Leakage current detection circuit and leakage current protection circuit

Abstract

The utility model relates to a leakage current detection circuit, which comprises a mutual inductance module, an excitation module, a signal processing module, a feedback self-checking module and a calculation module. The mutual inductance module comprises a magnetic core, a first winding and a second winding. The excitation module is used for generating excitation current in the first winding. The signal processing module is used for processing the output voltage signal of the first winding and outputting a processed signal, and the voltage signal corresponding to the excitation current is filtered out of the processed signal. The feedback self-checking module comprises a feedback circuit and a self-checking circuit, the feedback circuit is used for generating feedback current in the second winding according to the processed signal, and the self-checking circuit is used for generating self-checking current in the second winding according to the self-checking signal. And the calculation module is used for carrying out leakage current analysis according to the processed signal and outputting a self-checking signal in a self-checking mode. The utility model also relates to a leakage current protection circuit.

Description

Technical Field

[0001] The utility model relates to the field of leakage current detection, in particular to a leakage current detection circuit and a leakage current protection circuit. Background Art

[0002] In order to ensure the safety of electricity use, leakage current detection and leakage current protection in the power distribution process are crucial. According to the applicable detection current type, there are AC type, A type and B type leakage current detection. Unlike AC type and A type leakage current detection, B type leakage current detection can detect the DC component in the leakage current in addition to the AC leakage current. Therefore, it is widely used in three-phase variable speed industrial drives, single-phase / three-phase chargers for electric vehicles, three-phase photovoltaic system medical equipment, DC current loads, etc., providing effective monitoring and protection for circuits and electrical equipment.

[0003] The current mainstream B-type leakage current detection is based on fluxgate technology. The detected current passes through the magnetic core, injects an excitation signal into the winding wrapped around the magnetic core, excites the magnetic core and repeatedly saturates the magnetic core in the forward and reverse directions. In this process, the primary current affects the secondary induced electromotive force, and then the secondary output voltage signal is analyzed with the help of software or hardware. According to different requirements for detection accuracy, stability, size, etc., leakage current detection can be performed with the help of a single magnetic core or a dual magnetic core, and an open-loop detection scheme or a closed-loop detection scheme (that is, there is a feedback mechanism) can be adopted.

[0004] Safety standards require that the leakage current detection circuit or leakage current detection device has a self-test function, that is, regularly and manually actively introduce leakage current into the leakage current detection circuit to check whether the leakage current detection function of the leakage current detection circuit is normal. At present, the self-test function of the leakage current detection device is usually achieved by drawing leakage current from the mains, which requires the use of a separate self-test winding and a self-test circuit. And because the mains is AC, this method of drawing leakage current is actually unable to check whether the leakage current detection circuit's detection function of the DC component in the current is normal, and the self-test current amplitude and waveform are fixed, making the self-test function single. Utility Model Content

[0005] In order to solve the above problems, the utility model provides a leakage current detection circuit and a leakage current protection circuit, which adopt a closed-loop detection scheme of a single magnetic core and dual windings, and combine a self-test winding and a feedback winding, so that a separate self-test winding is not required. In addition, different types of self-test signals can be generated as needed through an algorithm.

[0006] An embodiment of the utility model provides a leakage current detection circuit, which can operate in a leakage current detection mode and a self-checking mode, wherein the leakage current detection circuit includes a mutual inductance module, an excitation module, a signal processing module, a feedback self-checking module and a calculation module.

[0007] The mutual inductance module includes a magnetic core, a first winding and a second winding. The magnetic core is used for a power line to pass through, and the first winding and the second winding are wound around the magnetic core.

[0008] The excitation module is connected to the first winding and is used to generate an excitation current in the first winding.

[0009] The signal processing module is connected to the first winding and the calculation module, and is used for processing the output voltage signal of the first winding and outputting a processed signal, wherein the voltage signal corresponding to the excitation current is filtered out of the processed signal.

[0010] The feedback self-test module is connected to the second winding and includes a feedback circuit and a self-test circuit. The feedback circuit is connected to the signal processing module and is used to generate a feedback current in the second winding according to the processed signal. The self-test circuit is connected to the calculation module and is used to generate a self-test current in the second winding according to the self-test signal.

