Patent Description:
Japanese Patent Laid-Open <CIT> (PTL <NUM>) describes a compact configuration suitable for a wind turbine generation system as an example power converter that performs DC/DC conversion in which an input and an output are insulated from each other through a transformer.

In the power converter of PTL <NUM>, a multiple winding transformer including a secondary winding divided into several portions is connected for each of the outputs of DC/AC transformers connected in parallel on the output side of the wind turbine generation system, and the outputs of AC/DC transformers, each arranged for a corresponding one of the divided portions of the secondary winding of the multiple winding transformer, are connected to each other in series, thereby achieving a configuration suitable for the wind turbine generation system.

PTL <NUM>: Japanese Patent Laid-Open <CIT>.

According to PTL <NUM>, a required step-up ratio can be obtained easily by connecting the outputs of the AC/DC converters, each connected to a corresponding one of the secondary windings of the multiple winding transformer, in series in place of increasing the turn ratios of the transformers. In particular, PTL <NUM> describes that increasing the number of secondary windings arranged in the multiple winding transformer can reduce the number of unit modules arranged in parallel, that is, the number of DC/AC transformers connected in parallel on the primary side (wind turbine generation facility side).

High-voltage, high-capacity DC/DC conversion use, however, needs the parallel arrangement of a high number of DC/AC transformers on the primary side of the transformer in order to obtain current capacity. Thus, application of the configuration of PTL <NUM> to high-capacity use results in the arrangement of a high number of multiple transformers which intend to have a relatively larger size. This may make it difficult for the power converter to have a smaller size.

The present invention has been made to solve the above problem, and therefore has an object to provide a power converter that performs DC/DC conversion through a transformer with a configuration suitable for miniaturization in high-voltage and/or high-capacity use. <CIT> relates to multiphase power converters having shared magnetic core Sections, wherein the multiphase power converter includes two switched mode subconverters and a control circuit. The subconverters have a shared core section. <CIT> relates to a switching power supply unit acting as a DC-DC converter. The switching power supply unit includes a transformer having a primary winding and a secondary winding. The secondary winding has a first secondary-sub-winding group and a second secondary-sub-winding group, which are connected in parallel to each other.

The present invention is defined by independent claim <NUM> as appended. Further embodiments are given in dependent claims.

According to the present invention, a configuration suitable for high voltage and/or high current can be obtained through series or parallel connection of the DC/AC converters between the first DC terminals and series or parallel connection of the AC/DC converters between the second DC terminals. Also, the power converter can be miniaturized with the use of the multiple transformer in which a magnetic path is shared among as many primary windings as DC/AC converters and a magnetic path is shared among as many secondary windings as AC/DC converters.

Embodiments of the present invention will now be described in detail with reference to the drawings, in which the same or corresponding portions are denoted by the same reference characters and description thereof will not be repeated.

<FIG> is a circuit diagram showing an example configuration of a power converter 10a according to Embodiment <NUM>.

Referring to <FIG>, power converter 10a includes a pair of first DC terminals <NUM>, which are connected with a positive power supply line PL0 and a negative power supply line NL0, a pair of second DC terminals <NUM>, which are connected with a positive power supply line PL3 and a negative power supply line NL3, n (n is a natural number where n ≥ <NUM>) DC/DC conversion units <NUM>, and a multiple transformer 300a. Power converter 10a performs power conversion (DC/DC conversion) for DC power conversion between first DC terminals <NUM> and second DC terminals <NUM>.

Each DC/DC conversion unit <NUM> has DC terminals <NUM> and DC terminals <NUM>. n DC terminals <NUM> corresponding one-to-one to n DC/DC conversion units <NUM> are connected between DC terminals <NUM> through positive power supply line PL0 and negative power supply line NL0.

In contrast, n DC terminals <NUM> corresponding one-to-one to n DC/DC conversion units <NUM> are connected in series between positive power supply line PL3 and negative power supply line NL3. That is to say, n DC terminals <NUM> are connected in series between DC terminals <NUM>.

The configuration of each DC/DC conversion unit <NUM> will now be described. DC/DC conversion unit <NUM> includes a DC/AC converter <NUM>, AC terminals <NUM> and <NUM>, and an AC/DC converter <NUM>, in addition to DC terminals <NUM> and <NUM>. AC terminals <NUM> are connected with one primary winding <NUM> of multiple transformer 300a. AC terminals <NUM> are connected with one secondary winding <NUM> of multiple transformer 300a.

<FIG> is a circuit diagram showing an example configuration of DC/DC conversion unit <NUM> shown in <FIG>.

Referring to <FIG>, DC/DC conversion unit <NUM> has DC/AC converter <NUM> connected between DC terminals <NUM> and AC terminals <NUM>, and AC/DC converter <NUM> connected between AC terminals <NUM> and DC terminals <NUM>.

DC/AC converter <NUM> has a DC capacitor Cdc1 and semiconductor switching elements Q11 to Q14. DC capacitor Cdc1 is connected between DC nodes Ndc11 and Ndc12 and is connected in parallel with DC terminals <NUM>. Semiconductor switching elements Q11 and Q12 are connected in series between DC nodes Ndc11 and Ndc12 through an AC node Nac11. Similarly, semiconductor switching elements Q13 and Q14 are connected in series between DC nodes Ndc11 and Ndc12 through an AC node Nac12.

Similarly, AC/DC converter <NUM> has a DC capacitor Cdc2 and semiconductor switching elements Q21 to Q24. DC capacitor Cdc2 is connected between DC nodes Ndc21 and Ndc22 and is connected in parallel with DC terminals <NUM>. Semiconductor switching elements Q21 and Q22 are connected in series between DC nodes Ndc21 and Ndc22 through an AC node Nac21. Similarly, semiconductor switching elements Q22 and Q24 are connected in series between DC nodes Ndc21 and Ndc22 through an AC node Nac22.

In DC/AC converter <NUM>, thus, a full-bridge circuit is composed of two switching legs with semiconductor switching elements Q11 and Q13 on the positive side and semiconductor switching elements Q12 and Q14 on the negative side. Similarly, also in AC/DC converter <NUM>, a full-bridge circuit is composed of two switching legs with semiconductor switching elements Q21 and Q23 on the positive side and semiconductor switching elements Q22 and Q24 on the negative side.

Semiconductor switching elements Q11 to Q14 and Q21 to Q24 may be, for example, any semiconductor switching element having a self-turn off function, for example, insulated gate bipolar transistors (IGBTs) to which diodes are connected in antiparallel. Each semiconductor switching elements Q11 to Q24 may be configured with a plurality of semiconductor elements connected in parallel, in accordance with current capacity for use.

