A leakage current detection circuit and an inverter using the same

Abstract

The utility model provides a kind of leakage current detection circuit and the inverter of application thereof, comprising: leakage current sensor, for sensing leakage current of inverter output side and generating original electric signal;Parallel signal conditioning module is electrically connected with leakage current sensor, for original electric signal is handled at least two parallel, wherein: the gain of first signal conditioning path is set to be suitable for handling leakage current of first range;The gain of second signal conditioning path is greater than the gain of first signal conditioning path, and is set to be suitable for handling leakage current of second range;Control unit is electrically connected with parallel signal conditioning module, for receiving and processing output signal from first signal conditioning path and second signal conditioning path.The utility model passes through double channel division of labour cooperation mechanism, solved in prior art when detecting large range sustained leakage current, cannot take into account small range mutation leakage current accurate measurement problem.

Description

Technical Field

[0001] This utility model relates to the field of power electronics technology, and in particular to a leakage current detection circuit and an inverter using the same. Background Technology

[0002] The leakage current problem of photovoltaic inverters is directly related to personal safety and stable equipment operation. Both domestic and international photovoltaic system standards mandate real-time and accurate detection of inverter leakage current. Currently, the industry generally adopts a solution combining leakage current sensors with signal conditioning circuits. The sensor converts the leakage current into a voltage signal, which is then conditioned by an operational amplifier and processed by the control chip.

[0003] However, as photovoltaic systems develop towards higher power and higher voltage, the continuous leakage current standard for photovoltaic systems requires a significant increase in the range of continuous leakage current amplitudes that need to be detected during inverter operation. This poses new challenges to the detection system: on the one hand, the use of large-range sensors leads to higher system costs; on the other hand, the increase in sensor range means that the sudden leakage currents at key safety thresholds such as 30mA, 60mA, and 150mA account for only a very small portion of the full range (as low as a few thousandths), making it difficult for the control unit to effectively distinguish and extract these weak sudden characteristics.

[0004] Therefore, existing detection methods cannot accurately measure both large-range continuous leakage current and small-sudden leakage current. Utility Model Content

[0005] To address the aforementioned problems, this invention provides a leakage current detection circuit and an inverter using it. Through a dual-channel collaborative mechanism, it solves the problem in the prior art that when detecting a large range of continuous leakage current, it is impossible to accurately measure a small range of sudden leakage current.

[0006] The objective of this utility model is achieved through the following technical solution: On one hand, embodiments of this utility model provide a leakage current detection circuit, including: A leakage current sensor is used to sense the leakage current on the output side of the inverter and generate a raw electrical signal. A parallel signal conditioning module, electrically connected to the leakage current sensor, is used to perform at least two parallel processing steps on the original electrical signal, wherein: The gain of the first signal conditioning path is set to be suitable for handling leakage current within the first range. The gain of the second signal conditioning path is greater than the gain of the first signal conditioning path, and it is set to be suitable for processing leakage current in the second range, wherein the upper limit of the second range is less than the lower limit of the first range. The control unit is electrically connected to the parallel signal conditioning module and is used to receive and process output signals from the first signal conditioning path and the second signal conditioning path.

[0007] Furthermore, the leakage current in the first range is a continuous leakage current in the ampere range.

[0008] Furthermore, the leakage current in the second range is a sudden leakage current or a small leakage current in the milliampere range.

[0009] Furthermore, the first signal conditioning path includes a first operational amplifier module and a first filter circuit connected in sequence, and the output terminal of the first filter circuit is connected to the control unit; the first operational amplifier circuit in the first operational amplifier module is configured as a differential amplifier circuit, including a first operational amplifier U1, resistors R1, R2, R3, and R4, and capacitors C1 and C2. The resistor R1 is connected in series between the first output terminal of the leakage current sensor and the inverting input terminal of the first operational amplifier U1; The resistor R2 is connected in series between the second output terminal of the leakage current sensor and the non-inverting input terminal of the first operational amplifier U1; The resistor R3 and the capacitor C1 are connected in parallel and between the inverting input terminal and the output terminal of the first operational amplifier to form a first feedback network. The resistor R4 and the capacitor C2 are connected in parallel and between the non-inverting input terminal of the first operational amplifier and the first reference voltage terminal Vref1, together forming the first matching network.

