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.

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.

DETAILED DESCRIPTION

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 withFIGS. 1, 2A-2F and 3-16.

FIG. 1illustrates a first type of a dual-input phase-shift full-bridge power converter.FIGS. 2A-2Fillustrate the six states for the continuous current mode operations of the first type of the dual-input phase-shift full-bridge power converter.FIG. 3illustrates the key waveforms during the six states of the first type of the dual-input phase-shift full-bridge power converter.FIG. 4illustrates the equivalent resonant circuit during the dead time of the first type of the dual-input phase-shift full-bridge power converter.FIG. 5illustrates a second type of a dual-input phase-shift full-bridge power converter.FIG. 6illustrates a third type of a dual-input phase-shift full-bridge power converter.FIG. 7illustrates a first type of a multiple-input phase-shift full-bridge power converter.FIG. 8illustrates a second type of a multiple-input phase-shift full-bridge power converter.FIG. 9illustrates a third type of a multiple-input phase-shift full-bridge power converter.FIG. 10illustrates a first type of a dual-input parallel resonant power converter.FIG. 11illustrates a second type of a dual-input parallel resonant power converter.FIG. 12illustrates a third type of a dual-input parallel resonant power converter type.FIG. 13illustrates a multiple-winding magnetic coupled multiple-input phase-shift full-bridge power converter.FIG. 14illustrates a first type of a dual-input series resonant power converter.FIG. 15illustrates a second type of a dual-input series resonant power converter.FIG. 16illustrates a third type of a dual-input series resonant power converter.

As stated above,FIG. 1illustrates a first type of a dual-input phase-shift full-bridge power converter100in accordance with an embodiment of the present invention.

Referring toFIG. 1, converter100includes a Direct Current (“DC”) voltage blocking capacitor Cbinserted between the input legs (legs of inputs Vin1and 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 (Vin1and Vin2) is connected to a high level switch (S1Hand S2H, respectively) and a low level switch (S1Land S2L, respectively) where node “a” is connected to blocking capacity Cbwhich is serially connected to leakage inductor Lr, which is coupled in series to the parallel connected magnetizing inductor Lmand primary winding NP1of the transformer T1. Switches S1Hand S1Lare connected serially. Similarly, switches S2Hand S2Lare connected serially. Furthermore, a terminal end of magnetizing inductor Lmis connected to node “b.” In one embodiment, the transformer magnetizing inductor Lmis much greater than the leakage inductor Lrat the corresponding winding. In one embodiment, the DC voltage blocking capacitor Cbis much greater than the capacitance of MOSFET parasitic capacitors Cp.

Converter100further includes a load (identified as “Load” inFIG. 1) coupled in parallel to the output capacitor Cout, which is in series to the output inductor Lout. The inductor Loutis connected in series to diodes D01and D02which are coupled to the secondary windings NS1and 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 inFIG. 1. The voltage at the transformer input winding of converter100is the differential voltage of the two pulsating voltages. In an input cell of converter100, 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 Cbis inserted in series with the two pulsating voltages and transformer T1.

Furthermore, transformer T1isolates the load from the sources thereby increasing the safety of converter100and 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 converter100can be divided into six states, shown inFIGS. 2A-2F, respectively, for deriving its sources-to-load voltage transfer ratio in accordance with an embodiment of the present invention.

Referring toFIGS. 2A-2F, the operational analysis of converter100is performed under the condition of Vin1>Vin2. Under such a condition, there are the following six different states:

State1(t0<t<t1) shown inFIG. 2A: In this state, input inductors, Lmand Lr, are energized by Vin1, hence, Vprihas a positive voltage. Therefore, the input energy is transferred from transformer winding NP1to winding NS1and then through D01to Lout, Coutand the load.

State2(t1<t<t2) shown inFIG. 2B: In this state, both S1Hand S2Hare turned on in this state, therefore, iLrflows 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.

State3(t2<t<t3) shown inFIG. 2C: In this state, S2Hand S1Lare turned on and the voltage polarity of the input inductors becomes negative, which means that the leakage inductor current iLrdecreases in this state and would eventually reverse its direction. However, the inductance, Lr, limits the changing rate of iLr. Thus, Lrsustains all the voltage Vin2+VCb, whereas, Vpriis 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 iD01decreases and the output diode current iD02increases.

State4(t3<t<t4) shown inFIG. 2D: State4begins when iD01decreases to zero and Vpribecomes negative. In State4, energy starts to be transferred from the inputs side to the output side through transformer winding NP1to NS2and then to D02.

State5(t4<t<t5) shown inFIG. 2E: In this state, no source is applied to the input energy storage components and the energy stored in Cbis continuously discharged.

State6(t5<t<t6) shown inFIG. 2F: In this state, a loop from Vin1, Cband transformer T1to ground is formed. Similar to state3, an opposite polarity is applied to the input inductors voltage and Vpriis 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:

It is noted that the average current of input winding, ipri, is zero in states3and6, 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 inFIGS. 2A-2F) are shown inFIG. 3in accordance with an embodiment of the present invention with Vin1>Vin2, where DL1and DL2are duty cycle losses caused by the leakage inductor Lrand Vsis 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-1to tifor i=1, 2, . . . , 6. The sources-to-loads voltage transfer ratio can be represented as (EQ 3):

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

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 converter100, a first order LC circuit is formed, shown inFIG. 4in accordance with an embodiment of the present invention.