[0011] The calculation module is used for performing leakage current analysis according to the processed signal, and for outputting the self-test signal in the self-test mode.

[0012] According to an embodiment of the present utility model, the excitation module includes a square wave excitation voltage generator, and the square wave excitation voltage generator is used to generate positive and negative square wave voltages of a predetermined frequency applied to the first winding.

[0013] According to an embodiment of the present invention, the predetermined frequency is a frequency greater than 5 times the frequency of the current being measured.

[0014] According to an embodiment of the utility model, the signal processing module includes a first resistor and a low-pass filter, wherein one end of the first resistor is connected to the first winding and the other end is grounded, so as to allow the output current of the first winding to flow back to the ground; and the low-pass filter is used to filter out the voltage signal corresponding to the excitation current from the output voltage signal.

[0015] According to an embodiment of the utility model, the feedback circuit generates a feedback current in the second winding according to the processed signal, so that the second winding generates a magnetic flux opposite to the magnetic flux generated by the measured current, and forms a zero magnetic flux state in the mutual inductance module.

[0016] According to an embodiment of the present utility model, the feedback circuit comprises a second resistor, one end of the second resistor is connected to the signal processing module and the other end of the second resistor is connected to the second winding.

[0017] According to an embodiment of the present utility model, the self-test circuit includes a third resistor and a capacitor connected in series.

[0018] According to an embodiment of the present utility model, the computing module is a microcontroller.

[0019] According to an embodiment of the utility model, the leakage current detection circuit further includes: a gain conversion module connected between the signal processing module and the calculation module and / or connected between the self-test circuit and the calculation module, and the gain conversion module is used to scale the signal.

[0020] An embodiment of the utility model provides a leakage current protection circuit, wherein the leakage current protection circuit comprises: a leakage current detection circuit according to one of the embodiments of the utility model; and a switch connected to the leakage current detection circuit and a power line, the switch being used to disconnect the power line in response to a leakage current detected by the leakage current detection circuit.

[0021] The leakage current detection circuit of the utility model adopts a double-winding closed-loop detection scheme, which achieves higher stability and accuracy compared with the leakage current detection circuit that adopts a single-winding open-loop detection scheme. The leakage current detection circuit of the utility model eliminates the need for an additional self-test winding, and the self-test function can be realized by only using the double winding of the closed-loop detection, thereby reducing the size and saving costs. In addition, the leakage current detection circuit of the utility model can customize different self-test leakage current waveforms through algorithms, and has better self-test capabilities. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the technical solutions of the embodiments of the present utility model, the following briefly introduces the drawings required for the description of the embodiments. Obviously, the drawings described below are only some exemplary embodiments of the present utility model, and for ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0023] Figure 1 A schematic diagram of a leakage current detection circuit according to an embodiment of the utility model is shown;

[0024] Figure 2 The formation of the output voltage signal waveform of the first winding according to the embodiment of the utility model is exemplarily shown;

[0025] Figure 3 Shown according to Figure 1 A schematic diagram of exemplary electrical components of a leakage current detection circuit;

[0026] Figure 4a and Figure 4bThe schematic diagram of the waveform of the leakage current and the processed signal according to the embodiment of the utility model is exemplarily shown;

[0027] Figure 5 A schematic diagram of a leakage current protection circuit according to an embodiment of the utility model is shown. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical solution and advantages of the utility model more obvious, the exemplary embodiments of the utility model will be described in detail with reference to the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the utility model, rather than all the embodiments of the utility model, and it should be understood that the utility model is not limited to the exemplary embodiments described here.

[0029] In this specification and the drawings, steps and elements that are substantially the same or similar are indicated by the same or similar reference numerals, and repeated descriptions of these steps and elements will be omitted. Meanwhile, in the description of the present utility model, the terms "first", "second", etc. are only used to distinguish the description, and cannot be understood as indicating or implying relative importance or ranking.

[0030] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art in the field of the present invention. The terms used herein are only for the purpose of describing the embodiments of the present invention and are not intended to limit the present invention.

[0031] Figure 1 A schematic diagram of a leakage current detection circuit according to an embodiment of the utility model is shown.

