Method for Weakening Residual Magnetism of Magnetic Core at One Time

Abstract

The present invention is a method for weakening the residual magnetism of a magnetic core at one time. Based on the magnetic properties and size structure of the magnetic core material, a reverse DC voltage excitation amplitude U for weakening different residual magnetism of the magnetic core is determined by numerical simulation calculation. m Measure the actual residual magnetism size and direction in the core of the magnetic core material to be tested, substitute the residual magnetism size into the empirical formula, and obtain the DC voltage amplitude U that weakens the residual magnetism of the core under the current residual magnetism size. m Finally, the direction of the DC voltage to be applied is determined according to the direction of the residual magnetism. The magnetic flux generated by the winding on one side of the core is opposite to the residual magnetism and has an amplitude of U m The demagnetization process ends when the current in the winding is 0 after the excitation is removed, and the residual magnetism of the core is weakened once. In the process of weakening the residual magnetism, it is only necessary to apply a DC voltage excitation to the winding once to weaken the residual magnetism of the core once.

Description

Technical Field

[0001] The present invention relates to the reduction of residual magnetism of magnetic materials, and particularly to a method for reducing the residual magnetism of a closed magnetic circuit core at one time. Background Art

[0002] Magnetic materials are important components of many power equipment. Due to their inherent hysteresis characteristics, a certain amount of residual magnetism usually remains in the core after maintenance tests or operation tripping. After a power equipment with a core structure is re-energized, under the action of a certain power supply voltage, the existence of residual magnetism will accelerate the half-cycle saturation of the core and easily generate an excitation inrush current with a very high amplitude. The excitation inrush current may cause adverse effects such as misoperation of relay protection, voltage drop of the power grid, and damage to sensitive power electronic devices. To effectively reduce the harm caused by residual magnetism, it is necessary to completely demagnetize the core before the power equipment is energized for operation.

[0003] The demagnetization methods for the core are mainly divided into the following three types: (1) Thermal demagnetization. The magnet is heated above the Curie temperature to disrupt the consistency of the magnetic domain arrangement of the magnet, so that the magnet does not show magnetism externally. However, it is difficult to achieve on-site for power equipment with a closed magnetic circuit structure. (2) AC demagnetization method. An industrial frequency voltage is applied to one side winding of the core until the core is saturated, and then the voltage amplitude is gradually reduced until the current decreases to zero. Since the rated voltage of large power equipment is relatively high, specific implementation requires a large-capacity power supply, which has certain potential safety hazards and takes a long time, and is not conducive to on-site application. (3) DC demagnetization method. Positive and negative DC currents are passed through one side winding of the core, and the current value at the reverse moment is gradually reduced in proportion to narrow the hysteresis loop of the core and achieve the purpose of eliminating residual magnetism. This method can reduce the capacity of the test power supply, but still requires a long demagnetization time.

[0004] At present, the magnitude and direction of the residual magnetism in the core can be measured. Some scholars have proposed applying an external excitation to the core and determining the magnitude and direction of the residual magnetism in the core through measurable parameters. However, a method for quickly and accurately reducing the known residual magnetism in the core needs to be further proposed. Summary of the Invention

[0005] The purpose of the present invention is to overcome the deficiencies in the prior art and provide a method for reducing the residual magnetism of the core at one time, solving the technical problem of being difficult to quickly and accurately reduce the residual magnetism in a core with a closed magnetic circuit structure.

[0006] The technical solution adopted by the present invention to solve this technical problem is: a method for reducing the residual magnetism of the core at one time, and the steps of this method are as follows:

[0007] First step, using a magnetic property measuring device, measure the local hysteresis loops of the magnetic core material to be measured under different residual magnetisms, establish a J-A hysteresis model, and obtain the corresponding J-A hysteresis model parameters under different residual magnetisms;

[0008] In the second step, the equivalent circuit for weakening the residual magnetism of the magnetic core is combined with the J-A hysteresis model using the field-circuit coupling method. A numerical simulation model for weakening the residual magnetism of the magnetic core is constructed through Simulink to obtain the numerical simulation model corresponding to the J-A hysteresis model parameters under different residual magnetisms.

