Reactor

Abstract

We provide reactors that reduce circuit losses. [Solution] The reactor comprises a core. The core has a permeability μ (ratio) at 1000 A / m that is 70% or less of the permeability at 500 A / m, and a relative permeability of 5 or more at 1000 A / m.

Description

[Technical Field]

[0001] This invention relates to a reactor. [Background technology]

[0002] A known type of circuit is the chopper circuit, which converts current and voltage into different magnitudes by switching them ON and OFF. A reactor is implemented in this chopper circuit. Generally, it is said that maintaining a high inductance value for the reactor, not only at low load currents but also at high load currents where the average current is greater than the average current at low loads, can suppress ripple current. In other words, a technique is employed to maintain a constant high inductance value from low load currents to high load currents (see Figure 4).

[0003] Furthermore, switching methods for turning switching elements ON and OFF are known, such as the soft switching method. When soft switching is performed at both low and high load currents, it is necessary to ensure that a negative current flows from the low load current to the high load current. In order to ensure that a negative current flows from the low load current to the high load current, the inductance value of the reactor is kept constant at a low value (see Figure 6). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2016-67187 [Overview of the project] [Problems that the invention aims to solve]

[0005] However, if the inductance value is kept constant, the ripple current in the low-load current region and the high-load current region will be approximately the same. In other words, if the inductance value of the reactor is kept constant at a low value, the current waveform at low load currents will shift too far to the negative side, resulting in a large ripple current at low load currents. A large ripple current leads to increased circuit losses.

[0006] The present invention was made to solve the above problems, and its objective is to provide a reactor that can reduce circuit losses. [Means for solving the problem]

[0007] The reactor of the present invention is characterized by comprising a core, wherein the permeability at 1000 A / m is 70% or less of the permeability at 500 A / m, and the relative permeability at 1000 A / m is 5 or more. [Effects of the Invention]

[0008] According to the present invention, a reactor capable of reducing circuit losses can be obtained. [Brief explanation of the drawing]

[0009] [Figure 1] This is a circuit diagram of a soft-switching chopper circuit in which the reactor of this embodiment is implemented. [Figure 2] This graph shows the current waveforms of the reactor under low and high load currents. [Figure 3] This graph shows the inductance value when the reactors are superimposed. [Figure 4] This graph shows the superposition characteristics of a typical reactor. [Figure 5] This graph shows the current waveform of a reactor that maintains high inductance superposition characteristics from low load current to high load current. [Figure 6]This graph shows the superposition characteristics of a conventional reactor that performs soft switching from low load current to high load current. [Figure 7] This graph shows the current waveform of a reactor that maintains low inductance superposition characteristics from low load current to high load current. [Figure 8] This graph shows the relationship between magnetic field strength and relative permeability. [Figure 9] This graph shows the relationship between magnetic field strength and permeability μ (ratio). [Modes for carrying out the invention]

[0010] [Embodiment] The reactor in this embodiment will be described with reference to the drawings. Figure 1 is a circuit diagram of a soft-switching chopper circuit in which the reactor of this embodiment is implemented. As shown in Figure 1, the reactor 3 of this embodiment is implemented in the soft-switching chopper circuit 10. The chopper circuit 10 of this embodiment is applicable to current ranges from a few amperes to about 20 amperes.

[0011] A chopper circuit 10 is a circuit that converts current and voltage into other magnitudes by switching them ON and OFF. One example of the conversion method used by the chopper circuit 10 is a soft-switching method. The chopper circuit 10 includes a DC power supply 1, a switching element 2, a reactor 3, a diode 4, and a capacitor 5.

[0012] DC power supply 1 is a component that supplies a stable DC voltage and current. The positive terminal of DC power supply 1 is connected in series with reactor 3. The negative terminal of DC power supply 1 is connected to the negative terminals of switching element 2 and capacitor 5.

[0013] The switching element 2 is a semiconductor element that turns on or off the current flowing through the circuit. The switching element 2 is connected to the reactor 3 and the anode of the diode 4. The switching element 2 performs ON and OFF operations of the switching element. The switching element 2 performs soft switching.

[0014] The switching element 2 performs soft switching for both a low load current and a high load current whose average current value is higher than the average value of the low load current. The low load current and the high load current can be defined as follows. In the inductance value during the superposition characteristic of the reactor 3 described later (see FIG. 3), the maximum inductance value at which the inductance value is maximum is L MAX , and when an arbitrary inductance value is defined as L, L / L MAX The current at which the value is 0.1 is defined as the maximum average current. The maximum average current indicates a current at which the inductance approaches saturation. A current having an average current value of less than half of the maximum average current is referred to as a low load current, and a current having an average current value of half or more of the maximum average current is referred to as a high load current. Note that the average current or the average value of the current refers to a current obtained by averaging the current over one cycle in the current waveform.

