An AFCI arcing detection circuit and protection timing optimization method for photovoltaic inverters

Abstract

This invention relates to the field of DC-side arc fault protection technology for photovoltaic inverters, specifically an AFCI arc fault detection circuit and protection timing optimization method applied to photovoltaic inverters. The detection circuit includes a photovoltaic high-voltage differential signal sampling module, a high-precision current sampling module, a secondary voltage reference source module, a secondary arc fault current reference source module, a secondary voltage detection module, a secondary arc fault current detection module, a first-level hardware judgment module, and a second-level hardware judgment module. It adopts a pure hardware architecture without MCU software processing. The secondary detection module uses a hardware comparator for parallel comparison. The optimization method includes synchronous signal acquisition, generation of secondary references, parallel comparison, two-level hardware judgment, and direct-drive shutdown. This invention achieves rapid hardware-level protection for arc faults ≤20μs, improves detection accuracy through dual-dimensional sampling and two-level judgment, enhances environmental adaptability through temperature drift suppression design, and features a simple structure, high integration, and excellent engineering practicality.

Description

Technical Field

[0001] This invention belongs to the field of DC-side arc fault protection technology for photovoltaic inverters, and in particular relates to an AFCI arc detection circuit and protection timing optimization method for photovoltaic inverters. Background Technology

[0002] In both grid-connected and off-grid photovoltaic (PV) power generation systems, the DC-side lines from PV modules to the inverter are highly susceptible to DC series arcing faults due to aging, poor contact, loose wiring, or external damage. DC arcs are characterized by low sustaining voltage, concentrated energy, and difficulty in self-extinguishing. Once an arc occurs, the local temperature can reach thousands of degrees Celsius, easily leading to cable burnout, equipment fires, and even PV site fires, seriously threatening system operational safety. Therefore, configuring arc fault detection and protection (AFCI) functions in PV inverters has become a necessary component of industry safety standards and product design.

[0003] Existing AFCI arc detection solutions for photovoltaic inverters generally adopt a sampling + analog-to-digital conversion + MCU software algorithm judgment approach. However, this traditional solution has the following problems: The protection response time is too long, requiring the signal to go through multiple stages such as sampling, ADC conversion, software filtering, algorithm calculation, and command output. The overall response delay is usually in the hundreds of milliseconds, making it impossible to quickly extinguish the arc in the early stages, resulting in a high risk of fault expansion. It also has a high degree of software dependence and insufficient reliability. Arc judgment relies entirely on software programs, making it susceptible to factors such as program crashes, digital signal interference, and computational dead zones, potentially leading to missed detections or delayed protection actions. Furthermore, the high-frequency arc signal acquisition accuracy is insufficient. Ordinary current transformers have poor high-frequency response characteristics, and the sampling circuit lacks temperature drift suppression design, making weak arc signals easily masked by noise or temperature drift, resulting in low detection sensitivity. Finally, the signal processing path is redundant, requiring the detection signal to be relayed through multiple software stages, preventing direct application to the drive shutdown port and further increasing the protection action delay. Summary of the Invention

[0004] To address the problems of excessively long protection response time, high software dependence, insufficient high-frequency arc signal acquisition accuracy, and redundant signal processing paths in existing AFCI arc detection schemes for photovoltaic inverters, this invention provides an AFCI arc detection circuit and protection timing optimization method for photovoltaic inverters. The technical solution adopted by this invention to solve the above problems is as follows: An AFCI arcing detection circuit for photovoltaic inverters includes: a photovoltaic high-voltage differential signal sampling module, a high-precision current sampling module, a secondary voltage reference source module, a secondary arcing current reference source module, a secondary voltage detection module, a secondary arcing current detection module, a first-stage hardware judgment module, and a second-stage hardware judgment module. The photovoltaic high-voltage differential signal sampling module acquires the photovoltaic DC side voltage signal and outputs it to the secondary voltage detection module. The secondary voltage detection module compares the voltage signal with the secondary voltage reference source and outputs the first voltage judgment signal and the second voltage judgment signal. The high-precision current sampling module collects the arcing current signal on the DC side of the photovoltaic system and outputs it to the secondary arcing current detection module. The secondary arcing current detection module compares the current signal with the secondary arcing current reference source and outputs the first current judgment signal and the second current judgment signal. The first-level hardware judgment module performs a joint hardware comparison of the first voltage judgment signal and the first current judgment signal, and the second-level hardware judgment module performs a joint hardware comparison of the second voltage judgment signal and the second current judgment signal. The output signals of the first-level hardware judgment module and the second-level hardware judgment module are directly connected to the inverter drive shutdown port, without MCU software processing, and the protection response time is ≤20μs.

