An electric leakage detection device, an electric leakage detection method, and a charging device

Abstract

The application discloses a leakage detection device, a leakage detection method and a charging device. The device comprises a zero sequence current transformer for sensing a leakage current signal; an excitation drive and a sampling resistor connected to the zero sequence current transformer respectively; a control circuit comprising a variable-frequency excitation circuit connected to the excitation drive, which is used to generate excitation signals of at least two preset excitation frequencies and alternately apply the excitation signals on the zero sequence current transformer through the excitation drive; a variable-frequency sampling circuit connected to the sampling resistor, which is used to sample the sampling resistor at a sampling frequency corresponding to the excitation frequency to obtain the leakage current signal; a comparison circuit connected to the variable-frequency sampling circuit, which is used to generate an alarm signal when the leakage current signal is greater than a preset threshold; and a communication interface connected to the comparison circuit, which is used to output the alarm signal. The leakage detection device drives the zero sequence current transformer through the excitation signals of at least two preset excitation frequencies, and the accuracy of leakage current signal detection can be improved.

Description

Technical Field

[0001] This invention relates generally to the field of leakage current detection, and more specifically to a leakage current detection device, a leakage current detection method, and a charging device. Background Technology

[0002] A Residual Current Device (RCD) is a leakage current detection device used to detect the magnitude of leakage current in a circuit. Without an RCD, when a person or animal comes into contact with high voltage, a leakage current to ground will be generated. If the leakage current exceeds a certain threshold, it can cause cardiac arrest, leading to cardiac fibrillation and potentially death. With an RCD installed, when leakage current exists and its magnitude exceeds a set threshold, the RCD will send an alarm signal to an actuator, triggering the actuator to quickly disconnect the circuit, thus protecting lives.

[0003] The main purpose of the actuating mechanism is to disconnect the power supply line at the downstream end. When the line is disconnected, there will be no voltage or current at the downstream end of the disconnector, thus achieving the purpose of protection. RCD onboard leakage current modules are currently widely used in charging piles and charging guns. They can be directly mounted on the circuit board. When an electric vehicle is charging, the RCD detects whether the leakage current exceeds a threshold during charging. If it exceeds the threshold, the RCD will send an alarm signal to other devices on the circuit board to execute a command to stop charging and disconnect the charging line, such as by disconnecting a closed relay or circuit breaker mechanism. Summary of the Invention

[0004] The summary section introduces a series of simplified concepts, which will be further explained in detail in the detailed description section. This summary section is not intended to limit the key and essential technical features of the claimed technical solution, nor is it intended to determine the scope of protection of the claimed technical solution.

[0005] One embodiment of the present invention provides a leakage current detection device, the leakage current detection device comprising:

[0006] Zero-sequence current transformer is used to sense leakage current signals;

[0007] Connect the excitation drive and sampling resistor of the zero-sequence current transformer;

[0008] A control circuit, connected to the excitation drive and the sampling resistor, the control circuit comprising:

[0009] The frequency conversion excitation circuit connected to the excitation drive is used to generate excitation signals of at least two preset excitation frequencies, and to alternately apply the excitation signals of the at least two preset excitation frequencies to the zero-sequence current transformer through the excitation drive.

[0010] A frequency conversion sampling circuit connected to the sampling resistor is used to sample the sampling resistor at a sampling frequency corresponding to the preset excitation frequency to obtain a leakage current signal.

[0011] A comparison circuit connected to the frequency conversion sampling circuit is used to compare the leakage current signal with a preset threshold, and generate an alarm signal when the leakage current signal is greater than the preset threshold;

[0012] A communication interface is connected to the comparison circuit and is used to output the alarm signal.

[0013] In one embodiment, the at least two preset excitation frequencies are excitation frequencies that cause the zero-sequence current transformer to enter a deep saturation state.

[0014] In one embodiment, at least one of the preset excitation frequencies is an excitation frequency that causes the zero-sequence current transformer to enter a deep saturation state.

[0015] In one embodiment, the frequency conversion excitation circuit switches the preset excitation frequency once every at least one cycle.

[0016] In one embodiment, the sampling frequency is an integer multiple of the preset excitation frequency.

[0017] In one embodiment, the control circuit further includes a feedback circuit connected to the frequency conversion sampling circuit and the excitation circuit respectively, for comparing the voltage generated on the sampling resistor by the leakage current signal with a preset voltage to generate a feedback signal, and feeding the feedback signal back to the excitation circuit; the excitation circuit is used to adjust the frequency of the excitation signal according to the feedback signal.

[0018] In one embodiment, the zero-sequence current transformer includes a magnetic core, a housing, and a coil, wherein the magnetic core is a nanocrystalline magnetic core.

[0019] In one embodiment, the magnetic core has a magnetic saturation intensity Bs≤1.2T, a magnetic permeability u>80000, and a coercivity Hc<4.5A / m after longitudinal magnetization.

[0020] In one embodiment, the frequency conversion sampling circuit includes a digital low-pass filter for filtering out information from the excitation signal.

[0021] Another aspect of this invention provides a leakage current detection method, the method comprising:

[0022] Obtain the leakage current signal induced by the zero-sequence current transformer;

[0023] Generate at least two preset excitation frequencies of excitation signals, and alternately apply the at least two preset excitation frequencies of excitation signals to the zero-sequence current transformer;

[0024] The leakage current signal is obtained by sampling at a sampling frequency corresponding to the preset excitation frequency.

