# Patent

## Title
Multiple-input soft-switching power converters

## Abstract

A multiple-input power converter transferring energy from multiple input sources to a load comprises a plurality of voltage inputs. The power converter implements soft-switching techniques thereby reducing the converter switching losses and increasing the converter efficiency while using fewer components than presently designed multiple-input power converters. Such a power converter may include multiple input sources, where serially connected switches are coupled to one of the multiple input sources in an input leg. A voltage blocking capacitor is inserted between these input legs. Furthermore, the power converter includes a transformer for isolating the load from the multiple input sources, where the voltage blocking capacitor is connected to the primary winding of the transformer.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is related to the following commonly owned co-pending U.S. patent application:

    
    
        Provisional Application Ser. No. 61/665,999, “Multiple Input Soft-Switching Power Converters,” filed Jun. 29, 2012, and claims the benefit of its earlier filing date under 35 U.S.C. §119(e).
    
    




TECHNICAL FIELD
The present invention relates generally to electrical power conversion, and more particularly to multiple-input power converters implementing soft-switching techniques thereby reducing the converter switching losses and increasing the converter efficiency while using fewer components than presently designed multiple-input power converters.
BACKGROUND
Most electrical systems are supplied by one kind of energy source, e.g., batteries, wind energy, solar energy, or utility energy. Certain special cases are supplied by two sources, such as uninterruptible power supplies. Electrical systems would beneficially be supplied by energy sources of all kinds. Renewable sources are of particular interest, as resources are further distributed about the terrestrial power grid. In islanded power systems, interfacing of multiple sources allows for improved reliability, flexibility, and use of preferred energy sources. The different sources, such as photovoltaic cells, fuel cells, and batteries, generally have different voltage and current characteristics. In some cases, one source is preferential to others; in other cases, a simultaneous combination of sources is appropriate for energy or resource use. Typically, each different source requires a different power converter. As a result, a single-input power converter may be utilized for converting the energy of a particular power source. However, a system with multiple single-input power converters can become complex with a large number of energy sources. As a result, multiple-input power converters may be used to convert energy from multiple energy sources. By integrating all the energy sources through a single conversion device, the structure is simplified resulting in a low cost, unified control and compact system.
Multiple-input power converters can be divided into the following categories: time-sharing multiple-input power converters, multiple-input power converters with pulsating current source cells; multiple-input power converters with pulsating voltage source cells; multiple-input power converters with alternative pulsating current source cells; multiple-input power converters with alternative pulsating voltage source cells; multiple-winding magnetic coupled multiple-input power converters; and multiple-input direct-connected push-pull power converters. Unfortunately, energy conversion using such multiple-input power converters either involves the utilization of a significant number of components or limited voltage conversion ratios which result in significant switching losses, a reduction in converter efficiency, and a limit in the scope of multiple-input power converter applications.
BRIEF SUMMARY
In one embodiment of the present invention, a multiple-input power converter transferring energy from multiple input sources to a load comprises a plurality of voltage inputs. The power converter further comprises a first plurality of serially connected switches coupled to a first voltage input of the plurality of voltage inputs in a first input leg. The power converter additionally comprises a second plurality of serially connected switches coupled to a second voltage input of the plurality of voltage inputs in a second input leg. Furthermore, the power converter comprises a first capacitor inserted between the first input leg and the second input leg. Additionally, the power converter comprises a load. In addition, the power converter comprises a transformer isolating the load from the plurality of voltage inputs, where the first capacitor is coupled to a primary winding of the transformer.
In another embodiment of the present invention, a multiple-input power converter transferring energy from multiple input sources to a load comprises a plurality of voltage inputs. The power converter further comprises a first inductor coupled to a first voltage input of the plurality of voltage inputs in a first input leg. The power converter additionally comprises a second inductor coupled to a second voltage input of the plurality of voltage inputs in a second input leg. Furthermore, the power converter comprises a first capacitor inserted between the first input leg and the second input leg. Additionally, the power converter comprises a load. In addition, the power converter comprises a transformer isolating the load from the plurality of voltage inputs, where the capacitor is coupled to a primary winding of the transformer.
The foregoing has outlined rather generally the features and technical advantages of one or more embodiments of the present invention in order that the detailed description of the present invention that follows may be better understood. Additional features and advantages of the present invention will be described hereinafter which may form the subject of the claims of the present invention.



BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
A better understanding of the present invention can be obtained when the following detailed description is considered in conjunction with the following drawings, in which:
FIG. 1 illustrates a first type of a dual-input phase-shift full-bridge power converter in accordance with an embodiment of the present invention;
FIGS. 2A-2F illustrate the six states for the continuous current mode operations of the first type of the dual-input phase-shift full-bridge power converter in accordance with an embodiment of the present invention;
FIG. 3 illustrates the key waveforms during the six states of the first type of the dual-input phase-shift full-bridge power converter in accordance with an embodiment of the present invention;
FIG. 4 illustrates the equivalent resonant circuit during the dead time of the first type of the dual-input phase-shift full-bridge power converter in accordance with an embodiment of the present invention;
FIG. 5 illustrates a second type of a dual-input phase-shift full-bridge power converter in accordance with an embodiment of the present invention;
FIG. 6 illustrates a third type of a dual-input phase-shift full-bridge power converter in accordance with an embodiment of the present invention;
FIG. 7 illustrates a first type of a multiple-input phase-shift full-bridge power converter in accordance with an embodiment of the present invention;
FIG. 8 illustrates a second type of a multiple-input phase-shift full-bridge power converter in accordance with an embodiment of the present invention;
FIG. 9 illustrates a third type of a multiple-input phase-shift full-bridge power converter in accordance with an embodiment of the present invention;
FIG. 10 illustrates a first type of a dual-input parallel resonant power converter in accordance with an embodiment of the present invention;
FIG. 11 illustrates a second type of a dual-input parallel resonant power converter in accordance with an embodiment of the present invention;
FIG. 12 illustrates a third type of a dual-input parallel resonant power converter type in accordance with an embodiment of the present invention;
FIG. 13 illustrates a multiple-winding magnetic coupled multiple-input phase-shift full-bridge power converter in accordance with an embodiment of the present invention;
FIG. 14 illustrates a first type of a dual-input series resonant power converter in accordance with an embodiment of the present invention;
FIG. 15 illustrates a second type of a dual-input series resonant power converter in accordance with an embodiment of the present invention; and
FIG. 16 illustrates a third type of a dual-input series resonant power converter in accordance with an embodiment of the present invention.



