Fractional transformer device

Abstract

A fractional transformer device has a first phase and a second phase. A respective one of the first phase and second phase of the fractional transformer device includes a first primary winding connected in series with a second primary winding. A first secondary winding is connected in parallel with a second secondary winding. A switching device is operatively connected to at least one of the first secondary winding and the second secondary winding. The switching device is configured to short one of first secondary winding or the second secondary winding when there is a drop in input voltage to the fractional transformer device. The fractional transformer device improves hold up time while ensuring high efficiency and high power density. No additional components are required. Based on an LLC topology, and by optimizing the magnetic core structure and power layout, peak efficiency is achieved.

Description

[0001] FRACTIONAL TRANSFORMER DEVICE

[0002] TECHNICAL FIELD

[0003] The aspects of the disclosed embodiments relate generally to power conversion apparatus and more particularly to generally to fractional transformers and more particularly to a fractional transformer with hold up time extension.

[0004] BACKGROUND

[0005] Power supply devices are known to experience voltage drops or even power failures. In a situation where power supply input power is interrupted, it is desirable for the power supply needs to maintain a stable output power for a period of time, so that a downstream device has time to save key information. Because of the information security of the users, the requirements for the hold up time are becoming higher and higher. Generally, when the hold up time of the power supply is increased, the size and cost of the power supply should not be increased at will.

[0006] Typical hold-up time extension solutions add additional components. Among other things, this can result in increased volume and cost. Other solutions may add more switching components or use the diodes to replace MOSFET devices. This can result in increased power loss.

[0007] Thus, there is a need for improved power supply that improves hold up time while ensuring high efficiency and high power density. Accordingly, it would be desirable to provide a device that addresses at least some of the problems described above.

[0008] SUMMARY

[0009] The aspects of the disclosed embodiments are directed to a fractional transformer device or apparatus that improves hold up time while ensuring high efficiency and high power density, without the need for additional components.

[0010] According to a first aspect, the above and further advantages are obtained by a fractional transformer device. In one embodiment, the fractional transformer device has a first phase and a second phase. A respective one of the first phase and second phase of the fractional transformer device includes a first primary winding connected in series with a second primary winding. A first secondary winding is connected in parallel with a second secondary winding. A switching device is operatively connected to at least one of the first secondary winding and the second secondary winding. The switching device is configured to short one of first secondary winding or the second secondary winding when there is a drop in input voltage to the fractional transformer device. The structure of the disclosed embodiments improves the hold up time while ensuring high efficiency and high power density. No additional components are required. Based on an LLC topology, and by optimizing the magnetic core structure and power layout, peak efficiency is achieved and the hold up time is increased.

[0011] In a possible implementation form, the switching device is a synchronous rectification (SR) MOSFET device. The use of MOSFET devices rather than diodes or other switching components results in less power loss and the use of less switching components.

[0012] In a possible implementation form the switching device comprises a first full bridge rectifier comprising four switches and the first secondary winding; a second full bridge rectifier comprising four switches and the second secondary winding; a third full bridge rectifier comprising four switches and the first secondary winding; and a fourth full bridge rectifier comprising four switches and the second secondary winding. The first full bridge rectifier, the second full bridge rectifier, the third full bridge rectifier and the fourth full bridge rectifier are connected in parallel. The fractional transformer device of the disclosed embodiments uses less switching components which results in at least less power loss. In a possible implementation form, a first leg of the first secondary winding is connected between a first up side switch and a first low side switch and a second leg of the first secondary winding is connected between a second up side switch and a second low side switch. When in a hold up state, a group of secondary windings are shorted to change the turns ratio of the transformer and increase the output voltage.

[0013] In a possible implementation form, a first leg of the second secondary winding is connected between a third up side switch and a third low side switch and a second leg of the second secondary winding is connected between a fourth up side switch and a fourth low side switch. When in a hold up state, a group of secondary windings are shorted to change the turns ratio of the transformer and increase the output voltage.

[0014] In a possible implementation form, the switching device, when there is a drop in the input voltage to the fractional transformer device, is configured to short one of the first low side switch and the second low side switch of the first phase and the first low side switch and second low side switch of the second phase; the third low side switch and fourth low side switch of the first phase and the third low side switch and the fourth low side switch of the second phase; the first upside switch and the second upside switch of the first phase and the first upside switch and the second upside switch of the second phase; or the third upside switch and the fourth upside switch of the first phase and the third upside switch and the fourth upside switch of the second phase. When in a hold up state, a group of secondary windings are shorted to change the turns ratio of the transformer and increase the output voltage.