A drive circuit <NUM> generates, in accordance with a control signal from a controller (not shown) that controls power converter 10a, gate signals <NUM> for controlling ON and OFF of semiconductor switching elements Q11 to Q14 and gate signals <NUM> for controlling ON and OFF of semiconductor switching elements Q21 to Q24. The voltage across a control electrode (gate) of each semiconductor switching element is controlled in accordance with a corresponding one of gate signals <NUM> and <NUM>, so that semiconductor switching elements Q11 to Q14 and Q21 to Q24 are switching-controlled. Drive circuit <NUM> can be formed of a known typical gate drive circuit.

<FIG> shows example operation waveforms of DC/DC conversion unit <NUM> shown in <FIG>.

Referring to <FIG>, at each leg of DC/AC converter <NUM>, semiconductor switching elements Q11 and Q14 on the positive side are turned on and off in a complementary manner to semiconductor switching elements Q12 and Q13 on the negative side. A dead time TD for preventing a short-circuit between DC nodes Ndc11 and Ndc12 in the same leg is provided between an ON period of semiconductor switching elements Q11 and Q14 on the positive side and an ON period of semiconductor switching elements Q12 and Q13 on the negative side. As a result of switching control of semiconductor switching elements Q11 to Q14, DC/AC power conversion is performed between a DC voltage between DC nodes Ndc11 and Ndc12 and an AC voltage V1 between AC nodes Nac11 and Nac12, that is, between AC terminals <NUM>.

Similarly, at each leg of AC/DC converter <NUM>, semiconductor switching elements Q21 and Q24 on the positive side are turned on and off in a complementary manner to semiconductor switching elements Q22 and Q23 on the negative side. A dead time TD as described above is provided between an ON period of semiconductor switching elements Q21 and Q24 on the positive side and an ON period of semiconductor switching elements Q22 and Q23 on the negative side. As a result of switching control of semiconductor switching elements Q21 to Q24, AC/DC power conversion is performed between an AC voltage V2 between AC terminals <NUM>, that is, between AC nodes Nac21 and Nac22 and a DC voltage between DC nodes Ndc21 and Ndc22.

Primary winding <NUM> and secondary winding <NUM> respectively connected to AC terminals <NUM> and <NUM> of the same DC/DC conversion unit <NUM> are wound around a core portion of multiple transformer 300a to be magnetically coupled to each other. Consequently, a voltage ratio between an amplitude (Vdc1) of AC voltage V1 between AC terminals <NUM> and an amplitude (Vdc2) of AC voltage V2 between AC terminals <NUM> has a value corresponding to the turn ratio between primary winding <NUM> and secondary winding <NUM>.

In DC/DC conversion unit <NUM>, a phase difference φ between AC voltage V1 output from DC/AC converter <NUM> and AC voltage V2 output from AC/DC converter <NUM> can be controlled to control transmission power. Phase difference φ can be controlled by a control signal input to drive circuit <NUM>. Specifically, drive circuit <NUM> generates, in accordance with the control signal with phase difference φ set for control of transmission power, gate signals <NUM> and <NUM> for the semiconductor switching elements so as to adjust the turn-on timing of the semiconductor switching elements on the positive side (i.e., the turn-on timing between Q11, Q14 and Q21, Q24) and the turn-off timing of the semiconductor switching elements on the negative side (i.e., the turn-off timing between Q12, Q13 and Q22, Q23) between DC/AC converter <NUM> and AC/DC converter <NUM>.

Setting the switching frequency of each of semiconductor switching elements Q11 to Q14 and Q21 to Q24 of smaller size to a higher frequency (e.g., not less than <NUM> which is higher than the frequency of a commercial AC power supply) may lead to an increase in the loss of multiple transformer 300a. In such a case, however, using an amorphous material as an iron core material can restrain an increase in the loss caused by a higher frequency.

Parallel connection of a snubber capacitor CS with each of semiconductor switching elements Q11 to Q14 and Q21 to Q24 allows the voltage waveform of each semiconductor switching element to have a sinusoidal-wave shape with the use of the resonance phenomenon due to the actions of snubber capacitors CS and inductances LS of AC nodes Nac11 to Nac22.

Consequently, soft switching is enabled owing to the application of zero-voltage switching in ON and OFF of each of semiconductor switching elements Q11 to Q14 and Q21 to Q24. Since the application of soft switching can reduce switching loss and electromagnetic noise, increasing the operating frequency can lead to a smaller size of multiple transformer 300a, which will be described below. Inductances LS can be leakage inductances of primary winding <NUM> and secondary winding <NUM>.

DC capacitors Cdc1 and Cdc2 can be, for example, electrolytic capacitors or film capacitors. Although a high-frequency current flows through DC capacitors Cdc1 and Cdc2, the degradation due to the high-frequency current can be restrained in the use of film capacitors, thus leading to a longer life.

The configurations of DC/AC converter <NUM> and AC/DC converter <NUM> which are shown in <FIG> are merely examples, and any circuit configuration is applicable as long as DC/AC conversion and AC/DC conversion can be performed as described above by ON and OFF of the semiconductor switching elements. Providing a similar configuration to each of a plurality of (n) DC/DC conversion units <NUM> can simplify tests and improve manufacturability.

Referring to <FIG> again, n DC/AC converters <NUM> and n AC/DC converters <NUM> are arranged corresponding to n DC/DC conversion units <NUM> in the whole power converter 10a. Multiple transformer 300a has n primary windings <NUM> and n secondary windings <NUM>.

In the example configuration of <FIG>, n DC/DC conversion units <NUM> are connected in parallel on the DC terminal <NUM> side and are connected in series on the DC terminal <NUM> side, as described above. Parallel connection of DC/DC conversion units <NUM> can deal with high current. In contrast, series connection of DC/DC conversion units <NUM> can deal with high voltage. In the example configuration of <FIG>, thus, power converter 10a is suitable for high-voltage, high-current use in which the DC voltage between DC terminals <NUM> is boosted and output to between DC terminals <NUM>.

In the example configuration of <FIG>, n DC/AC converters <NUM> can be connected in series on the DC terminal <NUM> side, whereas n AC/DC converters <NUM> can be connected in parallel on the DC terminal <NUM> side. In another configuration, n DC/AC converters <NUM> and n AC/DC converters <NUM> can be connected in series on both the DC terminal <NUM> side and the DC terminal <NUM> side, or n DC/AC converters <NUM> and n AC/DC converters <NUM> can be connected in parallel on both the DC terminal <NUM> side and the DC terminal <NUM> side.

<FIG> shows an example configuration of multiple transformer 300a in Embodiment <NUM>.

