CN113406531A

CN113406531A - Electric leakage detection device, electric leakage detection method and charging equipment

Info

Publication number: CN113406531A
Application number: CN202110529532.4A
Authority: CN
Inventors: 杜明胜
Original assignee: Shanghai Shengwei Electronic Technology Co ltd
Current assignee: Shanghai Shengwei Electronic Technology Co ltd
Priority date: 2021-05-14
Filing date: 2021-05-14
Publication date: 2021-09-17
Also published as: WO2022237796A1

Abstract

An electric leakage detection device, an electric leakage detection method, and a charging apparatus, the device comprising: the zero sequence current transformer is used for inducing a leakage current signal; the excitation driving and sampling resistors are respectively connected with the zero sequence current transformer; a control circuit, comprising: the variable-frequency excitation circuit is connected with the excitation drive and used for generating excitation signals of at least two preset excitation frequencies and applying the excitation signals to the zero-sequence current transformer alternately through the excitation drive; the variable-frequency sampling circuit is connected with the sampling resistor and is used for sampling the sampling resistor at a sampling frequency corresponding to the excitation frequency to obtain a leakage current signal; the comparison circuit is connected with the variable-frequency sampling circuit and is used for generating an alarm signal when the leakage current signal is greater than a preset threshold value; and the communication interface is connected with the comparison circuit and used for outputting an alarm signal. The leakage detection device drives the zero sequence current transformer through at least two excitation signals with preset excitation frequencies, and the accuracy of leakage current signal detection can be improved.

Description

Electric leakage detection device, electric leakage detection method and charging equipment

Technical Field

The present invention generally relates to the field of leakage detection, and more particularly, to a leakage detection device, a leakage detection method, and a charging apparatus.

Background

An RCD (Residual Current Device) is an electric leakage detection Device for detecting the magnitude of an electric leakage Current in a line. If no RCD is installed in the circuit, when a person or an animal contacts high voltage, leakage current can be generated to the ground, and when the leakage current exceeds a certain threshold value, the heart of the person or the animal can vibrate, so that the heart stops suddenly, and further life danger is caused. If the leakage detection device such as the RCD is installed in the circuit, when leakage current exists in the circuit and the magnitude of a leakage current signal exceeds a set threshold value, the RCD can send an alarm signal to the action mechanism to trigger the action mechanism to quickly break the circuit, so that the purpose of protecting life safety is achieved.

The action mechanism is mainly used for breaking a circuit of the rear end power supply, and when the circuit is broken, the rear end of the breaker does not have voltage and current, so that the protection purpose is realized. The RCD board-mounted leakage module is widely applied to charging piles and charging guns at present, can be directly installed on a circuit board, and when an electric automobile is charged, the RCD is used for detecting whether leakage current exceeds a threshold value in the charging process, if the leakage current exceeds the threshold value, the RCD can send out an alarm signal to other devices in the circuit board to execute a command of stopping charging and disconnect a charging circuit, such as a closed relay or a circuit breaker mechanism.

Disclosure of Invention

In this summary, concepts in a simplified form are introduced that are further described in the detailed description. This summary of the application is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.

An embodiment of the present invention provides an electrical leakage detection apparatus, including:

the zero sequence current transformer is used for inducing a leakage current signal;

the excitation driving and sampling resistor is connected with the zero sequence current transformer;

a control circuit connected to the excitation driver and the sampling resistor, the control circuit comprising:

the variable-frequency excitation circuit is connected with the excitation drive and is used for generating excitation signals with at least two preset excitation frequencies and applying the excitation signals with the at least two preset excitation frequencies to the zero sequence current transformer alternately through the excitation drive;

the variable-frequency sampling circuit is connected with the sampling resistor and is used for sampling the sampling resistor at a sampling frequency corresponding to the preset excitation frequency to obtain a leakage current signal;

the comparison circuit is connected with the frequency conversion sampling circuit and is used for comparing the leakage current signal with a preset threshold value and generating an alarm signal when the leakage current signal is greater than the preset threshold value;

and the communication interface is connected with the comparison circuit and used for outputting the alarm signal.

In one embodiment, the at least two preset excitation frequencies are both excitation frequencies for enabling the zero sequence current transformer to enter a deep saturation state.

In one embodiment, at least one of the preset excitation frequencies is an excitation frequency for bringing the zero sequence current transformer into a deep saturation state.

In one embodiment, the variable frequency excitation circuit switches the preset excitation frequency once every at least one period.

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

In one embodiment, the control circuit further comprises a feedback circuit respectively connected to the variable-frequency sampling circuit and the excitation circuit, and configured to compare a voltage generated by the leakage current signal across the sampling resistor with a preset voltage to generate a feedback signal, and feed the feedback signal back to the excitation circuit; the excitation circuit is configured to adjust a frequency of the excitation signal based on the feedback signal.

