Transformers for multiphase power converters

A transformer for a multiphase power converter includes a magnetic structure, a first coil configured to electrically couple to an input circuit or an output circuit of a subconverter of the multiphase power converter, and a second coil configured to electrically couple to an input circuit or an output circuit of another subconverter of the multiphase power converter. The magnetic structure includes a top member, a bottom member, and legs extending between the top member and the bottom member in substantially the same direction. The legs include two outer members and two inner members. The first coil is wound about one of the two inner members of the magnetic structure, and the second coil is wound about the other one of the two inner members of the magnetic structure. Other example transformers, and multiphase power converters including transformers are also disclosed.

FIELD

The present disclosure relates to transformers for multiphase power converters.

BACKGROUND

Power converters convert electrical power between inputs and outputs. The power converters sometimes include multiple phases each having a transformer. Each of the transformers may include windings and its own core for the windings. In such examples, each core may have an E-E or an E-I configuration. In other examples, the windings of multiple transformers may be wound on a shared magnetic core. In such examples, the shared magnetic core may have an E-E-I configuration.

SUMMARY

According to one aspect of the present disclosure, a multiphase power converter includes a plurality of subconverters each having an input circuit and an output circuit, and a transformer for the plurality of subconverters. The transformer includes a magnetic structure, a first coil electrically coupled to the input circuit or the output circuit of one of the subconverters, and a second coil electrically coupled to the input circuit or the output circuit of another one of the subconverters. The magnetic structure includes a top member, a bottom member, and a plurality of legs extending between the top member and the bottom member in substantially the same direction. The legs include two outer members and two inner members positioned between the two outer members. The first coil is wound about one of the two inner members of the magnetic structure, and the second coil is wound about the other one of the two inner members of the magnetic structure.

According to another aspect of the present disclosure, a transformer for a multiphase power converter includes subconverters each having an input circuit and an output circuit. The transformer includes a magnetic structure, a first coil configured to electrically couple to the input circuit or the output circuit of one of the subconverters, and a second coil configured to electrically couple to the input circuit or the output circuit of another one of the subconverters. The magnetic structure includes a top member, a bottom member, and a plurality of legs extending between the top member and the bottom member in substantially the same direction. The legs include two outer members and two inner members positioned between the two outer members. The first coil is wound about one of the two inner members of the magnetic structure, and the second coil is wound about the other one of the two inner members of the magnetic structure.

Corresponding reference numerals indicate corresponding (but not necessarily identical) parts and/or features throughout the several views of the drawings.

DETAILED DESCRIPTION

A transformer for a multiphase power converter according to one example embodiment of the present disclosure is illustrated inFIG.1, and indicated generally by reference number100. As shown inFIG.1, the transformer100includes a magnetic structure102, and coils104,106. The magnetic structure (e.g., a magnetic core)102includes multiple core sections. For example, the magnetic structure102includes members108,110, and legs extending between the members108,110in substantially the same direction. The legs include two outer members (e.g., legs)112a,112d, and two inner members (e.g., legs)112b,112cpositioned between the two outer members112a,112d. As shown inFIG.1, the coil104is wound about the inner member112b, and the coil106is wound about the inner member112c.

By employing any one of the transformers disclosed herein, the effective core area of its magnetic structure through which magnetic fluxes induced by coils will pass through may be increased as compared to conventional magnetic structures. For example, and as further explained below, the core sections of any one of the magnetic structures disclosed herein are arranged so that magnetic fluxes generated by the coils flow through a higher amount (and sometimes all) of the core sections as compared to conventional magnetic structures. In some examples, the magnetic structures disclosed herein may have, for example, an effective core area 33% larger than conventional magnetic structures. Additionally, the total volume of the magnetic structure may remain substantially the same as the total volume of conventional magnetic structures. As such, the effective core area per volume of the magnetic structure may be increased as compared to conventional magnetic structures. In other examples, the total volume of the magnetic structure may be reduced as compared to conventional magnetic structures, while the effective core area may remain substantially the same as the effective core area of the conventional magnetic structures. Because of the increased effective core area and/or reduced volume of the magnetic structure, a higher power density and efficiency of the multiphase power converter employing the transformer may be achieved as compared to multiphase power converter employing conventional transformers.

In the particular example ofFIG.1, the members108,110extend in substantially parallel planes separated by the legs112a,112b,112c,112d. Additionally, the legs112a,112b,112c,112dextend in substantially parallel planes that are perpendicular to the member planes. As such, the members108,110are substantially parallel to each other, and the legs112a,112b,112c,112dare substantially parallel to each other and substantially perpendicular to the members108,110. In such examples, the members108,110and the legs112a,112b,112c,112ddefine three windows, as shown inFIG.1.

In the example ofFIG.1, the members108,110and the legs112a,112b,112c,112dhave a generally rectangular-shape relative to their cross sections. In other embodiments, any one of the members108,110and/or legs112a,112b,112c,112dmay have another suitable cross-sectional shape if desired.

