Power converter

Abstract

To provide a power conversion device that has achieved size reduction and cost lowering while reducing the number of components.SOLUTION: A power conversion device comprises: an iron core that forms a magnetic circuit; a primary coil wound around the iron core; a secondary coil magnetically combined with the primary coil and wound around the iron core; and a smoothing coil electrically connected to the secondary coil and wound around the iron core. The iron core has: a first iron core; a second iron core that faces the first iron core, and disposed spaced apart from the first iron core; a central leg that connects between respective central portions of the first iron core and the second iron core opposite to each other; and a plurality of side legs that connects between respective end portions of the first iron core and the second iron core opposite to each other spaced apart from the central leg. The primary coil and the secondary coil are wound around a first side leg. The smoothing coil is wound around a second side leg. A magnetic path common to the primary coil, the secondary coil, and the smoothing coil is formed at the central leg.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] This application relates to a power conversion device.

Background Art

[0002] Due to recent environmental regulations and technological advancements surrounding automobiles, electric vehicles or hybrid vehicles have been developed and are becoming more widespread in various vehicle classes. In electrified vehicles that use a motor as a drive source, such as hybrid vehicles or electric vehicles, a plurality of power conversion devices are installed. A power conversion device is a device that converts an input current from DC to AC, from AC to DC, or converts an input voltage to a different voltage. In power conversion devices, a plurality of magnetic components including a core and windings are used. Specifically, as power conversion devices installed in electrified vehicles, there are chargers that convert commercial AC power to DC power to charge a high-voltage battery, DC / DC converters that convert the DC power of a high-voltage battery to DC power of a different voltage, inverters that convert the DC power from a high-voltage battery to AC power for a motor, and the like.

[0003] A DC / DC converter, for example, is installed in an electrified vehicle to charge a low-voltage lead battery from a high-voltage lithium-ion battery. To protect the surroundings from high voltage, the high-voltage lithium-ion battery is insulated from the chassis and the low-voltage system. In a DC / DC converter as well, generally, insulation between the high-voltage input side and the low-voltage output side is required by an isolation transformer. In a DC / DC converter, the DC input voltage is switched by semiconductor elements or the like and converted into a signal such as AC and input to the primary side of the isolation transformer. The output of the secondary side of the isolation transformer is rectified by semiconductor elements or the like and smoothed by a smoothing reactor, and then output from the DC / DC converter as a DC output voltage.

[0004] Isolated DC / DC converters installed in electric vehicles or hybrid vehicles are generally in the kW class or higher. As a result, isolation transformers and smoothing reactors are large and prone to overheating. Furthermore, isolated DC / DC converters with multiple magnetic components such as isolation transformers and smoothing reactors require fixing parts to secure each component, resulting in a large number of parts. A power conversion device configuration that reduces the number of parts has been disclosed (for example, Patent Document 1). In Patent Document 1, the iron core has a central leg and side legs, with the windings of the smoothing reactor wound around the central leg which has a gap, and the windings of the isolation transformer wound around the side legs. By integrating the isolation transformer and smoothing reactor, the power conversion device is miniaturized and the number of parts in the power conversion device is reduced. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Patent No. 6198994 [Overview of the project] [Problems that the invention aims to solve]

[0006] In particular, the secondary side of DC / DC converters used in electric vehicles often requires currents of several hundred amperes or more. Therefore, isolation transformers and smoothing reactors are generally of the planar type, using flat windings. By using a planar type, the cross-sectional area of ​​the windings can be increased to reduce losses, improve heat dissipation, and reduce the temperature rise of the coils. However, the projected area of ​​the winding portion of the planar type is large. When the configuration of Patent Document 1 is formed using a planar type, flat windings are arranged on each of the adjacent central leg and side legs, so the projected area of ​​the power conversion device integrating the isolation transformer and smoothing reactor increases, resulting in the problem of the power conversion device becoming larger. In addition, the smoothing reactor provided on the central leg has an external iron configuration. Therefore, the exposed portion of the windings of the smoothing reactor is small, and the windings cannot be cooled sufficiently, resulting in the problem of the power conversion device becoming larger due to constraints on heat generation. Furthermore, because it is necessary to secure areas for four flat windings—two between the central leg and one side leg of the core, and two between the central leg and the other side leg—the core becomes larger, which increases the cost of the power converter and leads to the problem of the power converter becoming larger.

[0007] Furthermore, when the primary winding of an isolation transformer is connected to a power conversion circuit having a semiconductor switching element, and especially when the power conversion circuit is a hard-switching type that adjusts the output voltage by changing the on-off duty cycle of the primary semiconductor switching element, high-frequency currents flow through the primary and secondary windings of the isolation transformer due to the leakage inductance of the isolation transformer and vibrations due to resonance of the primary semiconductor switching element that occur when the primary semiconductor switching element switches from on to off. Because high-frequency currents flow through the isolation transformer, the amount of heat generated by the isolation transformer increases, so each winding becomes larger to generate heat. Because each winding becomes larger, the enlarged windings are lined up adjacent to the central leg and side legs, which presents the problem of the power conversion device becoming larger.

[0008] Furthermore, the core also generates heat due to the leakage inductance of the isolation transformer and vibrations caused by resonance of the semiconductor switching elements on the primary side. Because the flat windings are adjacent, the central leg, which forms the central axis, and the side legs are spaced apart. In particular, when the configuration is designed to reduce costs and only the bottom side of the core is thermally connected to the cooler, the thermal resistance of the cooling paths on the top and bottom sides of the core via the central leg and side legs becomes large. To generate heat in the core, the core becomes larger, which increases the cost of the power converter and leads to the problem of the power converter becoming larger.

[0009] Therefore, the present invention aims to provide a power conversion device that is smaller and lower in cost while reducing the number of components. [Means for solving the problem]

[0010] The power converter disclosed herein comprises an iron core forming a magnetic circuit, a primary coil wound around the iron core, a secondary coil magnetically coupled to the primary coil and wound around the iron core, and a smoothing coil electrically connected to the secondary coil and wound around the iron core, wherein the iron core has a first iron core, a second iron core facing the first iron core and spaced apart from it, a central leg connecting the opposing central portions of the first and second iron cores, and a plurality of side legs spaced apart from the central leg and connecting the opposing end portions of the first and second iron cores, the primary coil and secondary coil wound around the first side leg, the smoothing coil wound around the second side leg, and a common magnetic path for the primary coil, secondary coil and smoothing coil is formed at the central leg. The central leg does not have a spaced gap in the central leg portion, and the first lateral leg does not have a spaced gap in the first lateral leg portion. It is. [Effects of the Invention]

[0011] According to the power conversion device disclosed herein, the core has a first core, a second core facing the first core and spaced apart from it, a central leg connecting the opposing central portions of the first and second cores, and a plurality of side legs spaced apart from the central leg and connecting the opposing end portions of the first and second cores. The primary coil and secondary coil are wound around the first side leg, and the smoothing coil is wound around the second side leg. A common magnetic path for the primary coil, secondary coil, and smoothing coil is formed at the central leg. As a result, only the windings of the isolation transformer are located between the central leg and the first side leg, and only the windings of the smoothing reactor are located between the central leg and the second side leg. Therefore, the winding areas that need to be secured between the central leg and the first side leg, and between the central leg and the second side leg, can be reduced. Since the winding area to be secured between the central leg and the first side leg, and between the central leg and the second side leg, is reduced, the core can be miniaturized and made less expensive while integrating the isolation transformer and smoothing reactor and reducing the number of parts. As the core is miniaturized and made less expensive, the power conversion device can be miniaturized and made less expensive. [Brief explanation of the drawing]

[0012] [Figure 1] This figure shows the circuit configuration of the power conversion device according to Embodiment 1. [Figure 2] This diagram shows the configuration of the magnetic components of the power converter according to Embodiment 1. [Figure 3] This diagram shows the operation of the circuit of the power converter according to Embodiment 1. [Figure 4] This diagram shows the magnetic flux generated in the magnetic components of the power converter according to Embodiment 1. [Figure 5] This diagram shows the operation of the circuit of the power converter according to Embodiment 1. [Figure 6] This diagram shows the operation of the circuit of the power converter according to Embodiment 1. [Figure 7] This diagram shows the magnetic flux generated in the magnetic components of the power converter according to Embodiment 1. [Figure 8]It is an exploded perspective view showing an overview of a magnetic component of a power conversion device according to Embodiment 1. [Figure 9] It is a diagram showing an overview of a magnetic component and a cooler of a power conversion device according to Embodiment 1. [Figure 10] It is a diagram showing the operation of a circuit of a power conversion device according to Embodiment 1. [Figure 11] It is a diagram showing the operation of a circuit of a power conversion device according to Embodiment 1. [Figure 12] It is a diagram showing the operation waveform of a circuit of a power conversion device according to Embodiment 1. [Figure 13] It is a plan view showing an overview of a main part of a power conversion device according to Embodiment 2. [Figure 14] It is a diagram showing an overview of a main part of a power conversion device according to Embodiment 3. [Figure 15] It is a diagram showing an overview of a magnetic component of a power conversion device according to Embodiment 4. [Figure 16] It is a diagram showing an overview of a main part of a power conversion device according to Embodiment 5. [Figure 17] It is a diagram showing the configuration of a magnetic component of a power conversion device according to Embodiment 6. [Figure 18] It is a diagram showing the configuration of another magnetic component of a power conversion device according to Embodiment 6. [Figure 19] It is a diagram showing the configuration of a magnetic component of a power conversion device according to Embodiment 7.

Embodiments for Carrying Out the Invention

[0013] Hereinafter, a power conversion device according to an embodiment of the present application will be described based on the drawings. In each drawing, the same or corresponding members and parts will be denoted by the same reference numerals and described.

