Large aperture ac-dc sensor based on fluxgate, stray current measurement method

Abstract

The application relates to a large-diameter AC / DC sensor based on a flux gate and a stray current measurement method, wherein the sensor comprises a sensor probe, an excitation circuit and a detection circuit; the excitation circuit comprises an overcurrent protection circuit and an H bridge; the input end and the output end of the H bridge are connected with an excitation power supply and the overcurrent protection circuit respectively, and the midpoint of the H bridge is connected with the sensor probe; the H bridge comprises an upper bridge arm and a lower bridge arm, and each bridge arm comprises at least a pair of MOS tubes with drain and source electrodes connected with each other in a cross mode; the overcurrent protection circuit is used for cooperatively adjusting the polarity and the amplitude of the voltage across the sensor probe through a preset reference voltage, an excitation current fed back by the sensor probe and the current flow direction of the H bridge; and the detection circuit is connected with one end of the sensor probe and the output end of the H bridge respectively and is used for detecting the direct current component and the alternating current component of the excitation current. The H bridge MOSFET driving reduces the cost of the sensor, and the large-diameter flexible design is suitable for different measurement scenes.

Description

Technical Field

[0001] This invention belongs to the field of fluxgate DC sensor technology, specifically relating to a large-aperture AC / DC sensor based on fluxgate and a stray current measurement method. Background Technology

[0002] With the widespread use of DC power transmission, new energy systems, and subway traction systems, stray current components have appeared at the neutral point of grounded power transformers within the power system. Once DC current appears at the neutral point, the transformer will be in an abnormal operating state of DC bias, meaning the transformer core will experience a magnetic flux density bias due to the DC current, leading to abnormal conditions such as overheating, vibration, increased noise, and increased losses. Measuring stray current at the transformer neutral point is an important means of early warning of DC bias risks in transformers.

[0003] Transformer stray current measurement primarily employs sensors to measure the current, specifically by sensing the magnetic field strength of the current being measured. Among existing magnetocurrent sensor technologies, Hall current sensors, using Hall elements as the sensing element, are the most widely used. However, Hall current sensors suffer from limitations in applications requiring high insulation distance and accuracy. These limitations stem from their relatively small aperture (typically 20mm) and the fact that their sensitivity, linearity, and temperature characteristics are constrained by the performance of the Hall element and electronic components.

[0004] In recent years, fluxgate current sensors have attracted attention due to their wide range of aperture options and significant advantages in current measurement in terms of accuracy, temperature stability, and bandwidth. They have begun to be widely used in industries such as transformers, power batteries, new energy vehicles, large medical equipment, urban rail transit, and new energy power generation.

[0005] Major domestic and international manufacturers of fluxgate current sensors include LEM (Switzerland), DANISENSE (Denmark), GMC (Germany), YOKOGAWA (Japan), Galaxy Electric, Jingheng KeDian, Xunlei Zhiyun, Beijing Senshe, Wuhan Tianrui, Acrel, Nanjing Xinrui Spectrum, Nanjing Qihuo, and CRRC Ningbo. However, existing fluxgate current sensors generally have a small aperture for the conductor through which the current is measured. For example, the DS1000UBSA sensor with a rated current of 1000A manufactured by DANISENSE in Denmark has a sensor aperture diameter of only 26.6mm; the DS2000IDLA sensor with a rated current of 2000A has a sensor aperture diameter of only 68mm. This aperture diameter is only sufficient to allow the conductor to pass through, without considering the safety insulation distance, and therefore cannot meet the insulation distance requirements when measuring current on high-voltage lines. Some existing large-diameter AC / DC current sensors, even with custom-designed cores of special diameter and well-designed insulation and shielding structures, only have a maximum core diameter of 120-150mm for the magnetic core sensing unit, which is insufficient to meet the stray current measurement requirements of various application scenarios.

[0006] In addition, most existing sensors require positive and negative power supplies. Primsci sensors have a power supply voltage of ± (14.25V~15.75V), AIT series sensors have an operating voltage range of ± (14.2V~15.8V), and CHCS-ITH-600S sensors support ± (14V~16V) power supply. The no-load power consumption of sensors under power supply mode is generally relatively high.