Referring to <FIG>, multiple transformer 300a has two annular rectangular iron cores 303x and 303y constituting the "core portion". Each of annular rectangular iron cores 303x and 303y can be formed of a plurality of ribbon-shaped magnetic materials stacked in the vertical direction in the sheet of paper of <FIG>. When annular rectangular iron cores 303x and 303y are collectively referred to, they are merely referred to as an annular rectangular iron core <NUM> as well.

Annular rectangular iron core <NUM> has iron core legs <NUM> and <NUM> extending in the up-down direction in the sheet of paper and yokes <NUM> and <NUM> connecting the ends of iron core legs <NUM> and <NUM> to each other. Primary windings <NUM> and secondary windings <NUM> of multiple transformer 300a are wound around one of two iron core legs of annular rectangular iron core 303x and its adjacent one of two iron core legs of annular rectangular iron core 303y. Hereinafter, one of iron core legs of each of annular rectangular iron cores 303x and 303y, around which primary windings <NUM> and secondary windings <NUM> are wound, will be denoted by a reference <NUM>, and the other iron core leg around which no windings are wound will be denoted by a reference <NUM>.

n primary windings <NUM> and n secondary windings <NUM> are wound around common annular rectangular iron cores 303x and 303y. It is thus understood that a magnetic path is shared among n primary windings <NUM> and a magnetic path is shared among n secondary windings <NUM>.

In each DC/DC conversion unit <NUM> (<FIG>), primary winding <NUM> is connected with AC terminals <NUM>, and secondary winding <NUM> is connected with AC terminals <NUM>. Primary winding <NUM> and secondary winding <NUM> are magnetically coupled to each other by annular rectangular iron cores 303x and 303y. One primary winding <NUM> and one secondary winding <NUM> connected with the same DC/DC conversion unit <NUM> are wound around annular rectangular iron cores 303x and 303y so as to be closer to each other than to primary winding <NUM> and secondary winding <NUM> connected with any other DC/DC conversion unit <NUM>.

Each of between primary winding <NUM> and annular rectangular iron core <NUM>, between secondary winding <NUM> and annular rectangular iron core <NUM>, and between primary winding <NUM> and secondary winding <NUM>, an insulating distance corresponding to a potential difference therebetween is maintained. It is known that a required insulating distance increases non-linearly, not proportionally, to an increase in potential difference.

As shown in <FIG>, on the secondary side on which DC/DC conversion units <NUM> are connected in series, a potential applied to secondary winding <NUM> through AC terminals <NUM> also increases due to a higher voltage generated between DC terminals <NUM>. This increases the insulating distance required between secondary winding <NUM> and annular rectangular iron core <NUM>, which may increase the size of multiple transformer 300a due to increased dimensions (in particular, the dimension in the up-down direction in the sheet of paper of <FIG>) of annular rectangular iron core <NUM>.

In the example configuration of <FIG>, thus, primary winding <NUM> is divided into a plurality of portions and arranged in the winding configuration corresponding to each DC/DC conversion unit <NUM>. Each winding after division is connected in parallel with AC terminals <NUM>. Further, secondary winding <NUM> is arranged to be sandwiched between primary windings <NUM> after division.

Consequently, at each end of annular rectangular iron core <NUM>, secondary winding <NUM> is arranged while sandwiching primary winding <NUM> between a corresponding one of yokes <NUM> and <NUM> and secondary winding <NUM>. When secondary winding <NUM> has high voltage, an insulating distance D1, which is necessary between secondary winding <NUM> and the iron core (ground potential), is much greater than an insulating distance D2, which is necessary between secondary winding <NUM> and primary winding <NUM>, and an insulating distance D3, which is necessary between primary winding <NUM> and the iron core, namely, ground potential, (D1 >> D2, D3 and D1 > (D2 + D3)).

Thus, the arrangement as shown in <FIG> can reduce the dimension of annular rectangular iron core <NUM> (iron core legs <NUM> and <NUM>) in the up-down direction in the sheet of paper. Although primary windings <NUM> after division are adjacent to each other between different DC/DC conversion units <NUM> in the example configuration of <FIG>, primary windings <NUM> have the same potential. Consequently, the division of primary winding <NUM> can avoid a significant increase in the dimensions of annular rectangular iron core <NUM> for leaving an insulating distance.

Primary winding <NUM> is divided and arranged to sandwich secondary winding <NUM> in the example configuration of <FIG> because, of primary winding <NUM> and secondary winding <NUM>, secondary winding <NUM> has a relatively high potential with respect to the iron core (ground potential). In the case where primary winding <NUM> has a potential higher than that of secondary winding <NUM> in power converter 10a, accordingly, secondary winding <NUM> may be divided and arranged to sandwich primary winding <NUM>, as opposed to the example of <FIG>.

<FIG> is a conceptual diagram illustrating an example magnetic circuit model of multiple transformer 300a in Embodiment <NUM>. For simplification of description, <FIG> does not reflect leakage flux and shows only a magnetic circuit formed in annular rectangular iron core <NUM> on one side when primary winding <NUM> is excited.

<FIG> also shows the magnetic circuit model when three (n = <NUM>) primary windings <NUM> are provided, and magnetic resistances R1 to R10 are generated in annular rectangular iron core <NUM> of multiple transformer 300a.

Referring to <FIG>, as current flows through three primary windings <NUM>, magnetomotive forces F1, F2, and F3, which respectively produce magnetic fluxes φ1, φ2, and φ3, are generated. Magnetomotive force F1 produces magnetic flux φ1 through a magnetic path M11. Magnetic paths M5, M12, and M1 serve as a path of magnetic flux φ1. Similarly, magnetomotive force F2 produces magnetic flux φ2 through magnetic path M12. Magnetic paths M6, M23, and M2 serve as a path of magnetic flux φ2. Also, magnetomotive force F3 produces magnetic flux φ3 through magnetic path M23. Magnetic paths M7, M33, and M3 serve as a path of magnetic flux φ3.

Herein, magnetic flux φ in the iron core can be calculated by Equation (<NUM>) below: <MAT> where V(θ) represents an AC voltage applied to primary winding <NUM>, θ and f respectively represent the phase and frequency of the AC voltage, and N represents the number of turns of primary winding <NUM>.

Based on Equation (<NUM>), a maximum value φmax of magnetic flux φ can be determined according to Equation (<NUM>) below: <MAT> where Vrms represents an effective value of an AC voltage applied to primary winding <NUM>, and K represents a constant of proportionality. K = <NUM>/<NUM> when AC voltage V(θ) has a sine wave, and K = <NUM>/<NUM> when AC voltage V(θ) has a rectangular wave.

