A closed loop zero flux current transformer

Abstract

The application discloses a closed-loop zero-flux current transformer, comprising: a signal detection module, which is used to obtain a secondary harmonic signal through a magnetic core assembly; a signal generation module, which is used to generate a pair of orthogonal local reference signals; a temperature sensing module, which is used to obtain the real-time temperature of the magnetic core assembly; a signal processing module, which is used to perform I / Q quadrature demodulation according to the secondary harmonic signal and the local reference signal, to obtain in-phase components and quadrature components; to correct the in-phase components and the quadrature components according to the current calibration parameters, and to calculate an initial error signal according to the corrected in-phase components and the quadrature components; to calculate a gain correction coefficient corresponding to the real-time temperature; to calculate a corrected error signal according to the initial error signal and the gain correction coefficient; and to calculate a primary current based on a feedback current generated by a feedback current generation module. The application combines quadrature demodulation and temperature partition compensation, and realizes accurate measurement of the current.

Description

Technical Field

[0001] This invention relates to the field of high-precision DC current measurement technology, and more specifically, to a closed-loop zero-flux current transformer. Background Technology

[0002] The magnetically modulated zero-flux current transformer consists of a high-permeability closed magnetic core, an excitation coil, an induction coil, and a feedback coil, and achieves high-precision measurement through a closed-loop servo circuit. Its structure is as follows: Figure 1 As shown, C1 and C2 are iron core 1 and iron core 2 respectively, W p For primary winding; W s W1 and W2 are the excitation coils on iron cores 1 and 2, respectively; W3 and W4 are the induction coils on iron cores 1 and 2. The core working principle of the magnetically modulated zero-flux current transformer is based on dynamic zero-flux balance. A high-frequency excitation current is injected into the excitation coil to make the iron core operate in a near-saturation state. When the primary winding carries the primary current Ip, the induction coil detects the DC flux and, through negative feedback, generates a compensating magnetic field in real time. H fb To completely cancel out the primary current under test. I p The generated DC magnetic field H m This ensures that the net DC magnetic field inside the magnetic core is zero.

[0003] Ideally, a separate high-frequency excitation source applies a sinusoidal current to the excitation coil, establishing a purely alternating detection magnetic field in the magnetic core. H e ( t )= H 0sin(ωt). Since the core's operating point is near the origin of the highly linear BH curve and there is no DC bias, the core's magnetization process is symmetrical. Therefore, the voltage signal picked up by the induction coil only contains odd harmonics (mainly the fundamental wave) and not even harmonics.

[0004] However, if there is a residual DC magnetic field that is not completely canceled out H r (For example, feedback current) I f (If the magnetization process is not precise enough), the magnetization process of the magnetic core will become asymmetrical. This asymmetry will directly lead to the generation of a second harmonic signal in the induced signal. This second harmonic component is the key error signal driving the entire closed-loop servo system.

[0005] The complex signal containing second harmonics, picked up by the induction coil, is amplified, filtered, and then sent to a phase-sensitive demodulator (PSD). The PSD extracts the signal from the signal. Hr A proportional DC error voltage. This error voltage is then processed by a servo controller (usually an integrator), whose output drives a power amplifier to inject feedback current into the feedback coil. I f This generates a compensating magnetic field. H fb .

[0006] The entire closed-loop system is continuously and dynamically adjusted. I fb until the residual magnetic field H r →0, at which point the second harmonic in the induced signal also approaches zero, and the system reaches equilibrium. According to Ampere's circuital law, at equilibrium: H m + H fb =0→ N p I p =N fb I fb ,in, N p , N fb These are the number of turns in the primary coil and the feedback coil, respectively. Therefore, accurate measurement of the feedback current is crucial. I f A single current can be obtained. I p Therefore, the accuracy of the system depends on whether the PSD can accurately and stably extract the second harmonic error signal from the inductive signal.

[0007] Both theory and practice have proven that the second harmonic component in the induced signal... V 2f ( t ) and residual DC magnetic field H r (Near the equilibrium point, it can be equivalent to) H m It is directly proportional to ), and its expression is: V 2f ( t )= K ( T ) ·H m · sin( 2ωt+φ ( T )) , in, K ( T) represents the temperature-dependent gain coefficient of the system. f ( T ) represents the temperature-dependent second harmonic phase shift.

[0008] The basic principle of PSD is to convert this signal V 2f ( t (and a reference signal of the same frequency) R ( t )=cos(2 ωt + i ref The components are multiplied together, and then filtered out using a low-pass filter (LPF). The mathematical derivation is as follows: V out (t)= LPF[ V 2f (t)*R ( t )] = LPF[ KH m sin( 2ωt+φ ) · cos( 2ωt+θ ref )] =2KH m · cos( f-i ref ), The above formula reveals the fundamental flaw of traditional single-channel PSDs: their output depends not only on the magnetic field being measured. H m It also strongly depends on the phase difference ( f - i ref In practical applications, changes in core material, coil winding process, and ambient temperature can lead to… f ( T Significant drift occurs. Even the reference phase i ref Even though the transformer is precisely calibrated at the factory, phase drift during operation can still introduce a non-negligible gain error, which severely restricts the long-term stability of the transformer.

[0009] To overcome the phase sensitivity problem of PSDs, a digital phase tracking compensation technique based on phase-locked loops (PLLs) has been proposed. Its core idea is to dynamically adjust the reference phase. i ref To make it always follow f ( T The change of ) thus ensures the cos( f - i ref )≈1. Although phase-locked loop (PLL) based phase tracking technology can effectively eliminate demodulation gain instability caused by second harmonic phase drift (i.e., ensure cos( f - i ref The PLL technology, while significantly improving the system's robustness to phase disturbances, has the following fundamental limitations: 1) It cannot handle zero-point drift; 2) It ignores analog channel hardware mismatch; 3) It lacks parameter self-adaptation and autonomous update capabilities. In summary, PLL technology only addresses one aspect of the challenges faced by high-precision zero-flux transformers (phase sensitivity), failing to provide effective solutions for core issues affecting accuracy and reliability, such as residual magnetism zero drift, hardware mismatch, and long-term parameter drift. Alternatively, self-testing or coarse calibration of the transformer can be achieved through external excitation based on primary-side injection self-testing or calibration technology. Its disadvantages are: 1) a fundamental architectural flaw—the main circuit must be interrupted; 2) low information acquisition efficiency, unable to decouple key error sources. In conclusion, primary-side injection technology not only has hard limitations in engineering applications but also inherent flaws in calibration principles and information theory. It cannot meet the comprehensive requirements of modern high-precision current transformers for autonomy, accuracy, and non-disruption.

[0010] Therefore, a new closed-loop zero-flux current transformer is needed. Summary of the Invention

[0011] This invention proposes a closed-loop zero-flux current transformer and a current measurement method to solve the problem of how to accurately measure current.