In the particular example ofFIG.1, the magnetic structure102includes only four legs112a,112b,112c,112dextending between the members108,110. In such examples, the cross-sectional area of each outer leg112a,112dmay be substantially equal, and the cross-sectional area of each inner leg112b,112cmay be substantially equal. Additionally, the cross-sectional area of each outer leg112a,112dmay be about half the cross-sectional area of each inner leg112b,112c.

In other embodiments, and as further explained below, the magnetic structure102may include additional legs extending between the members108,110. For example, the magnetic structure102may include an additional inner leg. In such examples, the amount of material forming each outer leg112a,112dmay be reduced. The material removed from each outer leg112a,112dmay be used to form the additional inner leg. As such, the reduction of material in each outer leg112a,112dmay be substantially equal to the amount of material in the additional inner leg. As a result, the cross-sectional area of each outer leg112a,112dmay be decreased as compared to embodiments employing only four legs. Thus, when an additional inner leg is employed, the cross-sectional area of each outer leg112a,112dmay be less than half the cross-sectional area of each inner leg112b,112c.

As explained above, the transformer100includes the coils104,106wound about the inner legs112b,112c. In the particular example ofFIG.1, the coils104,106are wound about only the inner legs112b,112c. Thus, no coil is wound about the outer leg112a, the outer leg112d, the member108, or the member110. In other examples, the transformer100may include one or more coils wound about another core member such as the outer leg112a, the outer leg112d, the member108and/or the member110if desired.

In the example ofFIG.1, the coils104,106may represent transformer windings in the multiphase power converter. For example, one of the coils (e.g., the coil104) may represent a primary winding or secondary winding of one phase of the power converter, and the other coil (e.g., the coil106) may represent a primary winding or secondary winding of another phase of the power converter. In such examples, the coil104may electrically couple to an input circuit in one phase if the coil104represents a primary winding. Alternatively, the coil104may electrically couple to an output circuit in one phase if the coil104represents a secondary winding. The coil106may electrically couple in a similar manner, but in another phase of the power converter.

In some examples, the transformer100includes multiple coils wound about each inner leg112b,112c. For example,FIG.2illustrates a transformer200similar to the transformer100ofFIG.1, but including two sets of coils wound about each inner leg. Specifically, and as show inFIG.2, the transformer200includes the magnetic structure102ofFIG.1, the coils104,106wound about the inner legs112b,112cofFIG.1, a coil204wound about the inner leg112b, and a coil206wound about the inner leg112c.

In the example ofFIG.2, the coils104,106,204,206may represent any one of the transformer windings in the multiphase power converter. For example, the coil104may represent a primary winding of one phase of the power converter, and electrically couple to an input circuit in that phase. Additionally, the coil204may represent a secondary winding in the same phase, and electrically couple to an output circuit in that phase. The coils106,206may represent similar (or different) transformer windings, and electrically couple in a similar manner as the coils104,204, but in another phase of the power converter.

Referring back toFIG.1, the magnetic structure102forms paths for magnetic flux generated (e.g., induced) by the coils104,106when the coils104,106are energized. For example,FIG.3illustrates the transformer100ofFIG.1with magnetic flux generated by the coils104,106. As shown inFIG.3, lines having a “dash-dot-dash” configuration represent the magnetic flux generated by the coil104, and lines having a “dash-dash-dash” configuration represent the magnetic flux generated by the coil106. The magnetic flux generated by the coils104,106flows through each of the legs112a,112b,112c,112d, and the members108,110of the magnetic structure (e.g. the shared magnetic core)102. As shown inFIG.3, all of the magnetic flux induced by the coil104passes through the center leg112b, and all of the magnetic flux induced by the coil106passes through the center leg112c.

The magnetic flux generated from the coils104,106may interact in the magnetic structure102. For example, and as shown inFIG.3, the magnetic flux generated from the coils104,106flows in opposite directions in the inner legs112b,112c, and portions of the members108,110. In such examples, the magnetic flux flowing in the opposite directions may at least partially cancel in the magnetic structure102. In some examples, the generated magnetic flux may completely cancel in the inner legs112b,112cand/or portions of the members108,110.

Additionally, the generated magnetic flux from the coils104,106may be driven out of phase. In such examples, some of the magnetic flux driven by the coil104may inductively (e.g., magnetically) couple to the coil106through the inner leg112c. Likewise, some of the magnetic flux driven by the coil106may inductively couple to the coil108through the inner leg112b. The amount of inductive coupling between the coils is a function of the magnetic structure's geometry including air gaps (if employed) within the magnetic paths.