[0005] As a further preferred technical solution of the detection circuit described in this invention, the high-precision current sampling module includes a nanocrystalline magnetic ring current transformer and a precision rectifier circuit. The nanocrystalline magnetic ring current transformer is adapted to the high-frequency arcing signal characteristics of the photovoltaic DC side and is used to collect the high-frequency arcing current signal of the photovoltaic DC side.

[0006] As a further preferred technical solution of the detection circuit described in this invention, the precision rectifier circuit includes an operational amplifier and a rectifier device, which is suitable for small signal sampling scenarios. The precision rectifier circuit is used to rectify the current signal and suppress temperature drift to ensure sampling accuracy.

[0007] As a further preferred technical solution of the detection circuit described in this invention, both the secondary voltage detection module and the secondary arcing current detection module adopt hardware comparators. The hardware comparators adopt a parallel comparison mode, acquire high voltage signals and simultaneously complete the comparison of voltage and current signals, adapting to the protection response requirements of ≤20μs.

[0008] As a further preferred technical solution of the detection circuit described in this invention, the photovoltaic high-voltage differential signal sampling module is composed of a sampling network consisting of multiple high-voltage resistors, which can step down the photovoltaic DC-side high-voltage signal and convert it into a low-voltage analog signal to realize high-voltage isolated voltage acquisition.

[0009] As a further preferred technical solution of the detection circuit described in this invention, the low-voltage analog signal output by the photovoltaic high-voltage differential signal sampling module is proportionally amplified and then sent to the secondary voltage detection module to ensure the accuracy of signal transmission.

[0010] A timing optimization method for AFCI arcing protection in photovoltaic inverters includes the following steps: S1: Synchronously acquire the photovoltaic DC side high-voltage differential voltage signal and arcing current signal; S2: Generate the secondary voltage reference signal and the secondary arcing current reference signal; S3: Compare the acquired voltage signal with the secondary voltage reference signal in hardware, and output the first and second voltage judgment signals; compare the acquired current signal with the secondary arcing current reference signal in hardware, and output the first and second current judgment signals; S4: Perform a first-level joint hardware comparison on the first voltage judgment signal and the first current judgment signal, and perform a second-level joint hardware comparison on the second voltage judgment signal and the second current judgment signal; S5: The hardware comparison result is directly connected to the inverter drive shutdown port, without the need for MCU software processing, to achieve hardware-level fast protection against arcing faults, with a protection response time of ≤20μs.

[0011] As a further preferred technical solution of the optimization method described in this invention, in step S1, the high-voltage differential voltage signal and the arcing current signal are acquired synchronously to ensure that the timing of the two signals is consistent.

[0012] As a further preferred technical solution of the optimization method described in this invention, in step S4, the two-level hardware judgment is performed sequentially, first completing the first-level joint comparison, and then completing the second-level joint comparison, thereby improving the accuracy of the judgment.

[0013] As a further preferred technical solution of the optimization method described in this invention, in step S5, the hardware comparison result is directly connected to the inverter drive shutdown port without undergoing digital signal processing and software logic operation.

