Leakage current detection circuit suitable for photovoltaic grid-connected inverter
By combining an AC sampling transformer with a DC sampling transformer and using a self-excited oscillation circuit for high-frequency processing, high-precision, wide-bandwidth detection of AC and DC leakage current in photovoltaic grid-connected inverters is achieved. This solves the problems of complex circuits, high costs, and low power density in existing technologies, and improves the safety and operating efficiency of the system.
Patent Information
- Application Number
- CN202423312738.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2024-12-31
- Publication Date
- 2026-01-20
- Estimated Expiration
- 2034-12-31
AI Technical Summary
Existing leakage current detection circuits for photovoltaic grid-connected inverters suffer from problems such as circuit complexity, high cost, insufficient detection accuracy, and low power density. In particular, they are difficult to process low-frequency signals in DC detection and have insufficient system operating efficiency.
The AC sampling transformer and DC sampling transformer work together, and a self-excited oscillation circuit is used for high-frequency processing. The AC and DC integrated detection is achieved through an amplification circuit and a digital signal processing unit, including threshold storage, signal comparison and switching circuit control.
It achieves high-precision, wide-bandwidth detection of AC and DC leakage current, simplifies circuit structure, reduces costs, improves system power density and real-time response capability, and ensures system safety.
Smart Images
Figure CN223815426U_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The utility model relates to detection technical field especially is applicable to photovoltaic grid-connected inverter's leakage current detection circuit. BACKGROUND
[0002] The application of leakage current detection technology in photovoltaic grid-connected inverters is mainly used for detecting leakage current in direct current and alternating current circuits to prevent electric shock accidents and ensure the safe and stable operation of the system. In the prior art, leakage current detection is mainly carried out separately for alternating current leakage current and direct current leakage current. The alternating current leakage current detection usually adopts a current transformer to realize leakage current collection by detecting the current difference between the phase line and the zero line, and the direct current leakage current detection usually adopts an independent sampling circuit and an analog signal processing unit. Although this method can meet the basic leakage current detection requirements, there are still the following problems in actual application:
[0003] 1. Complex circuit and high cost: Since the alternating current leakage current detection and the direct current leakage current detection are designed separately and operate independently, the circuit structure is complex and the number of components is large, which not only increases the cost but also reduces the reliability of the system.
[0004] 2. Difficulty in accurately processing low-frequency signals: The existing direct current leakage current detection circuit usually cannot directly process low-frequency direct current signals and needs complex signal amplification and filtering processing, which results in insufficient detection accuracy, especially when processing low-amplitude direct current components, which is prone to signal distortion or noise interference.
[0005] 3. Insufficient system power density and operation efficiency: Since the separation design of the alternating current and direct current leakage current detection modules occupies a large amount of circuit board space, it is difficult to further improve the power density of the system. In addition, the long signal processing path of the separation detection method easily causes signal delay, affecting the real-time performance of the leakage current detection and the operation efficiency of the system.
[0006] In order to overcome the above problems, some technical solutions try to integrate the alternating current and direct current detection modules or improve the signal processing unit to improve the detection accuracy. However, these methods also face new problems. For example, in the integrated design, since the processing requirements of alternating current signals and direct current signals cannot be met at the same time, the detection circuit often needs special customized design, which further increases the development difficulty and cost; and in the scheme of improving the signal processing unit, the complex filtering and amplification design has too high a requirement on the hardware performance, which still cannot effectively balance the contradiction between detection accuracy and power density.
[0007] Therefore, how to realize efficient integrated detection of alternating current and direct current leakage current, simplify the circuit structure, improve the detection accuracy and system power density, and effectively reduce the cost, has become a technical problem to be solved by the utility model. The utility model discloses a photovoltaic grid-connected inverter leakage current detection circuit
[0008] The utility model discloses a photovoltaic grid-connected inverter leakage current detection circuit, which is used to solve the problems of the existing leakage current detection technology circuit, such as complexity, insufficient detection accuracy, low power density and low operation efficiency.
[0009] To solve the above technical problems, the utility model adopts the following technical solutions:
[0010] A photovoltaic grid-connected inverter leakage current detection circuit includes:
[0011] An AC sampling transformer is used to detect the current difference between the phase line and the zero line and generate an AC signal reflecting the AC leakage current.
[0012] A DC sampling transformer is used to extract the DC component in the leakage current through a multi-turn coil and a magnetic core and output an electrical signal corresponding to the DC component.
[0013] A self-oscillating circuit is electrically connected to the DC sampling transformer and is used to oscillate the electrical signal and convert it into a high-frequency signal.