[0015] Further, unlike the definition based on the maximum average current described above, the boundary between the low load current and the high load current may be set based on 4A as the average current value. That is, it is preferable that the average value of the low load current is a current less than 4A, and the average value of the high load current is a current of 4A or more. In the following description, the low load current is described as a current having an average value of less than 4A, and the high load current is described as a current having an average value of 4A or more, but the boundary between the low load current and the high load current is not limited to 4A.

[0016] The reactor 3 is an electromagnetic component that converts electric energy into magnetic energy to store and release the magnetic energy. More specifically, the reactor 3 repeatedly stores and releases the magnetic energy converted from the electric energy in accordance with the ON and OFF of the switching element 2, whereby the chopper circuit 10 can perform voltage step-up and voltage step-down. The reactor 3 is connected to the positive electrode of the capacitor 5. The reactor 3 includes a core and a coil.

[0017] The core is made of a magnetic material. A coil is mounted on the core. Lead wires extend from the coil, and these lead wires are electrically connected to external equipment, including a circuit board. Power is supplied to the coil from the external equipment, and the coil generates a magnetic flux. The core becomes a closed magnetic circuit through which the magnetic flux generated by the coil passes.

[0018] Figure 2 is a graph showing the current waveforms of reactor 3 under low load current and high load current. As shown in Figure 2, reactor 3 has regions where the current falls below 0A under both low load and high load current.

[0019] Furthermore, reactor 3 controls the ripple current Δi at low load current. L The ripple current Δi is due to the high load current. H It is adjusted to be smaller than . In this embodiment, the ripple current Δi at low load current is adjusted by adjusting the inductance value when the reactor 3 has superimposed characteristics. L Δi of the ripple current under high load current H To make it smaller than that. The inductance value when reactor 3 has superimposed characteristics can be adjusted, for example, by making the soft magnetic powder contained in the core that makes up reactor 3 into a flattened shape.

[0020] Figure 3 is a graph showing the inductance value of reactor 3 under superposition characteristics. As shown in Figure 3, the inductance value of reactor 3 is not constant, but follows a curve that drops sharply under high load current. More specifically, in the low load current region where the average current is less than 4A, a high inductance value is maintained, while in the high load current region where the average current is 4A or more, the inductance value drops sharply.

[0021] Regarding the steep rate of reduction in inductance value, it is preferable that the reduction rate of the inductance value at the maximum average current is 50% or less compared to the inductance value at half the maximum average current. That is, it is preferable that (inductance value at maximum average current) / (inductance value at half the maximum average current) is 0.5 or less. By reducing the reduction rate to 50% or less, negative current can be flowed even at high load currents, enabling soft switching, and ripple current at low load currents can be reduced. However, it is preferable that the reduction rate is 5% or more. If the inductance decreases more steeply than 5%, the ripple current becomes unnecessarily large, and the losses of the chopper circuit 10 increase.

[0022] Furthermore, it is preferable that the inductance value at a current twice the maximum average current is reduced by 50% or less compared to the inductance value at the maximum average current. Looking at the graph in Figure 2, the current waveform at high load current shows a steep slope from around 10A. For example, if the inductance value is sharply reduced at 5A, immediately after entering the high load current region, the slope of the low load current region above 5A will also become steep, as shown in Figure 2, and the ripple current Δi at low load current will decrease. L It will get bigger.

[0023] Diode 4 is a semiconductor element that allows current to flow in a specific direction. The anode of diode 4 is connected to the switching element 2 and the reactor 3, and the cathode of diode 4 is connected to the positive terminal of capacitor 5.

[0024] Capacitor 5 is an electronic component that stores and releases electricity. The positive terminal of capacitor 5 is connected to the cathode of diode 4, and the negative terminal of capacitor 5 is connected to the DC power supply 1 and the switching element 2.

[0025] [Reactor] Next, the configuration of reactor 3 will be described in detail. Reactor 3 comprises a core and a coil. The core is made of a magnetic material. The core can be a compacted magnetic core, a ferrite core, a laminated steel sheet, or a metal composite core. A metal composite core is made by mixing magnetic powder and resin, and then hardening the resin.

[0026] In this embodiment, the core is a powder-compacted magnetic core. The powder-compacted magnetic core is produced by forming an insulating layer around soft magnetic powder and then press-molding it to create a compacted body. The powder-compacted magnetic core is then produced by annealing this compacted body.