[0014] Embodiment 1. Figure 1 shows an example of the circuit configuration of the power converter 100 according to Embodiment 1. Figure 2 is a schematic diagram showing the configuration of the isolation transformer 3 and smoothing reactor 5, which are magnetic components 90 of the power converter 100. Figures 3, 5, 6, 10, and 11 show the operation of the circuit of the power converter 100, illustrating the path of the current flowing through the circuit. Figures 4 and 7 show the magnetic flux generated in the magnetic component 90 of the power converter 100, illustrating the direction of the magnetic flux in the iron core 300. Figure 8 is an exploded perspective view showing a schematic of the magnetic component 90 of the power converter 100. Figure 9 shows a schematic of the magnetic component 90 and cooler 401 of the power converter 100. Figure 12 shows the operating waveform of the circuit of the power converter 100. The power converter 100 is a DC / DC converter that converts the input voltage Vin of the DC power supply 1 into a secondary DC voltage isolated by the isolation transformer 3 and outputs an output voltage Vout to a load such as a battery. The power conversion device 100 is not limited to a DC / DC converter.

[0015] <Power converter 100> An example of the circuit configuration of the power converter 100 will be explained with reference to Figure 1. In Figure 1, the left side is the input side and the right side is the output side. A DC power supply 1 is connected to the input side of the power converter 100, and a load (not shown), such as a low-voltage battery, is connected to the output side. In this embodiment, the specific configuration of the isolation transformer 3 and smoothing reactor 5 shown in Figure 1 will be described as the power converter 100, but the power converter 100 may also have a configuration that includes a full-bridge circuit 2, a rectifier circuit 4, and a smoothing capacitor 6. The power converter 100 includes a full-bridge circuit 2 connected to the DC power supply 1 and having a plurality of semiconductor switching elements 2a, 2b, 2c, and 2d, which converts the input DC voltage into an AC voltage and outputs it; an isolation transformer 3 which converts the voltage of the AC power output from the full-bridge circuit 2 and outputs it; a rectifier circuit 4 having rectifier diodes 4a and 4b that rectify the output of the isolation transformer 3; and a smoothing reactor 5 and a smoothing capacitor 6 that smooth the output of the isolation transformer 3. The output of the isolation transformer 3 is output to the load 7 as output voltage Vout via the smoothing reactor 5 and smoothing capacitor 6.

[0016] The full-bridge circuit 2 has a plurality of semiconductor switching elements 2a, 2b, 2c, and 2d. In this embodiment, the full-bridge circuit 2 has four semiconductor switching elements, but the number of semiconductor switching elements is not limited to this. The semiconductor switching elements are, for example, MOSFETs (Metal Oxide Semiconductor Field Effect Transistors) with diodes built into the source-drain junction. Note that the semiconductor switching elements are not limited to MOSFETs, but may also be self-extinguishing semiconductor switching elements such as IGBTs (Insulated Gate Bipolar Transistors) with diodes connected in antiparallel. The semiconductor switching elements are formed on a semiconductor substrate made of a semiconductor material such as silicon (Si), silicon carbide (SiC), or gallium nitride (GaN). Wide-bandgap semiconductors made of SiC, GaN, etc. may also be used as semiconductor switching elements.

[0017] The isolation transformer 3 has a primary coil 3a and secondary coils 3b and 3c. The primary coil 3a has primary terminals 31 and 32 at its ends. The primary terminals 31 and 32 are connected to the output side of the full-bridge circuit 2. The secondary coil 3b has a center tap terminal 34 and a secondary terminal 33 at its ends. The secondary coil 3c has a center tap terminal 34 and a secondary terminal 35 at its ends. The center tap terminal 34 is connected to the smoothing reactor 5.

[0018] The rectifier circuit 4 has rectifier diodes 4a and 4b, which are rectifier elements made of semiconductor elements. The secondary terminals 33 and 35 are connected to the cathodes of the rectifier diodes 4a and 4b, respectively. In this embodiment, there are two rectifier diodes, each shown as a single diode, but two or more diodes connected in parallel may also be used. Furthermore, self-extinguishing semiconductor switching elements such as MOSFETs may be used as rectifier elements. The smoothing reactor 5 has a smoothing coil 5a. The smoothing coil 5a has reactor terminals 51 and 52 at its ends. Reactor terminal 51 is connected to the center tap terminal 34, and reactor terminal 52 is connected to the smoothing capacitor 6 and the load 7.

[0019] The DC power supply 1 is, for example, an electrolytic capacitor. A power converter such as an AC / DC converter may be connected before the DC power supply 1. While a full-bridge circuit 2 is shown as an example for the primary circuit, other circuit configurations are acceptable as long as they convert DC voltage to AC voltage, such as a half-bridge or forward converter. Similarly, while a center-tap rectifier circuit is shown as an example for the secondary circuit, other circuit configurations are acceptable as long as they can rectify AC voltage, such as a full-bridge rectifier circuit. In this embodiment, the center-tap rectifier circuit has the anode terminals of rectifier diodes 4a and 4b grounded. However, this is not the only configuration; the secondary terminals 33 and 35 of the isolation transformer 3 are connected to the anode terminals of rectifier diodes 4a and 4b, respectively, the cathode terminals of rectifier diodes 4a and 4b are connected to the smoothing reactor 5, and the center-tap terminal 34 of the isolation transformer 3 is grounded.

[0020] <Isolation transformer 3, smoothing reactor 5> The configuration of the isolation transformer 3 and the smoothing reactor 5, which are the essential parts of this invention, will be explained with reference to Figure 2. The power converter 100 includes an iron core 300 that forms a magnetic circuit, a primary coil 3a wound around the iron core 300, secondary coils 3b and 3c that are magnetically coupled to the primary coil 3a and wound around the iron core 300, and a smoothing coil 5a that is electrically connected to the secondary coils 3b and 3c and wound around the iron core 300. The isolation transformer 3 is formed from the portions of the primary coil 3a and the secondary coils 3b and 3c wound around the iron core 300, and the smoothing reactor 5 is formed from the portion of the smoothing coil 5a wound around the iron core 300.

[0021] The core 300 includes a first core 301, a second core 302 positioned opposite the first core 301 and spaced apart from it, a central leg 312 connecting the opposing central portions of the first core 301 and the second core 302, and a plurality of side legs spaced apart from the central leg 312 and connecting the opposing end portions of the first core 301 and the second core 302. In this embodiment, the core 300 has two side legs, which are the first side leg 311 and the second side leg 313. The number of side legs is not limited to this. Also in this embodiment, the core 300 is divided into an E shape, and the two cores are formed in a symmetrical shape with respect to the dividing surface. By combining the two divided E-shaped cores, the central leg 312, the first side leg 311, and the second side leg 313 are formed. The iron core 300 is divided into E-type sections, but is not limited to this; it may also be divided into E-type and I-type sections. When the iron core 300 is divided into E-type and I-type sections, the E-type core is provided with a central leg 312, a first side leg 311, and a second side leg 313, while the I-type core does not have these legs, and the I-type core is formed in a rod-like shape. In this embodiment, a gap portion 321 is provided in the second side leg 313.

[0022] The primary coil 3a and the secondary coils 3b and 3c are wound around the first side leg 311, and the smoothing coil 5a is wound around the second side leg 313. A common magnetic path is formed at the central leg 312 for the primary coil 3a, the secondary coils 3b and 3c, and the smoothing coil 5a.

[0023] By configuring in this way, only the winding of the isolation transformer 3 is between the central leg 312 and the first side leg 311, and only the winding of the smoothing reactor 5 is between the central leg 312 and the second side leg 313. In the configuration described in the cited reference 1, both the winding of the isolation transformer and the winding of the smoothing reactor were provided between the central leg and the side leg. Since only the winding of the isolation transformer 3 is between the central leg 312 and the first side leg 311, and only the winding of the smoothing reactor 5 is between the central leg 312 and the second side leg 313, the area of the winding to be ensured between each of the central leg 312 and the first side leg 311 and between the central leg 312 and the second side leg 313 is reduced. Thus, while integrating the isolation transformer 3 and the smoothing reactor 5 to reduce the number of components, the core 300 can be miniaturized and cost-reduced. Since the core 300 is miniaturized and cost-reduced, the power conversion device 100 can be miniaturized and cost-reduced.

[0024] Also, the cross-sectional area of the core that shares the magnetic paths of the isolation transformer 3 and the smoothing reactor 5 requires the cross-sectional area for the isolation transformer 3 not to saturate and the cross-sectional area for the smoothing reactor 5 not to saturate. However, since the core that shares the magnetic paths of the isolation transformer 3 and the smoothing reactor 5 is only the central leg 312, the increased area of the cross-sectional area of the core for sharing the magnetic paths is minimized, the volume of the core 300 is suppressed, and the core 300 can be cost-reduced.

[0025] <Operation of the DC / DC converter> The operation of the DC / DC converter will be explained using Figures 3 to 7. As shown in Figure 3, initially, during the period when semiconductor switching elements 2a and 2d are ON, semiconductor switching elements 2b and 2c are OFF, and current flows from the DC power supply 1 to the semiconductor switching element 2a, the primary coil 3a of the isolation transformer 3, and then to the semiconductor switching element 2d. Simultaneously, current flows on the secondary side in the following order: the secondary coil 3c of the isolation transformer 3, the smoothing reactor 5, the load 7, and the rectifier diode 4b. The direction of the magnetic flux generated in the iron core 300 during this operation will be explained using Figure 4. In Figure 4, arrows indicate the direction of the magnetic flux (magnetic flux 41, 42, 43, 61, 62, 63). The magnetic flux of the isolation transformer 3 starts from the first side leg 311 (magnetic flux 41) around which the primary coil 3a is wound, passes through the first iron core 301 and the central leg 312 (magnetic flux 42), goes through the second iron core 302 (magnetic flux 43), and returns to the first side leg 311. Furthermore, the magnetic flux of the smoothing reactor 5 returns from the second side leg 313 (magnetic flux 61) around which the smoothing coil 5a is wound, through the first iron core 301 and the central leg 312 (magnetic flux 62), via the second iron core 302 (magnetic flux 63), and back to the second side leg 313.

