltaic inverter systems inherently possess various types of inductors. These can be filter inductors on the AC side of the inverter, or inductors in additional functional circuits of the photovoltaic inverter system, such as the PID repair circuit 100. The PID phenomenon occurs when a relatively high potential difference forms between the inside of the crystalline silicon module and its frame during grid-connected operation, leading to leakage current. This causes positive or negative ions to accumulate on the surface of the solar cells, forming an electrode effect. Alternatively, positively charged Na ions may enter the cell, forming defect centers, thus reducing the number of photogenerated carriers. To eliminate the impact of the PID phenomenon on the PV module, based on the principle of reversible ionization, the PID repair circuit 100 can apply a DC voltage between the negative terminal of the inverter's DC bus and ground at night, thereby repairing the ionization phenomenon in the PV module caused by the PID phenomenon.

[0045] Since the PID repair circuit 100 is inactive during the day, and ground fault detection in photovoltaic inverter systems is generally performed during the day, in order to reduce the impact of ground fault identification on the photovoltaic inverter system, this embodiment preferably uses voltage acquisition of the inductor in the PID repair circuit 100 to determine the ground fault.

[0046] Specifically, such as Figure 2 As shown, the PID repair circuit 110 draws power from the AC side of the inverter and outputs a DC voltage through the PID power supply. The positive terminal of the output is connected to the negative terminal of the DC bus; the negative terminal of the output is connected to ground. During the daytime, when the inverter is operating normally and connected to the grid, the PID repair circuit 100 does not operate. At this time, switch K1 is open, and the secondary side of the PID power supply can be equivalent to inductor L. PID With grounding resistance R PID The LR circuit 110 is formed by connecting them in series.

[0047] like Figure 2 As shown, Z PV+ and Z PV- Let these represent the positive and negative impedances of the photovoltaic module (PV) to ground, respectively. Taking the DC bus negative terminal to ground loop as an example, the equivalent grounding circuit of the photovoltaic inverter system is as follows: Figure 3 As shown. Where U equ Z is the equivalent voltage of the DC bus negative terminal to ground circuit. equTo correspond to the equivalent internal resistance, L PID R is the equivalent inductance of the secondary side of the PID power supply. PID This is the grounding resistor for the PID power supply.

[0048] When a negative-terminal ground fault occurs in the inverter, the equivalent impedance Z of the DC bus negative terminal to ground is... equ The voltage decreases, causing the DC bus negative terminal to ground to decrease. At this time, due to the equivalent inductance L on the secondary side of the PID power supply... PID The function of the current flowing through the PID power supply grounding resistor R PID The current cannot change abruptly, and the inductance L PID The voltage across the terminals changes abruptly. Therefore, this can be detected by detecting the equivalent inductance L on the secondary side of the PID power supply. PID The sudden voltage change at both ends is used to determine whether a ground fault has occurred in the inverter. That is, a voltage threshold V is set. th When the equivalent inductance L on the secondary side of the PID power supply is detected PID The sudden change in voltage V across the terminals L Greater than the voltage threshold V th When this occurs, it is determined that a ground fault has occurred in the inverter.

[0049] It should be noted that during inverter operation, uneven voltage distribution may occur between the upper and lower bus capacitors C1 and C2. Therefore, when setting the voltage threshold V... th When determining the specific value, those skilled in the art can set it reasonably according to the actual working conditions.

[0050] In this embodiment, as Figure 4 and Figure 5 As shown, the output signal of the acquisition circuit 200 is connected to a controller 220 for controlling the inverter. The controller 220 performs waveform blocking processing on the inverter based on the ground fault identification result of the acquisition circuit 200. That is, when the acquisition circuit 200 determines that a ground fault has occurred in the inverter, the controller 220 will perform waveform blocking processing on the inverter; when the acquisition circuit 200 determines that the inverter is in normal operation, the controller 220 controls the inverter to maintain normal operation.