[0012] To address the aforementioned problems, according to one aspect of the present invention, a closed-loop zero-flux current transformer is provided, the current transformer comprising: a magnetic core assembly, a signal detection module, a signal generation module, a temperature sensing module, a signal processing module, and a feedback current generation module; wherein... The signal detection module is connected to the magnetic core assembly and is used to obtain the second harmonic signal through the magnetic core assembly; The signal generation module is connected to the magnetic core assembly and is used to generate a pair of orthogonal local reference signals; The temperature sensing module is disposed on the magnetic core assembly and is used to obtain the real-time temperature of the magnetic core assembly. The signal processing module is used to perform I / Q quadrature demodulation based on the second harmonic signal and the local reference signal to obtain the in-phase component and the quadrature component; correct the in-phase component and the quadrature component according to the current calibration parameters, and calculate the initial error signal based on the corrected in-phase component and the quadrature component; calculate the gain correction coefficient corresponding to the real-time temperature; calculate the corrected error signal based on the initial error signal and the gain correction coefficient; and calculate the primary current based on the feedback current generated by the feedback current generation module. The feedback current generation module is used to receive the corrected error signal, generate a feedback current based on the corrected error signal, and apply the feedback current to the feedback coil of the magnetic core assembly to generate a compensation magnetic field opposite to the direction of the primary current DC bias magnetic field, thereby maintaining the DC bias magnetic flux in the magnetic core at zero.

[0013] Preferably, the signal processing module performs I / Q quadrature demodulation based on the second harmonic signal and the local reference signal to obtain in-phase and quadrature components, including: I= LPF[ V 2f (t)*R I ( t )] =2KH m · cos( f ), Q= LPF[ V 2f (t)*R Q ( t )] =2KH m · sin( f ), Where I represents the in-phase component; Q represents the quadrature component; and LPF represents low-pass filter. V 2f ( t () is a second harmonic signal; R I (t) and R Q (t) represents the orthogonal local reference signal; K is the system gain coefficient; H m It is a DC magnetic field; f This represents the phase shift of the second harmonic signal.

[0014] Preferably, the signal processing module corrects the in-phase and quadrature components according to the current calibration parameters, and calculates an initial error signal based on the corrected in-phase and quadrature components, including: , , , in, The corrected in-phase component; I represents the corrected quadrature component; Q represents the in-phase component; and I represents the quadrature component. k gain For I / Q gain calibration coefficients; d θ is the orthogonal error angle; e is the initial error signal.

[0015] Preferably, the signal processing module calculates the gain correction coefficient corresponding to the real-time temperature, including: Obtain the gain correction coefficients corresponding to multiple key temperature points calibrated, and calculate the gain correction coefficients corresponding to the real-time temperature using interpolation, piecewise constant lookup table, or polynomial fitting methods.

[0016] Preferably, the signal processing module calculates the corrected error signal based on the initial error signal and the gain correction coefficient, including: The initial error signal e is gain-corrected using the gain correction coefficient G(T) to obtain the corrected error signal e. cor =G(T)·e; where T is the real-time temperature. Preferably, wherein... The signal processing module is also used for: When the primary current I p Satisfy | I p |< c •FS and duration ≥ T1, and feedback current in T w When the standard deviation within a sliding window is less than ɛ·FS and the time since the last successful calibration is ≥T2, the system enters self-calibration mode to generate new calibration parameters; among which, c ε is the first preset proportional coefficient; α is the second preset proportional coefficient; FS is the full-scale measurement value; T1 is the first preset time; T2 is the second preset time.

[0017] Preferably, the signal processing module generates new calibration parameters in the following manner: Obtain the steady-state feedback current, and apply a compensation current that is equal in magnitude but opposite in direction to the steady-state feedback current to the feedback coil of the magnetic core assembly to achieve residual magnetism compensation and bring the operating point of the magnetic core to zero. Perform bipolar injection, including: injecting a positive test current + I cal After stabilization, sampling was performed to obtain (I) + Q + Inject negative test current - I cal After stabilization, sampling was performed to obtain (I) - Q - ); According to (I) + Q + ) and (I - Q - Calculate the new calibration parameters, including: , , in, k gain For I / Q gain calibration coefficients; d The orthogonal error angle; (I) + Q + Injecting positive test current + I cal The in-phase and quadrature components obtained after stabilization sampling; (I - Q - Injecting negative test current - I cal The in-phase and quadrature components obtained after stabilization sampling; For testing current I cal The known magnetic field generated.

[0018] Preferably, the signal processing module is further configured to: Real-time monitoring during self-calibration | I p | and when it is detected that |I p When |>η·FS and the duration is ≥T3, the self-calibration process is terminated, and the system switches to the redundant phase-sensitive demodulation PSD backup mode; where, I p 1 is the primary current; FS is the full-scale measurement value; η is the preset safety threshold ratio; T3 is the third preset time.

[0019] According to another aspect of the present invention, a current measurement method based on a closed-loop zero-flux current transformer as described in any of the preceding claims is provided, the method comprising: The second harmonic signal is obtained through the magnetic core assembly using the signal detection module; Using the signal generation module, a pair of orthogonal local reference signals are generated; The real-time temperature of the magnetic core assembly is obtained using a temperature sensing module. Using a signal processing module, I / Q quadrature demodulation is performed on the second harmonic signal and the local reference signal to obtain the in-phase component and the quadrature component; the in-phase component and the quadrature component are corrected according to the current calibration parameters, and the initial error signal is calculated based on the corrected in-phase component and the quadrature component; the gain correction coefficient corresponding to the real-time temperature is calculated; and the corrected error signal is calculated based on the initial error signal and the gain correction coefficient. The feedback current generation module receives the corrected error signal, generates a feedback current based on the corrected error signal, and applies the feedback current to the feedback coil of the magnetic core assembly to generate a compensation magnetic field opposite to the direction of the primary current DC bias magnetic field, thereby maintaining the DC bias magnetic flux in the magnetic core at zero. The primary current is calculated based on the feedback current using the signal processing module.

[0020] Preferably, the method of performing I / Q quadrature demodulation based on the second harmonic signal and the local reference signal to obtain in-phase and quadrature components includes: I= LPF[ V 2f (t)*R I ( t )] =2KH m · cos( f ), Q= LPF[ V 2f (t)*R Q ( t )] =2KH m · sin( f ), Where I represents the in-phase component; Q represents the quadrature component; and LPF represents low-pass filter. V 2f ( t () is a second harmonic signal; R I (t) and R Q (t) represents the orthogonal local reference signal; K is the system gain coefficient; H m It is a DC magnetic field; f This represents the phase shift of the second harmonic signal.