[0014] As described above, the beneficial effects of the AFCI arcing detection circuit and protection timing optimization method for photovoltaic inverters provided by this invention are: accurate arcing fault detection and enhanced anti-interference capability. The architecture employing dual-dimensional synchronous sampling of voltage and current combined with a two-level hardware joint judgment can simultaneously capture the voltage distortion and high-frequency current characteristics on the DC side when an arc occurs. Combined with the hierarchical verification logic of two-level reference thresholds, it can effectively identify weak initial arcing signals and improve the accuracy and reliability of detection. It also improves the response speed of circuit protection. The entire detection and judgment process is executed entirely by the hardware circuit, without relying on MCU chips or any software algorithms, and can stably control the response time of arcing fault protection. The time limit is kept within 20μs; the optimized protection timing improves the suppression effect of arc faults; the hardware judgment result is directly connected to the inverter drive shutdown port, and the signal transmission has no intermediate or parsing links, forming the shortest execution path of sampling-comparison-judgment-shutdown, which can quickly cut off the energy supply in the early stage of arc faults and suppress the high temperature and energy accumulation of arcs; the weak signal acquisition accuracy is high, the whole machine has strong environmental adaptability, and the nanocrystalline magnetic ring current transformer with excellent high-frequency characteristics can accurately capture the small high-frequency arc signals on the DC side. Combined with the precision rectifier circuit, it suppresses temperature drift and signal distortion, ensuring that the equipment can maintain stable detection accuracy under different temperatures and operating conditions, and improving the long-term stability of the whole machine. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 This is a schematic block diagram of the AFCI arc detection circuit applied to a photovoltaic inverter according to the present invention; Figure 2 This is a hardware circuit diagram of the AFCI arc detection circuit applied to a photovoltaic inverter as described in this invention; Figure 3 This is a flowchart of the AFCI arc protection timing optimization method for photovoltaic inverters described in this invention.

[0017] The component names corresponding to the markings in the attached diagram are as follows: 1. Photovoltaic high voltage differential signal sampling module, 2. Current sampling module, 21. Current transformer, 22. Precision rectifier circuit, 3. Second-level voltage reference source module, 4. Second-level arcing current reference source module, 5. Second-level voltage detection module, 6. Second-level arcing current detection module, 7. First-level hardware judgment module, 8. Second-level hardware judgment module. Detailed Implementation

[0018] To facilitate understanding of the present invention, a more complete description will be given below with reference to the accompanying drawings. Preferred embodiments of the invention are shown in the drawings. However, the invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of the invention.

[0019] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0020] Please refer to Figure 1 The AFCI arc detection circuit of the present invention includes a photovoltaic high voltage high differential signal sampling module 1, a current sampling module 2, a secondary voltage reference source module 3, a secondary arc current reference source module 4, a secondary voltage detection module 5, a secondary arc current detection module 6, a first-level hardware judgment module 7, and a second-level hardware judgment module 8. The components are connected in sequence and transmit signals directly through analog signal lines, without intermediate redundant links such as digital conversion, software calculation, and instruction relay. This forms the shortest signal link of sampling-reference-comparison-judgment-shutdown, which ensures a rapid response after an arc fault occurs. At the same time, through the coordinated cooperation of the components, both detection accuracy and anti-interference capability are taken into account.

[0021] Please refer to Figure 2 The photovoltaic high-voltage differential signal sampling module 1 is connected in parallel between the positive and negative terminals of the DC side of the photovoltaic inverter. It adopts a high-voltage differential voltage divider structure and is adapted to 500V-1500V high-voltage conditions. After stepping down and proportionally amplifying the DC side high-voltage signal, it outputs a stable voltage sampling signal to the secondary voltage detection module 5 to capture the voltage distortion signal generated by arcing fault.

[0022] The current sampling module 2 is connected in series in the DC side of the photovoltaic circuit. It consists of a current transformer 21 and a precision rectifier circuit 22. The current transformer 21 is made of nanocrystalline magnetic ring material and has high frequency response characteristics. It collects the high frequency current signal generated by the arcing fault on the DC side and converts it into an induced current signal, which is then transmitted to the precision rectifier circuit 22. The precision rectifier circuit 22 completes the signal rectification through an operational amplifier and rectifier device, while suppressing temperature drift. The processed current sampling signal is then output to the secondary arcing current detection module 6.