[0007] Furthermore, typical foreign companies include LEM Electronics' IT series AC / DC fluxgate current sensors, while domestic companies include Shenzhen Hangzhi Precision's IIT series AC / DC fluxgate current sensors. These companies produce and develop AC / DC sensors based on the fluxgate principle, achieving linearity at the ppm level. However, due to the high requirements for parameters such as the fluxgate core and windings, the core manufacturing process is complex and costly. Currently, the price of fluxgate current sensors ranging from 60A to 2000A is between several thousand and tens of thousands of yuan, which greatly limits their application range.

[0008] Existing stray current measurement methods mainly include the average current method and the duty cycle method. Both assume that the excitation core in the actual circuit has a high degree of nonlinearity and satisfies the self-inductance of the excitation winding in the linear region. Much greater than the self-inductance in the nonlinear region , making And simultaneously satisfy a series of simplifying conditions (such as , and This allows for the determination of an approximate linear relationship between the average current or duty cycle and the measured current. However, these measurement methods do not consider the influence of high-frequency noise, and the accuracy of the calculated measured current still has room for improvement.

[0009] In summary, most fluxgate current sensors currently have the following problems:

[0010] 1) The acquisition scheme uses a high-power operational amplifier as the core circuit for self-excited oscillation. Although it has high accuracy and good linearity, the cost is generally high. 2) Most of them require positive and negative power supply. However, the devices under test are often located in substations or rail transit, which makes it inconvenient to obtain power. In addition, the sensor power supply has a high no-load power consumption (about 1.8W (12V / 0.15A)). 3) The closed hard ring small aperture design cannot meet the insulation distance requirements and has limited applicability. 4) There is room for improvement in the accuracy of the measured current obtained by the algorithm in AC signal measurement. Summary of the Invention

[0011] To reduce the cost of fluxgate current sensors and improve their adaptability to different scenarios, a first aspect of this invention provides a large-aperture AC / DC sensor based on a fluxgate, comprising a sensor probe, an excitation circuit, and a detection circuit. The excitation circuit includes an overcurrent protection circuit and an H-bridge. The input and output terminals of the H-bridge are connected to the excitation power supply and the overcurrent protection circuit, respectively, and the midpoint of the H-bridge is connected to the sensor probe. The H-bridge includes an upper arm and a lower arm, each arm including at least a pair of MOSFETs with their drain and source terminals cross-connected. The overcurrent protection circuit is used to coordinately adjust the polarity and amplitude of the voltage across the sensor probe by using a preset reference voltage, the excitation current fed back from the sensor probe, and the current direction of the H-bridge. The detection circuit is connected to one end of the sensor probe and the output terminal of the H-bridge, respectively, and is used to detect the DC and AC components of the excitation current.

[0012] In some embodiments of the present invention, the upper arm of the H-bridge includes a first P-channel MOS transistor and a second P-channel MOS transistor; the lower arm of the H-bridge includes a first N-channel MOS transistor and a second N-channel MOS transistor.

[0013] Furthermore, the sources of both the first N-channel MOSFET and the second N-channel MOSFET are connected to an overcurrent protection circuit.

[0014] In some embodiments of the present invention, the overcurrent protection circuit includes a third N-channel MOSFET, a driving circuit, and a comparator. The drain, gate, and source of the third N-channel MOSFET are respectively connected to the output terminal of the lower arm of the H-bridge, the driving circuit, and the detection circuit. The non-inverting input and the inverting input of the comparator are respectively connected to a reference voltage source and a sampling resistor, and are used to compare a preset reference voltage and a sampled voltage signal, and output the comparison result to the driving circuit through a logic level. The driving circuit is used to control the on / off state of the gate of the third N-channel MOSFET based on the logic level.

[0015] Furthermore, the control of the gate of the third N-channel MOS transistor based on logic level includes: if the sampled voltage signal is higher than the preset reference voltage, then the gate of the third N-channel MOS transistor is controlled to be turned off.

[0016] In some embodiments of the present invention, the detection circuit includes a DC detection circuit and an AC detection circuit. The DC detection circuit includes, in sequence, an amplifier circuit, an inverter circuit, a low-pass filter circuit, and an analog-to-digital converter circuit. The AC detection circuit includes, in sequence, a buffer, a level converter, and a microcontroller.

[0017] In some embodiments of the present invention, the sensor probe employs a flexible structure.

[0018] Furthermore, the aperture of the sensor probe is less than or equal to 1500 mm.