DETAILED DESCRIPTION
In the following description, numerous specific details are set forth to provide a thorough understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention may be practiced without such specific details. In other instances, well-known circuits have been shown in block diagram form in order not to obscure the present invention in unnecessary detail. For the most part, details considering timing considerations and the like have been omitted inasmuch as such details are not necessary to obtain a complete understanding of the present invention and are within the skills of persons of ordinary skill in the relevant art.
As stated in the Background section, multiple-input power converters can be divided into the following categories: time-sharing multiple-input power converters, multiple-input power converters with pulsating current source cells; multiple-input power converters with pulsating voltage source cells; multiple-input power converters with alternative pulsating current source cells; multiple-input power converters with alternative pulsating voltage source cells; multiple-winding magnetic coupled multiple-input power converters; and multiple-input direct-connected push-pull power converters. Unfortunately, energy conversion using such multiple-input power converters either involves the utilization of a significant number of components or limited voltage conversion ratios which result in significant switching losses, a reduction in converter efficiency, and a limit in the scope of multiple-input power converter applications.
The principles of the present invention provide a means for implementing soft-switching techniques thereby reducing the converter switching losses and increasing the converter efficiency while using fewer components than presently designed multiple-input power converters as discussed below in connection with FIGS. 1, 2A-2F and 3-16.
FIG. 1 illustrates a first type of a dual-input phase-shift full-bridge power converter. FIGS. 2A-2F illustrate the six states for the continuous current mode operations of the first type of the dual-input phase-shift full-bridge power converter. FIG. 3 illustrates the key waveforms during the six states of the first type of the dual-input phase-shift full-bridge power converter. FIG. 4 illustrates the equivalent resonant circuit during the dead time of the first type of the dual-input phase-shift full-bridge power converter. FIG. 5 illustrates a second type of a dual-input phase-shift full-bridge power converter. FIG. 6 illustrates a third type of a dual-input phase-shift full-bridge power converter. FIG. 7 illustrates a first type of a multiple-input phase-shift full-bridge power converter. FIG. 8 illustrates a second type of a multiple-input phase-shift full-bridge power converter. FIG. 9 illustrates a third type of a multiple-input phase-shift full-bridge power converter. FIG. 10 illustrates a first type of a dual-input parallel resonant power converter. FIG. 11 illustrates a second type of a dual-input parallel resonant power converter. FIG. 12 illustrates a third type of a dual-input parallel resonant power converter type. FIG. 13 illustrates a multiple-winding magnetic coupled multiple-input phase-shift full-bridge power converter. FIG. 14 illustrates a first type of a dual-input series resonant power converter. FIG. 15 illustrates a second type of a dual-input series resonant power converter. FIG. 16 illustrates a third type of a dual-input series resonant power converter.
As stated above, FIG. 1 illustrates a first type of a dual-input phase-shift full-bridge power converter 100 in accordance with an embodiment of the present invention.
Referring to FIG. 1, converter 100 includes a Direct Current (“DC”) voltage blocking capacitor Cb inserted between the input legs (legs of inputs Vin1 and Vin2). With this blocking capacity Cb, the duty cycle of the input switches on each leg are not necessary symmetric in order to maintain the voltage balance of the magnetizing inductor Lm. Each input voltage (Vin1 and Vin2) is connected to a high level switch (S1H and S2H, respectively) and a low level switch (S1L and S2L, respectively) where node “a” is connected to blocking capacity Cb which is serially connected to leakage inductor Lr, which is coupled in series to the parallel connected magnetizing inductor Lm and primary winding NP1 of the transformer T1. Switches S1H and S1L are connected serially. Similarly, switches S2H and S2L are connected serially. Furthermore, a terminal end of magnetizing inductor Lm is connected to node “b.” In one embodiment, the transformer magnetizing inductor Lm is much greater than the leakage inductor Lr at the corresponding winding. In one embodiment, the DC voltage blocking capacitor Cb is much greater than the capacitance of MOSFET parasitic capacitors Cp.
Converter 100 further includes a load (identified as “Load” in FIG. 1) coupled in parallel to the output capacitor Cout, which is in series to the output inductor Lout. The inductor Lout is connected in series to diodes D01 and D02 which are coupled to the secondary windings NS1 and NS2, respectively, of transformer T1.
A pulsating voltage is applied to the corresponding input transformer or coupled-inductor winding of an isolated converter. In general, the pulsating voltage can be generated either by a single pulsating voltage or by two different pulsating voltages as shown in FIG. 1. The voltage at the transformer input winding of converter 100 is the differential voltage of the two pulsating voltages. In an input cell of converter 100, a DC voltage source is connected to the two switching legs to generate a pulsating voltage on the transformer input winding. However, additional control factors other than the phase differences are required for input cells to ensure the energy flows are all controllable, for example, a variable duty cycle. Yet, a variable duty cycle might cause a voltage unbalance on the magnetizing inductance of transformer T1. To avoid the possible voltage unbalance, DC voltage blocking capacitor Cb is inserted in series with the two pulsating voltages and transformer T1.
Furthermore, transformer T1 isolates the load from the sources thereby increasing the safety of converter 100 and providing a wider range of source-to-load voltage transfer ratios. The characteristic can be examined through the topology operational analysis. For example, the continuous current mode (CCM) operations of the first type of a dual-input phase-shift full-bridge power converter 100 can be divided into six states, shown in FIGS. 2A-2F, respectively, for deriving its sources-to-load voltage transfer ratio in accordance with an embodiment of the present invention.
Referring to FIGS. 2A-2F, the operational analysis of converter 100 is performed under the condition of Vin1>Vin2. Under such a condition, there are the following six different states:
State 1 (t0<t<t1) shown in FIG. 2A: In this state, input inductors, Lm and Lr, are energized by Vin1, hence, Vpri has a positive voltage. Therefore, the input energy is transferred from transformer winding NP1 to winding NS1 and then through D01 to Lout, Cout and the load.
State 2 (t1<t<t2) shown in FIG. 2B: In this state, both S1H and S2H are turned on in this state, therefore, iLr flows through both input sources, which implies that in this state the energy in one input source is transferred to the load and the other input source.
State 3 (t2<t<t3) shown in FIG. 2C: In this state, S2H and S1L are turned on and the voltage polarity of the input inductors becomes negative, which means that the leakage inductor current iLr decreases in this state and would eventually reverse its direction. However, the inductance, Lr, limits the changing rate of iLr. Thus, Lr sustains all the voltage Vin2+VCb, whereas, Vpri is zero in this state. That is, the input energy in this state does not transfer to the load side. Hence, a duty cycle loss (DL1) may be defined as (t3−t2)/T, where T is a period of time. In the meantime, the output diode current iD01 decreases and the output diode current iD02 increases.
State 4 (t3<t<t4) shown in FIG. 2D: State 4 begins when iD01 decreases to zero and Vpri becomes negative. In State 4, energy starts to be transferred from the inputs side to the output side through transformer winding NP1 to NS2 and then to D02.
State 5 (t4<t<t5) shown in FIG. 2E: In this state, no source is applied to the input energy storage components and the energy stored in Cb is continuously discharged.
State 6 (t5<t<t6) shown in FIG. 2F: In this state, a loop from Vin1, Cb and transformer T1 to ground is formed. Similar to state 3, an opposite polarity is applied to the input inductors voltage and Vpri is zero. A duty cycle loss (DL2) may be defined as (t6−t5)/T, where T is a period of time.
The dynamic equations of the capacitors remain the same in the six states:




  
    
      
        
          
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It is noted that the average current of input winding, ipri, is zero in states 3 and 6, which means that the energy at the input side does not transfer to the output side in these states.
The related key waveforms for deriving the sources-to-load voltage transfer ratio (shown in FIGS. 2A-2F) are shown in FIG. 3 in accordance with an embodiment of the present invention with Vin1>Vin2, where DL1 and DL2 are duty cycle losses caused by the leakage inductor Lr and Vs is the voltage at point “s” referring to the middle point of the center tapped transformer winding. Notice that state i is the time interval between ti-1 to ti for i=1, 2, . . . , 6. The sources-to-loads voltage transfer ratio can be represented as (EQ 3):




  
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where ø2=ø1+D2−D1, n=NP1:(NS1=NS2), and VCb=D1Vin1−D2Vin2. The duty cycle losses can be represented as (EQ 4):




  
    
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Moreover, in the topologies of the present invention (FIGS. 1 and 5-16), it is possible to implement soft-switching techniques, which can reduce the converter switching losses and increase the converter efficiency. During the dead times intervals (both switches are turned off in one input leg) of converter 100, a first order LC circuit is formed, shown in FIG. 4 in accordance with an embodiment of the present invention.
Referring to FIG. 4, the first order LC circuit includes a leakage inductor Lr in series with an equivalent resonant capacitor Ceq.
When the following condition is satisfied, soft-switching can be achieved on input switches (EQ 5):

LriLr2(0)≧CeqvCeq2(0)

