Common-mode EMI filter inductor broadband impedance prediction and improvement method

Abstract

The invention discloses a common-mode EMI filter inductor broadband impedance prediction and improvement method, which is characterized by comprising the following steps of: improving a common-mode EMI filter inductor high-frequency equivalent circuit; extracting parameters of an improved high-frequency equivalent circuit; optimizing a common mode EMI (Electro-Magnetic Interference) inductor; according to the invention, the broadband impedance value of the inductor and the accurate parameter value of each area in the inductor can be accurately obtained in advance without adopting an impedance measurement mode. In addition, the provided optimization design method can optimize and design the common-mode EMI filter inductor more conveniently and quickly.

Description

Technical Field

[0001] The present invention relates to the technical field of high-pressure valve cold sensor systems, and in particular to a method for predicting and improving the broadband impedance of a common-mode EMI filter inductor. Background Art

[0002] With the continuous development of economy and emerging industries, the demand for power resources is gradually increasing. In addition, due to my country's industrial structure, UHV DC transmission can well meet the requirements of high efficiency, low loss and long-distance transmission. The converter valve is an important component in UHV DC transmission. The average current is large during operation. After long-term operation, a large amount of heat will be generated, which will affect the normal operation of the converter valve. In severe cases, it may even cause a lockout accident in the DC transmission system, leading to the collapse of the main grid system. Therefore, the valve cooling system is one of the most important auxiliary systems of the converter valve. The valve cooling system sensor is used to collect important data in the circulating water and transmit it to the valve cooling control system for processing. Therefore, the stability of the valve cooling system sensor directly determines whether the valve cooling system can work normally. In the equipment layout of the converter station, a large number of power electronic devices are densely placed, and the high-frequency electromagnetic radiation generated is very easy to induce common-mode interference signals on the signal line. In addition, due to the miniaturization trend of sensor design, its internal circuit is also very easy to generate interference signals. Common-mode interference signals usually rely on common-mode inductors in common-mode filters for suppression. However, due to the influence of parasitic capacitance and leakage inductance, high-frequency signals often cause the broadband impedance of common-mode inductors to deviate from the characteristics of ideal inductors. Therefore, accurate modeling of common-mode inductors is essential for effectively optimizing common-mode filters and enabling devices to meet electromagnetic interference standards without increasing their weight and size.

[0003] At present, the commonly used common-mode EMI filter inductor high-frequency modeling methods are mainly divided into two types: behavioral method and physical method. The behavioral method requires the common-mode EMI filter inductor to be manufactured first, and then modeled by fitting means, which will greatly increase the design cost. The physical method can be further divided into finite element method and analytical method. Compared with the finite element method, the analytical method does not require a lot of time and computing resources, and can quickly obtain relatively high-precision impedance results based on the designed inductor geometry. Therefore, the analytical method is currently a more promising technology in the high-frequency modeling of common-mode EMI filter inductors. Many teams have proposed related methods, but these methods have the problems of narrow applicable core material range and overly simple assumptions. The current mainstream model regards each turn as an independent unit, taking into account the core material characteristics and the mutual coupling between turns and between turns and cores. Since the model can directly calculate the relevant parameters based on the geometric structure of the inductor, it has great design advantages in optimizing the design of common-mode EMI filter inductors. However, this model only partially considers the core material properties, treating it as a conductor, but does not take into account the electromagnetic field effects inside the core, which results in the more turns, the more accurate the model results, and vice versa, the fewer turns, the greater the error in the model results. Since the switching frequency is higher in current power electronic equipment, the inductance requirements are reduced, and common-mode EMI filter inductors with few turns or even single turns are gradually becoming popular. Therefore, the current analytical model needs to be further revised and improved to meet the current requirements for accurate modeling of common-mode EMI filter inductors with few turns.

[0004] Based on this, the present invention aims at the current research status, fully considers the actual geometric structure, material properties and electromagnetic field behavior of common-mode EMI filter inductors, and proposes a more compatible common-mode EMI filter inductor high-frequency modeling and optimization method to better help designers optimize common-mode EMI filter inductors, improve their high-frequency performance, and thus improve the noise reduction level of EMI filters. This method has low time and economic costs, good results, and therefore has high application value. Summary of the invention

[0005] In view of the shortcomings of the existing common-mode EMI filter inductor broadband modeling method, the present invention provides a common-mode EMI filter inductor broadband impedance prediction and improvement method. Its purpose is to eliminate the shortcomings of traditional common-mode EMI filter inductor modeling, so that the model can be applied to different situations and maintain a high modeling accuracy under different core materials and turns.