[0019] A second aspect of the present invention provides a method for measuring stray current using a large-aperture AC / DC sensor based on a fluxgate magnetometer provided in the first aspect, comprising: defining an excitation voltage duty cycle based on the peak duration of the excitation voltage within one self-excited oscillation cycle of the fluxgate magnetometer; determining an expression for the AC component of the stray current based on the excitation voltage duty cycle, using the loop equation of the magnetic core operating state and the differential equation of the excitation current; determining the direction of the stray current based on the real-time measured excitation voltage duty cycle; acquiring the DC and AC components of the excitation current in real time through a detection circuit; and calculating the amplitude of the stray current based on the DC and AC components of the excitation current, using the expression for the AC component of the stray current.

[0020] A third aspect of the present invention provides an electronic device comprising: one or more processors; and a storage device for storing one or more programs, wherein when the one or more programs are executed by the one or more processors, the one or more processors implement the stray current measurement method of the large-aperture AC / DC sensor with fluxgate provided in the second aspect of the present invention.

[0021] In a fourth aspect, the present invention provides a computer-readable medium having a computer program stored thereon, wherein the computer program, when executed by a processor, implements the stray current measurement method of the large-aperture AC / DC sensor with fluxgate provided in the second aspect of the present invention.

[0022] The beneficial effects of this invention are:

[0023] The excitation circuit uses an H-bridge MOSFET driver, significantly reducing sensor cost and lowering the sensor's no-load power consumption to below 0.1W. The sensor probe features a large-diameter, flexible 1500mm design, adaptable to various stray current measurement applications in power equipment. Measurement methods: It can measure both DC and AC signals. AC measurement is based on a duty cycle algorithm with added digital processing, improving AC signal measurement error by 3%. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the basic structure of a large-diameter AC / DC sensor with a fluxgate in some embodiments of the present invention;

[0025] Figure 2 This is a schematic diagram showing the current flow direction when the magnetic core excitation current begins to increase positively in some embodiments of the present invention;

[0026] Figure 3 This is a schematic diagram showing the current flow direction when the magnetic core excitation current begins to decrease in a positive direction in some embodiments of the present invention;

[0027] Figure 4 This is a schematic diagram showing the current flow direction when the magnetic core excitation current begins to increase in the reverse direction in some embodiments of the present invention;

[0028] Figure 5 This is a schematic diagram of the detection circuit in some embodiments of the present invention;

[0029] Figure 6 This is a schematic diagram of the magnetization curve, excitation voltage, and excitation current waveforms when the stray current is zero in some embodiments of the present invention.

[0030] Figure 7 This is a schematic diagram of the stray current as a timely magnetization curve, excitation voltage, and excitation current waveform in some embodiments of the present invention.

[0031] Figure 8 This is a schematic diagram of the magnetization curve, excitation voltage, and excitation current waveforms when the stray current is negative in some embodiments of the present invention.

[0032] Figure 9 This is a schematic diagram showing the waveforms of the current of each MOS transistor in the H-bridge and the DC component of the detection circuit in some embodiments of the present invention.

[0033] Figure 10 A waveform diagram of the AC signal sampled by the MCU;

[0034] Figure 11 This is a schematic diagram of the waveform of the AC signal after IIR filtering;

[0035] Figure 12 A schematic diagram of the spectrum of the AC principal component extracted by the Fast Fourier Transform;

[0036] Figure 13 A schematic diagram of the waveform of the AC principal component extracted by the Fast Fourier Transform. Detailed Implementation

[0037] The principles and features of the present invention are described below with reference to the accompanying drawings. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0038] refer to Figures 1 to 5 In a first aspect of the invention, a large-aperture AC / DC sensor based on fluxgate magnetometers is provided, comprising a sensor probe, an excitation circuit, and a detection circuit. The excitation circuit includes an overcurrent protection circuit and an H-bridge. The input and output terminals of the H-bridge are respectively connected to an excitation power supply and the overcurrent protection circuit, and the midpoint of the H-bridge is connected to the sensor probe. The H-bridge includes an upper arm and a lower arm, each arm including at least a pair of MOS transistors with their drains and sources cross-connected. The overcurrent protection circuit is used to coordinately adjust the polarity and amplitude of the voltage across the sensor probe by means of a preset reference voltage, the excitation current fed back from the sensor probe, and the current flow direction of the H-bridge. The detection circuit is connected to one end of the sensor probe and the output terminal of the H-bridge, respectively, and is used to detect the DC and AC components of the excitation current.

