Three-phase composite common inductor

Abstract

As a result, we provide a three-phase composite common inductor that can suppress the occurrence of magnetic saturation even in high-current applications. [Solution] A three-phase composite common inductor 1 that acts as a common inductance for common current and as a normal inductance for normal current comprises a first core 2, a second core 3, and a U-phase coil 4U, a V-phase coil 4V, and a W-phase coil 4W wound around the first core 2, wherein the second core 3 is made of a material with lower magnetic permeability than the first core 2.

Description

[Technical Field]

[0001] This invention relates to a three-phase composite common inductor. [Background technology]

[0002] Patent Document 1 discloses a three-phase composite common inductor (dual-mode choke coil) that acts as a common inductance (common-mode noise filter) for common currents and as a normal inductance (normal-mode noise filter) for normal currents. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] International Publication No. 2020 / 144795 [Overview of the project] [Problems that the invention aims to solve]

[0004] However, the three-phase composite common inductor described in Patent Document 1 has a problem in that a gap is provided for each of the three closed magnetic circuits for normal inductance, and the magnetic resistance of each closed magnetic circuit is set based on the gap dimension, so the range in which the magnetic resistance can be set is limited in relation to leakage flux, etc. In addition, in the three-phase composite common inductor described in Patent Document 1, a part of the core (second magnetic core) protrudes outward, so the volume expands and miniaturization is difficult. [Means for solving the problem]

[0005] The present invention was created in view of the above circumstances and with the aim of solving these problems, and the invention of claim 1 is a three-phase composite common inductor that acts as a common inductance with respect to a common current and as a normal inductance with respect to a normal current, comprising a first core, a second core, and a first phase coil, a second phase coil, and a third phase coil wound around the first core, wherein the first core comprises a first leg portion and a second leg portion that are in parallel with each other, a first connecting portion that connects one end of the first leg portion and the second leg portion together, and a second connecting portion that connects the other ends of the first leg portion and the second leg portion, wherein at least one of the first leg portion and the second leg portion has the first phase coil, the second phase coil, and the third phase coil wound sequentially from one end to the other end The second core is characterized in that it has three-phase coils wound around it, the second core has third and fourth legs that are in parallel with each other and connect the intermediate portions of the first and second legs, the first-phase coil, the second-phase coil, and the third-phase coil are edgewise coils made by winding flat wire at right angles, the first-phase coil is wound around at least one of the first and second legs between the first connecting portion and the third leg, the second-phase coil is wound around at least one of the first and second legs between the third and fourth legs, and the third-phase coil is wound around at least one of the first and second legs between the fourth leg and the second connecting portion, and the second core is made of a material with lower magnetic permeability than the first core. Furthermore, the invention of claim 2 is a three-phase composite common inductor as described in claim 1, characterized in that the first core is a ferrite core and the second core is a dust core with lower magnetic permeability than the ferrite core. Furthermore, the invention of claim 3 is a three-phase composite common inductor as described in claim 1, characterized in that the first core is formed by connecting two U-shaped cores. Furthermore, the invention of claim 4 is a three-phase composite common inductor as described in claim 1, characterized in that the first core is formed by connecting two U-shaped cores via two I-shaped cores. Furthermore, the invention of claim 5 is a three-phase composite common inductor as described in claim 4, characterized in that a gap is provided between the U-shaped core and the I-shaped core for adjusting the balance of the three-phase normal inductances. Furthermore, the invention of claim 6 is a three-phase composite common inductor as described in claim 1, wherein the second core further comprises a first plate portion arranged along the inner circumferential surface of the first leg portion and a second plate portion arranged along the inner circumferential surface of the second leg portion, one end of the third leg portion is connected to the first leg portion via the first plate portion, the other end of the third leg portion is connected to the second leg portion via the second plate portion, one end of the fourth leg portion is connected to the first leg portion via the first plate portion, and the other end of the fourth leg portion is connected to the second leg portion via the second plate portion. Furthermore, the invention of claim 7 is a three-phase composite common inductor as described in claim 1, wherein the second core further comprises a first auxiliary leg arranged along the side surface of the third leg and connecting the intermediate side surfaces of the first leg and the second leg, and a second auxiliary leg arranged along the side surface of the fourth leg and connecting the intermediate side surfaces of the first leg and the second leg. [Effects of the Invention]

