Arc fault detection circuit, photovoltaic inverter and photovoltaic system

Abstract

The utility model relates to the field of photovoltaic systems, in particular to an arc fault detection circuit, a photovoltaic inverter and a photovoltaic system. The arc detection circuit comprises at least one current detection unit which is used for being coupled with lines connected with a plurality of corresponding input ends so as to detect current signals of the lines connected with the input ends; the signal conversion unit is connected with the at least one current detection unit and is used for converting the current signal into a voltage signal; the signal processing unit is connected with the signal conversion unit and is used for processing the voltage signal to obtain a digital sampling signal; and the first control unit is connected with the signal processing unit and is used for determining whether an arc fault exists in a line connected with the plurality of input ends according to the digital sampling signal. The circuit is simple in structure, the size of the photovoltaic inverter is reduced, and the cost is saved.

Description

Technical Field

[0001] The present application relates to the field of photovoltaic power generation, and in particular to an arc fault detection circuit, a photovoltaic inverter and a photovoltaic system. Background Art

[0002] Solar energy is a widely distributed clean energy. In recent years, the installed capacity of photovoltaic power generation has been increasing around the world. However, there are some safety hazards in photovoltaic power generation systems. For example, insulation damage caused by aging of the line or animal gnawing may cause arc faults. In addition, the photovoltaic DC power supply outputs direct current, which does not naturally cross the zero point to automatically extinguish the arc. The high heat generated by the continuous burning of the arc may ignite nearby combustibles, causing fires, resulting in significant property losses or casualties.

[0003] Usually, a current transformer is connected in series in the input line of the photovoltaic inverter to detect the current, and the signal output by the current transformer is transmitted to the signal processing circuit to realize arc detection. If the photovoltaic inverter has multiple input lines, each input line requires a current transformer and a signal processing circuit, which will greatly increase the cost and the complexity of the circuit. Utility Model Content

[0004] Based on this, it is necessary to provide an arc fault detection circuit, a photovoltaic inverter and a photovoltaic system to address the above technical problems.

[0005] In a first aspect, an embodiment of the present application provides an arc fault detection circuit for a photovoltaic inverter, wherein the photovoltaic inverter has a plurality of input terminals, wherein the input terminals are used to connect to a photovoltaic DC power supply, and the arc detection circuit comprises:

[0006] At least one current detection unit, the current detection unit is used to couple with the lines connected to the corresponding multiple input terminals to detect the current signal of the line connected to each of the input terminals;

[0007] a signal conversion unit, connected to the at least one current detection unit, and configured to convert a current signal into a voltage signal;

[0008] A signal processing unit, connected to the signal conversion unit, for performing signal processing on the voltage signal to obtain a digital sampling signal;

[0009] The first control unit is connected to the signal processing unit and is used to determine whether there is an arc fault in the lines connected to the multiple input terminals according to the digital sampling signal.

[0010] In one embodiment, the current detection unit comprises a current transformer, and the current transformer is coupled to the lines to which the plurality of input terminals are connected.

[0011] In one embodiment, the signal conversion unit includes a first resistor, and the first resistor is connected in parallel to the output end of each of the current detection units.

[0012] In one embodiment, the signal processing unit includes:

[0013] A filter circuit, used for filtering the voltage signal;

[0014] An operational amplifier circuit, connected to the filter circuit, for amplifying the filtered voltage signal;

[0015] The analog-to-digital converter is connected to the operational amplifier circuit and is used to perform analog-to-digital conversion on the filtered and amplified voltage signal to obtain the digital sampling signal.

[0016] In one embodiment, the cutoff frequency of the filter circuit is adjustable, and the first control unit adjusts the cutoff frequency of the filter circuit multiple times to obtain digital sampling signals corresponding to current signals in different frequency bands.

[0017] In one embodiment, the filtering circuit includes a high-pass filter and a low-pass filter connected in series, or at least two high-pass filters connected in series.

