S.Sreevidya, A. Hemashekar / International Journal of Engineering Research and Applications                        (IJERA)...
S.Sreevidya, A. Hemashekar / International Journal of Engineering Research and Applications                        (IJERA)...
S.Sreevidya, A. Hemashekar / International Journal of Engineering Research and Applications                        (IJERA)...
S.Sreevidya, A. Hemashekar / International Journal of Engineering Research and Applications                        (IJERA)...
S.Sreevidya, A. Hemashekar / International Journal of Engineering Research and Applications                        (IJERA)...
S.Sreevidya, A. Hemashekar / International Journal of Engineering Research and Applications                             (I...
S.Sreevidya, A. Hemashekar / International Journal of Engineering Research and Applications                        (IJERA)...
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  1. 1. S.Sreevidya, A. Hemashekar / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue4, July-August 2012, pp.1745-1751Novel Soft-Switching Techniques Using A Full Bridge Topology In Fuel Cell Power Conversion *S.Sreevidya, **A. Hemasekhar, *PG student, SVPCET,PUTTUR, **M.tech.,(ph.D) Associate professor, HOD, SVPCET,PUTTUR,Abstract This paper presents a set of novel soft- Several approaches to realize dc–dc isolated powerswitching techniques to increase the power conversion for FC power sources have been proposedconversion efficiency in fuel cell (FC) systems based on full bridge, push–pull, and current-fedusing a full-bridge topology. For this purpose, a topologies. Some of the key contributions in the areaspecial right-aligned modulation sequence is include the study outlined in the following. A FCdeveloped to minimize conduction losses while power converter based on a controlled voltagemaintaining soft-switching characteristics in the doubler was introduced, which uses phase-shiftMOSFETs. Traditional auxiliary elements in the modulation to control the power flow through theprimary, such as series inductors that are transformer leakage inductance [3]. This interestingimpractical for realizing due to the extreme input topology proved to be less efficient than othercurrent, are avoided and reflected to the output of traditional topologies [4], but presents the advantagethe rectifier to minimize circulating current and of low component count. A FC inverter based on agenerate soft transitions in the output diodes. As a traditional push–pull dc–dc converter was presentedresult, the proposed combined techniques featuring low cost, low component count, and DSPsuccessfully reduce conduction losses, minimize control [5]. For example, maintaining ZVS (full-reverse-recovery losses in the output rectifiers, bridge) is difficult due to the poor voltage regulationminimize transformer ringing, and ensure low of the FC and the wide range of loading conditions,stress in all the switches. The high efficiency is which creates excessive conduction losses due tomaintained in the entire range of loading circulating current in the primary. The push pullconditions (0%–100%) while taking into topology reduces transformer utilization ,consideration remarkable challenges associated compromises magnetizing balance as the powerwith FC power conversion: high input current, rating increases as well as limiting the possibilitieslow voltage and poor regulation, and wide range for soft-switching operation.of loading conditions. A detailed analysis of the Current-fed-based topologies need bulkytechniques for efficiency gains are presented and a input inductors (high current), present oscillationsphase-shift zero-voltage switching topology is produced by the interaction between parasiticsemployed as a reference topology to highlight the (leakage inductance, intra winding capacitance, andmechanisms for performance enhancement and the input inductor), and could present excessivethe advantages in the use of the special degrading high-frequency ripple current in the outputmodulation. capacitors due to the absence of filter inductor. While the trend for high-input-voltage converters (e.g.,I. I NTRODUCTION connected to the line) has been to minimize switching FUEL Cells (FC) are power sources that losses and deal with relatively small line regulation,convert electrochemical energy into electrical energy FC power conversion presents the opposite scenariowith high efficiency, low emissions, and quiet with low input voltage, poor regulation, and veryoperation. A basic proton exchange membrane high input current. Unlike applications with high(PEM) single-cell arrangement is capable of input voltage, achieving ZVS with low voltage doesproducing unregulated voltage below1Vand consists not lead to substantial efficiency gains, given theof two electrodes (anode and cathode) linked by small energy stored in the MOSFETs outputelectrolyte [1]. The output current capability of a capacitance (Coss). The power dissipated in asingle cell depends on the electrode effective area, MOSFET due to the output capacitance during turnand several single cells are connected in series to on is a function of the square of the FC voltage vfc2 .form a FC stack. Due to the mechanical challenges Since FC are low-voltage high-current powerassociated with stacking several single cells, FC are sources, the relative importance of switching lossestypically low-voltage high current power sources and can be outweighed by conduction losses in thecan continuously run while reactant is fed into the MOSFETs that are a function of ifc2 . By taking intosystem [2]. consideration the aforementioned technical challenges, it becomes critical to address the 1745 | P a g e