[0032] like Figure 1 As shown, the leakage current detection circuit 100 may include, for example, a mutual inductance module 101, an excitation module 102, a signal processing module 103, a feedback self-test module 104, and a calculation module 105. The leakage current detection circuit according to the embodiment of the utility model can operate in a leakage current detection mode and a self-test mode. In the leakage current detection mode, the leakage current detection circuit detects whether there is leakage current in the power line, and in the self-test mode, the leakage current detection circuit self-tests whether the leakage current detection function is normal.

[0033] The mutual inductance module 101 may include, for example, a single magnetic core C, a first winding W1, and a second winding W2. The magnetic core C is passed through by power lines L1 and L2. The power lines L1 and L2 are only schematic. For example, in a single-phase power system, the power lines are a live line and a neutral line. In a three-phase four-wire power system, the power lines are three phase lines and a neutral line.

[0034] The first winding W1 and the second winding W2 are wound around the magnetic core C for generating and transmitting a magnetic field.

[0035] The excitation module 102 may be connected to the first winding W1, for example, to generate an excitation current in the first winding W1. The first winding W1 is loaded with an alternating excitation current with a fixed frequency and a fixed waveform, so that the magnetic core C is reciprocally magnetized to reach saturation.

[0036] pass Figure 2 The influence of the presence of leakage current on the output voltage signal waveform of the first winding is schematically explained. Figure 2 The formation of the output voltage signal waveform of the first winding according to the embodiment of the utility model is exemplarily shown.

[0037] Figure 2 The left side shows an example of an alternating excitation current waveform with a fixed frequency and a fixed waveform. It can be seen from the excitation current waveform that the magnetic core is repeatedly saturated under the application of the excitation current.

[0038] Figure 2 The waveform of the DC leakage current in the power lines L1 and L2 is exemplarily shown in the middle, wherein the waveform of the DC leakage current is a straight line.

[0039] Figure 2 The right side schematically shows the waveform of the output voltage signal of the first winding W1 when an excitation current is applied to the first winding W1 and a DC leakage current exists in the power supply lines L1 and L2 .

[0040] When there is no external current, i.e., leakage current in the power lines L1 and L2, the waveform of the output voltage signal of the first winding W1 should be consistent with the excitation current waveform, i.e., it only contains harmonics of the excitation waveform, and the waveform is symmetrical in positive and negative directions. When there is an external current containing a DC component, there are both a DC magnetic field and an excitation alternating magnetic field in the magnetic core C. The DC magnetic field generates an induced electromotive force and causes the excitation alternating magnetic field to saturate the magnetic core in advance in half of the excitation cycle, and delays the saturation of the magnetic core in the other half of the excitation cycle, thereby causing the waveform of the output voltage signal of the first winding W1 to be asymmetrical in the positive and negative half cycles in the excitation cycle, and in this way, a voltage is generated. Figure 2 The waveform is shown on the right.

[0041] Subsequently, the output voltage signal of the first winding W1 is processed with the help of the signal processing module 103 so that the voltage signal corresponding to the excitation current is filtered out, and the waveform corresponding to the measured current can be obtained, thereby realizing leakage current detection.

[0042] The signal processing module 103 is, for example, connected to the first winding W1 and the calculation module 105 , for processing the output voltage signal of the first winding W1 and outputting a processed signal from which the voltage signal corresponding to the excitation current generated by the excitation module 102 is filtered out.

[0043] According to the embodiment of the utility model, the output voltage signal is filtered before being output to the calculation module 105, which reduces the calculation cost of the calculation module 105 directly extracting signal features (high-frequency features, asymmetric time difference between positive and negative half cycles, asymmetric amplitude difference between positive and negative half cycles, etc.) from the output voltage signal, simplifies the circuit design, and reduces the detection error.

[0044] The feedback self-test module 104 can, for example, be connected to the second winding W2 and include a feedback circuit and a self-test circuit not shown, wherein the feedback circuit is used for closed-loop detection in a leakage current detection mode to improve the stability and accuracy of the detection, and the self-test circuit is used to simulate the presence of leakage current in the self-test mode.