[0025] The leakage current signal is compared with a preset threshold, and an alarm signal is generated when the leakage current signal is greater than the preset threshold.

[0026] Output the alarm signal.

[0027] In one embodiment, at least one of the preset excitation frequencies is an excitation frequency that causes the zero-sequence current transformer to enter a deep saturation state.

[0028] In one embodiment, each of the preset excitation frequencies is an excitation frequency that causes the zero-sequence current transformer to enter a deep saturation state.

[0029] In one embodiment, generating at least two preset excitation frequencies of the excitation signal includes switching the preset excitation frequency once every at least one cycle.

[0030] In one embodiment, the method further includes:

[0031] The voltage generated by the leakage current signal is compared with a preset voltage to generate a feedback signal, and the frequency of the excitation signal is adjusted according to the feedback signal.

[0032] In another aspect, the present invention provides a charging device, the charging device including the above-mentioned leakage current detection device; and an actuating mechanism connected to the leakage current detection device for disconnecting the power supply line when the alarm signal is received.

[0033] The leakage current detection device, leakage current detection method, and charging equipment of the present invention drive a zero-sequence current transformer with excitation signals of at least two preset excitation frequencies, which can improve the accuracy of leakage current signal detection. Attached Figure Description

[0034] The above and other objects, features, and advantages of this application will become more apparent from the more detailed description of the embodiments of this application in conjunction with the accompanying drawings. The accompanying drawings are used to provide a further understanding of the embodiments of this application and form part of the specification. They are used together with the embodiments of this application to explain this application and do not constitute a limitation thereof. In the accompanying drawings, the same reference numerals generally represent the same components or steps.

[0035] Figure 1 This is a circuit diagram of a type A and type AC leakage current detection device according to an embodiment of the present invention;

[0036] Figure 2 This is a schematic diagram of the magnetization curve of a type B leakage current detection device according to an embodiment of the present invention;

[0037] Figure 3 This is a schematic diagram illustrating the effect of an external magnetic field on the magnetization curve according to an embodiment of the present invention;

[0038] Figure 4 This is a schematic diagram of a leakage current detection device according to an embodiment of the present invention;

[0039] Figure 5 This is a waveform diagram of a zero-sequence current transformer entering a deep saturation state according to an embodiment of the present invention;

[0040] Figure 6 This is a waveform diagram of a zero-sequence current transformer entering a shallow saturation state according to an embodiment of the present invention;

[0041] Figure 7 This is a schematic diagram of open-loop frequency hopping according to an embodiment of the present invention;

[0042] Figure 8 This is a schematic flowchart of a leakage current detection method according to an embodiment of the present invention. Detailed Implementation

[0043] In the following description, numerous specific details are set forth in order to provide a more thorough understanding of the invention. However, it will be apparent to those skilled in the art that the invention can be practiced without one or more of these details. In other instances, certain technical features well-known in the art have not been described in order to avoid obscuring the invention.

[0044] It should be understood that the invention can be embodied in various forms and should not be construed as being limited to the embodiments set forth herein. Rather, providing these embodiments will make the disclosure thorough and complete, and will fully convey the scope of the invention to those skilled in the art. In the drawings, for clarity, the dimensions and relative dimensions of layers and regions may be exaggerated. The same reference numerals denote the same elements throughout.

[0045] It should be understood that when an element or layer is referred to as "on," "adjacent to," "connected to," or "coupled to" other elements or layers, it may be directly on, adjacent to, connected to, or coupled to other elements or layers, or there may be intervening elements or layers. Conversely, when an element is referred to as "directly on," "directly adjacent to," "directly connected to," or "directly coupled to" other elements or layers, there are no intervening elements or layers. It should be understood that although the terms first, second, third, etc., may be used to describe various elements, components, areas, layers, and / or portions, these elements, components, areas, layers, and / or portions should not be limited by these terms. These terms are only used to distinguish one element, component, area, layer, or portion from another element, component, area, layer, or portion. Therefore, without departing from the teachings of this invention, the first element, component, area, layer, or portion discussed below may be referred to as the second element, component, area, layer, or portion.

[0046] Spatial relation terms such as “below,” “under,” “below,” “under,” “above,” “above,” etc., are used herein for convenience of description to describe the relationship between one element or feature shown in the figure and other elements or features. It should be understood that, in addition to the orientation shown in the figure, spatial relation terms are intended to also include different orientations of the device in use and operation. For example, if the device in the figure is flipped, then the element or feature described as “below” or “under” the other element or feature will be oriented “above” the other element or feature. Therefore, the exemplary terms “below” and “under” can include both upper and lower orientations. The device may be otherwise oriented (rotated 90 degrees or otherwise) and the spatial descriptive terms used herein will be interpreted accordingly.

[0047] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. When used herein, the singular forms “a,” “an,” and “the” are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the terms “comprising” and / or “including,” when used in this specification, identify the presence of the stated features, integers, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups. When used herein, the term “and / or” includes any and all combinations of the associated listed items.

[0048] To fully understand this invention, a detailed structure will be presented in the following description to illustrate the technical solution proposed by this invention. Preferred embodiments of the invention are described in detail below; however, in addition to these detailed descriptions, the invention may have other embodiments.