[0015] In a possible implementation form, the fractional transformer device is an E-type core transformer with a first side leg, a second side leg and a center leg. A power coil is wound around respective ones of the first side leg and the second side leg. During normal operation, there is no magnetic flux in the center leg. When in a hold-up state, a group of secondary windings are shorted and the magnetic flux passes through the center leg of the E core. The transformer Lm decreases due to the change of the number of winding turns and the air gap of the center leg. The maximum gain increases.

[0016] In a possible implementation form, magnetic flux passes through the center leg of the E-type core transformer when the switching mechanism shorts one of the first secondary winding or the second secondary winding. During normal operation, there is no magnetic flux in the center leg. When in a hold-up state, a group of secondary windings are shorted and the magnetic flux passes through the center leg of the E core. The transformer Lm decreases due to the change of the number of winding turns and the Ae of the center leg. The maximum gain increases.

[0017] In a possible implementation form, the first phase of the fractional transformer device is disposed across a first circuit board and a second circuit board of the fractional transformer device. The switches of the same phase are distributed on two subboards to achieve a very high efficiency layout. On each sub-board, the ripple is reduced due to the interleaving of the first phase and the second phase, which reduces loss.

[0018] In a possible implementation form, the second phase of the fractional transformer device is disposed across the first circuit board and the second circuit board. The switches of the same phase are distributed on two sub-boards to achieve a very high efficiency layout. On each sub-board, the ripple is reduced due to the interleaving of the first phase and the second phase, which reduces loss.

[0019] According to a second aspect, the above and further advantages are obtained by a method. In one embodiment, when there is a drop in input voltage to a fractional transformer device, a switching frequency of the fractional transformer device is adjusted to a first switching frequency. A secondary winding of the fractional transformer device is shorted and the switching frequency is adjusted to a second switching frequency. When the hold-up scenario is entered, the switching frequency is increased to reduce the gain, and then the secondary-side winding is shorted. The turn ratio changes, increasing the output voltage. In a possible implementation form, the first switching frequency is greater than the switching frequency and the second switching frequency is fractional a gain corresponding to the first switching frequency. When the hold-up scenario is entered, the switching frequency is increased to reduce the gain, and then the secondary-side winding is shorted. The turn ratio changes, increasing the output voltage.

[0020] These and other aspects, implementation forms, and advantages of the exemplary embodiments will become apparent from the embodiments described herein considered in conjunction with the accompanying drawings. It is to be understood, however, that the description and drawings are designed solely for purposes of illustration and not as a definition of the limits of the disclosed invention, for which reference should be made to the appended claims. Additional aspects and advantages of the invention will be set forth in the description that follows, and in part will be obvious from the description, or may be learned by practice of the invention. Moreover, the aspects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.

[0021] BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In the following detailed portion of the present disclosure, the invention will be explained in more detail with reference to the example embodiments shown in the drawings, in which like references indicate like elements and:

[0023] Figure 1 illustrates a schematic diagram of an exemplary fractional transformer device incorporating aspects of the disclosed embodiments;

[0024] Figure 2 illustrates an exemplary method for a fractional transformer device incorporating aspects of the disclosed embodiments;

[0025] Figures 3 A and 3B illustrates a schematic block diagram of aspects of an exemplary fractional transformer device incorporating aspects of the disclosed embodiments;

[0026] Figure 4 illustrates a schematic block diagram of an exemplary fractional transformer device incorporating aspects of the disclosed embodiments; and

[0027] Figure 5 illustrates a schematic block diagram of an exemplary printed circuit board layout for a fractional transformer device incorporating aspects of the disclosed embodiments.

[0028] DETAILED DESCRIPTION OF THE DISCLOSED EMBODIMENTS

[0029] Figure 1 illustrates a schematic diagram of an exemplary fractional transformer device 100 incorporating aspects of the disclosed embodiments. The exemplary fractional transformer device 100 is configured to improve hold up time while ensuring high efficiency and high power density, without the need for additional components. The aspects of the disclosed embodiments can be advantageously implemented in a two-phase Inductor-Inductor-Capacitor (LLC) converter topology optimizing a magnetic core structure and a printed circuit board (PCB) layout.

[0030] Referring to Figure 1, the fractional transformer device 100 of the disclosed embodiments includes a first phase 102 (phase 1) and a second phase 202 (phase 2). For ease of the description herein, the elements and devices of the first phase 102 and the second phase 202 will be collectively referred to.