[0006] According to the invention of claim 1, a closed magnetic path for common inductance is formed by the first leg, the second leg, the first connecting portion, and the second connecting portion of the first core. A closed magnetic path for the normal inductance of the first phase is formed by the first leg, the second leg, and the first connecting portion of the first core and the third leg of the second core. A closed magnetic path for the normal inductance of the second phase is formed by the first leg and the second leg of the first core and the third leg and the fourth leg of the second core. A closed magnetic path for the normal inductance of the third phase is formed by the first leg, the second leg, and the second connecting portion of the first core and the fourth leg of the second core. And since the second core is formed of a material having a lower magnetic permeability than the first core, a large magnetic resistance can be set in the closed magnetic path for normal inductance without providing a gap. As a result, it is possible to provide a three-phase composite common inductor that can suppress the occurrence of magnetic saturation even in high-current applications. In addition, since the first-phase coil, the second-phase coil, and the third-phase coil are edge-wound coils in which a flat wire is wound at a right angle, not only can the coil density be increased to miniaturize the three-phase composite common inductor, but the outer peripheral shape of each coil can be planarized to improve the adhesion to the cooling member. Further, according to the invention of claim 2, since the first core is a ferrite core and the second core is a dust core having a lower magnetic permeability than the ferrite core, a three-phase composite common inductor applicable to high-current applications can be configured using inexpensive ferrite cores and dust cores. Further, according to the invention of claim 3, since the first core is formed by connecting two U-shaped cores, a three-phase composite common inductor applicable to high-current applications can be configured using inexpensive U-shaped cores. Further, according to the invention of claim 4, since the first core is formed by connecting two U-shaped cores via two I-shaped cores, not only can a three-phase composite common inductor applicable to high-current applications be configured using inexpensive U-shaped cores and I-shaped cores, but the lengths of the first leg and the second leg can be easily extended. Further, according to the invention of claim 5, since a gap for adjusting the balance of the three-phase normal inductance is provided between the U-shaped core and the I-shaped core, it is possible to prevent the performance degradation due to the imbalance of the three-phase normal inductance. Further, according to the invention of claim 6, the second core further includes a first plate portion and a second plate portion disposed along the inner peripheral surfaces of the first leg portion and the second leg portion, and the third leg portion and the fourth leg portion are connected to the first leg portion and the second leg portion via the first plate portion and the second plate portion. Therefore, the contact area between the first core and the second core can be enlarged, and magnetic saturation at the contact portion between the first core and the second core can be suppressed. Further, according to the invention of claim 7, the second core is disposed along the side surfaces of the third leg portion and the fourth leg portion, and further includes a first auxiliary leg portion and a second auxiliary leg portion that connect the side surfaces of the middle portions of the first leg portion and the second leg portion. Therefore, the contact area between the first core and the second core can be enlarged, and magnetic saturation at the contact portion between the first core and the second core can be suppressed.

Brief Description of the Drawings

[0007] [Figure 1] It is a perspective view of a three-phase composite common inductor according to an embodiment of the present invention. [Figure 2] (a) is a perspective view of the first core, (b) is a perspective view of the second core, and (c) is a perspective view showing a state where the second core is assembled to the first core. [Figure 3] (a) is a perspective view of the U-phase coil, V-phase coil, and W-phase coil, and (b) is a perspective view of the bobbin. [Figure 4] It is a diagram schematically showing the structure of a three-phase composite common inductor. [Figure 5] (a) is a diagram schematically showing the basic structure of a three-phase composite common inductor, and (b) is a magnetic equivalent circuit of the three-phase composite common inductor. [Figure 6] (a) is a diagram showing the flow of magnetic flux when a common current is input to a three-phase composite common inductor, and (b) is a magnetic equivalent circuit when a common current is input to the three-phase composite common inductor. [Figure 7] It is an explanatory diagram of the normal current input to a three-phase composite common inductor. [Figure 8] (a) is a diagram showing the flow of magnetic flux when a normal current is input to a three-phase composite common inductor, and (b) is the magnetic equivalent circuit when a normal current is input to a three-phase composite common inductor. [Figure 9] This figure schematically shows the structure of a three-phase composite common inductor according to the first modified example. [Figure 10] (a) is a schematic diagram showing the core structure of a three-phase composite common inductor according to the second modified example, and (b) is a schematic diagram showing the core structure of a three-phase composite common inductor according to the third modified example. [Modes for carrying out the invention]