[0006] To achieve the above object, the present invention provides the following technical solution: a method for predicting and improving the broadband impedance of a common-mode EMI filter inductor, comprising the following steps:

[0007] Improved common-mode EMI filter inductor high-frequency equivalent circuit, including consideration of the influence of the core material characteristics and characterization of it as the core time-varying parasitic capacitance C c , the core time-varying parasitic capacitance C c Connected in parallel to both ends of the first and last turns of the winding;

[0008] Improved high-frequency equivalent circuit parameter extraction, including parameter extraction in the circuit, taking into full account the actual geometric conditions of the inductor, and deriving analytical formulas to obtain more accurate parasitic capacitance values ​​for each area in the inductor;

[0009] Optimization of common-mode EMI inductors, including the optimization process of designing common-mode EMI filter inductors, designing the geometric structure and number of turns of common-mode EMI filter inductors according to the inductance requirements, and then calculating whether it is necessary to consider the core time-varying parasitic capacitance C c Incorporate it into the circuit model, finally calculate the impedance curve, and determine whether it meets the requirements.

[0010] Preferably, the steps of the improved common-mode EMI filter inductor high-frequency equivalent circuit include: a circuit model is formed by connecting the circuit models of two windings in parallel; in a single winding, each turn is regarded as an independent unit, including a series self-inductance L s and core loss R s and C in parallel tt , the C tc One end is connected to the left side of the unit and the other end is connected to the other C tc Share a common node.

[0011] Preferably, the step of extracting the improved high-frequency equivalent circuit parameters comprises:

[0012] S1. The calculation of inter-turn capacitance is divided into internal area, external area, and parallel area (front and back). The formula can be expressed as:

[0013]

[0014] The specific analytical formulas for S11 and inter-turn capacitance are as follows:

[0015]

[0016]

[0017] S2. For the calculation of the turn-to-core capacitance, it is also divided into the inner area, the outer area, and the parallel area (front and back). The formula can be expressed as:

[0018]

[0019] The specific analytical formulas for S21 and turn-to-core capacitance are as follows:

[0020]

[0021] S3. The geometric characteristics of the common-mode EMI filter inductor are fully considered, including the dielectric properties and thickness of the winding insulation, the actual winding length of the winding, and the actual distance from the equivalent turn to the core.

[0022] S31. In the actual winding length of the winding, the corrected parallel area length expression is:

[0023]

[0024] S32, the actual equivalent turn to core distance expression is:

[0025]

[0026] Preferably, the optimization of the common-mode EMI inductance includes the following steps: determining whether it is necessary to consider the core time-varying parasitic capacitance C c The method incorporated into the circuit model includes calculating the inductance value and the capacitance value, which includes the spatial parasitic capacitance and the core time-varying parasitic capacitance C c , compare the calculated value with the previously designed number of turns; if the designed number of turns is greater than this value, there is no need to include the core capacitor in the circuit model; if it is less than this value, the core capacitor needs to be built into the circuit model.

[0027] The common-mode EMI filter inductor high-frequency modeling optimization method according to claim 1 is characterized in that the optimization process of designing the common-mode EMI filter inductor includes targeted adjustment of the winding method, core material and winding model of the inductor.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] (1) The improved common-mode EMI filter inductor high-frequency circuit provided by the present invention fully considers the influence of the magnetic core material, so that the model is applicable to different magnetic core materials.

[0030] (2) The improved common-mode EMI filter inductor high-frequency circuit provided by the present invention takes into account the influence of the time-varying electromagnetic field inside the magnetic core, making the model suitable for the case of a small number of turns of a high dielectric constant magnetic core.

[0031] (3) The improved common-mode EMI filter inductor high-frequency circuit parameter calculation method provided by the present invention fully considers the actual geometric structure of the inductor, making the parameters used in modeling more accurate.

[0032] (4) The common-mode inductor optimization design method provided by the present invention can more conveniently design and optimize the common-mode EMI filter inductor. Combined with this process, the winding method, core material, winding model and other factors of the inductor can be adjusted in a targeted manner, so as to maximize the high-frequency performance of the common-mode EMI filter. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is the geometric structure diagram of the common mode EMI filter inductor;

[0034] Figure 2 It is a cross-sectional view of the common mode EMI filter inductor;

[0035] Figure 3 This is the high-frequency circuit diagram of the common-mode EMI filter inductor proposed by the present invention;

[0036] Figure 4 This is the turn-to-turn geometry diagram of the common-mode EMI filter inductor;

[0037] Figure 5 The geometric structure diagram between the turns and the magnetic core of the common mode EMI filter inductor;

[0038] Figure 6 It is the parallel region geometric structure diagram of the common mode EMI filter inductor;

[0039] Figure 7 A diagram showing a method for improving the design of a common-mode EMI filter inductor proposed by the present invention; DETAILED DESCRIPTION

[0040] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0041] The geometric structure diagram of the application object of the common mode EMI filter inductor broadband modeling method proposed in the present invention is as follows: Figure 1 As shown in Figure 1. The common mode EMI filter inductor consists of a magnetic core and two symmetrically wound windings. o and R co is the outer diameter of the common mode EMI filter inductor. in and R cin is the inner diameter of the common mode EMI filter inductor. Figure 2 Shows the cross-sectional structure of the common-mode EMI filter inductor, w c is the maximum distance between the turns and the core, w e is the minimum distance between the turns and the core, w plis the thickness of the insulation layer.