[0031] In one embodiment, a respective one of the first phase 102 and second phase 202 of the fractional transformer device 100 includes a first primary winding 104, 204 connected in series with a second primary winding 106, 206; a first secondary winding 108, 208 connected in parallel with a second secondary winding 110, 210; and switching devices 112, 212 operatively connected to at least one of the first secondary windings 108, 208 and the second secondary windings 110, 210. The switching devices 112, 212 are configured to short at least one of first secondary windings 108, 208 or the second secondary windings 110, 210 when there is a drop in input voltage to the fractional transformer device 100.

[0032] As is illustrated in the example of Figure 1, the respective switching devices 112, 212 include four parallel connected full bridge rectifiers. This includes, in the first phase 102, full bridge rectifiers 138 and 140, and in the second phase 202 full bridge rectifiers 238 and 240.

[0033] In the example of Figure 1, the first full bridge rectifier 138 has four switches 114, 116, 118, 120 and the first secondary winding 108. The second full bridge rectifier 140 has four switches 122, 124, 126, 128 and the second secondary winding 110. The third full bridge rectifier 238 has four switches 214, 216, 218, 220 and the first secondary winding 208. The fourth full bridge rectifier 240 comprises four switches 222, 224, 226, 228 and the second secondary winding 210.

[0034] As shown in Figure 1, in the first phase 102 and second phase 202, respectively, a first leg 130, 230 of the first secondary winding 108, 208 is connected between the first up side switch 114, 124 and the first low side switch 118, 128. A second leg 132, 232 of the first secondary winding 108, 208 is connected between the second up side switch 116, 126 and the second low side switch 120, 220.

[0035] As also shown in Figure 1 , for the respective phases 102, 202, a first leg 134, 234 of the second secondary winding 110, 210 is connected between a third up side switch 122, 222 and a third low side switch 126, 226. A second leg 136, 236 of the second secondary winding 110, 210 is connected between a fourth up side switch 124, 224 and a fourth low side switch 128, 228.

[0036] When in a holdup state, a group of the secondary windings 108, 208, 110, 210 are shorted to change the turns ratio of the fractional transformer device 100. For example, in one embodiment, shorting a pair of the secondary windings 108, 208, 110, 210 can change the turns ratio from 16 : 1 to 8 : 1.

[0037] Table 1, below, illustrates exemplary switch combinations for shorting the secondary windings of the first phase 102 and the second phase 202, respectively, of the fractional transformer device 100 of the disclosed embodiments. For example, by closing switches 126, 128, the secondary windings 110 of the first phase 102 are shorted. By closing switches 226, 228, the secondary windings 210 of the second phase 202 are shorted.

[0038] TABLE 1 Figure 2 illustrates an exemplary method 200 incorporating aspects of the disclosed embodiments. When the hold-up scenario is entered, the switching frequency is increased to reduce the gain, and then the secondary-side winding is shorted. The turn ratio changes, and the output voltage increases. To ensure that the output voltage is stable, the LLC frequency is switched by one beat to offset the sudden gain change caused by the change of the turn ratio. Finally, the minimum frequency is switched according to the gain curve after the short circuit, and the normal power-off logic is operated

[0039] For example, to start 202, when there is a drop 204 in input voltage to a fractional transformer device, such as the fractional transformer device 100 described with respect to F igure 1 , a hold-up scenario is entered. A switching frequency of the fractional transformer device is adjusted 206 to a first switching frequency X.

[0040] At least one secondary winding of the fractional transformer is shorted 208. As noted above, Table 1 illustrates exemplary combinations of secondary windings that can be shorted 208. The switching frequency of the fractional transformer device can then be adjusted 210 to a second switching frequency Y. In one embodiment, the first switching frequency X is greater than the switching frequency and the second switching frequency Y is fractional of a gain corresponding to the first switching frequency X.

[0041] For example, in one embodiment, the switching frequency can be adjusted to X kHz, where X= 0.5 x 60 kHz + 0.5 x 250 kHz, where the maximum frequency is 250 kHz. Y can be a frequency that is Yi of the gain corresponding to the X frequency.

[0042] Figures 3A and 3B illustrates aspects of an exemplary transformer structure 300 incorporating aspects of the disclosed embodiments. In this example, the transformer structure 300 shown in Figure 3A comprises an E-type core structure with a pair of side legs 302, 304 and a middle leg 306. The power coil can be would around the two side legs 302 and 304. The middle or center leg 306 is only configured to work during a hold up scenario or state.