[0010] Furthermore, the first operational amplifier module also includes a second operational amplifier circuit, which is configured as a differential amplifier circuit, including a second operational amplifier U2, resistors R5, R6, R7, and R8, capacitors C3 and C4. The resistor R5 is connected in series between the output terminal of the first operational amplifier U1 and the non-inverting input terminal of the second operational amplifier U2; The resistor R6 is connected in series between the first reference voltage terminal Vref1 and the inverting input terminal of the second operational amplifier U2; The resistor R8 and the capacitor C4 are connected in parallel and between the inverting input terminal and the output terminal of the second operational amplifier, together forming the second feedback network; The resistor R7 and capacitor C3 are connected in parallel and between the non-inverting input terminal and the second reference voltage terminal Vref2 of the second operational amplifier U2, together forming the second matching network.

[0011] Furthermore, the second signal conditioning path includes a second operational amplifier module and a second filter circuit connected in sequence, and the output terminal of the second filter circuit is connected to the control unit; the third operational amplifier circuit in the second operational amplifier module is configured as a differential amplifier circuit, and its input terminals include a first input terminal and a second input terminal; the third operational amplifier circuit includes a third operational amplifier U3, resistors R9, R10, R11, and R12, capacitors C5 and C6; The resistor R9 is connected in series between the first input terminal and the inverting input terminal of the third operational amplifier U3; The resistor R10 is connected in series between the second input terminal and the non-inverting input terminal of the third operational amplifier; The resistor R11 and the capacitor C5 are connected in parallel and between the inverting input terminal and the output terminal of the third operational amplifier U3 to form a third feedback network. The resistor R12 and the capacitor C6 are connected in parallel and between the non-inverting input terminal of the third operational amplifier U3 and the third reference voltage terminal Vref3, together forming the third matching network.

[0012] Furthermore, the first input terminal of the third operational amplifier circuit is connected to the first output terminal of the leakage current sensor; the second input terminal of the third operational amplifier circuit is connected to the second output terminal of the leakage current sensor.

[0013] Furthermore, the first input terminal of the third operational amplifier circuit is connected to the first reference voltage terminal Vref1 of the first operational amplifier circuit; the second input terminal of the third operational amplifier circuit is connected to the output terminal of the first operational amplifier U1.

[0014] Furthermore, the second operational amplifier module also includes a fourth operational amplifier circuit, which is configured as a differential amplifier circuit, including a fourth operational amplifier U4, resistors R13, R14, R15, R16, capacitor C7, and capacitor C8. The resistor R13 is connected in series between the output terminal of the third operational amplifier U3 and the non-inverting input terminal of the fourth operational amplifier U4; The resistor R14 is connected in series between the third reference voltage terminal Vref3 and the inverting input terminal of the fourth operational amplifier U4; The resistor R16 and the capacitor C8 are connected in parallel and between the inverting input terminal and the output terminal of the fourth operational amplifier U4 to form a fourth feedback network. The resistor R15 and the capacitor C7 are connected in parallel and between the non-inverting input terminal of the fourth operational amplifier U4 and the fourth reference voltage terminal Vref4, together forming the fourth matching network.

[0015] On one hand, embodiments of this utility model provide an inverter, comprising: A DC / AC circuit has its DC input terminal connected to a photovoltaic module and its AC output terminal connected to the power grid or load via a three-phase cable. The leakage current detection circuit described in any of the above embodiments has its leakage current sensor sleeved on the three-phase cable and its control unit connected to the DC / AC circuit.