[0018] In one embodiment, the high-pass filter includes a first operational amplifier, a first adjustable resistor, a second adjustable resistor, a first capacitor and a second capacitor, the first capacitor and the second capacitor are connected in series at the non-inverting input terminal of the first operational amplifier, one end of the first adjustable resistor is connected to a reference voltage source, and the other end is connected to the non-inverting input terminal of the first operational amplifier; the second adjustable resistor is connected between the middle node between the first capacitor and the second capacitor and the inverting input terminal of the first operational amplifier, and the inverting input terminal of the first operational amplifier is connected to its output terminal.

[0019] In one embodiment, the low-pass filter includes a second operational amplifier, a third adjustable resistor, a fourth adjustable resistor, a third capacitor and a fourth capacitor, the third adjustable resistor and the fourth adjustable resistor are connected in series at the non-inverting input terminal of the second operational amplifier, one end of the fourth capacitor is connected to a reference voltage source, and the other end is connected to the non-inverting input terminal of the second operational amplifier; the third capacitor is connected between the middle node between the third adjustable resistor and the fourth adjustable resistor and the inverting input terminal of the second operational amplifier, and the inverting input terminal of the second operational amplifier is connected to its output terminal.

[0020] In one embodiment, each of the input terminals is connected to a photovoltaic DC power supply through a switching circuit, and the switching circuit includes at least one switching element connected between the corresponding input terminal and the photovoltaic DC power supply. When an arc fault occurs, the first control unit outputs a control signal to control each of the switching circuits to cut off the output of each of the photovoltaic DC power supplies.

[0021] In one embodiment, the photovoltaic inverter further includes a first communication unit communicating with the switch circuit, the first communication unit receives the control signal and provides a communication signal to the switch circuit, and the switch circuit controls the on and off of the switch element according to the communication signal.

[0022] In the second aspect, the embodiment of the present application proposes a photovoltaic inverter, including multiple input terminals, multiple outputs, a DC-DC circuit connected in parallel, and a DC-AC circuit, wherein the multiple DC-DC circuits are respectively connected to corresponding input terminals, the DC-AC circuit is connected to the multiple DC-DC circuits, the input terminal is used to access a photovoltaic DC power supply, and the photovoltaic inverter also includes the arc fault detection circuit as described in the first aspect.

[0023] In a third aspect, an embodiment of the present application proposes a photovoltaic system, comprising a plurality of photovoltaic DC power supplies, and a photovoltaic inverter as described in the first aspect connected to the plurality of photovoltaic DC power supplies.

[0024] In one embodiment, the photovoltaic system further includes a plurality of switch circuits, which are connected between corresponding input terminals of the photovoltaic inverter and corresponding photovoltaic DC power sources, and include at least one switch element for controlling the output of the corresponding photovoltaic DC power source.

[0025] Compared with the related art, the arc detection circuit in the present application utilizes at least one current detection unit to couple with the lines connected to the corresponding multiple input terminals, and the multiple lines share one current detection unit to detect whether there is an arc fault in the lines connected to the input terminals. The circuit structure of the present application is simple, the volume of the photovoltaic inverter is reduced, and the cost is saved. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 A schematic diagram of the structure of an arc fault detection circuit in an embodiment provided by the present application;

[0027] Figure 2 A schematic structural diagram of a photovoltaic system in the first embodiment provided in this application;

[0028] Figure 3 A schematic diagram of the structure of a signal processing unit in the first embodiment provided in this application;

[0029] Figure 4A circuit structure diagram of a high-pass filter in the first embodiment provided in this application;

[0030] Figure 5 A circuit structure diagram of a low-pass filter in the first embodiment provided in this application;

[0031] Figure 6 A schematic diagram of the structure of the switch circuit in the first embodiment provided in this application;

[0032] Figure 7 A circuit structure diagram of a switch unit in the first embodiment provided in this application;

[0033] Figure 8 A circuit structure diagram of a DC-DC circuit in a first embodiment provided in the present application;

[0034] Fig. 9 This is a schematic structural diagram of a photovoltaic system in the second embodiment provided in the present application. DETAILED DESCRIPTION

[0035] In order to make the purpose, technical solutions and advantages of the present application clearer, the present application is described and illustrated below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not intended to limit the present application. Based on the embodiments provided in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present application. In addition, it can also be understood that although the efforts made in this development process may be complex and lengthy, for ordinary technicians in the field related to the contents disclosed in the present application, some changes such as design, manufacturing or production based on the technical contents disclosed in the present application are only conventional technical means, and should not be understood as insufficient contents disclosed in the present application.

