WO2017140225A1

WO2017140225A1 - Magnetic integrated device and power conversion circuit

Info

Publication number: WO2017140225A1
Application number: PCT/CN2017/073145
Authority: WO
Inventors: 胡长军
Original assignee: 中兴通讯股份有限公司
Priority date: 2016-02-16
Filing date: 2017-02-09
Publication date: 2017-08-24
Also published as: CN106057431A

Abstract

A magnetic integrated device and a power conversion circuit. The magnetic integrated device comprises a magnetic core assembly (10) containing N number of "日" shaped closed frames which are arranged closely and in a side-by-side manner; an air gap (13) is arranged on a center post (11) of each "日" shaped closed frame, and a coil (12) is wound on each center post; phases of coil currents in the center posts of the N number of "日" shaped closed frames are gradually increased or reduced from head to tail; a phase difference between the coil currents in the center posts of two adjacent "日" shaped closed frames is 360/N degrees, wherein N is a natural number greater than 1. The magnetic integrated device can reduce overall volume by means of sharing a magnetic circuit, as well as reduce magnetic core loss by means of a magnetic flux reduction in the shared magnetic circuit.

Description

Magnetic integrated device and power conversion circuit

Technical field

The present invention relates to the field of magnetic integration technologies, and in particular, to a magnetic integrated device and a power conversion circuit.

Background technique

With the development of switching devices and soft switching technologies, the switching power supply has been miniaturized by increasing the operating frequency. However, due to the limitations of magnetic devices, the method of high frequency has certain limitations. Because the working frequency is increased, the core loss of the magnetic device is significantly increased. Therefore, the magnetic core of the magnetic device is generally derated when the high frequency is operated, and the working magnetic density of the magnetic core is much smaller than the saturation magnetic density, which limits the magnetic device. A further reduction in volume. In order to further reduce the volume, weight and loss of magnetic devices and improve the performance of magnetic components, magnetic integration technology has been studied and applied to the design of power electronic magnetic devices.

The integration of magnetic devices actually has two meanings: one is to integrate multiple discrete magnetic components on one core structure, making full use of the voltage and current relationship of each magnetic component in a specific circuit topology and the magnetic flux in the magnetic circuit topology. The magnetic potential relationship realizes the integration of multiple magnetic components to reduce the volume, improve the power density of the switching power supply, reduce the loss, and improve the output filtering effect, for example, winding two or more inductors on one magnetic core. The second is to combine the magnetic component with the circuit board, for example, directly fabricating the magnetic component winding on the circuit board, and using the thick film technology to manufacture the magnetic core and the winding on the silicon wafer.

The existing magnetic components are mainly integrated with transformers and transformers, inductors and inductors, transformers and inductors. At present, it is mainly for transformers and transformers, transformers and inductors. For example, the secondary side of the transformer is combined with the inductor to reduce cost and copper loss. The magnetic components for inductors and inductors are relatively less integrated, and generally use EE, EFD and other types of magnetic cores to achieve independent magnetic integrators. When applied to a multi-channel parallel LLC circuit (LLC circuit is a resonant circuit), only a plurality of independent magnetic integrated devices can be implemented in parallel. Obviously, the device integrated by this integrated method is still large in size and takes up a lot of space. At the same time, the magnetic integrated device of this structure works independently in the multi-channel parallel LLC circuit, and it is difficult to reduce the core loss of the circuit ( Iron loss).

Summary of the invention

Embodiments of the present invention are directed to providing a magnetic integrated device and a power conversion circuit.

Embodiments of the present invention provide a magnetic integrated device including a magnetic core assembly formed with N side-by-side and close-set "day" shaped closed frames, each of said "day" shaped closed frames An air gap is disposed on the middle pillar; each of the middle pillars is wound with a coil, and a phase of a coil current on a center pillar of the N "day" shaped closed frames is incremented or decremented from beginning to end, and adjacent The phase difference of the coil currents on the center pillars of the two "day" shaped closed frames is 360/N degrees; wherein N is a natural number greater than one.

In one embodiment, the magnetic core assembly includes N E-type magnetic cores and an I-type sub-magnetic core, the opening faces N-1 E-type magnetic cores vertically above, and the one type I magnetic The core and an E-shaped magnetic core having an opening facing vertically downward are sequentially stacked from bottom to top to constitute a magnetic core assembly of the N "Day" shaped closed frames.

