Normal mode inductor for DC large current and noise filter

Abstract

The present invention realizes a noise filter by a magnetic core that does not cause magnetic saturation in a circuit in which a large current flows.　A large current is divided into a plurality of conductors, and a noise filter by a magnetic core is provided in each of the plurality of conductors.　The magnetic cores may be configured such that one conductor passes through a plurality of different magnetic cores, wherein the characteristics of the plurality of cores may be varied to widen the frequency band.　It is also possible to provide a core type noise filter capable of coping with common mode noise in addition to interruption of normal mode noise.

Description

Normal mode inductor for large DC currents and noise filters

[0001] The present invention relates to a large current normal mode inductor and noise filter that can effectively block noise in circuits through which large currents flow. More specifically, the present invention relates to a noise filter inductor device and noise filtering method that can be used as a noise filter in switching circuits through which large currents flow, and that achieves effective noise filtering by avoiding the effects of magnetic saturation in normal mode inductors.

[0002] Inverters and high-voltage DC / DC converters for power motors in electric vehicles, hybrid vehicles, electric aircraft, and other applications often switch between 10 kHz and 200 kHz. These harmonics can cause noise interference problems. For example, harmonic noise from switching can radiate from the harness between the inverter and battery in an electric vehicle, affecting AM radio, wireless, and in-vehicle communications. Harmonic switching noise also leaks from DC / DC converters used in electric vehicle development test benches and solar power generation systems, causing EMC problems. While normal mode and common mode noise generally coexist in power electrical circuits, noise filters using inductors with ring cores designed to filter normal mode noise in high-current circuits have been difficult to implement due to magnetic saturation caused by high currents. Therefore, in conventional technology, inductors with normal mode cores that block noise cannot be used in circuits with high currents, and core-based filters have typically been designed for common mode signals with common mode cores. Generally, most noise countermeasures have been developed at the level of handling voltage and current in the so-called low-voltage field, but noise countermeasures for circuits where extremely large currents flow, which is the field of the present invention, have been lacking. That is, in electric vehicles and hybrid vehicles where large currents flow, the method of containing noise radiation using shielded wire has been the norm. However, because wiring harnesses using shielded wire have a complex structure and are expensive, there has been a demand for a noise reduction method for large currents that reduces the noise itself.

[0003] Here, magnetic saturation means that even if a material has a high magnetic permeability, when a very large magnetic field is applied, the magnetic permeability decreases and eventually approaches the relative magnetic permeability of 1. In other words, the magnetic permeability μ of a vacuum ０ This is a phenomenon in which the relative permeability approaches 1. Therefore, when a ferrite core is used as a noise killer, for example, for an electric wire through which a strong magnetic field, i.e., a large current, flows, the inductance decreases due to the action of the strong magnetic field caused by the large current, making it unusable as a noise killer. Even in ferromagnetic materials, which have extremely high magnetic permeability, the permeability, i.e., the hysteresis curve in the B-H curve, experiences magnetic saturation, where the slope becomes zero at the upper and lower edges, i.e., the relative permeability becomes 1. When a magnetic field H is applied to a magnetic material, this magnetic saturation aligns the spins, but when all the spins are no longer aligned, the increase in magnetic flux density due to the alignment of the spins reaches a plateau, no matter how much the magnetic field is increased.

[0004] This causes magnetic saturation, where the magnetic flux density does not increase even if the magnetic field is further increased. When magnetic saturation occurs, the noise blocking effect due to energy consumption caused by the reversal of the magnetic moment of the magnetic core, as described below, disappears, the relative permeability becomes 1, and the noise current blocking effect due to inductance is also reduced. For this reason, magnetic cores have not been used in conventional technology as a means of suppressing normal mode noise propagating through electric wires carrying large currents.

[0005] Patent Document 1 discloses a noise filter having a divided magnetic core that surrounds a bus bar to attenuate noise propagating through the bus bar. In the case of wiring through which a large current flows, such as a bus bar, it is important to suppress magnetic saturation of the magnetic core, particularly in a differential mode noise filter. The noise filter described in Patent Document 1 below includes a gap spacer portion sandwiched between one core member and the other, thereby forming a gap between the two core members to suppress magnetic saturation (paragraph 0002). Patent Document 1 also introduces Japanese Patent Application Laid-Open No. 2005-93536. However, simply providing a gap is insufficient to effectively block normal mode noise in circuits through which large currents, such as those found in electric vehicles, flow.