In one embodiment, the zero sequence current transformer comprises a magnetic core, a protective shell and a coil, wherein the magnetic core is a nanocrystalline magnetic core.

In one embodiment, the magnetic saturation strength Bs of the magnetic core is less than or equal to 1.2T, the magnetic permeability u is greater than 80000, and the coercivity Hc after longitudinal magnetism is added is less than 4.5A/m.

In one embodiment, the variable frequency sampling circuit includes a digital low pass filter for filtering information of the excitation signal.

Another aspect of the embodiments of the present invention provides a leakage detection method, where the method includes:

acquiring a leakage current signal induced by a zero sequence current transformer;

generating excitation signals of at least two preset excitation frequencies, and alternately applying the excitation signals of the at least two preset excitation frequencies to the zero sequence current transformer;

sampling at a sampling frequency corresponding to the preset excitation frequency to obtain a leakage current signal;

comparing the leakage current signal with a preset threshold value, and generating an alarm signal when the leakage current signal is greater than the preset threshold value;

and outputting the alarm signal.

In one embodiment, each of the preset excitation frequencies is an excitation frequency for bringing the zero-sequence current transformer into a deep saturation state.

In one embodiment, the generating the excitation signals of at least two preset excitation frequencies includes: and switching the preset excitation frequency once every at least one period.

In one embodiment, the method further comprises:

and 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.

In another aspect, the present invention provides a charging device, including the leakage detecting apparatus described above; and the action mechanism is connected with the electric leakage detection device and used for breaking the power supply circuit when the alarm signal is received.

The leakage detection device, the leakage detection method and the charging equipment provided by the embodiment of the invention drive the zero sequence current transformer by at least two excitation signals with preset excitation frequencies, so that the accuracy of leakage current signal detection can be improved.

Drawings

The above and other objects, features and advantages of the present application will become more apparent by describing in more detail embodiments of the present application with reference to the attached drawings. The accompanying drawings are included to provide a further understanding of the embodiments of the application and are incorporated in and constitute a part of this specification, illustrate embodiments of the application and together with the description serve to explain the principles of the application. In the drawings, like reference numbers generally represent like parts or steps.

Fig. 1 is a circuit diagram of an a-type and AC-type leakage detecting device according to an embodiment of the present invention;

FIG. 2 is a diagram illustrating magnetization curves of a B-type leakage detection device according to an embodiment of the present invention;

FIG. 3 is a schematic illustration of an external magnetic field influencing magnetization curve according to one embodiment of the present invention;

FIG. 4 is a schematic diagram of a leakage detection device according to an embodiment of the present invention;

fig. 5 is a waveform diagram of a zero sequence current transformer entering a deep saturation state according to an embodiment of the present invention;

fig. 6 is a waveform diagram of a zero sequence current transformer entering a shallow saturation state according to an embodiment of the present invention;

FIG. 7 is a schematic diagram of open loop frequency hopping of one embodiment of the present invention;

fig. 8 is a schematic flow chart of a leakage detection method according to an embodiment of the invention.

Detailed Description

In the following description, numerous specific details are set forth in order to provide a more thorough understanding of the present invention. It will be apparent, however, to one skilled in the art, that the present invention may be practiced without one or more of these specific details. In other instances, well-known features have not been described in order to avoid obscuring the invention.

It is to be understood that the present invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. In the drawings, the size and relative sizes of layers and regions may be exaggerated for clarity. Like reference numerals refer to like elements throughout.

It will be understood that when an element or layer is referred to as being "on," "adjacent to," "connected to," or "coupled to" other elements or layers, it can be directly on, adjacent to, connected or coupled to the other elements or layers or intervening elements or layers may be present. In contrast, when an element is referred to as being "directly on," "directly adjacent to," "directly connected to" or "directly coupled to" other elements or layers, there are no intervening elements or layers present. It will be understood that, although the terms first, second, third, etc. may be used to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or section from another element, component, region, layer or section. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the present invention.

Spatial relational terms such as "under," "below," "under," "above," "over," and the like may be used herein for convenience in describing the relationship of one element or feature to another element or feature as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, then elements or features described as "below" or "beneath" other elements or features would then be oriented "above" the other elements or features. Thus, the exemplary terms "under" and "under" can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatial descriptors used herein interpreted accordingly.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and/or "comprising," when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. As used herein, the term "and/or" includes any and all combinations of the associated listed items.

In order to provide a thorough understanding of the present invention, a detailed structure will be set forth in the following description in order to explain the present invention. The following detailed description of preferred embodiments of the invention, however, the invention is capable of other embodiments in addition to those detailed.

Leakage detection devices such as RCDs (Residual Current devices) are classified into AC type leakage detection devices, a type a leakage detection devices, and B type leakage detection devices, in which:

the AC leakage detection device can detect AC leakage current, and when the AC leakage current exists in the line and reaches a set threshold, the AC leakage detection device sends a TRIP alarm signal to an external operating mechanism to break the main line.