[0008] [Basic Configuration of a Three-Phase Common Inductor] Embodiments of the present invention will be described below with reference to the drawings. In Figures 1 to 4, 1 is a three-phase composite common inductor, which acts as a common inductance with respect to common current and as a normal inductance with respect to normal current. For example, the three-phase composite common inductor 1 is used as a dual-mode noise filter to reduce common-mode noise and normal-mode noise in high-current applications such as high-capacity battery charging circuits, high-capacity power conditioner circuits, motor drive circuits for electric vehicles, and compressor drive circuits for hydrogen fuel cells.

[0009] As shown in Figures 1 to 4, the three-phase composite common inductor 1 comprises a first core 2, a second core 3, a U-phase coil 4U, a V-phase coil 4V, a W-phase coil 4W, and a bobbin 5.

[0010] The first core 2 comprises a first leg portion 21 and a second leg portion 22 arranged in parallel with each other, a first connecting portion 23 connecting one end of the first leg portion 21 and the second leg portion 22, and a second connecting portion 24 connecting the other ends of the first leg portion 21 and the second leg portion 22. At least one of the first leg portion 21 and the second leg portion 22 is wound with a U-phase coil 4U, a V-phase coil 4V, and a W-phase coil 4W in order from one end to the other.

[0011] The second core 3 includes a third leg portion 31 and a fourth leg portion 32 that are arranged in parallel with each other and connect the intermediate portions of the first leg portion 21 and the second leg portion 22. The second core 3 is made of a material with a lower magnetic permeability than the first core 2.

[0012] The U-phase coil 4U is wound around at least one of the first leg portion 21 and the second leg portion 22 between the first connecting portion 23 and the third leg portion 31. The V-phase coil 4V is wound around at least one of the first leg portion 21 and the second leg portion 22 between the third leg portion 31 and the fourth leg portion 32. The W-phase coil 4W is wound around at least one of the first leg portion 21 and the second leg portion 22 between the fourth leg portion 32 and the second connecting portion 24.

[0013] In such a three-phase composite common inductor 1, a closed magnetic circuit for common inductance (hereinafter sometimes referred to as a common closed magnetic circuit) is formed by the first leg 21, second leg 22, first connecting portion 23, and second connecting portion 24 of the first core 2; a closed magnetic circuit for U-phase normal inductance (hereinafter sometimes referred to as a U-phase normal closed magnetic circuit) is formed by the first leg 21, second leg 22, and first connecting portion 23 of the first core 2 and the third leg 31 of the second core 3; a closed magnetic circuit for V-phase normal inductance (hereinafter sometimes referred to as a V-phase normal closed magnetic circuit) is formed by the first leg 21 and second leg 22 of the first core 2 and the third leg 31 and fourth leg 32 of the second core 3; and a closed magnetic circuit for W-phase normal inductance (hereinafter sometimes referred to as a W-phase normal closed magnetic circuit) is formed by the first leg 21, second leg 22, and second connecting portion 24 of the first core 2 and the fourth leg 32 of the second core 3.

[0014] And since the second core 3 is formed of a material having a lower magnetic permeability than the first core 2, a large magnetic resistance can be set in the closed magnetic circuit for normal inductance without providing a gap, and a three-phase composite common inductor 1 capable of suppressing the occurrence of magnetic saturation even in a large current application can be obtained.