[0051] It is understood that the specific structure and working principle of controller 220 are well-known technologies to those skilled in the art, and therefore will not be described in detail here. Controller 220 can be implemented independently by using a separate control device, such as a CPLD; of course, the control function of the inverter can also be integrated into the main controller of the photovoltaic inverter system.

[0052] It should be noted that there are various specific structures for the acquisition circuit 200 that can acquire and judge the inductor voltage of the LR circuit 110. For ease of understanding, two specific examples will be used to illustrate this in detail below.

[0053] Example 1: such as Figure 4 As shown, the acquisition circuit 200 includes a voltage sampling unit 210 with a built-in voltage threshold. The acquisition terminal of the voltage sampling unit 210 is connected in parallel to the equivalent inductor L in the LR circuit 110. PID At both ends, the output of the voltage sampling unit 210 is directly connected to the input of the controller 220. The voltage sampling unit 210 can collect the inductor voltage of the LR circuit 110 and calculate the sudden change value. The voltage sampling unit 210 can send the ground fault judgment signal error indicated by the comparison result of the sudden change value and the voltage threshold to the controller 220, and then the controller 220 can send the corresponding control signal Lock to the inverter.

[0054] Example 2: such as Figure 5 As shown, the acquisition circuit 200 includes a voltage sampling unit 210 and a fault judgment unit 230 connected in signal connection. The acquisition terminal of the voltage sampling unit 210 is connected in parallel to the equivalent inductor L in the LR circuit 110. PID At both ends, the output of the voltage sampling unit 210 is connected to the input of the fault judgment unit 230. The voltage sampling unit 210 can collect the inductor voltage of the LR circuit 110, calculate the sudden change value, and send it to the fault judgment unit 230. The fault judgment unit 230 is connected to the controller 220. The fault judgment unit 230 compares the received sudden change value with the set voltage threshold, and then sends a ground fault judgment signal error to the controller 220. Subsequently, the controller 220 can send the corresponding control signal Lock to the inverter.

[0055] It is understood that both of the above examples can meet the requirements of this application, and the specific choice can be made according to the actual needs of those skilled in the art. The specific structure and working principle of the voltage sampling unit 210 are well known to those skilled in the art, and a voltage sensor can be selected as a common voltage sampling unit 210. The specific structure and working principle of the fault judgment unit 230 are also well known to those skilled in the art, and a comparator or logic gate circuit can be selected as a common fault judgment unit 230.

[0056] To facilitate understanding, the following is a simple description of the operation of the fault judgment unit 230 using a comparator as an example. One of the input terminals of the comparator is connected to the output terminal of the voltage sampling unit 210, and the voltage threshold V... th As another input to the comparator, the comparator's output is connected to the input of the controller 220. When the voltage sampling unit 210 samples the abrupt change in the inductor voltage V... L After being sent to the comparator, the comparator evaluates the mutation value V. L With voltage threshold V thThe comparison is performed, and the error result is sent to controller 220.

[0057] To further understand this, the above-described ground fault detection process will be briefly described from the perspective of voltage waveforms. For example... Figure 6 As shown, the bus voltage V bus The voltage V at the negative terminal of the DC bus to ground must always remain stable at time t1. PV- The decrease causes a sudden change in the voltage V across the equivalent inductance of the secondary side of the PID power supply. L And V L Greater than the voltage threshold V th If the Lock signal output by controller 220 is set to a high level, the system will detect the ground fault and perform the inverter's blocking process.

[0058] It is important to note that during the aforementioned grounding fault detection process, if the DC bus voltage undergoes a sudden change, a sudden voltage change will also occur across the equivalent inductance of the PID power supply secondary side, which will cause inaccurate sampling results from the voltage sampling unit 210. Therefore, the photovoltaic inverter ground impedance fault detection system of this application can only perform grounding fault detection when the DC bus voltage does not undergo a sudden change. When a sudden change in the DC bus voltage is detected, the voltage across the equivalent inductance of the PID power supply secondary side is not used as the basis for grounding fault judgment. Furthermore, inverter ground impedance faults include not only grounding faults but also leakage current faults. To ensure the normal operation of inverter ground impedance fault detection, a photovoltaic inverter ground impedance fault detection method is provided below.