The A-type leakage detection device can detect AC-type alternating current leakage, and can also detect pulsating direct current leakage such as A0, A90, A135 and the like, and when the AC-type leakage or A-type leakage current in a line reaches a set threshold value, the A-type leakage detection device sends a TRIP alarm signal to an external trigger mechanism to break a main line;

the B-type leakage detection device not only has the detection functions of the AC-type leakage module and the A-type leakage module, but also has the capability of detecting 2P-DC (two-phase rectification), 3P-DC (three-phase rectification), S-DC (smooth direct current) and F-type (10Hz, 50Hz and 1000Hz) compound waves, and when the leakage current value reaches a preset threshold value, the B-type leakage detection device can send out a TRIP alarm signal to an external trigger mechanism so as to break a main circuit.

The detection principle of the B-type leakage detecting device is completely different from the a-type and AC-type leakage detecting devices. As shown in fig. 1, the principle of the a-type and AC-type leakage detecting devices is to detect leakage current in the line completely passively; the B-type leakage detecting device needs an external excitation frequency to drive a ZCT (zero sequence current transformer) coil, so that the magnetic core thereof is magnetized, and the magnetization curve is as shown in fig. 2.

Therefore, the principle of the B-type leakage current detection device is shown in fig. 3. The influence of the external magnetic field is reflected on the change of the H axis, which means that the current changes when the excitation signal drives the ZCT magnetic core to be magnetized, and the voltage information including the excitation signal can be obtained by detecting the voltage on the sampling resistor, wherein the voltage information also includes the information of the external magnetic field generated by the leakage current; by filtering the information of the excitation signal, the information of the external magnetic field can be obtained, so that the information of the leakage current signal is obtained, and the function of detecting the alternating current and direct current leakage current signal is realized.

The principle of B-type leakage detection devices can be divided into open-loop and closed-loop types according to whether there is feedback from the excitation frequency, wherein:

the open-loop leakage detection principle is as follows: the excitation frequency of the excitation circuit is generated by the oscillation circuit, the oscillation frequency is comprehensively determined according to the characteristics of different transformers and the magnitude of the driving current, the excitation frequency is fixed, and the excitation frequency cannot be adjusted in real time in the application process;

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

The open-loop leakage detection device cannot adjust the excitation frequency in real time in the application process, and when the leakage current is sampled by the sampling resistor, the problem that the TRIP current threshold is too small when the leakage current frequency is large (for example, more than 1K Hz) is faced.

The excitation circuit of the closed-loop leakage detection device is greatly influenced by the residual magnetism Br, and particularly after the impact of large leakage current, the leakage current value is continuously measured, so that large deviation exists and the precision is seriously influenced; in addition, the closed-loop leakage detecting device has a problem that excitation cannot start oscillation after a large leakage current occurs.

Based on this, the embodiment of the present invention applies a frequency hopping technique to a leakage detection device, and is particularly applied to a B-type leakage detection module that needs an excitation signal, where frequency hopping mainly refers to a hopping application of an excitation frequency. In the embodiment of the invention, the ZCT coil is driven by the variable-frequency excitation circuit, the excitation circuit can generate excitation signals with various frequencies, the ZCT is driven by the excitation signals with various frequencies alternately in a time-interval mode to carry out periodic magnetization, and the ZCT can well complete the periodic magnetization under different excitation frequencies, so that the problems in the open-loop type leakage detection device and the closed-loop type leakage detection device are solved.

The following describes a leakage detection device, a leakage detection method, and a charging device in detail, according to embodiments of the present invention, with reference to the accompanying drawings. The features of the following examples and embodiments may be combined with each other without conflict.

Referring to fig. 1, the leakage detecting apparatus according to the embodiment of the present invention at least includes a zero sequence current transformer 401, a sampling resistor 402, an excitation driver 403, and a control circuit 404, where the zero sequence current transformer 401 is configured to sense a leakage current signal; the excitation drive 403 and the sampling resistor 402 are respectively connected with the zero sequence current transformer 401; a control circuit 404, which is connected to the excitation driver 403 and the sampling resistor 402, respectively, wherein the control circuit 404 includes: the variable frequency excitation circuit is connected with the excitation driver 403 and is used for generating excitation signals with at least two preset excitation frequencies, and the excitation signals with at least two preset excitation frequencies are alternately applied to the zero sequence current transformer 401 through the excitation driver 403; the variable-frequency sampling circuit is connected with the sampling resistor 402 and is used for sampling the sampling resistor 402 at a sampling frequency corresponding to the excitation frequency to obtain a leakage current signal; and the comparison circuit is connected with the variable-frequency sampling circuit and used for comparing the leakage current signal with a preset threshold value and generating an alarm signal when the leakage current signal is greater than the preset threshold value.