[0039] Specifically, the sensor probe includes a toroidal magnetic core and an excitation winding (with an internal resistance of Rc). The excitation circuit includes an overcurrent protection circuit and an H-bridge. The H-bridge consists of an inverter circuit composed of four switching transistors Q1A, Q1B, Q2A, and Q2B. Q1A and Q1B are P-channel MOSFETs, which conduct when the gate voltage is low; Q2A, Q2B, and Q3 are N-channel MOSFETs, which conduct when the gate voltage is high. Q1 and Q2 are P-channel and N-channel MOSFETs integrated in a single package, respectively, to ensure consistent transistor parameters and symmetrical oscillation waveforms.

[0040] refer to Figure 1 In some embodiments of the present invention, the upper arm of the H-bridge includes a first P-channel MOSFET and a second P-channel MOSFET; the lower arm of the H-bridge includes a first N-channel MOSFET and a second N-channel MOSFET.

[0041] Specifically, in the inverter circuit, the gate G of P-channel MOSFET Q1A and the drain D of Q1B are connected together, the gate G of Q1B and the drain D of Q1A are connected together, the source S of Q1A and Q1B are connected to the power switch Vcc, the drain D of N-channel MOSFETs Q2A and Q2B are connected to the drain D of P-channel MOSFETs Q1A and Q1B respectively, the gate G of Q2A and the drain D of Q2B are connected together, the gate G of Q2B and the drain D of Q2A are connected together, the excitation winding is connected between points ab, and the source S of Q2A and Q2B is connected to the drain D of Q3, forming an H-bridge inverter circuit.

[0042] refer to Figures 2 to 4 In some embodiments of the present invention, the overcurrent protection circuit includes a third N-channel MOSFET, a driving circuit, and a comparator. The drain, gate, and source of the third N-channel MOSFET are respectively connected to the output terminal of the lower arm of the H-bridge, the driving circuit, and the detection circuit. The non-inverting input and the inverting input of the comparator are respectively connected to a reference voltage source and a sampling resistor, and are used to compare a preset reference voltage and a sampled voltage signal, and output the comparison result to the driving circuit through a logic level. The driving circuit is used to control the on / off state of the gate of the third N-channel MOSFET based on the logic level.

[0043] Specifically, the non-inverting input terminal + of the voltage comparator U1 is connected to a reference source to obtain a reference voltage, the inverting input terminal - is connected to one end of the sampling resistor Rs, the output terminal is connected to the input terminal of the driving circuit, the output terminal of the driving circuit is connected to the gate G of MOSFET Q3, and the source S of MOSFET Q3 is connected to the sampling resistor Rs.

[0044] The oscillation process of the excitation circuit is as follows: When the 12V power supply has not yet started, the inverting input terminal - of the voltage comparator is at a low level, no current flows through Rs, the voltage at the non-inverting input terminal + is fixed at 177mV, the comparator output is at a high level, and after being driven, Q3 is in the conducting state; when the 12V power supply starts, the source of PMOS transistor Q1A is raised, the gate is at a low level, Q1A is turned on first, then the voltage at point a rises, the gates of Q1B and Q2B are at a high level, Q1B is cut off, Q2B is turned on, point b is still at a low level, Q2A is cut off, at this time a positive voltage is applied across the ab terminals of the magnetic core excitation winding, and the magnetic core excitation current begins to increase in the positive direction (T1), the system current loop at this time is as follows:

[0045] When the magnetic core approaches saturation, the current rises sharply, and the voltage Vs across the sampling resistor R23 increases to the set V. refWhen the voltage is set to 177mV, the comparator flips to output a low level. After being driven, Q3 G is at a low level, and Q3 is turned off. Since the current in the sensor core excitation winding cannot change instantaneously, the voltage across it becomes high at point b and low at point a. At this time, the inverter circuits Q1A and Q2B are turned off, and Q1B and Q2A are turned on, realizing the phase change of the circuit. At the same time, the current in the sampling resistor R23 is reversed, and its voltage Vs is lower than the set V. ref The comparator flips again to output a high level. After being driven, the gate (G) of Q3 is high, and Q3 turns on again. A negative voltage is applied to the magnetic core. At this time, the current in the excitation winding of the sensor core first decreases in the positive direction (T2) to zero and then slowly increases in the reverse direction (T3). The system current loop is as follows:

[0046] In some embodiments of the present invention, the detection circuit includes a DC detection circuit and an AC detection circuit, wherein the DC detection circuit sequentially includes an amplifier circuit, an inverter circuit, a low-pass filter circuit, and an analog-to-digital converter circuit.