When AC voltages applied to primary windings <NUM> have an equal maximum value, an equal frequency, and an equal phase, magnetic flux φ12 of magnetic path M12 = φ1 - φ2 = <NUM>, and magnetic flux φ23 of magnetic path M23 = φ2 - φ3 = <NUM>. Thus, the magnetic flux passes through other than magnetic path M12 and magnetic path M23, eliminating the need for iron cores for forming magnetic path M12 and magnetic path M23. This eliminates the need for the arrangement of iron cores (hereinafter also referred to as bypass iron cores) for forming magnetic paths corresponding to magnetic paths M12 and M23 indicated by the dotted lines in <FIG> between the portions, around which primary winding <NUM> (and secondary winding <NUM>) are wound, corresponding to different DC/DC conversion units <NUM>.

Such elimination of the need for arranging the bypass iron cores can miniaturize a multiple transformer owing to miniaturization of annular rectangular iron core <NUM>. The iron core portion (the portion corresponding to magnetic paths M1 to M3, M11, M5 to M7, and M33 in <FIG>) through which magnetic fluxes φ1 to φ3 pass in annular rectangular iron core <NUM> is also referred to as a "main iron core".

Contrastingly, when the applied AC voltages do not have an equal maximum value, an equal frequency, and an equal phase among primary windings <NUM>, magnetic fluxes φ12 and φ23 are not equal to zero, so magnetic fluxes φ1 to φ3 interfere with each other. The occurrence of such a phenomenon causes the interference of transmission power P of one DC/DC conversion units <NUM> and transmission power P of another DC/DC conversion unit <NUM>, which would be originally controlled individually. For example, a "cross-current" is generated, in which the power of any DC/DC conversion unit <NUM> flows into another DC/DC conversion unit <NUM>. Upon generation of a cross-current, DC/DC conversion unit <NUM> into which power has flowed from the other DC/DC conversion unit <NUM> transmits power higher than the original power to be transmitted, and accordingly has an increased power loss.

In other words, when the AC voltage applied to primary windings <NUM> can have a maximum value, an equal frequency, and an equal phase, multiple transformer 300a can be achieved with a simple configuration including a main iron core and windings (primary winding <NUM> and secondary winding <NUM>). As a result, multiple transformer 300a can be miniaturized, and a power loss in power conversion in each DC/DC conversion unit <NUM> can be restrained.

Herein, DC/DC conversion units <NUM> are configured equally and are usually used at the same frequency. Also, in order to operate DC/DC conversion units <NUM> equally, the maximum value of the AC voltage applied to primary winding <NUM> is made equal among DC/DC conversion units <NUM>. Similarly, the maximum value of the AC voltage applied to secondary winding <NUM> is made equal among DC/DC conversion units <NUM>.

Meanwhile, as shown in <FIG>, each DC/DC conversion unit <NUM> operates as drive circuit <NUM> generates gate signals <NUM> and <NUM> in response to control signals from the control circuit (not shown) of power converter 10a. Thus, as gate signals <NUM> of DC/AC converter <NUM> are shared and gate signals <NUM> of AC/DC converter <NUM> are shared among DC/DC conversion units <NUM>, DC/DC conversion units <NUM> can operate in the same phase. Specifically, semiconductor switching elements Q11 to Q14 can be turned on and off in the same phase such that the maximum value, frequency, and phase of AC voltage V1 between AC nodes Nac11 and Nac12 are made equal among n DC/AC converters <NUM>. Similarly, semiconductor switching elements Q21 to Q24 can be turned on and off in the same phase such that the maximum value, frequency, and phase of AC voltage V2 between AC nodes Nac21 and Nac22 are made equal among n AC/DC converters <NUM>.

<FIG> illustrates control in which gate signals <NUM> and <NUM> are shared. Alternatively, as semiconductor switching elements Q11 to Q14 are turned on and off in the same phase, different gate signals <NUM> can be used among DC/AC converters <NUM> as long as the maximum value, frequency, and phase of AC voltage V1 are equal among DC/AC converters <NUM>. For example, a delay time in a transmission path of gate signal <NUM> can be adjusted finely among DC/AC converters <NUM> to increase the degree of equality of AC voltage V1. Similarly, as semiconductor switching elements Q21 to Q24 are turned on and off in the same phase, different gate signals <NUM> can be used among AC/DC converters <NUM> as long as the maximum value, frequency, and phase of AC voltage V2 are equal among AC/DC converters <NUM>.

As described above, according to the power converter according to Embodiment <NUM>, the power converter can be miniaturized by using multiple transformer 300a, in which a magnetic path is shared among as many primary windings as DC/AC converters and a magnetic path is shared among as many secondary windings as AC/DC converters, in the configuration in which a plurality of DC/AC converters and a plurality of AC/DC converters are connected in series or in parallel on the primary side and the secondary side of the transformer, respectively, for high-voltage and/or high-current use.

As shown in <FIG>, further, the multiple transformer can be miniaturized further owing to miniaturization of iron cores by dividing one winding having a relatively lower voltage of the primary winding and the secondary winding and arranging the divided winding to sandwich the other winding having a higher voltage.

As the semiconductor switching elements of a plurality of DC/AC converters are controlled to be turned on and off in the same phase and the semiconductor switching elements of a plurality of AC/DC converters are controlled to be turned on and off in the same phase, an increase in power loss can be restrained in the configuration including a miniaturized multiple transformer and including no bypass iron cores.

Although semiconductor switching elements Q11 to Q14 and Q21 to Q24 used in Embodiment <NUM> are usually made of silicon (Si), semiconductor switching elements made of silicon carbide (SiC) or gallium nitride (GaN), which are wide bandgap semiconductors having a bandgap larger than that of silicon (Si), diamond, or the like can also be used. Consequently, higher voltages can be input to and output from each DC/AC converter <NUM> and each AC/DC converter <NUM>, leading to a configuration more suitable for high-voltage use. Also, the switching frequency of a semiconductor switching element can be made higher, further miniaturizing multiple transformer 300a.

Embodiment <NUM> has described the configuration and control in which DC/DC conversion units <NUM> operate equally to restrain an increase in power loss due to the generation of a cross-current. In the presence of individual differences among components of DC/DC conversion units <NUM>, however, the phase and the maximum value of the AC voltage are not necessarily equal among DC/DC conversion units <NUM>. For components to be shared among DC/DC conversion units <NUM>, the maximum value of voltage needs to be equal among DC/DC conversion units <NUM>. Embodiment <NUM> will thus describe the configuration and control for accommodating individual differences among components.

<FIG> is a voltage control waveform chart in a power converter according to Embodiment <NUM>.

<FIG> shows AC voltages V11, V12. V1n between AC terminals <NUM> of n DC/AC converters <NUM>. <FIG> shows AC voltage V21, V22. V2n between AC terminals <NUM> of n AC/DC converters <NUM>.