In one embodiment, the core assembly includes N E-type magnetic cores and an I-type sub-core, N openings facing the vertically upper E-type magnetic core and the one I-shaped sub-core from The bottom-up is sequentially stacked to form the core assembly of the N "day"-shaped closed frames.

In an embodiment, when the N is greater than 1, and less than or equal to 3, the direction of the coil currents on the adjacent two of the center pillars is opposite.

In an embodiment, when the N is greater than or equal to 5, the direction of the coil current on the center pillar of each "day" shaped closed frame in the N "day" shaped closed frames is the same.

Embodiments of the present invention also provide a power conversion circuit including magnetic An integrated device, the magnetic integrated device comprising a magnetic core assembly formed with N side-by-side and close-set "day" shaped closed frames, each of the "day" shaped closed frames having an air gap disposed on the center pillar a coil is wound on each of the middle pillars, and a phase of a coil current on a center pillar of the N "day" shaped closed frames is incremented or decremented from beginning to end, and two adjacent "days" are adjacent The phase difference of the coil current on the center pillar of the closed frame is 360/N degrees; wherein N is a natural number greater than one.

In an embodiment, the power conversion circuit further includes an N-phase parallel circuit, and a power input end of each of the upper-column coils of the magnetic integrated device is connected to one of the N-phase parallel circuits The current phase in each phase leg of the N-phase parallel circuit is the same as the current phase of the correspondingly connected coil.

Embodiments of the present invention provide an air gap by providing a magnetic core assembly formed with N side-by-side and close-set "day" shaped closed frames, and an air gap is disposed on a center pillar of each of the "day" shaped closed frames; The core assembly forms N-1 common magnetic circuits that reduce the overall volume by sharing a magnetic circuit when implementing the same number of inductors compared to existing stand-alone integrated devices; and, each of the center columns A coil is wound thereon, and the phase of the coil current on the center pillar of the N "day" shaped closed frame is incremented or decremented from beginning to end, and adjacent to the center pillars of the two "day" shaped closed frames The phase difference of the coil current is 360/N degrees, so that the current directions of the adjacent two coils can be set to be the same or opposite according to the integrated number, thereby reducing the magnetic flux on the common magnetic circuit of both, thereby reducing the core loss. .

DRAWINGS

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the embodiments or the description of the prior art will be briefly described below. Obviously, the drawings in the following description are only It is a certain embodiment of the present invention, and those skilled in the art can obtain other drawings according to the structures shown in the drawings without any creative work.

1 is a schematic structural view of an embodiment of a magnetic integrated device according to the present invention;

2 is a schematic structural view of another embodiment of a magnetic integrated device according to the present invention;

3 is an equivalent magnetic circuit diagram of a magnetic integrated device of the present invention;

4 is a waveform diagram of core loss simulation of the magnetic integrated device shown in FIG. 1;

Figure 5 is a waveform diagram of core loss simulation of an independent magnetic device;

6 is a waveform diagram of a core loss simulation of the magnetic integrated device shown in FIG. 2;

7 is a schematic structural view of a three-way interleaved LLC circuit implemented by the magnetic integrated device of the present invention.

Description of the reference numerals:

标号 Label		名称name
1010	磁芯组件 Core assembly
1111	中柱 Middle column
1212	线圈 Coil
1313	气隙Air gap

101101	E型子磁芯E-type magnetic core
102102	I型子磁芯Type I magnetic core

The implementation, functional features, and advantages of the present invention will be further described in conjunction with the embodiments.

detailed description

The technical solutions in the embodiments of the present invention are clearly and completely described in the following with reference to the accompanying drawings in the embodiments of the present invention. It is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative efforts are within the scope of the present invention.

It should be noted that all directional indications (such as up, down, left, right, front, back, ...) in the embodiments of the present invention are only used to explain between components in a certain posture (as shown in the drawing). Relative positional relationship, motion situation, etc., if the specific posture changes, the directional indication also changes accordingly.

In addition, the descriptions of "first", "second", and the like in the embodiments of the present invention are for the purpose of description only, and are not to be construed as indicating or implying their relative importance or implicitly indicating the number of technical features indicated. Thus, features defining "first" or "second" may include at least one of the features, either explicitly or implicitly. In addition, the technical solutions between the various embodiments may be combined with each other, but must be based on the realization of those skilled in the art, and when the combination of the technical solutions is contradictory or impossible to implement, it should be considered that the combination of the technical solutions does not exist. It is also within the scope of protection required by the embodiments of the present invention.