[0049] Residual current detection devices (RCDs) are classified into AC type, A type, and B type leakage current detection devices, among which:

[0050] The AC type leakage current detection device can detect AC type leakage current. When there is AC type leakage current in the line and the leakage current reaches the set threshold, the AC type leakage current detection device will send a TRIP (trip) alarm signal to the external working mechanism to disconnect the main line.

[0051] In addition to detecting AC leakage current, the Type A leakage current detection device can also detect pulsating DC leakage current such as A0, A90, and A135. When the AC or A leakage current in the circuit reaches the set threshold, the Type A leakage current detection device will send a TRIP alarm signal to the external triggering mechanism to disconnect the main circuit.

[0052] The Type B leakage current detection device has the detection functions of both Type AC and Type A leakage current modules, and it also has the ability to detect 2P-DC (two-phase rectification), 3P-DC (three-phase rectification), S-DC (smooth DC), and F-type (10Hz, 50Hz, 1000Hz) composite waves. When the leakage current value reaches the preset threshold, the Type B leakage current detection device will send a TRIP alarm signal to the external triggering mechanism to disconnect the main circuit.

[0053] The detection principle of the Type B leakage current detection device is completely different from that of the Type A and Type AC leakage current detection devices. For example Figure 1 As shown, the principle of type A and type AC leakage current detection devices is to passively detect leakage current in the circuit; while type B leakage current detection devices require an external excitation frequency to drive the ZCT (zero-sequence current transformer) coil, so that its core is magnetized, and the magnetization curve is as follows. Figure 2 As shown.

[0054] Therefore, the principle of the type B leakage current detection device is as follows: Figure 3 As shown, the influence of the external magnetic field is reflected in the change on the H-axis, which means that the current changes when the excitation signal drives the ZCT core to magnetize. By detecting the voltage on the sampling resistor, voltage information including the excitation signal can be obtained. This voltage information also includes information about the external magnetic field generated by the leakage current. By filtering out the excitation signal information, the information about the external magnetic field can be obtained, thereby obtaining the information about the leakage current signal, realizing the function of AC / DC leakage current signal detection.

[0055] Depending on whether feedback exists at the excitation frequency, the principle of the Type B leakage current detection device can be divided into open-loop and closed-loop types, among which:

[0056] The principle of open-loop leakage current detection is as follows: the excitation frequency of the excitation circuit is generated by the oscillation circuit. The oscillation frequency is determined by the characteristics of different current transformers and the magnitude of the drive current. The excitation frequency is fixed and cannot be adjusted in real time during application.

[0057] The closed-loop leakage current detection principle is as follows: the excitation frequency of the excitation circuit is related to the parameters of the ZCT. During the application process, a feedback signal is generated according to the magnitude of the current, and the frequency of the excitation current is adjusted according to the feedback signal until the circuit is in a stable state.

[0058] Open-loop leakage current detection devices cannot adjust the excitation frequency in real time during application. When sampling leakage current through a sampling resistor, they will face the problem of excessively small TRIP current threshold when the leakage current frequency is large (e.g., greater than 1 kHz).

[0059] The excitation circuit of a closed-loop leakage current detection device is greatly affected by the residual magnetism Br, especially after a large leakage current impact. When continuously measuring the leakage current value, there will be a large deviation, which seriously affects the accuracy. In addition, after a large leakage current occurs, the closed-loop leakage current detection device may fail to start oscillation.

[0060] Based on this, this invention applies frequency hopping technology to leakage current detection devices, specifically to Type B leakage current detection modules that require excitation signals. Frequency hopping primarily refers to the application of frequency hopping. This invention uses a variable frequency excitation circuit to drive the ZCT coil. The excitation circuit can generate excitation signals of multiple frequencies, using these signals to drive the ZCT periodically and alternately at different time intervals, ensuring that the ZCT can complete periodic magnetization well at different excitation frequencies. This solves the problems existing in the aforementioned open-loop and closed-loop leakage current detection devices.

[0061] The leakage current detection device, leakage current detection method, and charging device of the present invention will be described in detail below with reference to the accompanying drawings. Unless otherwise specified, the features of the following embodiments and implementations can be combined with each other.

[0062] See Figure 1The leakage current detection device of this invention includes at least a zero-sequence current transformer 401, a sampling resistor 402, an excitation drive 403, and a control circuit 404. The zero-sequence current transformer 401 is used to sense a leakage current signal. The excitation drive 403 and the sampling resistor 402 are respectively connected to the zero-sequence current transformer 401. The control circuit 404 is connected to both the excitation drive 403 and the sampling resistor 402. The control circuit 404 includes: a frequency conversion excitation circuit connected to the excitation drive 403, used to generate at least two preset excitation frequencies of excitation signals, and alternately apply the at least two preset excitation frequencies of excitation signals to the zero-sequence current transformer 401 through the excitation drive 403; a frequency conversion sampling circuit connected to the sampling resistor 402, used to sample the sampling resistor 402 at a sampling frequency corresponding to the excitation frequency to obtain a leakage current signal; and a comparison circuit connected to the frequency conversion sampling circuit, used to compare the leakage current signal with a preset threshold, and generate an alarm signal when the leakage current signal is greater than the preset threshold.