[0026] Next, as shown in Figure 5, the semiconductor switching elements 2a, 2b, 2c, and 2d are turned off, and no current flows on the primary side. Current flows on the secondary side in the following order: rectifier diodes 4a and 4b, secondary coils 3b and 3c of the isolation transformer 3, smoothing reactor 5, and load 7. At this time, no voltage is applied to the primary coil 3a of the isolation transformer 3, so the direction of the magnetic flux generated in the iron core 300 of the isolation transformer 3 is the same as the direction of the magnetic flux shown in Figure 4. Also, since no voltage is applied to the secondary coils 3b and 3c of the isolation transformer 3, the voltage of load 7 is applied to the smoothing reactor 5, and although the magnetic flux in the iron core 300 of the smoothing reactor 5 gradually decreases, the direction of the current flowing through the smoothing coil 5a does not change, so the direction of the magnetic flux generated in the iron core 300 of the smoothing reactor 5 is the same as the direction of the magnetic flux shown in Figure 4.

[0027] Next, as shown in Figure 6, during the period when semiconductor switching elements 2b and 2c are ON, semiconductor switching elements 2a and 2d are OFF, and current flows from the DC power supply 1 to semiconductor switching element 2c, the primary coil 3a of the isolation transformer 3, and then to semiconductor switching element 2b. Simultaneously, current flows on the secondary side in the following order: secondary coil 3b of the isolation transformer 3, smoothing reactor 5, load 7, and rectifier diode 4a. The direction of the magnetic flux generated in the iron core 300 during this operation is explained with reference to Figure 7. In Figure 7, arrows indicate the direction of the magnetic flux (magnetic flux 44, 45, 46, 64, 65, 66). The magnetic flux of the isolation transformer 3 starts from the first side leg 311 (magnetic flux 44) around which the primary coil 3a is wound, passes through the second iron core 302 and the central leg 312 (magnetic flux 45), goes through the first iron core 301 (magnetic flux 46), and returns to the first side leg 311. Furthermore, the magnetic flux of the smoothing reactor 5 returns from the second side leg 313 (magnetic flux 64) around which the smoothing coil 5a is wound, through the first iron core 301 and the central leg 312 (magnetic flux 65), via the second iron core 302 (magnetic flux 66), and back to the second side leg 313.

[0028] Next, as shown in Figure 5, the semiconductor switching elements 2a, 2b, 2c, and 2d are turned off, and no current flows on the primary side. On the secondary side, current flows in the following order: rectifier diodes 4a and 4b, secondary coils 3b and 3c of the isolation transformer 3, smoothing reactor 5, and load 7. At this time, no voltage is applied to the primary coil 3a of the isolation transformer 3, so the direction of the magnetic flux generated in the iron core 300 of the isolation transformer 3 is the same as the direction of the magnetic flux shown in Figure 7. Also, since no voltage is applied to the secondary coils 3b and 3c of the isolation transformer 3, the voltage of load 7 is applied to the smoothing reactor 5, and although the magnetic flux in the iron core 300 of the smoothing reactor 5 gradually decreases, the direction of the current flowing through the smoothing coil 5a does not change, so the direction of the magnetic flux generated in the iron core 300 of the smoothing reactor 5 is the same as the direction of the magnetic flux shown in Figure 7.

[0029] As described above, the output voltage Vout can be adjusted by simultaneously switching semiconductor switching elements 2a and 2d on and off, and simultaneously switching semiconductor switching elements 2b and 2c on and off, and by adjusting the ratio of the period when semiconductor switching elements 2a and 2d are ON or semiconductor switching elements 2b and 2c are ON to the period when semiconductor switching elements 2a to 2d are OFF.

[0030] <Structure of isolation transformer 3 and smoothing reactor 5> The specific structure of the isolation transformer 3 and the smoothing reactor 5 will be described using Figure 8. The same reference numerals are used for parts corresponding to those in Figure 2. The first iron core 301 is positioned on the upper side of the figure, and the second iron core 302 is positioned on the lower side of the figure. A central leg 312, a first side leg 311, and a second side leg 313 are provided between the first iron core 301 and the second iron core 302. In this embodiment, the central leg 312, the first side leg 311, and the second side leg 313 are cylindrical. The shape of the central leg 312, the first side leg 311, and the second side leg 313 is not limited to a cylindrical shape.

[0031] On the first side leg 311, the secondary coil 3c, primary coil 3a1, secondary coil 3b, and primary coil 3a2 are arranged in order from the side of the second iron core 302. In this embodiment, the primary coils 3a1 and 3a2 each have 3 turns, and the secondary coils 3b and 3c each have 1 turn. The number of turns for each coil is not limited to these. By connecting the inner terminal 36 of the primary coil 3a1 and the inner terminal 37 of the primary coil 3a2, a 6-turn primary coil 3a is formed. In this embodiment, the primary coil 3a is an example with 6 turns, and in order to suppress the increase in the projected area of ​​the primary coil 3a, the primary coil 3a is divided into primary coils 3a1 and 3a2. The primary coil 3a is wound three times from the primary terminal 31 as primary coil 3a1, and at the inner terminal 36 of the winding portion of primary coil 3a1 it is connected to the inner terminal 37 of the winding portion of primary coil 3a2, which is wound three times as primary coil 3a2 and ends at primary terminal 32.

[0032] The secondary coils 3b and 3c are configured such that they are connected to the center tap terminal 34b of the secondary coil 3c via the center tap terminal 34a, then made one turn in the secondary coil 3c, and finally reach the secondary terminal 35. The connection of the center tap terminals 34a and 34b may be achieved by having a bending structure in which at least one of the center tap terminals 34a and 34b approaches the other, or by providing a separate member such as a busbar outside the isolation transformer 3 to connect them. The connection of the inner terminals 36 and 37 of the winding section and the center tap terminals 34a and 34b is achieved by, for example, TIG welding or screw fastening. The connection of the center tap terminals 34a and 34b forms the center tap terminal 34 shown in Figure 1.

[0033] On the second side leg 313, smoothing coils 5a2 and 5a1 are arranged in order from the side of the second iron core 302. In this embodiment, smoothing coils 5a1 and 5a2 each have one turn. The number of turns of each smoothing coil is not limited to this. By connecting the connection terminal 53a of smoothing coil 5a1 and the connection terminal 53b of smoothing coil 5a2, a smoothing coil 5a with two turns is formed. This embodiment is an example where the smoothing coil 5a has two turns. The smoothing coil 5a is configured to have one turn from the reactor terminal 51 through smoothing coil 5a1, connected to the connection terminal 53b of smoothing coil 5a2 at the connection terminal 53a, have one turn through smoothing coil 5a2, and reach the reactor terminal 52. The connection of the connection terminals 53a and 53b may be achieved by having a bending structure in which at least one of the connection terminals 53a and 53b approaches the other, or a separate member such as a busbar may be provided outside the smoothing reactor 5 to connect them. The connection of terminals 53a and 53b is, for example, achieved by TIG welding or screw fastening.

[0034] In this embodiment, the primary coil 3a, secondary coils 3b and 3c, and smoothing coil 5a are each formed in a curved plate shape on a flat surface. The isolation transformer 3 and smoothing reactor 5 are planar type, using flat coils. By using a planar type, the cross-sectional area of ​​the coils can be increased to reduce losses, heat dissipation can be improved, and the temperature rise of the coils can be reduced. Because the temperature rise of the coils is reduced, each coil can be made smaller. Because each coil is made smaller, the power conversion device 100 can be made smaller and less expensive. Furthermore, since only the coil of the isolation transformer 3 is between the central leg 312 and the first side leg 311, and only the coil of the smoothing reactor 5 is between the central leg 312 and the second side leg 313, even if a planar type with a large projected area for the coil portion is used, the size of the power conversion device 100 can be suppressed.

[0035] <Cooler 401> A configuration in which the power converter 100 has a cooler 401 will be described. Figure 9(a) is a side view of the isolation transformer 3, the smoothing reactor 5, and the cooler 401, with a portion of the side wall of the recess 401a removed, and Figure 9(b) is a plan view of the isolation transformer 3, the smoothing reactor 5, and the cooler 401. As shown in Figure 9, the power converter 100 further comprises a cooler 401 having a recess 401a. The portion of the second iron core 302 opposite to the first iron core 301 is thermally connected to the bottom of the recess 401a, and the primary coil 3a or secondary coils 3b, 3c and the smoothing coil 5a are thermally connected to the cooling surface 401b, which is the portion of the cooler 401 surrounding the opening of the recess 401a. A cooling structure through which a refrigerant flows may be provided on the side of the cooler 401 opposite to the cooling surface 401b. The refrigerant is, for example, cooling water. By providing a cooling structure, the heat generated from the isolation transformer 3 and the smoothing reactor 5 can be cooled more efficiently. In this embodiment, since the secondary coil 3c is located on the side of the cooler 401, the secondary coil 3c is thermally connected to the cooling surface 401b. In this embodiment, the isolation transformer 3 and the smoothing reactor 5 are thermally connected to the cooler 401 at two points: the bottom surface of the iron core 300 and the secondary coil 3c and smoothing coil 5a2. With this configuration, the isolation transformer 3 and the smoothing reactor 5 can be efficiently cooled by the cooler 401 at two points. Since the isolation transformer 3 and the smoothing reactor 5 are efficiently cooled, the power conversion device 100 can be miniaturized. Details of the miniaturization will be described below.

[0036] In this embodiment, the integrated isolation transformer 3 and smoothing reactor 5 are cooled from the bottom by a cooler 401. Bottom cooling is a low-cost cooling method because it is a simple configuration in which heat-generating components are placed on the cooler 401. The second iron core 302 is cooled by the cooler 401 via a cooling member 413. The first iron core 301 transfers heat to the second iron core 302 via the central leg 312 and the first side leg 311, and is cooled by the cooler 401 via the cooling member 413. The primary coil 3a and secondary coils 3b and 3c are integrated by, for example, a resin member (not shown) to hold the windings and ensure insulation between the windings. The side of the secondary coil 3c facing the cooler 401 is exposed from the resin member, and each coil is cooled by the cooler 401 via the cooling member 411 from the side of the secondary coil 3c.