[0021] Preferably, the process involves correcting the in-phase and quadrature components according to current calibration parameters, and calculating an initial error signal based on the corrected in-phase and quadrature components, including: , , , in, The corrected in-phase component; I represents the corrected quadrature component; Q represents the in-phase component; and I represents the quadrature component. k gain For I / Q gain calibration coefficients; d θ is the orthogonal error angle; e is the initial error signal.

[0022] Preferably, calculating the gain correction coefficient corresponding to the real-time temperature includes: Obtain the gain correction coefficients corresponding to multiple key temperature points calibrated, and calculate the gain correction coefficients corresponding to the real-time temperature using interpolation, piecewise constant lookup table, or polynomial fitting methods.

[0023] Preferably, the calculation of the corrected error signal based on the initial error signal and the gain correction coefficient includes: The initial error signal e is gain-corrected using the gain correction coefficient G(T) to obtain the corrected error signal e. cor =G(T)·e; where T is the real-time temperature. Preferably, the method further includes: Using the signal processing module, when the primary current... I p Satisfy | I p |< c •FS and duration ≥ T1, and feedback current in T w When the standard deviation within a sliding window is less than ɛ·FS and the time since the last successful calibration is ≥T2, the system enters self-calibration mode to generate new calibration parameters; among which, c ε is the first preset proportional coefficient; α is the second preset proportional coefficient; FS is the full-scale measurement value; T1 is the first preset time; T2 is the second preset time.

[0024] Preferably, the method generates new calibration parameters by: Obtain the steady-state feedback current, and apply a compensation current that is equal in magnitude but opposite in direction to the steady-state feedback current to the feedback coil of the magnetic core assembly to achieve residual magnetism compensation and bring the operating point of the magnetic core to zero. Perform bipolar injection, including: injecting a positive test current + Ical After stabilization, sampling was performed to obtain (I) + Q + Inject negative test current - I cal After stabilization, sampling was performed to obtain (I) - Q - ); According to (I) + Q + ) and (I - Q - Calculate the new calibration parameters, including: , , in, k gain For I / Q gain calibration coefficients; d The quadrature error angle is (I+, Q+); (I-, Q-) are the in-phase and quadrature components obtained by sampling after the positive test current +Ical has stabilized; (I-, Q-) are the in-phase and quadrature components obtained by sampling after the negative test current -Ical has stabilized. The known magnetic field generated by the test current Ical.

[0025] Preferably, the method further includes: Using a signal processing module, real-time monitoring is performed during the self-calibration process. I p | and when it is detected that |I p When |>η·FS and the duration is ≥T3, the self-calibration process is terminated, and the system switches to the redundant phase-sensitive demodulation PSD backup mode; where, I p 1 is the primary current; FS is the full-scale measurement value; η is the preset safety threshold ratio; T3 is the third preset time.

[0026] This invention provides a closed-loop zero-flux current transformer and a current measurement method. The current transformer has a built-in feedback loop with a self-sensing, self-calibrating, and self-compensating mechanism. This mechanism directly quantifies the residual magnetism by utilizing the steady-state current of the feedback loop itself, and achieves multi-parameter decoupling through bipolar excitation within the feedback loop. Without interrupting the main circuit, it combines quadrature demodulation and temperature zone compensation to achieve comprehensive, accurate, and online compensation for multiple key error sources such as phase temperature drift, residual magnetism zero drift, I / Q channel gain mismatch, quadrature error, and system gain temperature drift. It also has autonomous triggering and safety monitoring capabilities. Attached Figure Description

[0027] Exemplary embodiments of the present invention can be more fully understood by referring to the following figures: Figure 1 This is a structural diagram of a magnetically modulated zero-flux current transformer. Figure 2 This is a schematic diagram of the structure of a closed-loop zero-flux current transformer 200 according to an embodiment of the present invention; Figure 3 This is a flowchart of signal processing according to an embodiment of the present invention; Figure 4 This is a flowchart of a current measurement method 400 for a closed-loop zero-flux current transformer according to an embodiment of the present invention. Detailed Implementation

[0028] Exemplary embodiments of the invention will now be described with reference to the accompanying drawings. However, the invention may be embodied in many different forms and is not limited to the embodiments described herein. These embodiments are provided to fully and completely disclose the invention and to fully convey its scope to those skilled in the art. The terminology used in the exemplary embodiments illustrated in the drawings is not intended to limit the invention. In the drawings, the same units / elements are referred to by the same reference numerals.

[0029] Unless otherwise stated, the terms used herein (including technical terms) have their common meaning as understood by one of ordinary skill in the art. Furthermore, it is understood that terms defined in commonly used dictionaries should be understood to have a meaning consistent with the context of their relevant field, and not to be interpreted as having an idealized or overly formal meaning.

[0030] Figure 2 This is a schematic diagram of the closed-loop zero-flux current transformer 200 according to an embodiment of the present invention. Figure 2 As shown, the closed-loop zero-flux current transformer provided in this embodiment of the invention has a built-in feedback loop with a self-sensing, self-calibrating, and self-compensating mechanism. This mechanism directly quantifies the residual magnetism by utilizing the steady-state current of the feedback loop itself, and achieves multi-parameter decoupling through bipolar excitation within the feedback loop. Without interrupting the main loop, it combines quadrature demodulation and temperature zone compensation to achieve comprehensive, accurate, and online compensation for multiple key error sources such as phase temperature drift, residual magnetism zero drift, I / Q channel gain mismatch, quadrature error, and system gain temperature drift. It also has autonomous triggering and safety monitoring capabilities. The closed-loop zero-flux current transformer 200 provided in this embodiment of the invention includes: a magnetic core assembly 201, a signal detection module 202, a signal generation module 203, a temperature sensing module 204, a signal processing module 205, and a feedback current generation module 206.

[0031] Preferably, the signal detection module 202 is connected to the magnetic core assembly 201 and is used to obtain the second harmonic signal through the magnetic core assembly.

[0032] Preferably, the signal generation module 203 is connected to the magnetic core assembly and is used to generate a pair of orthogonal local reference signals.

[0033] Preferably, the temperature sensing module 204 is disposed on the magnetic core assembly and is used to acquire the real-time temperature of the magnetic core assembly.

[0034] Preferably, the signal processing module 205 is configured to perform I / Q quadrature demodulation based on the second harmonic signal and the local reference signal to obtain the in-phase component and the quadrature component; correct the in-phase component and the quadrature component according to the current calibration parameters, and calculate the initial error signal based on the corrected in-phase component and the quadrature component; calculate the gain correction coefficient corresponding to the real-time temperature; calculate the corrected error signal based on the initial error signal and the gain correction coefficient; and calculate the primary current based on the feedback current generated by the feedback current generation module.

[0035] Preferably, the feedback current generation module 206 is used to receive the corrected error signal, generate a feedback current according to the corrected error signal, and apply the feedback current to the feedback coil of the magnetic core assembly to generate a compensation magnetic field opposite to the direction of the primary current DC bias magnetic field, thereby maintaining the DC bias magnetic flux in the magnetic core at zero.