[0009] In the third step, based on the known magnitude and direction of the residual magnetism in the magnetic core, a reverse DC voltage excitation that generates a magnetic flux opposite to the residual magnetism is applied to one side winding of the magnetic core. After the current reaches a steady state, it is removed. Taking the final magnetic flux density B(∞) = 0 in the magnetic core as the objective function, the numerical simulation model corresponding to the magnitude and direction of the residual magnetism in the second step is used to solve and determine the DC voltage amplitude U for weakening the residual magnetism of this magnetic core. m ;

[0010] Changing the magnitude of the residual magnetism corresponds to a set of J-A model parameters. Repeat the above process. Taking the final magnetic flux density B(∞) = 0 in the magnetic core as the objective function, obtain the DC voltage amplitude U for weakening the residual magnetism of this magnetic core corresponding to different magnitudes of the residual magnetism. m , and fit the empirical formula between U m and the absolute value of the residual magnetism;

[0011] In the fourth step, measure the actual magnitude and direction of the residual magnetism in the magnetic core of the material to be measured. Substitute the magnitude of the residual magnetism into the empirical formula to obtain the DC voltage amplitude U for weakening the residual magnetism of this magnetic core at the current magnitude of the residual magnetism. m , and finally determine the direction of the DC voltage to be applied according to the direction of the residual magnetism. Apply a one-time reverse DC voltage excitation that generates a magnetic flux opposite to the residual magnetism and has an amplitude of U m to one side winding of the magnetic core. When the current in the winding becomes 0 after the excitation is removed, the demagnetization process ends, and the one-time weakening of the residual magnetism of the magnetic core is achieved.

[0012] The equation of the J-A hysteresis model is:

[0013]

[0014]

[0015] H e = H + αM (3)

[0016] B = μ0(H + M) (4)

[0017] In the formula, M is the actual magnetization intensity, B is the magnetic flux density, H is the magnetic field intensity, M an is the magnetization intensity without hysteresis effect, μ0 is the permeability of free space, M s is the saturation magnetization intensity, a is the shape parameter of the magnetization curve without hysteresis effect, k is the irreversible loss coefficient, α is the magnetic domain coupling coefficient, c is the reversible magnetization coefficient, H eis the effective magnetic field intensity; t is the time, δ is the directional coefficient, when dH / dt>0, δ=1; when dH / dt<0, δ=-1; δ M To prevent the occurrence of non-physical solution coefficients, when sgn(dB / dt)·sgn(M an -M)>0,δ M =1; when sgn(dB / dt)·sgn(M an -M)<0,δ M =0.

[0018] The equivalent circuit for weakening the residual magnetism of the magnetic core includes a magnetic core, a DC power supply, a resistor R including an external series resistor and a winding resistor, and the magnetic core is composed of an excitation inductance L and an iron loss equivalent resistor R. Fe The magnetic properties of the magnetic core are represented by the JA hysteresis model. The magnetic core is connected in series with the resistor R to form a loop with the DC power supply, realizing the combination of the equivalent circuit that weakens the residual magnetism of the magnetic core and the JA hysteresis model.

[0019] The process of obtaining the numerical simulation model corresponding to the JA hysteresis model parameters under different remanence conditions is:

[0020] Formulas (5) and (6) obtained by combining the JA hysteresis model and the equivalent circuit of weakening the residual magnetism of the magnetic core are combined to form a numerical simulation model for weakening the residual magnetism of the magnetic core; the particle swarm optimization algorithm is used to identify the parameters of the JA model for the local hysteresis loop under different residual magnetism, and numerical simulation is performed using Simulink to obtain the numerical simulation model corresponding to the corresponding JA hysteresis model parameters under different residual magnetism;

[0021]

[0022]

[0023] Where u is the DC voltage source applied during the process of weakening the residual magnetism, i is the current in the winding, N is the number of winding turns used to apply excitation, S is the effective cross-sectional area of the square core, l is the average magnetic path length, H is the magnetic field intensity, and B is the magnetic flux density.

[0024] The method can be applied to electric power equipment with a magnetic core having a closed magnetic circuit structure, and only one DC voltage excitation needs to be applied to weaken the residual magnetism of the magnetic core.

