Device and method for determining the properties of a magnetic core

Abstract

To determine the properties of a magnetic core (1), a measuring volume has several subvolumes (2a - 2c), wherein - a centrally arranged subvolume (2b) has the shape of a hollow cylinder, - extending from the area of ​​the two base surfaces of the hollow cylinder of the centrally arranged sub-volume (2b) in the opposite direction, two further sub-volumes (2a) and (2c) - in the area of ​​the two base surfaces of the hollow cylinder of the centrally arranged partial volume (2b) a circuit board (3a, 3b) with measuring resistors (4) and measuring connection (4a) is arranged, - an inner conductor (5) is arranged in the measuring volume, which extends along the longitudinal axis of the measuring volume, - the two further sub-volumes (2a) and (2c) transfer the diameter of the centrally arranged sub-volume (2b), designed as a hollow cylinder, with decreasing diameter to electrical connections (6a) and (6b), - the electrical connections (6a) and (6b) are electrically connected to the inner conductor (5) and the measuring volume with several sub-volumes (2a - 2c), - the magnetic core (1), whose properties are determined, can be positioned within the centrally arranged partial volume (2b), which has the form of a hollow cylinder, and the inner conductor (5) can be guided through the magnetic core (1).

Description

[0001] The present invention relates to a device and a method for determining properties of a magnetic core having the features according to the patent claims.

[0002] Measurement setups for determining parameters of magnetic cores, such as toroidal cores, are state-of-the-art. In particular, they determine either the effect of the frequency-dependent permeability of the core (dispersion) or the saturation behavior. However, the dispersion behavior of toroidal cores in particular changes significantly with increasing saturation. Previous measurement setups assume an unsaturated core or only investigate the saturation behavior without determining the dispersion. To create a network model that can sufficiently accurately represent both the dispersion and saturation of a toroidal core, knowledge of the interdependence of both parameters is required. This network model is necessary for the simulation-based design of EMC filters with toroidal cores.Without a simulation model, the dimensioning of the toroidal core occurs late in the product development stage, which is particularly critical for the available installation space. Furthermore, if the design is carried out without simulating saturation effects, the core material is not optimally utilized, resulting in unnecessary increases in cost, weight, and installation space in the product.

[0003] According to document CN 104849680 A, it is state of the art to determine the characteristics of a magnetic core as part of the design of an EMC / EMI filter. However, in conjunction with simulation models and a network analyzer, only a broadband determination of the relative magnetic permeability of a magnetic core is performed.

[0004] A method for extracting the relative permeability of a toroidal core in a specific arrangement is also known from the further document KR 102537967 B1, wherein, among other things, the permeability of the core is determined in a specific frequency range.

[0005] It is an object of the present invention to improve the devices and methods for determining properties of a magnetic core according to the prior art.

[0006] This object is achieved by means of a device and a method having the features according to the patent claims, wherein in particular a structure for the metrological determination of the dispersion taking into account the saturation behavior of magnetic cores is proposed.

[0007] Advantageous embodiments of the present invention and a description of the effects achieved can be found in the following embodiment and the dependent patent claims.

[0008] According to Fig. 1 shows a magnetic core 1, which is in particular a toroidal core, i.e., a ring-shaped magnetic circuit that, for example, in conjunction with windings, can form an inductive component, such as a toroidal coil (of an EMC filter) or a toroidal transformer. The magnetic core can also have an air gap or be slotted. In particular, the (ring-shaped) magnetic core 1 is made of strip material, but it is also possible to manufacture it from ferrite or powder materials, for example.

[0009] Fig. Figure 2 shows, schematically or in a highly simplified exploded view, the structure of the device according to the invention or of a device configured to carry out the method specifically described below. This measurement setup for determining properties of the magnetic core 1 has a measurement volume with several sub-volumes 2a-2c. Circuit boards 3a, 3b with measuring resistors 4 are arranged between the sub-volumes 2a-2c. An inner conductor 5 is arranged in the measurement volume, which has / consists of several sub-volumes 2a-2c. The inner conductor 5 extends along the longitudinal axis of the measurement volume or along the longitudinal axes of the sub-volumes 2a-2c.