[0036] In this invention, a closed-loop zero-flux current transformer includes: a magnetic core assembly, a signal detection module, a signal generation module, a temperature sensing module, a signal processing module, and a feedback current generation module. The magnetic core assembly includes: a closed nanocrystalline magnetic core wound with an excitation coil, an induction coil, and a feedback coil. The signal processing module is a dual-core processor; the main core is responsible for I / Q demodulation and self-calibration algorithms, while the safety core is responsible for redundant PSD backup. The temperature sensing module is a temperature sensor mounted close to the magnetic core. The signal detection module is a high-speed ADC; the induction coil of the magnetic core assembly is connected to the high-speed ADC, and the feedback coil is also connected to the high-precision ADC. Except for the temperature sensing module, the connection methods of the other components of the closed-loop zero-flux current transformer of this invention are similar to... Figure 1 The structure is similar, and accurate current measurement can be achieved through signal processing by the signal processing module.

[0037] Preferably, the signal processing module 205 performs I / Q quadrature demodulation based on the second harmonic signal and the local reference signal to obtain in-phase and quadrature components, including: I= LPF[ V 2f (t)*R I ( t )] =2KH m · cos( f ), Q= LPF[ V 2f (t)*R Q ( t )] =2KH m · sin( f ), Where I represents the in-phase component; Q represents the quadrature component; and LPF represents low-pass filter. V 2f ( t () is a second harmonic signal; R I (t) and R Q (t) represents the orthogonal local reference signal; K is the system gain coefficient; H m It is a DC magnetic field; f This represents the phase shift of the second harmonic signal.

[0038] Preferably, the signal processing module 205 corrects the in-phase and quadrature components according to the current calibration parameters, and calculates an initial error signal based on the corrected in-phase and quadrature components, including: , , , in, The corrected in-phase component; I represents the corrected quadrature component; Q represents the in-phase component; and I represents the quadrature component. k gain For I / Q gain calibration coefficients; d θ is the orthogonal error angle; e is the initial error signal.

[0039] Preferably, the signal processing module 205 calculates the gain correction coefficient corresponding to the real-time temperature, including: Obtain the gain correction coefficients corresponding to multiple key temperature points calibrated, and calculate the gain correction coefficients corresponding to the real-time temperature using interpolation, piecewise constant lookup table, or polynomial fitting methods.

[0040] Preferably, the signal processing module 205 calculates the corrected error signal based on the initial error signal and the gain correction coefficient, including: The initial error signal e is gain-corrected using the gain correction coefficient G(T) to obtain the corrected error signal e. cor=G(T)·e; where T is the real-time temperature.

[0041] Combination Figure 3 As shown, in this invention, when self-calibration is not required, in order to fundamentally eliminate the sensitivity of traditional single-channel PSD to phase drift, the signal processing module uses quadrature demodulation (I / Q demodulation) technology to obtain I and Q values ​​for current measurement.

[0042] Specifically, the second harmonic signal obtained from the induction coil using the signal detection module is: V 2f ( t )= K ( T ) ·H m · sin( 2ωt+φ ( T )) , Using the signal generation module, a pair of orthogonal local reference signals are generated: R I ( t ) = sin( 2ωt ) ,R Q ( t ) = cos( 2ωt ), The signal processing module will V 2f ( t ) respectively with R I (t) and R Q Multiplying (t) and filtering by LPF yields the in-phase component (I) and the quadrature component (Q): I= LPF[ V 2f (t)*R I ( t )] =2KH m · cos( f ), Q= LPF[ V 2f (t)*R Q ( t )] =2KH m · sin( f ), At this point, the final error signal (i.e., the characterization of the magnetic field to be measured) is its magnitude: , The above equation shows that, under ideal conditions, the error signal e With phase f It is irrelevant; therefore, the effect of phase temperature drift can be completely eliminated.

[0043] Therefore, in this invention, during normal measurement, the original I and Q values ​​are corrected in real time using the currently stored calibration parameters. The correction method is as follows: , , The initial error signal obtained after correction is: , It can be seen that this signal has eliminated the effects of I / Q channel mismatch and residual magnetism. in, The corrected in-phase component; I represents the corrected quadrature component; Q represents the in-phase component; and I represents the quadrature component. k gain For I / Q gain calibration coefficients; d θ is the orthogonal error angle; e is the initial error signal.

[0044] Although I / Q demodulation eliminates phase temperature drift, the system gain... K ( T The amplitude of the error signal *e* still changes with temperature, causing a drift in the proportional relationship between the amplitude and the bias magnetic field it represents. If not compensated for, this drift directly affects the response of the feedback current generation module to the error signal, thus affecting the feedback current. I f Unable to accurately balance the primary current I p This ultimately affects the measurement accuracy.

[0045] Therefore, this invention employs a temperature zoning compensation strategy to correct the gain of the initial error signal e, including: Offline calibration: At five key temperature points—-40℃, 0℃, 25℃, 85℃, and 125℃—a known primary current is injected into the current transformer. I p Measure the corresponding error signal e and calibrate the gain correction coefficient at that temperature. G ( T ), so that the corrected error signal e cor = G (T )·e and primary current I p Maintain a fixed proportional relationship (i.e., e) cor = K 0· I p ,in K 0 represents the nominal gain at room temperature.

[0046] Online compensation: During operation, the signal processing module reads the real-time temperature T from the temperature sensor, calculates the gain correction coefficient G(T) at the current temperature using an interpolation algorithm, and performs real-time correction on the initial error signal to obtain the corrected error signal: e cor =G(T)·e. The corrected error signal e cor The output is sent to the feedback current generation module to drive the feedback coil to generate an accurate feedback current. I f This is done to maintain magnetic flux balance, thereby enabling accurate measurement of the primary current under magnetic flux balance. The measured value is obtained using Ampere's circuital law: I p =( N f / N p )* I f ; where N f Np represents the number of turns in the feedback coil, and Np represents the number of turns in the primary coil. The feedback current generation module receives the corrected error signal, generates a feedback current based on the corrected error signal, and applies the feedback current to the feedback coil of the magnetic core assembly to generate a compensation magnetic field opposite in direction to the DC bias magnetic field of the primary current, thus maintaining the DC bias flux in the magnetic core at zero.

[0047] With this compensation, the system can maintain high accuracy across the entire temperature range and fully comply with the working principle of a closed-loop zero-flux current transformer.

[0048] For interpolation algorithms in temperature zoning compensation, in addition to cubic spline interpolation, linear interpolation, piecewise constant lookup table (LUT), or polynomial fitting can also be used. The number and location of calibrated temperature points can also be adjusted according to requirements, for example, calibration can be performed only at three points: -25℃, 25℃, and 70℃, which is not limited here.