[0037] Similarly, the smoothing coils 5a1 and 5a2 are integrated by, for example, a resin member (not shown) to hold the windings and ensure insulation between them. The side of the smoothing coil 5a2 facing the cooler 401 is exposed from the resin member, and the smoothing coil 5a is cooled from the side of the smoothing coil 5a2 by the cooler 401 via the cooling member 412. Since there is often a step between the bottom surface of the second iron core 302 and the bottommost winding (secondary coil 3c, smoothing coil 5a2), in this embodiment, the cooler 401 is provided with a recess 401a into which the second iron core 302 fits. The configuration is not limited to the one in which the cooler 401 is provided with a recess 401a; a protruding portion is also provided that extends from the cooler 401 toward the bottommost winding (secondary coil 3c, smoothing coil 5a2), and the protruding portion is thermally connected to the bottommost winding.

[0038] The second core 302 is surrounded by the side walls of the recess 401a, and the secondary coil 3c and the smoothing coil 5a2 are thermally connected to the cooling surface 401b via cooling members 411 and 412 in many parts on the side of the cooler 401. Therefore, the primary coil 3a, the secondary coils 3b and 3c, and the smoothing coil 5a are cooled by the cooling surface 401b of the cooler 401 in parts that do not overlap with the core 300. The cooling members 411, 412, and 413 are, for example, grease or gap filler. In order to securely fix the core 300 to the cooler 401 via the cooling member 413, the core 300 may be pressed and fixed by springs or the like in the portion of the first core 301 above the first side leg 311 or the second side leg 313.

[0039] As explained above, the isolation transformer 3 and the smoothing reactor 5 have an internal iron configuration. Therefore, as shown in Figure 9(b), when viewed perpendicular to the cooling surface 401b, the primary coil 3a, secondary coils 3b and 3c can be cooled in the upper, lower, and right directions, which do not overlap with the iron core 300, and the smoothing coil 5a can be cooled in the upper, lower, and left directions, which do not overlap with the iron core 300. Since the primary coil 3a, secondary coils 3b and 3c, and smoothing coil 5a can be cooled in a large area around them, the primary coil 3a, secondary coils 3b and 3c, and smoothing coil 5a can be made smaller and less expensive. In addition, since the areas between the central leg 312 and the first side leg 311, and between the central leg 312 and the second side leg 313, which are reserved for arranging each coil, are reduced, the iron core 300 can be made even smaller and less expensive. Furthermore, since the first iron core 301 is cooled via the central leg 312 and the first side leg 311, the length from each part of the first iron core 301 to the central leg 312 and the first side leg 311 is shortened, which reduces thermal resistance and allows for further miniaturization and cost reduction of the iron core 300.

[0040] In this embodiment, an example of a planar type is shown in which flat windings are used as the primary coil 3a, secondary coils 3b and 3c, and smoothing coil 5a. In order to efficiently cool each coil in a planar type, it is common to cool each coil in the projection plane direction that can secure the cooling area for each coil. Therefore, in order to secure the cooling capacity, the projection area of ​​each coil is large when viewed perpendicular to the cooling surface 401b. Furthermore, since only the windings of the isolation transformer 3 are between the central leg 312 and the first side leg 311, and only the windings of the smoothing reactor 5 are between the central leg 312 and the second side leg 313, in the planar type isolation transformer 3 and smoothing reactor 5, the length of the dominant projection plane direction of the winding regions that need to be secured between the central leg 312 and the first side leg 311, and between the central leg 312 and the second side leg 313, respectively can be minimized, thereby greatly reducing the size and cost of the iron core 300. Furthermore, as mentioned above, since the first iron core 301 is cooled via the central leg 312 and the first side leg 311, in the planar-type isolation transformer 3 and smoothing reactor 5, the length from each part of the first iron core 301 to the central leg 312 and the first side leg 311 is dominant in terms of thermal resistance. By minimizing this dominant length, the effect of reducing thermal resistance is significant, and the iron core 300 can be further miniaturized and made less expensive.

[0041] Furthermore, when viewed perpendicular to the cooling surface 401b, the primary coil 3a, secondary coils 3b and 3c can be cooled in the upper, lower, and right directions, which do not overlap with the iron core 300, and the smoothing coil 5a can be cooled in the upper, lower, and left directions, which do not overlap with the iron core 300. As a result, the cooling area of ​​the coils in the planar configuration is increased, and the coils can be cooled efficiently. Consequently, the primary coil 3a, secondary coils 3b and 3c, and smoothing coil 5a of the isolation transformer 3 can be made smaller and less expensive. In addition, the areas between the central leg 312 and the first side leg 311, and between the central leg 312 and the second side leg 313, which are reserved for arranging the coils, are reduced, allowing for further miniaturization and cost reduction of the iron core 300.

[0042] <Full Bridge Circuit 2> The above has mainly described the structure of the isolation transformer 3 and the smoothing reactor 5, which are the essential parts of the present invention. As shown in Figure 1, the power conversion device 100 includes a full-bridge circuit 2, which is a power conversion circuit that converts DC power to AC power and has a plurality of semiconductor switching elements 2a, 2b, 2c, and 2d. The primary coil 3a is electrically connected to the output side of the full-bridge circuit 2, and the full-bridge circuit 2 is a circuit that uses a hard-switching method to adjust the output power by changing the on-off duty cycle of the plurality of semiconductor switching elements 2a, 2b, 2c, and 2d.

[0043] In this embodiment, as described above, an example is shown using a hard switching method to adjust the output voltage Vout by simultaneously turning semiconductor switching elements 2a and 2d on and off, and simultaneously turning semiconductor switching elements 2b and 2c on and off, and adjusting the ratio of on-periods to off-periods. The effects of using the hard switching method will be explained with reference to Figures 10 to 12. Figures 10 and 11 are diagrams showing the detailed operation of the circuit when semiconductor switching elements 2a to 2d are off. As omitted in the previous explanation using Figures 3, 5 and 6, when semiconductor switching elements 2a and 2d change from on to off, the leakage inductance 3d of the isolation transformer 3 tries to keep the current flowing through the primary coil 3a of the isolation transformer 3. Therefore, as shown in Figure 10, current flows in the following order: leakage inductance 3d, primary coil 3a, parasitic capacitance 20d of semiconductor switching element 2d, parasitic capacitance 20b of semiconductor switching element 2b, and leakage inductance 3d of the isolation transformer 3. Furthermore, current flows in the following order: leakage inductance 3d, primary coil 3a, parasitic capacitance 20c of semiconductor switching element 2c, parasitic capacitance 20a of semiconductor switching element 2a, and leakage inductance 3d. At this time, parasitic capacitances 20a and 20d are charged, and parasitic capacitances 20b and 20c are discharged.

[0044] Then, when parasitic capacitances 20a and 20d are charged to the input voltage Vin, parasitic capacitances 20b and 20c are discharged to 0V, and the current in the leakage inductance 3d is gone, parasitic capacitances 20a and 20d discharge. At that time, as shown in Figure 11, the current flows through the paths of parasitic capacitance 20d, primary coil 3a, leakage inductance 3d, parasitic capacitance 20b, and parasitic capacitance 20d, and parasitic capacitance 20a, parasitic capacitance 20c, primary coil 3a, leakage inductance 3d, and parasitic capacitance 20a. At this time, parasitic capacitances 20b and 20c are charged. When parasitic capacitances 20b and 20c are charged to almost the input voltage Vin, parasitic capacitances 20a and 20d are discharged to almost 0V, and the current in the leakage inductance 3d becomes zero, parasitic capacitances 20b and 20c discharge, and the current path returns to that shown in Figure 10. In this way, the operation of the circuits shown in Figures 10 and 11 is repeated.

[0045] Figure 12 will be used to explain the waveforms of each part of the circuit during operation as described above. In Figure 12, the horizontal axis represents time, and the vertical axis represents the amplitude of each waveform. Before t0, semiconductor switching elements 2a and 2d are on, and semiconductor switching elements 2b and 2c are off, and at t0, semiconductor switching elements 2a and 2d are turned off. From t0 to t1, the operation of the circuits in Figures 10 and 11 described above is repeated. From t1 to t2, semiconductor switching elements 2b and 2c are on, and semiconductor switching elements 2a and 2d are off, and at t2, semiconductor switching elements 2b and 2c are turned off. At t2, a current flows through the leakage inductance 3d in the opposite direction to that at t1, resulting in the operation of the circuit in Figure 11. When parasitic capacitances 20b and 20c are charged to the input voltage Vin, parasitic capacitances 20a and 20d are discharged to 0V, and the current through the leakage inductance 3d is gone, the circuit in Figure 10 is operated. The circuit operates similarly from t0 to t1 during t2 to t3. For simplicity, the amplitudes of the oscillations from t0 to t1 and t2 to t3 are assumed to be the same, but in reality, the amplitude gradually decreases because energy is consumed by the resistive components in the current path shown in Figures 10 and 11.

[0046] At this time, vibrations occurring between t0-t1 and t2-t3 cause heat to be generated in various parts of the core 300 of the isolation transformer 3 (the magnetic flux paths formed in the first side legs 311, the first core 301, the central leg 312, and the second core 302), as well as in the primary coil 3a and secondary coils 3b and 3c of the isolation transformer 3. In this embodiment, the primary coil 3a and secondary coils 3b and 3c are wound around the first side leg 311, the smoothing coil 5a is wound around the second side leg 313, and the magnetic path of the isolation transformer 3 and the smoothing reactor 5 is shared at the central leg 312. Therefore, only the coil of the isolation transformer 3 is located between the central leg 312 and the first side leg 311, and only the coil of the smoothing reactor 5 is located between the central leg 312 and the second side leg 313, thus minimizing the length in the projection plane direction of the coil region that needs to be secured between the central leg 312 and each side leg. Therefore, as described above, when using inexpensive bottom cooling, the first core 301 is cooled via the central leg 312 and the first side leg 311. As a result, in the isolation transformer 3, the length from each part of the first core 301 to the central leg 312 and the first side leg 311 can be minimized. Consequently, the thermal resistance of the core 300 is reduced, and the effects of miniaturization and cost reduction of the core 300 can be greatly enhanced in hard switching systems where the losses of the core 300 are large.