By allowing some of the magnetic flux generated by one coil (e.g., the coil104) to couple to the other coil (e.g., the coil106), the active start point of B-H curves in a multiphase power converter employing the transformer100ofFIG.1may be advantageously shifted. For example, the active start point of a B-H curve of each subconverter in the power converter may be shifted from zero to a negative value in the third quadrant. This may move unipolar first quadrant B-H loop operation to operation in the first and third quadrants, as further explained below. As a result, the flux swing before saturation may be increased, and the core area required for the magnetic flux may be reduced as compared to conventional multiphase power converter transformers.

Additionally, the magnetic flux interaction between the coils104,106may assist in reducing the volume of the magnetic structure102, as explained herein. For instance, the magnetic structure's geometry and the flux interaction may allow the coils104,106to share the outer legs112a,112d. For example, and as shown inFIG.3, each outer leg112a,112dmay provide return paths for magnetic flux generated by both coils104,106. Thus, the outer legs112a,112dmay be shared between the coils104,106. In such examples, the magnetic structure102may have at least two less legs (e.g., two less outer legs) as compared to multiphase power converters including conventional independent (e.g., separate) transformers. Thus, the size of the magnetic structure102may be reduced as compared to conventional magnetic structure(s) employed in multiphase power converters, as further explained herein. Because of the reduced size of the magnetic structure102, the power density of a multiphase power converter employing the transformer100may be increased and core losses in the multiphase power converter may be decreased as compared to conventional converters. This reduction of core losses may lead to higher efficiency.

In the particular example ofFIG.1, the magnetic structure102is formed of a single piece of material. In such examples, the magnetic structure102may have a monolithic construction. In other examples, the magnetic structure102may be formed from two or more separate pieces of material, and then coupled together. In such examples, any one or more portions of the magnetic structure102may have a particular shape. For example, the legs112a,112b,112c,112dand one of the members108,110may be formed of three substantially U-shaped core sections, and the other one of the members108,110may be formed of one or more substantially I-shaped core sections. In other examples, each of the legs112a,112b,112c,112dand members108,110may be separately formed (e.g., I-shaped core sections), and then coupled together.

In another example, the legs112a,112b,112c,112d, and one of the members108,110may be formed of a single piece of material, and the other one of the members108,110may be formed of a single piece of material. For example,FIGS.4and5illustrate a magnetic structure (e.g., a magnetic core)402substantially similar to the magnetic structure102ofFIG.1, but where core sections are formed out of two pieces of material. In such examples, the magnetic structure402may include an increased effective core area per volume and/or an a decreased volume per effective core area as compared to conventional magnetic structures, as explained herein.

As shown inFIGS.4and5, the magnet structure402includes members408,410, and legs412a,412b,412c,412dextending between the members408,410in substantially the same direction. The core sections of the magnet structure402may form paths for magnetic flux in a similar manner as explained above relative toFIG.3.

As shown, the legs412a,412b,412c,412dand the member410are formed of a single piece of material, and the member408is formed of a single piece of material. Alternatively, the legs412a,412b,412c,412dand the member408may be formed of a single piece of material, and the member410may be formed of a single piece of material. In other examples, the magnetic structure402may be formed of a single piece of material similar to the magnetic structure102ofFIG.1, and/or three or more pieces of material if desired. For example, each of the legs412a,412b,412c,412dand members408,410may be separately formed, and then coupled together.

In the particular example ofFIGS.4and5, the members408,410are I-shaped core sections. For example, the members408,410have a substantially rectangular shape. In other examples, one or both members408,410may have another suitable shape such as oval, square, etc. if desired.

The legs412a,412b,412c,412dmay have the same shape or different shapes. In the particular example ofFIGS.4and5, the legs412a,412bhave similar shapes, and the legs412b,412chave similar shapes. The shape of the legs412b,412cis different than the shape of the legs412a,412b. For example, the perimeter of each outer leg412a,412dgenerally follows a rectangular shape along three sides (e.g., the exterior facing sides), and a crescent shape along its interior facing side. In such examples, the outer legs412a,412dmay be referred to as crescent-shaped core sections. As shown inFIG.5, the perimeter of each inner leg412b,412cforms a generally round, oval, etc. like shape. In some examples, the curvature of the inner legs412b,412cadjacent the outer legs412a,412dsubstantially corresponds to the curvature of the outer legs412a,412d(e.g., along their interior facing sides). In other examples, the curvature of the inner legs412b,412cand the curvature of the outer legs412a,412dmay be different, the outer legs412a,412dmay have the same shape as the inner legs412b,412c, etc.

As shown inFIG.4, coils may be wound about core sections of the magnetic structure402. For example, the coils104,106ofFIGS.1and3are wound about the inner legs412b,412cof the magnetic structure402. The magnetic structure402and the coils104,106ofFIG.4form a transformer400. Additionally and/or alternatively, one or more coils may be wound about one or more of the other legs412a,412dand/or the members408,410if desired.