[0025] The test device for the method of the present invention to perform one-time weakening of the residual magnetism of the magnetic core includes: a signal generator, a power amplifier, a switch, an external series resistor, a square magnetic core, a fluxmeter, a current probe, and a digital oscilloscope; wherein the signal generator and the power amplifier are mainly used to provide DC voltage excitation, the external series resistor mainly plays the role of protecting the circuit and adjusting the time constant, the fluxmeter is used to observe and collect the change of the magnetic flux density in the magnetic core during the test, and the current probe and the digital oscilloscope are used to collect the winding current during the test.

[0026] The signal generator is connected to the power amplifier, and the power amplifier is connected to one side winding of the square magnetic core through the switch and the external series resistor; a current probe is installed between the square magnetic core and the power amplifier, and the current probe is connected to the digital oscilloscope; the other side winding of the square magnetic core is connected to the fluxmeter.

[0027] The present invention can reduce the time of the transient process by adjusting the size of the external series resistor, so that the demagnetization time is controlled within 1 s.

[0028] Compared with the prior art, the beneficial effects of the present invention are:

[0029] The prominent substantive feature of the present invention is: The method of the present invention is based on the magnetic properties and size structure of the magnetic core material, and determines the amplitude U of the reverse DC voltage excitation for weakening different residual magnetisms of the magnetic core through numerical simulation calculation. m During the process of weakening the residual magnetism, only one DC voltage excitation needs to be applied to the winding, and the one-time weakening of the residual magnetism of the magnetic core can be realized.

[0030] The remarkable progress of the present invention is:

[0031] 1. The operation of the present invention is simple and easy to implement. Based on the known residual magnetism in the magnetic core, only one DC voltage excitation with a specific amplitude needs to be applied, and the residual magnetism is directly weakened to nearly 0 at one time, omitting the steps of magnetizing the magnetic core to saturation and alternating the polarity, significantly reducing the demagnetization time, the power requirement of the demagnetization equipment, and the complexity of the demagnetization circuit.

[0032] 2. The method of the present invention has universal applicability and can be widely applied to various power equipment with magnetic cores having a closed magnetic circuit structure.

[0033] 3. The method of the present invention has the characteristics of good effect and high efficiency in weakening the residual magnetism. According to the residual magnetism in the magnetic core and the simulation calculation, the amplitude of the applied reverse DC voltage is determined, and the residual magnetism in the closed magnetic circuit magnetic core can be weakened targeted, and the residual magnetism is eliminated more quickly and thoroughly. Description of the Drawings

[0034] The present invention will be further described below with reference to the drawings and embodiments.

[0035] Figure 1It is a schematic block diagram of the operation process of the method of the present invention.

[0036] Figure 2 It is a schematic diagram of the dimensions of the square magnetic core selected in the embodiment of the present invention.

[0037] Figure 3 It is a comparison chart of the measured results and the calculated results of the local hysteresis loop in the embodiment of the present invention.

[0038] Figure 4 It is an equivalent circuit diagram for weakening the remanence of the square magnetic core in the embodiment of the present invention.

[0039] Figure 5 It is a schematic diagram of the test device for weakening the remanence of the square magnetic core in the embodiment of the present invention.

[0040] Figure 6 It is a waveform diagram of the change in the magnetic flux density in the magnetic core during the process of weakening the remanence in the embodiment of the present invention. Specific embodiments

[0041] The present invention will be further described in detail below with reference to the accompanying drawings.

[0042] Figure 1 As shown, the operation process of the present invention for weakening the remanence of the magnetic core at one time is as follows: The first step is to use a magnetic property measurement device to measure the local hysteresis loops of the magnetic core material under different remanences. The second step is to establish a numerical simulation model for weakening the remanence of the magnetic core based on the J-A hysteresis model and the field-circuit coupling method. The third step is to determine the amplitude U of the one-time reverse DC voltage applied to the winding under different remanences of the magnetic core through simulation calculation. m . The fourth step is to build a test device for weakening the remanence of the magnetic core. The fifth step is to determine the value of U based on the known actual remanence magnitude and direction in the magnetic core. A one-time DC voltage excitation with a magnetic flux opposite to the remanence and an amplitude of U is applied to one side winding of the magnetic core. When the winding current is 0 after the excitation is removed, the demagnetization process ends. m The value of the one-time DC voltage excitation with a magnetic flux opposite to the remanence and an amplitude of U is applied to one side winding of the magnetic core. When the winding current is 0 after the excitation is removed, the demagnetization process ends. m The value of the one-time DC voltage excitation with a magnetic flux opposite to the remanence and an amplitude of U is applied to one side winding of the magnetic core. When the winding current is 0 after the excitation is removed, the demagnetization process ends.