[0047] Furthermore, by sharing the magnetic paths of the isolation transformer 3 and the smoothing reactor 5 at the central leg 312, the cross-sectional area of ​​the central leg 312 becomes larger than the cross-sectional area of ​​the isolation transformer 3, as it requires the cross-sectional area necessary to prevent the isolation transformer 3 from saturating (the cross-sectional area of ​​the first side leg 311) and the cross-sectional area necessary to prevent the smoothing reactor 5 from saturating (the cross-sectional area of ​​the second side leg 313). Consequently, the thermal resistance of the central leg 312 decreases, and in the isolation transformer 3, the thermal resistance from each part of the first iron core 301 to the cooler 401 decreases. Therefore, in a hard switching method where the loss of the iron core 300 is large, additional costs due to the thermal buildup of the iron core 300 (such as increasing the size of the iron core or adding cooling components) can be suppressed.

[0048] Furthermore, since the primary coil 3a and secondary coils 3b and 3c are wound around the first side leg 311, and the smoothing coil 5a is wound around the second side leg 313, and the magnetic path of the isolation transformer 3 and the smoothing reactor 5 is shared at the central leg 312, the smoothing coil 5a is physically separated from the primary coil 3a and secondary coils 3b and 3c through which oscillating currents due to the hard switching method flow. As a result, the smoothing coil 5a is less susceptible to noise radiated from the primary coil 3a and secondary coils 3b and 3c, and the noise output from the power converter 100 can be reduced. Therefore, the noise filter required for the output of the power converter 100 can be made smaller and less expensive. In addition, since the central leg 312 is located between the primary coil 3a and secondary coils 3b and 3c and the smoothing coil 5a, the central leg 312 acts as a shield, further suppressing noise coupling from the primary coil 3a and secondary coils 3b and 3c to the smoothing coil 5a.

[0049] Furthermore, since the smoothing coil 5a is physically separated from the primary coil 3a and secondary coils 3b and 3c through which the oscillating current flows due to the hard switching method, thermal interference from the primary coil 3a and secondary coils 3b and 3c, which generate more heat due to the oscillating current, to the smoothing coil 5a is reduced, making it possible to miniaturize and reduce the cost of the smoothing coil 5a.

[0050] <Structure of the 300mm Iron Core> The details of the configuration of the iron core 300 will now be described. In this embodiment, the central leg 312 does not have a spaced gap in the central leg 312 portion. In this embodiment, the primary coil 3a, secondary coils 3b and 3c are wound around the first side leg 311, and the smoothing coil 5a is wound around the second side leg 313. Since the magnetic path of the isolation transformer 3 and the smoothing reactor 5 is shared at the central leg 312, there is no need to provide a gap in the central leg 312, which does not have coils wound around it and only shares a magnetic path. Therefore, eddy currents due to leakage flux from the gap in the central leg 312 do not occur in the primary coil 3a, secondary coils 3b and 3c, and smoothing coil 5a adjacent to the central leg 312. Since the generation of eddy currents is suppressed in each coil, losses in the primary coil 3a, secondary coils 3b and 3c, and smoothing coil 5a can be suppressed.

[0051] In this embodiment, the cross-sectional area of ​​the central leg 312 is smaller than the sum of the cross-sectional areas of the multiple side legs, namely the first side leg 311 and the second side leg 313. For example, when ferrite is used for the iron core 300, the smoothing reactor 5 experiences relatively small changes in applied voltage, resulting in low losses. On the other hand, because it is necessary to secure an inductance value for large currents, the cross-sectional area of ​​the second side leg 313 is constrained by the DC superposition characteristics. Furthermore, the isolation transformer 3 experiences large losses because relatively large input voltages are applied to it in both positive and negative directions. Therefore, the cross-sectional area of ​​the first side leg 311 is constrained by thermal formation. Consequently, the cross-sectional area of ​​the central leg 312 can be reduced to the cross-sectional area of ​​the smoothing reactor 5 required for the DC superposition characteristics of the smoothing reactor 5, or to the cross-sectional area of ​​the isolation transformer 3 required for thermal formation of the isolation transformer 3. This suppresses the enlargement of the iron core 300, making it possible to miniaturize and reduce the cost of the power conversion device 100.

[0052] In this embodiment, as shown in Figure 8, the central leg 312, the first side leg 311, and the second side leg 313 are cylindrical in shape, and the primary coil 3a, secondary coils 3b and 3c, and smoothing coil 5a are circular in shape. However, the embodiment is not limited to this. The central leg 312, the first side leg 311, and the second side leg 313 may be rectangular prisms, like those of a typical EE core. In that case, the primary coil 3a, secondary coils 3b and 3c, and smoothing coil 5a will have a rectangular shape with a right-angled curved portion and will be wound around the first side leg 311 and the second side leg 313. With this configuration, the central leg 312 and the primary coil 3a, secondary coils 3b and 3c, and smoothing coil 5a will be aligned in straight lines, eliminating wasted space and thus suppressing the enlargement of the iron core 300. This allows for miniaturization and cost reduction of the power conversion device 100.

[0053] In this embodiment, the iron core 300 is made of ferrite. Since ferrite is a material commonly used in the isolation transformer 3 and the smoothing reactor 5, the isolation transformer 3 and the smoothing reactor 5 can be manufactured from the same material. Because the isolation transformer 3 and the smoothing reactor 5 are manufactured from the same material, the cost of the iron core 300 can be reduced. As described above, the smoothing reactor 5 has low losses, and the cross-sectional area of ​​the second side leg 313 is constrained by the DC superposition characteristics. In addition, the isolation transformer 3 has high losses because relatively large input voltages are applied in both positive and negative directions, and the cross-sectional area of ​​the first side leg 311 is constrained by thermal formation. Therefore, when the iron core 300 of the isolation transformer 3 and the smoothing reactor 5 are integrated with ferrite, the effect of reducing the cross-sectional area of ​​the central leg 312 is significant, making it possible to miniaturize and reduce the cost of the iron core 300.

[0054] <Configuration of Rectifier Circuit 4> In this embodiment, as shown in Figure 1, the power converter 100 includes a rectifier circuit 4 having multiple rectifier elements, namely rectifier diodes 4a and 4b, which are electrically connected to the secondary coils 3b and 3c. The anode terminals of the rectifier diodes 4a and 4b are grounded. Therefore, since the secondary coils 3b and 3c are directly connected to the smoothing coil 5a via the center tap terminal 34, there is no need to provide terminals on the secondary coils 3b and 3c and the smoothing coil 5a for connection to the outside of the magnetic component 90, and the secondary coils 3b and 3c and the smoothing coil 5a can be connected within the magnetic component 90. Since the secondary coils 3b and 3c and the smoothing coil 5a are connected within the magnetic component 90, there is no need for space to provide connection terminals, and the magnetic component 90 can be miniaturized. In addition, since there is no need to provide connection terminals, the cost of parts required for connection terminals and the processing costs required for connection are eliminated, so the power converter 100 can be made less expensive.

[0055] <Configuration of primary coil 3a, secondary coils 3b and 3c> In this embodiment, the number of turns of the secondary coils 3b and 3c is less than the number of turns of the primary coil 3a. In this embodiment, an example is shown where the primary coil 3a has 6 turns and the secondary coils 3b and 3c each have 1 turn. However, as the number of turns of the secondary coils 3b and 3c decreases, the current in the secondary coils 3b and 3c increases, and the projected area of ​​the secondary coils 3b and 3c increases in order to generate heat in the coils. In this embodiment, only the winding of the isolation transformer 3 is between the central leg 312 and the first side leg 311, and only the winding of the smoothing reactor 5 is between the central leg 312 and the second side leg 313. Therefore, the coil area that needs to be secured between the central leg 312 and the first side leg 311, and between the central leg 312 and the second side leg 313, is reduced. As a result, even if the projected area of ​​the secondary coils 3b and 3c increases, the iron core 300 can be made smaller and less expensive. As described above, when using inexpensive bottom cooling, the first iron core 301 is cooled via the central leg 312 and the first side leg 311. Therefore, in the isolation transformer 3, the length from each part of the first iron core 301 to the central leg 312 and the first side leg 311 can be minimized, resulting in a significant reduction in thermal resistance and further miniaturization and cost reduction of the iron core 300.

[0056] Furthermore, as described above, when viewed perpendicular to the cooling surface 401b, the primary coil 3a and secondary coils 3b and 3c can be cooled in the upper, lower, and right directions that do not overlap with the iron core 300, while the smoothing coil 5a can be cooled in the upper, lower, and left directions that do not overlap with the iron core 300. As a result, the cooling area of ​​the coils is increased, and each coil can be cooled efficiently. Because each coil can be cooled efficiently, the primary coil 3a, secondary coils 3b and 3c, and smoothing coil 5a can be miniaturized, and the power conversion device 100 can be made smaller and less expensive. In addition, because the areas between the central leg 312 and the first side leg 311, and between the central leg 312 and the second side leg 313, which are reserved for arranging each coil, are reduced, the iron core 300 can be made even smaller and less expensive.