[0014] An amplification circuit is electrically connected to the AC sampling transformer and the self-oscillating circuit and is used to amplify the AC signal and the oscillated high-frequency signal.
[0015] A digital signal processing unit includes:
[0016] A threshold storage module is used to store a preset leakage current threshold.
[0017] A signal processing module is connected to the amplification circuit and is used to receive the amplified AC signal and high-frequency signal and compare the signals with the leakage current threshold.
[0018] A control signal output module is used to generate a control signal according to the comparison result.
[0019] A switching circuit is connected to the control signal output module of the digital signal processing unit and is used to cut off the power supply of the photovoltaic grid-connected inverter when receiving the control signal.
[0020] As a further solution of the utility model, the DC sampling transformer includes a magnetic core for coupling the DC component in the leakage current to a multi-turn coil, and the multi-turn coil is connected to the self-oscillating circuit for outputting an electrical signal corresponding to the DC component.
[0021] As a further scheme of the utility model, the self-oscillation circuit comprises an oscillation unit, which is used for oscillating the received direct current signal and generating a high frequency signal of 7-8 kHz.
[0022] As a further scheme of the utility model, the amplification circuit comprises: a first amplification unit, which is used for amplifying the alternating current signal; a second amplification unit, which is used for amplifying the high frequency signal after oscillation processing; and a filter unit, which is used for filtering high frequency noise in the signal.
[0023] As a further scheme of the utility model, the digital signal processing unit further comprises a filter module, which is connected with the signal processing module and is used for filtering the received alternating current signal and high frequency signal to filter high frequency noise and harmonic components.
[0024] As a further scheme of the utility model, the utility model further comprises an input filter and an output filter, the input filter is connected with the alternating current sampling transformer and is used for filtering high frequency noise and harmonic current at the power input end, and the output filter is connected with the amplification circuit and is used for filtering high frequency components in the amplified signal.
[0025] Compared with the prior art, the utility model has the beneficial effects that:
[0026] 1. The alternating current sampling transformer and the direct current sampling transformer are cooperatively applied, the direct current component is high-frequency processed through the direct current sampling transformer combined with the self-oscillation circuit, is uniformly transmitted to the amplification circuit and the digital signal processing unit, so that the detection scheme of alternating current and direct current integration is realized on the hardware.
[0027] 2. Based on the double detection of the alternating current sampling transformer and the direct current sampling transformer, combined with the high-frequency processing of the self-oscillation circuit, the dynamic gain adjustment of the amplification circuit, the noise suppression of the filter and the intelligent control of the digital signal processing unit, a multi-module deep cooperation structure is formed, which can meet the high precision, wide frequency band and multi-scene requirements of the leakage current detection.
[0028] The additional aspects and advantages of the utility model will be partially given in the following description, partially will become obvious from the following description, or will be understood through the practice of the utility model. BRIEF DESCRIPTION OF DRAWINGS
[0029] In order to more clearly illustrate the technical scheme in the embodiments of the utility model or the prior art, the following will briefly introduce the drawings needed to be used in the embodiment or the prior art description, obviously, the drawings in the following description are only some embodiments of the utility model, and for those skilled in the art, other drawings can also be obtained without creative labor under the premise of the drawings.
[0030] Figure 1 : System overall circuit structure diagram.
[0031] Figure 2 : AC leakage current detection module circuit diagram.
[0032] Figure 3 : DC leakage current detection module circuit diagram.
[0033] Figure 4 : Digital signal processing and response control module circuit diagram. DETAILED DESCRIPTION
[0034] The technical solutions in the embodiments of the present application will be clearly and completely described below. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the present application.
[0035] Please refer to Figure 1 — Figure 4 In the embodiments of the present application, a leakage current detection circuit suitable for a photovoltaic grid-connected inverter comprises: an AC sampling transformer, configured to detect the current difference between a phase line and a zero line and generate an AC signal reflecting AC leakage current; a DC sampling transformer, configured to extract a DC component in the leakage current through a multi-turn coil and a magnetic core and output an electric signal corresponding to the DC component; a self-oscillation circuit, electrically connected with the DC sampling transformer, configured to perform oscillation processing on the electric signal and convert the electric signal into a high-frequency signal;
[0036] An amplification circuit, electrically connected with the AC sampling transformer and the self-oscillation circuit, configured to amplify the AC signal and the high-frequency signal after oscillation; a digital signal processing unit, comprising:
[0037] a threshold storage module, configured to store a preset leakage current threshold; a signal processing module, connected with the amplification circuit, configured to receive the amplified AC signal and high-frequency signal and compare the signals with the leakage current threshold; and a control signal output module, configured to generate a control signal according to the comparison result.