[0016] Compared with the prior art, the beneficial effects of this utility model are as follows: This utility model uses at least two independent signal conditioning paths to perform different gain and filtering processing on the voltage signal output by the same leakage current sensor, fundamentally solving the contradiction between range and accuracy that the traditional single-channel solution cannot take into account, and at the same time realizing wide-range monitoring of ampere-level continuous leakage current and high-precision capture of milliampere-level sudden leakage current. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the circuit structure of a photovoltaic system provided in an embodiment of this application; Figure 2 , Figure 3 This is a circuit schematic diagram of a leakage current detection circuit provided in an embodiment of this application; Figure 4 This is a circuit diagram of the first signal conditioning path of a leakage current detection circuit provided in an embodiment of this application; Figure 5 This application provides a circuit diagram of the second signal conditioning path of a leakage current detection circuit. Detailed Implementation

[0018] The technical solution of this utility model will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this utility model. Based on the embodiments of this utility model, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this utility model.

[0019] In the description of this utility model, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the accompanying drawings and are only for the convenience of describing this utility model 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 therefore should not be construed as a limitation of this utility model. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0020] In the description of this utility model, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "joining" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; 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; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this utility model based on the specific circumstances. Furthermore, the technical features involved in the different embodiments of this utility model described below can be combined with each other as long as they do not conflict with each other.

[0021] Combination Figure 1 As shown, the inverter of this utility model includes a DC / AC circuit and a leakage current detection circuit, which will be described in detail below. The DC side of the DC / AC circuit is connected to the photovoltaic module, and the AC side is connected to the power grid through a three-phase cable. The sensor of the leakage current detection device is sleeved on the three-phase cable.

[0022] Specifically, in combination Figure 2 , Figure 3 As shown, the leakage current detection circuit mainly consists of a leakage current sensor, a parallel signal conditioning module, and a control unit. The leakage current sensor is mounted on the AC output terminal of the inverter, preferably a Hall current sensor, to sense the ground leakage current generated during inverter operation and output a voltage signal proportional to the leakage current value. In a specific embodiment, the Hall current sensor has a range of -10A to 10A and a gain coefficient of 0.2V / A, which can linearly convert the sensed leakage current into a differential voltage signal of -2V to 2V and transmit it to the subsequent parallel signal conditioning module.

[0023] The parallel signal conditioning module performs at least two parallel processing steps on the raw voltage signal output by the leakage current sensor. In practical applications, zero or multiple signal conditioning paths can be configured depending on the detection accuracy and functional requirements. This embodiment uses a two-channel example: the first signal conditioning path is dedicated to processing large-range continuous leakage current signals, while the second signal conditioning path is dedicated to processing small-range abrupt leakage current signals. This parallel processing architecture is the core of achieving high-precision detection across the entire range.

[0024] The control unit has multiple independent signal acquisition channels for synchronously receiving output signals from the first and second signal conditioning paths and performing corresponding data processing and protection logic judgments.

[0025] Specifically, in combination Figure 4 As shown, the first signal conditioning path includes a first operational amplifier module and a first filter module. The first operational amplifier module further includes a first operational amplifier circuit and a second operational amplifier circuit, which together form a two-stage differential amplifier structure.

[0026] The first operational amplifier circuit is configured as a typical differential amplifier circuit, with its core components being the first operational amplifier U1, resistors R1, R2, R3, and R4, and capacitors C1 and C2. Resistor R1 is connected in series between the first output terminal of the leakage current sensor and the inverting input terminal of the first operational amplifier U1. Resistor R2 is connected in series between the second output terminal of the leakage current sensor and the non-inverting input terminal of the first operational amplifier U1. Resistor R3 and capacitor C1 are connected in parallel between the inverting input terminal and the output terminal of the first operational amplifier, forming the first feedback network. Resistor R4 and capacitor C2 are connected in parallel between the non-inverting input terminal and the first reference voltage terminal Vref1 of the first operational amplifier, together forming the first matching network. This network is used to maintain impedance balance at the input terminals, improve the common-mode rejection ratio, set the main gain of this stage, and suppress high-frequency noise.