[0063] Because the leakage current detection device of this embodiment adopts a forced excitation circuit structure and uses frequency hopping technology to alternately generate excitation signals of different preset excitation frequencies to excite the zero-sequence current transformer 401, it can solve the problem in open-loop leakage current detection devices that the AC leakage current signal is easily identified as the DC leakage current signal when the leakage current frequency is large at a single excitation frequency, and the resulting problem of the preset threshold being too low. Because the embodiment of this invention uses a forced excitation circuit, the problem of excitation failure to start oscillation that exists in closed-loop leakage current detection devices is also eliminated.

[0064] The leakage current detection device in this embodiment of the invention is a type B leakage current detection device. The frequency conversion excitation circuit generates an excitation signal to drive the coil of the zero-sequence current transformer 401, causing its core to be magnetized. The zero-sequence current transformer 401 is used to detect the magnitude of leakage current in the circuit and specifically includes a core, a casing, and a coil. To make the zero-sequence current transformer 401 more suitable for frequency-modulated excitation and easier to enter the deep saturation state described below, the core of the zero-sequence current transformer 401 in this embodiment of the invention meets the following conditions: magnetic saturation intensity Bs ≤ 1.2T, permeability u > 80000, and coercivity Hc after longitudinal magnetization < 4.5A / m. Furthermore, the cross-sectional area Ac of the core is matched with the sampling resistor, the excitation frequency, and the operating voltage, specifically calculated using the following formula:

[0065]

[0066] In formula (1), f is the excitation frequency, V ext A is the amplitude of the excitation voltage of the excitation signal. c Where N is the cross-sectional area of ​​the magnetic core, and B is the turns ratio of the magnetic core.m This represents the maximum magnetic flux density.

[0067] The leakage current detection device of this invention employs fluxgate magnetization technology, using an excitation signal to magnetize its core. Simultaneously, when the leakage current signal generates an external magnetic field, by filtering out the information from the excitation signal, the information of the external magnetic field can be obtained, thereby acquiring the information of the leakage current signal. See also... Figure 2 For example, the principle of magnetization is as follows: If a ferromagnetic material is magnetized from a fully demagnetized state to saturation Bs along the magnetization curve OS, and then the external magnetic field H is decreased, the value of B will no longer decrease according to the original initial magnetization curve (OS), but will decrease more slowly along a higher B. This is because the magnetic domains undergoing rigid rotation retain the direction of the external magnetic field. Even when the external magnetic field H = 0, B is not equal to 0, meaning there is still a residual magnetic induction intensity Br. This characteristic of the magnetization curve and demagnetization curve not coinciding is called the irreversibility of magnetization. The phenomenon that the change in magnetic induction intensity B lags behind the change in magnetic field intensity H is called hysteresis.

[0068] To reduce magnetic flux density (B), a magnetic field strength -H must be applied in the opposite direction to the original magnetic field. Only when this reverse magnetic field strength increases to -Hc can B = 0 in the magnetic medium. This does not mean the magnetic medium has returned to a disordered state; rather, some magnetic domains retain their original magnetization direction, while others change to the direction of the external magnetic field under the influence of the reverse magnetic field. When these two parts are equal, the combined magnetic flux density is zero. If the reverse magnetic field strength is further increased, the number of reversed magnetic domains in the ferromagnetic material increases, and the reverse magnetic flux density increases. As the value of -H increases, the reversed B also increases. When the reverse magnetic field strength increases to -Hs, B = -Bs, reaching reverse saturation. To make -H = 0 and B = -Br, a forward magnetic flux density (HC) must be applied to make -Br zero. If H increases further to Hs, B reaches its maximum value Bs, and the magnetic medium reaches forward saturation again. The change in magnetic field strength is Hs—0—-HC—-Hs—0—HC—Hs, and correspondingly, the change in magnetic induction intensity is Bs—Br—0—-BS—-Br—0—Bs, thus forming a hysteresis loop symmetrical about the origin, called the saturation hysteresis loop or the maximum hysteresis loop.

[0069] like Figure 3 As shown, during magnetization, if there is no external magnetic field, the magnetic field remains in equilibrium. When an external magnetic field is generated due to the presence of a leakage current signal I (AC or DC leakage current signal), the external magnetic field will disrupt the original magnetic field equilibrium, and the magnetization curve will shift left and right on the horizontal axis (H-axis). The change in the magnetic field will affect the current generated in the coil of the zero-sequence current transformer 401.

[0070] In this embodiment of the invention, at least two different preset excitation frequencies are used to alternately excite the zero-sequence current transformer 401. The zero-sequence current transformer 401 is connected to a control circuit 404, which can be implemented as an MCU (microcontroller unit) or other control unit or circuit with similar functions. The excitation signals are generated by a frequency conversion excitation circuit in the control circuit 404. The start and stop output of each frequency are precisely controlled by the frequency conversion excitation circuit, and the different frequencies are switched seamlessly. Simultaneously, since the current driving capability of the frequency conversion excitation circuit itself is weak, an excitation driver 403 is connected between the frequency conversion excitation circuit and the zero-sequence current transformer 401. The excitation driver 403 increases the current output capability, achieving a function similar to an amplifier.

