Fluxgate-based high-precision AC / DC hybrid leakage current protection circuit and method

Abstract

The invention discloses a high-precision alternating current and direct current mixed leakage current protection circuit and method based on a fluxgate. The protection circuit is composed of an FPGA and a peripheral circuit thereof, a power supply and a conversion circuit thereof, a communication circuit, an electric leakage sensing and measuring circuit, and an AD conversion and sampling conditioning circuit. According to the invention, the measurement precision and accuracy are effectively improved through signal compensation calculation; the timeliness and effectiveness of protection are enhanced through mutual cooperation of two protection modes of an effective value and an instantaneous value; accurate instantaneous value protection is carried out by using the inverse time limit characteristic of the leakage current; classification threshold protection is carried out through spectral analysis and waveform identification, so that the probability of false operation and missing operation is effectively reduced; fFT transformation is adopted to convert to a frequency domain for discrimination, and an improved formula is utilized to calculate a frequency domain output variance to further refine and distinguish waveforms. According to the invention, high-precision measurement of the leakage current can be realized, complex waveforms can be effectively handled, and rapid and reliable protection of electrical equipment can be realized.

Description

Technical Field

[0001] The invention relates to the field of leakage current protection, and particularly to a high-precision AC-DC hybrid leakage current protection circuit and method based on a fluxgate. Background Art

[0002] In modern power systems, AC-DC hybrid circuits are increasingly widely used, such as industrial automation equipment, new energy power generation systems, electric vehicle charging facilities, etc. However, the leakage current problem in AC-DC hybrid circuits poses a serious threat to the safe operation of power systems. Leakage current not only causes waste of electrical energy, but may also trigger electrical fires, electric shock accidents, etc., causing damage to personnel safety and normal operation of equipment.

[0003] Currently, the existing leakage current protection devices on the market have many deficiencies:

[0004] Low detection accuracy: For the detection of AC-DC hybrid leakage current, traditional devices often have difficulty achieving high-precision measurement. Due to the different characteristics of AC and DC signals, the complexity of the mixed signal makes the existing detection methods and technologies difficult to accurately capture and analyze the magnitude and characteristics of the leakage current, resulting in large errors in the detection results and unable to meet the requirements for high-precision leakage current detection.

[0005] Slow response speed: When leakage current occurs, it is crucial to respond quickly and take protective measures. However, the existing protection devices often take a long time to respond after detecting the leakage current, which may cause serious damage to the equipment before the protection action, and cannot effectively guarantee the safety of the power system.

[0006] Single function: Most traditional protection devices can only provide single protection for AC or DC leakage current, and cannot comprehensively detect and protect AC-DC hybrid leakage current at the same time. In practical applications, the leakage current situation in AC-DC hybrid circuits is complex and changeable, and a single-function protection device is difficult to meet the actual needs.

[0007] Limited communication ability: With the development of the intelligence of power systems, the demand for remote monitoring and management is increasing day by day. Some existing protection devices lack effective communication functions and cannot transmit leakage current detection data and device operation status information to the remote monitoring center in time, which is not conducive to the centralized management and fault troubleshooting of power systems. Summary of the Invention

[0008] To solve at least some of the above problems, the invention provides a high-precision AC-DC hybrid leakage current protection circuit and method based on a fluxgate. To achieve the above object, the following technical solutions are provided:

[0009] On the one hand, the present invention provides a high-precision AC-DC hybrid leakage current protection circuit based on a fluxgate, which includes five parts: an FPGA and its peripheral circuits, a power supply and its conversion circuit, a communication circuit, a leakage current sensing and measuring circuit, and an AD conversion and sampling conditioning circuit; the leakage current sensing and measuring circuit uses a voltage-source type fluxgate sensor based on the fluxgate principle, and realizes threshold setting through resistors R1 and R2, and sets the maximum value of the output voltage of the operational amplifier to U H , and the minimum value is set to 0. When the voltage fed back by the sampling resistor R s reaches the preset threshold, the polarity of the output voltage of the operational amplifier will reverse, so that the circuit generates a square wave voltage signal with periodic jump characteristics, which can accurately sense the leakage current in the AC-DC hybrid circuit at the same time, and the measuring circuit amplifies and filters the electrical signal output by the sensor.