[0036] Reference to "embodiments" in this application means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those of ordinary skill in the art that the embodiments described in this application may be combined with other embodiments without conflict.

[0037] Unless otherwise defined, the technical terms or scientific terms involved in this application should be understood by people with ordinary skills in the technical field to which this application belongs. The words "one", "a", "a", "the" and the like involved in this application do not indicate a quantitative limitation, and may represent the singular or plural. The terms "include", "comprise", "have" and any of their variations involved in this application are intended to cover non-exclusive inclusions; for example, a process, method, system, product or device that includes a series of steps or modules (units) is not limited to the listed steps or units, but may also include steps or units that are not listed, or may also include other steps or units inherent to these processes, methods, products or devices. The words "connect", "connected", "coupled" and the like involved in this application are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. The "multiple" involved in this application refers to greater than or equal to two. "And / or" describes the association relationship of associated objects, indicating that there can be three relationships, for example, "A and / or B" can represent: A exists alone, A and B exist at the same time, and B exists alone. The terms "first", "second", "third" and the like involved in the present application are merely used to distinguish similar objects and do not represent a specific ordering of the objects.

[0038] The embodiment of the present application proposes an arc fault detection circuit for a photovoltaic inverter, wherein the photovoltaic inverter has multiple input terminals, and the input terminals are used to connect to a photovoltaic DC power supply. The arc detection circuit includes: at least one current detection unit 331, and the current detection unit 331 is used to couple with the lines connected to the corresponding multiple input terminals to detect the current signal of the lines connected to each of the input terminals; a signal conversion unit 332, connected to the at least one current detection unit 331, and used to convert the current signal into a voltage signal; a signal processing unit 333, connected to the signal conversion unit 332, and used to perform signal processing on the voltage signal to obtain a digital sampling signal; a first control unit 334, connected to the signal processing unit 333, and used to determine whether there is an arc fault in the lines connected to the multiple input terminals based on the digital sampling signal.

[0039] There is current in the line connected to the input end of the inverter. When there is an arc in the line, the current detection unit 331 will induce a current signal of the corresponding frequency. The signal conversion unit 332 converts the current signal into a voltage signal. The signal processing unit 333 processes the voltage signal to obtain a digital sampling signal. The first control unit 334 performs calculations and determines whether there is an arc fault based on the digital sampling signal. In this embodiment, the current detection unit 331 detects the current signal of the line connected to the multiple input ends coupled thereto, and the lines of the multiple input ends share one current detection unit 331, which can reduce the number of current detection units 331 and the subsequent circuits. In addition, when there are multiple current detection units 331, the multiple current detection units 331 share the subsequent circuit. Therefore, the circuit structure of the arc fault detection circuit of this embodiment is simpler, which reduces the volume of the photovoltaic inverter and saves costs.

[0040] When there are fewer input terminals, only one current detection unit 331 may be used to collect current signals in all circuits.

[0041] The first control unit 334 can be any one of a microcontroller unit (MCU), a central processing unit (CPU), a field programmable gate array (FPGA), and a digital signal processor (DSP). Of course, the specific form of the first control unit 334 is not limited to the above examples.

[0042] Figure 2 A schematic diagram of the structure of a photovoltaic system in the first embodiment provided in the present application. The photovoltaic system includes a plurality of photovoltaic DC power supplies 10, a switch circuit 20 correspondingly connected to each of the photovoltaic DC power supplies 10, and a photovoltaic inverter 30 connected to the plurality of switch circuits 20. The photovoltaic inverter 30 includes a plurality of input terminals, a plurality of outputs connected in parallel to a DC-DC circuit 310, and a DC-AC circuit 320, wherein the plurality of DC-DC circuits 310 are respectively connected to corresponding input terminals, the DC-AC circuit 320 is connected to the plurality of DC-DC circuits 310, the input terminals are used to access the photovoltaic DC power supplies 10, and the photovoltaic inverter 30 also includes an arc fault detection circuit 330.