[0015] [Basic Operation of Three-Phase Composite Common Inductor] Next, the basic operation of the three-phase composite common inductor 1 based on the three-phase composite common inductor 1 having the basic configuration shown in FIG. 5 will be described with reference to FIGS. 6 to 8.

[0016] However, in FIGS. 5 to 8, i u , i v , i w are the input currents of the respective coils 4U, 4V, 4W, R1 to R4 are the magnetic resistances of the respective parts of the first core 2, R a is the magnetic resistance of the third leg 31, R b is the magnetic resistance of the fourth leg 32, n is the number of turns of the respective coils 4U, 4V, 4W, ni u is the magnetic flux source of the U phase, ni v is the magnetic flux source of the V phase, ni w is the magnetic flux source of the W phase, φ u is the magnetic flux generated by the U-phase coil 4U, φ v is the magnetic flux generated by the V-phase coil 4V, φ w is the magnetic flux generated by the W-phase coil 4W.

[0017] (Common Inductance) FIG. 6(a) is a diagram showing the flow of magnetic flux when a common current is input to the three-phase composite common inductor, and FIG. 6(b) is an equivalent magnetic circuit when a common current is input to the three-phase composite common inductor. As shown in FIG. 6(a), when a common current is simultaneously input to the three-phase coils 4U, 4V, 4W, the magnetic fluxes φ u , φ v , φ w generated by the respective coils 4U, 4V, 4W flow in the directions indicated by the dotted lines in FIG. 6(a). Here, the main magnetic flux direction is the direction indicated by the thick dotted line in FIG. 6(a), and each magnetic flux φ u , φv , φ w Since they flow in the same direction, the total magnetic flux φ is as shown in [Equation 1] below.

[0018]

number

[0019] Furthermore, as shown by the thin dotted line in Figure 6(a), each magnetic flux φ u , φ v , φ w Some of the magnetic force flows into the third leg 31 and fourth leg 32 of the second core 3, but the permeability of the second core 3 is sufficiently lower than that of the first core 2 (e.g., 1-2%), and the magnetic resistance R of the third leg 31 and fourth leg 32 a , R b Since the magnetic resistances R1 to R4 of each part of the first core 2 are much larger, the magnetic flux flowing through the third leg 31 and the fourth leg 32 due to the common current becomes almost negligible. Therefore, the amount of magnetic flux φ generated by each coil 4U, 4V, and 4W due to the common current is u , φ v , φ w The common inductance L is given by the following equations [Equation 2] and [Equation 3].

[0020]

number

[0021]

number

[0022] (Normal inductance) Figure 7 is an explanatory diagram of the normal current input to a three-phase composite common inductor, Figure 8(a) shows the flow of magnetic flux when a normal current is input to a three-phase composite common inductor, and Figure 8(b) is the magnetic equivalent circuit when a normal current is input to a three-phase composite common inductor. As shown in Figure 7, the three-phase AC current waveforms are 120° out of phase with each other, so the sum of the three-phase currents is always zero at any given time. Furthermore, the sum of the currents of any two of the three phases is the same as the current of the remaining phase, but in opposite directions. For example, the dotted waveform in Figure 7 represents the U-phase current i u and V-phase current i v This shows the total current, and this current is the W-phase current i w It has the same value, but in the opposite direction.

[0023] As shown in Figure 8(a), when a normal current is input to the three-phase coils 4U, 4V, and 4W, the magnetic flux φ generated by each phase coil 4U, 4V, and 4W is determined by the characteristics of the three-phase AC current waveform described above. u , φ v , φ w These currents flow through the U-phase normally closed magnetic circuit, V-phase normally closed magnetic circuit, and W-phase normally closed magnetic circuit, respectively. For example, as shown in the magnetic equivalent circuit in Figure 9, focusing on the U-phase coil 4U, the magnetic flux φ generated by this U-phase coil 4U due to the normal current is u Since it does not flow through the V-phase and W-phase normally closed magnetic circuits, but flows through the U-phase normally closed magnetic circuit, the U-phase current i u For this, the other two phase magnetic circuits are effectively blocked. As a result, the normal inductance L of the U-phase coil 4U u(Normal) This is as shown in [Equation 4] below.