[0043] The aspects of the disclosed embodiments innovate the magnetic structure design of the fractional transformer. Air gaps 308 are set for the three legs 302, 304, 306 of the E-type core 300 shown in Figure 3A. During normal operation, there is no magnetic flux in the center leg 306, which is similar to the “UI” core. Referring to Figure 3B, in a hold-up state, a group of secondary windings 310 are shorted to change the turn ratio of the transformer.

[0044] Referring to Figure 3B, in the shorted state, the magnetic flux passes through the center leg 306 of the E core structure 300. Magnetic flux does not pass through the leg 310 of the shorted secondary winding. Flux path 312 illustrates the magnetic flux path ofphase 1 or phase 2 in the hold up scenario. The magnetic flux path only flows through the center leg 306 of the fractional transformer device of the disclosed embodiments in the hold-up scenario.

[0045] In the hold up scenario, and the transformer magnetizing inductance (Lm) decreases due to the change of the number of winding turns and the effective cross-sectional area (Ae) of the center leg 306, increasing the maximum gain. The effective cross- sectional area (Ae) of the center leg 306 only needs to ensure that will not saturate in the hold-up state. Therefore, the Ae of the center leg 306 may be relatively reduced, and the extra space used to increase the Ae of side legs 302, 304, so as to obtain higher working efficiency. In addition, to resolve a problem of sharp spikes output due to a sudden turn ratio change, in accordance with the aspects of the disclosed embodiment, in a hold-up scenario, the switching frequency is increased by one beat to reduce the gain.

[0046] Figure 4 illustrates another example of an exemplary structure of a fractional transformer 400 incorporating aspects of the disclosed embodiments. The first phase 402 and the second phase 402 of the fractional transformer 400 are illustrated. For the purposes of the description herein, only the first phase 402 will be discussed in detail as the structure of the second phase 404 is the same. As shown in Figure 4, the first phase 402 includes a first primary winding 406 connected in series with a second primary winding 408. A secondary winding 410 of the first phase 402 is also shown here.

[0047] In a normal, non hold-up scenario, flux paths 412 and 414 illustrate the magnetizing flux paths of the fractional transformer 400. Path 416 illustrates the flux path cancellation.

[0048] Figure 5 illustrates an exemplary printed circuit board (PCB) layout 500 of a fractional transformer device incorporating aspects of the disclosed embodiments. In one embodiment, the switching structure of the same phase is distributed across two subboards, namely First sub-board 502 and Second sub-board 504, also referred to herein as first circuit board 502 and second circuit board 504. In one embodiment, the First sub-board 502 can be positioned above or below the Second sub-board 504, in a stacked PCB structure.

[0049] In the example of Figure 5, the layout 500 of the PCB includes the following:

[0050] 506: LLC Phase 1 on First circuit board 502

[0051] 508: Resonant Inductor

[0052] 510: LLC Phase 2 on Second circuit board 504

[0053] 512: Connection of Transformer Phase 1 with First circuit board 502 and also Second circuit board 504

[0054] 514: Connection of Transformer Phase 2 with First circuit board 502 and also Second circuit board 504

[0055] On each sub-board 502, 504 the ripple is reduced due to the interleaving of phase 1 and phase 2, which reduces loss. In a single phase design process, the ripple current flow path is minimized. The intra-phase shortest current return path and inter-phase ripple cancellation improve efficiency in the full load range. Peak efficiency can reach approximately 98.6%, for example.

[0056] The aspects of the disclosed embodiments extend hold up time without adding any additional components. In some scenarios the hold up time up can be extended to, for example, 15 milliseconds (ms) at 3 Kilowatts (kW) with 820 microfarad (uF) capacitance, or 17.5ms at 2.6kW with 820uF capacitance. The structure of the fractional transformer device of the disclosed embodiments can realize high power density and ultra-high efficiency. For example, the peak efficiency the of DC-DC converter in some scenarios can reach approximately 98.6%.

[0057] The fractional transformer device of the disclosed embodiments does not require additional components. Resonance parameters are not changed during normal operation. Hold up time is extended, while providing high dynamic performance.

[0058] Thus, while there have been shown, described, and pointed out, fundamental novel features of the invention as applied to the exemplary embodiments thereof, it will be understood that various omissions, substitutions and changes in the form and details of devices and methods illustrated, and in their operation, may be made by those skilled in the art without departing from the spirit and scope of the presently disclosed invention. Further, it is expressly intended that all combinations of those elements, which perform substantially the same function in substantially the same way to achieve the same results, are within the scope of the invention. Moreover, it should be recognized that structures and / or elements shown and / or described in connection with any disclosed form or embodiment of the invention may be incorporated in any other disclosed or described or suggested form or embodiment as a general matter of design choice. It is the intention, therefore, to be limited only as indicated by the scope of the claims appended hereto.