[0043] Figure 2 The dimensions of the square magnetic core in the embodiment of the present invention are shown. The width of each magnetic core lamination is 80 mm, the thickness of the magnetic core lamination is 20 mm, the square magnetic core is a ring-shaped cube as a whole, the side length of the inner square of the magnetic core as a whole is 400 mm, and the side length of the outer square of the magnetic core is 560 mm.

[0044] Figure 3 The comparison chart of the local hysteresis loop measured and the calculation result of the J-A hysteresis model when the remanence B of the square magnetic core is 1.2 T in the embodiment of the present invention is shown. r The comparison chart of the local hysteresis loop measured and the calculation result of the J-A hysteresis model when the remanence B of the square magnetic core is 1.2 T in the embodiment of the present invention is shown.

[0045] Figure 4In the embodiment of the present invention, the equivalent circuit diagram when weakening the remanence of the magnetic core. U is the DC power supply, i is the current in the winding, R includes the external series resistance and the winding resistance, the part within the dashed box is the equivalent part of the magnetic core, L is the exciting inductance, and R Fe is the equivalent resistance of iron loss.

[0046] Figure 5 The test device for weakening the remanence of the square magnetic core in the embodiment of the present invention is shown. It includes: a signal generator 1, a power amplifier 2, a switch 4, an external series resistance 3, a square magnetic core 7, a fluxmeter 8, a current probe 6, and a digital oscilloscope 5. Among them, the signal generator and the power amplifier are mainly used to provide DC voltage excitation, the external series resistance mainly plays the role of protecting the circuit and adjusting the time constant, the fluxmeter is used to observe and collect the change of the magnetic flux density in the magnetic core during the test, and the current probe and the digital oscilloscope are used to collect the winding current during the test. The value of the external series resistance is 4Ω, and the amplitude of the required DC voltage excitation is below 2V, which can reduce the requirements of the equipment for weakening the remanence of the magnetic core on the power supply.

[0047] Figure 6 In the embodiment of the present invention, the remanence B of the square magnetic core r = 1.2T, the waveform diagram of the change of the magnetic flux density in the magnetic core before and after the process of weakening the remanence.

[0048] The process of the method for weakening the remanence of the magnetic core at one time in the present invention is as follows:

[0049] In the first step, using a magnetic property measurement device, the local hysteresis loops of the magnetic core material at different remanences are measured. The Jiles-Atherton (J-A) hysteresis model is used to describe the hysteresis characteristics of ferromagnetic materials, and the particle swarm optimization algorithm is used to identify the J-A hysteresis model parameters for the local hysteresis loops at different remanences, that is, the corresponding relationship between the remanence magnitude and the J-A hysteresis model parameters is obtained.

[0050] The J-A hysteresis model equation is as follows:

[0051]

[0052]

[0053] H e = H + αM (3)

[0054] B = μ0(H + M) (4)

[0055] In the formula, M is the actual magnetization intensity, B is the magnetic flux density, H is the magnetic field intensity, M an is the magnetization intensity without hysteresis effect, μ0 is the vacuum permeability, and its value is 4π·10 -7 H / m, M sis the saturation magnetization, a is the shape parameter of the magnetization curve without hysteresis effect, k is the irreversible loss coefficient, α is the coupling coefficient between magnetic domains, c is the reversible magnetization coefficient, H e is the effective magnetic field strength; δ is the directional coefficient, t is the time, when dH / dt>0, δ=1; when dH / dt<0, δ=-1. M To prevent the occurrence of non-physical solution coefficients, when sgn(dB / dt)·sgn(M an -M)>0,δ M =1; when sgn(dB / dt)·sgn(M an -M)<0,δ M =0.

[0056] In the second step, the equivalent circuit for weakening the core remanence is combined with the JA hysteresis model by using the field-circuit coupling method. The parameters of the JA hysteresis model are changed accordingly under different remanences, and a numerical simulation model for weakening the core remanence is constructed through Simulink.