  2. 2. S.Sreevidya, A. Hemashekar / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue4, July-August 2012, pp.1745-1751following relevant points in FC power conversion: 1) successful design of power conditioning stages. Bothneed for reduction in conductions losses, and thus, PEMFC and direct methanol FC (DMFC) belong tounnecessary circulating current in the primary; 2) this category. The factors that mainly contribute toimpracticality of realizing high-current inductors the output voltage behavior in a DMFC are fuel(costly and bulky) and using series capacitors in the (methanol concentration), fuel flow rate (supplied toprimary (reduced lifetime due to ripple current); 3) the anode), air/oxygen flow rate (supplied to theminimize substantial reverse-recovery losses in the cathode), and operating temperature [1]. As well, theoutput rectifiers (due to the high output voltage); 4) output current is a significant factor that affects theminimize the associated transformer oscillations output voltage and, hence, its output power. To better(ringing); and 5) ensure that the high efficiency, by illustrate this behavior, a set of experiments werecombining points 1) to 5), is maintained under the FC performed with a Nafion115 membrane (Aldrich) in awide input voltage range and 0%–100% loading 5.3-cm2 active area cell fed with 1 mol aqueousconditions. This paper addresses the challenges 1) to MeOH and oxygen at variable flow rates.Fig. 25) by proposing a set of soft-switching techniques in shows a family of polarization curves (voltage versusa full-bridge forward topology. For this purpose, a current) under different operating conditions. Thespecial modulation sequence is developed to figure shows how the output voltage and powerminimize conduction losses while maintaining soft- availability of the FC are modified by the operatingswitching characteristics in the MOSFETs and soft conditions (e.g., operating temperature, oxygen flowtransitions in the output rectifiers. Auxiliary elements rate, and output current using a fixed methanolin the primary, such as series inductors and capacitors concentration). It is interesting to note how the outputthat are impractical to realize due the extreme input voltage of this DMFC is greatly affected by itscurrent are avoided by reflecting them to the operating temperature and output current (fuel andsecondary of the circuit to minimize circulating oxygen flow rates are close to optimal in this case).current and generate soft transitions in the switches. This results in a significant change of the availableThese variations are conceptually depicted in Fig. 1 output power, the area under the polarization curve.indicating three major modifications suited for FC Therefore, in order to obtain a desired output power,power conversion. The proposed combined it is first necessary to modify the operating conditionstechniques have the ability to maintain high to increase the area under the polarization curve (forefficiency in the entire operating range of the FC example, by increasing the operating temperature). It(wide input voltage) and under any loading condition. should be pointed out that the transition from a givenDetailed analysis of the techniques for efficiency polarization curve to another through variation ingains is presented and a phase-shift ZVS topology is operating conditions is very slow.employed as a reference topology to highlight themechanisms for performance enhancement and theadvantages in the use of the special modulation. Fig. 2. Steady-state characteristic of a 5.3-cm2 polymer-electrolyte single FC (DMFC). Polarization curves as a function (mL/min).Fig. 1. Conceptual schematic and gate waveformsillustrating Lzvs inductor reflection to the output of The main reasons for this behavior are thethe rectifier_1, right-aligned gate signals for the high heat capacity of the cell, and the slow massupper switches _2, and +50% duty cycle in the lower transport processes in the flow fields and electrodes.switches _3. However, a fast dynamic response exists when the output current changes for fixed operating condition. As a result of this example, the poor voltageII. FC VOLTAGE REGULATION This section briefly revisits the regulation regulation, high current, and low-voltagecharacteristic of a polymer-electrolyte FC under characteristics are highlighted. The same principledifferent operating conditions, providing the basis for follows for larger electrode areas required to produce 1746 | P a g e