Embodiments of the present invention provide a magnetic integrated device.

Referring to FIG. 1 to FIG. 3, in the embodiment of the present invention, the magnetic integrated device includes N formed The core assembly 10 is arranged side by side and adjacent to the "day" shaped closed frame. The magnetic core assembly 10 of this structure has N center pillars 11 and N-1 common magnetic circuits, such as the magnetic circuit G1 in FIG. G2. Wherein, the coil 12 is wound on the center pillar 11 of each of the "day"-shaped closed frames, and each of the center pillars 11 is further provided with an air gap 13 which has a large magnetic resistance and can prevent magnetic saturation. , reducing the magnetic permeability, so that the coil 12 on the N middle pillars 11 is equivalent to N independent inductors without the core saturation, wherein the air gap 13 is used to make the coils 12 on the N middle pillars 11 The inductance is equal. It is apparent that the magnetic core assembly 10 of this configuration reduces the overall volume by sharing the magnetic circuit when achieving the same amount of inductance.

In addition, in order to reduce core loss, the phase of the coil 12 current on the center pillar 11 of the N "day" shaped closed frames is incremented or decremented from beginning to end, and two adjacent "day" fonts are closed. The phase difference of the coil 12 current on the center pillar 11 of the frame is 360/N degrees; wherein N is a natural number greater than one. For example, as shown in FIG. 1, when the number of "day" shaped closed frames is three, the phase of the coil 12 current on the center pillar 11 of the first "day" shaped closed frame is 0 degrees, and the second The phase of the coil 12 current on the center pillar 11 of the "day" shaped closed frame is 120 degrees, and the phase of the coil 12 current on the center pillar 11 of the third "day" shaped closed frame is 240 degrees, or it can be considered The phase of the coil 12 current on the center pillar 11 of the first "day" shaped closed frame is 360 degrees, and the phase of the coil 12 current on the center pillar 11 of the second "day" shaped closed frame is 240 degrees. The phase of the coil 12 current on the center pillar 11 of the third "day" shaped closed frame is 120 degrees.

It should be noted that the magnetic circuit formed by the magnetic core assembly 10 is a low reluctance magnetic circuit, and the magnetic resistance in the air gap is much larger than the magnetic resistance in the magnetic circuit, and the decoupling integration is realized by providing a low reluctance magnetic circuit. As shown in the equivalent magnetic circuit of the magnetic integrated device shown in FIG. 3, the air gap 13 of the center pillar 11 generates a magnetic resistance R which is much larger than the magnetic resistance of the loop. The input excitation is sinusoidal, and the generated magnetic potential Φ also changes sinusoidally. The magnetic flux generated by the adjacent windings is superimposed on the common magnetic path, which affects the core loss. When the two adjacent windings generate the same magnetic field direction, they are forward decoupling; when the adjacent two windings generate magnetic When the fields are in opposite directions, they are decoupled in the opposite direction. When there is a phase difference between the coil currents between the adjacent two coils 12, the generated magnetic flux may be superimposed or reduced on the common magnetic circuit, which may affect the core loss, wherein the magnetic flux reduction is beneficial to the reduction of the core loss. small. By setting a proper phase difference, the current directions of the adjacent two coils 12 can be the same or opposite, thereby reducing the magnetic flux on the common magnetic circuit of the two, that is, reducing the magnetic core by reverse decoupling. loss.

Wherein, the winding direction of the coil 12 can be correspondingly set by corresponding to a different number of "day" type closed frames, so that when the current corresponding to the phase is input at the power input end of each coil 12, the adjacent two coils 12 can be made. The current phase difference is appropriate to reduce core loss.