[0057] As described above, in the power converter 100 according to Embodiment 1, the iron core 300 has a first iron core 301, a second iron core 302 facing the first iron core 301 and spaced apart from it, a central leg 312 connecting the opposing central portions of the first iron core 301 and the second iron core 302, and a plurality of side legs spaced apart from the central leg 312 and connecting the opposing end portions of the first iron core 301 and the second iron core 302, and the primary coil 3a and secondary coils 3b, 3c are wound around the first side leg 311 As the smoothing coil 5a is wound around the second side leg 313, and a common magnetic path is formed around the central leg 312 for the primary coil 3a, secondary coils 3b and 3c, and smoothing coil 5a, only the windings of the isolation transformer 3 remain between the central leg 312 and the first side leg 311, and only the windings of the smoothing reactor 5 remain between the central leg 312 and the second side leg 313. This reduces the winding area that needs to be secured between the central leg 312 and the first side leg 311, and between the central leg 312 and the second side leg 313. As the winding area that needs to be secured between the central leg 312 and the first side leg 311, and between the central leg 312 and the second side leg 313 is reduced, the isolation transformer 3 and the smoothing reactor 5 can be integrated to reduce the number of parts, while the iron core 300 can be made smaller and less expensive. Since the iron core 300 is made smaller and less expensive, the power converter 100 can also be made smaller and less expensive.

[0058] When the primary coil 3a, secondary coils 3b and 3c, and smoothing coil 5a are each formed in a curved plate shape on a flat surface, the isolation transformer 3 and smoothing reactor 5 are planar type using flat coils. This allows for an increase in the cross-sectional area of ​​the coils, reducing losses and improving heat dissipation, thereby reducing the temperature rise of the coils. Because the temperature rise of the coils is reduced, each coil can be made smaller. Because each coil is made smaller, the power conversion device 100 can be made smaller and less expensive. Furthermore, since only the coil of the isolation transformer 3 is located between the central leg 312 and the first side leg 311, and only the coil of the smoothing reactor 5 is located between the central leg 312 and the second side leg 313, even if a planar type with a large projected area for the coil portion is used, the size of the power conversion device 100 can be suppressed.

[0059] In the case where the power converter 100 includes a full-bridge circuit 2 which is a power conversion circuit that converts DC power to AC power and has a plurality of semiconductor switching elements 2a, 2b, 2c, and 2d, and the primary coil 3a is electrically connected to the output side of the full-bridge circuit 2, and the full-bridge circuit 2 is a circuit that uses a hard switching method to adjust the output power by changing the on-off duty cycle of the plurality of semiconductor switching elements 2a, 2b, 2c, and 2d, the present invention has a miniaturized iron core 300, so the thermal resistance of the iron core 300 is reduced even in a hard switching method where the loss of the iron core 300 is large, and thus the effects of miniaturization and cost reduction of the iron core 300 can be greatly increased.

[0060] If the central leg 312 does not have a spaced gap in its portion, the present invention has a configuration in which the primary coil 3a, secondary coils 3b and 3c are wound around the first side leg 311, and the smoothing coil 5a is wound around the second side leg 313, with the magnetic path of the isolation transformer 3 and the smoothing reactor 5 being shared at the central leg 312. Therefore, since there is no need to provide a gap in the central leg 312, which does not have coils wound around it and only shares a magnetic path, eddy currents due to leakage flux from the gap in the central leg 312 do not occur in the primary coil 3a, secondary coils 3b and 3c, and smoothing coil 5a adjacent to the central leg 312. Since the generation of eddy currents is suppressed in each coil, losses in the primary coil 3a, secondary coils 3b and 3c, and smoothing coil 5a can be suppressed.

[0061] If the cross-sectional area of ​​the central leg 312 is smaller than the sum of the cross-sectional areas of the multiple side legs, namely the first side leg 311 and the second side leg 313, then in the present invention, the cross-sectional area of ​​the central leg 312 can be reduced to the cross-sectional area of ​​the smoothing reactor 5 required for the DC superposition characteristics of the smoothing reactor 5, or to the cross-sectional area of ​​the isolation transformer 3 required for the thermal establishment of the isolation transformer 3. As a result, the enlargement of the iron core 300 is suppressed, and the power conversion device 100 can be made smaller and less expensive.

[0062] If the iron core 300 is made of ferrite, since ferrite is a material commonly used in both the isolation transformer 3 and the smoothing reactor 5, the isolation transformer 3 and the smoothing reactor 5 can be manufactured from the same material. Because the isolation transformer 3 and the smoothing reactor 5 are manufactured from the same material, the cost of the iron core 300 can be reduced.

[0063] The power converter 100 has a rectifier circuit 4 which has multiple rectifier elements, namely rectifier diodes 4a and 4b, and is electrically connected to the secondary coils 3b and 3c. When the anode terminals of the rectifier diodes 4a and 4b are grounded, the secondary coils 3b and 3c are directly connected to the smoothing coil 5a via the center tap terminal 34. Therefore, there is no need to provide terminals on the secondary coils 3b and 3c and the smoothing coil 5a for connection to the outside of the magnetic component 90, and the secondary coils 3b and 3c and the smoothing coil 5a can be connected within the magnetic component 90. Since the secondary coils 3b and 3c and the smoothing coil 5a are connected within the magnetic component 90, there is no need for space to provide connection terminals, and the magnetic component 90 can be miniaturized. In addition, since there is no need to provide connection terminals, the cost of the parts required for connection terminals and the processing costs required for connection are eliminated, so the power converter 100 can be made less expensive.

[0064] When the number of turns of the secondary coils 3b and 3c is less than the number of turns of the primary coil 3a, the current in the secondary coils 3b and 3c increases as the number of turns of the secondary coils 3b and 3c decreases. Although the projected area of ​​the secondary coils 3b and 3c increases in order to generate heat in the coils, in the configuration of the present invention, the coil regions that need to be secured between the central leg 312 and the first side leg 311, and between the central leg 312 and the second side leg 313 are reduced. Therefore, even if the projected area of ​​the secondary coils 3b and 3c increases, the iron core 300 can be made smaller and less expensive.

[0065] If the power converter 100 is equipped with a cooler 401 having a recess 401a, and the portion of the second iron core 302 opposite to the first iron core 301 is thermally connected to the bottom of the recess 401a, and the primary coil 3a or secondary coils 3b, 3c and the smoothing coil 5a are thermally connected to the cooling surface 401b, which is the portion of the cooler 401 surrounding the opening of the recess 401a, then the isolation transformer 3 and the smoothing reactor 5 are thermally connected to the cooler 401 at two points: the bottom surface of the iron core 300 and the primary coil 3a or secondary coils 3b, 3c and the smoothing coil 5a2. As a result, the isolation transformer 3 and the smoothing reactor 5 can be efficiently cooled by the cooler 401 at two points. Because the isolation transformer 3 and the smoothing reactor 5 are efficiently cooled, the power converter 100 can be made smaller.

[0066] Embodiment 2. A power converter 100 according to Embodiment 2 will now be described. Figure 13 is a plan view showing the main parts of the power converter 100 according to Embodiment 2, with the first iron core 301 removed from the magnetic component 90. In Figure 13, the primary coil 3a, secondary coils 3b and 3c, and smoothing coil 5a are shown as disc shapes, only their outer shapes are shown, for simplicity. The power converter 100 according to Embodiment 2 has a different configuration of the central leg 312 than Embodiment 1.

[0067] Embodiment 1 shows an example in which the central leg 312 is cylindrical in shape. The central leg 312 is positioned with a gap between it and the adjacent primary coil 3a, secondary coils 3b and 3c, and smoothing coil 5a. In this embodiment, the side surface of the central leg 312 has a shape that conforms to the side surface shape of the primary coil 3a, secondary coils 3b and 3c, and smoothing coil 5a that are opposite the side surface of the central leg 312. Because the primary coil 3a, secondary coils 3b and 3c, and smoothing coil 5a are disc-shaped, the central leg 312 has a shape that is constricted in the center.

[0068] When the central leg 312 is provided in a cylindrical shape, there is wasted space between the central leg 312 and the primary coil 3a and secondary coils 3b and 3c, and between the central leg 312 and the smoothing coil 5a. By configuring it in this way, the wasted space can be reduced, and the distance between the primary coil 3a and secondary coils 3b and 3c and the smoothing coil 5a (distance L1 in Figure 13) can be shortened. Since distance L1 is shortened, the distance between the first side leg 311 and the second side leg 313 is also shortened, so the iron core 300 can be made smaller. Since the iron core 300 is made smaller, the power conversion device 100 can be made smaller and less expensive.

[0069] Embodiment 3. A power converter 100 according to Embodiment 3 will now be described. Figure 14 is a schematic diagram of the magnetic component 90 of the power converter 100 according to Embodiment 3. Figure 14(a) is a side view showing the isolation transformer 3, smoothing reactor 5, and cooler 401 with a part of the side wall of the recess 401a removed, and Figure 14(b) is a plan view of the isolation transformer 3, smoothing reactor 5, and cooler 401. The power converter 100 according to Embodiment 3 has a different configuration of the iron core 300 than that of Embodiment 1.

[0070] The thickness of one or both portions of the first core 301 and the second core 302, with which the magnetic flux of the smoothing coil 5a links, is greater than the respective thicknesses of the first core 301 and the second core 302, with which the magnetic fluxes of the primary coil 3a and the secondary coils 3b and 3c link. In the configuration of the magnetic component 90 shown in Figure 14(a), the thickness of both portions of the first core 301 and the second core 302 is greater than the respective thicknesses of the first core 301 and the second core 302, with which the magnetic fluxes of the primary coil 3a and the secondary coils 3b and 3c link.

[0071] The isolation transformer 3 tends to have a greater overall coil thickness than the smooth reactor 5 because it has a primary coil 3a and secondary coils 3b and 3c. As a result, there was wasted space between the smooth coil 5a and the first core 301, and between the smooth coil 5a and the second core 302. By increasing the thickness of the first core 301 and the second core 302 to fill this wasted space, as shown in Figure 14(b), the size of the first core 301 and the second core 302 in the short-side direction, when viewed perpendicular to the cooling surface 401b, can be reduced, thereby reducing the projected area of ​​the isolation transformer 3 and the smooth reactor 5. This is more effective when the size of the first core 301 and the second core 302 in the short-side direction, when viewed perpendicular to the cooling surface 401b, is determined by the constraints of the cross-sectional area of ​​the smooth reactor 5.