[0010] Preferably, it includes the compensation calculation of the fluxgate sensor current signal:

[0011]

[0012] Among them, i(t) is the actually measured leakage current value; I mp is the magnetic saturation current.

[0013] On the other hand, the present invention also provides a high-precision AC-DC hybrid leakage current protection method based on a fluxgate, which includes the following steps:

[0014] b. Initialization stage: Set initial values for various variables, registers, and status flags in the system, and at the same time initialize parameters such as the sampling frequency and protection threshold; b. AD sampling: Convert the sampling signal into a digital quantity; c. Judgment of whether the sampling result exceeds the instantaneous peak value: Determine whether the sampling result exceeds the instantaneous peak value; d. Judgment of the end of the fundamental wave period: Judge whether the fundamental wave period ends; e. Instantaneous value fast-acting protection: When the instantaneous value of the signal exceeds the protection value, start leakage protection and other measures to avoid equipment damage; f. RMS value protection; g. Leakage protection or end.

[0015] Preferably, the step f. RMS value protection includes: waveform recognition, which analyzes the digital signal obtained by sampling to clarify its waveform characteristics, and then sets the RMS value protection.

[0016] Preferably, step e specifically includes: e1. Signal acquisition and caching: To ensure the continuity and accuracy of signal processing, a buffer with the property of first-in-first-out is set; e2. Threshold setting: Based on the rated parameters of the electrical equipment, the safe operating range, and the maximum abnormal current situation that may be encountered, the action threshold of instantaneous value fast protection is comprehensively set; e3. Inverse time calculation: According to the magnitude of the current exceeding the threshold at present, and based on the pre-determined inverse time characteristic parameters, calculate the time when the protection device should act; e4. Anti-interference processing: To avoid false triggering caused by instantaneous interference, an anti-interference time window and a debounce mechanism are set.

[0017] Preferably, the inverse time calculation formula is as follows:

[0018]

[0019] where, t act is the action time of the protection device; T k is the time constant, which is used to adjust the time scale of the inverse time curve and is determined according to the device characteristics and application requirements; T s is the standard time constant, which is a fixed reference value used to standardize the inverse time characteristic curve, facilitating performance comparison and parameter coordination between different protection devices; i(t) is the actually measured leakage current value; I set is the action current setting value of the protection device, that is, when the current reaches or exceeds it, the protection device starts to act according to the inverse time characteristic; para is the inverse time exponent, which determines the shape of the inverse time curve, and different values may be selected for different application scenarios to meet specific protection requirements; I d is the DC component of the leakage current, and λ is its influence factor.

[0020] Preferably, step f specifically includes:

[0021] f1. Spectrum analysis; f2. Waveform classification: According to the frequency, amplitude, and phase information obtained from the spectrum analysis, divide the signal waveform into different categories and make relevant judgments based on different thresholds; f3. Wait for the program loop period: When it is judged that there is no overcurrent, the system enters the waiting state and waits for the arrival of the next sampling period; f4. When a signal overcurrent occurs, when it is judged that there is an overcurrent, the system needs to take corresponding measures to protect the electrical equipment and prevent safety accidents, and generate an alarm signal or a control signal.

[0022] Preferably, the step f2 specifically includes: f21. Obtaining the FFT amplitude output and performing harmonic compensation; f22. Judging whether it is a pure DC signal. If it is a pure DC signal, enter the corresponding processing module; f23. Judging whether it is a pure AC signal. If it is not a pure AC signal, it is determined as an AC-DC mixed signal; f24. Processing of the AC-DC mixed signal: For the AC-DC mixed signal, remove the DC component from the AC-DC mixed signal to make the signal become a pure AC signal; f25. Calculating the mean square error and judging the waveform.

[0023] Preferably, the control signal is used to control the circuit breaker and relay equipment to cut off the circuit, thereby avoiding damage to the equipment caused by overcurrent.

[0024] Preferably, the calculation of the mean square error and the waveform judgment are specifically as follows: After removing the DC component, calculate the mean square error of the signal, measure the fluctuation degree of the signal through the mean square error, and judge the waveform type according to the output result.