[0071] Specifically, embodiments of the present invention can employ open-loop fluxgate technology, that is, using at least two fixed excitation signals with preset excitation frequencies to excite the zero-sequence current transformer 401, thereby avoiding the problem of excitation failure to oscillate in closed-loop fluxgate technology. Alternatively, embodiments of the present invention can also employ closed-loop fluxgate technology, whereby the control circuit 404 further includes a feedback circuit connected to both the frequency conversion sampling circuit and the excitation circuit, used to compare the voltage generated across the sampling resistor by the leakage current signal with a preset voltage to generate a feedback signal, which is then fed back to the excitation circuit; the excitation circuit adjusts the preset excitation frequency according to the feedback signal.

[0072] Furthermore, this embodiment of the invention combines open-loop frequency hopping technology with the deep saturation performance of the zero-sequence current transformer to improve the performance of the leakage current detection device. Specifically, at least one preset excitation frequency is the excitation frequency that causes the zero-sequence current transformer 401 to enter a deep saturation state. Further, each preset excitation frequency generated by the frequency conversion excitation circuit is an excitation frequency that causes the zero-sequence current transformer 401 to enter a deep saturation state. When the excitation signal causes the zero-sequence current transformer 401 to be in a deep saturation state, the performance of the zero-sequence current transformer 401 is minimally affected by the residual magnetism Br, even to the point of being negligible. Therefore, there is no problem of measurement accuracy being affected after a large leakage current, thereby reducing the measurement error caused by residual magnetism in open-loop and closed-loop leakage current detection and improving measurement accuracy.

[0073] For ease of understanding, see Figure 5 , Figure 6 ,in Figure 5 This is the waveform information captured on the sampling resistor 402 when the zero-sequence current transformer 401 enters a deep saturation state. Figure 6 It is the waveform information captured on the sampling resistor 402 when the zero-sequence current transformer 401 enters a shallow saturation state.

[0074] Among them, see Figure 5When the excitation signal drives the zero-sequence current transformer 401 into deep saturation, the waveform captured by the sampling resistor 402 exhibits a flat region on the vertical axis, with a flattening period existing on both the positive and negative half-axis of the vertical axis. The theoretical values ​​of the entire flattening region are symmetrically distributed on both the positive and negative half-axis of the vertical axis, and the duration of the flattening region is generally greater than 5% of the current excitation frequency period. For comparison, see [link to relevant documentation]. Figure 6 When the excitation signal drives the zero-sequence current transformer 401 into shallow saturation, only a peak region in the waveform captured by the sampling resistor 402 enters a relatively deep saturation. This peak region is also symmetrically distributed on the positive and negative half-axis of the vertical axis, but the time to enter saturation is very short, generally accounting for less than 5% of the current excitation frequency period.

[0075] Depend on Figure 5 , Figure 6 It can be seen that when the zero-sequence current transformer 401 is not affected by external magnetic fields (except for the geomagnetic field), the waveform of its deep saturation state reflected on the sampling resistor will have an output voltage that reaches the highest output voltage of the excitation driver 403 for a certain period of time, and this will last for a period of time, generally more than 5% of the current excitation frequency period. The waveform of the shallow saturation state reflected on the sampling resistor will at most have only one peak time that reaches the highest output voltage of the excitation driver 403. This means that the highest output voltage of the waveform reflected on the sampling resistor in the shallow saturation state must be less than the waveform voltage reflected on the sampling resistor in the deep saturation state. At most, only a moment during the peak (less than 5% of the excitation frequency period) is equal to the voltage in the deep saturation state.

[0076] Because the zero-sequence current transformer 401 remains saturated for a period (greater than 5%) within an excitation cycle under deep saturation, the influence of residual magnetism on the zero-sequence current transformer 401 is very small. This means that even after a very large leakage current (tens or hundreds of amperes or more) impacts the zero-sequence current transformer 401, the frequency converter excitation circuit will force the zero-sequence current transformer 401 to follow a similar path. Figure 2 Magnetization is achieved by driving the current transformer to a deep saturation state, thereby eliminating the adverse effects of residual magnetism and preventing residual magnetism from causing a deviation in the magnetization curve. In contrast, if the excitation current causes the zero-sequence current transformer 401 to enter a shallow saturation state, the excitation drive cannot achieve 100% deep saturation. Therefore, the influence of residual magnetism cannot be completely eliminated. If a large leakage current impacts the zero-sequence current transformer 401 at this time, residual magnetism will accumulate continuously, eventually causing the entire magnetized balanced magnetic field to deteriorate even without external magnetic field influence (except for the Earth's magnetic field). Figure 3 The deviation shown ultimately led to a large error in the leakage current detection device, causing the actuator to malfunction and thus disconnecting the main circuit that should have been working normally.

[0077] Since deep saturation ensures that the zero-sequence current transformer 401 reaches 100% saturation under the drive of the excitation signal, while shallow saturation is a peak saturation method, it cannot guarantee that the zero-sequence current transformer 401 will fully enter the saturation state. On the contrary, it may fail to reach the required saturation, for example, only reaching 80% saturation. Therefore, preferably, each excitation frequency generated by the frequency converter excitation circuit can guarantee sufficient capability to drive the zero-sequence current transformer 401 into the deep saturation state described above. However, in some embodiments, some excitation frequencies can drive the zero-sequence current transformer 401 into deep saturation, while the remaining excitation frequencies can drive the zero-sequence current transformer 401 into shallow saturation. The influence of residual magnetism is eliminated by using the excitation frequency that can drive the zero-sequence current transformer 401 into deep saturation. For example, when there are three preset excitation frequencies, all three preset excitation frequencies can be the excitation frequencies that drive the zero-sequence current transformer 401 into deep saturation, or two preset excitation frequencies can operate in deep saturation, and one preset excitation frequency can operate in shallow saturation.