[0057] The equivalent circuit for weakening residual magnetism is as follows Figure 4 As shown, Figure 4 The magnetic core represented by the dotted box in the middle, the magnetic characteristics of the core are represented by the JA hysteresis model, which realizes the combination of circuit and magnetic field changes;

[0058] pass Figure 4 The equivalent circuit of is easy to get:

[0059]

[0060]

[0061] Where u is the DC voltage source applied during the process of weakening the residual magnetism, i is the current in the winding, N is the number of winding turns used to apply excitation, S is the effective cross-sectional area of the square core, l is the average magnetic path length, H is the magnetic field intensity, and B is the magnetic flux density.

[0062] Formulas (5) and (6) obtained by combining the JA hysteresis model and the equivalent circuit of weakening the residual magnetism of the magnetic core are combined to form a numerical simulation model for weakening the residual magnetism of the magnetic core; the particle swarm optimization algorithm is used to identify the parameters of the JA model for the local hysteresis loop under different residual magnetism, and numerical simulation is performed using Simulink to obtain the numerical simulation model corresponding to the corresponding JA hysteresis model parameters under different residual magnetism. The subsequent solution is numerically solved using the numerical simulation model built by Simulink;

[0063] The third step is to determine the DC voltage amplitude U that weakens the magnetic core under different remanence mBased on the numerical simulation model, when the remanence magnitude and its direction in the magnetic core are known, a reverse DC voltage excitation that generates a magnetic flux opposite to the remanence is applied to one side winding of the magnetic core. After the current reaches a steady state, it is removed. Taking the final magnetic flux density B(∞) = 0 in the magnetic core as the objective function and solving through the numerical model, the DC voltage amplitude U applied to weaken the remanence of the magnetic core can be determined. m 。

[0064] Changing the remanence magnitude corresponds to a set of J-A model parameters. After changing the J-A model parameters, repeat the above process to determine the DC voltage amplitude U for weakening different remanences of the magnetic core. m That is, establish the corresponding U for different remanence magnitudes. m ,Fit out the m empirical formula between U and the absolute value of the remanence. Later, when the remanence is known, substitute it into the empirical formula to directly determine U for application. m for application.

[0065] The present invention directly weakens the known remanence, that is, weakens as much as there is. After applying a DC voltage excitation that generates a magnetic flux opposite to the remanence, the circuit will experience a transient process. When the current no longer changes and reaches a steady state, the voltage excitation can be removed. To ensure the remanence weakening effect, the present invention considers the entire demagnetization implementation process. When an external excitation is applied to weaken the magnetic flux density in the magnetic core to magnitude A, due to the hysteresis characteristic of the magnetic material, the magnetic flux density in the magnetic core will decrease after the excitation is removed, that is, smaller than A. Therefore, when solving using the numerical simulation model, the change in the magnetic flux density in the magnetic core after the excitation is removed must be considered to ensure that the final remanence is 0 after the excitation is applied and removed. At this time, the excitation amplitude U m is what is required in this application.

[0066] Step 4: Build a test device for weakening the remanence of the magnetic core and perform an actual one-time treatment to weaken the remanence of the magnetic core material to be measured.

[0067] Step 5: Weaken the remanence in the closed magnetic circuit magnetic core. Measure the actual remanence magnitude and direction in the magnetic core of the magnetic core material to be measured. Substitute the remanence magnitude into the empirical formula to obtain the DC voltage amplitude U for weakening the remanence of the magnetic core under the current remanence magnitude. m Finally, determine the direction of the magnetic flux to be generated according to the direction of the remanence, and apply a one-time reverse DC voltage excitation that generates a magnetic flux opposite to the remanence and has an amplitude of U m to one side winding of the magnetic core. When the current in the winding is 0 after the excitation is removed, the demagnetization process ends, and the one-time weakening of the remanence of the magnetic core is achieved.

[0068] Embodiment

[0069] To enable those skilled in the art to better understand the technical solutions in the present invention, the technical solutions in the embodiments of the present invention will be fully described below in conjunction with the accompanying drawings. Due to space limitations, the following embodiments are only some of the embodiments included in the present invention, rather than all embodiments. Based on the technical principles and design ideas of the present invention, several improvements and deformations can be made, such as changing the excitation waveform used to weaken the remanence. All other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the scope of protection of the present invention.