[0025] The beneficial effects of the present invention are as follows:

[0026] 1. The present invention provides a high-precision AC-DC mixed leakage current protection circuit. In terms of signal detection, compared with traditional protection circuits, it can accurately capture both tiny DC leakage and complex AC leakage situations. This enables the protection device to more timely and accurately judge the leakage state, providing a reliable data basis for subsequent protection actions, and greatly reducing the possibility of misjudgment and missed judgment. Its measurement accuracy can reach 1 mA.

[0027] 2. The present invention provides a high-precision AC-DC mixed leakage current protection method. In terms of precise measurement, it innovatively uses a fluxgate sensor to achieve precise measurement of high-precision current, and proposes an accurate signal compensation calculation scheme, effectively improving the accuracy and accuracy of current measurement, and being able to more sensitively capture the subtle changes in current, providing a reliable data basis for subsequent protection actions.

[0028] 3. The present invention provides a high-precision AC-DC mixed leakage current protection method. In terms of the protection mechanism, it organically combines and operates in coordination the two protection methods of the effective value and the instantaneous value. Among them, the effective value algorithm can, based on its analysis of waveform characteristics, provide accurate waveform prediction information for the instantaneous value algorithm in advance, enabling the instantaneous value protection to quickly and accurately respond when facing current spike conditions, greatly enhancing the timeliness and effectiveness of the protection.

[0029] 4. The present invention provides a high-precision AC-DC hybrid leakage current protection method. In terms of dealing with current spikes, it cleverly utilizes the inverse time characteristic of the leakage current to construct an accurate instantaneous value protection strategy. According to the principle that the current magnitude is inversely proportional to the operating time, when a spike current appears, it can quickly calculate and implement a protection operating time adapted to its amplitude, avoiding damage to equipment due to instantaneous high-current impact, and ensuring the safe and stable operation of the equipment under complex current conditions.

[0030] 5. The present invention provides a high-precision AC-DC hybrid leakage current protection method. In terms of improving the reliability of leakage protection, in the effective value protection process, first, a comprehensive spectrum analysis is carried out to deeply analyze the frequency composition of the signal; then, an improved waveform recognition step is implemented to more accurately identify the signal waveform category; finally, classification threshold protection is implemented based on accurate classification to ensure that the most appropriate protection measures can be taken under different waveform characteristics, effectively reducing the probability of misoperation and leakage operation.

[0031] 6. The present invention provides a high-precision AC-DC hybrid leakage current protection method. In terms of waveform classification and recognition, the waveform classification protection sub-module uses advanced FFT transformation technology to convert the signal to the frequency domain for in-depth discrimination, and further uses an optimized improved formula to calculate the variance of the frequency domain output, thereby realizing a more detailed and accurate distinction and recognition of the waveform, providing a solid basis for subsequent targeted protection actions, and effectively improving the overall performance and reliability of leakage protection. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments recorded in the embodiments of the present application. For those of ordinary skill in the art, other drawings can also be obtained based on these drawings.

[0033] Figure 1 is the structural diagram of the high-precision AC-DC hybrid leakage current protection circuit of the present invention;

[0034] Figure 2 is the structural diagram of the voltage source type fluxgate sensor of the present invention;

[0035] Figure 3 is the overall flow chart of the high-precision AC-DC hybrid leakage current protection method of the present invention;

[0036] Figure 4 is the flow chart of the effective value protection module of the present invention;

[0037] Figure 5 is the flow chart of the waveform classification sub-module of the present invention. Detailed implementation manners