[0047] Specifically, the detection circuit consists of two parts: an AC detection circuit and a DC detection circuit. The AC detection circuit includes a buffer, a level converter, and a microcontroller (MCU); the DC detection circuit includes an amplifier circuit, an inverter circuit, a low-pass filter circuit, and an ADC sampling circuit.

[0048] In the AC detection circuit, the voltage at the b end of the excitation winding is amplified, filtered, and converted by a buffer to protect other components in the circuit from voltage fluctuations. The voltage output by the buffer (about 10V) is converted to a 3.3V voltage signal, which is then input to the microprocessor MCU to acquire the square wave signal. The AC component is then output using IIR and FFT algorithms.

[0049] The amplifier circuit in the DC detection circuit amplifies the voltage Vs signal at the sampling resistor Rs by a factor, and the inverter circuit flips the amplified Vs signal. When the switch is turned to 1, the amplified Vs signal is taken.

[0050] When the switch is set to 2, the inverted Vs signal is taken. The switch switching is controlled by the high and low levels of the buffer output. When the level is high, switch 1 is connected to take the amplified signal. When the level is low, switch 2 is connected to take the inverted amplified signal. Finally, the high-frequency voltage signal is filtered out by the low-pass filter circuit, and the DC component can be obtained by ADC sampling.

[0051] It should be noted that a common power amplifier with a drive current of 8A, such as the OPA549, costs around 200 yuan, while the Q1 and Q2 MOSFETs in this solution cost only 2 to 3 yuan each, greatly reducing the cost. No additional heat dissipation is required, and the hardware size is only 1 / 3 of the former.

[0052] Furthermore, to meet the measurement requirements of transformer neutral points, cables of various voltage levels, metal frames, and other large-sized stray current paths, the traditional closed-loop hard-ring small-aperture sensor structure design has been adjusted to an open-loop large-aperture flexible structure design. Although the measurement performance is lower than that of the closed-loop hard-ring small-aperture design (e.g., the aperture of the Seth sensor is about 20mm, the measurement range is 60A~24000A, and the accuracy is at the ppm level) (e.g., the sensor designed by Wang Nong of Harbin Institute of Technology in "Research on Self-Excited Oscillation Fluxgate Method for Precision Measurement of DC Large Current" has an aperture of less than 80mm, a measurement range of ±600A, and a measurement accuracy of 0.3%), it is sufficient to meet the daily stray current measurement requirements of transformers and cables of various voltage levels (aperture size reaches 1500mm; DC measurement range: ±200A; DC measurement accuracy: 1%±0.1A).

[0053] Example 2

[0054] refer to Figures 6 to 13 In a second aspect, the present invention provides a method for measuring stray current of a large-aperture AC / DC sensor based on a fluxgate provided in the first aspect, comprising: S100. defining an excitation voltage duty cycle based on the peak duration of the excitation voltage of the fluxgate within one self-excited oscillation cycle;

[0055] Specifically, set and Excitation voltage The duration of the positive and negative peak values, and the self-excited oscillation period. Define excitation voltage The duty cycle is ,but The expression is:

[0056] (1),

[0057] Based on the duty cycle of the excitation voltage, the expression for the AC component of the stray current is determined by the loop equation of the core working state and the differential equation of the excitation current.

[0058] Specifically, set At that time, excitation voltage The voltage level just changes from a negative peak to a positive peak, at which point the excitation current... It just reached the negative peak value, so we can get:

[0059] (2),

[0060] exist During the specified time period, magnetic core C1 operates in the negative saturation region of the magnetization curve. Assume the self-inductance of the excitation winding is... The excitation voltage is According to the loop equation when the magnetic core C1 is operating in the saturation region , can be obtained Excitation current during the time period Differential equation:

[0061] (3),

[0062] set up , By solving, we can obtain for:

[0063] (4),

[0064] Let the measured current be The current referred to the excitation winding is denoted as: Known At any moment, the excitation current Just reached the negative saturation value We can obtain:

[0065] (5),

[0066] Equation (5) Substitution formula (4) We can obtain:

[0067] (6),

[0068] exist During the specified time period, magnetic core C1 operates in the linear region of the magnetization curve, at which time the self-inductance of the excitation winding is... The excitation voltage is still Using the differential equation of the excitation current We can obtain:

[0069] (7),

[0070] set up , By solving, we can obtain for:

[0071] (8),

[0072] Known At any moment, the excitation current Just reached the positive saturation value We can obtain:

[0073] (9),

[0074] Formula (9) Substitution formula (8) We can obtain:

[0075] (10)

[0076] exist During the specified time period, magnetic core C1 operates in the forward saturation region, and the self-inductance of the excitation winding changes from L to However, the excitation voltage is still [missing information]. ,according to We can obtain:

[0077] (11),

[0078] set up By solving, we can obtain for:

[0079] (12),

[0080] Known At any moment, the excitation current Just reached the positive saturation value We can obtain:

[0081] (13)

[0082] Formula (13) Substitution formula (12) We can obtain:

[0083] (14)

[0084] Similarly, we can obtain the time intervals of the negative half-cycle. , , The expression is:

[0085] (15)

[0086] (16)

[0087] (17)

[0088] From equations (6), (10), and (14), we can obtain From equations (15), (16), and (17), we can obtain :

[0089] (18)

[0090] (19)

[0091] In actual circuits, satisfying , and Furthermore, the magnetic core C1 exhibits high nonlinearity, satisfying... , making After simplification, we get:

[0092] (20)

[0093] (twenty one),

[0094] Substituting equations (20) and (21) into equation (1), we get:

[0095] (twenty two),

[0096] Known ,and Substituting into equation (22), we get:

[0097] (twenty three),

[0098] Specifically, when the measured current i p When =0, the magnetization curve and excitation voltage of the excitation core C1 of the self-excited fluxgate during the transition from power-on to normal operation are shown. V cc and excitation current i s Changes such as Figure 6 As shown in the figure. In the figure, it is assumed that the magnetization curve of the nonlinear magnetic core C1 is a three-segmented line as shown, where L and l These represent the self-inductance of the excitation winding Ws when the magnetic core C1 operates in the linear and saturation regions, respectively; Ψ s + and These represent the flux linkage when the magnetic core C1 just reaches positive saturation and negative saturation, respectively. I + S_H and These represent the positive and negative saturation currents of the magnetic core C1, respectively; I + max and These represent the maximum positive and negative excitation currents of the magnetic core C1, respectively; V + cc and V - cc They represent the excitation voltages, respectively. V cc The positive and negative peak values.

[0099] S200. Determine the direction of stray current based on the real-time measured duty cycle of the excitation voltage;

[0100] Specifically, excitation voltage V cc Excitation current is generated by exciting the nonlinear magnetic core C1. i s Assuming the circuit parameters are set reasonably, there are I + max =- I - max = I max and I + S_H =- I - S_H And there are I max > I S_H This ensures that the magnetic core C1 can be fully saturated. When the measured current... i p When ≠0, due to the measured current i p During the positive half-cycle of the excitation current and i s In the same direction / opposite direction, thus causing the magnetic core C1 to saturate earlier / later; during the negative half-cycle of the excitation current, the measured current... i p and i s Reverse / same direction causes the saturation of magnetic core C1 to be delayed / advanced, because the measured current... i p The existence of excitation current i s The waveform is no longer symmetrical, such as Figure 7 and Figure 8 As shown.

[0101] When the measured current i p When positive, the direction is as follows Figure 7 As shown, in the excitation current i s During the positive half-cycle, the measured current i p With excitation current i s The same direction causes the magnetic core C1 to saturate prematurely; in the excitation current i s During the negative half-cycle, the measured current i p With excitation currenti s The opposite direction causes the magnetic core C1 to saturate with hysteresis.

[0102] When the measured current i p When it is negative, the direction is as follows: Figure 8 As shown, in the excitation current i s During the positive half-cycle, the measured current i p With excitation current i s The opposite direction causes the magnetic core C1 to saturate with hysteresis; in the excitation current i s During the negative half-cycle, the measured current i p With excitation current i s The same direction causes the magnetic core C1 to saturate prematurely.

[0103] When the excitation voltage duty cycle is 50%, the measured current is zero; when the duty cycle is less than 50%, the measured current is in the positive direction; when the duty cycle is greater than 50%, the measured current is in the negative direction.