[0070] In the embodiments of the present invention, the selected closed magnetic circuit square magnetic core has a specification of B30P105, and the dimensions of the magnetic core are as follows: the width of each magnetic core sheet is 80 mm, the lamination thickness of the magnetic core is 20 mm, the square magnetic core is in the shape of a ring-shaped cube as a whole, the side length of the inner square of the magnetic core as a whole is 400 mm, and the side length of the outer square of the magnetic core is 560 mm.

[0071] Step 1: Based on the established magnetic property measurement device, measure the magnetic properties of the magnetic core material. Among them, the power supply uses a square wave voltage excitation, and by changing the amplitude of the square wave voltage, the local hysteresis loops of the B30P105 material under different remanences are measured.

[0072] The Jiles-Atherton (J-A) hysteresis model is used to describe the hysteresis characteristics of the magnetic core material. The basic equation of the J-A hysteresis model is as follows:

[0073]

[0074]

[0075] H e = H + αM (9)

[0076] B = μ0(H + M) (10)

[0077] In the formula, M is the actual magnetization intensity, B is the magnetic flux density, M an is the magnetization intensity without hysteresis effect, μ0 is the magnetic permeability of vacuum, and its value is 4π·10 -7 H / m, M s is the saturation magnetization intensity, a is the shape parameter of the magnetization curve without hysteresis effect, k is the irreversible loss coefficient, α is the coupling coefficient between magnetic domains, c is the reversible magnetization coefficient, H e is the effective magnetic field intensity. δ is the direction coefficient, t is the time. When dH / dt > 0, δ = 1; when dH / dt < 0, δ = -1. δ M is a coefficient that can prevent non-physical solutions from occurring. When sgn(dB / dt)·sgn(M an - M) > 0, δ M= 1; when sgn(dB / dt)·sgn(M an - M) < 0, δ M = 0.

[0078] Using the particle swarm global optimization algorithm, the parameters of the measured local hysteresis loop are identified, and the J - A hysteresis model parameters of the local hysteresis loop under different remanences are extracted. Taking the remanence B r = 1.2T in the square magnetic core as an example, the J - A model parameters are: M s = 1.656×10 6 A / m, α = 2.713×10 -5 , a = 15.1455 A / m, c = 0.2861 A / m, k = 25.6602. The comparison between the measured results and the simulation calculation results of the hysteresis loop when B r = 1.2T is shown as Figure 3 follows.

[0079] Step 2, Figure 4 is the equivalent circuit model of the shown embodiment. R includes the external series resistance and the winding resistance in the loop. The dotted box is the equivalent part of the magnetic core, L is the excitation inductance, and R Fe is the equivalent resistance of iron loss. It is easy to obtain:

[0080]

[0081] In the formula, u is the DC voltage source applied during the process of weakening the remanence, i is the current in the winding, N is the number of turns of the winding for applying the excitation, S is the effective cross - sectional area of the square magnetic core, l is the average magnetic path length, H is the magnetic field strength, and B is the magnetic flux density.

[0082] Based on equations (7) - (12), using the field - circuit coupling method, a numerical simulation model for weakening the remanence of the square magnetic core is built through Simulink. Among them, the number of winding turns N = 50, l = 1.92m, S = 0.0016m 2 , R = 4.1Ω. The hysteresis characteristics of the square magnetic core are described by the J - A hysteresis model, and the J - A hysteresis model parameters change accordingly under different remanences, that is, for different remanence magnitudes, each remanence corresponds to a set of J - A hysteresis model parameters.

[0083] Step 3, according to the known B in the square magnetic core r= 1.2T, a reverse DC voltage excitation that generates a magnetic flux opposite to the remanence is applied to the winding. After the excitation is removed, with the target of the final magnetic flux density B(∞) = 0 in the magnetic core, the established numerical simulation model is used for solution. That is, when the magnitude of the remanence is known, the J-A hysteresis model parameters are known. Then, with the target of the final magnetic flux density B(∞) = 0 in the magnetic core, the DC voltage source u applied during the process of weakening the remanence at this time can be determined, and the weakening of the square magnetic core B r The amplitude U of the reverse DC voltage applied when B m = 1.2T is 1.47V.