[0038] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Apparently, the described embodiments are only some, but not all, of the embodiments of the present invention. Components of the embodiments of the present invention usually described and illustrated in the accompanying drawings here can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0039] Figure 1 It is a structural diagram of a high-precision AC / DC hybrid leakage current protection circuit. It includes five parts: an FPGA and its peripheral circuits, a power supply and its conversion circuit, a communication circuit, a leakage current sensing and measuring circuit, and an AD conversion and sampling conditioning circuit. For the FPGA and its peripheral circuits, a high-performance FPGA is used as the core processing unit, which has powerful parallel processing capabilities and high-speed data processing speeds. The internal logic circuit can be flexibly configured through programming. The peripheral circuits include a clock circuit, a reset circuit, a configuration circuit, etc., providing stable working conditions for the FPGA; for the power supply and its conversion circuit, it supports multiple power input methods, filters and stabilizes the input power supply, and converts it into DC power supplies of different voltage levels required by each module inside the device, and has overvoltage and overcurrent protection functions; for the leakage current sensing and measuring circuit, a high-precision leakage current sensor is used, based on the fluxgate principle, which can accurately sense the leakage current in the AC / DC hybrid circuit at the same time, and the measuring circuit amplifies and filters the electrical signal output by the sensor; for the AD conversion and sampling conditioning circuit, a high-precision AD conversion chip is used to convert the analog signal output by the leakage current sensing and measuring circuit into a digital signal, and the sampling conditioning circuit samples and conditions the input analog signal to ensure that the AD conversion chip receives a signal that meets the requirements.

[0040] Figure 2 It is a structural diagram of a voltage source type fluxgate sensor. The threshold setting of the voltage source type fluxgate transformer is mainly achieved through resistors R1 and R2. The maximum value of the output voltage of the operational amplifier is set as UH, and the minimum value is set as 0. When the system is in the working state, if the sampling resistor R sWhen the feedback voltage reaches a pre-set threshold, the polarity of the output voltage of the operational amplifier will reverse, thus enabling the circuit to generate a square-wave voltage signal with periodic jumps. Under the action of the signal magnetization mechanism, the electromagnetic characteristics exhibit specific periodic changes at different time intervals, enabling the detection coil to sense the external magnetic field signal and thus achieve the purpose of measuring current.

[0041] When the measured value i(t) is less than 3 mA, it is calculated according to the following formula:

[0042]

[0043] When the measured value i(t) is greater than 3 mA, it is calculated according to the following formula:

[0044]

[0045] Among them, the maximum value of the amplifier output voltage is U H , the sampling resistor R s , the saturation magnetic field strength H, the number of turns of the coil N2, the average magnetic path length l of the magnetic core, the magnetic saturation current I mp . Further calculation compensation is carried out:

[0046]

[0047] Figure 3This is the overall flowchart of the high-precision AC-DC hybrid leakage current protection method. The following is a detailed explanation of the specific functions of each step in the working process of this leakage protection system: (1) Start and initialization, which is the starting point for the operation of the entire system. Initialization operations usually include setting initial values for various variables, registers, status flags, etc. in the system to ensure that the system starts running from a known and stable state. Initialize parameters such as the sampling frequency and protection threshold. (2) AD sampling, which converts the sampling signal into a digital signal for subsequent digital signal processing. The sampling frequency and accuracy determine the accuracy and integrity of the acquired signal. An appropriate sampling frequency can ensure that important information in the signal is not lost. (3) Judgment on whether the sampling result exceeds the instantaneous peak value. The instantaneous peak value is an important reference value. Judging whether the sampling result exceeds the instantaneous peak value is mainly to detect whether there are abnormal large currents or voltage spikes that may cause damage or failure to electrical equipment. If the sampling result does not exceed the instantaneous peak value (N), it means that the current signal is within the normal range, and the system can continue the next round of sampling to continuously monitor the electrical signal. If it exceeds the instantaneous peak value (Y), it indicates that an abnormal situation may have occurred, and further analysis and processing are required. (4) Judgment on the end of the fundamental wave period. The sampling signal is periodic, and the fundamental wave period is usually 20 ms. Judging whether the fundamental wave period ends helps the system to perform accurate signal analysis on a complete cycle. If the fundamental wave period has not ended (N), then return to continue sampling because incomplete cycle data may lead to inaccurate analysis results. If the fundamental wave period ends (Y), it means that enough data has been acquired for reliable analysis, and the system can enter the next step of processing. (5) Instantaneous value fast action protection module. The instantaneous value refers to the electrical signal value at a certain moment. When the instantaneous value of the signal exceeds the protection value (Y), it means that there may be a situation that is harmful to electrical equipment, such as a short circuit or other faults at the current moment. This module can react quickly and initiate leakage protection and other measures to avoid equipment damage. If it does not exceed the protection value (N), the system returns to continue sampling. (6) RMS value protection module. The RMS value reflects the DC value corresponding to the heat generated by alternating current in one cycle being equal to the heat generated by direct current under the same conditions. Waveform recognition is to analyze the sampled digital signal to determine its waveform characteristics. Different electrical faults or normal operating states often correspond to different waveforms. Through waveform recognition, different types of waveforms such as sine waves and half waves can be distinguished, and then it can be judged whether the electrical system is in a normal operating state or the specific fault type can be identified. In an electrical system, the RMS value is an important parameter. When the RMS value exceeds the protection value (Y), it indicates that there are faults such as overload and overcurrent in the electrical system, and leakage protection and other operations need to be initiated. If it does not exceed the protection value (N), the system returns to continue sampling. (7) Leakage protection and end. When the above protection module determines that the signal exceeds the protection value, the system will initiate leakage protection measures.The function of leakage protection is to quickly cut off the circuit to prevent personal electric shock injuries and damage to electrical equipment caused by leakage.