[0023] The secondary voltage reference source module 3 provides two levels of voltage reference signals to the secondary voltage detection module 5, and the secondary arcing current reference source module 4 provides two levels of current reference signals to the secondary arcing current detection module 6. The two levels of references correspond to the judgment thresholds for slight arcing and severe arcing, respectively. The thresholds can be flexibly adjusted according to the inverter power to balance detection sensitivity and anti-interference.

[0024] Both the secondary voltage detection module 5 and the secondary arc current detection module 6 use high-speed hardware comparators and work synchronously in parallel mode. The secondary voltage detection module 5 compares the voltage sampling signal with the two-stage voltage reference and outputs the first voltage judgment signal and the second voltage judgment signal. The secondary arc current detection module 6 compares the current sampling signal with the two-stage current reference and outputs the first current judgment signal and the second current judgment signal.

[0025] The first-level hardware judgment module 7 receives the first voltage judgment signal and the first current judgment signal, and completes the initial screening of arcing faults through hardware and logic. When only the two signals are valid at the same time, it outputs the primary fault signal. The second-level hardware judgment module 8 receives the second voltage judgment signal and the second current judgment signal, and completes the secondary confirmation of the fault. When only the two signals are valid at the same time, it outputs the final fault signal.

[0026] Please refer to Figure 3 The implementation steps of the AFCI arc protection timing optimization method are as follows: This method relies on the above-mentioned detection circuit to optimize the timing of the entire process and eliminate redundant links. S1: The photovoltaic high voltage differential signal sampling module 1 and the current sampling module 2 synchronously acquire the photovoltaic DC side high voltage differential voltage signal and high frequency arcing current signal. The two modules are synchronously triggered to ensure that the timing of the two signals is consistent. After the signal is acquired, the preprocessing of step-down, amplification, rectification and temperature drift suppression is completed.

[0027] S2: The secondary voltage reference source module 3 generates two-level voltage reference signals, and the secondary arcing current reference source module 4 generates two-level current reference signals. The reference signals and sampling signals are output synchronously to ensure that the comparison reference is in a stable state.

[0028] S3: The secondary voltage detection module 5 and the secondary arcing current detection module 6 perform hardware comparison in parallel, and output two levels of voltage and current judgment signals respectively. There is no batch processing delay, and the signal identification is completed quickly.

[0029] S4: The first-level hardware judgment module 7 first performs a preliminary joint judgment to screen non-fault interference signals. After confirming the primary fault, the second-level hardware judgment module 8 performs a second joint judgment to complete the final confirmation of the arcing fault.

[0030] S5: The output signal of the two-level hardware judgment module is directly connected to the inverter drive shutdown port. Without digital processing and software calculation, the shortest path triggers the drive shutdown, realizing hardware-level fast protection of ≤20μs. It cuts off the energy supply in the early stage of arcing to avoid the fault from escalating. Example 1:

[0031] The AFCI arcing detection circuit and protection timing optimization method of this invention are integrated into a 1500V / 20A string photovoltaic inverter to build an equivalent test platform for outdoor photovoltaic power stations. The ambient temperature range is -40℃ to 85℃, with ±10% grid fluctuation, 50% to 100% load switching, and 10kHz to 1MHz high-frequency electromagnetic interference superimposed. The arcing generator simulates two types of series arcing faults, namely minor and severe, and full-condition verification tests are carried out.

[0032] In this example, the voltage and current references for the two-stage AFCI determination are set as follows:

[0033] The synchronous trigger circuit operates at a frequency of 1MHz to ensure that the sampling timing of the photovoltaic high-voltage differential signal sampling module 1 and the high-precision current sampling module 2 is completely synchronized.