[0024]

number

[0025] Here, AL a This is the AL value of the third leg portion 31. In other words, the magnetic resistance R1 and Ra included in the U-phase normal closed magnetic circuit are the normal inductance L of the U-phase coil 4U. u(Normal) Determine the following. Also, when the core cross-sectional area is Ae, the magnetic flux density B of the U-phase normally closed magnetic circuit is as shown in [Equation 5] below.

[0026]

number

[0027] When B < Bs (Bs: saturation magnetic flux density of the first core 2 and the second core 3), since the first core 2 does not reach magnetic saturation, if the magnetic resistance R of the second core 3 is designed to be large, magnetic saturation can be avoided even at a higher normal current while maintaining a predetermined normal inductance, and a design with a higher normal impedance becomes possible. Similarly, the normal inductances L of the other two phases, the normal inductance L, etc. can also be designed. However, in the V-phase normal closed magnetic circuit, there are two magnetic resistances R, R due to the third leg 31 and the fourth leg 32, so the normal inductance L of the V-phase is as shown in [Equation 6] below. a by designing it large, magnetic saturation can be avoided even at a higher normal current while maintaining a predetermined normal inductance, Lu(Normal) and a design with a higher normal impedance becomes possible. Similarly, the normal inductances L of the other two phases, the normal inductance L, v(Normal) the normal inductance L, w(Normal) and the normal impedance can also be designed. However, in the V-phase normal closed magnetic circuit, there are two magnetic resistances R, a R, b existing due to the third leg 31 and the fourth leg 32, so the normal inductance L of the V-phase v(Normal) is as follows in [Equation 6].

[0028]

Equation

[0029]

Equation

[0030] [Configuration of Coil, First Core, and Second Core] Next, the configurations of the coils 4U, 4V, 4W, the first core 2, and the second core 3 will be described with reference to FIGS. 1 to 4.

[0031] As shown in Figures 1 and 3, each coil 4U, 4V, and 4W is an edgewise coil made by winding a flat wire at a right angle. Each coil 4U, 4V, and 4W in this embodiment includes a first winding section 4a wound on the first leg section 21, a second winding section 4b wound on the second leg section 22, and a connecting section 4c that connects the first winding section 4a and the second winding section 4b. However, each coil 4U, 4V, and 4W may be wound on either the first leg section 21 or the second leg section 22. Furthermore, each coil 4U, 4V, and 4W is assembled to the first core 2 while housed in a resin bobbin 5.

[0032] The first core 2 is composed of, for example, a ferrite core, and the second core 3 is composed of, for example, a dust core with lower magnetic permeability than the ferrite core. For example, the magnetic permeability of the second core 3 is said to be about 1-2% of the magnetic permeability of the first core 2.

[0033] Furthermore, the first core 2 is formed by connecting two U-shaped cores 2b via two I-shaped cores 2a. In this way, a first core 2 with long first legs 21 and second legs 22 can be constructed without using a special U-shaped core with long legs.

[0034] Furthermore, the second core 3 further comprises a first plate portion 33 arranged along the inner circumferential surface of the first leg portion 21 and a second plate portion 34 arranged along the inner circumferential surface of the second leg portion 22. One end of the third leg portion 31 is connected to the first leg portion 21 via the first plate portion 33, and the other end of the third leg portion 31 is connected to the second leg portion 32 via the second plate portion 34. Similarly, one end of the fourth leg portion 32 is connected to the first leg portion 21 via the first plate portion 33, and the other end of the fourth leg portion 32 is connected to the second leg portion 22 via the second plate portion 34. The first plate portion 33 and the second plate portion 34 are made of the same core material as the third leg portion 31 and the fourth leg portion 32, and the contact area with the first leg portion 21 and the second leg portion 22 is larger than the contact area with the third leg portion 31 and the fourth leg portion 32.