[0045] The feedback circuit is, for example, connected to the signal processing module 103 and receives a processed signal from the signal processing module 103, and is used to generate a feedback current in the second winding W2 according to the processed signal. An exemplary feedback mechanism is that by generating a feedback current in the second winding W2, the second winding W2 generates a magnetic flux opposite to the magnetic flux generated by the measured current, i.e., the leakage current, and the feedback circuit is designed in such a way that a zero magnetic flux state is formed in the mutual inductance module 101, thereby achieving a feedback effect of reducing errors. Other known feedback mechanisms are also conceivable.

[0046] According to the embodiments of the present utility model, higher accuracy and stability are achieved through closed-loop detection, so that leakage current detection and subsequent leakage current protection are more reliable.

[0047] The self-test circuit is connected to the calculation module 105, for example. In the self-test mode, the power lines L1 and L2 are disconnected. Then, the self-test signal is designed and outputted with the aid of the calculation module 105. The self-test signal can be designed as required, for example, a DC or AC signal is set, the amplitude and frequency of the signal are set, etc. The self-test circuit generates a self-test current in the second winding W2 according to the self-test signal, and the self-test current generates a magnetic field in the magnetic core C, thereby simulating the situation where there is a leakage current in the power lines L1 and L2. In the case of a self-test current simulating a leakage current, when other modules work normally as in the leakage current detection mode, it is judged that the leakage current detection circuit passes the self-test. When the waveform of the processed signal and the waveform of the self-test signal, for example, have a frequency deviation, it is judged that the leakage current detection circuit has not passed the self-test, and further inspection of the leakage current detection circuit is required.

[0048] According to the embodiment of the utility model, by combining the self-test winding with the feedback winding, a separate self-test winding is not required, thus reducing the cost and the volume.

[0049] The calculation module 105 is used, for example, to perform leakage current analysis based on the processed signal. There are different leakage current detection standards for different leakage current types, and the calculation module 105 can determine whether there is leakage current and calculate the specific value of the leakage current according to the corresponding leakage current detection standard. In the self-test mode, the calculation module 105 can also be used to design and output a self-test signal. After outputting the self-test signal, the process of the calculation module 105 performing leakage current analysis based on the processed signal is the same as in the leakage current detection mode.

[0050] According to the embodiments of the utility model, different self-test signals can be customized as needed and leakage currents of different types, sizes and frequencies can be simulated, which advantageously improves the self-test function of the leakage current detection circuit.

[0051] Figure 3 Shown according to Figure 1 Schematic diagram of exemplary electrical components of a leakage current detection circuit.

[0052] like Figure 3 As shown, the excitation module 102 may include, for example, a square wave excitation voltage generator, which is used to generate a positive and negative square wave voltage of a predetermined frequency applied to the first winding W1, thereby generating an excitation current of a predetermined frequency in the first winding W1. The excitation module 102 may be implemented, for example, by a comparator, a self-excited oscillation circuit, and the like.

[0053] Preferably, the predetermined frequency is a frequency greater than 5 times, for example, 8 times, or 10 times the frequency of the measured current. For example, when the frequency of the measured current is 1000 Hz, the predetermined frequency may be 8000 Hz. Advantageously, by setting a predetermined frequency significantly higher than the frequency of the measured current, the leakage current signal can be effectively distinguished from the excitation signal in the subsequent signal processing process, that is, a better filtering effect can be achieved.

[0054] The signal processing module 103 may include, for example, a first resistor R1 and a low-pass filter LP.

[0055] One end of the first resistor R1 is connected to the first winding W1 and the other end is grounded, so as to return the output current of the first winding W1 to the ground. The frequency and magnitude of the excitation current can be changed by setting the number of turns of the first winding W1 and / or the size of the first resistor R1. Therefore, the first resistor R1 can also be equipped with the excitation module 102, for example, and the present invention does not limit this.

[0056] The low-pass filter LP is used, for example, to receive the output voltage signal from the first winding W1 and filter out the voltage signal corresponding to the excitation current from the output voltage signal. Since the excitation current has the predetermined frequency that is significantly greater than the frequency of the current to be measured, the voltage signal corresponding to the excitation current can be filtered out by the low-pass filter LP. In this way, the waveform of the processed signal can reflect the waveform of the current to be measured.