  3. 3. S.Sreevidya, A. Hemashekar / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue4, July-August 2012, pp.1745-1751high currents, and a number of singles cells in series For example, the IRFB4110 has 3.7 mΩ atto conform a FC stack (i.e.,20 V/60 A for a 25◦C and 6 mΩ at 100◦C (typical), resulting in 35-Wcommercial Ballard Nexa PEMFC). conduction losses under 75-A rms at 100◦C. When the switching losses areIII. RIGHT-ALIGNED MODULATION analyzed, the same power device experiences lessAND PRIMARY INDUCTOR than 6.5 W during the turn- ON transition due to itsELIMINATION IN THE FULL-BRIDGE output capacitance Coss when switching at 40 kHzTOPOLOGY with vfc = 22 V as given in the following: This section presents in a sequential andconceptual manner the steps taken to fulfill therequirements toward increasing the efficiency of thefull-bridge forward converter in FC power Therefore, it can be inferred that in thisconversion. A description of the power-loss particular low-voltage high-current application, themechanisms in the input stage is first presented, efficiency gain resulting from reducing circulatingfollowed by the analysis of the output rectifier. Each current in four switches outweighs those of switchingdesign goal is addressed by the combined effects of losses, especially under heavy loading conditions.the proposed soft-switching techniques. When the lower switches are considered, the scenario is even more favorable, as M2 and M4 not onlyA. Full-Bridge Input Stage benefit from lower conduction losses, but also The conduction losses in the MOSFETs due operate in ZVS due to the modification_3 in theto circulating current [design goal (a)] and the high- modulation (+50% duty cycle). In addition, thecurrent bulky inductor in the primary are eliminated reduction in the conduction interval also helps to[goal (b)] by removing the traditional Lzvs inductor reduce copper losses in the transformer windings andin the primary and by forcing a right-aligned favors the use of planar magnetics with their inherentsequence of pulses in the upper switches as illustrated low leakage inductance to increase power transfer.in Fig. 1 (modifications _1 and _2). In order toillustrate the gains of the two changes with a practical B. Output Rectifier Stageexample, Fig. 3 presents the conduction losses of a The output rectifiers contribute to powercommercial MOSFET (IRFB4110) with low RdsON losses due to conduction and reverse recovery. Sinceas a function of duty cycle for the voltage the output voltage of the power converter is high (i.e.,polarization curve of a commercial hydrogen FC 220 V to supply a single-phase inverter), the(Ballard Nexa 1.2 kW). conduction current is typically a few amperes per It can be seen in Fig. 3 that the total kilowatt of output power (i.e., 4.54 A), making theconduction losses under phase-shift ZVS (+ curve reverse-recovery losses the dominant factor. Reverse-that includes circulating current) are considerably recovery charge is a function of the forwardhigher than losses only associated with power conduction current (IF ) and the rate of change oftransferred to the secondary current (di/dt), as well as operating temperature of the device.The reverse-recovery losses can be estimated by using the recovery charge, switching frequency (Fsw ), and reverse applied voltage (VR), including the peak ringing value as followsFig. 3. Conduction losses of a commercial MOSFET(IRFB4110) due to circulating current as a functionof duty cycle for the voltage polarization curve of acommercial FC vfc . Fig. 4. Reverse-recovery losses: conceptual The losses have been calculated using the relationship between rate of change of current di/dt,rms value of the current through switchM1 and the initial forward current IF and reverse-recovery chargeMOSFET ON-resistance RdsON , which is a function Qrr for IF 3 > IF 2 > IF 1 .of the device temperature As a simple review of this combined effects, Fig. 4 shows a conceptual relationship among di/dt, the IF , and Qrr in which the initial forward current is given by IF 3 > IF 2 > IF 1. As indicated in (3) the 1747 | P a g e
  4. 4. S.Sreevidya, A. Hemashekar / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue4, July-August 2012, pp.1745-1751reverse-recovery losses can be reduced by means of producing a Lzvs like effect. Once the primarycontrolling di/dt [design goal (c)] and by reducing the current reaches the current level of the filter inductorreverse peak voltage VR produced by transformer reflected to the primary iL interval T1 ends.oscillations[design goal (d)]. For this purpose, theLzvs inductor is reflected to the secondary and placedat the output of each upper rectifier D5 and D7(modification _3 ). This technique limits the di/dtinthe upper rectifiers, eliminates reverse recovery in thelower diodes D6 and D8 , and reduces significantlythe transformer oscillations by preventing a