Because the leakage detection device of the embodiment of the invention adopts a forced excitation circuit structure and adopts a frequency hopping technology to alternately generate excitation signals with different preset excitation frequencies to excite the zero-sequence current transformer 401, the problem that an alternating current leakage current signal is easily identified as a direct current leakage current signal when the leakage current frequency is higher under a single excitation frequency and the problem that the preset threshold value is too low caused by the problem in the open-loop leakage detection device can be solved; because the embodiment of the invention adopts the forced excitation circuit, the problem that excitation cannot start oscillation in the closed-loop leakage detection device does not exist.

The leakage detection device of the embodiment of the invention is a B-type leakage detection device, and the variable-frequency excitation circuit generates an excitation signal to drive the coil of the zero-sequence current transformer 401, so that the magnetic core of the zero-sequence current transformer is magnetized. The zero-sequence current transformer 401 is used for detecting the magnitude of leakage current in a line, and specifically includes a magnetic core, a protective case, and a coil. In order to make the zero-sequence current transformer 401 more suitable for a frequency modulation type excitation mode and more easily enter a deep saturation state described below, the magnetic core of the zero-sequence current transformer 401 in the embodiment of the present invention satisfies the following conditions: the magnetic saturation intensity Bs of the magnetic core is less than or equal to 1.2T, the magnetic conductivity u is more than 80000, and the coercive force Hc after longitudinal magnetism is added is less than 4.5A/m. Further, the size of the cross-sectional area Ac of the magnetic core is matched with the size of the sampling resistor, the size of the excitation frequency and the working voltage, and can be specifically calculated by the following formula:

in the formula (1), f is the excitation frequency, V_extAmplitude of excitation voltage for excitation signal, A_cIs the cross-sectional area of the core, N is the turns ratio coefficient of the core, B_mIs the maximum magnetic induction intensity.

The leakage detection device of the embodiment of the invention adopts the fluxgate technology, and magnetizes the magnetic core of the leakage detection device through the excitation signal; meanwhile, when the leakage current signal generates an external magnetic field, the information of the external magnetic field can be obtained by filtering the information of the excitation signal, so that the information of the leakage current signal is obtained. Referring to fig. 2, the principle of the magnetization process is, for example: if the ferromagnetic material is magnetized from a fully demagnetized state to saturation Bs along the magnetization curve OS, then if the external magnetic field H is reduced, the B value will no longer decrease according to the original initial magnetization curve (OS), but will decrease more slowly along the higher B, since the rigidly rotating magnetic domains retain the external magnetic field direction. Even when the external magnetic field H is 0, B is not equal to 0, that is, a residual magnetic induction Br remains. The property that the magnetization curve is not coincident with the demagnetization curve is called irreversibility of magnetization. The phenomenon in which the change in magnetic induction B lags behind the magnetic field strength H is called hysteresis.

If B is decreased, a field strength-H opposite to the original field must be applied, and when this opposite field strength is increased to-Hc, B in the magnetic medium is made 0. This does not mean that the magnetic medium recovers the disordered state, but a part of the magnetic domain still retains the original magnetization magnetic field direction, and the other part changes into the external magnetic field direction under the action of the reverse magnetic field, and when the two parts are equal, the resultant magnetic induction intensity is zero. If the reverse magnetic field strength is further increased, the reversed magnetic domains in the ferromagnetic substance are increased, the reverse magnetic induction is increased, and the reverse B is also increased as the-H value is increased. When the reverse magnetic field strength increases to-Hs, then B ═ Bs reaches reverse saturation. if-H is made 0 and B is made-Br, then it is necessary to add HC in the forward direction to make-Br zero. If H increases to Hs again, B reaches the maximum value Bs, and the magnetic medium reaches forward saturation again. Thus, the change of the magnetic field intensity is Guo Wei Hs-0-HC-Hs, and correspondingly, the change process of the magnetic induction intensity is Bs-Br-0-BS-Br-0-Bs, so that a loop symmetrical to the origin is formed, and the loop is called a saturation hysteresis loop or a maximum hysteresis loop.

As shown in fig. 3, during magnetization, if there is no influence of an external magnetic field, the magnetic field is always in an equilibrium state, and when an external magnetic field is generated due to the presence of a leakage current signal I (an alternating current leakage current signal or a direct current leakage current signal), the external magnetic field breaks the magnetic field equilibrium of the original magnetization, and the magnetization curve moves left and right on the horizontal axis (H axis). The change of the magnetic field affects the current generated in the coils of the zero sequence current transformer 401 to change.

In the embodiment of the present invention, at least two excitation signals with 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, the control circuit 404 may be implemented as an MCU (micro control unit) or other control unit or circuit with similar functions, the excitation signal is generated by a variable frequency excitation circuit in the control circuit 404, the start output and the stop output of each frequency are precisely controlled by the variable frequency excitation circuit, and the switching between different frequencies is performed in a seamless switching manner. Meanwhile, as the current driving capability of the variable frequency excitation circuit is weaker, an excitation drive 403 is connected between the variable frequency excitation circuit and the zero sequence current transformer 401, and the current output capability is increased through the excitation drive 403, so that the function similar to an amplifier is realized.