In this embodiment, it should be further explained that, since the air column 13 is disposed at the center pillar 11 of the magnetic core, the magnetic columns on both sides are not provided with the air gap 13, and the magnetic core magnetic circuit formed is a low reluctance magnetic circuit, and the air gap is formed. The magnetic reluctance in 13 is much larger than the reluctance in the magnetic circuit, and decoupling integration is achieved by providing a low reluctance magnetic circuit. As shown in FIG. 3, the equivalent magnetic circuit of the magnetic integrated device composed of the magnetic core assemblies 10 of a plurality of "day" shaped closed frames, the magnetic resistance (R1, R2, ... Rn) generated by the air gap 13 of the center pillar 11 is large. The reluctance of the loop. When the input excitation sinusoidal changes, the generated magnetic potential Φ also changes sinusoidally, and the magnetic flux generated by the adjacent coils 12 is superimposed on the common magnetic circuit. Since the magnetic fluxes are mutually reduced due to the opposite directions, the core loss can be reduced. .

It is worth mentioning that when N different coils 12 are integrated and the input excitation has a phase difference, the magnetic flux change of the magnetic circuit becomes complicated. By adjusting the flow direction of the coil 12 current, the common magnetic circuit can be reduced to a large extent. Core loss. Specifically, when the N is greater than 1, and less than or equal to 3, the direction of the current of the coils 12 on the adjacent two of the center pillars 11 is opposite, and a better effect can be achieved. As shown in FIG. 1, in FIG. 1, N is equal to 3, and common magnetic paths G1 and G2 are formed. It is assumed that the three integrated coils of the magnetic integrated device in the G1 to G2 direction are divided into a first coil, a second coil, and a third. a coil, wherein the excitation currents between the first coil and the second coil are 120 degrees out of phase, and the excitation currents between the second coil and the third coil are out of phase by 120, and the excitation current phase between the third coil and the first coil Equivalent to a difference of 240 degrees. Since the magnetic fluxes are superimposed on the common magnetic circuits G1 and G2, The result is the loss of the core. The simulation analysis by finite element software proves the effect of this embodiment on reducing the core loss. The average value of the core loss of the magnetic integrated device shown in Figure 4 is about 1.75 watts (W), while Figure 5 The average value of the core loss of the core loss of the medium independent magnetic device is about 1.50 watts (W). Obviously, the core loss of the magnetic integrated device to which the present embodiment is applied is remarkably reduced.

In addition, when the N is greater than or equal to 5, the direction of the current of the coil 12 on the center pillar 11 of each "day" shaped closed frame in the N "day" shaped closed frames is set to be the same, which can achieve better. Effect. As shown in FIG. 2, the magnetic core assembly 10 of the five "day"-shaped closed frames is formed with common magnetic circuits G1, G2, G3, and G4, assuming that the magnetic integrated device has five coils 12 in the G1 to G4 directions. Dividing into a first coil, a second coil, a third coil, a fourth coil and a fifth coil, the excitation current between the second coil and the first coil is 72 degrees out of phase, between the third coil and the second coil The excitation currents are phase-shifted by 72 degrees, the excitation currents between the fourth coil and the third coil are out of phase by 72 degrees, and the excitation currents between the fifth coil and the fourth coil are phase-shifted by 72 degrees. Since the magnetic fluxes are superimposed in the common magnetic circuits G1, G2, G3, and G4, the loss of the magnetic core is affected. The simulation analysis by finite element software proves the effect of this embodiment on reducing the core loss. The average value of the core loss of the magnetic integrated device shown in Figure 6 is about 2.00 watts (W), while Figure 5 The average value of the core loss of the core loss of the medium independent magnetic device is about 1.50 watts (W). Obviously, the core loss of the magnetic integrated device to which the present embodiment is applied is remarkably reduced.

In summary, compared with the prior art, the present invention has an advantage in that on the one hand, a plurality of magnetic devices are combined by a common magnetic circuit, the overall volume of the magnetic device is reduced, and on the other hand, by designing a coil excitation input form, The core loss is reduced to a large extent.

In the above embodiment, the magnetic core assembly 10 can be realized by any sub-magnetic core capable of forming a "day" shaped closed frame. In this embodiment, the magnetic core assembly 10 can be realized by the following manner. Referring to FIG. 1 and FIG. The core assembly 10 includes N E-type magnetic cores 101 and an I-type magnetic core 102, the opening faces the N-1 E-type magnetic cores 101 vertically above, the one I-type magnetic core 102 and one The E-shaped magnetic cores 101 having the openings facing vertically downward are sequentially stacked from bottom to top to constitute the core assembly 10 of the N "day"-shaped closed frames.