[0027] The second operational amplifier circuit is also configured as a differential amplifier circuit, with its core components being the second operational amplifier U2, resistors R5, R6, R7, and R8, and capacitors C3 and C4. Resistor R5 is connected in series between the output of the first operational amplifier U1 and the non-inverting input of the second operational amplifier U2. Resistor R6 is connected in series between the first reference voltage terminal Vref1 and the inverting input of the second operational amplifier U2. Resistor R8 and capacitor C4 are connected in parallel between the inverting input and output of the second operational amplifier, forming the second feedback network. Resistor R7 and capacitor C3 are connected in parallel between the non-inverting input of the second operational amplifier U2 and the second reference voltage terminal Vref2, forming the second matching network.

[0028] It should be noted that this embodiment uses a two-stage series differential operational amplifier circuit as an example. In practical applications, the number of operational amplifier circuits cascaded in the first operational amplifier module can be increased or decreased according to the specific requirements of the system for gain, bandwidth and filtering characteristics.

[0029] The signal processing mechanism of the first signal conditioning pathway (GFCI1) is as follows: The design goal of this path is to achieve distortion-free transmission of large-range continuous leakage current signals, and its processing includes two stages: amplitude conditioning and frequency conditioning.

[0030] Amplitude Conditioning: The first operational amplifier module precisely conditions the voltage amplitude signal output by the leakage current sensor through a two-stage differential amplifier circuit. When its resistors satisfy the symmetrical condition R1=R2, R3=R4, R5=R6, R7=R8, the total voltage gain coefficient of this path can be simplified to V1=(R3÷R1)×(R8÷R6). By configuring the resistance ratio of these resistors, the gain coefficient V1 can be set to an appropriate value suitable for processing a wide range of signals from -10A to 10A. Its primary task is to ensure that the voltage signal output by the leakage current sensor can be completely and linearly mapped to the optimal input range of the control unit's analog-to-digital converter (ADC), avoiding signal saturation or distortion.

[0031] Frequency Conditioning: The first operational amplifier module and the first filter circuit together form a frequency selection network, whose core task is to filter out high-frequency noise and retain complete signal amplitude information. In the amplification stage, C1 and R3, and C3 and R7 respectively form two first-order low-pass filter units to perform preliminary frequency shaping on the signal. The signal amplified by operational amplifier U2 is further enhanced by the subsequent first filter circuit, ultimately limiting the bandwidth of the output signal to below 1kHz. This frequency conditioning process aims to effectively filter out high-frequency noise and its harmonics generated by the inverter switching, while completely retaining the low-frequency amplitude signal characterizing the leakage current. Ultimately, this ensures that a voltage signal corresponding to the full range of -10A to 10A can be transmitted to the control unit without attenuation.

[0032] It should be noted that while using only one large-range leakage current sampling circuit can meet the basic requirements of national photovoltaic standards for wide-range detection, the transmitted signal will inevitably have both a high voltage amplitude range and a wide frequency range. Although this signal theoretically contains a low-frequency abrupt change component that characterizes personal safety risks, this component is negligible in the entire signal spectrum, both in terms of amplitude and frequency proportion. This makes it difficult for the control unit to accurately identify and extract the weak abrupt leakage current characteristics when faced with such a wide-ranging and extremely low signal-to-noise ratio mixed signal, thus making it impossible to make rapid and accurate judgments and provide protection for critical personal safety thresholds such as 30mA, 60mA, and 150mA.

[0033] To address the aforementioned problems, this invention innovatively introduces a second signal conditioning path. Instead of imposing unrealistic performance requirements on a single circuit, it decomposes and processes the complex raw signal through a functionally specialized parallel path.

[0034] Specifically, in combination Figure 5As shown, the second signal conditioning path includes a second operational amplifier module and a second filter circuit connected in sequence. The output of the second filter circuit is connected to the dedicated acquisition channel of the control unit. The second operational amplifier module further includes a third operational amplifier circuit and a fourth operational amplifier circuit, which together form a two-stage differential amplifier structure.