[0043] The photovoltaic DC power source may be a single photovoltaic module, a single photovoltaic cell substring, a plurality of photovoltaic modules connected in series and / or in parallel, or a plurality of photovoltaic cell substrings connected in series and / or in parallel.

[0044] In this embodiment, only one current detection unit 331 is used to collect current signals in all circuits. Figure 2 As shown, the current detection unit 331 includes a current transformer, and the current transformer is coupled with the lines connected to the multiple input terminals. The lines connected to the multiple input terminals (i.e., input lines) pass through the magnetic ring of the current transformer, and each input line only passes through one positive line or negative line, and the positive line or negative line passed through is consistent, and the current transformer can collect current signals in multiple input lines. When an arc fault occurs in any of the input lines, the frequency spectrum of the current signal obtained by the first control unit 334 will be abnormal, and it can be judged whether an arc fault has occurred. Therefore, this embodiment reduces the number of current detection units 331 and their subsequent circuits.

[0045] The signal conversion unit 332 includes a first resistor Rd, and the first resistor Rd is connected in parallel with the output end of the current detection unit 331. The first resistor Rd can convert the current signal into a voltage signal.

[0046] like Figure 3 As shown, the signal processing unit 333 includes: a filter circuit 3331, used to filter the voltage signal; an operational amplifier circuit 3332, connected to the filter circuit 3331, used to amplify the filtered voltage signal; an analog-to-digital converter 3333, connected to the operational amplifier circuit 3332, used to perform analog-to-digital conversion on the filtered and amplified voltage signal to obtain the digital sampling signal.

[0047] The operational amplifier circuit 3332 includes at least one operational amplifier.

[0048] The first control unit 334 determines whether an arc has occurred on the line according to the digital sampling signal. Exemplarily, the first control unit 334 stores the spectrum characteristics of the current signal when an arc fault occurs (for example, the amplitude of the current signal in different frequency bands), including which frequency bands have relatively high amplitudes of the current signal. The first control unit 334 obtains the spectrum characteristics of the current signal according to the digital sampling signal, and compares the spectrum characteristics obtained in real time with the stored spectrum characteristics of the current signal when an arc fault occurs. If the spectrum characteristics when an arc fault occurs are met, it is determined that an arc fault has occurred at this time.

[0049] Conventional arc fault detection is to detect current signals with a frequency in the range of 30kHz-200kHz. Since the frequency range is relatively wide, it is easy to be interfered by other signals of normal operation inside the photovoltaic inverter 30, thus causing misjudgment.

[0050] To solve this technical problem, in some embodiments, the signal processing unit 333 can process the voltage signal in frequency bands, processing only the voltage signal of the corresponding frequency band each time, and obtaining digital sampling signals corresponding to the current signals of different frequency bands through multiple processing.

[0051] Specifically, the cutoff frequency of the filter circuit 3331 can be set to be adjustable. The filter circuit 3331 only passes the voltage signal of the frequency band corresponding to the current cutoff frequency each time, and filters out the voltage signals of other frequency bands until the signals of all desired frequency bands are sampled.

[0052] The first control unit 334 adjusts the cutoff frequency of the filter circuit 3331 multiple times, and detects the current signals of different frequency bands separately to obtain the digital sampling signals corresponding to the current signals of different frequency bands. Since the current signal of a wider frequency range is divided into multiple current signals of different frequency bands with smaller frequency ranges, the signal interference from the inside of the photovoltaic inverter 30 can be reduced, and the spectrum data of the current signal of each frequency band can be obtained more accurately. Therefore, this embodiment can more accurately realize the detection of arc faults.