where Ceq equals to 2Coss (Coss is the parasitic capacitance of input switches); vCeq(0) equals the input voltage, and iLr(0) and vCeq(0) are the initial conditions of Lr and Ceq, respectively. Soft-switching can mitigate some of the mechanisms of switching losses (e.g., losses due to high voltage and high current present in the switch during transitions and losses due to shorting device capacitances) and possibly reduce the generation of EMI. In implementing soft-switching, semiconductor devices are switched on or off at the zero crossing of their voltage or current waveforms thereby eliminating the switching loss caused by IGBT (Insulated-Gate Bipolar Transistor) current tailing and by stray inductances as well as eliminating the switching loss induced by diode stored charge and device output capacitances.
In addition, the topologies of the present invention (FIGS. 1 and 5-16) have lower component numbers when compared to the multiple-input converters that are currently used. In other words, the cost of implementing the topologies of the present invention is less than the cost of implementing the multiple-input converters that are currently used.
Other multiple-input converters implementing the principles of the present invention are discussed below in connection with FIGS. 5-16. Each of the multiple-input soft-switching power converters of FIGS. 5-16 isolates the loads from the sources via a transformer thereby increasing the safety of the system and providing wider ranges of source-to-load voltage transfer ratios as well as implements soft-switching techniques in a manner that reduces the converter switching losses and number of components and increases the converter efficiency. It is noted that previously discussed components will be labeled with the same element numbers in these Figures and will not be reiterated for the sake of brevity.
A second type of a dual-input phase-shift full-bridge power converter 500 implementing the principles of the present invention is shown in FIG. 5 in accordance with an embodiment of the present invention.
Referring to FIG. 5, in comparison to converter 100 of FIG. 1, converter 500 additionally includes serially connected diodes D03 and D04 which are coupled in parallel to serially connected diodes D01 and D02. The anode of diode D01 and the cathode of diode D04 are connected to the secondary winding (NS1) of transformer T1.
A third type of a dual-input phase-shift full-bridge power converter 600 implementing the principles of the present invention is shown in FIG. 6 in accordance with an embodiment of the present invention.
Referring to FIG. 6, in comparison to converter 100 of FIG. 1, converter 600 includes two serially connected output capacitors, C01 and C02, which are in parallel to serially connected output diodes D01 and D02. Converter 600 further includes output inductor L01 in series with output capacitor C01 and output diode D01. Furthermore, converter 600 includes output inductor L02 in series with output capacitor C02 and output diode D02. The anode of diode D01 and a terminal of output capacitor C02 are connected to the secondary winding (NS1) of transformer T1.
A first type of a multiple-input phase-shift full-bridge power converter 700 implementing the principles of the present invention is shown in FIG. 7 in accordance with an embodiment of the present invention.
Referring to FIG. 7, in comparison to converter 100 of FIG. 1, converter 700 includes multiple levels of input voltages, inductors and switches coupled to the output voltage Vdc1. For example, input voltages (Vin1 . . . VinN) are coupled in series to inductors L1 . . . LN, which are coupled in series to switches S1H . . . SNH, where N is a positive integer number. Furthermore, each of the switches S1H . . . SNH is coupled in parallel to switches S1L . . . SNL. Similarly, multiple levels of input voltages, inductors and switches are coupled to the output voltage Vdc2. For example, input voltages (Vinx . . . VinM) are coupled in series to inductors Lx . . . LM, which are coupled in series to switches SxH . . . SMH, where M is a positive integer number. Furthermore, each of the switches SxH . . . SMH is coupled in parallel to switches SxL . . . SML. The terminal of blocking capacity Cb is coupled to inductor LM and switch SMH.
A second type of a multiple-input phase-shift full-bridge power converter 800 implementing the principles of the present invention is shown in FIG. 8 in accordance with an embodiment of the present invention.
Referring to FIG. 8, in comparison to converter 700 of FIG. 7, converter 800 includes the circuitry of converter 500 of FIG. 5 coupled to the secondary windings NS1 of transformer T1.
A third type of a multiple-input phase-shift full-bridge power converter 900 implementing the principles of the present invention is shown in FIG. 9 in accordance with an embodiment of the present invention.
Referring to FIG. 9, in comparison to converter 700 of FIG. 7, converter 900 includes the circuitry of converter 600 of FIG. 6 coupled to the secondary windings NS1 of transformer T1.
A first type of a dual-input parallel resonant power converter 1000 implementing the principles of the present invention is shown in FIG. 10 in accordance with an embodiment of the present invention.
Referring to FIG. 10, in comparison to converter 500 of FIG. 5, converter 1000 includes inductors L1 and L2 which replace switches S1H and S2H. Furthermore, blocking capacity Cb is directly connected to the primary windings NP1 of transformer T1. Additionally, the secondary windings NS1 of transformer T1 are connected to inductor Lm and capacitor Cp in parallel.
A second type of a dual-input parallel resonant power converter 1100 implementing the principles of the present invention is shown in FIG. 11 in accordance with an embodiment of the present invention.
Referring to FIG. 11, in comparison to converter 1000 of FIG. 10, converter 1100 includes a set of serially connected output capacitors, C01 and C02, and a set of serially connected diodes, D01 and D02, where each of these sets of capacitors and diodes is connected in parallel to the load. The anode of diode D01 and the terminal of capacitor C02 are connected to the secondary windings NS1 of transformer T1.
A third type of a dual-input parallel resonant power converter 1200 implementing the principles of the present invention is shown in FIG. 12 in accordance with an embodiment of the present invention.
Referring to FIG. 12, in comparison to converter 1000 of FIG. 10, converter 1200 includes a diode D01 connected in parallel to the load and capacitor Cout. Diode D01 is in series with capacitor Cp1 which is serially connected to capacitor Cp2 which is in series with diode D02 which is in series with diode D01. Furthermore, converter 1200 includes an inductor Lm located in parallel to capacitor Cp1. Inductor Lm and capacitor Cp1 are connected across secondary windings NS1 of transformer T1 and capacitor Cp2 is connected across secondary windings NS2 of transformer T1.
A multiple-winding magnetic coupled multiple-input phase-shift full-bridge power converter 1300 implementing the principles of the present invention is shown in FIG. 13 in accordance with an embodiment of the present invention.
Referring to FIG. 13, converter 1300 includes multiple levels of input voltages, blocking capacitors and switches coupled to the primary wirings of transformer T1. For example, input voltages, Vin1 . . . Vinx, Vin2 . . . Viny, are coupled in series to switches S1H . . . SxH, S2H . . . SyH, respectively, which are connected in series to switches S1L . . . SxL, S2L . . . SyL, respectively, where x and y are positive integer numbers. Furthermore, each level includes a blocking capacitor C12 . . . Cxy coupled to the terminal of switches S1H . . . SxH, respectively, and to the primary windings N12 . . . Nxy of transformer T1. Additionally, converter 1300 includes an output capacitor, Cout, coupled in parallel to the load which is coupled in parallel to serially connected switches, SLa, SLb and SLc, SLd. The terminals of switches SLa and SLd are connected to the secondary windings NL of transformer T1.
A first type of a dual-input series resonant power converter 1400 implementing the principles of the present invention is shown in FIG. 14 in accordance with an embodiment of the present invention.
Referring to FIG. 14, in comparison to converter 500 of FIG. 5, converter 1400 does not include inductor Lout.
A second type of a dual-input series resonant power converter 1500 implementing the principles of the present invention is shown in FIG. 15 in accordance with an embodiment of the present invention.
Referring to FIG. 15, in comparison to converter 600 of FIG. 6, converter 1500 does not include inductors L01 and L02.
A third type of a dual-input series resonant power converter 1600 implementing the principles of the present invention is shown in FIG. 16 in accordance with an embodiment of the present invention.
Referring to FIG. 16, in comparison to converter 100 of FIG. 1, converter 1600 does not include inductor Lout.
The descriptions of the various embodiments of the present invention have been presented for purposes of illustration, but are not intended to be exhaustive or limited to the embodiments disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The terminology used herein was chosen to best explain the principles of the embodiments, the practical application or technical improvement over technologies found in the marketplace, or to enable others of ordinary skill in the art to understand the embodiments disclosed herein.