FIG.6illustrates an equivalent circuit600of the magnetic structure402ofFIGS.4and5with the coils104,106wound about the inner legs412b,412cof the magnetic structure402. As shown inFIG.6, the equivalent circuit600includes two voltage sources V1, V2representing magneto-motive forces in the magnetic structure402, and various resistances R1, R2, R3, R4representing reluctances in different core sections of the magnetic structure402.

In the example ofFIG.6, the voltage source V1represents a magneto-motive force from the coil104, and is calculated by multiplying the number of turns (N) of the coil104by the amount of current (Imag1) flowing through the coil104. Similarly, the voltage source V2represents a magneto-motive force from the coil106, and is calculated by multiplying the number of turns (N) of the coil106by the amount of current (Imag2) flowing through the coil106. Additionally, the resistances R1represent reluctances in the inner legs412b,412c, the resistances R2represent reluctances in the outer legs412a,412d, the resistances R3represent reluctances in the outer portions of each member408,410, and the resistances R4represent reluctances in the inner portion of each member408,410.

The reluctance (R) in each core section may be calculated using equation (1) below. In equation (1), Lc is the length of the core section, Ac is the cross-sectional area of the core section through which the magnetic flux passes, and μ is the permeability of the magnetic material in the core section.

In the particular example ofFIG.6, the cross-sectional area of the inner portion of each member408,410is half the cross-sectional area of each inner leg412b,412c. Additionally, the length of the inner portion of each member408,410is the same as the length of the inner leg412b,412c. The cross-sectional area and the length of the outer legs412a,412dare the same as the cross-sectional area and the length of the inner portion of each member408,410. Thus, if the reluctance of each inner leg412b,412cis equal to the value RC (as shown inFIG.6), the reluctances of the inner portion of each member408,410and the reluctances of the outer legs412a,412dare equal to the value 2*RC when using equation (1) above, as shown inFIG.6.

Likewise, the cross-sectional area of the outer portions of each member408,410is half the cross-sectional area of each inner leg412b,412c. The length of the outer portions of each member408,410is half the length of the inner leg412b,412c. As such, if the reluctance of each inner leg412b,412cis equal to the value RC (as above), the reluctance of the inner portion of each member408,410is equal to the value RC (as shown inFIG.6) when using equation (1).

The magnetic flux (Φ) in the core sections may be calculated using equation (2) below. In equation (2), N is the number of turns of the coil, Imag is the magnitude of the current flowing through the coil, and R is the total equivalent reluctance based on the path of the magnetic flux.

As shown inFIG.6, Φ_1A represents the magnetic flux generated by the coils104,106in the outer leg412aand the outer portions of each member408,410adjacent to the outer leg412a, and Φ_2A represents the magnetic flux generated by the coils104,106in the outer leg412dand the outer portions of each member408,410adjacent to the outer leg412d. Additionally, Φ_m represents the magnetic flux generated by the coils104,106in the inner portions of each member408,410. Φ_1, Φ_2represent the magnetic flux generated by the coils104,106in the inner legs412b,412c, respectively.

The magnetic fluxes Φ_1A, Φ_2A, Φ_m, Φ_1, Φ_2may be calculated with equations (3)-(7) below. In the particular example ofFIG.4, the number of turns (N) of the coils104,106is the same. In other examples, the number of turns of the coils104,106may be different if desired. In equations (3)-(7), the current flowing through the coil104is represented by Imag1, the current flowing through the coil106is represented by Imag2, and the RC value (e.g., 35*RC and 7*RC) represents the total equivalent reluctance based on the path of the magnetic flux.

In some examples, the magnetic flux in the magnetic structure402and the current flowing through the coils104,106may be the only time dependent variables in equations (2)-(7). This may be the case when the transformer400(and/or any of the other transformers disclosed herein) is employed in a multiphase power converter including, for example, two or more interleaved forward subconverters. In such examples, the time dependent variables may be expressed as equation (8) below.

As further explained below, when one of the subconverters of the multiphase power converter is in its idle period, little to no current flows through the subconverter. For example, each forward subconverter includes a repeating cycle of a conduction period, a reset period, and an idle period. The conduction period is a period where power is transferred via the transformer, the reset period is a period where the transformer releases its energy stored during the conduction period for demagnetizing (e.g., resetting) the transformer, and the idle period is a period where the transformer is demagnetized and power is not transferred via the transformer. Typically, when one of the subconverters is in its conduction period, the other subconverter(s) are in their reset period or idle period.

Equations (3)-(7) above may be used to determine whether current is flowing through one of the subconverters during its idle period. For example, when a subconverter A of the multiphase power converter (e.g., the subconverter including an input and/or output circuit electrically coupled to the coil106) is in its idle period, the current Imag2flowing through the coil106is zero. During this period, another subconverter B of the multiphase power converter (e.g., the subconverter including an input and/or output circuit electrically coupled to the coil104) may be in its conduction period. In such examples, equations (9) and (10) below may be derived based on equations (3)-(7).