[0038] A switching circuit, connected with the control signal output module of the digital signal processing unit, configured to cut off the power supply of the photovoltaic grid-connected inverter when the control signal is received.
[0039] The direct current sampling mutual inductor comprises a magnetic core for coupling a direct current component in a leakage current to a multi-turn coil; the multi-turn coil is connected with a self-oscillation circuit for outputting an electric signal corresponding to the direct current component; the self-oscillation circuit comprises an oscillation unit for oscillating the received direct current electric signal and generating a high frequency signal of 7-8 kHz; the amplification circuit comprises a first amplification unit for amplifying an alternating current signal; a second amplification unit for amplifying the high frequency signal after oscillation processing; and a filter unit for filtering high frequency noise in the signal.
[0040] The digital signal processing unit further comprises a filter module connected with the signal processing module for filtering the received alternating current signal and high frequency signal to filter high frequency noise and harmonic components.
[0041] Embodiment 1
[0042] In the actual application scenario of photovoltaic grid-connected inverters, accurate detection of leakage current is crucial for the safe operation of the system. In particular, in high-power photovoltaic grid-connected inverters, due to the presence of photovoltaic module-to-ground capacitance, an alternating current and direct current mixed form of leakage current is generated. If real-time detection and rapid power cutoff cannot be achieved, it may lead to equipment damage or even electric shock accidents. In the prior art, a separate alternating current leakage current detection and direct current leakage current detection scheme is usually adopted, but this approach has problems such as complex circuit, insufficient detection accuracy, and limited power density, making it difficult to meet the efficient operation requirements of modern photovoltaic systems.
[0043] The present embodiment provides a leakage current detection circuit suitable for photovoltaic grid-connected inverters, which significantly improves detection accuracy, anti-interference ability and system power density through integrated AC / DC detection and multi-module cooperative work.
[0044] In practical applications, the leakage current detection circuit of the present application is integrated into a photovoltaic grid-connected inverter for monitoring the leakage current between the direct current bus and the alternating current output. The circuit comprises an alternating current sampling transformer, a direct current sampling mutual inductor, a self-oscillation circuit, an amplification circuit, a digital signal processing unit and a switching circuit. The specific working mode is as follows:
[0045] In normal operation of the inverter, the AC sampling transformer generates an AC signal reflecting the AC leakage current by detecting the current difference between the phase line and the zero line. At the same time, the DC sampling transformer extracts the leakage current on the DC bus through multiple turns of the coil and the magnetic core, and outputs an electrical signal corresponding to the DC component. The traditional DC detection circuit cannot effectively process low-frequency DC signals, but the high sensitivity design of the DC sampling transformer in this embodiment allows accurate extraction and transmission of low-frequency DC components to the self-oscillating circuit.
[0046] The self-oscillating circuit is connected to the DC sampling transformer, which processes the extracted DC leakage current signal to high frequency, converting the low-frequency signal to a high-frequency signal of 7 to 8 kHz. This process overcomes the noise interference problem in low-frequency signal processing of traditional DC detection circuits. At the same time, the AC signal and the high-frequency processed DC signal enter the amplification circuit, which is amplified through multiple stages and dynamic gain adjustment to ensure that the signal amplitude meets the input requirements of the digital signal processing unit, further improving the accuracy of signal processing.
[0047] The amplified AC signal and high-frequency signal are transmitted to the digital signal processing unit. The digital signal processing unit converts the analog signal to a digital signal through an analog-to-digital conversion module, and combines the pre-set leakage current threshold to perform real-time comparison through a signal processing module. Once the leakage current exceeds the threshold, the control signal output module generates a control signal immediately, triggering the switch circuit to cut off the power supply. This fast response mechanism significantly improves the safety of the system, helping to avoid the risk of equipment damage and personal injury.
[0048] In actual operation, this embodiment can efficiently detect AC and DC leakage currents in a wide frequency range (0 to 700 Hz) and accurately process the low-frequency components of the DC signal. Compared to the traditional separate detection scheme, the detection circuit structure is simplified, the number of components is reduced through integrated design, the production cost is reduced, the detection accuracy is improved, the self-oscillating circuit significantly reduces noise interference, the power density is improved, the integrated design saves circuit board space, and meets the application requirements of high-power inverters. The intelligent digital signal processing unit and control signal output module ensure the ability to cut off the power supply in real time.
