A demagnetization control method and device for an online clamp meter with auxiliary winding

Abstract

The application discloses a demagnetization control method and device for an online clamp meter with an auxiliary winding, and the method comprises the following steps: switching a pressurizing clamp from a pressurizing function to a measuring function; and applying an alternating demagnetization excitation with a constant amplitude and an adjustable frequency through the auxiliary winding. The measuring clamp and the pressurizing clamp synchronously output a measuring voltage signal, a control unit performs time normalization processing on each channel signal according to a current demagnetization excitation period, and a demagnetization state index J m and J p is constructed. The demagnetization index is composed of a waveform distortion index constructed based on a fitting residual of a fundamental wave and an odd harmonic energy ratio. The control unit takes a larger one of J m and J p as a demagnetization control index and adjusts a subsequent demagnetization excitation frequency according to the index until the indexes both satisfy demagnetization setting conditions, and then the demagnetization is stopped and the pressurizing clamp is restored to the pressurizing function. The application can simultaneously consider the demagnetization consistency of the measuring clamp core and the pressurizing clamp core in an online installation scene, and improves the stability and the measuring reliability of the online clamp meter in long-term operation.

Description

Technical Field

[0001] This invention relates to the field of online clamp meter magnetic state control and demagnetization control technology, specifically to a demagnetization control method and apparatus for online clamp meters with auxiliary windings. Background Technology

[0002] In grounding loop detection, condition monitoring, and related engineering testing scenarios, clamp-on devices are widely used in field measurements due to their advantages such as no need for wire disconnection, convenient installation, and strong adaptability to the field environment. For some scenarios requiring long-term operation, periodic testing, or continuous condition monitoring, clamp-on devices are usually installed online or in a routine manner to reduce the workload of repeated disassembly and assembly, and to improve the continuity and convenience of field use.

[0003] However, during long-term operation, the iron core of an online clamp-on device is susceptible to the effects of long-term alternating magnetic fields, repeated measurement excitations, inrush currents, complex electromagnetic environments, and asymmetrical operating conditions, gradually accumulating residual magnetism. Once residual magnetism exists in the iron core, its magnetization operating point will deviate from the ideal symmetrical state, leading to problems such as increased distortion of the response waveform, enhanced odd harmonic components, decreased repeatability, and deterioration of measurement accuracy during subsequent operation, thus affecting the long-term operational stability and measurement reliability of the device.

[0004] In a type of clamp-on device designed for online applications, auxiliary windings can be incorporated to achieve functions such as pressurization, auxiliary excitation, signal injection, or extended testing, forming a multi-clamp collaborative structure including measuring clamps and pressurizing clamps. For this type of device, because the measuring clamps and pressurizing clamps perform different functions, their core magnetization histories are typically inconsistent. In particular, the pressurizing clamp often repeatedly applies pressure or measures voltage during long-term operation, while the measuring clamp primarily handles signal acquisition; therefore, the remanent magnetization states of their cores may differ significantly.

[0005] Existing demagnetization methods typically focus on single magnetic circuits or apply alternating excitation in an open-loop manner. These approaches struggle to ensure consistent demagnetization across multiple clamp cores simultaneously. If demagnetization completion is determined solely by feedback from a single clamp, one clamp may have achieved good demagnetization while another retains significant residual magnetism. Furthermore, some methods rely on additional excitation current detection paths, hindering integration with online clamping devices; the demagnetization completion conditions are also unclear, making it difficult to develop automated control processes suitable for online installation scenarios.

[0006] Therefore, it is necessary to propose a demagnetization control method and device suitable for online clamping devices with auxiliary windings, which can simultaneously ensure the demagnetization consistency of the corresponding iron cores of the measuring clamp and the pressure clamp without disassembling the device, and realize automatic control of the demagnetization process and restoration of the working mode. Summary of the Invention

[0007] 1. The technical problem to be solved:

[0008] To address the aforementioned technical problems, this invention provides a demagnetization control method and apparatus for online clamp meters with auxiliary windings, solving the problems in the prior art of simultaneously ensuring the consistency of demagnetization of the cores of the measuring clamp and the pressure clamp, the complexity of online implementation, and the insufficient degree of automation in the demagnetization process.