[0078] The zero-sequence current sensor 401 is also connected to a sampling resistor 402, which is connected to a frequency conversion sampling circuit in the control circuit 404. The frequency conversion sampling circuit is used to collect the voltage signal on the sampling resistor 402 and calculate the magnitude of the current signal from the voltage signal.

[0079] While the excitation circuit outputs different excitation frequencies, the frequency conversion sampling circuit also samples the voltage across the sampling resistor at a sampling frequency corresponding to the preset excitation frequency. The sampling frequency is either equal to the preset excitation frequency, or N times the preset excitation frequency, where N is an integer not less than 2.

[0080] Since the sampling on the sampling resistor is frequency-converted, different preset excitation frequencies result in different sampling frequencies. Moreover, this frequency-converted sampling method is continuously repeated. If there are three different preset excitation frequencies, it means that there are at least three different sampling frequencies. Similarly, if there are five or more preset excitation frequencies, it means that there are five or more sampling frequencies.

[0081] Furthermore, the frequency conversion sampling circuit also includes a digital low-pass filter, used to filter out the excitation signal information from the received signal and retain the leakage current signal information. In conventional leakage current detection devices, if the frequency of the AC leakage current signal is the same as the excitation frequency or the AC leakage frequency is an integer multiple of the sampling frequency, the AC signal may be misjudged as a DC signal during threshold judgment, thus requiring the use of a high-order filter. However, in the leakage current detection device according to the present invention, since the sampling frequency is constantly changing, it is equivalent to sampling the leakage current signal in an automatic frequency-shifting or phase-shifting manner. This avoids the possibility of misjudging AC leakage as DC leakage when the AC leakage frequency is an integer multiple of the sampling frequency, which occurs when the same sampling frequency is used for sampling. It also eliminates the blind zone problem that exists in the low-pass digital filter when facing AC leakage signals with the same excitation frequency, thus eliminating the problem of excessively small high-frequency thresholds in certain frequency bands when the leakage current frequency is large (e.g., greater than 1 kHz). Since the above problems can be solved by using digital filters, the leakage current detection device of this invention does not require a high-order low-pass filter. The function of an external hardware high-order low-pass filter can be realized based on a digital low-pass filter, saving the cost of hardware circuits and PCB board space.

[0082] See Figure 7 For example, the frequency converter excitation circuit can alternately generate at least three different preset excitation frequencies, each excitation signal outputting one or more cycles. That is, the frequency converter excitation circuit switches the preset excitation frequency every at least one cycle, and the excitation signals of each preset excitation frequency switch seamlessly. Taking 1kHz, 2kHz, and 3kHz preset excitation frequencies as an example, the frequency converter excitation circuit alternately outputs 1kHz, 2kHz, and 3kHz excitation frequencies, driving the zero-sequence current transformer 401 to enter the deep saturation state described above. For example, the working logic of the excitation signals of the three excitation frequencies is as follows: First, output a 1kHz excitation signal for three cycles, then output a 2kHz excitation signal for three cycles, then output a 3kHz excitation signal for three cycles, and then output a 1kHz excitation signal for three cycles again, and so on in a cyclical manner.

[0083] It should be noted that the preset excitation frequencies in the embodiments of the present invention are not limited to three types, but may include two or more types. Furthermore, the embodiments of the present invention do not restrict the output order of the preset excitation frequencies; for example, they may be as follows: Figure 7The frequency hopping sequence shown is 1kHz, 2kHz, 3kHz, but it can also be 2kHz, 1kHz, 3kHz or 3kHz, 2kHz, 1kHz. The hopping order can be fixed or random. The number of output cycles for each preset excitation frequency can be three cycles, one, two, or more cycles, and the number of output cycles for each preset frequency can be the same or different. More output cycles result in a longer sampling time and more stable sampling; fewer output cycles result in faster frequency switching and better avoidance of false detections. Generally, a good balance between stability and accuracy can be achieved when the number of output cycles is five to six.

[0084] The frequency converter sampling circuit is connected to the comparator circuit. The comparator circuit determines whether there is leakage current flowing through the zero-sequence current transformer 401 based on the sampled leakage current signal, and whether the magnitude of the leakage current signal is greater than a preset threshold. When the leakage current signal is greater than the preset threshold, the comparator circuit outputs an alarm signal. The alarm signal may include a TRIP signal, used to control the actuating mechanism to disconnect the power supply line. The actuating mechanism is used to trigger an external mechanical tripping device. The actuating mechanism can be purely mechanical, a hybrid of mechanical and electronic, or purely electronic. The actuating mechanism can be directly connected to the control circuit 404 or connected to external equipment.

[0085] The control circuit 404 may also include an external communication interface for communicating with external devices, receiving and sending various information between the leakage current detection device and the external devices, and the alarm signal may also include an alarm signal sent to the external devices.