[0027] Soft magnetic powders are primarily composed of iron. Examples of soft magnetic powders include pure iron powder, permalloy (Fe-Ni alloy) with iron as the main component, Si-containing iron alloy (Fe-Si alloy), Sendust alloy (Fe-Si-Al alloy), or mixtures of two or more of these powders.

[0028] In this embodiment, a flattened soft magnetic powder is used. That is, the soft magnetic powder has few irregularities and a flat shape. The flattening ratio is preferably 15 or more. The flattening ratio can be determined by dividing the major axis of the flattened soft magnetic powder by the thickness of the soft magnetic powder (major axis of soft magnetic powder / thickness of soft magnetic powder). By using a flattened soft magnetic powder, the permeability of the reactor 3 at 1000 (A / m) can be 70% or less of the permeability at 500 (A / m), and the relative permeability at 1000 (A / m) can be made 5 or more. By setting the permeability of the reactor 3 within this range, a reactor 3 having the superimposed inductance characteristics shown in Figure 3 can be obtained. Furthermore, for the reactor 3, it is preferable that the permeability at 1000 (A / m) is 60% or less of the permeability at 500 (A / m), and more specifically, 59.9% or less. In this embodiment, the device is used for current applications ranging from a few A to approximately 20 A, and to accommodate magnetic field strengths in the range of 500 to 1000 A / m, the permeability at 1000 A / m is compared with that at 500 A / m, and the relative permeability at 1000 A / m is set to be 5 or higher to prevent magnetic saturation up to 1000 A / m.

[0029] An insulating layer made of an insulating material is formed around the soft magnetic powder. The insulating layer ensures electrical insulation between the particles of the soft magnetic powder and reduces eddy current losses in the compacted magnetic core. Silane compounds, silicone resins, and silicone oligomers can be used as insulating materials. One type of insulating material may be used, or two or more types may be used. When two or more types are used, each type of insulating layer may be laminated, or a single-layer insulating layer may be formed by mixing two or more types of insulating materials.

[0030] In this way, soft magnetic powder with an insulating layer formed around it is filled into a mold and molded under a predetermined pressure to form a compacted powder body. Then, this compacted powder body is annealed to form a compacted magnetic core.

[0031] The coil is composed of a single flat, rectangular conductive member insulated with enamel or the like. The coil is formed by winding the conductive member into a cylindrical shape while shifting the winding position in the direction of the winding axis. Examples of conductive members include copper wire. The coil may be a flatwise coil, where the wide side of the flat rectangular wire is bent, or an edgewise coil, where the narrow side of the flat rectangular wire is bent. The type of wire and winding method of the coil are not limited to these, and other forms may be used. The reactor 3 is equipped with an insulating member that insulates the core from the coil.

[0032] [Effects and Effects] This section explains the relationship between the superposition characteristics of the inductance of reactor 3 and the current waveform of reactor 3. Figure 4 is a graph showing the superposition characteristics of a typical reactor. As shown in Figure 4, generally, a reactor is considered good if it maintains a high value at a constant level from low load current to high load current. In other words, a reactor whose inductance value drops quickly when the current is increased is considered to have poor magnetic properties.

[0033] FIG. 5 is a graph showing current waveforms of a reactor that maintains high inductance superimposition characteristics from a low load current time to a high load current time. In FIG. 5, the solid line represents the waveform at the time of low load current with an average value of 1A (black circle mark in FIG. 4), and the dotted line represents the waveform at the time of high load current with an average value of 5A (black triangle mark in FIG. 4). As shown in FIG. 5, at the time of low load current, there is a region that reaches a position below 0A, but at the time of high load current, there is no region that reaches a position below 0A. Therefore, this reactor cannot perform soft switching at the time of high load current.

[0034] In order to pass a current below 0A at the time of high load current, it is necessary to lower the inductance value at the time of superimposition characteristics. FIG. 6 is a graph showing the superimposition characteristics of a conventional reactor that performs soft switching from the low load current time to the high load current time. As shown in FIG. 6, the conventional reactor keeps the inductance value at the time of superimposition characteristics constant at a low value.

[0035] FIG. 7 is a graph showing current waveforms of a reactor that maintains low inductance superimposition characteristics from a low load current time to a high load current time. The solid line and dotted line in FIG. 7 are the same as those in FIG. 5, the solid line represents the waveform at the time of low load current, and the dotted line represents the waveform at the time of high load current. As shown in FIG. 7, a current below 0A is generated even at the time of high load current, and soft switching can be performed not only at the time of low load current but also at the time of high load current. However, the negative current flowing at the time of low load current also increases. Therefore, the ripple current Δi2 at the time of low load current is larger than the ripple current Δi1 at the time of low load current shown in FIG. 5. As a result, the loss of the chopper circuit increases.