The embodiment of the invention can specifically adopt an open-loop fluxgate technology, that is, the zero-sequence current transformer 401 is excited by adopting excitation signals of at least two fixed preset excitation frequencies, so as to avoid the problem that excitation cannot start oscillation in the closed-loop fluxgate technology. Alternatively, however, the embodiment of the present invention may also adopt a closed-loop fluxgate technology, that is, the control circuit 404 further includes a feedback circuit respectively connected to the frequency conversion sampling circuit and the excitation circuit, and configured to compare a voltage generated by the leakage current signal on the sampling resistor with a preset voltage to generate a feedback signal, and feed the feedback signal back to the excitation circuit; the excitation circuit is used for adjusting the preset excitation frequency according to the feedback signal.

Furthermore, the embodiment of the invention combines the open-loop frequency hopping technology with the deep saturation performance of the zero-sequence current transformer to improve the performance of the leakage detection device. Specifically, the at least one preset excitation frequency is an excitation frequency for bringing the zero-sequence current transformer 401 into a deep saturation state. Further, each preset excitation frequency generated by the variable frequency excitation circuit is an excitation frequency for making the zero sequence current transformer 401 enter a deep saturation state. When the zero sequence current transformer 401 is in a deep saturation state by the excitation signal, the influence of the residual magnetism Br on the performance of the zero sequence current transformer 401 is very small or even negligible, so that the problem that the measurement accuracy is influenced after a large leakage current passes does not exist, the measurement error caused by the residual magnetism in open-loop and closed-loop leakage detection can be reduced, and the measurement accuracy is improved.

For convenience of understanding, refer to fig. 5 and fig. 6, where fig. 5 is waveform information captured on the sampling resistor 402 when the zero-sequence current transformer 401 enters a deep saturation state, and fig. 6 is waveform information captured on the sampling resistor 402 when the zero-sequence current transformer 401 enters a shallow saturation state.

Referring to fig. 5, when the zero-sequence current transformer 401 is driven to be deeply saturated by the excitation signal, the waveform captured on the sampling resistor 402 appears to have a flat area on the vertical axis and has a flat time on both the positive and negative half axes of the vertical axis. On the positive and negative half-axes of the longitudinal axis, the theoretical values of the whole flat area are symmetrically distributed, and the time length of the flat area is generally more than 5% of the current excitation frequency period. In contrast, referring to fig. 6, when the zero-sequence current transformer 401 is driven by the excitation signal to enter shallow saturation, only a peak region in the waveform captured by the sampling resistor 402 enters deeper saturation, and the peak region is also symmetrically distributed on the positive and negative half axes of the vertical axis, but the time for entering saturation is very short, and generally only occupies less than 5% of the current excitation frequency period.

As can be seen from fig. 5 and 6, under the condition that the zero-sequence current transformer 401 is not affected by the external magnetic field (except the geomagnetic field), the waveform of the deep saturation state reflected on the sampling resistor must have a time period during which the output voltage reaches the highest output voltage of the excitation driver 403, and the time period lasts for a time period, which is generally longer than 5% of the current excitation frequency period; the waveform represented by the shallow saturation state on the sampling resistor has at most one peak time to reach the highest output voltage of the excitation driver 403, which means that the highest output voltage of the waveform represented by the shallow saturation state on the sampling resistor must be less than the waveform voltage represented by the deep saturation on the sampling resistor, and at most only one instant of the peak time (less than 5% of the period of the excitation frequency) is equal to the voltage at the deep saturation.

Because the zero-sequence current transformer 401 is always saturated for a period of time (greater than 5%) in an excitation period in a deep saturation state, the influence of residual magnetism on the zero-sequence current transformer 401 itself is very small, so that after a very large leakage current (more than tens and hundreds of amperes) impacts the zero-sequence current transformer 401, the zero-sequence current transformer 401 is forcibly driven by a variable frequency excitation circuit to be magnetized in a manner similar to that of fig. 2, and the transformer is driven to reach a deep saturation state, thereby eliminating the adverse effect of residual magnetism and avoiding the magnetization curve deviation caused by residual magnetism. In contrast, if the zero-sequence current transformer 401 is in a shallow saturation state by the excitation current, the zero-sequence current transformer 401 cannot reach a deep saturation state of 100% by excitation driving, the influence of residual magnetism cannot be completely magnetized away, and if a large leakage current impacts the zero-sequence current transformer 401 at this time, the residual magnetism is continuously accumulated, so that the deviation shown in fig. 3 occurs in the whole magnetized balanced magnetic field without the influence of an external magnetic field (except for the geomagnetic field), and finally a large error occurs in the leakage detection device, so that a malfunction of an action mechanism is caused, and thus the normally working main line is broken.