[0035] Furthermore, the second core 3 includes a first auxiliary leg 35 positioned along the side of the third leg 31 and connecting the intermediate side surfaces of the first leg 21 and the second leg 22, and a second auxiliary leg 36 positioned along the side of the fourth leg 32 and connecting the intermediate side surfaces of the first leg 21 and the second leg 22. The first plate 33 and the second plate 34 are made of the same core material as the third leg 31 and the fourth leg 32.

[0036] [Effects of the Embodiment] In this embodiment configured as described, a closed magnetic path for common inductance is formed by the first leg 21, second leg 22, first connecting portion 23, and second connecting portion 24 of the first core 2; a closed magnetic path for U-phase normal inductance is formed by the first leg 21, second leg 22, and first connecting portion 23 of the first core 2 and the third leg 31 of the second core 3; a closed magnetic path for V-phase normal inductance is formed by the first leg 21 and second leg 22 of the first core 2 and the third leg 31 and fourth leg 32 of the second core 3; and a closed magnetic path for W-phase normal inductance is formed by the first leg 21, second leg 22, and second connecting portion 24 of the first core 2 and the fourth leg 32 of the second core 3. Furthermore, since the second core 3 is made of a material with lower magnetic permeability than the first core 2, a large magnetic resistance can be set in the closed magnetic path for normal inductance without providing a gap. As a result, it becomes possible to provide a three-phase composite common inductor 1 that can suppress the occurrence of magnetic saturation even in high-current applications.

[0037] Furthermore, since the first core 2 is a ferrite core and the second core 3 is a dust core with lower magnetic permeability than the ferrite core, a three-phase composite common inductor 1 applicable to high-current applications can be constructed using inexpensive ferrite cores and dust cores.

[0038] Furthermore, since the U-phase coil 4U, V-phase coil 4V, and W-phase coil 4W are edgewise coils made by winding flat wire at a right angle, it is possible to increase the coil density and miniaturize the three-phase composite common inductor 1. In addition, the outer shape of each coil 4U, 4V, and 4W can be made flat, improving contact with the cooling material.

[0039] Furthermore, since the first core 2 is formed by connecting two U-shaped cores 2b via two I-shaped cores 2a, not only can a three-phase composite common inductor 1 applicable to high-current applications be constructed using inexpensive U-shaped cores 2b and I-shaped cores 2a, but the lengths of the first leg 21 and the second leg 22 can also be easily extended.

[0040] Furthermore, the second core 3 further comprises a first plate portion 33 and a second plate portion 34 arranged along the inner circumferential surfaces of the first leg portion 21 and the second leg portion 22, and the third leg portion 31 and the fourth leg portion 32 are connected to the first leg portion 21 and the second leg portion 22 via the first plate portion 33 and the second plate portion 34. This increases the contact area between the first core 2 and the second core 3, and suppresses magnetic saturation at the contact portion between the first core 2 and the second core 3.

[0041] Furthermore, the second core 2 is further equipped with first auxiliary legs 35 and second auxiliary legs 36, which are arranged along the sides of the third leg portion 31 and the fourth leg portion 32 and connect the intermediate sides of the first leg portion 21 and the second leg portion 22. This increases the contact area between the first core 2 and the second core 3, and suppresses magnetic saturation at the contact point between the first core 2 and the second core 3.

[0042] [Differentiation] Next, a modified example of the three-phase composite common inductor 1 will be described with reference to Figures 9 and 10. However, for components common to the previously described embodiment, the same reference numerals as in the previously described embodiment may be used, and the description of the previously described embodiment may be referred to.

[0043] Figure 9 is a schematic diagram showing the structure of a three-phase composite common inductor according to the first modified example. The first modification differs from the previously described embodiment in that the first core 2 is formed by connecting two U-shaped cores 2b. According to this first modification, a three-phase composite common inductor 1 applicable to high-current applications can be constructed using inexpensive U-shaped cores 2b.