[0049] Preferably, the signal processing module is further configured to: When the primary current I p Satisfy | I p |< c •FS and duration ≥ T1, and feedback current in T wWhen the standard deviation within a sliding window is less than ɛ·FS and the time since the last successful calibration is ≥T2, the system enters self-calibration mode to generate new calibration parameters; among which, c ε is the first preset proportional coefficient; α is the second preset proportional coefficient; FS is the full-scale measurement value; T1 is the first preset time; T2 is the second preset time.

[0050] Preferably, the signal processing module 205 generates new calibration parameters in the following manner: Obtain the steady-state feedback current, and apply a compensation current that is equal in magnitude but opposite in direction to the steady-state feedback current to the feedback coil of the magnetic core assembly to achieve residual magnetism compensation and bring the operating point of the magnetic core to zero. Perform bipolar injection, including: injecting a positive test current + I cal After stabilization, sampling was performed to obtain (I) + Q + Inject negative test current - I cal After stabilization, sampling was performed to obtain (I) - Q - ); According to (I) + Q + ) and (I - Q - Calculate the new calibration parameters, including: , , in, k gain For I / Q gain calibration coefficients; d The quadrature error angle is (I+, Q+); (I-, Q-) are the in-phase and quadrature components obtained by sampling after the positive test current +Ical has stabilized; (I-, Q-) are the in-phase and quadrature components obtained by sampling after the negative test current -Ical has stabilized. The known magnetic field generated by the test current Ical.

[0051] In actual measurement processes, inherent differences exist in the analog front-ends (amplifiers, ADCs, etc.) of the I and Q channels, leading to gain mismatch and quadrature error. Gain mismatch refers to: I Channel gain is α , Q The channel gain is 1 (based on Q). Quadrature error refers to: Q There is a small angular deviation in the channel reference signal. β .

[0052] At this point, the actual I and Q outputs become: , If the modulus is still calculated using the ideal formula, a significant error will be introduced: , This error directly translates into a deviation in the final current reading, and is one of the key factors affecting long-term accuracy.

[0053] Therefore, in order to solve the above-mentioned non-ideal problems and zero residual magnetism drift, this invention designs a complete self-calibration process.

[0054] Specifically, in combination Figure 3 As shown, in this invention, the current transformer automatically enters calibration mode when the following conditions are met simultaneously: (a) Primary current | I p |< c • FS duration ≥ T1; (b) Feedback current I fb In T w The standard deviation within each sliding window is <ɛ·FS; (c) The time since the last successful calibration is ≥ T2.

[0055] in, c ɛ is the first preset scaling factor, and ɛ is the second preset scaling factor. d For orthogonal error angles, T1 and T w T2 is a preset time parameter. As an example, γ = 0.5%, α = 0.1%, T1 = 100ms, and T... w =5, T2=1h.

[0056] Under steady-state conditions that meet the triggering condition, record the steady-state current of the feedback loop. I fbss The current is used entirely to counteract the residual magnetism of the magnetic core. B r The resulting static bias magnetic field H b Therefore, apply - to the feedback coil I fbss This is done to achieve residual magnetism compensation, so that the operating point of the magnetic core is brought to zero.

[0057] After remanence compensation, bipolar injection is performed, including: Inject positive test current + I cal After stabilization, sampling is performed to obtain (I) + Q + ); Inject negative test current - I calAfter stabilization, sampling is performed to obtain (I) - Q - ).

[0058] Based on the IQ values ​​under the non-ideal model condition, these four sets of measurements can be expressed as follows: in, k 1= K / 2, It is by I cal The known magnetic field produced H res It is the residual bias after remanent magnetization compensation.

[0059] Through calculation, gain mismatch, quadrature error, and residual magnetism can be completely decoupled, and then the I / Q gain calibration coefficients can be calculated. k gain for: , Calculate the orthogonal error angle d for: , By calibrating the gain calibration coefficient and the quadrature error angle, real-time correction of the original I and Q values ​​can be achieved.

[0060] In this invention, the test current is injected bipolarly. I cal Besides using a DC square wave, sine waves, triangular waves, or other known waveforms can also be used. As long as a pair of excitations with equal amplitude and opposite polarity can be provided, and their steady-state responses can be stably acquired, it can be used for parameter decoupling calculations. The injected amplitude... I cal It doesn't have to be a fixed value; it can also be an adaptive value related to the current range.

[0061] For calibration trigger conditions, in addition to trigger conditions based on primary current amplitude and steady-state time, trigger conditions based on cumulative temperature change (e.g., ΔT>10℃) or fixed time period (e.g., every 24 hours) can also be used. The trigger logic can also be initiated by an external master controller actively issuing commands through a communication bus (e.g., CAN, SPI), rather than relying entirely on the internal state machine for autonomous judgment.

[0062] Preferably, the signal processing module 205 is further configured to: Real-time monitoring during self-calibration | I p | and when it is detected that |I pWhen |>η·FS and the duration is ≥T3, the self-calibration process is terminated, and the system switches to the redundant phase-sensitive demodulation PSD backup mode; where, I p 1 is the primary current; FS is the full-scale measurement value; η is the preset safety threshold ratio; T3 is the third preset time.

[0063] Combination Figure 3 As shown, in this invention, the entire calibration process can also be monitored. I p If an excessive current is detected, then |I| is satisfied. p If η·FS remains above T3, all calibration injection actions are immediately stopped, main loop control is restored, and the system switches to the redundant PSD backup mode executed by the safety core to ensure functional safety. Here, η is the preset safety threshold ratio (relative to full scale FS), and T3 is the preset safety response time. For example, η = 5% and T3 = 10μs can be used.

[0064] The threshold (e.g., 5%FS) and duration (e.g., 10μs) for security monitoring can be adjusted according to the security level requirements of specific application scenarios. In addition to using an independent PSD core, the redundant backup mode can also employ a simplified open-loop measurement mode or a prediction mode based on historical data as a temporary emergency output.

[0065] The core of this invention lies in constructing a tightly coupled, indivisible three-level progressive self-calibration architecture based on current measurement via demodulation. The ingenuity of this architecture is reflected in the strong dependencies and synergies among its components: First stage (residual magnetism compensation): Utilizing the steady-state output of the feedback loop under zero input. I fbss As a direct observation of remanence, this step is a prerequisite for subsequent accurate calibration. Without this compensation, the remanence bias will overlap with the channel mismatch effect, leading to decoupling failure.

[0066] The second stage (bipolar injection): must be performed on the feedback side, not the primary side. Injection on the feedback side allows the injected signal to establish a direct, linear mathematical relationship with the error sources to be calibrated (residual magnetism, channel mismatch). Injection on the primary side results in a signal path that traverses the entire unknown sensing link, introducing more uncertainty and making precise decoupling impossible.