[0010] A centrally located sub-volume 2b has, as shown in Fig. 2 and Fig. 3, the (inner) shape of a hollow cylinder. In the area of ​​the two base surfaces of the hollow cylinder of the partial volume 2b, a circuit board 3a, 3b with measuring resistors 4 is positioned / arranged. The two further partial volumes 2a and 2c are connected to the respective circuit board 3a, 3b with measuring resistors 4 and measuring connection 4a, or starting from the area of ​​the base surfaces of the hollow cylinder of the partial volume 2b, where the circuit boards 3a, 3b with measuring resistors 4 are arranged, the two further partial volumes 2a and 2c extend in opposite directions. The two further partial volumes 2a and 2c each have the (inner) shape of a cone or truncated cone, so that the measuring volume tapers in both directions of its longitudinal extent, starting from the first partial volume 2b. I.e. the two further partial volumes 2a and 2c transfer the diameter of the first partial volume 2b, which is designed as a hollow cylinder, conically orwith a (continuously) decreasing diameter to the diameter of suitable electrical (measuring / supply) connections or contacts 6a and 6b, such as sockets, plugs or similar, as shown in . Fig. 2 and Fig. 3 are shown symbolically or schematically, wherein these electrical connections 6a and 6b (among others) are electrically connected to the inner conductor 5 and the measuring volume or the partial volumes 2a - 2c.

[0011] As in Fig. 2 and Fig. 3, the measuring volume with a plurality of partial volumes 2a - 2c is arranged within a housing or is made of elements that form a wall, wherein the housing / the elements can have a wall or external shape that deviates or can deviate from the (inner) shape of the measuring volume that is formed from the plurality of partial volumes 2a - 2c, and for example does not have an (outer) shape of a cylinder or hollow cylinder or cone or truncated cone, but a rectangular shape, which can be advantageous in practical application.

[0012] The measuring volume, comprising the several sub-volumes 2a - 2c or the housing / the elements forming a wall is / are made of electrically conductive material, in particular of aluminum.

[0013] Fig. Figure 3 shows the measuring volume (in a longitudinal section) with a magnetic core 1, whose properties are being determined. The magnetic core 1, designed here as a toroidal core / toroidal strip core, is inserted into the measuring volume or is arranged / positioned in the measuring volume, in the region of the partial volume 2b, which has the shape of a hollow cylinder, and is fixed in a suitable manner (not shown). The inner diameter or the inner surface of the magnetic core 1 points in the direction of the inner conductor 5. This means that the inner conductor 5 is guided through the magnetic core / toroidal core 1 or through its recess / opening (in the center). The inner conductor 5 is in the Fig. 2 and Fig. 3 is designed and shown as a single piece, but can also be constructed from several individual elements. The inner conductor 5 is made of an electrically conductive material.

[0014] One of the circuit boards 3a, 3b arranged in the area of ​​the base surfaces or ends of the hollow cylinder of the partial volume 2b with measuring resistors 4 and measuring connection 4a is in Fig. 4 is shown in simplified or schematic form. The circuit boards 3a, 3b each have, according to their arrangement at the two (circular) ends of the hollow cylinder of the partial volume 2b, a circular area 4b without (continuous) conductive lamination. The measuring resistors 4, which the circuit boards 3a, 3b have, are arranged in particular between the inner conductor 5 (in Fig. 4 shows only the recess in the center of the circuit boards 3a, 3b through which the inner conductor 5 is guided) and the measuring volume / partial volume 2a - 2c or the housing / wall and the respective measuring connection 4a, or form an electrical connection. The resistors 4 are arranged in the circular area 4b, in particular radially between the inner conductor 5 and the housing / wall / the measuring volume / partial volumes 2a - 2c and the measuring connection 4a, as shown in Fig. 4 is indicated by dashed lines. This means that the circular area 4b between the inner conductor contact (circle in the middle) and the “outer conductor” (circle outside) does not have any conductive lamination, except for the pads for the cascade of measuring resistors 4. Fig. The area 4c of the circuit boards 3a, 3b outside the circular area 4b shown in Figure 4 has a conductive lamination and vias 4d, so that a conductive electrical connection is established or exists between the partial volumes 2a and 2b, or 2b and 2c. This means that the areas 4c of the front and back of the circuit boards 3a, 3b are connected, in particular at regular intervals, with through-holes 4d, so that an electrical connection exists or a current flow is possible.