[0009] 2. Technical Solution:

[0010] A demagnetization control method for an online clamp meter with an auxiliary winding, characterized in that it includes:

[0011] Step 1: Based on the preset demagnetization trigger conditions, the online clamp meter device enters the demagnetization mode; the online clamp meter device includes a pressure clamp, a measuring clamp, an auxiliary winding, and a control unit;

[0012] Step 2: The pressure clamp switches from the pressure function to the measurement function after a preset stabilization time; the pressure clamp performs the pressure function in the normal measurement mode of the device, applying the measurement excitation voltage according to the corresponding measurement circuit of the control unit; in the demagnetization mode of the device, it performs the measurement function, which is exactly the same as the measurement clamp function, providing the control unit with the voltage signal across the sampled coil.

[0013] Step 3: Apply an alternating demagnetizing excitation with constant amplitude and adjustable frequency to the magnetic circuit corresponding to the online clamp meter through the auxiliary winding;

[0014] Step 4: The measuring clamp and the pressure clamp after switching to the measuring function each output a measuring voltage signal to the control unit;

[0015] Step 5: The control unit performs time normalization processing on the received measurement voltage signal according to the current demagnetization excitation cycle, and calculates the measurement clamp demagnetization state index J. m and the demagnetization status index J of the pressure clamp p ;

[0016] Step Six: The control unit selects the demagnetization status index J of the measuring clamp. m and the demagnetization status index J of the pressure clamp p The index with the larger median value is used as the demagnetization control index J. ctrl The frequency of subsequent alternating demagnetization excitation is adjusted according to the selected demagnetization control index.

[0017] Step 7: Preset demagnetization settings. When the demagnetization control index J... ctrl When the preset demagnetization conditions are met, the demagnetization excitation stops, and the pressure clamp is switched back to the pressure function.

[0018] Furthermore, the preset demagnetization triggering conditions are one or more of the following: periodic maintenance, self-test triggering, periodic demagnetization after long-term operation, recovery processing after experiencing impact conditions, and demagnetization triggering after detecting abnormal waveforms.

[0019] Furthermore, the measured voltage signal is an induced voltage signal related to the rate of change of magnetic flux of the corresponding clamp core.

[0020] Furthermore, in step five, the control unit performs time normalization processing on the received measured voltage signal according to the current demagnetization excitation cycle as follows: For the k-th demagnetization excitation cycle, let the cycle start time be t. k The period length is T k Define the normalized time variable for:

[0021] (1);

[0022] The measured voltage signal within this period is mapped to a normalized signal. for:

[0023] (2).

[0024] Furthermore, the demagnetization status index J of the measuring clamp m and the demagnetization status index J of the pressure clamp p Collectively referred to as demagnetization state index J; the demagnetization state index J is expressed as:

[0025] (3);

[0026] In the above formula, D is the waveform distortion index, which is used to characterize the degree of deviation of the current measured waveform from the normalized fundamental frequency component; E3, E5, and E7 are the third, fifth, and seventh harmonic amplitudes corresponding to the current demagnetization excitation fundamental frequency; E1 is the demagnetization excitation fundamental frequency amplitude; and w1 and w2 are weighting coefficients. It is a tiny positive number;

[0027] Among them, the waveform distortion index D is defined using the fundamental wave fitting residual type:

[0028] (4);

[0029] In the above formula, The measured voltage signal after time normalization for the current demagnetization cycle; The fundamental component of the signal is fitted as follows:

[0030] (5);

[0031] Among them, a1 and b1 are connected through... The fundamental frequency is obtained by orthogonal projection or least squares fitting, as shown in the following formula:

[0032] (6).

[0033] Furthermore, step six specifically includes:

[0034] S61: The demagnetization control index is defined as follows:

[0035] (7);

[0036] In the above formula, J ctrl For demagnetization control indicators;

[0037] S62: Preset lower limit of demagnetization excitation frequency f min upper frequency limit f max and the adjustment scale parameter is J s ; Obtain the target frequency corresponding to the kth demagnetization cycle. for:

[0038] (8);

[0039] In the above formula, J ctrl, k This is the demagnetization control index obtained in the k-th demagnetization cycle; sat(x,0,1) represents limiting the variable x in the interval from 0 to 1.

[0040] The lower limit of the demagnetization excitation frequency f min To ensure that the magnetic state of the iron core can be fully reversed in the early stage of demagnetization, it is determined based on the amplitude of the excitation voltage of the auxiliary winding, the number of turns of the auxiliary winding, the effective cross-sectional area of ​​the iron core and the upper limit of the allowable magnetic flux swing, and is checked in conjunction with the upper limit of the auxiliary winding current and the heat generation constraint.

[0041] The upper limit of the demagnetization excitation frequency f max To ensure that the single-cycle action is small enough in the later stage of demagnetization to promote smooth convergence of the magnetic state, while still maintaining an effective ability to adjust the core state, it is determined based on the minimum effective magnetic flux swing, the identifiability of the dual-channel demagnetization state index, and the system's sampling and driving capabilities.