[0035] The third operational amplifier circuit is configured as a differential amplifier circuit, with its core components being the third operational amplifier U3, resistors R9, R10, R11, and R12, and capacitors C5 and C6. Resistor R9 is connected in series between the first reference voltage terminal Vref1 and the inverting input terminal of the third operational amplifier U3. Resistor R10 is connected in series between the output terminal of the first operational amplifier U1 and the non-inverting input terminal of the third operational amplifier. Resistor R11 and capacitor C5 are connected in parallel between the inverting input terminal and the output terminal of the third operational amplifier U3, forming the third feedback network, used to set the gain of this stage and assist in filtering. Resistor R12 and capacitor C6 are connected in parallel between the non-inverting input terminal and the third reference voltage terminal Vref3, together forming the third matching network to ensure impedance balance at the input terminals.

[0036] The fourth operational amplifier circuit further amplifies and conditions the signal. Its core components include the fourth operational amplifier U4, resistors R13, R14, R15, and R16, and capacitors C7 and C8. Resistor R13 is connected in series between the output of the third operational amplifier U3 and the non-inverting input of the fourth operational amplifier U4. Resistor R14 is connected in series between the third reference voltage terminal Vref3 and the inverting input of the fourth operational amplifier U4. Resistor R16 and capacitor C8 are connected in parallel between the inverting input and output of the fourth operational amplifier U4, forming the fourth feedback network. Resistor R15 and capacitor C7 are connected in parallel between the non-inverting input and the fourth reference voltage terminal Vref4 of the fourth operational amplifier U4, together forming the fourth matching network.

[0037] It should be noted that the above embodiments are merely a preferred implementation of this utility model and are not intended to limit the scope of this utility model. Under the core concept of this utility model, the specific implementation of the second signal conditioning path has a high degree of flexibility.

[0038] First, in this embodiment, the second signal conditioning path is described as sharing the first-stage operational amplifier circuit with the first signal conditioning path, i.e., obtaining the signal from its output. This shared front-end design facilitates circuit integration and utilizes the first-stage operational amplifier as a buffer to improve signal quality. However, as... Figure 3As shown, in practical applications, depending on the system's specific requirements for isolation, noise performance, or cost, the input terminal of the second signal conditioning path can also be directly connected to the output terminal of the leakage current sensor, forming a completely independent parallel processing channel with the first signal conditioning path. Both of these input methods fall within the protection scope of this utility model.

[0039] Secondly, this embodiment uses a two-stage cascaded differential operational amplifier circuit to form the second operational amplifier module as an example to achieve sufficiently high gain and filtering effect. However, in practical applications, the number of cascaded operational amplifier circuits in the second operational amplifier module is not fixed. Those skilled in the art can flexibly increase or decrease the number of cascaded operational amplifier circuits according to the specific gain requirements of the system for small-range signals, the target frequency response characteristics, and the required filtering depth.

[0040] As long as the parallel dual-channel basic architecture of this utility model is adopted, in which the second signal conditioning path achieves accurate measurement of small-range sudden leakage current through a gain higher than that of the first signal conditioning path and a dedicated low-pass filter design, then regardless of how its input node is selected or how its internal operational amplifier stages are increased or decreased, it should be considered within the protection scope of this utility model patent.

[0041] Signal processing mechanism of the second signal conditioning pathway (GFCI2): The second signal conditioning path is the core innovation of this utility model. Its design purpose is to accurately extract the low-frequency, small-amplitude mutation components that are crucial to personal safety from the complex full-spectrum leakage current signal. Its signal processing also follows the principle of combining amplitude conditioning and frequency conditioning.