## Claims

1. A multiple-input power converter transferring energy from multiple input sources to a load, the multiple-input power converter comprising:
a plurality of voltage inputs;
a first plurality of serially connected switches coupled to a first voltage input of said plurality of voltage inputs in a first input leg;
a second plurality of serially connected switches coupled to a second voltage input of said plurality of voltage inputs in a second input leg;
a first capacitor inserted between said first input leg and said second input leg;
a load;
a transformer isolating said load from said plurality of voltage inputs, wherein said first capacitor is coupled to a primary winding of said transformer;
a second capacitor connected in parallel to said load;
a third plurality of serially connected switches connected in parallel to said load; and
a fourth plurality of serially connected switches connected in parallel to said load;
wherein a terminal of a first switch of said third plurality of serially connected switches is connected to a secondary winding of said transformer, wherein a terminal of a first switch of said fourth plurality of serially connected switches is connected to said secondary winding of said transformer.

2. A multiple-input power converter transferring energy from multiple input sources to a load, the multiple-input power converter comprising:
a plurality of voltage inputs;
a first plurality of serially connected switches coupled to a first voltage input of said plurality of voltage inputs in a first input leg;
a second plurality of serially connected switches coupled to a second voltage input of said plurality of voltage inputs in a second input leg;
a first capacitor inserted between said first input leg and said second input leg;
a load;
a transformer isolating said load from said plurality of voltage inputs, wherein said first capacitor is coupled to a primary winding of said transformer;
a leakage inductor coupled in series to said first capacitor, wherein said leakage inductor is connected to said primary winding of said transformer; and
a magnetizing inductor coupled in series with said leakage inductor.