[0042] The adjustment scale parameter J s This is a preset positive value used to characterize the mapping scale between the demagnetization control index and the frequency adjustment range. It is obtained through experimental calibration, empirical tuning, or factory parameter setting.

[0043] Furthermore, in step seven, the preset demagnetization setting conditions include: J ctrl Less than the preset demagnetization control threshold, J m Within a consecutive preset number of cycles, its value is lower than the corresponding preset threshold, J pWithin a consecutive preset number of cycles, its value is lower than the corresponding preset threshold, and the adjacent cycle J m The change is less than the corresponding preset value, and the adjacent period J p The change is less than the corresponding preset value; the demagnetization excitation stops when one or more of the preset demagnetization settings are met.

[0044] A demagnetizing device for an in-line clamp meter with an auxiliary winding, comprising:

[0045] The pressure clamp is used to perform the pressure function under normal operating conditions and to switch to the measurement function in demagnetization mode.

[0046] Measuring clamp, used to output a measured voltage signal;

[0047] Auxiliary winding, used to apply alternating demagnetizing excitation;

[0048] The mode switching unit is used to switch between the pressure clamp function and the measurement function;

[0049] The signal acquisition unit is used to acquire the measurement voltage signal output by the measuring clamp and the pressure clamp;

[0050] The control unit is used to perform time normalization processing on the measured voltage signal, calculate the corresponding demagnetization state index, and adjust the demagnetization excitation frequency and control the end of demagnetization based on the feedback of the larger index.

[0051] The control unit is also used to automatically restore the pressure clamp to the pressure function after demagnetization is completed.

[0052] 3. Beneficial effects:

[0053] (1) The present invention provides a demagnetizing device for online clamp meters with auxiliary windings, which can simultaneously ensure the demagnetizing consistency of the two iron cores of the pressure clamp and the measuring clamp, avoiding the problem that only one clamp body is fully demagnetized while the other clamp body has residual magnetism; at the same time, the demagnetizing process can be completed without disassembling the online clamp meter, which is suitable for long-term online installation scenarios.

[0054] (2) In the demagnetization control method for online clamp meters with auxiliary windings provided by the present invention, the use of time normalization processing and dimensionless index construction method is beneficial to realize unified comparison between different cycles and different clamps in the frequency conversion demagnetization scenario; by using the larger demagnetization state index as the control basis, the side with poor demagnetization can be constrained first, thereby improving the overall demagnetization reliability. Attached Figure Description

[0055] Figure 1 This is an overall structural diagram of a demagnetizing device for an online clamp meter with an auxiliary winding according to the present invention;

[0056] Figure 2 This is a schematic diagram of an embodiment of the dual clamps and auxiliary winding involved in the present invention;

[0057] Figure 3 This is a schematic diagram of the demagnetization excitation waveform and the corresponding frequencies for each demagnetization cycle, as shown in the embodiment.

[0058] Figure 4 Normalized waveforms of different frequency signals in the example;

[0059] Figure 5 Normalized U in the remanent magnetization state of the embodiment m Waveform diagram;

[0060] Figure 6 Normalized U after demagnetization in the example m Waveform diagram;

[0061] Figure 7 This is a flowchart illustrating the demagnetization control process for an online clamp meter with auxiliary windings according to the present invention. Detailed Implementation

[0062] The present invention will now be described in detail with reference to the accompanying drawings.

[0063] As attached Figure 7 As shown, a demagnetization control method for an online clamp meter with an auxiliary winding is characterized by comprising:

[0064] Step 1: Based on the preset demagnetization trigger conditions, the online clamp meter device enters the demagnetization mode; the online clamp meter device includes a pressure clamp, a measuring clamp, an auxiliary winding, and a control unit;

[0065] Step 2: The pressure clamp switches from the pressure function to the measurement function after a preset stabilization time; the pressure clamp performs the pressure function in the normal measurement mode of the device, applying the measurement excitation voltage according to the corresponding measurement circuit of the control unit; in the demagnetization mode of the device, it performs the measurement function, which is exactly the same as the measurement clamp function, providing the control unit with the voltage signal across the sampled coil.