[0059] Another aspect of this application provides a method for detecting ground impedance faults in photovoltaic inverters, such as... Figure 8 As shown, one preferred embodiment includes the following online monitoring process: sampling the DC bus voltage while the inverter is operating in grid-connected mode. If the DC bus voltage does not change abruptly, the inverter's grounding fault is determined using the aforementioned photovoltaic inverter-to-ground impedance fault detection system; otherwise, the leakage current on the inverter's AC side is sampled for leakage current fault determination.

[0060] Understandably, before performing ground fault detection, the inverter's DC bus voltage can be sampled and detected. If the DC bus voltage does not change abruptly, then the ground fault detection of the inverter can be determined using the aforementioned change in the equivalent inductance voltage of the PID power supply secondary side. If the DC bus voltage changes abruptly, then the inverter's ground impedance fault can be determined based on the change in leakage current.

[0061] It should be understood that a ground fault in an inverter may be caused by a decline in the internal insulation performance of the inverter, or it may be due to other reasons. Figure 7The leakage current i caused by the internal grounding fault shown cm An accidental grounding failure will cause the current to flow to the ground, at which point the leakage current sensor will not detect an increase in leakage current. Grounding faults in the inverter can also be caused by damage to the insulation of external cables, leading to an increase in the inverter's leakage current detection value. Therefore, when a grounding fault is detected without a sudden change in the DC bus voltage, the specific location of the grounding fault can be determined by detecting the leakage current on the AC side of the inverter. For ease of understanding, the specific process for locating a grounding fault will be explained in detail below.

[0062] Specifically, such as Figure 8 As shown, the sudden change value V of the equivalent inductor voltage on the secondary side of the PID power supply is... L Sampling is performed, and if a mutation value V is detected... L Greater than or equal to voltage threshold V th Continue monitoring the leakage current i on the AC side of the inverter. cm Perform the test. If the leakage current i cm Greater than or equal to the set first current threshold I th1 If the ground fault occurs outside the inverter, it is assumed to occur inside the inverter; otherwise, it is assumed to occur inside the inverter. It is important to note the first current threshold I. th1 The specific value can be selected by those skilled in the art based on their actual needs.

[0063] In this embodiment, as Figure 8 As shown, the leakage current fault diagnosis includes the following process: The leakage current on the AC side of the inverter is detected; if the leakage current i... cm Greater than or equal to the set second current threshold I th2 If the inverter experiences a leakage current fault, it is considered to have a fault; otherwise, the inverter is considered to be operating normally. Simultaneously, the sudden change in the equivalent inductor voltage V on the secondary side of the PID power supply is considered. L During sampling, if a mutation value V is detected L Less than the voltage threshold V th Alternatively, the leakage current i on the AC side of the inverter can be further monitored. cm The detection is performed, and then compared with the second current threshold I. th2 The comparison results are used to determine whether the inverter has a leakage current fault. It is important to note the second current threshold I. th2 The specific value can be selected by those skilled in the art based on their actual needs, the second current threshold I th2 The value can be related to the first current threshold I. th1 The values ​​are the same.

[0064] In this embodiment, in order to ensure the safe operation of the inverter, ground fault detection is required before the inverter is started. The process of ground fault judgment based on the inverter startup is as follows: the operating status of the inverter is detected. If the inverter is operating in grid-connected state, online monitoring of ground fault is performed. Otherwise, ground fault judgment is performed by detecting the ground voltage.