In such examples, the change in the magnetic flux Φ_1over time may be limited by the power converter's bulk input voltage Vbulk divided by the number of turns N of the coil104. In such examples, equations (9) and (10) show that the magnetic flux Φ_2may be limited to − 4/11 (i.e., −0.36) of the change in the magnetic flux Φ_1when the subconverter A is in its idle period. As such, the magnetic flux Φ_2will produce a low voltage (e.g., −0.36*Vbulk) on the coil106(e.g., a primary winding of the subconverter A). As a result, little to no current flows through the subconverter A (e.g., primary side power switches, body diodes of the power switches, reset components such diodes, etc.). The subconverter B experiences similar results when in its idle period, and the change in the magnetic flux Φ_2over time is limited by the bulk input voltage Vbulk divided by the number of turns N of the coil106.

When the change in the magnetic flux Φ_1, Φ_2over time (dΦ_1/dt, dΦ_2/dt) is limited as explained above, flux densities in the magnetic structure402may be normalized to the center legs412b,412crather than in the outer legs412a,412d. For example,FIG.7illustrates a graph700showing the flux densities B_1, B_2, B_1A, B_m corresponding to the magnetic fluxes Φ_1, Φ_2, Φ_1A, Φ_m, respectively, in the magnetic structure402. As shown, the peak-to-peak values of the flux densities B_1, B_2(corresponding to the magnetic fluxes in the center legs412b,412c) are nominal, the peak-to-peak value of the flux density B_m (corresponding to the magnetic flux in the inner portions of each member408,410) is larger than the peak-to-peak values of the flux densities B_1, B_2, and the peak-to-peak value of the flux density B_1A is less than the peak-to-peak values of the flux densities B_1, B_2. Although not shown, the peak-to-peak value of a flux density corresponding to the magnetic flux Φ_2A in the outer leg412dis similar to the peak-to-peak value of the flux density B_1A. As such, the outer legs412a,412dmay have a reduced peak-to-peak flux density, and the flux density B_m (corresponding to the magnetic in the inner portions of each member408,410) may have an increased peak-to-peak flux density as compared to conventional magnetic structures.

FIG.8illustrates the magnetic structure402ofFIGS.4and5divided into different sections 1, 2, 3, 4, 5. Specifically, section 1 is to the left of line A, section 2 is between lines A, B, section 3 is between lines B, C, section 4 is between lines C, D, and section 5 is the magnetic structure402is to the right of line D. As such, section 1 includes the outer leg412aand portions of the members408,410, section 2 includes the inner leg412band portions of the members408,410, section 3 includes inner portions of the members408,410, section 4 includes the inner leg412cand portions of the members408,410, and section 5 includes the outer leg412dand portions of the members408,410. As shown inFIG.8, the volume (Vol_1) of section 1, the volume (Vol_2) of section 2, the volume (Vol_4) of section 4, and the volume (Vol_5) of section 5 are approximately equal.

In some examples, the flux swing within the magnetic structure402(and/or any other magnetic structure disclosed herein) may be reduced as compared to conventional magnetic structures. For example, the volume for each of the five sections may be normalized to the total volume. As such, each section 1, 2, 3, 4, 5 may have a normalized volume of ⅕ of the total core volume. In such examples, the reduced peak-to-peak flux density (e.g., in sections 1 and 5 including the outer legs412a,412d) is seen in ⅖ of the total core volume, the increased peak-to-peak flux density (e.g., in section 3 including inner portions of the members408,410) is seen in ⅕ of the total core volume, and the nominal peak-to-peak flux density (e.g., in sections 2, 4 including inner legs412b,412c) is seen in ⅖ of the total core volume. As a result, the magnetic structure402experiences an overall net decrease in flux swing within the core volume.

Additionally, the core loss of the magnetic structure402may be reduced as compared to conventional magnetic structures. For example, core loss is a function of the peak-to-peak flux density and the switching frequency of power switches in the subconverters. As such, when the magnetic structure402experiences an overall net decrease in flux swing within the core volume, the core loss of the magnetic structure402is reduced as compared to conventional magnetic structures. For example, and as shown in Table 1 below, the normalized core loss due to the decrease in flux swing in section 1 is 1/25 (i.e., the normalized volume (⅕) in section 1 multiplied by the normalized core loss density (⅕) in section 1). The other normalized core losses (due to the flux swing) in sections 2-5 are shown in table 1. The total normalized core loss due to the decrease in flux swing in the magnetic structure402is obtained by adding the core losses for each section. As shown in Table 1, the total normalized core loss (due to the flux swing) in the entire magnetic structure402is 0.88 ( 22/25).