zero-voltage state at the secondary. As will be seen, thetechnique avoids simultaneous conduction of D5 , D6, D7 , and D8 , thus reducing undesirable ringing thatoccurs when the primary current matches the inductoroutput current, which results in a severe voltage stepin the secondary that creates ringing, and therefore,electromagnetic interference (EMI). In the followingsection, the operation of the full-bridge forward Fig. 5. Switching sequence for MOSFETsM1 ,M2converter and the effect of the proposed ,M3 , andM4 (transitions intervals have beenmodifications for efficiency improvements are exaggerated for clarity).presented in detail over the various switchingintervals. Interval T2 : MOSFETs M1 and M4 are in the ON-state and their current continue to ramp upIV. OPERATION INTERVALS AND LOSS- with slope voltage, auxiliary inductor, and outputREDUCTION EFFECTS filter inductor reflected to the primary. Here, V`o, The combination of the proposed L`a, and L` denote, respectively, the output voltage,techniques, Lzvs inductor reflection to the output of auxiliary inductor, and output filter inductor reflectedthe rectifier (1), right-aligned gate signals for the to the primary. Interval T3 : Begins when gateupper switches (2), and +50% duty cycle in the lower signal G1 drops causing M1 to turn off and D2 toswitches (3) are investigated in detail in this section. start conduction. This interval is a shortFig. 5 shows the switching sequence for MOSFETs blanking/dead time betweenM1 andM2 , and finishesM1 , M2 , M3 , andM4 along with the main when the gate signal G2 rises. The behavior ofM2waveforms for the techniques under study. Transition and D2 is the same as M4 and D4 in the nextintervals have been exaggerated for clarity. The switching cycle. Interval T4 : M2 turns on withstructures acquired by the power converter during the ZVS, given that D2 was forward-biased during T3 .switching intervals are depicted in Fig. 6. The This interval is also brief and extending G4 slightlyswitching sequence results in 12 different intervals beyond 50% is to ensure ZVS on both lowerT1–T12, which are used to explain the behavior of switches. Interval T5 : The energy stored in thethe converter. In order to examine various efficiency- leakage inductance Llk is returned to the dc-busgain mechanisms, a detailed analysis of the current capacitors through D3 body diode. Since theand voltage waveform is presented for the upper and traditional Lzvs has been reflected to the secondary,lower MOSFETs, followed by the upper and lower the inductance in the primary Llk can be dramaticallyoutput rectifiers. minimized by using a planar transformer. The transformer primary current ip is, therefore, reset toA .Detailed Analysis of the MOSFETs Operation zero during this short interval. The waveforms for MOSFETs M1 and M4 Interval T6 : The circulating current in the primary isand their respective body diodes D1 and D4 are eliminated, translating into tangible efficiency gainsshown in Fig. 7 during a full-cycle period, including given the high input current that is characteristic inthe gate signals G1 and G4, drain to- source voltages FC power conversion. The remaining intervals T7–vM1 and vM4 , currents for the MOSFETs n-channel T12 repeats the same behavior for M2 and M3 andiM1 and iM4 , and the body diodesiD1andiD4. their corresponding body diodes D2 and D3 .Interval T1 : The right-aligned modulation, whichensures no circulating current in the primary, starts B. Output Rectifier Operationwith interval T1. The upperMOSFETM1 turns on In order to complete the analysis of thewith zero-current switching (ZCS), and the current waveforms and efficiency gains, the output rectifierpath is through M4 that is already in the ON state. An should be investigated. The current and voltageinteresting effect in the primary current rate of waveforms for D7 (upper) and D8 (lower) diodes arechange di/dt can be identified during the T1 interval, presented in Fig. 8, where both conduction losses andwhich is inherently limited by the action of the reverse-recovery instants can be identifiedinductors La and Llk reflected to the primary, 1748 | P a g e
  5. 5. S.Sreevidya, A. Hemashekar / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue4, July-August 2012, pp.1745-1751Fig. 6. Power-converter structures for intervals T1 –T12 .. Interval T1 : The current in diode D7 1) The auxiliary inductors La and Lb shape theinitiates the recovery process and di/dt is limited by current waveforms of D5 and D7 during reverseLb , like in phase-shift ZVS. However, due to the recovery. Therefore, the inductor values can beinterleaving action of La and Lb , only three diodes selected to achieve a desired Qrr in the upper diodesare forward-biased (rather than four), preventing a and, hence, control the total reverse recovery powerzero-state in the transformer secondary. Recall that losses.in traditional full-bridge converters, all four diodes 2) DiodesD6 andD8 experience negligible reverse-are in conduction in the absence of a pulse in