[0034] During the testing process, cyclic tests were conducted under normal operating conditions, interference conditions, and arcing fault conditions, with a total of 50 valid tests completed. The entire timing sequence of the drive shutdown process was acquired in real time using a high-precision oscilloscope, and key indicators such as protection response time, fault identification accuracy, and false triggering were recorded.

[0035] Under normal operating conditions: The photovoltaic side outputs a stable 1500V / 20A. The photovoltaic high-voltage differential signal sampling module 1 outputs PV_Vsignal=3.00V, which is higher than the two-stage voltage reference. The high-precision current sampling module 2, after processing by the current transformer 21 and the precision rectifier circuit 22, outputs PV_Isignal=0.40V, which is lower than the two-stage current reference. The secondary voltage detection module 5 and the secondary arcing current detection module 6 both output low levels. The first-stage hardware judgment module 7 and the second-stage hardware judgment module 8 show no valid fault signals, and the inverter is operating normally in grid connection.

[0036] Minor arcing / interference condition: Poor connector contact triggers a minor series arc, causing the photovoltaic voltage to momentarily drop to 1410V and the current spike to 33A. PV_Vsignal drops to 2.82V, below the first-level voltage reference but above the second-level voltage reference; PV_Isignal rises to 0.66V, above the first-level current reference but below the second-level current reference. Second-level voltage detection module 5 and second-level arcing current detection module 6 output a valid first-level judgment signal and an invalid second-level signal. First-level hardware judgment module 7 outputs a warning signal, while second-level hardware judgment module 8 has no output. The system determines this as minor interference, issuing only an alarm without shutting down, thus avoiding false protection.

[0037] Dangerous arcing condition: The arc continues to worsen, causing the photovoltaic voltage to plummet to 1180V and the current to surge to 58A. PV_Vsignal drops to 2.36V, below the two-stage voltage reference, while PV_Isignal rises to 1.16V, above the two-stage current reference. The secondary voltage detection module 5 and the secondary arcing current detection module 6 output two valid judgment signals, while the first-stage hardware judgment module 7 and the second-stage hardware judgment module 8 simultaneously output fault signals, shutting off the direct-drive inverter's shut-off port and cutting off the energy supply.

[0038] The input-output logic relationship of the two-level judgment module under the above three working conditions is as follows:

[0039] Test results show that the protection response time of this circuit meets the design requirement of ≤20μs, the arcing fault identification accuracy is high, the anti-interference ability is strong, the sampling accuracy is stable in a wide temperature environment, and the operation of each hardware module is reliable.

[0040] The integrated circuit inverter is connected to the photovoltaic string for continuous load operation. The circuit is fault-free, the protection action is precise, it uses conventional components, has low integration difficulty, is compatible with photovoltaic inverters of different power, and has strong engineering practicality.

[0041] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any way. Any simple modifications, alterations, and equivalent changes made to the above embodiments based on the technical essence of the present invention shall still fall within the protection scope of the present invention.

Claims

1. An AFCI arc detection circuit for use in photovoltaic inverters, characterized in that, include: Photovoltaic high voltage differential signal sampling module (1), high precision current sampling module (2), secondary voltage reference source module (3), secondary arc current reference source module (4), secondary voltage detection module (5), secondary arc current detection module (6), first-level hardware judgment module (7), and second-level hardware judgment module (8); The photovoltaic high voltage differential signal sampling module (1) collects the photovoltaic DC side voltage signal and outputs it to the secondary voltage detection module (5). The secondary voltage detection module (5) compares the voltage signal with the secondary voltage reference source module (3) and outputs the first voltage judgment signal and the second voltage judgment signal. The high-precision current sampling module (2) collects the arcing current signal on the DC side of the photovoltaic system and outputs it to the secondary arcing current detection module (6). The secondary arcing current detection module (6) compares the current signal with the secondary arcing current reference source module (4) and outputs the first current judgment signal and the second current judgment signal. The first-level hardware judgment module (7) performs a joint hardware comparison of the first voltage judgment signal and the first current judgment signal, and the second-level hardware judgment module (8) performs a joint hardware comparison of the second voltage judgment signal and the second current judgment signal. The output signals of the first-level hardware judgment module (7) and the second-level hardware judgment module (8) are directly connected to the inverter drive shutdown port, without MCU software processing, and the protection response time is ≤20μs.