[0048] The specific method of the instantaneous value fast protection module is as follows: a. Signal acquisition and caching: To ensure the continuity and accuracy of signal processing, a buffer with the characteristics of First-In-First-Out (FIFO) is set; b. Threshold setting: According to the rated parameters of the electrical equipment, the safe operating range, and the maximum abnormal current that may be encountered, the action threshold of the instantaneous value fast protection is comprehensively set; c. Inverse time calculation: According to the magnitude of the current exceeding the threshold at present, based on the pre-determined inverse time characteristic parameters, calculate the time when the protection device should act; d. Anti-interference processing: To avoid false triggering caused by momentary interference, an anti-interference time window and a debounce mechanism are set; The inverse time calculation formula is as follows:

[0049]

[0050] where, t act is the action time of the protection device; T k is the time constant, which is used to adjust the time scale of the inverse time curve and is determined according to the device characteristics and application requirements; T s is the standard time constant, which is a fixed reference value used to standardize the inverse time characteristic curve for facilitating performance comparison and parameter coordination between different protection devices; i(t) is the actually measured leakage current value; I set is the action current setting value of the protection device, that is, when the current reaches or exceeds it, the protection device starts to act according to the inverse time characteristic; para is the inverse time index, which determines the shape of the inverse time curve, and different values may be selected in different application scenarios to meet specific protection requirements; I d is the DC component of the leakage current, and λ is its influence factor.

[0051] Figure 4It is the flowchart of the effective value protection module. The following is a detailed explanation of each step in this flowchart: (1) Spectrum analysis: Analyze the collected signal in the frequency domain, and use the Fast Fourier Transform (FFT) to convert the time-domain signal into a frequency-domain signal. In this way, the amplitude and phase information of the signal at different frequency components can be obtained. Through spectrum analysis, the information of harmonics such as 100Hz, 150Hz, 200Hz, etc. in the signal can be detected. (2) Waveform classification sub-module: This step is based on the results of spectrum analysis to classify the waveform of the signal. According to the frequency, amplitude, phase and other information obtained from spectrum analysis, the signal waveform is divided into different categories, and relevant judgments are made based on different thresholds. The overcurrent threshold is usually set according to the rated current of the electrical equipment and safety standards. If the current value is less than or equal to the threshold, it is judged as not overcurrent (N); if the current value is greater than the threshold, it is judged as overcurrent (Y). (3) Wait for the program cycle (when not overcurrent): When it is judged as not overcurrent, the system enters the waiting state and waits for the next sampling period to arrive. During this period, the system can maintain the monitoring of the system state to ensure that no new abnormal situations occur, and store or record some data for subsequent analysis or report generation. (4) Send a signal (when overcurrent): When it is judged as overcurrent, the system needs to take corresponding measures to protect the electrical equipment and prevent safety accidents, and generate an alarm signal or a control signal. The alarm signal can be in the form of sound, light, etc., which is used to remind the operator; the control signal can be used to control devices such as circuit breakers and relays to cut off the circuit, thereby avoiding damage to the equipment caused by overcurrent. Send the generated signal to the corresponding device or system, such as sending the control signal to the control circuit of the circuit breaker to make it act to cut off the circuit.