[0049] For example, in a 500 kW photovoltaic power station grid-connected inverter, this circuit can accurately detect a leakage current of only 0.5 mA between the bus and the ground, and complete the cut-off operation within 10 milliseconds when the leakage current exceeds the threshold of 5 mA. In the traditional scheme, the DC leakage current signal is easily disturbed by noise, leading to false negatives or delayed cut-off, posing a significant safety hazard. The application of this embodiment completely solves this problem, not only improving safety, but also reducing maintenance costs due to false negatives.
[0050] Embodiment 2:
[0051] In the practical application of new energy electric vehicle charging piles, the performance of the leakage current detection system directly affects the charging safety and the efficiency of the equipment. Since the charging pile involves both DC high-voltage input and AC output interface, the leakage current detection needs to monitor the DC leakage current between the DC bus and the ground, as well as the AC leakage current in the AC power supply line. In this scenario, the conventional separate leakage current detection scheme faces problems such as complex structure, inaccurate detection, insufficient real-time response capability, and is difficult to adapt to the urgent needs of electric vehicle charging piles for efficient and safe leakage current detection.
[0052] The leakage current detection circuit provided by the embodiment successfully applies to electric vehicle charging piles through an AC-DC integrated detection structure combined with the cooperative work of the filter and the intelligent control unit, significantly improving the real-time performance and reliability of leakage current detection.
[0053] In actual use, the leakage current detection circuit of the present application is integrated into the charging pile control system to monitor the leakage current between the DC input end and the ground and the leakage current of the AC power supply interface. The specific working process is as follows: during the charging process, the DC leakage current on the DC bus is extracted by the DC sampling transformer, and a signal reflecting the DC component is generated through the coupling of the multi-turn coil and the magnetic core. At the same time, the AC leakage current in the AC power supply line is detected by the AC sampling transformer through the current difference between the phase line and the zero line to generate an AC signal. This design realizes the synchronous sampling of AC and DC signals, ensuring the completeness of the detection. The DC signal is transmitted to the self-oscillation circuit by the DC sampling transformer, and the oscillation circuit converts the DC signal into a high-frequency signal (7 kHz to 8 kHz) to adapt to the bandwidth requirements of subsequent signal processing. The AC signal and the high-frequency processed DC signal enter the amplification circuit together, are amplified by multiple stages through the dynamic gain adjustment module, and are effectively filtered by the filter to remove noise interference and harmonic components. Such a design ensures the stability and accuracy of signal transmission, providing high-quality signals for subsequent intelligent judgment. The amplified AC signal and high-frequency DC signal are received by the digital signal processing unit, converted into digital signals by the analog-to-digital converter, and then compared with the preset leakage current threshold by the digital signal processing module in real time. Once the leakage current exceeds the safety threshold, the control signal output module in the digital signal processing unit immediately sends a signal to trigger the switching circuit of the charging pile to cut off the power supply, thereby effectively preventing electric shock accidents or equipment damage.
[0054] For example, in a set of 120-kilowatt electric vehicle charging pile test, the detection circuit of the application can accurately detect the direct current side leakage current of 0.3 milliampere, and complete the power cut-off operation within 5 milliseconds when detecting a leakage current of 5 milliampere. Compared with the traditional scheme, its response speed is improved by nearly one time, and the detection accuracy is improved by more than 40%, effectively solving the problems of slow response and high false alarm rate in the traditional detection scheme.
[0055] Embodiment 3:
[0056] The leakage current detection circuit and its working principle of the application are described in detail below in combination with the drawings. Each figure corresponds to the display of different functional modules and overall circuit design.
[0057] Referring to Figure 1 , the overall structure of the leakage current detection circuit is shown, including an alternating current sampling transformer, a direct current sampling transformer, a self-oscillation circuit, an amplification circuit, a digital signal processing unit and a switching circuit. The alternating current sampling transformer is used to detect the current difference between the phase line and the zero line, and outputs a signal reflecting the alternating current leakage current; the direct current sampling transformer extracts the direct current component through a magnetic core and a multi-turn coil, and outputs a signal corresponding to the direct current leakage current. After being processed by oscillation and dynamically gain-adjusted, the two signals enter the digital signal processing unit, which judges whether there is a leakage fault through a preset threshold value, and controls the switching circuit to quickly cut off the power supply. Through the deep cooperation between the modules, the overall structure realizes efficient detection of alternating and direct current leakage currents.
[0058] Referring to Figure 2 , the design of the alternating current sampling transformer and its related filter is shown. The alternating current input enters the sampling transformer after being suppressed by the input filter to suppress high-frequency noise. The primary winding of the transformer is connected to the phase line and the zero line, and the secondary winding generates an electrical signal corresponding to the alternating current leakage current. After passing through the filter circuit composed of capacitors and resistors, it enters the amplification circuit for further processing. This module effectively suppresses interference through filter design, ensuring the clarity of the alternating current leakage current signal.