[0042] Amplitude Conditioning: The second operational amplifier module performs specialized processing on the signal amplitude through its multi-stage differential amplifier circuit. The total voltage gain coefficient of this channel is set to a value significantly greater than the gain V1 of the first channel, aiming to amplify the weak milliampere-level leakage current signal to the optimal voltage range that the control unit ADC can accurately sample. Furthermore, since operational amplifiers U3 and U4 are powered by a single power supply (e.g., VCC=12V), their output voltage range is strictly limited to a linear range of 0 to 12V. When the leakage current corresponding to the input signal exceeds -3A to 3A, the output voltage after amplification by the high-gain V2 will exceed the linear range of the operational amplifier, entering a saturation or clipping state. This non-linear saturation characteristic ensures that the second signal conditioning path maintains a linear response and effective output only for small-range currents within the range of -3A to 3A, while automatically ignoring currents exceeding this range, thus achieving accurate detection of small-range leakage currents at the hardware level.

[0043] Frequency Conditioning: The second operational amplifier module and the second filter circuit together form a filter network with an extremely low cutoff frequency. In the amplifier circuit, C5 and R11, and C7 and R15 respectively form two first-order low-pass filter stages for initial frequency selection. The signal amplified by operational amplifier U4 is further enhanced by the subsequent second filter circuit, which ultimately limits the bandwidth of the output signal to below 16Hz. This ultra-low cutoff frequency of 16Hz aims to completely filter out mid-to-high frequency interference generated by inverter switching noise, power grid frequency and its harmonics, retaining only the characteristic frequency component of the relatively slowly changing contact leakage current, thereby greatly improving the signal-to-noise ratio.

[0044] In summary, this invention utilizes at least two independent signal conditioning paths to apply different gains and filters to the voltage signal output from the same leakage current sensor, thereby enabling specialized measurement of leakage currents of varying magnitudes. The first signal conditioning path transmits the voltage amplitude information corresponding to a continuous leakage current of several amperes without distortion. Simultaneously, filtering appropriately limits the signal bandwidth to remove unnecessary high-frequency noise, providing accurate data for the control unit to assess the overall insulation status of the system. The second signal conditioning path, through the synergistic effect of high-gain amplification and ultra-low-pass filtering, selectively filters out high-amplitude and high-frequency components from the original signal, ultimately outputting a low-amplitude, low-frequency sampling signal to the control unit. This signal perfectly meets the precise judgment requirements for critical safety thresholds such as 30mA, 60mA, and 150mA, and is specifically designed for achieving rapid and reliable personal safety protection.

[0045] It should be emphasized that the above are merely preferred embodiments of the present utility model and are not intended to limit the present utility model in any way. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present utility model shall still fall within the scope of the technical solution of the present utility model.

Claims

1. A leakage current detection circuit, characterized in that, include: A leakage current sensor is used to sense the leakage current on the output side of the inverter and generate a raw electrical signal. A parallel signal conditioning module, electrically connected to the leakage current sensor, is used to perform at least two parallel processing steps on the original electrical signal, wherein: The gain of the first signal conditioning path is set to be suitable for handling leakage current within the first range. The gain of the second signal conditioning path is greater than the gain of the first signal conditioning path, and it is set to be suitable for processing leakage current in the second range, wherein the upper limit of the second range is less than the lower limit of the first range. The control unit is electrically connected to the parallel signal conditioning module and is used to receive and process output signals from the first signal conditioning path and the second signal conditioning path.

2. The leakage current detection circuit according to claim 1, characterized in that, The leakage current in the first range is a continuous leakage current in the ampere range.

3. The leakage current detection circuit according to claim 1, characterized in that, The leakage current in the second range is a sudden leakage current or a small leakage current in the milliampere range.

4. The leakage current detection circuit according to claim 1, characterized in that, The first signal conditioning path includes a first operational amplifier module and a first filter circuit connected in sequence, and the output terminal of the first filter circuit is connected to the control unit; the first operational amplifier circuit in the first operational amplifier module is configured as a differential amplifier circuit, including a first operational amplifier U1, resistors R1, R2, R3, R4, capacitors C1 and C2. The resistor R1 is connected in series between the first output terminal of the leakage current sensor and the inverting input terminal of the first operational amplifier U1; The resistor R2 is connected in series between the second output terminal of the leakage current sensor and the non-inverting input terminal of the first operational amplifier U1; The resistor R3 and the capacitor C1 are connected in parallel and between the inverting input terminal and the output terminal of the first operational amplifier to form a first feedback network. The resistor R4 and the capacitor C2 are connected in parallel and between the non-inverting input terminal of the first operational amplifier and the first reference voltage terminal Vref1, together forming the first matching network.