[0006] Patent Document 2 discloses that "the ferrite core of the filter unit described above to be installed in an inverter device as an EMC filter must be selected to have appropriate impedance characteristics and high-frequency characteristics corresponding to the magnitude and frequency of the noise current, the inverter carrier frequency, etc. In practice, EMC filters selected for various inverter device models with different ratings are installed and verified, and their noise reduction effects are evaluated and determined. For example, when the amount of noise current generated is large, in order to avoid magnetic saturation of the ferrite core, it is necessary to select and modify the filter unit 3, such as by increasing the number of ring-shaped ferrite cores 1 shown in Figure 8 and arranging multiple ferrite cores coaxially and winding cable 2 around these ferrite cores together" (paragraph 0007). However, even if multiple ferrite cores are arranged coaxially, they cannot be used in circuits through which currents that would magnetically saturate the multiple cores flow.

[0007] Patent Document 3 discloses that "when a filter is inserted into a signal line, particularly a power line, the magnetic saturation of the core material limits the effective current value" (paragraph 0039), and that "therefore, in a line noise attenuator according to an embodiment of the present invention, the number of windings in one core material is limited to the limit number of turns at which magnetic saturation occurs at the desired signal current value, and an element in which this inductor 1 is combined in parallel with resistor 2 is used as a unit element, thereby achieving practical application of a noise attenuator that can withstand the desired current of a power line, etc. Note that the limit number of turns at which magnetic saturation occurs is determined by the current value flowing in the conductor line, and is not uniquely determined, but is adjusted according to the current value" (paragraph 0040). In other words, this invention limits the number of turns of the conductor wire wound around the filter core to a level that does not cause magnetic saturation, but this conventional technology is only suitable for currents in power lines of communication devices, etc., and cannot be used as a noise filter in circuits through which much larger currents flow.

[0008] JP 2018-125426 A JP 2011-192825 A JP 2010-130368 A

[0009] Therefore, an object of the present invention is to provide an inductor that uses a magnetic core, is easy to handle, and can effectively filter normal mode noise without magnetic saturation even when used as a noise countermeasure in a circuit through which an extremely large current not previously seen, i.e., a current of several hundred amperes to over one thousand amperes, flows, and a noise filter using the inductor.

[0010] The present invention includes the following aspects. [1] A noise filter inductor having one input terminal and one output terminal, wherein a conductor is divided into multiple conductors between the two terminals, and each of the multiple conductors passes through a magnetic core. [2] The inductor according to [1], wherein the conductor passing through the magnetic core is wound around the core one or more times. [3] The inductor according to [1], wherein the core and the multiple conductors are configured so that magnetic saturation occurs when the sum of currents flowing through the multiple conductors between the input terminal and the output terminal passes through one core, but magnetic saturation does not occur even when each of the divided currents of the multiple conductors passes through each core. [4] The inductor according to [1], wherein the conductor wound around one core is further divided into multiple conductors. [5] A noise filter that removes normal mode and / or common mode noise by connecting line-to-line and line-to-ground capacitors to a plurality of inductors according to [1] to [4]. [6] The noise filter according to [5], which has an even number of inductors and further has a common mode winding core through which a set of the plurality of conductors with opposite current directions passes, thereby serving as a core for common mode noise.

[0011] The inventors of the present application recognized that in order to effectively block normal mode noise, it is necessary to maintain the required inductance without causing magnetic saturation, and arrived at the following configuration.

[0012] High-current normal-mode inductors prevent saturation by dividing the current into gapped cores in parallel, but parallel connection of cores or gaps reduces inductance. However, winding wire around the core increases the inductance value by the square of the number of turns, making it possible to maintain the required inductance in normal mode even with high currents. In other words, even if the total current flowing through the inductor of the present invention is large enough to magnetically saturate a single core, by dividing this current into multiple conductors and providing an annular core for each conductor, the current passing through the holes in each annular core can be reduced to a level that does not reach magnetic saturation. By winding the conductors multiple times around the annular core to compensate for the reduced combined inductance, magnetic saturation does not occur, thereby not interfering with the core's noise filtering effect. Furthermore, because the total current flowing through the multiple conductors is the desired high current, the annular core's noise-blocking effect effectively filters normal-mode noise, even in a conductor carrying a large current.