Further, if the switching frequency of the subconverters is reduced, the core loss may be further reduced as compared to conventional converters. For example, the switching frequency may be reduced by 33% (e.g., a 67% reduced frequency) to allow for slower switching of power switches in the subconverters. In such examples, the normalized core loss density due to the reduced frequency may be 0.5, as shown in Table 1 above. As a result, the total normalized core loss due to the reduced frequency and flux swing in the magnetic structure402may be obtained by multiplying the normalized core loss density due to the reduced frequency (0.5) by the normalized core loss due to the reduced flux swing (0.88). As shown in Table 1, the total normalized core loss is 0.44. Thus, the magnetic structure402may include a larger effective core area (e.g., a 33% increase, etc.) as compared to a conventional magnetic structure having separate transformers, while maintaining the same volume as the conventional structure, and experiencing 44% of the core loss experienced with the conventional magnetic structure.

In other examples, the total volume of the magnetic structure402may be reduced (e.g., a 33% reduction, etc.) as compared the conventional structure having separate transformers. In such examples, the effective core area of the magnetic structure402may be the same as the effective core area of the conventional structure. Additionally, the number of turns of the coils104,106, the volt-seconds (e.g., the magnetic flux), and/or the frequency may be the same as the number of turns, the volt-seconds, and/or the frequency of the conventional structure. In such cases, the overall core loss density (e.g., taking into account the flux swing and frequency) may be 0.88. However, because the core volume is reduced as compared to the conventional structure, the total core loss may be reduced as compared to the core loss in the conventional structure. For example, if the core volume is reduced by 33% (e.g., a reduction of 67%) as compared to the volume of the conventional structure, the total core loss is reduced to 0.59 (e.g., 0.88*0.67). As such, in this example, the magnetic structure402may experience 59% of the core loss for the conventional structure.

In some examples, any one of the magnetic structures disclosed may include one or more additional legs. Coils may or may not be wound about the additional legs. For example,FIG.9illustrates a magnetic structure902that is substantially similar to the magnetic structures102,402ofFIGS.1-5, but including an additional inner leg. Specifically, and as shown inFIG.9, the magnetic structure902includes the member410ofFIGS.4and5, and legs912a,912b,912c,912d,912e. In the particular example ofFIG.9, no coil is wound about the leg912e. The legs912a,912b,912c,912dare similar to the legs412a,412b,412c,412dofFIGS.4and5. However, the inner legs912b,912chave a circular cross-sectional shape.

The legs912a,912b,912c,912d,912eextend between the member410and another member (not shown) such as the member108ofFIGS.1-3, the member408ofFIGS.4-5, etc. As such, the legs912a,912b,912c,912d,912eseparate the members.

Additionally, and as shown inFIG.9, the leg912eis positioned between the legs912b,912c. In such examples, a transformer including the magnetic structure902may experience less inductive (e.g., magnetic) coupling between when one subconverter of a multiphase power converter utilizes the transformer and another one subconverter of the multiphase power converter utilizes the transformer.

In the particular example ofFIG.9, the leg912ehas a triangular-shaped cross section. For example, the perimeter of the leg912eincludes a flat (e.g., straight) exterior facing side, and two curved (e.g., crescent-shaped) interior facing sides. The curvature of the interior facing sides may substantially correspond to the curvature of the inner legs912b,912c. As shown, the exterior facing side of the leg912eis adjacent to an edge of the member410, and the interior facing sides of the leg912emeet (e.g., form an edge) between the inner legs912b,912c. As such, the leg912eextends between the inner legs912b,912cand the coils (not shown) wound about the inner legs912b,912c.

In some examples, the effective core area of the magnetic structure902may be substantially similar (and in some cases the same) as the effective core area of the magnetic structure402. For example, the amount of material forming the outer legs912a,912dmay be reduced as compared to the outer legs412a,412d. This material may be used to form the leg912e. As such, the reduction of material in each outer leg912a,912dmay be substantially equal to the amount of material in the inner leg912e. In such examples, the cross-sectional area of the combination of the outer legs912a,912dand the inner leg912emay be about half the cross-sectional area of the inner legs912b,912c.

In other examples, the magnetic structures disclosed herein may include additional legs with coils wound thereon. For example,FIG.10illustrates a magnetic structure1002having a stacked configuration. The magnetic structure1002is substantially similar to the magnetic structure402ofFIGS.4and5, but includes four additional legs. Specifically, the magnetic structure1002includes legs1012a,1012b,1012c,1012d, a member1010, and the legs412a,412b,412c,412dand the members408,410ofFIGS.4and5. As shown, the legs412a,412b,412c,412dextend between the members408,410, and the legs1012a,1012b,1012c,1012dextend between the members410,1010. The members408,410,1010extend in parallel planes, and the legs412a,412b,412c,412d,1012a,1012b,1012c,1012dextend in planes substantially perpendicular to the members408,410,1010.

The legs1012a,1012b,1012c,1012dare substantially aligned with the legs412a,412b,412c,412d. Specifically, the legs1012a,1012b,1012c,1012dare substantially aligned with the legs412a,412b,412c,412d, respectively, in a stacked configuration (e.g., in a longitudinal direction), as shown inFIG.10. In other examples, one or more of the legs1012a,1012b,1012c,1012dmay be offset relative to the legs412a,412b,412c,412d.