[0072] Embodiment 4. A power converter 100 according to Embodiment 4 will now be described. Figure 15 is a schematic diagram of the magnetic component 90 of the power converter 100 according to Embodiment 4, showing the secondary coil 3b and smoothing coil 5a1 after removing the first iron core 301 from the magnetic component 90. In the power converter 100 according to Embodiment 4, the secondary coil 3b and the smoothing coil 5a1 are integrated into one unit.

[0073] The secondary coil 3b and the smoothing coil 5a1 are arranged side by side and electrically and mechanically coupled by an integration portion 8a to form an integrated coil member 8. The integration portion 8a is the part to which the center tap terminal 34a and the reactor terminal 51 are coupled. In this embodiment, the shape of the central leg 312, the first side leg 311, and the second side leg 313 is a rectangular prism shape. The primary coil 3a, the secondary coils 3b and 3c, and the smoothing coil 5a are rectangular in shape with right-angled curved portions.

[0074] With this configuration, the integrated coil member 8 is formed from, for example, a single sheet metal part, thus reducing the number of parts that make up the coil. This eliminates the need for processing costs to connect the secondary coil 3b and the smoothing coil 5a1, and thus reduces the cost of the magnetic component 90. Furthermore, since the area required for connection is eliminated in the magnetic component 90, the magnetic component 90 can be made smaller.

[0075] Embodiment 5. A power converter 100 according to Embodiment 5 will now be described. Figure 16 is a schematic diagram of the magnetic component 90 of the power converter 100 according to Embodiment 5, and is a side view showing the isolation transformer 3, smoothing reactor 5, and cooler 401 with a part of the side wall of the recess 401a removed. The power converter 100 according to Embodiment 5 has a different configuration of the iron core 300 than Embodiment 1.

[0076] In this embodiment, a gap portion 321 is provided in the central leg 312 and any of the side legs around which one of the primary coil 3a, secondary coils 3b, 3c, or smoothing coil 5a is wound, and which does not form a common magnetic path for the primary coil 3a, secondary coils 3b, 3c, or smoothing coil 5a. A spacer member 320 is inserted into the gap portion 321. In this embodiment, a gap portion 321 is provided in the second side leg 313 around which the smoothing coil 5a is wound, and a spacer member 320 is inserted into the gap portion 321. The spacer member 320 is made of, for example, a resin material.

[0077] In the example shown in Figure 9 of Embodiment 1, the second side leg 313 around which the smoothing coil 5a is wound has a gap portion 321, and the gap portion 321 is a space without a spacer member 320. As shown in Figure 16, by inserting the spacer member 320 into the gap portion 321, the second side leg 313 can be fixed from the upper part of the first iron core 301 when fixing the iron core 300 to the cooler 401. Since the second side leg 313 is fixed from the upper part of the first iron core 301, the vibration resistance of the gap portion 321 of the second side leg 313 can be improved.

[0078] Embodiment 6. A power converter 100 according to Embodiment 6 will now be described. Figure 17 is a schematic diagram showing the configuration of the isolation transformer 3 and smoothing reactor 5, which are magnetic components 90 of the power converter 100 according to Embodiment 6. The power converter 100 according to Embodiment 6 has a different configuration from Embodiment 1 in the part of the iron core 300 around which the coil is wound.

[0079] In this embodiment, the primary coil 3a and secondary coils 3b and 3c are wound around the first side leg 311, the smoothing coil 5a is wound around the central leg 312, and a common magnetic path for the primary coil 3a, secondary coils 3b and 3c, and smoothing coil 5a is formed around the second side leg 313. With this configuration, only the coil of the smoothing reactor 5 is located between the central leg 312 and the second side leg 313, thus reducing the area of ​​coil that needs to be secured between the central leg 312 and the second side leg 313. As the area of ​​coil is reduced, the isolation transformer 3 and the smoothing reactor 5 can be integrated to reduce the number of parts, while the iron core 300 can be made smaller and less expensive.

[0080] In this embodiment, the cross-sectional area of ​​the second side leg 313 is smaller than the sum of the cross-sectional areas of the multiple side legs excluding the second side leg 313 and the central leg 312. The cross-sectional area of ​​the portion of the core 300 that shares the magnetic path between the isolation transformer 3 and the smoothing reactor 5 requires a cross-sectional area to prevent saturation of both the isolation transformer 3 and the smoothing reactor 5. Since the second side leg 313, which shares the magnetic path between the isolation transformer 3 and the smoothing reactor 5, is located to the left of the central leg 312, which consists only of the coil of the smoothing reactor 5, the area of ​​increase in the cross-sectional area of ​​the second side leg 313 that shares the magnetic path can be reduced. Because the increase in the cross-sectional area of ​​the second side leg 313 is reduced, the increase in the volume of the core 300 is suppressed, and the cost of the core 300 can be reduced.

[0081] The second side leg 313 does not have a spaced gap in its portion. In this embodiment, the primary coil 3a, secondary coils 3b and 3c are wound around the first side leg 311, the smoothing coil 5a is wound around the central leg 312, and the magnetic path of the isolation transformer 3 and the smoothing reactor 5 is shared at the second side leg 313. Therefore, since the second side leg 313 does not have a coil wound around it and only shares a magnetic path, there is no need to provide a gap in the second side leg 313, which is adjacent to the second side leg 313. As a result, eddy currents due to leakage flux from the gap in the second side leg 313 do not occur in the smoothing coil 5a adjacent to the second side leg 313. Since the generation of eddy currents in the smoothing coil 5a is suppressed, losses in the smoothing coil 5a can be suppressed. Furthermore, when fixing the core 300 to the cooler 401, the first side legs 311 and the second side legs 313, which are located at both ends of the core 300, can be fixed from the upper part of the first core 301, thereby improving the vibration resistance of the core 300. In addition, since the length from each part to the left of the central leg 312 of the core 300 to the second side legs 313 is shortened, the thermal resistance of the core 300 is reduced, making it possible to further miniaturize and reduce the cost of the core 300.

[0082] The configuration of another magnetic component 90 according to this embodiment will now be described. Figure 18 is a plan view showing a part of the configuration of another magnetic component 90 of the power converter 100 according to Embodiment 6, with the first iron core 301 removed from the magnetic component 90. In Figure 18, the smoothing coil 5a is shown as a disc shape, showing only its outer shape for simplicity. The second side leg 313 is positioned at a distance from the adjacent smoothing coil 5a, and the side surface of the second side leg 313 has a shape that conforms to the side surface shape of the smoothing coil 5a facing the side surface of the second side leg 313.

[0083] This configuration reduces the wasted space between the second side leg 313 and the smoothing coil 5a, thereby shortening the distance (distance L2 in Figure 18) between the end of the second side leg 313 and the smoothing coil 5a. As distance L2 is shortened, the distance between the first side leg 311 and the second side leg 313 is also shortened, allowing the core 300 to be miniaturized. As the core 300 is miniaturized, the power conversion device 100 can be made smaller and less expensive.

[0084] Embodiment 7. A power converter 100 according to Embodiment 7 will now be described. Figure 19 is a plan view showing the configuration of the isolation transformer 3 and smoothing reactor 5, which are magnetic components 90 of the power converter 100 according to Embodiment 7, with the first iron core 301 removed from the magnetic components 90. In Figure 19, the primary coil 3a, secondary coils 3b and 3c, and smoothing coil 5a are shown as disc shapes, only their outer shapes are shown, for simplicity. In addition to the configuration of Embodiment 1, the power converter 100 according to Embodiment 7 has a configuration in which the iron core 300 has a further number of side legs.

[0085] In this embodiment, in addition to the first side leg 311 and the second side leg 313, a plurality of side legs, namely a third side leg 314 and a fourth side leg 315, are further provided. Each of the first side leg 311, the second side leg 313, the third side leg 314, and the fourth side leg 315 is spaced apart from the central leg 312 and arranged to surround the central leg 312. In the figure, the outer shape of the second core 302 is formed in a rectangular shape, and each of the first side leg 311, the second side leg 313, the third side leg 314, and the fourth side leg 315 is provided at the corners of the second core 302. The outer shape of the second core 302 and the arrangement of each side leg are not limited to this. The primary coil 3a and the secondary coils 3b and 3c are wound around the third side leg 314, and the smoothing coil 5a is wound around the fourth side leg 315.

[0086] The primary coil 3a, secondary coils 3b and 3c, and smoothing coil 5a are divided and wound around two side legs. For example, the primary coil 3a and secondary coils 3b and 3c are arranged in parallel on the first side leg 311 and the third side leg 314, and the smoothing coil 5a is arranged in parallel on the second side leg 313 and the fourth side leg 315. The coil connections are not limited to this; the primary coil 3a and secondary coils 3b and 3c may be arranged in series on the first side leg 311 and the third side leg 314, and the smoothing coil 5a may be arranged in series on the second side leg 313 and the fourth side leg 315. The method of dividing the primary coil 3a, secondary coils 3b and 3c, and smoothing coil 5a around the four side legs is arbitrary.

[0087] This configuration allows each coil to be separated and arranged, thus reducing the height of each coil and the iron core 300. Even when there are height restrictions in the placement of the power converter 100, the power converter 100 can be easily installed.

[0088] Furthermore, although this application describes various exemplary embodiments and examples, the various features, aspects, and functions described in one or more embodiments are not limited to the application of a particular embodiment, but can be applied individually or in various combinations to the embodiments. Accordingly, countless variations not illustrated are conceivable within the scope of the technology disclosed herein. These include, for example, modifying, adding or omitting at least one component, or even extracting at least one component and combining it with components of other embodiments.

[0089] The various aspects of this disclosure are summarized below as an appendix.