[0067] The third level (parameter decoupling): the specific addition and subtraction formulas used depend entirely on the correct execution of the first two levels of operations for their effectiveness. Only when residual magnetism is initially compensated and the injection occurs on the feedback side, ( I + Q + )and( I- Q -The difference between the two values ​​reflects channel mismatch, while the sum reflects residual magnetism.

[0068] The three parts form a logical closed loop, and none of them can be omitted. Any attempt to replace any part with a common practice (such as primary-edge injection or ignoring remanent magnetization compensation) will cause the entire calibration mechanism to fail and make it impossible to solve the three major technical problems at the same time.

[0069] The closed-loop zero-flux current transformer of the present invention systematically solves the core error source in the long-term operation of high-precision zero-flux current transformers in principle, and its beneficial effects are specifically reflected in the following four aspects: 1. Significantly improves long-term measurement accuracy and stability Problems addressed: Resolving temperature-induced phase / gain drift, residual magnetism zero-point drift, and I / Q channel mismatch.

[0070] Effect description: Eliminating phase sensitivity: By employing an I / Q quadrature demodulation architecture, the measurement result is expressed as the magnitude of the error signal. This fundamentally eliminates the output's dependence on the second harmonic phase. f This eliminates the dependence on temperature, thus completely avoiding the gain instability problem caused by phase drift due to temperature changes.

[0071] Actively suppressing zero-point drift: Innovatively utilizing the current of the feedback loop under zero-input steady state. I fbss As a direct observation of the remanent magnetic bias of the magnetic core, and applied - I fb_ss Real-time compensation is performed. This method directly addresses the source of error and can effectively suppress static zero-point offset caused by residual magnetism and aging.

[0072] Precise calibration of channel mismatch: by performing bipolar injection (+) in the feedback loop. I cal and- I cal ), and utilize (I + Q + ) and (I - Q - The operation achieves complete decoupling and independent quantization of I / Q channel gain mismatch and quadrature error. This enables the system to generate accurate correction parameters and provide targeted compensation for hardware non-ideals.

[0073] Full-temperature-range gain stability: A temperature-sensitivity mapping table S(T) is established through offline calibration, and interpolation compensation is performed during operation, which effectively corrects the overall gain temperature drift of the entire signal link, including the magnetic core, coil, ADC, etc.

[0074] 2. Achieve online, uninterrupted self-calibration To address the problem: to enable on-site autonomous calibration without interrupting the normal operation of the main circuit.

[0075] Effect description: Non-invasive calibration: All calibration actions (residual magnetization compensation, bipolar injection) are completed within the feedback loop, without needing to connect to or interfere with the primary side current circuit being measured. This ensures that the current measurement function of the main circuit remains continuous and uninterrupted throughout the entire calibration cycle, meeting the stringent high availability requirements of critical applications such as energy storage BMS and rail transit.

[0076] Autonomous operation: The system has a built-in intelligent state machine that can automatically identify when the primary current is in a low-amplitude steady state window and trigger the calibration process under this condition. No external commands or manual intervention are required throughout the process, which greatly simplifies operation and maintenance.

[0077] 3. Construct a highly reliable functional safety mechanism To address the issue: ensure that the calibration process itself does not introduce safety risks.

[0078] Effect description: Real-time safety monitoring: During calibration, the system continuously monitors the primary current status at a high frequency. If an abnormally high current is detected, the calibration operation can be immediately stopped, and the normal control of the main servo loop can be instantly restored, ensuring that the system maintains basic measurement and protection functions under any operating condition.

[0079] Redundant backup design: Employing a dual-core processor architecture, the main core handles the high-precision self-calibration algorithm, while the safety core runs simplified, certified redundant PSD logic. In the event of a main core failure or calibration anomaly, it can seamlessly switch to the safety core mode, providing basic protection that meets functional safety standards.

[0080] 4. Reduce total life-cycle costs and improve project usability. To address the issue: reduce reliance on one-time factory calibration and subsequent return-to-factory maintenance.

[0081] Effect description: Relaxed hardware matching requirements: Since the gain and quadrature error of the I / Q channels can be precisely calibrated using digital algorithms, the system no longer relies on the ultra-high precision hardware matching of the analog front-end circuit. This allows for the use of lower-cost, more flexible general-purpose components, reducing hardware design complexity and material costs.

[0082] Extending the maintenance-free period: By autonomously compensating for progressive performance degradation such as residual magnetic drift and channel aging on-site, the rate of accuracy deterioration of the current transformer is significantly slowed down, thereby greatly extending its maintenance-free operating life and reducing the frequency of factory calibration and related maintenance costs.

[0083] In summary, this invention constructs a closed-loop, autonomous, and secure high-precision mutual inductance system, which not only overcomes the inherent defects of existing solutions in terms of technology, but also demonstrates significant advantages in engineering implementation, reliability, and economy, providing a solid technical foundation for the in-depth application of closed-loop zero-flux current transformers in key industrial fields.

[0084] Figure 4 This is a flowchart of a current measurement method 400 for a closed-loop zero-flux current transformer according to an embodiment of the present invention. Figure 4 As shown, the current measurement method 400 based on the closed-loop zero flux current transformer as described in any of the above embodiments of the present invention starts from step 401. In step 401, the second harmonic signal is obtained through the magnetic core assembly using the signal detection module.

[0085] In step 402, a pair of orthogonal local reference signals are generated using the signal generation module.

[0086] In step 403, the real-time temperature of the magnetic core assembly is obtained using a temperature sensing module.

[0087] In step 404, the signal processing module performs I / Q quadrature demodulation on the second harmonic signal and the local reference signal to obtain the in-phase component and the quadrature component; the in-phase component and the quadrature component are corrected according to the current calibration parameters, and the initial error signal is calculated based on the corrected in-phase component and the quadrature component; the gain correction coefficient corresponding to the real-time temperature is calculated; and the corrected error signal is calculated based on the initial error signal and the gain correction coefficient.

[0088] Preferably, the method of performing I / Q quadrature demodulation based on the second harmonic signal and the local reference signal to obtain in-phase and quadrature components includes: I= LPF[ V 2f (t)*R I ( t )] =2KH m · cos( f ), Q= LPF[ V 2f (t)*R Q( t )] =2KH m · sin( f ), Where I represents the in-phase component; Q represents the quadrature component; and LPF represents low-pass filter. V 2f ( t () is a second harmonic signal; R I (t) and R Q (t) represents the orthogonal local reference signal; K is the system gain coefficient; H m It is a DC magnetic field; f This represents the phase shift of the second harmonic signal.

[0089] Preferably, the process involves correcting the in-phase and quadrature components according to current calibration parameters, and calculating an initial error signal based on the corrected in-phase and quadrature components, including: , , , in, The corrected in-phase component; I represents the corrected quadrature component; Q represents the in-phase component; and I represents the quadrature component. k gain For I / Q gain calibration coefficients; d θ is the orthogonal error angle; e is the initial error signal.