[0053] Taking the current signal with a frequency in the range of 30kHz-200kHz as an example, the current signal in the range of 30kHz-200kHz is separated into several frequency bands by adjusting the cutoff frequency of the filter circuit 3331. For example, the first control unit 334 adjusts the cutoff frequency of the filter circuit 3331 to first obtain the digital sampling signal corresponding to the current signal in the frequency band of 30kHz-60kHz, and then the first control unit 334 adjusts the cutoff frequency of the filter circuit 3331 again to obtain the digital sampling signal corresponding to the current signal in the frequency band of 60kHz-90kHz, ..., until the current signals in the range of 30kHz-200kHz are sampled, and finally the first control unit 334 determines whether there is an arc fault according to the frequency spectrum characteristics corresponding to the current signal in the range of 30kHz-200kHz.

[0054] For example, if the switching frequency of the DC-DC circuit 310 in the photovoltaic inverter 30 is 40kHz, then when the current signal in the frequency band of 70kHz to 100kHz is collected separately, the influence of the DC-DC circuit 310 will be relatively small, and the sampling will be more accurate. Therefore, through segmented detection, the first control unit 334 can more accurately realize the detection of arc faults.

[0055] It should be noted that the signal processing unit 333 with frequency band processing function in this embodiment can also be used in an arc fault detection circuit in which a current detection unit is coupled one-to-one with an input line, and can also be used in a photovoltaic inverter with a single input terminal.

[0056] In some embodiments, the filter circuit 3331 can be composed of a low-pass filter and a high-pass filter with adjustable cutoff frequency, and the high-pass filter and the low-pass filter can be connected in series, and the order of front and back is not fixed. The filter circuit 3331 can also be composed of two high-pass filters with adjustable cutoff frequencies, and the two high-pass filters are connected in series to obtain a better filtering effect.

[0057] like Figure 4 As shown, the high-pass filter includes a first operational amplifier OPA, a first adjustable resistor R1, a second adjustable resistor R2, a first capacitor C1 and a second capacitor C2, the first capacitor C1 and the second capacitor C2 are connected in series at the non-inverting input terminal of the first operational amplifier OPA, one end of the first adjustable resistor R1 is connected to a reference voltage source Vref, and the other end is connected to the non-inverting input terminal of the first operational amplifier OPA; the second adjustable resistor R2 is connected between the middle node of the first capacitor C1 and the second capacitor C2 and the inverting input terminal of the first operational amplifier OPA, and the inverting input terminal of the first operational amplifier OPA is connected to its output terminal.

[0058] Specifically, the cutoff frequency of the high-pass filter is related to the resistance values ​​of the first adjustable resistor R1 and the second adjustable resistor R2, and the cutoff frequency can be adjusted by adjusting the resistance values ​​of the first adjustable resistor R1 and the second adjustable resistor R2.

[0059] like Figure 5 As shown, the low-pass filter includes a second operational amplifier OPB, a third adjustable resistor R3, a fourth adjustable resistor R4, a third capacitor C3 and a fourth capacitor C4, the third adjustable resistor R3 and the fourth adjustable resistor R4 are connected in series at the non-inverting input terminal of the second operational amplifier OPB, one end of the fourth capacitor C4 is connected to the reference voltage source Vref, and the other end is connected to the non-inverting input terminal of the second operational amplifier OPB; the third capacitor C3 is connected between the middle node of the third adjustable resistor R3 and the fourth adjustable resistor R4 and the inverting input terminal of the second operational amplifier OPB, and the inverting input terminal of the second operational amplifier OPB is connected to its output terminal.

[0060] Specifically, the cutoff frequency of the low-pass filter is related to the resistance values ​​of the third adjustable resistor R3 and the fourth adjustable resistor R4, and the cutoff frequency thereof can be adjusted by adjusting the resistance values ​​of the third adjustable resistor R3 and the fourth adjustable resistor R42.

[0061] For high-pass filters and low-pass filters, as the resistance of the adjustable resistor increases, the corresponding cut-off frequency also increases; as the resistance of the adjustable resistor decreases, the corresponding cut-off frequency also decreases. Therefore, by adjusting the adjustable resistors (R1-R4) of the high-pass filter and the low-pass filter, the voltage signals corresponding to the current signals of different frequency bands can be obtained.