Referring toFIG. 4, the first order LC circuit includes a leakage inductor Lrin 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 Ceqequals to 2Coss(Cossis the parasitic capacitance of input switches); vCeq(0) equals the input voltage, and iLr(0) and vCeq(0) are the initial conditions of Lrand 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 withFIGS. 5-16. Each of the multiple-input soft-switching power converters ofFIGS. 5-16isolates 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 converter500implementing the principles of the present invention is shown inFIG. 5in accordance with an embodiment of the present invention.

Referring toFIG. 5, in comparison to converter100ofFIG. 1, converter500additionally includes serially connected diodes D03and D04which are coupled in parallel to serially connected diodes D01and D02. The anode of diode D01and the cathode of diode D04are connected to the secondary winding (NS1) of transformer T1.

A third type of a dual-input phase-shift full-bridge power converter600implementing the principles of the present invention is shown inFIG. 6in accordance with an embodiment of the present invention.

Referring toFIG. 6, in comparison to converter100ofFIG. 1, converter600includes two serially connected output capacitors, C01and C02, which are in parallel to serially connected output diodes D01and D02. Converter600further includes output inductor L01in series with output capacitor C01and output diode D01. Furthermore, converter600includes output inductor L02in series with output capacitor C02and output diode D02. The anode of diode D01and a terminal of output capacitor C02are connected to the secondary winding (NS1) of transformer T1.

A first type of a multiple-input phase-shift full-bridge power converter700implementing the principles of the present invention is shown inFIG. 7in accordance with an embodiment of the present invention.

Referring toFIG. 7, in comparison to converter100ofFIG. 1, converter700includes 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. . . SNHis 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. . . SMHis coupled in parallel to switches SxL. . . SML. The terminal of blocking capacity Cbis coupled to inductor LMand switch SMH.

A second type of a multiple-input phase-shift full-bridge power converter800implementing the principles of the present invention is shown inFIG. 8in accordance with an embodiment of the present invention.

Referring toFIG. 8, in comparison to converter700ofFIG. 7, converter800includes the circuitry of converter500ofFIG. 5coupled to the secondary windings NS1of transformer T1.

A third type of a multiple-input phase-shift full-bridge power converter900implementing the principles of the present invention is shown inFIG. 9in accordance with an embodiment of the present invention.

Referring toFIG. 9, in comparison to converter700ofFIG. 7, converter900includes the circuitry of converter600ofFIG. 6coupled to the secondary windings NS1of transformer T1.

A first type of a dual-input parallel resonant power converter1000implementing the principles of the present invention is shown inFIG. 10in accordance with an embodiment of the present invention.

A second type of a dual-input parallel resonant power converter1100implementing the principles of the present invention is shown inFIG. 11in accordance with an embodiment of the present invention.

Referring toFIG. 11, in comparison to converter1000ofFIG. 10, converter1100includes a set of serially connected output capacitors, C01and C02, and a set of serially connected diodes, D01and D02, where each of these sets of capacitors and diodes is connected in parallel to the load. The anode of diode D01and the terminal of capacitor C02are connected to the secondary windings NS1of transformer T1.

A third type of a dual-input parallel resonant power converter1200implementing the principles of the present invention is shown inFIG. 12in accordance with an embodiment of the present invention.

Referring toFIG. 12, in comparison to converter1000ofFIG. 10, converter1200includes a diode D01connected in parallel to the load and capacitor Cout. Diode D01is in series with capacitor Cp1which is serially connected to capacitor Cp2which is in series with diode D02which is in series with diode D01. Furthermore, converter1200includes an inductor Lmlocated in parallel to capacitor Cp1. Inductor Lmand capacitor Cp1are connected across secondary windings NS1of transformer T1and capacitor Cp2is connected across secondary windings NS2of transformer T1.

A multiple-winding magnetic coupled multiple-input phase-shift full-bridge power converter1300implementing the principles of the present invention is shown inFIG. 13in accordance with an embodiment of the present invention.

Referring toFIG. 13, converter1300includes 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. . . Cxycoupled to the terminal of switches S1H. . . SxH, respectively, and to the primary windings N12. . . Nxyof transformer T1. Additionally, converter1300includes an output capacitor, Cout, coupled in parallel to the load which is coupled in parallel to serially connected switches, SLa, SLband SLc, SLd. The terminals of switches SLaand SLdare connected to the secondary windings NLof transformer T1.

A first type of a dual-input series resonant power converter1400implementing the principles of the present invention is shown inFIG. 14in accordance with an embodiment of the present invention.

A second type of a dual-input series resonant power converter1500implementing the principles of the present invention is shown inFIG. 15in accordance with an embodiment of the present invention.

A third type of a dual-input series resonant power converter1600implementing the principles of the present invention is shown inFIG. 16in accordance with an embodiment of the present invention.