[0084] Step 4, build an experimental device for weakening the remanence of the square magnetic core as shown in Figure 5 . The signal generator (WF1974) is used to output a DC voltage signal and apply it to one side winding of 50 turns through a power amplifier. The current probe (N2782B) and the oscilloscope (DSOX6004A) are used to collect the current in the winding. The other side winding of the magnetic core is connected to a fluxmeter (Flux-meter480), which is used to observe and collect the change of the magnetic flux density in the magnetic core during the experiment.

[0085] Step 5, preset a remanence of 1.2T for the square magnetic core, and apply a one-time DC voltage excitation with a magnetic flux opposite to the remanence and an amplitude U m = 1.47V. When the current in the winding is 0 after the excitation is removed, the demagnetization process ends. Figure 6 The figure shows the waveform diagram of the change of the magnetic flux density in the magnetic core during the process of weakening the remanence in the embodiment. After applying the method of the present invention, the remanence in the square magnetic core is only 1.6% of the initial remanence, that is, the remanence is weakened from 1.2T to 0.019T. It can be seen that the remanence in the magnetic core is accurately eliminated, which can meet the engineering requirements. And by connecting an external resistor in series to adjust the time constant of the transient process, the entire process of weakening the remanence only takes 0.6s.

[0086] In this embodiment, the resistance value of the external series resistor 3 is 4Ω, and the voltage amplitude of the DC voltage source is 1.47V.

[0087] For the known residual magnetism, the present invention directly applies a short-time DC voltage excitation to weaken the residual magnetism in the magnetic core to be close to 0. A numerical simulation model for weakening the residual magnetism of the magnetic core is built by using the field-circuit coupling method, and different J-A model parameters are determined based on the hysteresis loops measured under different residual magnetism conditions, that is, the corresponding J-A model parameters are adopted for different residual magnetisms in the magnetic core to ensure the accuracy of the simulation model. In the present application, a set of J-A model parameters corresponds to a residual magnetism magnitude, rather than always using a fixed set of parameters to simulate all cases in the prior art. The present invention only uses a DC voltage excitation with a fixed amplitude under a fixed polarity. The applied voltage is a DC voltage excitation, and there is no need to use an external excitation with an alternating polarity and a continuously decreasing amplitude.

[0088] Matters not described in the present invention are applicable to the prior art.

Claims

1. A method for weakening the residual magnetism of a magnetic core at one time, characterized in that: The steps of this method are: The first step is to use a magnetic property measurement device to measure the local hysteresis loop of the magnetic core material under different remanence, establish a JA hysteresis model, and obtain the corresponding JA hysteresis model parameters under different remanence; In the second step, the equivalent circuit for weakening the core remanence is combined with the JA hysteresis model by using the field-circuit coupling method, and a numerical simulation model for weakening the core remanence is constructed through Simulink to obtain the numerical simulation model corresponding to the JA hysteresis model parameters under different remanence conditions; Step 3: Based on the known magnitude and direction of the residual magnetism in the magnetic core, apply a reverse DC voltage excitation to the winding on one side of the magnetic core to generate a magnetic flux opposite to the residual magnetism. After the current reaches a steady state, remove it. Using the magnetic core's final magnetic flux density B(∞) = 0 as the objective function, solve it with the numerical simulation model corresponding to the magnitude and direction of the residual magnetism in Step 2 to determine the DC voltage amplitude U for weakening the residual magnetism of the magnetic core m ; Changing the magnitude of the remanence corresponds to a set of J-A model parameters. Repeating the above process, with the final magnetic flux density B(∞) = 0 in the magnetic core as the objective function, the DC voltage amplitude U for weakening the remanence of the magnetic core corresponding to different magnitudes of the remanence is obtained. m , and fitting out the empirical formula between U m and the absolute value of the remanence; Step 4: Measure the actual residual magnetism magnitude and direction inside the core of the magnetic core material to be measured. Substitute the residual magnetism magnitude into the empirical formula to obtain the DC voltage amplitude U for weakening the residual magnetism of the core at the current residual magnetism magnitude. m , and finally determine the direction of the DC voltage to be applied according to the direction of the residual magnetism. Apply a one-time reverse DC voltage excitation with a magnetic flux opposite to the residual magnetism and an amplitude of U m to one side winding of the core. When the current in the winding is 0 after the excitation is removed, the demagnetization process ends, and the residual magnetism of the core is weakened in one-time.