[0062] Since the cutoff frequency of the filter is related to the capacitance of the capacitor and the resistance of the resistor in the filter, in other embodiments, when the resistance of the resistor in the filter is fixed, the capacitor in the filter can be set as an adjustable capacitor, and the filter cutoff frequency can be adjusted by adjusting the capacitance of the capacitor.

[0063] It should be noted that the high-pass filter and low-pass filter of the present application are not limited to Figure 4 and Figure 5 The structure shown can also be a filter with adjustable cutoff frequency in other structural forms.

[0064] In some embodiments, the input end is connected to the photovoltaic DC power source 10 through a switching circuit 20. When an arc fault occurs, the first control unit 334 outputs a control signal to control the switching circuit 20 to cut off the output of each photovoltaic DC power source 10 to avoid further losses caused by the arc fault.

[0065] The photovoltaic inverter also includes a first communication unit 340, which is used for communication between the photovoltaic inverter 30 and the switch circuit 20. The first communication unit 340 receives the control signal and provides a communication signal to the switch circuit 20. The switch circuit 20 controls the on and off of the switch element according to the communication signal.

[0066] It should be noted that, in some other embodiments, the first communication unit 340 may also be disposed outside the photovoltaic inverter or in the arc fault detection circuit 330 .

[0067] like Figure 6 As shown, the switch circuit 20 includes at least one switch unit 210, which is connected to the corresponding photovoltaic DC power supply 10, and the switch unit 210 includes at least one switch element for controlling the output of the photovoltaic DC power supply 10; a second communication unit 230, which is communicatively connected to the first communication unit 340; and a second control unit 220, which is connected to the second communication unit 230 and the corresponding switch unit 210, and is used to control the switch unit 210 to cut off the output of the photovoltaic DC power supply 10 when an arc fault occurs.

[0068] The second control unit 220 can be any one of a microcontroller unit (MCU), a central processing unit (CPU), a field programmable gate array (FPGA), and a digital signal processor (DSP). Of course, the specific form of the second control unit 220 is not limited to the above examples.

[0069] The first communication unit 340 is connected to the second communication unit 230 in communication, and the communication methods include but are not limited to PLC communication, wireless communication, etc. When an arc fault occurs, according to the communication status between the first communication unit 340 and the second communication unit 230 (for example, the communication signal is lost, resulting in communication interruption) or the shutdown instruction in the communication signal provided by the first communication unit 340, the second control unit 220 controls the switch unit 210 to cut off the output of all photovoltaic DC power sources 10, thereby avoiding further losses caused by the arc fault and ensuring the safety of the photovoltaic system.

[0070] In an example embodiment, if Figure 7 As shown, the switch unit 210 includes switch tubes S5, S6, and a diode D1. The switch tube S6 and the diode D1 are connected in parallel with the output end of the switch unit 210, and the switch tube S5 is connected in series between the input end and the output end of the switch unit 210, and is used to control the connection between the output end of the photovoltaic DC power supply 10 and the input end of the photovoltaic inverter 30.

[0071] The second control unit 220 controls the output of the corresponding photovoltaic DC power source 10 by controlling the switch tube S5 . When the switch tube S5 is disconnected, the output of the corresponding photovoltaic DC power source 10 is cut off.

[0072] Furthermore, the DC-DC circuit 310 performs DC conversion and may be a boost circuit, a buck circuit, a buck-boost circuit, or the like.

[0073] like Figure 8As shown, taking the DC-DC circuit 310 as a boost circuit as an example, the DC-DC circuit 310 includes switches S3, S4, an inductor L2, an input capacitor Cin2, and an output capacitor Cout2. The first end of the second inductor L2 is connected to the input end of the DC-DC circuit 310, the second end is connected to the first end of the switch S3, the second end of the switch S3 is connected to the output end of the DC-DC circuit 310, and the first end of the fourth switch S4 is connected to the second end of the inductor L2; the input capacitor Cin2 is connected in parallel to the input end of the DC-DC circuit 310, and the output capacitor Cout2 is connected in parallel to the output end of the DC-DC circuit 310.