In Embodiment <NUM>, DC/AC converters <NUM> operate in common in accordance with a common gate signals <NUM>, and accordingly, AC voltage V1 has the same phase among n DC/AC converters <NUM>. Also, AC/DC converters <NUM> operate in common in accordance with a common gate signals <NUM>, and accordingly, AC voltage V2 has the same phase among n AC/DC converters <NUM>.

Contrastingly, in Embodiment <NUM>, the power transmission by each of n DC/DC conversion units <NUM> is adjusted individually such that AC voltages V11 to V1n have the same amplitude (maximum voltage Vdc1) and AC voltages V21 to V2n have the same amplitude (maximum voltage Vdc2). Phase difference φ described with reference to <FIG> is thus set individually for each DC/DC conversion unit <NUM>.

As a result, drive circuit <NUM> individually generates gate signals <NUM> and <NUM> for each DC/DC conversion unit <NUM> in accordance with phase difference φ set for each DC/DC conversion unit <NUM>. Consequently, AC voltages V11 to V1n do not have an equal phase as shown in <FIG>, and AC voltages V21 to V2n do not have an equal phase as shown in <FIG>.

In n DC/AC converters <NUM>, semiconductor switching elements Q11 to Q14 are individually controlled to be turned on and off by individual gate signals <NUM> such that AC voltages V11 to V1n between AC nodes Nac11 and Nac12 have an equal maximum value and an equal frequency. Similarly, semiconductor switching elements Q21 to Q24 are individually controlled to be turned on and off such that AC voltage V2 between AC nodes Nac21 and Nac22 has an equal maximum value and an equal frequency also in n AC/DC converters <NUM>.

As a result, the phase of the AC voltage is not equal among primary windings <NUM> and among secondary windings <NUM>, and accordingly, in the magnetic circuit model shown in <FIG>, a magnetic flux φ12 (φ1 - φ2) of magnetic path M12 and a magnetic flux φ23 (φ2 - φ3) of magnetic path M23 are not zero, and magnetic flux φ1 due to magnetomotive force F1 thus interferes with magnetic fluxes φ2 and φ3. Similarly, magnetic flux φ2 due to magnetomotive force F2 interferes with magnetic fluxes φ1 and φ3, and magnetic flux φ3 due to magnetomotive force F3 interferes with magnetic fluxes φ1 and φ2.

Consequently, the transmission power in one DC/DC conversion unit <NUM> interferes with the transmission power of another DC/DC conversion unit <NUM>, which would be originally controlled individually, leading to the generation of a cross-current described above. The generation of a cross-current may result in an increase in power loss, a decrease in controllability, and a decrease in operation reliability of DC/DC conversion unit <NUM>.

Thus, a multiple transformer 300b shown in <FIG> is used in the power converter according to Embodiment <NUM>, in place of multiple transformer 300a shown in <FIG>. In other words, the power converter according to Embodiment <NUM> can be configured by replacing multiple transformer 300a with multiple transformer 300b shown in <FIG>, connecting each AC terminal <NUM> to its corresponding primary winding <NUM> of multiple transformer 300b, and connecting each AC terminal <NUM> to its corresponding secondary winding <NUM> of multiple transformer 300b in power converter 10a shown in <FIG>.

Referring to <FIG>, multiple transformer 300b according to Embodiment <NUM> differs from multiple transformer 300a (<FIG>) according to Embodiment <NUM> in that the "core portion" further includes bypass iron cores <NUM> arranged between iron core legs <NUM> and <NUM> in each of annular rectangular iron cores 303x and 303y. Since the other components of multiple transformer 300b are similar to those of multiple transformer 300a, detailed description thereof will not be repeated.

As shown in <FIG>, primary winding <NUM> and secondary winding <NUM> corresponding to the same DC/DC conversion unit <NUM> are wound adjacent to each other. Bypass iron core <NUM> is arranged such that an area of iron core leg <NUM>, around which primary winding <NUM> and secondary winding <NUM> are both not wound, is connected with iron core leg <NUM>. This area is located between different DC/DC conversion units <NUM>. For example, in the configuration in which n DC/DC conversion units <NUM> are arranged, (n - <NUM>) bypass iron cores <NUM> are arranged. In other words, primary winding <NUM> and secondary winding <NUM> connected to each DC/DC conversion unit <NUM> are wound for each area magnetically separated by bypass iron core <NUM> in iron core legs <NUM> and <NUM>.

<FIG> shows a magnetic circuit model of multiple transformer 300b.

Referring to <FIG>, in multiple transformer 300b shown in <FIG>, magnetic paths M12 and M23 indicated by the dotted lines in <FIG> are actually formed by the arrangement of bypass iron cores <NUM>. Each bypass iron core <NUM> thus forms a path for magnetically separating primary windings <NUM> corresponding to different DC/DC conversion units <NUM> from each other and secondary windings <NUM> corresponding to different DC/DC conversion units <NUM> from each other. Since bypass iron cores <NUM> is provided, magnetic resistances R8 and R9 are small compared with the case of <FIG>.

Thus, when the AC voltage amplitude is not uniform among DC/DC conversion units <NUM>, or even when the phase of the AC voltage is not equal due to control for providing a uniform voltage amplitude, magnetic fluxes φ1 to φ3 shown in <FIG> can pass through bypass iron core <NUM> and return to primary winding <NUM> (magnetic paths M1 to M3) producing magnetomotive forces F1 to F3, and accordingly, do not interfere with another primary winding <NUM>. In each DC/DC conversion unit <NUM>, accordingly, primary winding <NUM> and secondary winding <NUM> are magnetically coupled without the generation of a cross-current.

Therefore, in the power converter according to Embodiment <NUM>, a multiple transformer with bypass iron cores can be used to prevent the generation of a cross-current between DC/DC conversion units <NUM>, thereby restraining a power loss and improving controllability and operation reliability.

The dimensions of bypass iron core <NUM> can be minimized through analysis below.

<FIG> is a conceptual waveform chart for illustrating a flux behavior in two primary windings adjacent to each other with a bypass iron core therebetween.

Referring to <FIG>, it is supposed that a phase difference Δθ and a voltage difference ΔV (ΔV = Vdc1 - Vdc2) are generated between AC voltages V11 and V12 of adjacent primary windings <NUM>.

Magnetomotive forces F1 and F2 are generated in the magnetic circuit model shown in <FIG> in accordance with AC voltages V11 and V12, so that magnetic fluxes φ1 and φ2 in <FIG> are generated. Magnetic flux φ1 is indicated by a triangular wave that is in the same phase with AC voltage V11 and has an amplitude φ1max, and magnetic flux φ2 is indicated by a triangular wave that is in the same phase with AC voltage V12 and has an amplitude φ2max. Thus, magnetic flux φ2 has a maximum amplitude at a timing (θ = θ0) at which AC voltage V12 changes from -Vdc22 to Vdc22. At this time, magnetic flux φ12 in magnetic path M12 corresponding to bypass iron core <NUM> is represented by Equation (<NUM>) below. <MAT> where D represents on-duty of semiconductor switching elements Q11 to Q14 and Q21 to Q24 in DC/DC conversion unit <NUM>, and K represents a constant of proportionality common to Equation (<NUM>) and Equation (<NUM>).