As shown in FIG. 1, the two openings face the E-shaped magnetic core 101 vertically above, an I-type magnetic core 102, and an E-shaped magnetic core 101 whose opening faces vertically downward, which are sequentially stacked from bottom to top. Together, a magnetic core assembly 10 of three "day" shaped closed frames is formed. The side legs of the E-shaped magnetic core 101 do not open the air gap 13 to form a magnetic circuit with multiple closed loops. The air gap 13 is provided only on the center pillars 11 of the three "day" shaped closed frames, so that the inductances of the three coils 12 are equal. Wherein, as an embodiment, an air gap 13 is provided at one end of the center pillar 11 and another adjacent magnetic core thereof to facilitate winding of the coil 12. It can be understood that the use of the plurality of E-type magnetic cores 101 and one of the I-type magnetic cores 102 to achieve the mutual sharing of one magnetic circuit between the two adjacent inductor coils 12 reduces the overall volume of the core assembly 10. When more pieces need to be provided, the E-shaped magnetic core 101 having the opening facing vertically upward may be further added. For example, in the magnetic integrated device shown in FIG. 2, the E-type is directed from the four openings toward the vertical direction. The sub-core 101, an I-type magnetic core 102, and an E-shaped magnetic core 101 having an opening facing vertically downward are sequentially stacked from bottom to top to form a core assembly of five "day"-shaped closed frames. 10.

In this embodiment, it should be noted that the core assembly 10 can also be replaced by the following manner. Specifically, the core assembly 10 includes N E-type magnetic cores 101 and an I-type magnetic core 102. The E-shaped magnetic core 101 and the one I-type magnetic core 102 with the N openings facing vertically upward are sequentially stacked from bottom to top to constitute the magnetic core assembly 10 of the N "day"-shaped closed frames. . This method is basically the same as the implementation of the magnetic core assembly 10 described above, and is realized by the cooperation of the E-type magnetic core 101 and the I-type magnetic core 102. The difference is that, in this embodiment, the I-type magnetic core 102 Set on the outermost side.

It should be noted that the magnetic integrated device of the above two structures is composed of N E-type magnetic cores 101 and an I-shaped magnetic core integrated through a common magnetic circuit and the same number of independent magnetic devices (independent magnetic devices are generally An E-type magnetic core 101 and an I-type magnetic core 102 are stacked. In comparison, N-1 I-type magnetic cores 102 can be reduced.

The embodiment of the present invention further provides a power conversion circuit. The power conversion circuit includes the above-mentioned magnetic integrated device. The specific structure of the power conversion circuit refers to the above embodiment, and the power conversion circuit according to the embodiment of the present invention is further provided. All the technical solutions of all the above embodiments are adopted, so that at least all the beneficial effects brought by the technical solutions of the above embodiments are not repeated herein.

Further, the power conversion circuit further includes an N-phase parallel circuit, and a power input end of the coil 12 on each of the center pillars 11 of the magnetic integrated device is connected to a phase branch of the N-phase parallel circuit. The current phase in each phase leg of the N-phase parallel circuit is the same as the current phase of the correspondingly connected coil 12. And, the output of the coil 12 on each of the center pillars 11 is connected to a corresponding input end of the transformer.

Specifically, as shown in FIG. 7 , a three-phase interleaved LLC circuit, each phase branch corresponding to an input power supply, respectively V _in1 , V _in2 , V _in3 , processed through MOS tube, diode and capacitor To the power input end of the corresponding coil 12, it is ensured that the current phase in each phase branch of the three-phase interleaved LLC circuit is the same as the current phase of the corresponding three coils L _r1 , L _r2 , L _r3 . Wherein, the currents in the adjacent branches of the three-phase interleaved LLC circuit are opposite in direction, and the output ends of the magnetic integrated device are respectively connected to the primary coils L _r1 , L _r2 , L _{r3 of the} three transformers T1 in one-to-one correspondence, three The secondary coils of the transformer T1 are connected in parallel and output from the common output terminal V0.

The above description is only an embodiment of the present invention, and is not intended to limit the scope of the patents of the embodiments of the present invention. The equivalent structural transformations made by the description of the embodiments of the present invention and the contents of the drawings are used in the inventive concept of the embodiments of the present invention. , or direct/indirect use in other related technical fields are included in the scope of patent protection of the present invention.