[0066] Step 3: Apply an alternating demagnetizing excitation with constant amplitude and adjustable frequency to the magnetic circuit corresponding to the online clamp meter through the auxiliary winding;

[0067] Step 4: The measuring clamp and the pressure clamp after switching to the measuring function each output a measuring voltage signal to the control unit;

[0068] Step 5: The control unit performs time normalization processing on the received measurement voltage signal according to the current demagnetization excitation cycle, and calculates the measurement clamp demagnetization state index J. m and the demagnetization status index J of the pressure clamp p ;

[0069] Step Six: The control unit selects the demagnetization status index J of the measuring clamp. m and the demagnetization status index J of the pressure clamp p The index with the larger median value is used as the demagnetization control index J. ctrl The frequency of subsequent alternating demagnetization excitation is adjusted according to the selected demagnetization control index.

[0070] Step 7: Preset demagnetization settings. When the demagnetization control index J... ctrl When the preset demagnetization conditions are met, the demagnetization excitation stops, and the pressure clamp is switched back to the pressure function.

[0071] Furthermore, the preset demagnetization triggering conditions are one or more of the following: periodic maintenance, self-test triggering, periodic demagnetization after long-term operation, recovery processing after experiencing impact conditions, and demagnetization triggering after detecting abnormal waveforms.

[0072] Furthermore, the measured voltage signal is an induced voltage signal related to the rate of change of magnetic flux of the corresponding clamp core.

[0073] Furthermore, in step five, the control unit performs time normalization processing on the received measured voltage signal according to the current demagnetization excitation cycle as follows: For the k-th demagnetization excitation cycle, let the cycle start time be t. k The period length is T k Define the normalized time variable for:

[0074] (1);

[0075] The measured voltage signal within this period is mapped to a normalized signal. for:

[0076] (2).

[0077] Furthermore, the demagnetization status index J of the measuring clamp m and the demagnetization status index J of the pressure clamp p Collectively referred to as demagnetization state index J; the demagnetization state index J is expressed as:

[0078] (3);

[0079] In the above formula, D is the waveform distortion index, which is used to characterize the degree of deviation of the current measured waveform from the normalized fundamental frequency component; E3, E5, and E7 are the third, fifth, and seventh harmonic amplitudes corresponding to the current demagnetization excitation fundamental frequency; E1 is the demagnetization excitation fundamental frequency amplitude; and w1 and w2 are weighting coefficients. It is a tiny positive number;

[0080] Among them, the waveform distortion index D is defined using the fundamental wave fitting residual type:

[0081] (4);

[0082] In the above formula, The measured voltage signal after time normalization for the current demagnetization cycle; The fundamental component of the signal is fitted as follows:

[0083] (5);

[0084] Among them, a1 and b1 are connected through... The fundamental frequency is obtained by orthogonal projection or least squares fitting, as shown in the following formula:

[0085] (6).

[0086] Furthermore, step six specifically includes:

[0087] S61: The demagnetization control index is defined as follows:

[0088] (7);

[0089] In the above formula, J ctrl For demagnetization control indicators;

[0090] S62: Preset lower limit of demagnetization excitation frequency f min upper frequency limit f max and the adjustment scale parameter is J s ; Obtain the target frequency corresponding to the kth demagnetization cycle. for:

[0091] (8);

[0092] In the above formula, J ctrl, k This is the demagnetization control index obtained in the k-th demagnetization cycle; sat(x,0,1) represents limiting the variable x in the interval from 0 to 1.

[0093] The lower limit of the demagnetization excitation frequency f min To ensure that the magnetic state of the iron core can be fully reversed in the early stage of demagnetization, it is determined based on the amplitude of the excitation voltage of the auxiliary winding, the number of turns of the auxiliary winding, the effective cross-sectional area of ​​the iron core and the upper limit of the allowable magnetic flux swing, and is checked in conjunction with the upper limit of the auxiliary winding current and the heat generation constraint.

[0094] The upper limit of the demagnetization excitation frequency f maxTo ensure that the single-cycle action is small enough in the later stage of demagnetization to promote smooth convergence of the magnetic state, while still maintaining an effective ability to adjust the core state, it is determined based on the minimum effective magnetic flux swing, the identifiability of the dual-channel demagnetization state index, and the system's sampling and driving capabilities.

[0095] The adjustment scale parameter J s This is a preset positive value used to characterize the mapping scale between the demagnetization control index and the frequency adjustment range. It is obtained through experimental calibration, empirical tuning, or factory parameter setting.

[0096] Furthermore, in step seven, the preset demagnetization setting conditions include: J ctrl Less than the preset demagnetization control threshold, J m Within a consecutive preset number of cycles, its value is lower than the corresponding preset threshold, J p Within a consecutive preset number of cycles, its value is lower than the corresponding preset threshold, and the adjacent cycle J m The change is less than the corresponding preset value, and the adjacent period J p The change is less than the corresponding preset value; the demagnetization excitation stops when one or more of the preset demagnetization settings are met.