In Equation (<NUM>), φ1max corresponds to φmax shown in Equation (<NUM>). In Equation (<NUM>), Δθ/(2π·D) is usually smaller than one, and accordingly, φ12 shown in Equation (<NUM>) is smaller than φmax, that is, a maximum magnetic flux in the main iron core.

Herein, a sectional area Sp of bypass iron core <NUM> can be determined by Equation (<NUM>) below:
<MAT> where h represents the height of the stack of ribbon-shaped magnetic materials in the main iron core, Wp represents the width of bypass iron core <NUM>, and LF represents the space factor of the iron core material.

Maximum magnetic flux density Bpmax generated in bypass iron core <NUM> is represented by Bpmax = φ12/Sp. Maximum magnetic flux density Bmax in the main iron core is represented by Bmax = φmax/Sm using sectional area Sm of the main iron core. Since φ12 < φmax as described above, sectional area Sp required for making maximum magnetic flux density Bpmax generated in bypass iron core <NUM> equal to maximum magnetic flux density Bmax in the main iron core is smaller than sectional area Sm of the main iron core.

Herein, to satisfy Bpmax ≤ Bmax with height h of the stack of bypass iron core <NUM> aligned with that of the main iron core, width Wp of bypass iron core <NUM> can be determined by Equation (<NUM>) below:
<MAT> where φ12 is common to Equation (<NUM>) and Equation (<NUM>).

Substitution of Bmax = φmax/Sm into Equation (<NUM>) results in Equation (<NUM>) below.

Since Sm/(h × LF) corresponds to the width of the main iron core corresponding to maximum magnetic flux density Bmax in the main iron core, width Wp of bypass iron core <NUM> can be made smaller than the width of the main iron core, according to (φ12/φmax) < <NUM>. This can lead to miniaturization of multiple transformer 300b including bypass iron core <NUM>.

In Embodiment <NUM>, multiple transformer 300b having the arrangement of bypass iron cores <NUM> can be used to prevent the generation of a cross-section due to magnetic interference between windings, as described above. Meanwhile, it is feared that multiple transformer 300b may have a size larger than that of multiple transformer 300a. Thus, the configuration of Embodiment <NUM> including multiple transformer 300a can be used by carefully selecting the components of each DC/DC conversion unit <NUM> to restrain the generation of a cross-section associated with variations in individual difference. Such selection, however, may increase a manufacturing cost and a time for manufacturing steps. Thus, selection of any one of the power converters according to Embodiments <NUM> and <NUM> can be appropriately determined in accordance with a required cost or required reliability.

Embodiment <NUM> will describe a configuration for continuing an operation, in the event of failure of some of DC/DC conversion units <NUM>, using the other normal DC/DC conversion units <NUM> in the power converter according to Embodiment <NUM>.

<FIG> is a circuit diagram showing a configuration of a power converter according to a comparative example of Embodiment <NUM>.

Referring to <FIG>, a power converter 10b according to the comparative example differs from power converter 10a (<FIG>) according to Embodiment <NUM> in that short-circuit devices <NUM> are further arranged corresponding to DC/DC conversion units <NUM>. Since the other components of power converter 10b are similar to those of power converter 10a, detailed description thereof will not be repeated.

Short-circuit devices <NUM> are arranged corresponding to DC terminals of series-connected converters, that is, DC terminals <NUM> of AC/DC converters <NUM> in <FIG>. Each short-circuit device <NUM> is normally open, whereas it is controlled to be short-circuited in response to a control signal from the control circuit (not shown) of power converter 10b. Consequently, a short-circuit can be established by short-circuit device <NUM> between DC terminals <NUM> in DC/DC conversion unit <NUM> in which a failure has occurred.

An example in which only an n-th DC/DC conversion unit <NUM> in which a failure has occurred will be described with reference to <FIG>. In this case, in order to continue the operation of power converter 10b, its corresponding short-circuit device <NUM> is controlled to be short-circuited. Further, since the supply of gate signals <NUM> and <NUM> to n-th DC/DC conversion unit <NUM> is stopped, semiconductor switching elements Q11 to Q14 and Q21 to Q24 are fixed in the OFF state.

In contrast, in the other (n-<NUM>) DC/DC conversion units <NUM>, short-circuit devices <NUM> are maintained open, and AC/DC power conversion and DC/AC power conversion are performed through switching control of semiconductor switching elements Q11 to Q14 and Q21 to Q24 according to gate signals <NUM> and <NUM>.

Thus, n-th DC/DC conversion unit <NUM> in which a failure has occurred can be disconnected, and DC terminals <NUM> of the other (n-<NUM>) DC/DC conversion units <NUM> can be connected in series between DC terminals <NUM>. It is not necessary to arrange short-circuit devices <NUM> to DC/AC converters <NUM> connected in parallel between DC terminals <NUM>.

In the n-th DC/DC conversion unit <NUM>, AC voltage is not applied from DC/AC converter <NUM> and AC/DC converter <NUM> to AC terminals <NUM> and <NUM> due to stop of gate signals <NUM> and <NUM>. Consequently, the applied AC voltage does not have an equal maximum value and an equal phase among primary windings <NUM> and secondary windings <NUM> of multiple transformer 300a, thus causing a cross-current due to magnetic interference between the windings.

At this time, even when semiconductor switching elements Q11 to Q14 and Q21 to Q24 are fixed in the OFF state, a diode rectifier (full-wave rectifier) is formed of antiparallel diodes of the semiconductor switching elements in DC/AC converter <NUM> and AC/DC converter <NUM>. The output of DC/DC conversion unit <NUM> operating as the diode rectifier is smaller than that of any other DC/DC conversion unit <NUM> operating normally through power conversion because short-circuit device <NUM> is being interrupted.

As the operation of power converter 10b is to be continued in this state, a cross-current may cause a high current to flow from DC/DC conversion unit <NUM> operating normally into short-circuit device <NUM> being interrupted. As a result, the operation of power converter 10b may not be continued due to the occurrence of a failure or stop of protection which is caused by overcurrent, occurring in DC/DC conversion unit <NUM> operating normally.

<FIG> is a circuit diagram showing a configuration of a power converter according to Embodiment <NUM>.