[0015] Through this construction with the resistors 4 distributed over the radius and the through-holes 4d (in the area 4c), by means of the circuit boards 3a, 3b or with this / these round coaxial device(s) it is possible to carry out a voltage measurement between the inner conductor 5 and the “outer conductor”, i.e. the measuring volume / partial volume 2a - 2c or the housing / wall / partial volumes 2a - 2c and at the respective measuring connection 4a, and to do so without reflections and asymmetries, as with a direct tap or a single series resistor. In other words: The voltage measurement(s) are specifically performed between two points, namely the intersection / electrical contact of 3a or 3b (circuit boards) and 5 (inner conductor), as well as 3a or 3b (circuit boards) and 2a or 2c (“outer conductor” or measuring volume / partial volume), with the measured value being tapped via 4a in each case. The design of such circuit boards 3a, 3b orPrinted circuit boards with low signal distortion (dispersion) and reflection are used in the field of time domain measurement technology for fast pulsed signals with high voltages in specific applications.

[0016] As in connection with Fig. 2, the two further partial volumes 2a and 2c transfer the diameter / radius of the hollow cylinder of the first partial volume 2b conically or with a (continuously) decreasing diameter / radius towards, i.e. onto (or onto the diameter / radius of) suitable electrical (measuring) connections or contacts 6a and 6b, such as sockets, plugs or similar, as described in Fig. 2 and Fig. 3 are shown symbolically or schematically, with these electrical connections 6a and 6b being electrically connected to both the inner conductor 5 and the housing / wall / partial volumes 2a-2c. In particular, the electrical connections 6a and 6b are designed as 7 / 16 plugs.

[0017] According to Fig. 5, in conjunction with an equivalent circuit diagram, shows that a supply current is impressed on one of these plugs / connectors 6a and the other plug / connector 6b is terminated with a resistor 7 of, in particular, 50 ohms.

[0018] The supply current is determined from the voltage drop across the (terminating) resistor 7. Voltages are measured via the measuring terminals 4a on the circuit boards 3a, 3b within the measuring volume, which are arranged between the sub-volumes 2a - 2c (shown here only schematically or, for simplicity, uniformly as hollow cylinders). Assuming quasi-static conditions, the voltage drop in the hollow cylinder / in the measuring volume / in the sub-volumes 2a - 2c can be determined using network theory. Quasi-static conditions here means that the selected frequency is chosen such that no effects occur in the structure / in the measuring volume / in the sub-volumes 2a - 2c that are attributable to wave propagation in electrically large structures, i.e., the structure is significantly smaller than the smallest excited wavelength. Thus, the resistors 4 used can be regarded as discrete components in the sense of network theory.

[0019] The measuring procedure or the method carried out in connection with the device according to the invention is characterized in detail by the fact that between the inner conductor 5 and the measuring volume / the partial volumes 2a - 2c / the hollow cylinder wall or the housing / the wall of the measuring volume, a sinusoidal voltage with a certain frequency is applied by means of the connection 6a, so that a supply current with a defined amplitude flows (as in Fig. 5 (shown schematically in the diagram section at the bottom left).

[0020] The voltage drops between the inner conductor 5 and the measuring volume / partial volumes 2a - 2c / the hollow cylinder wall or the housing / the wall of the measuring volume via the measuring resistors 4, which are provided on the circuit boards 3a, 3b.

[0021] These resistors 4 represent a voltage divider (to protect the measuring instruments), at the end of which a measuring terminal 4a is provided, to which a measuring instrument with a specific internal resistance (as in Fig. 5 by means of the symbol for a resistor) a voltage (magnitude and phase) proportional to the interior of the measuring volume / to the interior of the partial volumes 2a - 2c / to the interior of the hollow cylinder 2b can be measured.

[0022] The voltage drop (magnitude and phase) across the toroidal (band) core 1 is determined from the difference between the voltages (magnitude and phase) measured (using measuring devices connected to the respective measuring terminals 4a) before and after the toroidal (band) core 1, i.e. from the difference between the electrical voltages measured by means of the (first) circuit board 3a with resistors 4 and the voltages measured by means of the (second) circuit board 3b with resistors 4. In addition, the voltage (magnitude and phase) at the terminating resistor 7 is measured (as in Fig. 5 (shown schematically in the diagram section bottom right) and the supply current flowing in the inner conductor 5 is determined using Ohm's law. From the current and voltage quantities, the amplitudes of the fundamental waves and the phase shift between current and voltage are calculated in order to establish or determine the complex impedance of the magnetic core 1 or toroidal (strip) core 1. From the impedance, the complex permeability is established as a function of various saturation currents, as is generally known to those skilled in the art. The procedure is repeated for different frequencies, i.e., sinusoidal voltages are repeatedly applied at different frequencies.