[0065] Specifically, the process of determining a ground fault in the inverter through ground voltage detection is as follows: The inverter's ground voltage is detected. If the ground voltage is within a set range, the inverter is considered to have no ground fault and is connected to the grid. After grid connection is completed, online monitoring of the ground fault is performed. Otherwise, the inverter is considered to have a ground fault and cannot be connected to the grid. It should be noted that those skilled in the art can select the normal range for the ground voltage based on actual operating conditions.

[0066] The basic principles, main features, and advantages of this application have been described above. Those skilled in the art should understand that this application is not limited to the above embodiments. The embodiments and descriptions in the specification are merely the principles of this application. Various changes and modifications can be made to this application without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claims. The scope of protection claimed by this application is defined by the appended claims and their equivalents.

Claims

1. A method for detecting ground impedance faults in a photovoltaic inverter, characterized in that, This includes the following online monitoring process: Sampling of DC bus voltage is performed when the inverter is operating in grid-connected mode; If the DC bus voltage does not change abruptly, the inverter grounding fault is determined by the photovoltaic inverter ground impedance fault detection system; otherwise, the leakage current of the inverter is sampled to determine the leakage current fault. The photovoltaic inverter ground impedance fault detection system includes: PID repair circuit; the PID repair circuit is connected in parallel to the negative terminal of the DC bus and the AC side of the inverter, and the PID repair circuit is adapted to be equivalent to an LR circuit connected between the negative terminal of the DC bus and ground in the non-operating state; and Acquisition circuit; the acquisition circuit is adapted to detect the inductor voltage of the LR circuit, so that when the detected sudden change value of the inductor voltage of the LR circuit is greater than a set voltage threshold, it is determined that the inverter has a ground fault. When a ground fault is detected in a scenario where the DC bus voltage does not change abruptly, it is suitable to locate the specific location of the ground fault by detecting the leakage current on the AC side of the inverter. The location of ground faults includes the following process: the leakage current on the AC side of the inverter is detected. If the leakage current is greater than or equal to the set first current threshold, the ground fault is determined to occur outside the inverter; otherwise, the ground fault is determined to occur inside the inverter. Leakage current fault detection includes the following process: detect 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, the inverter is considered to have a leakage current fault; otherwise, the inverter is considered to be operating normally. The ground fault detection process before inverter startup is as follows: The operating status of the inverter is detected. If the inverter is operating in grid-connected mode, online monitoring of ground faults is performed; otherwise, ground faults are determined by detecting the ground voltage.

2. The method for detecting ground impedance faults in photovoltaic inverters as described in claim 1, characterized in that, The output signal of the acquisition circuit is connected to a controller for controlling the inverter. The controller performs waveform blocking processing on the inverter based on the ground fault identification result of the acquisition circuit.

3. The method for detecting ground impedance faults in photovoltaic inverters as described in claim 2, characterized in that, The acquisition circuit includes a voltage sampling unit with the voltage threshold built in; The voltage sampling unit is adapted to collect the inductor voltage of the LR circuit and calculate the abrupt change value. The voltage sampling unit is also adapted to send the ground fault judgment signal indicated by the comparison result of the abrupt change value and the voltage threshold to the controller.

4. The method for detecting ground impedance faults in photovoltaic inverters as described in claim 2, characterized in that, The acquisition circuit includes a voltage sampling unit and a fault judgment unit with signal connection; The voltage sampling unit is adapted to collect the inductor voltage of the LR circuit, calculate the sudden change value, and then send it to the fault judgment unit; The fault judgment unit is connected to the controller by a signal. The fault judgment unit compares the set voltage threshold with the received sudden change value, and then sends a ground fault judgment signal to the controller.

5. The method for detecting ground impedance faults in photovoltaic inverters as described in claim 1, characterized in that, The process of the inverter judging ground fault by detecting the ground voltage is as follows: the inverter's ground voltage is detected. If the ground voltage is within the set range, the inverter is determined to have no ground fault and is connected to the grid. After the grid connection is completed, the online monitoring of ground fault is performed; otherwise, the inverter is determined to have a ground fault and cannot be connected to the grid.

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