the recovery losses, unlike the phase-shift ZVS topology,primary. This modification will lead to reduced which is explained by near-zero forward currentringing during T2 . when the reduced reverse voltage is applied. Interval T2 : The interval T2 begins once D5 3) The presence of La and Lb reduce oscillations andreaches the current level of the filter inductor. Diode the peak reverse voltage applied to D6 and D8 thatD7 recovers with a soft transitions due to the results from transformer ringing. Transformermoderate di/dt and also experiences a reduced oscillation results in undesirable effect, such as highblocking voltage in the presence of low transformer maximum reverse voltage rating for the diodes, EMI,ringing, both helping to reduce reverse-recovery over voltage between windings, and power losses inlosses. This can be explained due to the fact that the auxiliary snubber circuits. The concept of avoiding azero voltage condition in the secondary of the zero-voltage condition on the transformer secondarytransformer is eliminated with the interleaving action is addressed by preventing simultaneous conductionof La and Lb , thus preventing an abrupt voltage step of D5 , D6 , D7 , and D8 . As a result, the turn-ONin the transformer secondary that excites the pulse is partially reflected to the secondary of theparasitics that cause self-resonance (leakage transformer as if the converter were operating ininductance, intra-/inter windings). While traditional discontinuous conduction mode. Hence, thefull-bridge ZVS requires a snubber to limit the oscillations are reduced under any loading condition.ringing, the proposed technique eliminates the These combined improvements increase thesnubber while reducing the overall reverse-recovery efficiency of the rectifier stage in addition to thelosses in the upper diodes. efficiency gains of the MOSFET. The behavior of theInterval T3: defines the conduction interval of D7. converter highlights the advantages of the proposedIntervals T4–T5 : Initiates the reverse recovery in D8 techniques in full-bridge topology for FC power. conversion Interval T6 : The recovery of D8 does not .experience reverse voltage due to the interleaving C. Frequency Response and Dynamic Behavioreffect of La and Lb Therefore, the transition has The frequency response of the control-to-outputnegligible losses. This effect leads to substantial characteristic of the full-bridge topology, which is aefficiency gains in the lower diodes D6 and D8 . For buck-derived topology, is dominated by the transferthe proposed soft-switching techniques reveal the function of the output filter (L and C). When thefollowing improvements. converter is operated in phase-shift ZVS, a series inductance is required to limit the current rate of 1749 | P a g e
  6. 6. S.Sreevidya, A. Hemashekar / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue4, July-August 2012, pp.1745-1751change in the primary to generate soft transitions in VI. Simulation Resultsthe switches. This limitation, reduces the effective In order to improve the efficiency in fullduty cycle reflected to the secondary, therefore, bridge fuel cell power conversion by using softaffecting the control-to-output characteristic. In switching techniques, the system has been simulated.closed-loop operation using traditional compensation The converter was built using the parameters and(small signal), the artificial dumping does not have parts in Table I, and a phase-shift ZVS topology wasany noticeable effect in phase and gain margins. A employed as a reference topology. For the ZVSsimilar behavior is experienced when the proposed operation, the inductor Lzvt was included and La andtechniques are employed using traditional Lb were removed.compensators, therefore, showing a dynamic On the other hand, the proposedresponse similar to that of a phase-shift ZVS. modifications were tested using La and Lb and In this study, in order to facilitate the removing Lzvt . The practical implementation of theefficiency evaluation process, multiple measurements converter follows current trends by using DSPwere performed with a closed loop controller (small- control and modulation , in particular to simplify thesignal) in steady-state operation. The controller was task of generating the right-aligned modulation. Asrealized with an inner current loop (inductor current) well, as part of the requirements to realize theand an outer voltage loop. Both control loops and the proposed techniques, the drivers of the uppermodified modulation were implemented digitally MOSFETs was arranged to produce actual pulseusing TMS320F2808 fixed-point DSP. Validation of width modulation, rather than the fixed 50% dutythe waveforms and comparative efficiency cycle employed in the phase-shift ZVS counterpart.measurements are presented in the following section. Operation of proposed circuit is described inV Conventional Circuit figures as follows. In this case input voltage is The conventional circuit for efficiency gains 24volts. Fig 8(a) shows the