[0042] The common mode EMI filter inductor high frequency circuit model proposed by the present invention is as follows: Figure 3 As shown in Figure 1. The model consists of two winding circuit models connected in parallel. Each turn is considered as an independent unit, including the series self-inductance (L s ) and core loss (R s ), and the parallel C tt . C tc One end is connected to the left side of the unit and the other end is connected to the other C tc share a common node. Since the last turn has no adjacent turns, the inter-turn capacitance between the first and second turns is divided into two equal parts. One part is connected in parallel with the last turn, and each part represents half of the inter-turn capacitance. C generated by the time-varying electric field c It can only be connected in parallel to the common terminals of the two windings, and C tc There is a common node to reflect the equipotential surface. It should be noted that although there are two windings on the common-mode EMI filter inductor, it can be seen from the characteristics of the coupled inductor that the final equivalent magnetic field energy is equivalent to the magnetic field energy generated by one winding. Therefore, the calculation of the time-varying core capacitance only needs to consider the number of turns of one winding. Finally, the impedance of each frequency can be determined using circuit analysis methods (node ​​voltage method, network analysis method) to obtain the impedance curve. After the circuit model is constructed, the subsequent physical parameter derivation can be carried out. In traditional models, capacitance expressions are usually obtained using simplified geometric structures, resulting in significant errors in capacitance and impedance curves. Therefore, in order to improve the accuracy of the model, it is necessary to consider the actual geometry, including complete insulation, winding bending, and spiral length.

[0043] For the modeling of complex inductance, the complex relative permeability of the core is the key factor in inductance modeling, which is represented by its real part μ r ' and the imaginary part μ r ". Therefore, ignoring the winding loss, the impedance (Z) of a single turn can be expressed as follows:

[0044]

[0045] In common mode EMI filter inductors, the self-inductance of a single turn can be expressed as L ii The leakage inductance between turn i and turn j is represented by L σij The mutual inductance between turns i and j is represented by M ij The relationship between these parameters is as follows:

[0046] L ii =M ij +L σij

[0047] In the present invention, due to the high magnetic permeability of the common mode EMI filter inductor, the magnitude of the leakage inductance is several orders of magnitude smaller than the self-inductance, so the leakage inductance can be ignored.

[0048] like Figure 4 , 5 , 6, d c represents the conductor radius, w i Represents the thickness of the wire insulation layer, w pl Represents the thickness of the core insulation layer, l w Represents the front winding length, l' w Represents the winding length on the back side. Among them, C of different material areas tt and C tc The analysis and calculation can be performed by the following methods:

[0049]

[0050] In the formula, dS represents the differential area, x represents the path of the electric field line, ∈ r is the relative dielectric constant of the medium. When calculating parasitic capacitance, three different regions can be identified, namely the external region (C tto , C tco ), internal area (C ttin , C tcin ) and the positive side area (C ttl , C tcl ), dorsal region (C ttl ' w , C tcl ' w ). However, the conventional method does not take winding insulation into account. When winding insulation is taken into account, C tt It can be restated as follows:

[0051] C tt =C ttin +C tto +C ttl +C ttl'w

[0052] The specific expansion form of the parameters in Ctt is as follows:

[0053]

[0054] In addition, in the traditional model, the coil length is usually assumed to be the perimeter of the rectangle. However, during the winding process, the coil length on the other side of the parallel region does not directly correspond to half of the difference between the inner and outer diameters of the inductor. Therefore, the present invention makes a correction, such as Figure 6 As shown. w The length can be calculated using the law of cosines.

[0055]

[0056] Furthermore, C tc It can be restated as follows:

[0057] C tc =C tcin +C tco +C tcl +C tcl'w

[0058] The specific expansion form of the parameters in Ctc is as follows:

[0059]

[0060] like Figure 2 As shown in the figure, since the conductor and the magnetic core are not evenly fitted, the distance between the turns and the magnetic core needs to be adjusted. However, in the traditional model, the winding transition area is often ignored. Therefore, the present invention adopts the capacitance equivalent method, and the equivalent turn spacing is given here:

[0061]

[0062] Time-varying core capacitance C c The calculation can be directly based on the following formula:

[0063] C c =ε0ε r l / 8 / π / N 2

[0064] After completing the construction and verification of the accurate model, the present invention provides a method for designing, optimizing and verifying the common-mode EMI filter inductor. Figure 7 As shown, first, engineers can design the geometry and number of turns of the common-mode EMI filter inductor according to the inductance requirements. Then calculate the inductance value and capacitance value (space parasitic capacitance and core time-varying parasitic capacitance); the next step is to calculate The value of is calculated and compared with the number of turns designed previously. If the number of turns designed is greater than this value, the core capacitor does not need to be included in the circuit model. If it is less than this value, the core capacitor needs to be built into the circuit model. Finally, the impedance curve is calculated and it is determined whether it meets the requirements. If not, repeat this process.