[0013] Furthermore, the characteristics of the core as a noise filter vary depending on its material, shape, dimensions, whether or not a gap is provided in the core, the total magnetic reluctance of the core when a gap is provided, and the overall magnetic permeability of the core. Therefore, by using the most suitable core in accordance with the overall performance requirements of the inductor of the present invention, it is possible to construct a noise filter inductor with the desired characteristics.

[0014] The noise blocking effect on the conductor passing through the hole in the annular core is that the core and conductor form an inductor, and the reactance and resistance components of the inductor's impedance limit the noise current by reactance at high frequencies, and by the energy consumption effect caused by the reversal of the magnetic moment of the magnetic material that makes up the core, and each has different frequency characteristics.

[0015] Furthermore, if a gap is provided in the core, the magnetic flux density generated in response to the magnetomotive force generated by the current flowing through the conductor passing through the hole in the core decreases due to the increased magnetic resistance of the magnetic circuit, so the saturation current value at which magnetic saturation occurs can be increased. However, this also reduces magnetic loss, so the noise current limiting effect due to the energy consumption effect is reduced.

[0016] Furthermore, if magnetic saturation is prevented by inserting a gap in the core, the wires and busbars used for large currents require a large cross-sectional area, but they cannot be easily wound around the core. Therefore, the required cross-sectional area can be obtained by dividing the wires and busbars into sections with smaller cross-sectional areas.

[0017] Furthermore, in a structure in which a conductor is wound around a core, in addition to the conductor passing through the core without any windings, it is also possible to have the conductor wound around the core multiple times before connecting to both terminals of the inductor, such as passing through the core with only one winding, two windings, three windings, etc. Winding in this way provides a wider range of adjustment for the inductance value, making it easier to manufacture an inductor with the desired characteristics.

[0018] It is also possible to create a circuit that adds capacitors and common mode cores in addition to normal mode cores to create a filter that can be adapted to noise conditions. These additions make it possible to change the characteristics of the noise filter. For example, capacitors can be placed between lines and between grounds, or between cores, allowing for a wide variety of configurations.

[0019] The present invention provides a novel noise filter design that enables use of a normal mode core in circuits carrying large DC currents, such as those found in electric vehicles and high-current power supplies, where noise filters using conventional cores are unable to be used due to magnetic saturation. The noise filter inductor of the present invention has two connection terminals, and when a large current flows between these terminals, the inductor functions as a noise filter that provides the desired noise blocking function. This effectively blocks electromagnetic radiation from noise-generating circuits beyond the noise-blocked circuit, eliminating the need for conventional complex and heavy shielded cables, shielded connectors, and shielded lithium-ion batteries. Furthermore, the filter characteristics of the inductor of the present invention can be adjusted to desired values ​​by optimizing the core and overall inductor structure, including the noise-blocking core structure, material, conductor arrangement, and the presence and number of windings.

[0020] Although the term "inductor" is used in this invention, this does not mean that the inductance component of impedance is utilized, but rather that the term is used simply because the inductor functions as a low-pass filter that blocks high-frequency waves known as noise. Since the focus is on magnetic saturation, it goes without saying that the emphasis is on the resistance component of impedance, and when used in an actual circuit, the elements of resistance, induction, and capacitance are all to be taken into consideration.

[0021] Fig. 1 is a schematic diagram illustrating that 1-A is a conventional configuration that causes magnetic saturation, and 1-B is a configuration of the present invention that does not cause magnetic saturation. Fig. 2 is a schematic diagram of an inductor in which a conductor is wound multiple times around a core, which is an embodiment of the present invention. Fig. 3 is a schematic diagram of an inductor for normal mode noise, which is an embodiment of the present invention. Fig. 4 is a schematic diagram of a filter for normal mode noise, which is an embodiment of the present invention. Fig. 5 is a schematic diagram of a noise filter having a common mode core, which is an embodiment of the present invention.