2. A timing optimization method for AFCI arcing protection applied to photovoltaic inverters, characterized in that, Includes the following steps: S1: Synchronously acquire the photovoltaic DC side high-voltage differential voltage signal and arcing current signal; S2: Generate the secondary voltage reference signal and the secondary arcing current reference signal; S3: Compare the acquired voltage signal with the secondary voltage reference signal in hardware, and output the first and second voltage judgment signals. Compare the acquired current signal with the secondary arcing current reference signal in hardware, and output the first and second current judgment signals. S4: Perform a first-level joint hardware comparison between the first voltage judgment signal and the first current judgment signal, and perform a second-level joint hardware comparison between the second voltage judgment signal and the second current judgment signal. S5: The hardware comparison result is directly connected to the inverter drive shutdown port, without the need for MCU software processing, to achieve hardware-level fast protection against arcing faults, with a protection response time of ≤20μs.

3. The AFCI arc detection circuit for photovoltaic inverters according to claim 1, characterized in that: The high-precision current sampling module (2) includes a current transformer (21) and a precision rectifier circuit (22). The current transformer (21) adopts a nanocrystalline magnetic ring structure, which is adapted to the high-frequency arcing signal characteristics of the photovoltaic DC side and is used to collect the high-frequency arcing current signal of the photovoltaic DC side.

4. The AFCI arc detection circuit for photovoltaic inverters according to claim 3, characterized in that: The precision rectifier circuit (22) includes an operational amplifier and a rectifier device, which is suitable for small signal sampling scenarios. The precision rectifier circuit (22) is used to rectify the current signal and suppress temperature drift to ensure sampling accuracy.

5. The AFCI arc detection circuit for photovoltaic inverters according to claim 1, characterized in that: Both the secondary voltage detection module (5) and the secondary arc current detection module (6) adopt hardware comparators. The hardware comparators adopt a parallel comparison mode, collect high voltage signals and simultaneously complete the comparison of voltage and current signals, adapting to the protection response requirements of ≤20μs.

6. The AFCI arc detection circuit for photovoltaic inverters according to claim 1, characterized in that: The photovoltaic high-voltage differential signal sampling module (1) consists of a sampling network composed of multiple high-voltage resistors, which can step down the photovoltaic DC side high-voltage signal and convert it into a low-voltage analog signal to realize high-voltage isolated voltage acquisition.

7. The AFCI arc detection circuit for photovoltaic inverters according to claim 6, characterized in that: The low-voltage analog signal output by the photovoltaic high-voltage differential signal sampling module (1) is amplified proportionally and then sent to the secondary voltage detection module (5) to ensure the accuracy of signal transmission.

8. The AFCI arc protection timing optimization method for photovoltaic inverters according to claim 2, characterized in that: In step S1, the high voltage differential signal and the arcing current signal are synchronously triggered by the photovoltaic high voltage differential signal sampling module (1) and the high precision current sampling module (2) to ensure that the timing of the two signals is consistent.

9. The AFCI arc protection timing optimization method for photovoltaic inverters according to claim 2, characterized in that: In step S4, the two-level hardware judgment is performed sequentially. First, the first-level hardware judgment module (7) completes the first-level joint comparison, and then the second-level hardware judgment module (8) completes the second-level joint comparison to improve the accuracy of the judgment.

10. The AFCI arc protection timing optimization method for photovoltaic inverters according to claim 2, characterized in that: In step S5, the output signals of the first-level hardware judgment module (7) and the second-level hardware judgment module (8) are directly connected to the inverter drive shutdown port without undergoing digital signal processing and software logic operation.

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