[0052] Figure 5It is the flowchart of the waveform classification sub-module. (1) Obtain the FFT amplitude output and perform harmonic compensation; (2) Determine whether it is a pure DC signal. Check whether the signal after FFT and harmonic compensation is a pure DC signal. If the signal has an amplitude only at 0 Hz (DC), then it can be determined as a pure DC signal. If it is a pure DC signal (Y), the process enters the corresponding processing module. If it is not a pure DC signal (N), then enter the next judgment. (3) Determine whether it is a pure AC signal. After excluding the pure DC signal, further determine whether the signal is a pure AC signal. A pure AC signal usually refers to a signal without a DC component and whose frequency components conform to the characteristics of a specific AC signal. If it is a pure AC signal (Y), then enter the corresponding processing module. If it is not a pure AC signal (N), then it is determined as an AC-DC mixed signal. (4) Process the AC-DC mixed signal. For the AC-DC mixed signal, it is necessary to further remove the DC component. Remove the DC component from the AC-DC mixed signal to make the signal a pure AC signal. This step usually uses subtracting the average value of the signal to remove the DC component. (5) Calculate the sum of the amplitudes from the 2nd to the 8th. (6) After removing the DC component, calculate the mean square error of the signal. The mean square error can be used to measure the degree of signal fluctuation, and judge the waveform type (DC, sine wave, half wave, 90° wave, 135° wave, others) according to the output result. The formula is as follows:

[0053]

[0054] Among them, I 50Hz is the amplitude of the current at 50 Hz, and x i is the i-th amplitude. Normalization processing is performed using this reference, so as to achieve accurate judgment with the same precision for currents with different amplitudes.

[0055] Table 1 shows the operating times for different residual current values.

[0056] Table 1 Operating Times for Different Residual Current Values

[0057]

[0058] Those of ordinary skill in the art can realize that the units and device steps of each example described in combination with the embodiments disclosed herein can be implemented by electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are executed in a hardware or software manner depends on the specific application and design constraints of the technical solution. Professional technicians can use different devices for each specific application to implement the described functions, but such implementation should not be considered to exceed the scope of the embodiments of this application.

[0059] The above embodiments are only used to illustrate the embodiments of the present application, rather than limiting the embodiments of the present application. Those of ordinary skill in the relevant technical field can also make various changes and modifications without departing from the spirit and scope of the embodiments of the present application. Therefore, all equivalent technical solutions also belong to the scope of the embodiments of the present application. The patent protection scope of the embodiments of the present application shall be defined by the claims.

Claims

1. A high-precision AC-DC hybrid leakage current protection circuit based on a fluxgate, characterized in that It includes an FPGA and its peripheral circuits, a power supply and its conversion circuits, a communication circuit, a leakage current sensing and measuring circuit, and an AD conversion and sampling conditioning circuit; the leakage current sensing and measuring circuit uses a voltage source type fluxgate sensor based on the fluxgate principle, and the threshold is set through resistors R1 and R2, and the maximum value of the output voltage of the operational amplifier is set to U H , the minimum value is set to 0, when the voltage fed back by the sampling resistor R s reaches the preset threshold, the polarity of the output voltage of the operational amplifier will reverse, so that the circuit generates a square wave voltage signal with periodic jump characteristics, which can accurately sense the leakage current in the AC-DC hybrid circuit at the same time, and the measuring circuit amplifies and filters the electrical signal output by the sensor.

2. The high-precision AC-DC hybrid leakage current protection circuit according to claim 1, characterized in that, It also includes the compensation calculation of the fluxgate sensor current signal: Among them, i(t) is the actually measured leakage current value; I mp is the magnetic saturation current.