Referring to <FIG>, a power converter 10c according to Embodiment <NUM> differs from power converter 10a according to Embodiment <NUM> in that it further includes short-circuit devices <NUM> similar to those of power converters 10b (<FIG>) according to the comparative example and AC interruption devices <NUM>. Since the other components of power converter 10c other than AC interruption devices <NUM> are similar to those of power converter 10b (<FIG>) according to the comparative example, detailed description thereof will not be repeated.

AC interruption device <NUM> is arranged between secondary winding <NUM> and AC/DC converter <NUM> (AC node) in each DC/DC conversion unit <NUM>. AC interruption device <NUM> is normally conductive, whereas it is controlled to be open in response to a control signal from the control circuit (not shown) of power converter 10c. Consequently, a current path between secondary winding <NUM> and AC/DC converter <NUM> can be interrupted in DC/DC conversion unit <NUM> in which a failure has occurred.

This can interrupt the current path that causes a cross-current from DC/DC conversion unit <NUM> operating normally to DC/DC conversion unit <NUM>, supply of gate signals <NUM> and <NUM> thereto has been stopped due to the occurrence of a failure.

Thus, according to Embodiment <NUM>, even in the event of failure of some DC/DC conversion units <NUM> in the power converter in which multiple transformer 300a including no bypass iron core <NUM> is used, short-circuit device <NUM> and AC interruption device <NUM> can continue the operation of the power converter using the other normal DC/DC conversion units <NUM>.

In the example configuration of <FIG>, AC interruption device <NUM> can be further arranged between primary winding <NUM> and the AC node of DC/AC converter <NUM>, in addition to between secondary winding <NUM> and the AC node of AC/DC converter <NUM>. This can restrain a cross-current also on the DC/AC converter <NUM> side, further improving reliability.

<FIG> is a circuit diagram showing a configuration of a power converter 10d according to a modification of Embodiment <NUM>.

Referring to <FIG>, power converter 10d according to the modification of Embodiment <NUM> differs from power converter 10a according to Embodiment <NUM> in that it further includes short-circuit devices <NUM> similar to those of power converters 10b (<FIG>) according to the comparative example and DC interruption devices <NUM>. Since the components of power converter 10d other than DC interruption devices <NUM> are similar to those of power converter 10b (<FIG>) according to the comparative example, detailed description thereof will not be described. In other words, power converter 10d differs from power converter 10c according to Embodiment <NUM> in that DC interruption devices <NUM> are arranged in place of AC interruption devices <NUM>.

DC interruption device <NUM> is connected in series with the DC node of AC/DC converter <NUM> in each DC/DC conversion unit <NUM>. DC interruption device <NUM> is connected to the AC/DC converter <NUM> side relative to short-circuit device <NUM>.

DC interruption device <NUM> is normally conductive, whereas it is controlled to be open in response to a control signal from the control circuit (not shown) of power converter 10d. In DC/DC conversion unit <NUM> in which a failure has occurred, DC interruption device <NUM> is controlled to be open.

Opening DC interruption devices <NUM> arranged as described above can also interrupt the current path that causes a cross-current from DC/DC conversion unit <NUM> operating normally to DC/DC conversion unit <NUM> in which a failure has occurred, as in Embodiment <NUM>.

Thus, even in the event of failure of some of DC/DC conversion units <NUM> in the power converter in which multiple transformer 300a including no bypass iron cores <NUM> is used, the modification of Embodiment <NUM> can also continue the operation of the power converter using the other normal DC/DC conversion units <NUM>.

In the example configuration of <FIG>, in addition to the DC nodes of AC/DC converters <NUM>, DC interruption devices <NUM> can be arranged further to the DC nodes of DC/AC converters <NUM>. DC interruption device <NUM> is preferably connected between DC terminal <NUM> and DC/AC converter <NUM>. This can restrain a cross-current also on the DC/AC converter <NUM> side, further improving reliability.

Embodiment <NUM> will describe a configuration for continuing an operation as in Embodiment <NUM> in the event of failure of some of DC/DC conversion units <NUM> in the power converter according to Embodiment <NUM>, that is, the power converter in which multiple transformer 300b including bypass iron cores <NUM> is used.

Referring to <FIG>, a power converter 10e according to Embodiment <NUM> differs from the power converter according to Embodiment <NUM> in that short-circuit devices <NUM> are further arranged corresponding to DC/DC conversion units <NUM> as in Embodiment <NUM>. In other words, the configuration of power converter 10e is similar to that of power converter 10b (<FIG>) according to the comparative example except for the use multiple transformer 300b in place of multiple transformer 300a.

Also in power converter 10e, short-circuit devices <NUM> are arranged corresponding to DC terminals <NUM> of AC/DC converters <NUM> connected in series between DC terminals <NUM>. Each short-circuit device <NUM> is usually open, whereas it is controlled to be short-circuited in DC/DC conversion unit <NUM> in which a failure has occurred.

In power converter 10e, primary winding <NUM> and secondary winding <NUM> are magnetically separated from each other between DC/DC conversion units <NUM> by bypass iron cores <NUM> arranged in multiple transformer 300b. Thus, even when AC interruption devices <NUM> or DC interruption devices <NUM> shown in <FIG> or <FIG> are not provided, a cross-current from DC/DC conversion unit <NUM> operating normally is not caused to DC/DC conversion unit <NUM> in which a failure has occurred and has been disconnected by short-circuit device <NUM>.

As a result, even in the event of failure of some of DC/DC conversion units <NUM> in the power converter in which multiple transformer 300b including bypass iron cores <NUM> is used, the operation of the power converter can be continued using the other normal DC/DC conversion units <NUM>.

AC interruption devices <NUM> and DC interruption devices <NUM>, which have been described respectively in Embodiment <NUM> and the modification thereof, can be further arranged in the circuit configuration described in Embodiment <NUM>.

<FIG> is a circuit diagram illustrating a configuration of a power converter according to a first modification of Embodiment <NUM>.

Referring to <FIG>, a power converter 10f according to the first modification of Embodiment <NUM> further includes AC interruption devices <NUM> in addition to the components of power converter 10e (<FIG>) according to Embodiment <NUM>.

AC interruption device <NUM> is arranged between secondary winding <NUM> and AC/DC converter <NUM> (AC node) in each DC/DC conversion unit <NUM>, as in power converter 10c (<FIG>). In an alternative configuration, AC interruption device <NUM> can be further arranged between primary winding <NUM> and the AC node of DC/AC converter <NUM>.

Each AC interruption device <NUM> is usually conductive, whereas it is controlled to be open in DC/DC conversion unit <NUM> in which a failure has occurred, in response to a control signal from the control circuit (not shown) of power converter 10f. In other words, in DC/DC conversion unit <NUM> in which a failure has occurred, short-circuit device <NUM> is controlled to be short-circuited, and AC interruption device <NUM> is controlled to be open.