[0104] The duty cycle D can be used to determine not only the measured current. i p Besides determining the direction and presence / absence, the duty cycle D and the measured current can also be calculated. i p The relationship between the two is used to calculate the measured current. i p The magnitude of the signal is determined by the following: the DC component is obtained directly through hardware circuit processing and ADC sampling; the AC component is based on the duty cycle algorithm and further processed by digital processing (IIR filtering and FFT algorithm) to remove high-frequency signals and obtain a more accurate AC signal.

[0105] S300. The DC and AC components of the excitation current are acquired in real time through the detection circuit; S400. Based on the DC and AC components of the excitation current, the amplitude of the stray current is calculated using the expression for the AC component of the stray current.

[0106] S500. Based on the magnitude and direction of the stray current, the phasor value of the stray current is obtained through IIR filtering and fast Fourier analysis.

[0107] Specifically, by adjusting the duty cycle To obtain the measured current of different amplitudes To facilitate subsequent time-domain digital signal processing, the measured current is... Recorded as The IIR filter is a recursive filter whose output depends not only on the current and past input signals but also on the past output signals. This feedback mechanism allows the IIR filter to achieve high filtering characteristics with a lower order. The output of the IIR filter can be represented by a difference equation, as shown in equation (24); the system function of the IIR filter is shown in equation (25).

[0108] (twenty four),

[0109] in, It is the output signal of the filter; It is the input signal; and These are the coefficients of the filter; It is a delay period. and These are the number of delay terms for the input and output signals, respectively.

[0110] (25)

[0111] in, It is a complex frequency variable.

[0112] The time-domain digital signal after IIR filtering is subjected to FFT analysis to obtain the frequency-domain digital signal, thus obtaining a more accurate AC component. The FFT analysis is shown in equation (26):

[0113] (26)

[0114] in, Given the input sequence, the included angle , The length of the input sequence is , It is a frequency domain signal.

[0115] (27)

[0116] (28)

[0117] (29)

[0118] In equations (27) to (29) , for The real and imaginary parts, and The amplitude and phase of the signal.

[0119] refer to Figure 9By acquiring the voltage waveform at position Vs, it can be seen that the excitation current changes when the inverter circuits Q1 (including Q1A and Q1B), Q2 (including Q2A and Q2B), and Q3 switch between high and low levels. i s The waveform is symmetrical (excitation current). i s The positive and negative half-cycles are symmetrical, as shown in the figure before (d) and after (e) phase inversion. Therefore, the measured current... i p =0; when i p When the excitation current is -50A, the excitation current is... i s The waveform is no longer asymmetrical; the negative half-cycle reaches saturation earlier, while the positive half-cycle lags behind (excitation current). i s The positive and negative half-cycles are asymmetrical, as shown in the figures before (f) and after (g) inversion. The DC component can be obtained through a filter circuit (as shown in figure (h)). i s= V f / R s ，i p N P= i s N s The DC stray current can then be calculated. i p .

[0120] The AC signal at point b of the excitation winding is sampled by the MCU, and after digital processing (IIR filtering and FFT algorithm), a 5Hz AC signal is obtained as follows: Figure 10-13 As shown, by comparing the measured current data before and after the three amplitude digitization processes, it can be seen that the relative error has been reduced from the original 5% to less than 2%.

[0121] The flowcharts and block diagrams in the accompanying drawings illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer program products according to various embodiments of this disclosure. In this regard, each block in a flowchart or block diagram may represent a module, segment, or portion of code containing one or more executable instructions for implementing a specified logical function. It should also be noted that in some alternative implementations, the functions indicated in the blocks may occur in a different order than those indicated in the drawings. For example, two consecutively indicated blocks may actually be executed substantially in parallel, and they may sometimes be executed in reverse order, depending on the functions involved. It should be noted that each block in the block diagrams and / or flowcharts, and combinations of blocks in the block diagrams and / or flowcharts, can be implemented using a dedicated hardware-based system that performs the specified function or operation, or using a combination of dedicated hardware and computer instructions.