[0057] The feedback circuit may include, for example, a second resistor R2. In this embodiment, one end of the second resistor R2 is connected to the signal processing module 103 to receive the processed signal, and the other end is connected to the second winding W2. The processed signal is, for example, a voltage signal, which is converted into a feedback current signal through the second resistor R2 and applied to the second winding W2. For example, the size of the second resistor R2 may be determined based on the dynamic stability and the amplitude of the output current expected to be achieved by the feedback mechanism, and the utility model does not limit this.

[0058] The self-test circuit may include, for example, a third resistor R3 and a capacitor C1 connected in series. In this embodiment, one end of the third resistor R3 is connected to the calculation module 105 to receive a self-test signal, one end of the capacitor C1 is connected to one end of the second winding W2 to apply a self-test current to the second winding W2, and the other end of the second winding W2 is grounded.

[0059] Since in practical applications, the self-test signal is usually an AC signal, the capacitor C1 is exemplarily shown in this embodiment. In the case where the self-test signal is a DC signal, the capacitor C1 can be omitted without affecting the realization of the self-test function.

[0060] The computing module 105 may be, for example, a microcontroller (MCU). The microcontroller may include an integrated external analog-to-digital converter and a digital-to-analog converter to receive the processed signal and output a self-test signal in a self-test mode.

[0061] like Figure 3 As shown, the leakage current detection circuit 100 according to the utility model may also include a first gain conversion module GS1 connected between the self-test circuit and the calculation module 105 and a second gain conversion module GS2 connected between the signal processing module 103 and the calculation module 105. The gain conversion module is used to scale the signal so as to meet the signal amplitude requirements of the calculation module 105 when receiving and outputting the signal. For example, the amplitude of the processed signal may be very small and needs to be amplified before it can be received and processed by the calculation module 105.

[0062] Figure 4a and Figure 4b A schematic diagram of the waveforms of the leakage current and the processed signal according to an embodiment of the present utility model is exemplarily shown.

[0063] For example, the leakage current detection circuit according to the present invention is verified by simulation, and the waveform of the measured current is compared with the waveform of the processed signal, wherein the waveform information includes frequency and amplitude.

[0064] Different from Figure 2 The DC leakage current represented by a straight line is shown in Figure 4a The upper part shows the waveform of 30mA 135° pulsating DC leakage current. Figure 4b The upper part of the figure shows the waveform of the AC leakage current of 50mA and 50Hz. Figure 4a and Figure 4b The waveforms of the corresponding processed signals are shown in the lower part of .

[0065] like Figure 4a As shown, the frequency of the waveform of the processed signal is substantially consistent with the frequency of the waveform of the pulsating DC leakage current, and the amplitude of the waveform of the processed signal starts from 0. In a leakage current detection circuit that cannot detect a DC component, the amplitude of the waveform should start from a negative value.

[0066] like Figure 4b As shown, the frequency of the waveform of the processed signal is substantially consistent with the frequency of the waveform of the AC leakage current.

[0067] The amplitude of the waveform of the processed signal is, for example, associated with the first winding W1 and the first resistor R1.

[0068] It can be known from the simulation results that the leakage current detection circuit according to the embodiment of the utility model can realize DC and AC leakage current detection with high accuracy.

[0069] Figure 5 A schematic diagram of a leakage current protection circuit according to an embodiment of the utility model is shown.

[0070] like Figure 5 As shown, the leakage current protection circuit 200 includes a leakage current detection circuit and a switch S according to one of the embodiments of the present utility model, wherein the switch is connected to the leakage current detection circuit (especially the calculation module 105) and the power lines L1 and L2, and is used to disconnect the power lines L1 and L2 in response to the leakage current detected by the leakage current detection circuit, thereby protecting the circuit and electrical equipment.

[0071] The disconnection response mechanism may include, for example, determining whether the magnitude of the leakage current exceeds a threshold, whether the duration of the leakage current exceeds a threshold, etc.