As shown inFIG.10, the legs1012a,1012b,1012c,1012dextend on a side of the member410opposing the legs412a,412b,412c,412d. For example, the legs1012a,1012b,1012c,1012dextend from one side of the member410, and the legs412a,412b,412c,412dextend from another (opposing) side of the member410. In other examples, one or more of the legs1012a,1012b,1012c,1012dmay extend on the side of the member410adjacent to the legs412a,412b,412c,412d.

FIG.11illustrates a magnetic structure1102similar to the magnetic structure1002ofFIG.10, but having a side-by-side configuration. Specifically, the magnetic structure1102includes legs1112a,1112b,1112c,1112d, members1108,1110, and the legs412a,412b,412c,412dand members408,410ofFIGS.4and5. As shown, the legs412a,412b,412c,412dextend between the members408,410, and the legs1112a,1112b,1112c,1112dextend between the members1108,1110. The members408,410,1108,1110extend in parallel planes, and the legs412a,412b,412c,412d,1112a,1112b,1112c,1112dextend in planes substantially perpendicular to the members408,410,1108,1110.

The legs1112a,1112b,1112c,1112dare substantially aligned with the legs412a,412b,412c,412d. Specifically, the legs1112a,1112b,1112c,1112dare substantially aligned with the legs412a,412b,412c,412din a side-by-side configuration. For example, and as shown inFIG.11, the legs1112a,1112b,1112c,1112dare positioned adjacent to the legs412a,412b,412c,412d, respectively, in a lateral direction.

In the examples ofFIGS.10and11, one or more coils may be wound about each inner leg412b,412c,1012b,1012c,1112b,1112c. In such examples, each coil may represent a primary transformer winding or a secondary transformer winding of one phase (e.g., corresponding to one subconverter) of a multiphase power converter. As such, each magnetic structures1002,1102ofFIGS.10and11may be part of a transformer employed in a power converter having four subconverters.

The coils disclosed herein may be any suitable types of coils. For example, one or more of the coils may include conductive wire coils (e.g., wire windings) as shown inFIGS.1-4, etc. Alternatively, one or more of the coils may include plate coils (e.g., plate windings). For example,FIG.12illustrates a transformer1200including the magnetic structure402ofFIGS.4and5, and plate coils wound about its inner legs (not shown). Specifically, and as shown inFIG.12, the transformer1200includes coils1204,1212,1214wound about one of the inner legs (e.g., the leg412b), and coils1206,1216,1218wound about the other inner leg (e.g., the leg412c). In such examples, the coils1204,1212,1214may represent one or more primary windings and/or secondary windings of one power converter phase, and the coils1206,1216,1218may represent one or more primary windings and/or secondary windings of another power converter phase.

Additionally, the coils may include any suitable number of turns. For example, in the embodiment ofFIG.2, the coils104,106,204,206may have the same number of turns. In other examples, the coils104,106may have a larger or smaller number of turns as the coils204,206. In such examples, the turn ratio of the coils104,204may be the same as the turn ratio of the coils204,206. In some examples, the turn ratio of the coils104,204may be different than the turn ratio of the coils204,206.

In some examples, the magnetic structures disclosed herein may include an air gap between core sections. For example, in the embodiment ofFIG.4, the inner legs412b,412cand the member408may define air gaps. Specifically, an air gap may be between the inner leg412band the member408, and/or an air gap may be between the inner leg412cand the member408. In such examples, the air gap(s) may assist in reducing third quadrant operation, reducing the peak flux density in the outer legs412a,412b, reducing inductive (e.g., magnetic) coupling, and maintaining the reluctance of the inner legs412b,412c. In other examples, no air gap may be between the inner legs412b,412cand the member408. In such examples, the inductive coupling may allow a shorter reset time of the transformer as compared to embodiments with air gap(s).

The transformers disclosed herein may employed in any suitable multiphase power converter. For example, the transformers may be used in AC/DC power converters including interleaved forward converter topologies, as explained below. In some examples, the AC/DC power converters may have a high power rating such as 2800 W, 3200 W, etc.

The transformers may be particularly useful in a multiphase power converter (e.g., a multiphase forward power converter, etc.) utilizing the first quadrant of a B-H curve. For example,FIG.13illustrates a graph1300showing possible relative B-H curves (e.g., loops) of the flux densities B_1, B_2, B_1A, B_m ofFIG.7. As shown, the curves of the flux densities B_1, B_2(corresponding to the magnetic fluxes Φ_1, Φ_2in the center legs412b,412cof the magnetic structure402) are the same. Additionally, the curve of the flux density B_1A (corresponding to the magnetic flux Φ_1A in the outer leg412aof the magnetic structure402) remains within the first quadrant, and the curves of the flux densities B_1, B_2are substantially within the first quadrant. Additionally, the curves of the flux densities B_1, B_2, B_m start in the third quadrant. This may result in lower reset times for the magnetic structure402as compared to conventional magnetic structures.