[0090] Preferably, calculating the gain correction coefficient corresponding to the real-time temperature includes: Obtain the gain correction coefficients corresponding to multiple key temperature points calibrated, and calculate the gain correction coefficients corresponding to the real-time temperature using interpolation, piecewise constant lookup table, or polynomial fitting methods.

[0091] Preferably, the calculation of the corrected error signal based on the initial error signal and the gain correction coefficient includes: The initial error signal e is gain-corrected using the gain correction coefficient G(T) to obtain the corrected error signal e. cor =G(T)·e; where T is the real-time temperature. In step 405, the feedback current generation module receives the corrected error signal, generates a feedback current based on the corrected error signal, and applies the feedback current to the feedback coil of the magnetic core assembly to generate a compensation magnetic field opposite to the direction of the primary current DC bias magnetic field, maintaining the DC bias magnetic flux in the magnetic core at zero.

[0092] In step 406, the primary current is calculated based on the feedback current using the signal processing module.

[0093] Preferably, the method further includes: Using the signal processing module, when the primary current... I p Satisfy | I p |< c •FS and duration ≥ T1, and feedback current in T w When the standard deviation within a sliding window is less than ɛ·FS and the time since the last successful calibration is ≥T2, the system enters self-calibration mode to generate new calibration parameters; among which, c ε is the first preset proportional coefficient; α is the second preset proportional coefficient; FS is the full-scale measurement value; T1 is the first preset time; T2 is the second preset time.

[0094] Preferably, the method generates new calibration parameters by: Obtain the steady-state feedback current, and apply a compensation current that is equal in magnitude but opposite in direction to the steady-state feedback current to the feedback coil of the magnetic core assembly to achieve residual magnetism compensation and bring the operating point of the magnetic core to zero. Perform bipolar injection, including: injecting a positive test current + I cal After stabilization, sampling was performed to obtain (I) + Q + Inject negative test current - I cal After stabilization, sampling was performed to obtain (I) - Q - ); According to (I) + Q + ) and (I - Q - Calculate the new calibration parameters, including: , , in, k gain For I / Q gain calibration coefficients; d The quadrature error angle is (I+, Q+); (I+, Q+) represents the injected positive test current +I. cal The in-phase and quadrature components obtained after stabilization sampling; (I-, Q-) represents the injected negative test current -I cal The in-phase and quadrature components obtained after stabilization are used to sample the test current I. cal The known magnetic field generated.

[0095] Preferably, the method further includes: Using a signal processing module, real-time monitoring is performed during the self-calibration process. I p | and when it is detected that |I p When |>η·FS and the duration is ≥T3, the self-calibration process is terminated, and the system switches to the redundant phase-sensitive demodulation PSD backup mode; where, I p 1 is the primary current; FS is the full-scale measurement value; η is the preset safety threshold ratio; T3 is the third preset time.

[0096] The current measurement method 400 of the closed-loop zero flux current transformer of the present invention corresponds to the closed-loop zero flux current transformer 200 of another embodiment of the present invention, and will not be described again here.

[0097] The present invention has been described with reference to a few embodiments. However, it will be apparent to those skilled in the art that other embodiments besides those disclosed above fall equivalently within the scope of the present invention.

[0098] Generally, all terms used in this invention are interpreted according to their ordinary meaning in the art, unless otherwise expressly defined herein. All references to “a / the / the [device, component, etc.]” ​​are openly interpreted as at least one instance of said device, component, etc., unless otherwise expressly stated. The steps of any method disclosed herein need not be performed in the exact order disclosed, unless explicitly stated otherwise.

[0099] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention can take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0100] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure oneOne or more processes and / or boxes Figure one A device that provides the functions specified in one or more boxes.

[0101] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure one One or more processes and / or boxes Figure one The function specified in one or more boxes.

[0102] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure one One or more processes and / or boxes Figure one The steps of the function specified in one or more boxes.

[0103] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the protection scope of the present invention.

Claims

1. A closed-loop zero-flux current transformer, characterized in that, The current transformer includes: a magnetic core assembly, a signal detection module, a signal generation module, a temperature sensing module, a signal processing module, and a feedback current generation module; wherein, The signal detection module is connected to the magnetic core assembly and is used to obtain the second harmonic signal through the magnetic core assembly; The signal generation module is connected to the magnetic core assembly and is used to generate a pair of orthogonal local reference signals; The temperature sensing module is disposed on the magnetic core assembly and is used to obtain the real-time temperature of the magnetic core assembly. The signal processing module is used to perform I / Q quadrature demodulation based on the second harmonic signal and the local reference signal to obtain the in-phase component and the quadrature component; correct the in-phase component and the quadrature component according to the current calibration parameters, and calculate the initial error signal based on the corrected in-phase component and the quadrature component; calculate the gain correction coefficient corresponding to the real-time temperature; calculate the corrected error signal based on the initial error signal and the gain correction coefficient; and calculate the primary current based on the feedback current generated by the feedback current generation module. The feedback current generation module is used to receive the corrected error signal, generate a feedback current based on the corrected error signal, and apply the feedback current to the feedback coil of the magnetic core assembly to generate a compensation magnetic field opposite to the direction of the primary current DC bias magnetic field, thereby maintaining the DC bias magnetic flux in the magnetic core at zero.

2. The current transformer according to claim 1, characterized in that, The signal processing module performs I / Q quadrature demodulation based on the second harmonic signal and the local reference signal to obtain in-phase and quadrature components, including: I= LPF[ V 2f (t)*R I ( t )] =2KH m · cos( φ ), Q= LPF[ V 2f (t)*R Q ( t )] =2KH m · sin( φ ), Where I represents the in-phase component; Q represents the quadrature component; and LPF represents low-pass filter. V 2f ( t () is a second harmonic signal; R I (t) and R Q (t) represents the orthogonal local reference signal; K is the system gain coefficient; H m It is a DC magnetic field; φ This represents the phase shift of the second harmonic signal.

3. The current transformer according to claim 1, characterized in that, The signal processing module corrects the in-phase and quadrature components according to the current calibration parameters, and calculates the initial error signal based on the corrected in-phase and quadrature components, including: ， ， ， in, The corrected in-phase component; I represents the corrected quadrature component; Q represents the in-phase component; and I represents the quadrature component. k gain For I / Q gain calibration coefficients; δ θ is the orthogonal error angle; e is the initial error signal.

4. The current transformer according to claim 1, characterized in that, The signal processing module calculates the gain correction coefficient corresponding to the real-time temperature, including: Obtain the gain correction coefficients corresponding to multiple key temperature points calibrated, and calculate the gain correction coefficients corresponding to the real-time temperature using interpolation, piecewise constant lookup table, or polynomial fitting methods.