[0090] (Note 1) The iron core that forms the magnetic circuit, The primary coil wound around the aforementioned iron core, The primary coil is magnetically coupled to the secondary coil wound around the iron core, The system comprises a smoothing coil electrically connected to the secondary coil and wound around the iron core, The iron core comprises a first iron core, a second iron core facing the first iron core and spaced apart from it, a central leg connecting the opposing central portions of the first and second iron cores, and a plurality of side legs spaced apart from the central leg and connecting the opposing end portions of the first and second iron cores. The primary coil and the secondary coil are wound around the first side leg. The smoothing coil is wound around the second side leg, A power conversion device in which a common magnetic path for the primary coil, the secondary coil, and the smoothing coil is formed in the central leg. (Note 2) The iron core that forms the magnetic circuit, The primary coil wound around the aforementioned iron core, The primary coil is magnetically coupled to the secondary coil wound around the iron core, The system comprises a smoothing coil electrically connected to the secondary coil and wound around the iron core, The iron core comprises a first iron core, a second iron core facing the first iron core and spaced apart from it, a central leg connecting the opposing central portions of the first and second iron cores, and a plurality of side legs spaced apart from the central leg and connecting the opposing end portions of the first and second iron cores. The primary coil and the secondary coil are wound around the first side leg. The smoothing coil is wound around the central leg, A power conversion device in which a common magnetic path for the primary coil, the secondary coil, and the smoothing coil is formed in the second side leg. (Note 3) The power conversion device according to Appendix 1 or 2, wherein each of the primary coil, the secondary coil, and the smoothing coil is formed in the shape of a curved plate on a flat surface. (Note 4) It further comprises a power conversion circuit that has multiple semiconductor switching elements and converts between DC power and AC power, The primary coil is electrically connected to the output side of the power conversion circuit. The power conversion device according to any one of the appendices 1 to 3, wherein the power conversion circuit is a hard switching type circuit that adjusts the output power by changing the on-off duty cycle of the plurality of semiconductor switching elements. (Note 5) The power conversion device according to Appendix 1 or 3, wherein the central leg does not have a spaced gap portion in the central leg portion. (Note 6) The power conversion device according to Appendix 2 or 3, wherein the second side leg does not have a spaced gap portion in the second side leg portion. (Note 7) The power conversion device according to Appendix 1 or 3, wherein the cross-sectional area of ​​the central leg is smaller than the sum of the cross-sectional areas of the plurality of side legs. (Note 8) The power conversion device according to Appendix 2 or 3, wherein the cross-sectional area of ​​the second side leg is smaller than the sum of the cross-sectional areas of the plurality of side legs excluding the second side leg and the central leg. (Note 9) The central leg is positioned with a gap between it and the adjacent primary coil, secondary coil, and smoothing coil, The power conversion device according to Appendix 1 or 3, wherein the side surface of the central leg has a shape that conforms to the respective side shapes of the primary coil, the secondary coil, and the smoothing coil that are facing the side surface of the central leg. (Note 10) The second side leg is positioned at a distance from the adjacent smoothing coil, The power conversion device according to Appendix 2 or 3, wherein the side surface of the second side leg has a shape that conforms to the side shape of the smoothing coil facing the side surface of the second side leg. (Note 11) The power conversion device according to any one of the appendices 1 to 10, wherein the thickness of one or both portions of the first core and the second core, in which the magnetic flux of the smoothing coil is linked, is greater than the respective thicknesses of the first core and the second core, in which the magnetic fluxes of the primary coil and the secondary coil are linked. (Note 12) The power conversion device described in any one of the appendices 1 to 11, wherein the iron core is made of ferrite. (Note 13) The rectifier circuit further comprises multiple rectifier elements and is electrically connected to the secondary coil, The power conversion device according to any one of the appendices 1 to 12, wherein the anode terminal of each of the plurality of rectifier elements is grounded. (Note 14) The power conversion device described in Appendix 13, wherein the secondary coil and the smoothing coil are arranged side by side and electrically and mechanically coupled by an integrated portion to form an integrated coil member. (Note 15) The power conversion device according to any one of the appendices 1 to 14, wherein the number of turns of the secondary coil is less than the number of turns of the primary coil. (Note 16) Any portion of the central leg and any of the multiple side legs around which the primary coil, the secondary coil, and the smoothing coil are wound, and which does not form a common magnetic path for the primary coil, the secondary coil, and the smoothing coil, has a spaced gap. A power conversion device according to any one of the appendices 1 to 15, wherein a spacer member is inserted into the gap portion. (Note 17) The cooler further comprises a recessed section, The portion of the second core opposite to the first core is thermally connected to the bottom of the recess. The power conversion device according to any one of the appendices 1 to 16, wherein the primary coil or the secondary coil and the smoothing coil are thermally connected to the portion of the cooler surrounding the opening of the recess. (Note 18) The plurality of side legs, a third side leg and a fourth side leg, are provided. Each of the first, second, third, and fourth side legs is spaced apart from the central leg and arranged to surround it. The primary coil and the secondary coil are wound around the third side leg. The power conversion device according to Appendix 1 or 3, wherein the smoothing coil is wound around the fourth side leg. [Explanation of symbols]

[0091] 1 DC power supply, 2 Full bridge circuit, 2a, 2b, 2c, 2d Semiconductor switching elements, 3 Isolation transformer, 3a, 3a1, 3a2 Primary coil, 3b, 3c Secondary coil, 3d Leakage inductance, 4 Rectifier circuit, 4a, 4b Rectifier diode, 5 Smoothing reactor, 5a, 5a1, 5a2 Smoothing coil, 6 Smoothing capacitor, 7 Load, 8 Integrated coil component, 8a Integrated section, 20a, 20b, 20c, 20d Parasitic capacitance, 31, 32 Primary terminals, 33, 35 Secondary terminals, 34, 34a, 34b Center tap terminals, 36, 37 Inner terminals, 51, 52 Reactor terminals, 53a, 53b Connection terminals, 41, 42, 43, 44, 45, 46, 61, 62, 63, 64, 65, 66 Magnetic flux, 90 Magnetic component, 100 Power converter, 300 Iron core, 301 First iron core, 302 Second iron core, 312 Center leg, 311 First side leg, 313 Second side leg, 314 Third side leg, 315 Fourth side leg, 320 Spacer member, 321 Gap section, 401 Cooler, 401a Recess, 401b Cooling surface, 411, 412, 413 Cooling member

Claims

1. The iron core that forms the magnetic circuit, The primary coil wound around the aforementioned iron core, The primary coil is magnetically coupled to the secondary coil wound around the iron core, The system comprises a smoothing coil electrically connected to the secondary coil and wound around the iron core, The iron core comprises a first iron core, a second iron core facing the first iron core and spaced apart from it, a central leg connecting the opposing central portions of the first and second iron cores, and a plurality of side legs spaced apart from the central leg and connecting the opposing end portions of the first and second iron cores. The primary coil and the secondary coil are wound around the first side leg. The smoothing coil is wound around the second side leg, A common magnetic path is formed in the central leg for the primary coil, the secondary coil, and the smoothing coil. The aforementioned central leg does not have a spaced gap portion in the central leg portion. The first side leg is a power conversion device in which there is no spaced gap portion in the first side leg portion.

2. The power conversion device according to claim 1, wherein each of the primary coil, the secondary coil, and the smoothing coil is formed in the shape of a curved plate on a flat surface.

3. It further comprises a power conversion circuit that has multiple semiconductor switching elements and converts between DC power and AC power, The primary coil is electrically connected to the output side of the power conversion circuit. The power conversion device according to claim 1, wherein the power conversion circuit is a circuit that uses a hard switching method to adjust the output power by changing the on-off duty cycle of the plurality of semiconductor switching elements.

4. The power conversion device according to claim 1, wherein the cross-sectional area of ​​the central leg is smaller than the sum of the cross-sectional areas of the plurality of side legs.

5. The central leg is positioned with a gap between it and the adjacent primary coil, secondary coil, and smoothing coil, The power conversion device according to claim 1, wherein the side surface of the central leg has a shape that conforms to the respective side shapes of the primary coil, the secondary coil, and the smoothing coil that are facing the side surface of the central leg.

6. The power conversion device according to claim 1, wherein the thickness of one or both portions of the first core and the second core, in which the magnetic flux of the smoothing coil is linked, is greater than the respective thicknesses of the first core and the second core, in which the magnetic flux of the primary coil and the secondary coil are linked.

7. The power conversion device according to claim 1, wherein the iron core is made of ferrite.

8. The rectifier circuit further comprises multiple rectifier elements and is electrically connected to the secondary coil, The power conversion device according to claim 1, wherein the anode terminal of each of the plurality of rectifier elements is grounded.

9. The power conversion device according to claim 8, wherein the secondary coil and the smoothing coil are arranged side by side and are electrically and mechanically coupled by an integrated portion to form an integrated coil member.

10. The power conversion device according to claim 1, wherein the number of turns of the secondary coil is less than the number of turns of the primary coil.

11. Any portion of the central leg and any of the multiple side legs around which the primary coil, the secondary coil, and the smoothing coil are wound, and which does not form a common magnetic path for the primary coil, the secondary coil, and the smoothing coil, has a spaced gap. The power conversion device according to claim 1, wherein a spacer member is inserted into the gap portion.

12. The cooler further comprises a recessed section, The portion of the second core opposite to the first core is thermally connected to the bottom of the recess. The power conversion device according to claim 1, wherein the primary coil or the secondary coil and the smoothing coil are thermally connected to the portion of the cooler surrounding the opening of the recess.

13. An iron core forming a magnetic circuit, The primary coil wound around the aforementioned iron core, The primary coil is magnetically coupled to the secondary coil wound around the iron core, The system comprises a smoothing coil electrically connected to the secondary coil and wound around the iron core, The iron core comprises a first iron core, a second iron core facing the first iron core and spaced apart from it, a central leg connecting the opposing central portions of the first and second iron cores, and a plurality of side legs spaced apart from the central leg and connecting the opposing end portions of the first and second iron cores. The primary coil and the secondary coil are wound around the first side leg. The smoothing coil is wound around the second side leg, A common magnetic path is formed in the central leg for the primary coil, the secondary coil, and the smoothing coil. The plurality of side legs, a third side leg and a fourth side leg, are provided. Each of the first, second, third, and fourth side legs is positioned at a distance from the central leg, surrounding it. The primary coil and the secondary coil are wound around the third side leg. The smoothing coil is a power conversion device wound around the fourth side leg.

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