[0097] The demagnetization setting conditions are typically determined by applying different degrees of residual magnetism to the measuring clamp, and obtaining the J value without affecting the measurement results based on the required measurement accuracy. m and J p And select the smaller value as J ctrl Threshold, J measured after actual demagnetization ctrl If the value does not exceed this threshold, the demagnetization setting condition is considered met. The threshold J is... ctrl J was obtained through laboratory demagnetization calibration of the device itself, and different devices... ctrl They are independent of each other.

[0098] A demagnetizing device for an in-line clamp meter with an auxiliary winding, comprising:

[0099] The pressure clamp is used to perform the pressure function under normal operating conditions and to switch to the measurement function in demagnetization mode.

[0100] Measuring clamp, used to output a measured voltage signal;

[0101] Auxiliary winding, used to apply alternating demagnetizing excitation;

[0102] The mode switching unit is used to switch between the pressure clamp function and the measurement function;

[0103] The signal acquisition unit is used to acquire the measurement voltage signal output by the measuring clamp and the pressure clamp;

[0104] The control unit is used to perform time normalization processing on the measured voltage signal, calculate the corresponding demagnetization state index, and adjust the demagnetization excitation frequency and control the end of demagnetization based on the feedback of the larger index.

[0105] The control unit is also used to automatically restore the pressure clamp to the pressure function after demagnetization is completed.

[0106] Example 1:

[0107] like Figure 1 The diagram shown is an overall structural diagram of a demagnetizing device for an online clamp meter with an auxiliary winding according to the present invention. The device includes a pressure clamp, a measuring clamp, an auxiliary winding, a mode switching unit, a signal acquisition unit, and a control unit. In this embodiment, the dual clamps and the auxiliary winding adopt the method shown in the attached diagram. Figure 2 The typical structure of the wire clamp meter shown has an auxiliary winding that is connected to both the pressure clamp and the measuring clamp via a chain. It should be noted that... Figure 2 Only an example of an in-line clamp with an auxiliary winding is given, and the open structure of the double clamp is not shown in the diagram.

[0108] The clamping device is used to apply pressure in normal operation and switches to measurement mode in demagnetization mode. The measuring clamp is used to output a measurement voltage signal. The auxiliary winding is used to apply alternating demagnetization excitation. The mode switching unit is used to switch between the pressure application function and the measurement function of the clamping device. The signal acquisition unit is used to acquire the measurement voltage signals output by the measuring clamp and the clamping device. The control unit is used to perform time normalization processing on the measurement voltage signal, calculate the corresponding demagnetization state index, and adjust the demagnetization excitation frequency and control the end of demagnetization based on the feedback of the larger index.

[0109] Example 2:

[0110] As attached Figure 7 The diagram shows the specific process for implementing online demagnetization control using the present invention.

[0111] The online clamp meter enters demagnetization mode when preset demagnetization trigger conditions are met. These conditions may include periodic maintenance, self-test triggering, periodic demagnetization after long-term operation, recovery processing after experiencing impact conditions, or demagnetization triggering upon detecting abnormal waveforms. Upon entering demagnetization mode, the clamping clamp is first switched from pressure application to measurement function, and a preset stabilization time is waited for to minimize the impact of switching transients on subsequent sampling and judgment.

[0112] After the clamping clamp enters the measurement function, it applies an alternating demagnetizing excitation with constant amplitude and adjustable frequency to the corresponding magnetic circuit of the online clamp meter through the auxiliary winding. For ease of MCU implementation, this invention preferably uses a segmented frequency update method based on the demagnetizing cycle. That is, during the kth demagnetizing cycle, the frequency remains a constant value f. k ,but:

[0113] (9);

[0114] Among them, T k The length of the kth demagnetization cycle.

[0115] Let the amplitude of the auxiliary winding demagnetization excitation voltage be U. d Then, during the kth demagnetization cycle, the frequency-converted alternating voltage u applied to the auxiliary winding is... a (t) can be uniformly represented as:

[0116] (10);

[0117] Where the starting time is t k f k This is the demagnetization excitation frequency; The initial phase is preferably set to 0. It should be noted that this invention does not strictly limit the demagnetizing excitation to a sine wave or a square wave, as long as it meets the basic requirements of constant amplitude, adjustable frequency, and alternating application. This embodiment uses a sine wave as an example. (Appendix) Figure 3 The demagnetizing excitation waveform in the form of a sine wave in this embodiment is shown in Figure (a), and the corresponding frequency diagram for each demagnetizing cycle is shown in Figure (b).