[0036] Accordingly, as shown in FIG. 2, in the chopper circuit of the present invention, the ripple current Δi at the time of low load current L is the ripple current Δi at the time of high load current HThe reactor 3 is controlled to be smaller than the specified value. This suppresses the increase in ripple current at low load currents, allows switching to occur from low load currents to high load currents, and reduces losses in the chopper circuit 10.

[0037] In particular, in this embodiment, as shown in Figure 3, the inductance value of the reactor 3 during superposition characteristics is controlled to maintain a high value at low load currents and to decrease at high load currents. This allows for soft switching at both low and high load currents while suppressing ripple current without the use of auxiliary circuits, reducing the number of components and lowering manufacturing costs and the size of the chopper circuit 10.

[0038] Furthermore, the core has a permeability at 1000 A / m that is 70% or less of the permeability at 500 A / m, and a relative permeability of 5 or more at 1000 A / m. In other words, it has a range in which the permeability decreases sharply between magnetic fields of 500 and 1000 A / m. As a result, in the current range from a few A to about 20 A, there is no need to drastically reduce or increase the number of coil turns, thus providing a high degree of design flexibility.

[0039] [Examples] The present invention will be described in more detail based on the examples. However, the present invention is not limited to the following examples. Cores for Examples 1-3 and Comparative Examples 1 and 2 were prepared. The cores for Examples 1-3 and Comparative Example 1 are compacted magnetic cores, while the core for Comparative Example 2 is a ferrite core.

[0040] In Example 1, Sendust alloy powder (Fe-Si-Al alloy powder) was used as the soft magnetic powder. Flattened powder was used for the Sendust alloy powder. The flattening ratio of the Sendust alloy powder was 67. An insulating layer was formed on this Sendust alloy powder.

[0041] Silicone resin was used as the insulating material to form the insulating layer. 3.0 wt% of the silicone resin was added to the Sendust alloy powder and mixed. After mixing, the mixture was dried at room temperature for 1 hour. This resulted in Sendust alloy powder with an insulating layer formed on top.

[0042] Sendust alloy powder with an insulating layer formed on it was filled into a mold and pressure-molded to produce a toroidal powder compact with an outer diameter of 16.5 mm, an inner diameter of 11.0 mm, and a height of 1.0 mm. Finally, the powder compact was heat-treated. In this way, a powder magnetic core, which will serve as the core of Example 1 and has the following characteristics, was produced.

[0043] Example 2 differs from Example 1 only in the pressure used for compression molding and the heat treatment conditions of the compacted body; otherwise, the materials, manufacturing method, and conditions are the same as in Example 1. In this way, a compacted magnetic core, which will serve as the core of Example 2 and have the following characteristics, was fabricated.

[0044] Example 3 differs from Example 1 only in the pressure used for compression molding, the heat treatment conditions of the compacted body, and the amount of silicone resin added. Otherwise, the materials, manufacturing method, and conditions are the same as in Example 1. The amount of silicone resin added was 2.0 wt% relative to the Sendust alloy powder. In this way, a compacted magnetic core, which will serve as the core of Example 2 and has the following characteristics, was fabricated.

[0045] The core of Comparative Example 1, like that of Example 1, used Sendust alloy powder (Fe-Si-Al alloy powder) as the soft magnetic powder, but it was not flattened. The soft magnetic powder used in Comparative Example 1 had an average particle diameter (D50) of 0.969. Silicone resin was used as the insulating material to constitute the insulating layer. Silicone resin was added and mixed at a concentration of 1-2 wt% relative to the Sendust alloy powder. After mixing, it was heat-dried. The drying temperature was 200°C and the drying time was 2 hours. This resulted in Sendust alloy powder with an insulating layer formed on top. The Sendust alloy powder was then filled into a mold and pressure-molded to produce a toroidal powder compact with an outer diameter of 26.0 mm, an inner diameter of 18.0 mm, and a height of 5.0 mm. Finally, the powder compact was heat-treated.

[0046] The core in Comparative Example 2 is a ferrite core. The data used for the ferrite core is that of a JFE Ferrite MB1H.