Industrial applicability

The technical solution of the embodiment of the present invention is provided by setting N with side by side and close to the setting a magnetic core assembly of a "day" shaped closed frame, an air gap is disposed on a center pillar of each of the "day" shaped closed frames; the magnetic core assembly forms N-1 common magnetic circuits, and an existing Compared to a stand-alone integrated device, the overall volume is reduced by sharing a magnetic circuit when achieving the same number of inductances; and a coil is wound around each of the center pillars, the center pillar of the N "day" shaped closed frames The phase of the coil current is incremented or decremented from beginning to end, and the phase difference of the coil currents on the center pillars of two adjacent "day" shaped closed frames is 360/N degrees, which can be set according to the number of integrated The current directions of the adjacent two coils are the same or opposite, thereby causing the magnetic flux on the common magnetic path of both to be reduced, thereby reducing the core loss.

Claims

A magnetic integrated device comprising a magnetic core assembly formed with N side-by-side and close-set "day" shaped closed frames, each of the "day" shaped closed frames having an air gap disposed on the center pillar; a coil is wound on the center pillar, and a phase of a coil current on a center pillar of the N "Day" shaped closed frames is incremented or decremented from beginning to end, and two adjacent "day" fonts are closed. The phase difference of the coil current on the center pillar of the frame is 360/N degrees; wherein N is a natural number greater than one.
A magnetic integrated device according to claim 1, wherein said magnetic core assembly comprises N E-shaped sub-cores and an I-type sub-core, the openings facing N-1 E-type magnetic cores vertically above, The one I-type magnetic core and an E-shaped magnetic core having an opening facing vertically downward are sequentially stacked from bottom to top to constitute a magnetic core assembly of the N "Day" shaped closed frames.
The magnetic integrated device of claim 1 wherein said core assembly comprises N E-shaped sub-cores and an I-type sub-core, N openings facing vertically above the E-shaped sub-core and said An I-type sub-core is stacked in this order from bottom to top to form the core assembly of the N "Day" shaped closed frames.
The magnetic integrated device according to any one of claims 1 to 3, wherein when the N is greater than 1, and less than or equal to 3, the direction of the coil currents on the adjacent two of the center pillars is opposite.
The magnetic integrated device according to claim 4, wherein a coil current on a center pillar of each of the "day" shaped closed frames in the N "day" shaped closed frames when said N is greater than or equal to 5 The direction is the same.
A power conversion circuit comprising a magnetic integrated device, the magnetic integrated device comprising a core assembly formed with N side-by-side and close-set "day" shaped closed frames, each of said "days An air gap is disposed on the center pillar of the font closed frame; each of the center pillars is wound with a coil, and the phase of the coil current on the center pillar of the N "day" shaped closed frames is first The tail is incremented or decremented, and the phase difference of the coil currents on the center pillars of two adjacent "day" shaped closed frames is 360/N degrees; wherein N is a natural number greater than one.
A power conversion circuit according to claim 6, wherein said power conversion circuit further comprises an N-phase parallel circuit, said power supply input of each of said upper column coils of said magnetic integrated device being connected to said N-phase parallel A phase leg in the circuit, the current phase in each phase leg of the N-phase parallel circuit is the same as the current phase of the correspondingly connected coil.
The power conversion circuit according to claim 6, wherein said magnetic core assembly comprises N E-shaped sub-cores and an I-type sub-core, the openings are oriented toward N-1 E-type magnetic cores vertically above, The one I-type magnetic core and an E-shaped magnetic core having an opening facing vertically downward are sequentially stacked from bottom to top to constitute a magnetic core assembly of the N "Day" shaped closed frames.
The power conversion circuit according to claim 6, wherein said magnetic core assembly comprises N E-shaped sub-cores and an I-type sub-core, N openings are oriented vertically above the E-shaped sub-core and said An I-type sub-core is stacked in this order from bottom to top to form the core assembly of the N "Day" shaped closed frames.
The power conversion circuit according to any one of claims 6 to 9, wherein when the N is greater than 1, and less than or equal to 3, the direction of the coil currents on the adjacent two of the center pillars is opposite.
The power conversion circuit according to claim 10, wherein, when said N is greater than or equal to 5, coil currents on the center pillar of each of the "day" shaped closed frames in the N "day" shaped closed frames The direction is the same.