[0023] Preferably, the frequency-dependent empty impedance of the measurement setup (with all its elements, in particular those with the reference symbols 2a - 2c, 3a, 3b, 4, 5, 6a, 6b, 7) is first determined from an empty measurement without the magnetic core 1 or toroidal (strip) core 1 inserted into the measurement volume, using the voltage drop determined (as described above) and the supply current. To measure a magnetic core 1 or toroidal (strip) core 1, a supply current with a set frequency is then specified (when it is inserted into the measurement volume), and the amplitude of the fundamental wave is determined from the voltage drop measured in the time domain. The frequency-dependent impedance of the entire setup is determined from the amplitude of the fundamental wave and the supply current. By subtracting the empty impedance, the impedance of the magnetic core 1 or toroidal (strip) core 1 is obtained, which is both frequency-dependent and dependent on the amplitude of the supply current. The procedure is repeated for different frequencies.

[0024] Measuring the quantities in the time domain allows for the evaluation of higher harmonics for further investigations. If the material parameters of the magnetic core 1 are to be determined using the inventive setup only from the fundamental wave, measurements in the frequency domain are also possible. However, measurements in the frequency domain can only be converted into time domain properties for linear components. Since the device is designed to record non-linear component properties, two taps and measurement of the voltages on the measuring device with internal resistance (as in Fig. 5 by means of the symbol for a resistor) and at the terminating resistor 7 (as shown in Fig. 5) in the time domain, wherein the source (at the connector / connectors 6a, as shown in Fig. 5) can be operated in the frequency or time domain.

[0025] The proposed measurement setup / device enables the metrological determination of the dispersion of magnetic cores 1, in particular toroidal (strip) cores 1, taking the supply current into account. Dispersion here refers to the effect of the frequency-dependent permeability of the toroidal core. Due to the geometry, the impedance results directly from the permeability and thus also includes the dispersion. The permeability, and analogously the impedance, also depend on the saturation (level of the supply current). By traversing a characteristic field for different frequencies and different supply currents, the permeability (for a magnetic core 1) can be described as a function of the supply current and the frequency.

[0026] This enables the use of the fundamental wave-based impedance in a network simulation for simulation-supported design. The special combination of the round coaxial structure (the measurement volume / sub-volume 2b), which originates from high-frequency measurement technology, with the circuit boards 3a, 3b, which originate from time-domain measurement technology, allows the simultaneous measurement of magnitude and phase to determine the characteristic map without causing unacceptably high reflections in the RF system. This means that the structure consisting of two conically tapered geometries (sub-volumes 2a, 2c) with a hollow cylinder in the center (sub-volume 2b) was chosen because this structure has low reflections in the considered frequency range (DC or 0 Hz to 100 MHz). Any change in the slope of the conductive edges of the coaxial waveguide leads to reflections, as well as field distortions for the electric or magnetic field.To achieve sufficiently low-reflection implementation in the frequency range, the conical widening of the outer conductor (measuring volume / partial volume 2a - 2c) and the radially symmetrical distributed arrangement of the resistors 4 on the circuit boards 3a, 3b were chosen.

[0027] The device according to the invention or this structure allows the use of conventional high-frequency amplifiers for generating characteristic curve fields up to the saturation range, so that the simulation-supported design of EMC filters with toroidal (band) cores 1 can be carried out in conjunction with a network model that sufficiently accurately represents both the dispersion and saturation of a magnetic core 1 or toroidal (band) core 1, since this model includes the dependence of both parameters. Using a network or simulation model that sufficiently accurately represents both the dispersion and saturation of a magnetic core 1 or toroidal (band) core 1, the dimensioning of the toroidal (band) core 1 can be carried out at an early stage or in the product development stage, which is particularly advantageous with regard to the available installation space.When designed with such a simulative investigation of saturation effects, the core material is also used more optimally, so that costs, weight and installation space in the product are reduced.