[0047] Coils were attached to the cores of Examples 1-3 and Comparative Examples 1 and 2 to fabricate reactors. In Examples 1-3, coils were fabricated by winding φ0.5 mm copper wire 40 times. The permeability was then measured using a DC magnetization characteristic tester (SK110, manufactured by Metron Giken). The permeability was also measured for Comparative Examples 1 and 2. The measured permeability is differential permeability, which is a value calculated from the DC BH curve (μ = ΔB / ΔH). The measured permeability can be considered the same as the relative permeability.

[0048] The measurement results are shown in Figure 8. Figure 8 is a graph showing the relationship between magnetic field strength and relative permeability. In Figure 8, the thin solid line represents Example 1, the thick solid line represents Example 2, the dotted line represents Example 3, the dashed line represents Comparative Example 1, and the double dashed line represents Comparative Example 2. The relative permeability at 1000 (A / m) is shown in Table 1.

[0049] [Table 1]

[0050] As shown in Figure 8 and Table 1, the relative permeability of Examples 1-3 and Comparative Example 2 is 5 or higher at 1000 A / m. On the other hand, for Comparative Example 1, which uses a ferrite core, the value was close to 0 before reaching 500 A / m, confirming that magnetic saturation had occurred.

[0051] Table 2 also shows the relative permeability and fluctuation rate at 500 A / m. The fluctuation rate shown in Table 2 is the ratio of the permeability at 1000 A / m to the permeability at 500 A / m.

[0052] [Table 2]

[0053] As shown in Table 2 and Figure 8, it was confirmed that the permeability at 1000 A / m and Comparative Example 2 were 70% or less of the permeability at 500 A / m. More specifically, it was confirmed that the permeability at 1000 A / m was 60 (59.9)% or less of the permeability at 500 A / m. On the other hand, it was confirmed that the permeability at 1000 A / m and the permeability at 500 A / m were the same for Comparative Example 1.

[0054] Furthermore, the relationship between permeability μ (ratio) and magnetic field strength was calculated for Examples 1-3 and Comparative Examples 1 and 2. The results are shown in Figure 9. Permeability μ (ratio) is the ratio value when the maximum differential permeability is set to 1. Note that the types of lines in the graph in Figure 9 are the same as in Figure 8.

[0055] As shown in Figure 9, Examples 1-3 exhibit a range where the magnetic permeability drops sharply in the 500-1000 (A / m) range. On the other hand, Comparative Example 1, in which the soft magnetic powder is not flattened, drops sharply from around 2000 (A / m) above 1000 (A / m). Comparative Example 2 drops sharply before 100 (A / m) and reaches magnetic saturation around 100 (A / m). In the current range of a few A to about 20 A, in order to make Comparative Examples 1 and 2 drop sharply in the 500-1000 (A / m) range like Examples 1-3, it would be necessary to drastically reduce (Comparative Example 2) or increase (Comparative Example 1) the number of coil turns, which is not practical. On the other hand, Examples 1-3 can achieve this characteristic solely through the core characteristics, increasing the design freedom of other parameters such as the number of turns and gap.

[0056] Thus, it was confirmed that in Examples 1 to 3 using flattened powder, the permeability at 1000 (A / m) was 70% or less of the permeability at 500 (A / m), and the relative permeability at 1000 (A / m) was 5 or more. Furthermore, as shown in Figure 3, the inductance value of the reactor using the cores of Examples 1 to 3 during superposition characteristics can be adjusted so that it maintains a high value at low load currents and decreases sharply at high load currents, thereby suppressing ripple current at low load currents and reducing losses in the chopper circuit.

[0057] [Other embodiments] While embodiments of the present invention have been described herein, these embodiments are presented as examples and are not intended to limit the scope of the invention. The above embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the scope of the invention. Embodiments and their variations are included in the scope and essence of the invention, as well as in the claims and their equivalents.

[0058] In the above embodiment, the chopper circuit 10 was a boost type, but the chopper circuit 10 is not limited to this. The chopper circuit 10 may be a buck type or a buck-boost type. [Explanation of Symbols]

[0059] 10. Chopper Circuit 1 DC power supply 2 Switching elements 3 Reactor 4 diodes 5 Capacitors

Claims

1. Equipped with a core, The core has a permeability at 1000 A / m that is 70% or less of the permeability at 500 A / m, and a relative permeability at 1000 A / m that is 5 or more. A reactor characterized by the following.

2. The aforementioned core is a compacted magnetic core, The compacted magnetic core has soft magnetic powder, The soft magnetic powder has a flattened shape. The reactor according to claim 1, characterized by the following:

3. It is used in soft-switching chopper circuits. A reactor according to claim 1 or 2, characterized by the following:

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