5. The leakage current detection circuit according to claim 4, characterized in that, The first operational amplifier module further includes a second operational amplifier circuit, which is configured as a differential amplifier circuit, including a second operational amplifier U2, resistors R5, R6, R7, and R8, capacitors C3 and C4. The resistor R5 is connected in series between the output terminal of the first operational amplifier U1 and the non-inverting input terminal of the second operational amplifier U2; The resistor R6 is connected in series between the first reference voltage terminal Vref1 and the inverting input terminal of the second operational amplifier U2; The resistor R8 and the capacitor C4 are connected in parallel and between the inverting input terminal and the output terminal of the second operational amplifier, together forming the second feedback network; The resistor R7 and capacitor C3 are connected in parallel and between the non-inverting input terminal of the second operational amplifier U2 and the second reference voltage terminal Vref2, together forming the second matching network.

6. The leakage current detection circuit according to claim 4, characterized in that, The second signal conditioning path includes a second operational amplifier module and a second filter circuit connected in sequence, and the output terminal of the second filter circuit is connected to the control unit; the third operational amplifier circuit in the second operational amplifier module is configured as a differential amplifier circuit, and its input terminals include a first input terminal and a second input terminal; the third operational amplifier circuit includes a third operational amplifier U3, resistors R9, R10, R11, and R12, capacitors C5 and C6; The resistor R9 is connected in series between the first input terminal and the inverting input terminal of the third operational amplifier U3; The resistor R10 is connected in series between the second input terminal and the non-inverting input terminal of the third operational amplifier; The resistor R11 and the capacitor C5 are connected in parallel and between the inverting input terminal and the output terminal of the third operational amplifier U3 to form a third feedback network. The resistor R12 and the capacitor C6 are connected in parallel and between the non-inverting input terminal of the third operational amplifier U3 and the third reference voltage terminal Vref3, together forming the third matching network.

7. The leakage current detection circuit according to claim 6, characterized in that, The first input terminal of the third operational amplifier circuit is connected to the first output terminal of the leakage current sensor; the second input terminal of the third operational amplifier circuit is connected to the second output terminal of the leakage current sensor.

8. The leakage current detection circuit according to claim 6, characterized in that, The first input terminal of the third operational amplifier circuit is connected to the first reference voltage terminal Vref1 of the first operational amplifier circuit; the second input terminal of the third operational amplifier circuit is connected to the output terminal of the first operational amplifier U1.

9. The leakage current detection circuit according to claim 6, characterized in that, The second operational amplifier module also includes a fourth operational amplifier circuit, which is configured as a differential amplifier circuit, including a fourth operational amplifier U4, resistors R13, R14, R15, R16, capacitor C7, and capacitor C8. The resistor R13 is connected in series between the output terminal of the third operational amplifier U3 and the non-inverting input terminal of the fourth operational amplifier U4; The resistor R14 is connected in series between the third reference voltage terminal Vref3 and the inverting input terminal of the fourth operational amplifier U4; The resistor R16 and the capacitor C8 are connected in parallel and between the inverting input terminal and the output terminal of the fourth operational amplifier U4 to form a fourth feedback network. The resistor R15 and the capacitor C7 are connected in parallel and between the non-inverting input terminal of the fourth operational amplifier U4 and the fourth reference voltage terminal Vref4, together forming the fourth matching network.

10. An inverter, characterized in that, include: A DC / AC circuit has its DC input terminal connected to a photovoltaic module and its AC output terminal connected to the power grid or load via a three-phase cable. The leakage current detection circuit as described in any one of claims 1-9 has its leakage current sensor sleeved on the three-phase cable and its control unit connected to the DC / AC circuit.

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