<FIG> is a circuit diagram illustrating a configuration of a power converter according to a second modification of Embodiment <NUM>.

Referring to <FIG>, a power converter <NUM> according to the second modification of Embodiment <NUM> further includes DC interruption devices <NUM> in addition to the components of power converter 10e (<FIG>) according to Embodiment <NUM>.

DC interruption device <NUM> is connected in series with the DC node of AC/DC converter <NUM>, corresponding to DC/DC conversion unit <NUM>, on the AC/DC converter <NUM> side relative to short-circuit device <NUM>, as in power converter 10d (<FIG>). Alternatively, DC interruption device <NUM> may be further arranged to the DC node of DC/AC converter <NUM>. In this case, DC interruption device <NUM> is preferably connected between DC terminal <NUM> and DC/AC converter <NUM>.

Each DC interruption device <NUM> is normally conductive, whereas it is controlled to be open in DC/DC conversion unit <NUM> in which a failure has occurred, in response to a control signal from the control circuit (not shown) of power converter <NUM>. In other words, in DC/DC conversion unit <NUM> in which a failure has occurred, short-circuit device <NUM> is controlled to be short-circuited, and DC interruption device <NUM> is controlled to be open.

By further arranging AC interruption devices <NUM> or DC interruption devices <NUM> as in the first or second modification of Embodiment <NUM>, the generation of a cross-current can be prevented more reliably to further improve reliability when the operation is continued by interruption of short-circuit device <NUM> corresponding to DC/DC conversion unit <NUM> in which a failure has occurred in the power converter in which multiple transformer 300b including bypass iron core <NUM> is used.

In Embodiments <NUM> and <NUM> and the modifications thereof, short-circuit device <NUM> is arranged corresponding to DC/AC converter <NUM> and/or AC/DC converter <NUM> connected in series between DC terminals <NUM> and <NUM> in the power converter including multiple transformer 300a or 300b. Thus, in contrast to the example configurations of <FIG>, in the circuit configuration in which AC/DC converters <NUM> are connected in parallel between DC terminals <NUM> whereas DC/AC converters <NUM> are connected in series between DC terminals <NUM>, short-circuit device <NUM> is arranged corresponding to DC terminals <NUM> of each of DC/AC converters <NUM>.

Also, in the circuit configuration in which DC/AC converters <NUM> are connected in series and AC/DC converters <NUM> are connected in series both of between DC terminals <NUM> and between DC terminals <NUM>, respectively, short-circuit device <NUM> is arranged corresponding to both of DC terminals <NUM> of each DC/AC converter <NUM> and DC terminals <NUM> of each AC/DC converter <NUM>.

AC interruption device <NUM> or DC interruption device <NUM> is at least arranged corresponding to DC/AC converter <NUM> and/or AC/DC converter <NUM> in which short-circuit device <NUM> is arranged.

Embodiment <NUM> will describe an example configuration of a winding conductor used in primary winding <NUM> and secondary winding <NUM> of multiple transformers 300a and 300b in Embodiments <NUM> to <NUM>.

Used as the winding of a high-capacity multiple transformer is usually a winding including a plurality of narrow and small conductor element wires including an element wire insulation. The use of such a winding causes a leakage magnetic flux of the transformer to be interlinked with the winding, thus reducing an eddy-current loss of the winding to be generated.

However, setting the switching frequencies of semiconductor switching elements Q11 to Q14 and Q21 to Q24 to higher frequencies (e.g., not less than <NUM> which is higher than the frequency of a commercial AC power supply) may cause the currents input to primary winding <NUM> and secondary winding <NUM> to have a frequency higher than <NUM> as described above, and in the above winding, current passes through only near the surface of the conductor element wire due to the generation of the skin effect. This increases equivalent resistance values of the conductor element wires, which may increase losses in multiple transformers 300a and 300b.

<FIG> is a conceptual sectional view for illustrating an example winding conductive wire <NUM> according to Embodiment <NUM>.

Referring to <FIG>, winding conductive wire <NUM> is formed of a litz wire including intertwined conductor element wires <NUM> each having an element wire insulation <NUM>. The use of the litz wire can restrain the skin effect and the proximity effect at high frequencies, thus restraining an increase in the loss due to higher frequencies.

Embodiment <NUM> can use winding conductive wire <NUM> formed of a litz wire in primary windings <NUM> and secondary windings <NUM> of multiple transformers 300a and 300b, thus achieving higher frequencies while restraining an increase in the loss of multiple transformers 300a and 300b. As a result, multiple transformers 300a and 300b can be miniaturized.

For the purpose of clarification, it has been initially intended at the time of filing of the present application to appropriately combine the configurations described in a plurality of embodiments described above, including any combination not mentioned in the specification, within the scope of the appended claims.

Claim 1:
A power converter that performs DC voltage conversion between a pair of first DC terminals (<NUM>) and a pair of second DC terminals (<NUM>), the power converter comprising:
a plurality of DC/AC converters (<NUM>) each having DC nodes (<NUM>), the DC nodes of the plurality of DC/AC converters (<NUM>) being connected in parallel or in series between the first DC terminals (<NUM>);
a plurality of AC/DC converters (<NUM>) each having DC nodes (<NUM>), the DC nodes of the plurality of AC/DC converters (<NUM>) being connected in parallel or in series between the second DC terminals (<NUM>); and
a multiple transformer (300a) connected between the DC/AC converters (<NUM>) and the AC/DC converters (<NUM>),
the multiple transformer (300a) including
a plurality of primary windings (<NUM>) each connected to a corresponding one of AC nodes (<NUM>) of the respective DC/AC converters (<NUM>),
a plurality of secondary windings (<NUM>) each connected to a corresponding one of AC nodes (<NUM>) of the respective AC/DC converters (<NUM>), and
a core portion (<NUM>) around which the primary windings (<NUM>) and the secondary windings (<NUM>) are wound, the core portion (<NUM>) being configured such that a magnetic path is shared among the primary windings (<NUM>) and the secondary windings (<NUM>), wherein
each winding of one of a group of the primary windings (<NUM>) and a group of the secondary windings (<NUM>) is so divided as to be wound around first portions of the core portion (<NUM>) respectively, and
each winding of the other of the group of the primary windings (<NUM>) and the group of the secondary windings (<NUM>) is wound around a second portion of the core portion (<NUM>) without being divided, the second portion being sandwiched between the first portions of the core portion (<NUM>), a corresponding winding of the one group being wound around the first portions,
characterised in that
either the primary windings (<NUM>) or the secondary windings (<NUM>), depending on which is rated for the relatively lower voltage, are the ones being divided and sandwiching the other of the secondary windings (<NUM>) and the primary windings (<NUM>) having the relatively higher voltage than said lower voltage.