3. A high-precision AC-DC hybrid leakage current protection method based on a fluxgate, comprising the high-precision AC-DC hybrid leakage current protection circuit based on a fluxgate according to any one of claims 1-2, characterized in that, The method includes the following steps: a. Initialization: Set initial values for various variables, registers, and status flags within the system, and simultaneously initialize the sampling frequency and protection threshold; b. AD sampling: Convert the sampling signal into a digital quantity; c. Instantaneous peak value judgment of the sampling result: Determine whether the sampling result exceeds the instantaneous peak value; d. Fundamental wave period judgment: Judge whether the fundamental wave period has ended; e. Instantaneous value fast-acting protection: When the instantaneous value of the signal exceeds the protection value, initiate the leakage protection measure to avoid equipment damage; f. RMS value protection; g. Leakage protection or end.

4. The high-precision AC / DC hybrid leakage current protection method based on a fluxgate according to claim 3, wherein The step f. RMS value protection includes: waveform recognition, which analyzes the digital signal obtained by sampling to clarify its waveform characteristics, and then sets the RMS value protection.

5. The high-precision AC / DC hybrid leakage current protection method based on a fluxgate according to claim 3, characterized in that, The step e specifically includes: e1. Signal acquisition and caching: To ensure the continuity and accuracy of signal processing, set up a buffer with the first-in-first-out characteristic; e2. Threshold setting: Based on the rated parameters of the electrical equipment, the safe operating range, and the maximum abnormal current that may be encountered, comprehensively set the action threshold of the instantaneous value fast protection; e3. Inverse time calculation: According to the magnitude of the current exceeding the threshold currently, calculate the time when the protection device should act based on the pre-determined inverse time characteristic parameters; e4. Anti-interference processing: To avoid false triggering caused by momentary interference, set up an anti-interference time window and a debounce mechanism.

6. The high-precision AC-DC hybrid leakage current protection method based on a fluxgate according to claim 4, wherein, The inverse time calculation formula is as follows: where t act is the operating time of the protection device; T k is the time constant, which is used to adjust the time scale of the inverse time curve and is determined according to the device characteristics and application requirements; T s is the standard time constant, which is a fixed reference value used to standardize the inverse time characteristic curve, facilitating performance comparison and parameter coordination between different protection devices; i(t) is the actually measured leakage current value; I set is the set value of the operating current of the protection device, that is, when the current reaches or exceeds this value, the protection device starts to act according to the inverse time characteristic; para is the inverse time exponent, which determines the shape of the inverse time curve. Different application scenarios may select different values to meet specific protection requirements; I d is the DC component of the leakage current, and λ is its influence factor.

7. The high-precision AC / DC hybrid leakage current protection method based on a fluxgate according to claim 3, wherein The step f specifically includes: f1. Spectrum analysis; f2. Waveform classification: According to the frequency, amplitude, and phase information obtained from the spectrum analysis, divide the signal waveform into different categories and make relevant judgments based on different thresholds; f3. Wait for the program loop period: When it is judged that there is no overcurrent, the system enters the waiting state and waits for the arrival of the next sampling period; f4. When the signal is overcurrent, when it is judged that there is overcurrent, the system needs to take corresponding measures to protect the electrical equipment and prevent safety accidents, and generate an alarm signal or a control signal.

8. The high-precision AC-DC hybrid leakage current protection method based on a fluxgate according to claim 6, wherein The step f2 specifically includes: f21. Obtain the FFT amplitude output and harmonic compensation; f22. Judge whether it is a pure DC signal. If it is a pure DC signal, enter the corresponding processing module; f23. Judge whether it is a pure AC signal. If it is not a pure AC signal, it is recognized as an AC-DC mixed signal; f24. AC-DC mixed signal processing: For the AC-DC mixed signal, remove the DC component from the AC-DC mixed signal to make the signal become a pure AC signal; f25. Mean square error calculation and waveform judgment.

9. The high-precision AC-DC hybrid leakage current protection method based on a fluxgate according to claim 6, wherein The control signal is used to control the circuit breaker and relay equipment to cut off the circuit, thereby avoiding damage to the equipment caused by overcurrent.

10. The high-precision AC-DC hybrid leakage current protection method based on a fluxgate according to claim 7, characterized in that, The mean square error calculation and waveform judgment are specifically to calculate the mean square error of the signal after removing the DC component, measure the fluctuation degree of the signal through the mean square error, and judge the waveform type according to the output result.

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