[0118] Due to the demagnetization excitation amplitude U d To maintain a constant frequency, the main method for regulating the demagnetization process is to change the demagnetization excitation frequency f. k At lower frequencies, the single-cycle duration is longer and the single-cycle flux swing is larger, which is beneficial for sufficient reversal in the early stages of demagnetization; at higher frequencies, the single-cycle duration is shorter and the single-cycle flux swing is smaller, which is beneficial for smooth convergence in the later stages of demagnetization. For an auxiliary winding with N turns... a The corresponding effective cross-sectional area of ​​the iron core is A. e In the case of the kth demagnetization cycle, the equivalent flux swing of a single half-cycle is approximately:

[0119] (11);

[0120] The corresponding equivalent magnetic flux density swing is approximately:

[0121] (12);

[0122] As shown in equation (12), the lower the frequency, the larger the swing amplitude of the equivalent magnetic induction intensity in a single half-cycle; the higher the frequency, the smaller the swing amplitude in a single half-cycle. Therefore, this invention adjusts f... k To adjust the rate of magnetic state contraction during demagnetization.

[0123] Lower limit of demagnetization excitation frequency f minTo ensure that the magnetic state of the iron core can be fully reversed in the early stage of demagnetization, its setting should take into account the amplitude of the auxiliary winding excitation voltage, the number of turns of the auxiliary winding, the effective cross-sectional area of ​​the iron core, the upper limit of the allowable magnetic flux swing, the upper limit of the auxiliary winding current, and the heat generation constraint.

[0124] upper limit of demagnetization excitation frequency f max To ensure that the single-cycle action is small enough in the later stage of demagnetization to promote smooth convergence of the magnetic state, while still maintaining effective adjustment capability of the core state, its setting should comprehensively consider the minimum effective magnetic flux swing, the identifiability of the dual-channel demagnetization state index, and the system's sampling and driving capability.

[0125] In a preferred estimation method, the lower limit frequency and the upper limit frequency can be approximated as follows:

[0126] (13);

[0127] in, This is the initial flux swing required during the initial stage of demagnetization; This is the minimum flux swing that can maintain effective regulation capability even in the later stages of demagnetization; and it has .

[0128] Under demagnetizing excitation, the measuring clamp outputs a measuring voltage signal. The clamping clamp outputs a measurement voltage signal after switching to measurement function. The aforementioned signals are all induced voltage signals related to the rate of change of magnetic flux of their respective clamp cores. Since the demagnetization process is controlled by frequency conversion, the physical duration corresponding to different demagnetization cycles is different. Therefore, this invention uses the current demagnetization cycle as the analysis benchmark and performs time normalization processing on the dual-channel signals as shown in formula (1).

[0129] For the measuring clamp channel and the pressure clamp channel, the normalized result can be written as:

[0130] (14);

[0131] In the above formula, These represent the normalized results for the measuring clamp channel and the pressure clamp channel, respectively.

[0132] At this point, the single-cycle signal within any demagnetization cycle is uniformly mapped to the normalized time interval [0, 1], facilitating the subsequent extraction of the fundamental fitting component and odd harmonic amplitude according to the "current cycle fundamental wave," such as... Figure 4 As shown. Figure 4 In the diagram, the coordinate system in the first row represents the result before normalization, and the coordinate system in the second row represents the result after normalization. Normalization does not change the value of the vertical axis; it only maps the horizontal axis of each single-cycle signal to the same interval.

[0133] For any channel, the present invention defines the demagnetization state index J as obtained as shown in equations (3) to (6) above. According to equation (4), the greater the deviation between the current normalized waveform and its fundamental fitting component, the larger D is, indicating that the current magnetic state deviates more from the ideal symmetrical demagnetization state.

[0134] For normalized signals The nth harmonic coefficient can be expressed as:

[0135] (15);

[0136] Then the amplitude E of the nth harmonic n for:

[0137] (16);

[0138] This yields the current demagnetization excitation fundamental frequency amplitude E1 and the amplitudes of the third, fifth, and seventh harmonics E3, E5, and E7.

[0139] The demagnetization status indicators for the two channels of the measuring clamp and the pressure clamp are as follows:

[0140] (17);

[0141] Further define the demagnetization control index as follows:

[0142] (7);

[0143] The meaning of adopting formula (7) is: to prioritize the side with the worse current demagnetization state as the control basis, so as to ensure that both the measuring clamp and the pressure clamp iron core eventually reach a better demagnetization state. Figure 5 The normalized U in the state with remanence is given. m The waveform, due to the residual magnetism in the iron core, U m The waveform shows obvious distortion, at which point J m The calculated value is 0.2567. Figure 6 The normalized U after demagnetization is given. m Waveform, corresponding J m The calculated value is only 0.0408.