input voltage of proposedin full-bridge fuel cell power conversion is shown in circuit and fig 8(b) shows the switching pulse andfigure7 below. A fixed DC is converted into AC by drain-source voltage. Pulse width is made equal toinverter. It is boosted by using a high frequency soft switching time to ensure zero voltage switching.transformer then this boosted ac voltage is passed Fig.9(a) shows the output voltage and Fig.9(b) showsthrough a rectifier to convert it as DC voltage. the output current. The dc motor output voltageMOSFETS will have high switching speed and initially increases linearly and becomes constant.frequency.N-Channel MOSFETs will have 3xtimes The Dc output voltage and output current will havehigh switching speed compared to than that of P- less ripples. Fig.10(a) shows the dc motor speed inchannel. Faster switching speeds can be obtained rpm and Fig.10(b) shows the dc motor torque in N-m.with well-designed gate driver circuits. TO charge The dc motor speed increases linearly then becomesthe gate capacitance at turn ON large current (1-2A) constant and also torque decreases slightly andis required also switching times will be small. becomes constant. (a) Fig 7. Circuit Diagram for conventional circuit Due to gate leakage current, Nano-amps areneeded to maintain the gate voltage once the device isON. A negative voltage is often applied at turn OFFto discharge the gate for speedy switch OFF.Theswitching pulses given to M3 and M4 are similar tothat of M1&M2. The dc output voltage and currentwill have ripples because of the convertor circuit hadused a half wave rectifier. In order to reduce theripples will go for a proposed circuit with full waverectifier. (b) 1750 | P a g e
  7. 7. S.Sreevidya, A. Hemashekar / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue4, July-August 2012, pp.1745-1751Fig8. (a) Input voltage (b) Switching pulse and impractical high-current inductors in the primary; 3)Drain-Source voltage (Vds) reduction of reverse-recovery losses in the output rectifiers; 4) minimization of transformer oscillations (ringing); and 5) improved efficiency under the FC wide input voltage range and 0%–100% loading conditions. As anticipated by the analysis, by taking advantage of the opportunities for performance enhancements, considerable efficiency gains were observed in the entire range of operation of the system while maintaining the simplicity and ruggedness of the full-bridge topology. (a) REFERENCES [1] M. Nymand and M. A. E. Andersen, “High- efficiency isolated boost DC-DC converter for high-power low-voltage fuel-cell applications,” IEEE Trans. Ind. Electron., vol. 57, no. 2, pp. 505–514, Feb. 2010. [2] M. Ordonez, P. Pickup, J. E. Quaicoe, and M. T. Iqbal, “Electrical dynamic response of a direct methanol fuel cell,” IEEE Power (b) Electron. Soc. Newslett., vol. 19, no. 1, pp.Fig9. (a) Output voltage (b) Output current 10–15, Jan. 2007. [3] J. Wang, F. Z. Peng, J. Anderson, A. Joseph, and R. Buffenbarger, “Low cost fuel cell converter system for residential power generation,” IEEE Trans. Power Electron., vol. 19, no. 5, pp. 1315–1322, Sep. 2004. [4] J. Wang, M. Reinhard, F. Z. Peng, and Z. Qian, “Design guideline of the isolated DC- DC converter in green power applications,” in Proc. IEEE Power Electron. Motion Control Conf., 2004, vol. 3, pp. 1756–1761. (a) [5] R. Gopinath, S. Kim, J. Hahn, P. N. Enjeti, M. B. Yeary, and J.W. Howze, “Development of a low cost fuel cell inverter system with DSP control,” IEEE Trans. Power Electron., vol. 19, no. 5, pp. 1256–1262, Sep. 2004. [6] L. Palma [19] J.-M. Kwon and B.-H. Kwon, “High step-up active-clamp converter with (b) input-current doubler and output-voltage Fig .10. DC Motor (a) Speed (b) Torque doubler for fuel cell power systems,” IEEE Trans. Power Electron., vol. 24, no. 1, pp.VII. CONCLUSION 108–115, Jan. 2009. Power Electron., vol. A set of novel soft-switching techniques for 24, no. 6, pp. 1437–1443, Jun. 2009.the full-bridge topology were investigated in this [7] D. G. Holmes, P. Atmur, C. C. Beckett, M.study including the reflection of the traditional Lzvs P. Bull,W. Y. Kong,W. J. Luo, D. K. C. Ng,inductor to the output of the rectifier, right-aligned N. Sachchithananthan, P. W. Su, D. P.modulation for the upper switches, and +50% duty Ware, and P. Wrzos, “An innovative,cycle in the lower switches. The study presented in efficient current-fed push-pull gridthis paper identified the main power-loss mechanism connectable inverter for distributedin full-bridge FC power conversion in the presence of generation systems,” in Proc. IEEE Powerthe poor voltage regulation of polymer-electrolyte FC Electron. Spec. Conf., 2006, pp. 1504–1510.and the wide range of loading conditions. The combined techniques successfullyaddressed the most important power loss effects andissues in FC power conversion: 1) reduction inunnecessary high circulating currents in the primary,and thus, conduction losses; 2) elimination of 1751 | P a g e

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