[0065] The high-frequency circuit model of the common-mode EMI filter inductor proposed above takes each turn as an independent unit, and each unit is connected according to the actual geometric structure and electromagnetic field distribution. The circuit fully considers the actual high-frequency electromagnetic field behavior of the inductor, and on this basis, the core capacitance caused by the dielectric properties of the core is taken into account in the circuit. Compared with the existing high-frequency circuit model of the common-mode EMI filter inductor, this method is more accurate and more compatible when performing broadband modeling for cores with high dielectric constants and few turns. In addition, the parameter acquisition in the high-frequency circuit model comprehensively considers the actual geometric structure of the filter inductor, so that the calculated capacitance parameters also have higher accuracy.

[0066] The common-mode EMI filter inductor optimization design method mentioned above, through this process, engineers can more conveniently design and optimize the common-mode EMI filter inductor. Combined with this process, targeted adjustments to the inductor's winding method, core material, winding model and other factors can maximize the high-frequency performance of the common-mode EMI filter.

[0067] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for predicting and improving broadband impedance of common mode EMI filter inductors, characterized in that: The following steps are involved: Improved common-mode EMI filter inductor high-frequency equivalent circuit, including consideration of the influence of the core material characteristics and characterization of it as the core time-varying parasitic capacitance C c , the core time-varying parasitic capacitance C c Connected in parallel to both ends of the first and last turns of the winding; Improved high-frequency equivalent circuit parameter extraction, including parameter extraction in the circuit, taking into full account the actual geometric conditions of the inductor, and deriving analytical formulas to obtain more accurate parasitic capacitance values ​​for each area in the inductor; Optimization of common-mode EMI inductors, including the optimization process of designing common-mode EMI filter inductors, designing the geometric structure and number of turns of common-mode EMI filter inductors according to the inductance requirements, and then calculating whether it is necessary to consider the core time-varying parasitic capacitance C c Incorporate it into the circuit model, finally calculate the impedance curve, and determine whether it meets the requirements.

2. The method for predicting and improving broadband impedance of a common-mode EMI filter inductor according to claim 1, characterized in that: The steps of the improved common-mode EMI filter inductor high-frequency equivalent circuit include: a circuit model is formed by connecting the circuit models of two windings in parallel; in a single winding, each turn is regarded as an independent unit, including a series self-inductance L s and core loss R s and C in parallel tt , the C tc One end is connected to the left side of the unit and the other end is connected to the other C tc Share a common node.

3. The method for predicting and improving broadband impedance of a common-mode EMI filter inductor according to claim 1, characterized in that: The step of extracting the improved high-frequency equivalent circuit parameters comprises: S1. The calculation of inter-turn capacitance is divided into internal area, external area, and parallel area (front and back). The formula can be expressed as: C tt =C ttin +C tto +C ttl +C ttl′w The specific analytical formulas for S11 and inter-turn capacitance are as follows: S2. For the calculation of the turn-to-core capacitance, it is also divided into the inner area, the outer area, and the parallel area (front and back). The formula can be expressed as: C tc =C tcin +C tco +C tcl +C tcl′w The specific analytical formulas for S21 and turn-to-core capacitance are as follows: S3. The geometric characteristics of the common-mode EMI filter inductor are fully considered, including the dielectric properties and thickness of the winding insulation, the actual winding length of the winding, and the actual distance from the equivalent turn to the core. S31. In the actual winding length of the winding, the corrected parallel area length expression is: S32, the actual equivalent turn to core distance expression is:

4. The method for predicting and improving broadband impedance of a common-mode EMI filter inductor according to claim 1, characterized in that: The common mode EMI inductor is optimized The following steps are included to determine whether it is necessary to consider the core time-varying parasitic capacitance C c The method incorporated into the circuit model includes calculating the inductance value and the capacitance value, which includes the spatial parasitic capacitance and the core time-varying parasitic capacitance C c , compare the calculated value with the number of turns designed previously; If the number of turns designed is greater than this value, there is no need to include the core capacitance in the circuit model. If it is less than this value, the core capacitance needs to be built into the circuit model.

5. The common mode EMI filter inductor high frequency modeling optimization method according to claim 1 is characterized in that: The optimization process for designing a common-mode EMI filter inductor includes targeted adjustment of the inductor's winding method, core material, and winding model.

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