[0044] Figure 10(a) schematically shows the core structure of a three-phase composite common inductor according to the second modified example, and Figure 10(b) schematically shows the core structure of a three-phase composite common inductor according to the third modified example. The second and third modified embodiments differ from the previously described embodiments in that a gap 37 is provided between the U-shaped core 2b and the I-shaped core 2a for adjusting the balance of the three-phase normal inductances. According to these second and third modified embodiments, performance degradation due to imbalance in the three-phase normal inductances can be prevented. For example, the U-phase normal closed magnetic circuit and the W-phase normal closed magnetic circuit have a magnetic resistance R of either the third leg 31 or the fourth leg 32. a , R b Although a third leg 31 and a fourth leg 32 intervene, the V-phase normally closed magnetic circuit has two magnetic resistances R a , R b Because of the intervening element, the U-phase normal closed magnetic circuit and the W-phase normal closed magnetic circuit have a magnetic resistance R due to the gap 37. g By adding this, the imbalance in the normal inductance of the three phases can be eliminated.

[0045] It should be noted that the present invention is not limited to the embodiments described above, and various modifications and changes are possible within the scope of the claims. [Explanation of Symbols]

[0046] 1. Three-phase composite common inductor 2. First Core 21 1st leg 22 Second leg 23 1st connection part 24 2nd connection part 2a I-shaped core 2b U-shaped core 3. Second Core 31 Third leg 32 4th leg 33 1st plate part 34 2nd plate part 35 1st auxiliary leg 36 2nd auxiliary leg 37 Gap 4U U-phase coil (first phase coil) 4V V-phase coil (second phase coil) 4W W-phase coil (3rd phase coil) 4a Winding part 4b Winding section 4c connection part 5 bobbins

Claims

1. A three-phase composite common inductor that acts as a common inductance for common current and as a normal inductance for normal current, The first core and The second core and The first core comprises a first phase coil, a second phase coil, and a third phase coil, The first core is, The first and second legs are arranged in parallel to each other, A first connecting portion that connects one end of the first leg portion and the second leg portion, It comprises a second connecting portion that connects the other ends of the first leg portion and the second leg portion, At least one of the first leg portion and the second leg portion is wound with the first phase coil, the second phase coil and the third phase coil in order from one end to the other end. The second core comprises a third leg portion and a fourth leg portion that are arranged in parallel with each other and connect the intermediate portions of the first leg portion and the second leg portion, The first phase coil, the second phase coil, and the third phase coil are edgewise coils made by winding flat wire at a right angle. The first phase coil is wound around at least one of the first leg portion and the second leg portion between the first connecting portion and the third leg portion. The second phase coil is wound around at least one of the first leg and the second leg between the third leg and the fourth leg. The third phase coil is wound around at least one of the first leg and the second leg between the fourth leg and the second connecting portion. A three-phase composite common inductor characterized in that the second core is formed of a material with lower magnetic permeability than the first core.

2. The three-phase composite common inductor according to claim 1, characterized in that the first core is a ferrite core and the second core is a dust core with lower magnetic permeability than the ferrite core.

3. The three-phase composite common inductor according to claim 1, characterized in that the first core is formed by connecting two U-shaped cores.

4. The three-phase composite common inductor according to claim 1, characterized in that the first core is formed by connecting two U-shaped cores via two I-shaped cores.

5. The three-phase composite common inductor according to claim 4, characterized in that a gap is provided between the U-shaped core and the I-shaped core for adjusting the balance of the three-phase normal inductances.

6. The second core is, A first plate portion is arranged along the inner circumferential surface of the first leg portion, The device further comprises a second plate portion arranged along the inner circumferential surface of the second leg portion, One end of the third leg is connected to the first leg via the first plate, The other end of the third leg is connected to the second leg via the second plate, One end of the fourth leg is connected to the first leg via the first plate, The three-phase composite common inductor according to claim 1, characterized in that the other end of the fourth leg is connected to the second leg via the second plate.

7. The second core is, A first auxiliary leg is positioned along the side surface of the third leg and connects the intermediate side surfaces of the first and second legs, The three-phase composite common inductor according to claim 1, further comprising a second auxiliary leg positioned along the side surface of the fourth leg and connecting the intermediate side surfaces of the first leg and the second leg.

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