5. The current transformer according to claim 1, characterized in that, The signal processing module calculates the corrected error signal based on the initial error signal and the gain correction coefficient, including: The initial error signal e is gain-corrected using the gain correction coefficient G(T) to obtain the corrected error signal e. cor =G(T)·e; where T is the real-time temperature.

6. The current transformer according to claim 1, characterized in that, The signal processing module is further configured to: When the primary current I p Satisfy | I p |< γ •FS and duration ≥ T1, and feedback current in T w When the standard deviation within a sliding window is less than ɛ·FS and the time since the last successful calibration is ≥T2, the system enters self-calibration mode to generate new calibration parameters; among which, γ ε is the first preset proportional coefficient; α is the second preset proportional coefficient; FS is the full-scale measurement value; T1 is the first preset time; T2 is the second preset time.

7. The current transformer according to claim 6, characterized in that, The signal processing module generates new calibration parameters in the following manner: Obtain the steady-state feedback current, and apply a compensation current that is equal in magnitude but opposite in direction to the steady-state feedback current to the feedback coil of the magnetic core assembly to achieve residual magnetism compensation and bring the operating point of the magnetic core to zero. Perform bipolar injection, including: injecting a positive test current + I cal After stabilization, sampling was performed to obtain (I) + Q + Inject negative test current - I cal After stabilization, sampling was performed to obtain (I) - Q - ); According to (I) + Q + ) and (I - Q - Calculate the new calibration parameters, including: ， ， in, k gain For I / Q gain calibration coefficients; δ The orthogonal error angle; (I) + Q + Injecting positive test current + I cal The in-phase and quadrature components obtained after stabilization sampling; (I - Q - Injecting negative test current - I cal The in-phase and quadrature components obtained after stabilization sampling; For testing current I The known magnetic field produced by cal.

8. The current transformer according to claim 6, characterized in that, The signal processing module is further configured to: Real-time monitoring during self-calibration | I p | and when it is detected that |I p When |>η·FS and the duration is ≥T3, the self-calibration process is terminated and switched to the redundant phase-sensitive demodulation PSD backup mode. in, I p 1 is the primary current; FS is the full-scale measurement value; η is the preset safety threshold ratio; T3 is the third preset time.

9. A current measurement method based on a closed-loop zero-flux current transformer according to any one of claims 1-8, characterized in that, The method includes: The second harmonic signal is obtained through the magnetic core assembly using the signal detection module; Using the signal generation module, a pair of orthogonal local reference signals are generated; The real-time temperature of the magnetic core assembly is obtained using a temperature sensing module. Using a signal processing module, I / Q quadrature demodulation is performed on the second harmonic signal and the local reference signal to obtain the in-phase component and the quadrature component; the in-phase component and the quadrature component are corrected according to the current calibration parameters, and the initial error signal is calculated based on the corrected in-phase component and the quadrature component; the gain correction coefficient corresponding to the real-time temperature is calculated; and the corrected error signal is calculated based on the initial error signal and the gain correction coefficient. The feedback current generation module receives the corrected error signal, generates a feedback current based on the corrected error signal, and applies the feedback current to the feedback coil of the magnetic core assembly to generate a compensation magnetic field opposite to the direction of the primary current DC bias magnetic field, thereby maintaining the DC bias magnetic flux in the magnetic core at zero. The primary current is calculated based on the feedback current using the signal processing module.

10. The method according to claim 9, characterized in that, Based on the second harmonic signal and the local reference signal, I / Q quadrature demodulation is performed to obtain the in-phase component and the quadrature component, including: I= LPF[ V 2f (t)*R I ( t )] =2KH m · cos( φ ), Q= LPF[ V 2f (t)*R Q ( t )] =2KH m · sin( φ ), Where I represents the in-phase component; Q represents the quadrature component; and LPF represents low-pass filter. V 2f ( t () is a second harmonic signal; R I (t) and R Q (t) represents the orthogonal local reference signal; K is the system gain coefficient; H m It is a DC magnetic field; φ This represents the phase shift of the second harmonic signal.

11. The method according to claim 9, characterized in that, The in-phase and quadrature components are corrected according to the current calibration parameters, and the initial error signal is calculated based on the corrected in-phase and quadrature components, including: ， ， ， in, The corrected in-phase component; I represents the corrected quadrature component; Q represents the in-phase component; and I represents the quadrature component. k gain For I / Q gain calibration coefficients; δ θ is the orthogonal error angle; e is the initial error signal.

12. The method according to claim 9, characterized in that, Calculating the gain correction coefficient corresponding to the real-time temperature includes: Obtain the gain correction coefficients corresponding to multiple key temperature points calibrated, and calculate the gain correction coefficients corresponding to the real-time temperature using interpolation, piecewise constant lookup table, or polynomial fitting methods.

13. The method according to claim 9, characterized in that, The corrected error signal is calculated based on the initial error signal and the gain correction coefficient, including: The initial error signal e is gain-corrected using the gain correction coefficient G(T) to obtain the corrected error signal e. cor =G(T)·e; where T is the real-time temperature.

14. The method according to claim 9, characterized in that, The method further includes: Using the signal processing module, when the primary current... I p Satisfy | I p |< γ •FS and duration ≥ T1, and feedback current in T w When the standard deviation within a sliding window is less than ɛ·FS and the time since the last successful calibration is ≥T2, the system enters self-calibration mode to generate new calibration parameters; among which, γ ε is the first preset proportional coefficient; α is the second preset proportional coefficient; FS is the full-scale measurement value; T1 is the first preset time; T2 is the second preset time.

15. The method according to claim 14, characterized in that, The method generates new calibration parameters in the following manner: Obtain the steady-state feedback current, and apply a compensation current that is equal in magnitude but opposite in direction to the steady-state feedback current to the feedback coil of the magnetic core assembly to achieve residual magnetism compensation and bring the operating point of the magnetic core to zero. Perform bipolar injection, including: injecting a positive test current + I cal After stabilization, sampling was performed to obtain (I) + Q + Inject negative test current - I cal After stabilization, sampling was performed to obtain (I) - Q - ); According to (I) + Q + ) and (I - Q - Calculate the new calibration parameters, including: ， ， in, k gain For I / Q gain calibration coefficients; δ The orthogonal error angle; (I) + Q + Injecting positive test current + I cal The in-phase and quadrature components obtained after stabilization sampling; (I - Q - Injecting negative test current - I cal The in-phase and quadrature components obtained after stabilization sampling; For testing current I cal The known magnetic field generated.

16. The method according to claim 14, characterized in that, The method further includes: Using a signal processing module, real-time monitoring is performed during the self-calibration process. I p | and when it is detected that |I p When |>η·FS and the duration is ≥T3, the self-calibration process is terminated, and the system switches to the redundant phase-sensitive demodulation PSD backup mode; where, I p 1 is the primary current; FS is the full-scale measurement value; η is the preset safety threshold ratio; T3 is the third preset time.

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