[0074] The DC-AC circuit 320 performs direct current to alternating current conversion, for example, a full-bridge circuit, a half-bridge circuit, a multi-level inverter circuit, or a dual active bridge inverter circuit.

[0075] When there are many input terminals of the photovoltaic inverter 30, because the input line must meet the overcurrent capacity, there are requirements for the wire diameter, and the size of the magnetic ring of the current transformer is limited, so the inner diameter of the magnetic ring of the current transformer may not be enough. At this time, the arc fault detection circuit 330 can use multiple current transformers, and each current transformer collects the current signal in part of the line respectively.

[0076] Fig. 9 This is a schematic diagram of the structure of a photovoltaic system in the second embodiment provided in this application. Fig. 9 As shown, the arc fault detection circuit 330 includes two current detection units 331, which respectively collect current signals in part of the input lines, and the current detection unit 331 is taken as a current transformer. The outputs of the two current detection units 331 are connected in parallel to the signal conversion unit 332, and the collected current signals are converted into voltage signals by the signal conversion unit 332. The signal processing unit 333 processes the voltage signals to obtain digital sampling signals, and the first control unit 334 determines whether there is an arc fault in the lines connected to the multiple input terminals according to the digital sampling signals. When an arc fault occurs in any of the input lines, the frequency spectrum of the current signal obtained by the first control unit 334 will be abnormal, so it can be judged whether an arc fault occurs.

[0077] The two current transformers share a signal conversion unit 332, a signal processing unit 333 and a first control unit 334, so as to realize the detection of arc faults of multiple input lines with fewer components and simpler circuits, occupy a small internal space of the photovoltaic inverter and have lower costs, and therefore have high practical value.

[0078] An embodiment of the present application further proposes a photovoltaic inverter, comprising a plurality of input terminals, a plurality of output DC-DC circuits connected in parallel, and a DC-AC circuit, wherein the plurality of DC-DC circuits are respectively connected to corresponding input terminals, the DC-AC circuit is connected to the plurality of DC-DC circuits, the input terminals are used to access a photovoltaic DC power supply, and the photovoltaic inverter also includes the arc fault detection circuit in the above embodiment.

[0079] The embodiment of the present application further provides a photovoltaic system, comprising a plurality of photovoltaic DC power supplies, and the photovoltaic inverter in the above embodiment connected to the plurality of photovoltaic DC power supplies.

[0080] In some embodiments, the photovoltaic system further includes a plurality of switching circuits, which are connected between corresponding input terminals of the photovoltaic inverter and corresponding photovoltaic DC power sources, and include at least one switching element for controlling the output of the corresponding photovoltaic DC power source.

[0081] The switch circuit is, for example, as described in the above embodiment and will not be described in detail here.

[0082] In some embodiments, the photovoltaic system is a household photovoltaic system. When an arc fault is detected in any circuit, the output of all photovoltaic DC power supplies is immediately cut off to ensure the safety of the household photovoltaic system.

[0083] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0084] The above embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the utility model patent. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be subject to the attached claims.

Claims

1. An arc fault detection circuit for a photovoltaic inverter, wherein the photovoltaic inverter has a plurality of input terminals, wherein the input terminals are used to access a photovoltaic DC power supply, wherein: The arc fault detection circuit comprises: At least one current detection unit, the current detection unit is used to couple with the lines connected to the corresponding multiple input terminals to detect the current signal of the line connected to each of the input terminals; a signal conversion unit, connected to the at least one current detection unit, and configured to convert a current signal into a voltage signal; A signal processing unit, connected to the signal conversion unit, for performing signal processing on the voltage signal to obtain a digital sampling signal; The first control unit is connected to the signal processing unit and is used to determine whether there is an arc fault in the lines connected to the multiple input terminals according to the digital sampling signal.

2. The arc fault detection circuit according to claim 1, characterized in that: The current detection unit includes a current transformer coupled to the lines to which the plurality of input terminals are connected.