[0072] According to the embodiments of the utility model, the leakage current detection circuit adopts a closed-loop detection scheme of a single magnetic core and dual windings, thereby ensuring high detection accuracy and stability while reducing the size; by combining the self-test winding and the feedback winding, the separate self-test winding is omitted, further reducing the size and cost; by performing signal processing on the output voltage signal, the circuit design is simplified and the calculation cost is reduced; through the calculation module, different types of self-test signals can be generated, thereby improving the self-test function.

[0073] In general, various example embodiments of the present invention may be implemented in hardware or dedicated circuits, software, firmware, logic, or any combination thereof. Certain aspects may be implemented in hardware, while other aspects may be implemented in firmware or software that may be executed by a controller, microprocessor, or other computing device. When various aspects of the embodiments of the present invention are illustrated or described as block diagrams, flow charts, or using some other graphical representation, it will be understood that the blocks, devices, systems, techniques, or methods described herein may be implemented as non-limiting examples in hardware, software, firmware, dedicated circuits or logic, general hardware or controllers or other computing devices, or some combination thereof.

[0074] The exemplary embodiments of the present invention described in detail above are merely illustrative and not restrictive. It should be understood by those skilled in the art that various modifications and combinations may be made to these embodiments or their features without departing from the principles and spirit of the present invention, and such modifications should fall within the scope of the present invention.

Claims

1. A leakage current detection circuit, used for performing leakage current detection on a current under test, capable of operating in a leakage current detection mode and a self-test mode, characterized in that: The leakage current detection circuit includes a mutual inductance module, an excitation module, a signal processing module, a feedback self-checking module and a calculation module: The mutual inductance module comprises a magnetic core, a first winding and a second winding, the magnetic core is used for a power line to pass through, and the first winding and the second winding are wound around the magnetic core; The excitation module is connected to the first winding and is used to generate an excitation current in the first winding; The signal processing module is connected to the first winding and the calculation module, and is used to process the output voltage signal of the first winding and output a processed signal, wherein the voltage signal corresponding to the excitation current is filtered out of the processed signal; The feedback self-test module is connected to the second winding and includes a feedback circuit and a self-test circuit, the feedback circuit is connected to the signal processing module and is used to generate a feedback current in the second winding according to the processed signal, and the self-test circuit is connected to the calculation module and is used to generate a self-test current in the second winding according to the self-test signal; as well as The calculation module is used for performing leakage current analysis according to the processed signal, and for outputting the self-test signal in the self-test mode.

2. The leakage current detection circuit according to claim 1, characterized in that: The excitation module includes a square wave excitation voltage generator, which is used to generate positive and negative square wave voltages of a predetermined frequency applied to the first winding.

3. The leakage current detection circuit according to claim 2, characterized in that: The predetermined frequency is a frequency greater than 5 times the frequency of the current being measured.

4. The leakage current detection circuit according to claim 1, characterized in that: The signal processing module includes a first resistor and a low-pass filter, wherein: One end of the first resistor is connected to the first winding and the other end is grounded, so as to make the output current of the first winding return to the ground; and The low-pass filter is used to filter out the voltage signal corresponding to the excitation current from the output voltage signal.

5. The leakage current detection circuit according to claim 1, characterized in that: The feedback circuit generates a feedback current in the second winding according to the processed signal, so that the second winding generates a magnetic flux opposite to the magnetic flux generated by the measured current and forms a zero magnetic flux state in the mutual inductance module.

6. The leakage current detection circuit according to claim 1, characterized in that: The feedback circuit includes a second resistor, one end of which is connected to the signal processing module and the other end of which is connected to the second winding.

7. The leakage current detection circuit according to claim 1, characterized in that: The self-test circuit includes a third resistor and a capacitor connected in series.

8. The leakage current detection circuit according to claim 1, characterized in that: The computing module is a microcontroller.

9. The leakage current detection circuit according to claim 1, characterized in that: The leakage current detection circuit also includes: A gain conversion module connected between the signal processing module and the calculation module and / or connected between the self-checking circuit and the calculation module, wherein the gain conversion module is used to scale the signal.

10. A leakage current protection circuit, characterized in that: The leakage current protection circuit comprises: The leakage current detection circuit according to any one of claims 1 to 9; and A switch is connected to the leakage current detection circuit and the power line, and is used to disconnect the power line in response to the leakage current detected by the leakage current detection circuit.

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