[0086] In one embodiment, the comparator circuit is also connected to an analog-to-digital converter (ADC). The ADC performs analog-to-digital conversion based on the type and magnitude of the leakage current signal to generate an analog signal, i.e., a pulse signal, representing the magnitude of the leakage current signal. Besides representing the magnitude of the leakage current signal, the pulse signal can also represent its waveform information, frequency, etc. For example, the ADC can generate a PWM (Pulse Width Modulation) signal with a corresponding duty cycle based on the magnitude of the leakage current signal. The duty cycle of the PWM signal is the proportion of the high level within a pulse cycle. The higher the magnitude of the leakage current signal, the higher the duty cycle of the PWM signal generated by the ADC. The client can determine the magnitude of the leakage current signal based on the duty cycle of the PWM signal. Furthermore, for different types of leakage current signals, PWM signals can be output through different external communication ports, allowing external devices to determine the type of leakage current signal based on the external communication port outputting the PWM signal. This achieves the goal of representing the magnitude and type of the leakage current signal through a digital signal, eliminating the need for additional algorithms configured on the client side. For example, the frequencies of the PWM signals generated by different analog-to-digital conversion circuits can be the same or different. In some embodiments, in addition to representing the magnitude of the leakage current signal by the duty cycle of the PWM signal, the frequency of the AC leakage current signal can also be represented by the frequency of the PWM signal.

[0087] In some embodiments, the control circuit 404 further includes a self-test circuit for performing a system self-test to obtain a fault status signal. Further, the control circuit 404 also includes a logic circuit connected to the self-test circuit, for generating a combination signal of a high-level signal and / or a low-level signal based on the fault status signal, and outputting the combination signal through an external communication port to indicate the fault status type of the external device.

[0088] Based on the above description, the leakage current detection device of this invention drives the zero-sequence current transformer with excitation signals of at least two preset excitation frequencies, which can avoid misdetecting the AC signal as a DC signal when the AC leakage current signal frequency is high, thereby avoiding the problem of the threshold being too small in the high-frequency band and improving the accuracy of leakage current signal detection.

[0089] Another aspect of the present invention provides a leakage current detection method, which can be based on a reference... Figure 4 The leakage current detection device described herein is used to achieve this. The following only describes the main steps of the leakage current detection method; more details can be found above.

[0090] Figure 8 A schematic flowchart of a leakage current detection method 800 according to an embodiment of the present invention is shown. Figure 8As shown, the leakage current detection method 800 of this embodiment includes the following steps:

[0091] In step S810, the leakage current signal induced by the zero-sequence current transformer is acquired;

[0092] In step S820, at least two preset excitation frequencies are generated, and the at least two preset excitation frequencies are alternately applied to the zero-sequence current transformer.

[0093] In step S830, sampling is performed at a sampling frequency corresponding to the preset excitation frequency to obtain the leakage current signal;

[0094] In step S840, the leakage current signal is compared with a preset threshold, and an alarm signal is generated when the leakage current signal is greater than the preset threshold.

[0095] In step S850, the alarm signal is output.

[0096] In one embodiment, at least one preset excitation frequency is an excitation frequency that causes the zero-sequence current transformer to enter a deep saturation state. Further, each preset frequency is an excitation frequency that causes the zero-sequence current transformer to enter a deep saturation state.

[0097] In one embodiment, generating an excitation signal with at least two preset excitation frequencies includes switching the preset excitation frequencies once every at least one cycle.

[0098] In one embodiment, the method further includes: comparing the voltage generated by the leakage current signal with a preset voltage to generate a feedback signal, and adjusting the frequency of the excitation signal according to the feedback signal.

[0099] The leakage current detection method according to the present invention drives a zero-sequence current transformer by using excitation signals with at least two preset excitation frequencies. This can avoid misdetecting AC signals as DC signals when the frequency of AC leakage current signals is high, thereby avoiding the problem of excessively small thresholds in the high-frequency band and improving the accuracy of leakage current signal detection.

[0100] This invention also provides a charging device, including the leakage current detection device described above and an actuating mechanism connected to the leakage current detection device. The actuating mechanism is used to disconnect the power supply line when the leakage current detection device detects a leakage current signal greater than a preset threshold. The charging device of this invention can be implemented as a charging pile, charging gun, or other charging equipment for charging vehicles. The leakage current detection device can be an onboard leakage current detection device, which can be directly mounted on the PCB board of the charging device. When the charging device is charging an electric vehicle, the leakage current detection device can detect whether the leakage current exceeds a threshold during the charging process. When the leakage current exceeds the threshold, it sends an alarm signal to the MCU or other devices on the PCB board to execute a command to stop charging, and disconnects the charging line through the actuating mechanism, such as by disconnecting a closed relay or circuit breaker mechanism.

[0101] Numerous specific details are set forth in the specification provided herein. However, it will be understood that embodiments of the invention may be practiced without these specific details. In some instances, well-known methods, structures, and techniques have not been shown in detail so as not to obscure the understanding of this specification.

[0102] Similarly, it should be understood that, in order to streamline the invention and aid in understanding one or more of the various aspects of the invention, features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof in the description of exemplary embodiments of the invention. However, this approach should not be construed as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Rather, as reflected in the corresponding claims, its inventive point lies in solving the corresponding technical problem with fewer features than all of those in a single disclosed embodiment. Therefore, the claims following the detailed description are hereby expressly incorporated into that detailed description, wherein each claim itself is a separate embodiment of the invention.