Since deep saturation can ensure that the zero-sequence current transformer 401 can enter saturation by 100% under the driving of the excitation signal, while shallow saturation is a peak saturation mode, it cannot be well ensured that the zero-sequence current transformer 401 completely enters a saturation state, and on the contrary, the zero-sequence current transformer may not enter the required saturation state, for example, only enters a saturation state of 80%. Therefore, preferably, each excitation frequency generated by the variable frequency excitation circuit can ensure enough capability to drive the zero sequence current transformer 401 into the deep saturation state described above. However, in some embodiments, a part of the excitation frequencies may be capable of driving the zero-sequence current transformer 401 into a deep saturation state, and the rest of the excitation frequencies may drive the zero-sequence current transformer 401 into a shallow saturation state, so as to eliminate the influence of residual magnetism by the excitation frequencies capable of driving the zero-sequence current transformer 401 into the deep saturation state. For example, when there are three preset excitation frequencies, the three preset excitation frequencies may be all excitation frequencies at which the zero sequence current transformer 401 enters a deep saturation state, or two preset excitation frequencies may operate in a deep saturation state, where one preset excitation frequency operates in a shallow saturation state.

The zero sequence current sensor 401 is further connected with a sampling resistor 402, the sampling resistor 402 is connected with a variable frequency sampling circuit in the control circuit 404, and the variable frequency sampling circuit is used for collecting voltage signals on the sampling resistor 402 and converting the voltage signals into current signals.

When the excitation circuit outputs different excitation frequencies, the variable-frequency sampling circuit also collects the voltage on the sampling resistor according to the sampling frequency corresponding to the output preset excitation frequency. The sampling frequency is equal to the preset excitation frequency, or the sampling frequency is N times of the preset excitation frequency, and N is an integer not less than 2.

Because the sampling on the sampling resistor is in a frequency conversion mode, different sampling frequencies exist under different preset excitation frequencies, and the frequency conversion sampling mode is continuously and circularly performed, if three different preset excitation frequencies exist, at least three different sampling frequencies exist, and similarly, if five or more preset excitation frequencies exist, five or more sampling frequencies exist.

Furthermore, the frequency conversion sampling circuit also comprises a digital low-pass filter which is used for filtering the information of the excitation signal in the received signal and retaining the information of the leakage current signal. In the conventional leakage detecting device, if the frequency of the ac leakage current signal is equal to the excitation frequency or the ac leakage frequency is an integral multiple of the sampling frequency, there is a problem that the ac signal is determined to be a dc signal when the threshold value is determined, and therefore, a high-order filter needs to be used. According to the leakage detection device provided by the embodiment of the invention, because the sampling frequency changes constantly, the leakage current signal is sampled in an automatic frequency shift or phase shift manner, so that the possibility that alternating current leakage is judged as direct current leakage by mistake under the condition that the alternating current leakage frequency is integral multiple of the sampling frequency when the same sampling frequency is adopted for sampling is avoided, the blind zone problem of a low-pass digital filter when facing the alternating current leakage signal with the same excitation frequency is eliminated, and the problem that the high-frequency threshold value of certain frequency bands is too small when the leakage current frequency is larger (for example, larger than 1K Hz) is also eliminated. Because the digital filter can solve the problems, the leakage detection device provided by the embodiment of the invention can realize the function of an external hardware high-order low-pass filter based on the digital low-pass filter without a high-order low-pass filter, thereby saving the cost of a hardware circuit and the space of a PCB (printed circuit board).

Referring to fig. 7, for example, the variable frequency excitation circuit may alternately generate excitation signals of at least three different preset excitation frequencies, each of which outputs one or more cycles, that is, the variable frequency excitation circuit switches the preset excitation frequency every other at least one cycle, and the excitation signals of the preset excitation frequencies are seamlessly switched. Taking three preset excitation frequencies of 1K Hz, 2K Hz and 3K Hz as an example, the variable frequency excitation circuit outputs the excitation frequencies of 1K Hz, 2K Hz and 3K Hz in an alternating manner, and the zero sequence current transformer 401 enters the deep saturation state described above through excitation driving. Illustratively, the operating logic for the excitation signals at the three excitation frequencies is as follows: firstly, outputting an excitation signal of 1K Hz for three periods, then outputting an excitation signal of 2K Hz for three periods, then outputting an excitation signal of 3K Hz for three periods, and then outputting an excitation signal of 1K Hz for three periods again, and circulating and reciprocating in sequence.