3. The arc fault detection circuit according to claim 1, characterized in that: The signal conversion unit includes a first resistor, and the first resistor is connected in parallel to the output end of each of the current detection units.

4. The arc fault detection circuit according to claim 1, characterized in that: The signal processing unit comprises: A filter circuit, used for filtering the voltage signal; An operational amplifier circuit, connected to the filter circuit, for amplifying the filtered voltage signal; The analog-to-digital converter is connected to the operational amplifier circuit and is used to perform analog-to-digital conversion on the filtered and amplified voltage signal to obtain the digital sampling signal.

5. The arc fault detection circuit according to claim 4, characterized in that: The cutoff frequency of the filter circuit is adjustable, and the first control unit adjusts the cutoff frequency of the filter circuit multiple times to obtain digital sampling signals corresponding to current signals in different frequency bands.

6. The arc fault detection circuit according to claim 5, characterized in that: The filter circuit includes a high-pass filter and a low-pass filter connected in series, or at least two high-pass filters connected in series.

7. The arc fault detection circuit according to claim 6, characterized in that: The high-pass filter includes a first operational amplifier, a first adjustable resistor, a second adjustable resistor, a first capacitor and a second capacitor. The first capacitor and the second capacitor are connected in series at the non-inverting input terminal of the first operational amplifier. One end of the first adjustable resistor is connected to a reference voltage source, and the other end is connected to the non-inverting input terminal of the first operational amplifier. The second adjustable resistor is connected between the middle node of the first capacitor and the second capacitor and the inverting input terminal of the first operational amplifier, and the inverting input terminal of the first operational amplifier is connected to its output terminal.

8. The arc fault detection circuit according to claim 6 or 7, characterized in that: The low-pass filter includes a second operational amplifier, a third adjustable resistor, a fourth adjustable resistor, a third capacitor and a fourth capacitor. The third adjustable resistor and the fourth adjustable resistor are connected in series to the non-inverting input terminal of the second operational amplifier. One end of the fourth capacitor is connected to a reference voltage source, and the other end is connected to the non-inverting input terminal of the second operational amplifier. The third capacitor is connected between the middle node between the third adjustable resistor and the fourth adjustable resistor and the inverting input terminal of the second operational amplifier, and the inverting input terminal of the second operational amplifier is connected to its output terminal.

9. The arc fault detection circuit according to claim 1, characterized in that: Each of the input terminals is connected to a photovoltaic DC power supply through a switching circuit. The switching circuit includes at least one switching element connected between the corresponding input terminal and the photovoltaic DC power supply. When an arc fault occurs, the first control unit outputs a control signal to control each of the switching circuits to cut off the output of each of the photovoltaic DC power supplies.

10. The arc fault detection circuit according to claim 9, characterized in that: The photovoltaic inverter further includes a first communication unit communicating with the switch circuit, the first communication unit receives the control signal and provides a communication signal to the switch circuit, and the switch circuit controls the on and off of the switch element according to the communication signal.

11. A photovoltaic inverter, comprising a plurality of input terminals, a plurality of output DC-DC circuits and a DC-AC circuit connected in parallel, wherein the plurality of DC-DC circuits are respectively connected to corresponding input terminals, the DC-AC circuit is connected to the plurality of DC-DC circuits, the input terminals are used to access a photovoltaic DC power supply, and characterized in that: The photovoltaic inverter further comprises an arc fault detection circuit as claimed in any one of claims 1 to 10.

12. A photovoltaic system, characterized in that: The invention comprises a plurality of photovoltaic direct current power sources, and a photovoltaic inverter as claimed in claim 11 connected to the plurality of photovoltaic direct current power sources.

13. The photovoltaic system according to claim 12, characterized in that: The photovoltaic system further comprises a plurality of switch circuits, wherein the switch circuits are connected between corresponding input terminals of the photovoltaic inverter and corresponding photovoltaic DC power sources, and comprise at least one switch element for controlling the output of the corresponding photovoltaic DC power source.

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