[0122] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A large-aperture AC / DC sensor based on fluxgate magnetometers, comprising a sensor probe, an excitation circuit, and a detection circuit, characterized in that, The excitation circuit includes an overcurrent protection circuit and an H-bridge. The input and output terminals of the H-bridge are connected to the excitation power supply and the overcurrent protection circuit, respectively, and the midpoint of the H-bridge is connected to the sensor probe. The H-bridge includes an upper arm and a lower arm, each arm including at least a pair of MOSFETs with their drains and sources cross-connected. The overcurrent protection circuit is used to coordinately adjust the polarity and amplitude of the voltage across the sensor probe by using a preset reference voltage, the excitation current fed back from the sensor probe, and the current direction of the H-bridge. The detection circuit is connected to one end of the sensor probe and the output terminal of the H-bridge, respectively, and is used to detect the DC and AC components of the excitation current. The detection circuit includes a DC detection circuit and an AC detection circuit. The DC detection circuit includes, in sequence, an amplifier circuit, an inverter circuit, a low-pass filter circuit, and an analog-to-digital converter circuit. The AC detection circuit includes, in sequence, a buffer, a level converter, and a microcontroller. The stray current measurement method of the large-aperture AC / DC sensor includes: defining the excitation voltage duty cycle based on the peak duration of the excitation voltage within one self-excited oscillation cycle of the fluxgate; determining the expression for the AC component of the stray current based on the excitation voltage duty cycle, using the loop equation of the core operating state and the differential equation of the excitation current; determining the current direction of the stray current based on the real-time measured excitation voltage duty cycle; acquiring the DC and AC components of the excitation current in real time through a detection circuit; calculating the amplitude of the stray current based on the DC and AC components of the excitation current, using the expression for the AC component of the stray current; and obtaining the phasor value of the stray current based on its amplitude and current direction using an IIR filter and fast Fourier analysis. The expression for the AC component of the stray current is: ,in, D Indicates the duty cycle of the excitation voltage; I p Represents the AC component of stray current; R c and R S These represent the internal resistance of the excitation winding and the sampling resistance, respectively; During the specified time period, magnetic core C1 operates in the negative saturation region of the magnetization curve. V H Represented as: ； exist During the specified time period, magnetic core C1 operates in the linear region of the magnetization curve. V H Represented as: ， exist During the specified time period, magnetic core C1 operates in the positive saturation region. V H Represented as: ， in, i s Indicates the excitation current. l This indicates the self-inductance of the excitation winding when the magnetic core C1 operates in the negative saturation region of the magnetization curve; L This indicates the self-inductance of the excitation winding when the magnetic core C1 operates in the linear region of the magnetization curve; T p The duration of the positive peak value of the excitation voltage; The method of determining the direction of the stray current AC component based on the real-time excitation voltage duty cycle includes: if the excitation voltage duty cycle is equal to 50%, the stray current is zero; if the excitation voltage duty cycle is less than 50% but greater than zero, the direction of the stray current is positive; if the excitation voltage duty cycle is greater than 50%, the direction of the stray current is negative.

2. The large-aperture AC / DC sensor based on fluxgate magnetometer according to claim 1, characterized in that, The upper arm of the H-bridge includes a first P-channel MOSFET and a second P-channel MOSFET; the lower arm of the H-bridge includes a first N-channel MOSFET and a second N-channel MOSFET.

3. The large-aperture AC / DC sensor based on fluxgate magnetometer according to claim 2, characterized in that, The sources of both the first N-channel MOSFET and the second N-channel MOSFET are connected to the overcurrent protection circuit.

4. The large-aperture AC / DC sensor based on fluxgate magnetometer according to claim 1, characterized in that, The overcurrent protection circuit includes a third N-channel MOSFET, a driving circuit, and a comparator. The drain, gate, and source of the third N-channel MOSFET are connected to the output of the lower arm of the H-bridge, the driving circuit, and the detection circuit, respectively. The non-inverting input and the inverting input of the comparator are connected to a reference voltage source and a sampling resistor, respectively, to compare a preset reference voltage and a sampled voltage signal, and output the comparison result to the driving circuit through a logic level. The driving circuit is used to control the on / off state of the gate of the third N-channel MOS transistor based on logic levels.

5. The large-aperture AC / DC sensor based on fluxgate magnetometer according to claim 4, characterized in that, The control of the gate of the third N-channel MOS transistor based on logic level includes: if the sampled voltage signal is higher than the preset reference voltage, then the gate of the third N-channel MOS transistor is controlled to be turned off.

6. The large-aperture AC / DC sensor based on fluxgate magnetometer according to claim 1, characterized in that, The sensor probe adopts a flexible structure.

7. The large-aperture AC / DC sensor based on fluxgate magnetometer according to claim 6, characterized in that, The aperture of the sensor probe is less than or equal to 1500 mm.

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