[0059] Referring to Figure 3 , the combined design of the direct current sampling transformer and the self-oscillation circuit is shown. The direct current sampling transformer couples the direct current component in the leakage current to the multi-turn coil through the magnetic core, generating a signal reflecting the direct current leakage current. After entering the self-oscillation circuit, the signal is converted to a high-frequency signal of 7 kilohertz to 8 kilohertz by the oscillation unit, which facilitates subsequent amplification and digital processing. Through this design, the detection accuracy of the direct current signal is significantly improved, especially in the processing of low-frequency direct current components, overcoming the problem of large noise interference in traditional circuits.
[0060] And, referring to Figure 4The specific design of the digital signal processing unit and the switch control circuit is shown. The amplified alternating current signal and high-frequency direct current signal are transmitted to an analog-to-digital converter, and after being converted into a digital signal, the signal is analyzed by a signal processing module and compared with a preset leakage current threshold. When the detected leakage current exceeds the threshold, the control signal output module generates a control signal to trigger the protection mechanism through the switch circuit to cut off the power supply. The switch circuit design also includes a protection module to suppress the influence of transient overcurrent on the system.
[0061] In the utility model, unless another definite provision and limitation, the terms "mount", "set", "connect", "fix", "screw" and so on should do the broad sense understanding, for example, can be fixed connection, also can be detachable connection, or be integrated;Can be mechanical connection, also can be electrical connection;Can be directly connected, also can be indirectly connected through the intermediate medium, can be the communication or the interaction relationship of two elements inside two elements, unless another definite limitation, for the ordinary skilled person in the art, can understand the specific meaning of the above terms in the utility model according to specific circumstances.
[0062] For those skilled in the art, it is obvious that the utility model is not limited to the details of the above exemplary embodiments, and the utility model can be realized in other specific forms without departing from the spirit or basic characteristics of the utility model. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting, and the scope of the utility model is defined by the appended claims rather than the above description, and therefore all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be included in the utility model.
Claims
1. A leakage current detection circuit suitable for use in a photovoltaic grid-tied inverter, characterized by, The application relates to a leakage current detection device for photovoltaic grid-connected inverters. The device comprises: an alternating current sampling transformer for detecting the current difference between a phase line and a zero line and generating an alternating current signal reflecting the alternating leakage current; a direct current sampling transformer for extracting the direct current component in the leakage current through a multi-turn coil and a magnetic core and outputting an electric signal corresponding to the direct current component; a self-oscillation circuit electrically connected to the direct current sampling transformer for oscillating the electric signal and converting the electric signal into a high-frequency signal; an amplification circuit electrically connected to the alternating current sampling transformer and the self-oscillation circuit for amplifying the alternating current signal and the oscillated high-frequency signal; a digital signal processing unit comprising: a threshold storage module for storing a preset leakage current threshold; a signal processing module connected to the amplification circuit for receiving the amplified alternating current signal and high-frequency signal and comparing the signals with the leakage current threshold; a control signal output module for generating a control signal according to the comparison result; and a switching circuit connected to the control signal output module of the digital signal processing unit for cutting off the power supply of the photovoltaic grid-connected inverter when the control signal is received. The direct current sampling transformer comprises a magnetic core for coupling the direct current component in the leakage current to a multi-turn coil; the multi-turn coil is connected to the self-oscillation circuit for outputting an electric signal corresponding to the direct current component. The self-oscillation circuit comprises an oscillation unit for oscillating the received direct current signal and generating a high-frequency signal of 7-8 kHz. The amplification circuit comprises a first amplification unit for amplifying the alternating current signal, a second amplification unit for amplifying the oscillated high-frequency signal, and a filter unit for filtering high-frequency noise in the signals. The digital signal processing unit further comprises a filter module connected to the signal processing module for filtering the received alternating current signal and high-frequency signal to filter high-frequency noise and harmonic components. The device further comprises an input filter connected to the alternating current sampling transformer for filtering high-frequency noise and harmonic current at the power input end and an output filter connected to the amplification circuit for filtering high-frequency components in the amplified signals. 2. The leakage current detection circuit for photovoltaic grid-tied inverters according to claim 1, wherein, 3. The leakage current detection circuit for photovoltaic grid-tied inverters according to claim 1, wherein, 4. The leakage current detection circuit for photovoltaic grid-tied inverters according to claim 1, wherein, 5. The leakage current detection circuit for photovoltaic grid-tied inverters according to claim 1, wherein, 6. The leakage current detection circuit for photovoltaic grid-tied inverters according to claim 1, wherein,