[0028] For an example core 1 with constructed saturation behavior, the principal curves for the real and imaginary part of the (complex) permeability determined (here from a simulation) as a function of different supply currents / frequencies are shown in Fig. 6. A possible application for the material parameters determined with the presented method is a network model of the toroidal core 1, as already described. This means that by means of the device according to the invention (and the associated method), it is possible to create a network model that can represent both dispersion and saturation of a toroidal core 1 with sufficient accuracy, precisely this dependence of both parameters, as in Fig. 6 shown.

Claims

[1] Device for determining properties of a magnetic core (1) comprising a measuring volume with several sub-volumes (2a - 2c), wherein - a centrally arranged partial volume (2b) has the shape of a hollow cylinder, - two further sub-volumes (2a) and (2c) extend in opposite directions from the area of the two base surfaces of the hollow cylinder of the centrally arranged sub-volume (2b), - in the area of the two base surfaces of the hollow cylinder of the centrally arranged partial volume (2b) a printed circuit board (3a, 3b) with measuring resistors (4) and measuring connection (4a) is arranged, - an inner conductor (5) is arranged in the measuring volume, which extends along the longitudinal axis of the measuring volume, - the two further sub-volumes (2a) and (2c) transfer the diameter of the centrally arranged sub-volume (2b) designed as a hollow cylinder with decreasing diameter to electrical connections (6a) and (6b), - the electrical connections (6a) and (6b) are electrically connected to the inner conductor (5) and the measuring volume with several sub-volumes (2a - 2c), - the magnetic core (1), the properties of which are determined, can be positioned within the centrally arranged partial volume (2b), which has the shape of a hollow cylinder, and the inner conductor (5) can be guided through the magnetic core (1). [2] Device according to claim 1, wherein the magnetic core (1) is a toroidal core made of strip material. [3] Device according to claim 1 or 2, wherein the measuring volume with a plurality of sub-volumes (2a - 2c) is arranged within a housing or is made of elements that form a wall, wherein the housing / the elements have / have an outer shape that deviates from the inner shape of the measuring volume that is formed from the plurality of sub-volumes (2a - 2c). [4] Device according to claim 1 to 3, wherein - the printed circuit boards (3a, 3b) each have a circular area (4b) without an electrically conductive lamination at the two ends of the hollow cylinder of the partial volume (2b), according to their arrangement, and the measuring resistors (4) are arranged in the circular area (4b), wherein an electrically conductive connection exists between the inner conductor (5) guided through the printed circuit boards (3a, 3b), the measuring resistors (4), the measuring volume / partial volumes (2a - 2c) and the respective measuring connection (4a), - the printed circuit boards (3a, 3b) have a further region (4c) outside the circular region (4b) which has a conductive lamination and through-contacts (4d), so that an electrically conductive connection exists between the partial volumes (2a) and (2b) and (2b) and (2c). [5] Device according to claim 4, wherein the resistors (4) are arranged in the circular region (4b) radially between the inner conductor (5) and the measuring volume / partial volumes (2a - 2c) and the measuring connection (4a). [6] Device according to claim 1 to 5, wherein the inner conductor (5) is designed in one piece or is constructed from several individual elements. [7] Device according to claim 1 to 6, wherein the electrical connections (6a) and (6b) are designed as 7 / 16 plugs. [8] Method for determining properties of a magnetic core (1) by means of a device having the features according to claims 1 to 7, wherein - by means of an electrical connection (6a) between the inner conductor (5) and the measuring volume / partial volumes (2a - 2c) a voltage with a specific frequency is applied so that a supply current flows, - the supply current is determined at a resistor (7) with which the further electrical connection (6b) is terminated, - the voltage drop across the magnetic core (1) is determined based on the difference between the voltages measured at the measuring terminals (4a) of the printed circuit boards (3a, 3b) with measuring resistors (4) before and after the magnetic core (1), - depending on the determined electrical quantities, the amplitudes of the fundamental waves and the phase shift between current and voltage are calculated in order to determine the complex impedance of the magnetic core (1), - the complex permeability is determined from the complex impedance, - different frequencies and different supply currents are set so that the complex permeability of the magnetic core (1) is determined as a function of the supply current and the frequency. [9] Method according to claim 8, wherein a simulation-supported design of an EMC filter with a magnetic core (1) in conjunction with a network model is carried out as a function of the complex permeability as a function of the supply current and the frequency. [10] Method according to claim 8, wherein frequencies are set in the range between 0 Hz and 100 MHz.

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