[0144] The control unit obtains the demagnetization control index based on the k-th demagnetization cycle. Calculate the target frequency for the next cycle. Preset the lower limit f of the demagnetization excitation frequency. min upper frequency limit f max The adjustment scale parameter is J. s The target frequency corresponding to the kth demagnetization cycle is defined as follows:

[0145] (8);

[0146] Here, sat(x,0,1) represents limiting the variable x within the interval from 0 to 1. When J ctrl, k When it is large, the target frequency Closer to f min This helps ensure sufficient reversal during the initial stage of demagnetization; when J ctrl, k When gradually decreasing, the target frequency Gradually increase and approach f max This helps reduce the single-cycle action and promotes smooth convergence in the later stages of demagnetization.

[0147] Demagnetization is considered complete when any of the following conditions are met: J ctrl Less than the preset demagnetization control threshold, J m Within a consecutive preset number of cycles, its value is lower than the corresponding preset threshold, J p Within a consecutive preset number of cycles, its value is lower than the corresponding preset threshold, and the adjacent cycle J m The change is less than the corresponding preset value, and the adjacent period J p The change is less than the corresponding preset value.

[0148] The above-mentioned judgment conditions can reduce misjudgments caused by single-cycle fluctuations and improve the stability of the demagnetization end judgment.

[0149] After demagnetization is complete, the control unit stops the auxiliary winding demagnetization excitation and, through the mode switching unit, restores the pressure clamp from measurement function to pressure function, allowing the device to return to normal operation. This forms a complete control closed loop. The complete demagnetization operation process is as follows: Figure 7 As shown.

[0150] It should be noted that the auxiliary winding in this invention can be implemented using the auxiliary excitation structure in an existing online clamp meter with an auxiliary winding. The core of this invention lies in achieving consistent demagnetization control of the dual iron cores based on the auxiliary winding, without limiting the specific structural form of the auxiliary winding body.

[0151] Although the present invention has been disclosed above with reference to preferred embodiments, these are not intended to limit the invention. Any person skilled in the art can make various changes or modifications without departing from the spirit and scope of the invention. Therefore, the scope of protection of the present invention should be defined by the scope of the claims of this application.

Claims

1. A demagnetization control method for an online clamp meter with an auxiliary winding, characterized in that: include: Step 1: Based on the preset demagnetization trigger conditions, the online clamp meter device enters the demagnetization mode; The online clamp meter device includes a pressure clamp, a measuring clamp, an auxiliary winding, and a control unit; Step 2: The pressure clamp switches from the pressure function to the measurement function after a preset stabilization time; the pressure clamp performs the pressure function in the normal measurement mode of the device, applying the measurement excitation voltage according to the corresponding measurement circuit of the control unit; in the demagnetization mode of the device, it performs the measurement function, which is exactly the same as the measurement clamp function, providing the control unit with the voltage signal across the sampled coil. Step 3: Apply an alternating demagnetizing excitation with constant amplitude and adjustable frequency to the magnetic circuit corresponding to the online clamp meter through the auxiliary winding; Step 4: The measuring clamp and the pressure clamp after switching to the measuring function each output a measuring voltage signal to the control unit; Step 5: The control unit performs time normalization processing on the received measurement voltage signal according to the current demagnetization excitation cycle, and calculates the measurement clamp demagnetization state index J. m and the demagnetization status index J of the pressure clamp p ; Step Six: The control unit selects the demagnetization status index J of the measuring clamp. m and the demagnetization status index J of the pressure clamp p The index with the larger median value is used as the demagnetization control index J. ctrl The frequency of subsequent alternating demagnetization excitation is adjusted according to the selected demagnetization control index. Step 7: Preset demagnetization settings. When the demagnetization control index J... ctrl When the preset demagnetization conditions are met, the demagnetization excitation stops, and the pressure clamp is switched back to the pressure function.

2. The demagnetization control method for an online clamp meter with auxiliary winding according to claim 1, characterized in that: The preset demagnetization triggering conditions are one or more of the following: periodic maintenance, self-test triggering, periodic demagnetization after long-term operation, recovery processing after experiencing impact conditions, and demagnetization triggering after detecting abnormal waveforms.

3. The demagnetization control method for an online clamp meter with auxiliary winding according to claim 1, characterized in that: The measured voltage signal is an induced voltage signal that is related to the rate of change of magnetic flux of the corresponding clamp core.