[0022] The basic principle of the present invention is shown in Figure 1. In the conventional configuration shown in 1-A, conductor 1, through which a large current flows, passes the large current flowing from input electrode 3 to output electrode 4 and penetrates a hole in core 2. In the present invention shown in 1-B, this conductor is divided into multiple conductors, and in the example shown, it is divided into three conductors 1a, 1b, and 1c, each of which penetrates a hole in cores 2a, 2b, and 2c. The three conductors are configured so that approximately equal currents flow, and in order to increase the noise blocking effect, it is important to keep the state of the multiple conductors as similar as possible in order to improve the noise filter characteristics.

[0023] In the case of Figure 1-A, the core material is such that when 30 A passes through the core holes, magnetic saturation occurs due to the current. In the present invention of Figure 1-B, three conductors carrying 10 A, i.e., 1a, b, and 1c, are passed through the holes of three cores made of the same material, i.e., 2a, 2b, and 2c. Just as in the case of 1-A, which has a single conductor, input and output electrodes 3 and 4 are provided in 1-B as well. In the present invention, if the three cores 2a, 2b, and 2c in 1-B have the same dimensions as core 2 in 1-A, which saturated at 30 A, they would not saturate at 10 A, of course. However, since the current is reduced to 10 A even with smaller dimensions, it is sufficient to use dimensions that do not saturate at 10 A.

[0024] It goes without saying that the inductor of the present invention may be used as a noise filter in combination with a capacitor, and by providing necessary shielding and grounding, the noise blocking effect may be enhanced. As shown in Figure 2, the conductors 16a, 16b, and 16c passing through the cores may be wound multiple times around the cores 2a1, 2b1, and 2c1. Figure 2 shows an example in which the conductors are wound only once. Increasing the number of turns increases the inductance, but also makes magnetic saturation more likely to occur. Therefore, by selecting an appropriate number of turns, it becomes easier and more diverse to obtain the desired characteristics of the inductor as a whole.

[0025] As shown in Figure 3, by configuring the normal mode core so that multiple conductors each have multiple turns penetrating it, the inductor of the present invention can both adjust the inductance by changing the number of turns and avoid saturation by dividing it into multiple conductors, as described above. The use of multiple cores also increases the degree of freedom in overall shape. For example, a large current Ia flowing from the power supply to the motor, which is the drive current for a motor, flows from input electrode 3a to output electrode 4a, and a return current Ib from the motor flows from input electrode 3b to output electrode 4b. The normal mode noise current is a high-frequency current that alternates between flowing from 3a to 4a, from 3b to 4b, or the opposite direction.

[0026] As shown in FIG. 4, by providing capacitors Ca, Cag, and Cbg between the lines of the inductor and the ground, the inductor can be used as a noise filter.

[0027] As shown in FIG. 5, by providing a common mode core 7 in addition to the normal mode core in FIG. 4, it is possible to use it as a filter that reduces both common mode and normal mode noise.

[0028] 1: Conductor 1a, 1b, 1c: Multiple conductors 2a, 2b, 2c: Normal mode core 2a2, 2b2, 2c2: Cores without conductor winding 2a1, 2b1, 2c1: Cores with conductor winding 3, 3a, 3b: Input electrodes 4, 4a, 4b: Output electrodes 7: Common mode core Ca, Cag, Cbg: Capacitors

Claims

1. A noise filter inductor having one input terminal and one output terminal, in which the conductor splits into multiple wires between the two terminals, and each of the multiple split wires passes through a magnetic core.

2. An inductor as claimed in claim 1, in which the conductor passing through the magnetic core is wound around the core one or more times.

3. An inductor as claimed in claim 1, wherein the core and the multiple conductors are configured so that the sum of the currents flowing between the input terminal and the output terminal through the multiple conductors causes magnetic saturation when they pass through one core, but magnetic saturation does not occur even when each of the divided currents of the multiple conductors passes through its own core.

4. The inductor according to claim 1, wherein the conductor wound around one core is further divided into a plurality of conductors.

5. A noise filter that removes normal mode and / or common mode noise by connecting a plurality of inductors as defined in claims 1 to 4 with line-to-line and line-to-ground capacitors.

6. A noise filter as claimed in claim 5, comprising an even number of inductors and further comprising a common mode winding core through which the sets of conductors with opposite current directions pass, thereby serving as a common mode noise core.

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