Claims

CLAIMSWhat is claimed is:

1. A fractional transformer device (100) comprising a first phase (102) and a second phase (202), wherein a respective one of the first phase (102) and the second phase (202) of the fractional transformer device (100) comprises: a first primary winding (104, 204) connected in series with a second primary winding (106, 206); a first secondary winding (108, 208) connected in parallel with a second secondary winding (110, 210); a switching device (112, 212) operatively connected to at least one of the first secondary winding (108, 208) and the second secondary winding (110, 210), the switching device (112, 212) configured to short one of first secondary winding (108, 208) or the second secondary winding (110, 210) when there is a drop in input voltage to the fractional transformer device (100).

2. The fractional transformer device (100) according to claim 1, wherein the switching device (112, 212) comprises a synchronous rectification (SR) MOSFET device.

3. The fractional transformer device (100) according to any one of claims 1 or 2, wherein the switching device (112, 212) comprises: a first full bridge rectifier (138) comprising four switches (114, 116, 118, 120) and the first secondary winding (108); a second full bridge rectifier (140) comprising four switches (122, 124, 126, 128) and the second secondary winding (110); a third full bridge rectifier (238) comprising four switches (214, 216, 218, 220) and the first secondary winding (208); and a fourth full bridge rectifier (240) comprising four switches (222, 224, 226, 228) and the second secondary winding (210); wherein the first full bridge rectifier (138), the second full bridge rectifier (140), the third full bridge rectifier (238) and the fourth full bridge rectifier (240) are connected in parallel.

4. The fractional transformer device (100) according to claim 3, wherein a first leg (130, 230) of the first secondary winding (108, 208) is connected between a first up side switch (114, 124) and a first low side switch (118, 128) and a second leg (132, 232) of the first secondary winding (108, 208) is connected between a second up side switch (116, 126) and a second low side switch (120, 220).

5. The fractional transformer device (100) according to any one of claims 3 or 4, wherein a first leg (134, 234) of the second secondary winding (110, 210) is connected between a third up side switch (122, 222) and a third low side switch (126, 226) and a second leg (136, 236) of the second secondary winding (110, 210) is connected between a fourth up side switch (124, 224) and a fourth low side switch (128, 228).

6. The fractional transformer device (100) according to any one of claims 3 to 5, wherein the switching device (112, 212), when there is a drop in the input voltage to fractional transformer device (100), is configured to short one of: the first low side switch (118) and the second low side switch (120) of the first phase (102) and the first low side switch (218) and second low side switch (220) of the second phase (202); the third low side switch (126) and fourth low side switch (128) of the first phase (102) and the third low side switch (226) and the fourth low side switch (228) of the second phase; the first upside switch (114) and the second upside switch (116) of the first phase (102) and the first upside switch (214) and the second upside switch (216) of the second phase (202); or7the third upside switch (122) and the fourth upside switch (124) of the first phase (102) and the third upside switch (222) and the fourth upside switch (224) of the second phase (202).

7. The fractional transformer device (100) according to any one of the preceding claims, wherein the fractional transformer device (100) is an E-type core transformer (300) with a first side leg (302), a second side leg (304) and a center leg (306), wherein a power coil is wound around respective ones of the first side leg (302) and the second side leg (304).

8. The fractional transformer device (100) according to claim 7, wherein magnetic flux passes through the center leg (306) of the E-type core transformer (300) when the switching mechanism (112, 212) shorts one of the first secondary winding (108, 208) or the second secondary winding (110, 210).

9. The fractional transformer device (100) according to any one of the preceding claims wherein the first phase (102) of the fractional transformer device (100) is disposed across a first circuit board (502) and a second circuit board (504) of the fractional transformer device (100).

10. The fractional transformer device (100) according to claim 9, wherein the second phase (202) of the fractional transformer device (100) is disposed across the first circuit board (502) and the second circuit board (504).

11. A method (200), when there is a drop (204) in input voltage to a fractional transformer device, comprising: adjusting (206) a switching frequency of the fractional transformer device to a first switching frequency; shorting (208) a secondary winding of the fractional transformer device; and adjusting (210) the switching frequency to a second switching frequency.

12. The method (200) according to claim 11, wherein the first switching frequency is greater than the switching frequency and the second switching frequency is fractional of a gain corresponding to the first switching frequency.8

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