[0103] Those skilled in the art will understand that, apart from the mutual exclusion of features, all features disclosed in this specification (including the accompanying claims, abstract, and drawings) and all processes or elements of any method or apparatus so disclosed can be combined in any combination. Unless otherwise expressly stated, each feature disclosed in this specification (including the accompanying claims, abstract, and drawings) may be replaced by an alternative feature serving the same, equivalent, or similar purpose.

[0104] Furthermore, those skilled in the art will understand that although some embodiments described herein include certain features but not others included in other embodiments, combinations of features from different embodiments are intended to be within the scope of the invention and form different embodiments. For example, in the claims, any of the claimed embodiments can be used in any combination.

[0105] It should be noted that the above embodiments are illustrative of the invention and not restrictive, and that those skilled in the art can devise alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses should not be construed as limiting the claims. The invention can be implemented by means of hardware comprising several different elements and by means of a suitably programmed computer. In the unit claims enumerating several means, several of these means may be embodied by the same item of hardware. The use of the words first, second, and third, etc., does not indicate any order. These words can be interpreted as names.

[0106] The above description is merely a specific embodiment of the present invention or an explanation of that embodiment. The scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. The scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. An electric leakage detecting device, characterized by comprising: The leakage detection device is a B-type leakage detection device, and the leakage detection device comprises: a zero sequence current transformer for sensing a leakage current signal; an excitation drive and a sampling resistor connected to the zero sequence current transformer; a control circuit connected to the excitation drive and the sampling resistor, the control circuit comprising: a variable-frequency excitation circuit connected to the excitation drive, for generating periodic excitation signals of at least two preset excitation frequencies, and alternately applying the excitation signals of the at least two preset excitation frequencies on the zero sequence current transformer through the excitation drive, the variable-frequency excitation circuit switching the preset excitation frequencies every at least one period, and the excitation voltage amplitudes of the periodic excitation signals of the at least two preset excitation frequencies being not 0; a variable-frequency sampling circuit connected to the sampling resistor, for sampling the sampling resistor at at least two sampling frequencies corresponding to the at least two preset excitation frequencies one by one, to obtain a leakage current signal, the sampling frequencies being integer multiples of the preset excitation frequencies; a comparison circuit connected to the variable-frequency sampling circuit, for comparing the leakage current signal with a preset threshold, and generating an alarm signal when the leakage current signal is greater than the preset threshold.

2. The electric leakage detection apparatus according to claim 1, wherein At least one of the preset excitation frequencies is an excitation frequency for making the zero sequence current transformer enter a deep saturation state.

3. The electric leakage detecting apparatus according to claim 2, wherein Each of the preset excitation frequencies is an excitation frequency for making the zero sequence current transformer enter a deep saturation state.

4. The electric leakage detecting apparatus according to claim 1, wherein The zero sequence current transformer comprises a magnetic core, a protective shell and a coil, and the magnetic core is a nanocrystalline magnetic core.

5. The electric leakage detecting apparatus according to claim 4, wherein The magnetic saturation strength Bs of the magnetic core is less than or equal to 1.2 T, the magnetic permeability u is greater than 80,000, and the coercive force Hc after adding the magnetic field is less than 4.5 A / m.

6. The electric leakage detecting apparatus according to claim 1, wherein The variable-frequency sampling circuit comprises a digital low-pass filter for filtering out information of the excitation signal.

7. The electric leakage detecting apparatus according to claim 1, wherein The control circuit further comprises a feedback circuit connected to the variable-frequency sampling circuit and the excitation circuit respectively, for comparing a voltage generated by the leakage current signal on the sampling resistor with a preset voltage, to generate a feedback signal, and feeding back the feedback signal to the variable-frequency excitation circuit; and the variable-frequency excitation circuit is configured to adjust the size of the preset excitation frequency according to the feedback signal.

8. An electric leakage detection method characterized by comprising: The leakage detection method is applied to a B-type leakage detection device, and the method comprises: obtaining a leakage current signal sensed by a zero sequence current transformer; generating periodic excitation signals of at least two preset excitation frequencies, and alternately applying the excitation signals of the at least two preset excitation frequencies on the zero sequence current transformer, wherein the preset excitation frequencies are switched every at least one period, and the excitation voltage amplitudes of the periodic excitation signals of the at least two preset excitation frequencies are not 0; sampling at at least two sampling frequencies corresponding to the at least two preset excitation frequencies one by one, to obtain a leakage current signal, the sampling frequencies being integer multiples of the preset excitation frequencies; comparing the leakage current signal with a preset threshold, and generating an alarm signal when the leakage current signal is greater than the preset threshold; outputting the alarm signal.

9. The electric leakage detecting method according to claim 8, wherein At least one of the preset excitation frequencies is an excitation frequency that makes the zero sequence current transformer enter a deep saturation state.

10. The electric leakage detecting method according to claim 9, wherein Each of the preset excitation frequencies is an excitation frequency that makes the zero sequence current transformer enter a deep saturation state.

11. The electric leakage detection method according to claim 8, wherein Further comprising: The voltage generated by the leakage current signal is compared with a preset voltage to generate a feedback signal, and the frequency of the excitation signal is adjusted according to the feedback signal.

12. A charging device, characterized by The charging device comprises: The leakage detection device according to any one of claims 1 to 7; And an action mechanism connected to the leakage detection device, used to disconnect the power supply line when the alarm signal is received.

Images