2. The method for weakening the remanence of a magnetic core at one time according to claim 1, characterized in that, The equation of the JA hysteresis model is: H e = H + αM (3) B=μ0(H+M) (4) Wherein, M is the actual magnetization intensity, B is the magnetic flux density, H is the magnetic field intensity, M an is the magnetization intensity without hysteresis effect, μ0 is the magnetic permeability of vacuum, M s is the saturation magnetization intensity, a is the shape parameter of the magnetization curve without hysteresis effect, k is the irreversible loss coefficient, α is the coupling coefficient between magnetic domains, c is the reversible magnetization coefficient, H e is the effective magnetic field intensity; t is the time, δ is the direction coefficient, when dH / dt > 0, δ = 1; when dH / dt < 0, δ = -1; δ M is the coefficient that can prevent non - physical solutions. When sgn(dB / dt)·sgn(M an - M) > 0, δ M = 1; when sgn(dB / dt)·sgn(M an - M) < 0, δ M = 0.

3. The method for reducing the residual magnetism of a magnetic core at one time according to claim 1, characterized in that, The equivalent circuit for weakening the remanent magnetism of the magnetic core includes a magnetic core, a DC power supply, and a resistor R that includes an external series resistor and a winding resistor. The magnetic core is composed of a parallel connection of an excitation inductance L and an iron loss equivalent resistor R Fe The magnetic characteristics of the magnetic core are represented by the J-A hysteresis model. After the magnetic core is connected in series with the resistor R and forms a loop with the DC power supply, the equivalent circuit for weakening the remanent magnetism of the magnetic core is combined with the J-A hysteresis model.

4. The method for weakening the residual magnetism of a magnetic core at one time according to claim 1, characterized in that, The process of obtaining the numerical simulation model corresponding to the JA hysteresis model parameters under different remanence conditions is: Formulas (5) and (6) obtained by combining the JA hysteresis model and the equivalent circuit of weakening the residual magnetism of the magnetic core are combined to form a numerical simulation model for weakening the residual magnetism of the magnetic core; the particle swarm optimization algorithm is used to identify the parameters of the JA model for the local hysteresis loop under different residual magnetism, and numerical simulation is performed using Simulink to obtain the numerical simulation model corresponding to the corresponding JA hysteresis model parameters under different residual magnetism; ∮ l ∮H·dl = Ni (6) Where u is the DC voltage source applied during the process of weakening the residual magnetism, i is the current in the winding, N is the number of winding turns used to apply excitation, S is the effective cross-sectional area of the square core, l is the average magnetic path length, H is the magnetic field intensity, and B is the magnetic flux density.

5. The method for weakening the residual magnetism of a magnetic core at one time according to any one of claims 1 to 4, characterized in that: The method can be applied to electric power equipment with a magnetic core having a closed magnetic circuit structure, and only one DC voltage excitation needs to be applied to weaken the residual magnetism of the magnetic core.

6. The method for weakening the residual magnetism of a magnetic core at one time according to any one of claims 1 to 4, characterized in that: The test device used for performing the method of weakening the residual magnetism of the magnetic core once comprises: a signal generator, a power amplifier, a switch, an external series resistor, a square magnetic core, a fluxmeter, a current probe and a digital oscilloscope; wherein the signal generator and the power amplifier are mainly used to provide DC voltage excitation, the external series resistor mainly plays the role of protecting the circuit and adjusting the time constant, the fluxmeter is used to observe and collect the change of the magnetic flux density in the magnetic core during the test, and the current probe and the digital oscilloscope are used to collect the winding current during the test; The signal generator is connected to the power amplifier, and the power amplifier is connected to one side winding of the square magnetic core through a switch and an external series resistor; a current probe is installed between the square magnetic core and the power amplifier, and the current probe is connected to a digital oscilloscope; the other side winding of the square magnetic core is connected to a fluxmeter.

7. The method for weakening the remanence of a magnetic core at one time according to claim 6, wherein By adjusting the size of the external series resistor, the time of the transient process can be reduced so that the demagnetization time is controlled within 1s.

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