4. The demagnetization control method for an online clamp meter with auxiliary winding according to claim 1, characterized in that: In step five, the control unit performs time normalization processing on the received measured voltage signal according to the current demagnetization excitation cycle: for the k-th demagnetization excitation cycle, let the cycle start time be t. k The period length is T k Define the normalized time variable for: (1)； The measured voltage signal within this period is mapped to a normalized signal. for: (2)。 5. The demagnetization control method for an online clamp meter with auxiliary winding according to claim 4, characterized in that: The demagnetization status index J of the measuring clamp m and the demagnetization status index J of the pressure clamp p Collectively referred to as demagnetization state index J; the demagnetization state index J is expressed as: (3)； In the above formula, D is the waveform distortion index, which is used to characterize the degree of deviation of the current measured waveform from the normalized fundamental frequency component; E3, E5, and E7 are the third, fifth, and seventh harmonic amplitudes corresponding to the current demagnetization excitation fundamental frequency; E1 is the demagnetization excitation fundamental frequency amplitude; and w1 and w2 are weighting coefficients. It is a tiny positive number; Among them, the waveform distortion index D is defined using the fundamental wave fitting residual type: (4)； In the above formula, The measured voltage signal after time normalization for the current demagnetization cycle; The fundamental component of the signal is fitted as follows: (5)； Among them, a1 and b1 are connected through... The fundamental frequency is obtained by orthogonal projection or least squares fitting, as shown in the following formula: (6)。 6. The demagnetization control method for an online clamp meter with auxiliary winding according to claim 5, characterized in that: Step six specifically includes: S61: The demagnetization control index is defined as follows: (7)； In the above formula, J ctrl For demagnetization control indicators; S62: Preset lower limit of demagnetization excitation frequency f min upper frequency limit f max and the adjustment scale parameter is J s ; Obtain the target frequency corresponding to the kth demagnetization cycle. for: (8)； In the above formula, J ctrl, k This is the demagnetization control index obtained in the k-th demagnetization cycle; sat(x,0,1) represents limiting the variable x in the interval from 0 to 1. The lower limit of the demagnetization excitation frequency f min To ensure that the magnetic state of the iron core can be fully reversed in the early stage of demagnetization, it is determined based on the amplitude of the excitation voltage of the auxiliary winding, the number of turns of the auxiliary winding, the effective cross-sectional area of ​​the iron core and the upper limit of the allowable magnetic flux swing, and is checked in conjunction with the upper limit of the auxiliary winding current and the heat generation constraint. The upper limit of the demagnetization excitation frequency f max To ensure that the single-cycle action is small enough in the later stage of demagnetization to promote smooth convergence of the magnetic state, while still maintaining an effective ability to adjust the core state, it is determined based on the minimum effective magnetic flux swing, the identifiability of the dual-channel demagnetization state index, and the system's sampling and driving capabilities. The adjustment scale parameter J s This is a preset positive value used to characterize the mapping scale between the demagnetization control index and the frequency adjustment range. It is obtained through experimental calibration, empirical tuning, or factory parameter setting.

7. A demagnetization control method for an online clamp meter with an auxiliary winding according to claim 6, characterized in that: In step seven, the preset demagnetization settings include: J ctrl Less than the preset demagnetization control threshold, J m Within a consecutive preset number of cycles, its value is lower than the corresponding preset threshold, J p Within a consecutive preset number of cycles, its value is lower than the corresponding preset threshold, and the adjacent cycle J m The change is less than the corresponding preset value, and the adjacent period J p The change is less than the corresponding preset value; the demagnetization excitation stops when one or more of the preset demagnetization settings are met.

8. A demagnetizing device for an online clamp meter with an auxiliary winding, wherein demagnetization is achieved using the demagnetizing control method as described in any one of claims 1-7, characterized in that: include: The pressure clamp is used to perform the pressure function under normal operating conditions and to switch to the measurement function in demagnetization mode. Measuring clamp, used to output a measured voltage signal; Auxiliary winding, used to apply alternating demagnetizing excitation; The mode switching unit is used to switch between the pressure clamp function and the measurement function; The signal acquisition unit is used to acquire the measurement voltage signal output by the measuring clamp and the pressure clamp; The control unit is used to perform time normalization processing on the measured voltage signal, calculate the corresponding demagnetization state index, and adjust the demagnetization excitation frequency and control the end of demagnetization based on the feedback of the larger index. The control unit is also used to automatically restore the pressure clamp to the pressure function after demagnetization is completed.

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