3. The multiple-input power converter as recited in claim 2, wherein said first capacitor is configured to maintain a voltage balance of said magnetizing inductor in response to a duty cycle of said first and second plurality of serially connected switches not being symmetric.

4. The multiple-input power converter as recited in claim 2 further comprising:
a first and a second diode connected to a first and a second secondary windings of said transformer, respectively; and
a second capacitor in parallel with said load and said first and second diodes.

5. The multiple-input power converter as recited in claim 4 further comprising:
a first inductor serially connected to said first diode and to said second capacitor in parallel with said load.

6. The multiple-input power converter as recited in claim 2 further comprising:
a first and a second diode serially connected; and
a third and a fourth diode serially connected;
wherein said first and second diodes are in parallel to said load, wherein said third and fourth diodes are in parallel with said load and in parallel with said first and second diodes.

7. The multiple-input power converter as recited in claim 6 further comprising:
a second capacitor in parallel with said load.

8. The multiple-input power converter as recited in claim 7 further comprising:
a first inductor in series with said second capacitor.

9. A multiple-input power converter transferring energy from multiple input sources to a load, the multiple-input power converter comprising:
a plurality of voltage inputs;
a first plurality of serially connected switches coupled to a first voltage input of said plurality of voltage inputs in a first input leg;
a second plurality of serially connected switches coupled to a second voltage input of said plurality of voltage inputs in a second input leg;
a first capacitor inserted between said first input leg and said second input leg;
a load;
a transformer isolating said load from said plurality of voltage inputs, wherein said first capacitor is coupled to a primary winding of said transformer;
a second and a third capacitor serially connected; and
a first and a second diode serially connected;
wherein said second and third capacitors are in parallel with said load, wherein said first and second diodes are in parallel with said load, wherein a cathode of said first diode is connected to a secondary winding of said transformer, wherein a terminal of said third capacitor is connected to said secondary winding of said transformer.

10. The multiple-input power converter as recited in claim 9 further comprising:
a first inductor connected in series with said second capacitor and said first diode; and
a second inductor connected in series with said third capacitor and said second diode.

11. A multiple-input power converter transferring energy from multiple input sources to a load, the multiple-input power converter comprising:
a plurality of voltage inputs;
a first inductor coupled to a first voltage input of said plurality of voltage inputs in a first input leg;
a second inductor coupled to a second voltage input of said plurality of voltage inputs in a second input leg;

a first capacitor inserted between said first input leg and said second input leg;
a load; and
a transformer isolating said load from said plurality of voltage inputs, wherein said capacitor is coupled to a primary winding of said transformer.

12. The multiple-input power converter as recited in claim 11 further comprising:
a first switch serially connected to said first inductor; and
a second switch serially connected to said second inductor;
wherein a terminal of said first capacitor is connected to a terminal of said first inductor.

13. The multiple-input power converter as recited in claim 11 further comprising:
a second and a third capacitor serially connected; and
a first and a second diode serially connected;
wherein said second and third capacitors are in parallel with said load, wherein said first and second diodes are in parallel with said load, wherein a cathode of said first diode is connected to a secondary winding of said transformer, wherein a terminal of said third capacitor is connected to said secondary winding of said transformer.

14. The multiple-input power converter as recited in claim 13 further comprising:
a magnetizing inductor coupled in parallel to a fourth capacitor, wherein said magnetizing inductor and said fourth capacitor are connected across said secondary winding of said transformer.

15. The multiple-input power converter as recited in claim 11 further comprising:
a second capacitor in parallel with said load;
a third and a fourth capacitor serially connected, wherein said third and fourth capacitors are in parallel with said second capacitor;
a first diode connected in parallel with said second capacitor and said load and connected in series with said third capacitor; and
a second diode in series with said fourth capacitor;
wherein a cathode of said first diode is connected to a first secondary winding of said transformer, wherein a cathode of said second diode is connected to a second secondary winding of said transformer.