It should be noted that the preset excitation frequencies in the embodiment of the present invention are not limited to three, and may be two or more, and the output sequence of the preset excitation frequencies in the embodiment of the present invention is not limited, for example, the preset excitation frequencies may be frequency hopped sequentially in the sequence of 1KHz, 2KHz, and 3KHz as shown in fig. 7, or may be frequency hopped sequentially in the sequence of 2KHz, 1KHz, and 3KHz, 2KHz, and 1KHz, and the frequency hopping sequence may be fixed or random. The number of output cycles per preset excitation frequency may be three cycles or one, two or more cycles, and the number of output cycles per preset frequency may be the same or different. The more the output cycles are, the longer the sampling time is, and the more stable the sampling is; the fewer the number of cycles output, the faster the frequency switches, and the more false detections can be avoided. Generally, a better balance between stability and accuracy is achieved when the number of output cycles is five to six cycles.

The frequency conversion sampling circuit is connected with the comparison circuit, and the comparison circuit judges whether leakage current flows through the zero sequence current transformer 401 according to the leakage current signal obtained by sampling, and judges whether the magnitude of the leakage current signal is larger than a preset threshold value. When the leakage current signal is larger than the preset threshold value, the comparison circuit outputs an alarm signal. Wherein, the alarm signal can comprise a TRIP signal for controlling the action mechanism to break the power supply circuit. The actuating mechanism is used for triggering an external mechanical tripping device, and can be purely mechanical, can also be a mixture of mechanical and electronic, and can also be purely electrical. The actuator may be connected directly to the control circuit 404 or may be connected to an external device.

The control circuit 404 may further include an external communication interface for enabling communication with an external device, receiving and transmitting various information between the electrical leakage detection apparatus and the external device, and the alarm signal may also include an alarm signal transmitted to the external device.

In one embodiment, the comparing circuit is further connected to an analog-to-digital conversion circuit, and the analog-to-digital conversion circuit is configured to perform analog-to-digital conversion according to 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. The pulse signal may indicate not only the magnitude of the leakage current signal but also waveform information of the leakage current signal, a frequency of the leakage current signal, and the like. Illustratively, the analog-to-digital conversion circuit may generate a PWM (Pulse Width Modulation) signal having a corresponding duty ratio according to the magnitude of the leakage current signal. The duty ratio of the PWM signal, that is, the proportion of the high level in the whole period in one pulse period, is higher, the higher the magnitude of the leakage current signal is, the higher the duty ratio of the PWM signal generated by the analog-to-digital conversion circuit is, and the client can determine the magnitude of the leakage current signal according to the duty ratio of the PWM signal. Further, for different types of leakage current signals, the PWM signals can be output through different external communication ports, so that the external device can determine the type of the leakage current signal according to the external communication port outputting the PWM signal, thereby achieving the purpose of representing the size and the signal type of the leakage current signal through a digital signal without configuring an additional algorithm at the client. For example, the frequencies of the PWM signals generated by the different analog-to-digital conversion circuits may be the same or different, and in some embodiments, the frequency of the ac leakage current signal may be represented by the frequency of the PWM signal in addition to the magnitude of the leakage current signal being represented by the duty ratio of the PWM signal.

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

Based on the above description, the leakage detection apparatus according to the embodiment of the present invention drives the zero sequence current transformer by at least two excitation signals with preset excitation frequencies, so that it is possible to avoid that an ac signal is erroneously detected as a dc signal when the ac leakage current signal frequency is high, thereby avoiding the problem that the threshold is too small in a high frequency band, and improving the accuracy of leakage current signal detection.

Another aspect of the embodiments of the present invention provides a leakage detection method, which may be implemented by the leakage detection apparatus described with reference to fig. 4. Only the main steps for describing the leakage detection method will be described below, and more details can be referred to above.

FIG. 8 shows a schematic flow diagram of a method 800 of electrical leakage detection according to one embodiment of the present invention. As shown in fig. 8, a leakage detection method 800 according to an embodiment of the present invention includes the following steps:

in step S810, a leakage current signal induced by the zero sequence current transformer is obtained;

in step S820, generating excitation signals of at least two preset excitation frequencies, and applying the excitation signals of at least two preset excitation frequencies to the zero sequence current transformer alternately;

in step S830, sampling at a sampling frequency corresponding to the preset excitation frequency to obtain a leakage current signal;

in step S840, 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;

in step S850, the alarm signal is output.

In one embodiment, the at least one preset excitation frequency is an excitation frequency for bringing the zero-sequence current transformer into a deep saturation state. Further, each preset frequency is an excitation frequency for enabling the zero-sequence current transformer to enter a deep saturation state.

In one embodiment, generating the excitation signals at the at least two preset excitation frequencies comprises: and switching the preset excitation frequency once every at least one period.

In one embodiment, the method further comprises: and 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.

According to the leakage detection method provided by the embodiment of the invention, the zero sequence current transformer is driven by the excitation signals with at least two preset excitation frequencies, so that the alternating current signal can be prevented from being mistakenly detected as the direct current signal when the alternating current leakage current signal frequency is higher, the problem that the threshold value is too small in a high frequency band is further avoided, and the accuracy of leakage current signal detection is improved.