FIG.14illustrates an isolated two-phase interleaved forward power converter1400including two subconverters1402,1404, and any one of the transformers disclosed herein for the subconverters1402,1404. In the example ofFIG.14, each subconverter1402,1404includes a two-transistor forward converter topology. As such, the power converter1400may be considered an interleaved two-transistor forward (ITTF) power converter.

As shown inFIG.14, each subconverter1402,1404includes an input circuit1406,1408and an output circuit1410,1412. Specifically, the input circuit1406of the subconverter1402includes power switches (e.g., MOSFETs) Q1, Q2, the input circuit1408of the subconverter1404includes power switches (e.g., MOSFETs) Q3, Q4, the output circuit1410of the subconverter1402includes a rectification circuit having a diode D5, and the output circuit1412of the subconverter1404includes a rectification circuit having a diode D6. In other examples, the rectification circuits may include other suitable switching devices such as MOSFETs, etc.

In the example ofFIG.14, each coil of the transformer represents a primary or secondary winding, as explained above. For example, if the transformer200ofFIG.2is employed, the coil104may represent a primary winding P1electrically coupled to the input circuit1406of the subconverter1402, the coil204may represent a secondary winding S1electrically coupled to the output circuit1410of the subconverter1402, the coil106may represent a primary winding P2electrically coupled to the input circuit1408of the subconverter1404, the coil206may represent a secondary winding S2electrically coupled to the output circuit1412of the subconverter1404.

In other examples, the transformers disclosed herein may be employed in other suitable multiphase power converters. For example, any one of the transformers may be used in a multiphase power converter having a bridge converter topology (e.g., a half-bridge converter topology, a full-bridge converter topology, etc.). In such examples, the transformer may assist in zero voltage switching (ZVS) of power switches in the multiphase power converter by allowing magnetic flux to inductively couple between subconverters and portions of the transformer's magnetic core (as explained herein). In contrast, conventional multiphase power converters typical achieve ZVS by using on large circulating currents (e.g., a resonant current in a phase-shifted bridge, a captured magnetizing current resonating with a parasitic capacitance, etc.).

FIG.15illustrates a two-phase interleaved bridge converter1500including two subconverters1502,1504, and any one of the transformers disclosed herein for the subconverters1502,1504. In the example ofFIG.15, each subconverter1502,1504includes a half-bridge converter topology. As shown inFIG.15, the subconverter1502includes an input circuit1506having two power switches Q1, Q2and two capacitors C1, C2, and an output circuit1510having a rectification circuit (e.g., a diode rectification circuit as shown inFIG.14, etc.). Likewise, the subconverter1504includes an input circuit1508having two power switches Q3, Q4and two capacitors C3, C4, and an output circuit1512having a rectification circuit.

In the example ofFIG.15, each coil of the transformer represents a primary or secondary winding, as explained above. For example, if the transformer200ofFIG.2is employed, the coils104,106may represent primary windings P1, P2electrically coupled to the input circuits1506,1508, respectively. Additionally, the coils204,206may represent secondary windings S1, S2electrically coupled to the output circuits1510,1512, respectively.

The multiphase power converter transformers disclosed herein may have multiple advantages over conventional multiphase power converter transformers. For example, the transformers disclosed herein may have a larger effective core area (while maintaining the same volume), a smaller volume (while maintaining the effective core area), etc. as compared to conventional transformers. In some examples, the effective core area may be over 30% larger and/or the volume may be over 30% smaller than the effective core area and/or volume of conventional transformers. For example, in some embodiments, the effective core area of the transformer's magnetic structure (e.g., the magnetic structure ofFIGS.4and5) may be 260 mm2, and the effective core area of a conventional magnetic structure having an EIE configuration may be 195 mm2. This results in reduced switching frequencies (e.g., slower switching) for power switches in the multiphase power converter, reduced coil turns, reduced core losses, reduced switching losses, increased holdup times (e.g., due to leakage inductance effects, etc.), higher power density, and higher efficiency (e.g., above 95%, etc) as compared to multiphase power converter with conventional transformers.

Additionally, the transformers may include less core sections (e.g., outer legs, etc.) than conventional separated transformers. As a result, some inductive (e.g., magnetic) coupling may occur in the subject transformers. This coupling may remove resonance in the multiphase power converter after the reset period, and in turn reduce core loss. In some cases, the inductive coupling may drive the magnetic flux into the third quadrant (e.g., as shown inFIG.13). This may result in lower reset times as compared to conventional transformers.

Further, the transformers may experience peak-to-peak magnetic flux cancellation in at least some of the core sections. In such examples, the transformers may have reduced core losses in the core sections experiencing magnetic flux cancellation.