The embodiment of the invention also provides charging equipment which comprises the leakage detection device and an action mechanism connected with the leakage detection device, wherein the action mechanism is used for disconnecting the power supply circuit when the leakage detection device detects that the magnitude of the leakage current signal is greater than a preset threshold value. The charging device of the embodiment of the invention can be realized as a charging device for charging vehicles, such as a charging pile, a charging gun and the like, the leakage detection device can be a board-mounted leakage detection device which can be directly mounted on a PCB (printed Circuit Board) of the charging device, when the charging device charges an electric automobile, the leakage detection device can be used for detecting whether the magnitude of leakage current exceeds a threshold value in the charging process, and sending an alarm signal to an MCU (micro control Unit) or other devices on the PCB when the magnitude of the leakage current exceeds the threshold value so as to execute a charging stopping command, and breaking a charging circuit through an actuating mechanism, such as a closed relay or a breaker mechanism and the like.

In the description provided herein, numerous specific details are set forth. It is understood, however, 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 in order not to obscure an understanding of this description.

Similarly, it should be appreciated that in the description of exemplary embodiments of the invention, various features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the invention and aiding in the understanding of one or more of the various inventive aspects. However, the method of the present invention should not be construed to reflect the intent: that the invention as claimed requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single disclosed embodiment. Thus, the claims following the detailed description are hereby expressly incorporated into this detailed description, with each claim standing on its own as a separate embodiment of this invention.

It will be understood by those skilled in the art that all of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and all of the processes or elements of any method or apparatus so disclosed, may be combined in any combination, except combinations where such features are mutually exclusive. Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise.

Furthermore, those skilled in the art will appreciate that while some embodiments described herein include some features included in other embodiments, rather than other features, combinations of features of different embodiments are meant to be within the scope of the invention and form different embodiments. For example, in the claims, any of the claimed embodiments may be used in any combination.

It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The invention may be implemented by means of hardware comprising several distinct elements, and by means of a suitably programmed computer. In the unit claims enumerating several means, several of these means may be embodied by one and the same item of hardware. The usage of the words first, second and third, etcetera do not indicate any ordering. These words may be interpreted as names.

The above description is only for the specific embodiment of the present invention or the description thereof, and the protection scope of the present invention is not limited thereto, and any person skilled in the art can easily conceive of the changes or substitutions within the technical scope of the present invention, and the changes or substitutions should be covered within the protection scope of the present invention. The protection scope of the present invention shall be subject to the protection scope of the claims.

Claims

1. An electrical leakage detection device, characterized in that it comprises:

and the comparison circuit is connected with the frequency conversion sampling circuit and used for comparing the leakage current signal with a preset threshold value and generating an alarm signal when the leakage current signal is greater than the preset threshold value.

2. The electrical leakage detection device according to claim 1, wherein at least one of said predetermined excitation frequencies is an excitation frequency for bringing said zero sequence current transformer into a deep saturation state.

3. The electrical leakage detection device according to claim 2, wherein each of said predetermined excitation frequencies is an excitation frequency for bringing said zero sequence current transformer into a deep saturation state.

4. The earth leakage detection device of claim 1, wherein said variable frequency excitation circuit switches said predetermined excitation frequency once every at least one cycle.

5. The electrical leakage detection device according to claim 1, wherein the sampling frequency is an integer multiple of the preset excitation frequency.

6. The electrical leakage detection device 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.

7. An electric leakage detecting device according to claim 6, wherein said magnetic core has a magnetic saturation strength Bs ≦ 1.2T, a magnetic permeability u >80000, and a coercive force Hc after longitudinal magnetization ≦ 4.5A/m.

8. The electrical leakage detection device of claim 1, wherein said variable frequency sampling circuit comprises a digital low pass filter for filtering information of said excitation signal.

9. The leakage detection device of 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 across the sampling resistor with a preset voltage to generate a feedback signal, and feeding the feedback signal back to the variable-frequency excitation circuit; the frequency conversion excitation circuit is used for adjusting the preset excitation frequency according to the feedback signal.

10. A method of electrical leakage detection, the method comprising:

and outputting the alarm signal.

11. The electrical leakage detection method according to claim 10, wherein at least one of the predetermined excitation frequencies is an excitation frequency for bringing the zero-sequence current transformer into a deep saturation state.

12. The electrical leakage detection method according to claim 11, wherein each of the predetermined excitation frequencies is an excitation frequency for bringing the zero-sequence current transformer into a deep saturation state.

13. The electrical leakage detection method of claim 10, wherein generating the excitation signals of at least two predetermined excitation frequencies comprises: and switching the preset excitation frequency once every at least one period.

14. A leakage detecting method according to claim 10, further comprising:

15. A charging apparatus, characterized in that the charging apparatus comprises:

the electrical leakage detection device according to any one of claims 1 to 9;

and the action mechanism is connected with the electric leakage detection device and used for breaking the power supply circuit when the alarm signal is received.