a novel boost resonant converter for solar … · 2017. 8. 17. · these make the single-panel pv...

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Int. J. Elec&Electr.Eng&Telecoms. 2015 Vidya Y Rao and Pinto Pius A J, 2015

A NOVEL BOOST RESONANT CONVERTER FORSOLAR RENEWABLE ENERGY APPLICATIONS

Vidya Y Rao1* and Pinto Pius A J1

*Corresponding Author: Vidya Y Rao,[email protected]

Photovoltaic power conditioning requires efficient power conversion and maximum power pointtracking to counteract the effects of panel mismatch, shading, and general variance in poweroutput during a daily cycle. An integrated boost resonant converter with low component count,galvanic isolation, as well as high efficiency across a wide input and load range is proposed inthis paper. The proposed circuit is simulated using Matlab/Simulink and the results are obtained.

Keywords: Integrated Boost Resonant (IBR), Isolated dc-dc microconverter, Photovoltaic(PV), LLC resonant converter

INTRODUCTIONThe growth of the electrical energy demandalong with awareness of environmentalimpacts from the continuous utilization offuels has led to the survey of renewableenergy sources as photovoltaic technology.The free and richly available solar energy canbe converted into electrical energy usingphotovoltaic (PV) cells. PV sources have theadvantages of low maintenance cost,absence of moving/ rotating parts, andpollution-free energy conversion process.Their main disadvantages are low energyconversion efficiency, nonlinear v-i and p-icharacteristics. PV voltage variesconsiderably with panel construction andoperating temperature, while the PV current

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1 Department of Electrical and Electronics, St. Joseph Engineering College, Vamanjoor, Mangalore, India.

changes largely due to solar irradiance andshading conditions [1]. In spite of thesedisadvantages, PV systems have becomeone of the most popular substitutes to theconventional energy resources such as waterpumping, refrigeration, air conditioning,electric vehicles as well as, military and spaceapplications.

Power conversion for solar renewableenergy applications, requires a compliantsystem that is adept of responding to a widerange of input voltage and current conditions.The fundamental unit required to connect a PVsystem to utility is the inverter which convertsdc input to an ac output. The utility networkconsists of ac generation transmission anddistribution.

Research Paper

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Since PV panels produce dc current thiscauses some difficulty. To adjust the dc sourceto ac system power conditioning system isrequired. If a converter is designed only forhigh peak efficiency, the range of conditionscommon to many PV installations will force theconverter into another operating region whereit is much less efficient.

More important in the PV PCS designprocess is the need of galvanic isolationbetween the PV panel and the electric utilitysystem. Galvanic isolation is preferred forseveral reasons such as improved voltageboost ratio, reduced ground leakage current,

and overall safety improvement during faultconditions [2].

Block diagrams showing the microinverterand microconverter structures are shown inFigures 1 and 2. PV panels connected inparallel can be more useful than a seriesconnected system [4]-[7] and Maximum PowerPoint Tracking (MPPT) can achieve muchbetter energy harvesting system [3].

These make the single-panel PVmicroinverter (dc–ac), or at least an isolatedmicroconverter (dc–dc), an attractive option.There are different methods proposed formicroconversion [8].

Continuous Conduction Mode (CCM)flyback converter can be used as analternative for the dc-dc conversion stage. Ithas the advantage of simple construction andlow circulating energy. The switching loss forboth the primary switch and the diode can bequite large, and the overall system efficiencyis typically low. Improvements in flybackefficiency can be made using alternatives suchas zero-voltage transition or active clamp.However, this effectively trades switching lossfor circulating energy, reducing efficiency athigh line or low power.

Another option is the series-resonantconverter, and more recently the LLC resonantconverter [9]-[10]. The series resonant or LLCconverter achieves nearly Zero VoltageSwitching (ZVS) and Zero Current Switching(ZCS) with low energy and gives high peakefficiency when the converter is operated nearthe resonant frequency of the tank circuit. Asthe operating frequency diverges from theresonant frequency, the amount of circulatingenergy increases.

Figure 1: Distributed MicroinverterStructure

Figure 2: Distributed MicroconverterStructure

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One more option is using the series-resonant converter as an unregulated dc–dctransformer (DCX). This approach has theadvantage of almost no switching loss, little orno circulating energy, and very high peakefficiency. This concept of using the seriesresonant DCX requires an additional elementto provide regulation capability. The proposedmethod integrates a traditional boostconverter element into the DCX with only theaddition of a single inductor.

CONVERTER SYNTHESISAND OPERATIONBy considering the series resonant DCX asthe series-resonant DCX as part of the newhybrid circuit, it is important to notice the half-wave resonant behaviour. When eitherswitches are on a resonant circuit is formedby a combination of the input-side capacitors,transformer leakage inductance and theoutput-side capacitors. Due to theunidirectional nature of the output diodes onlya resonant period consisting of one half-sinewave is evident and prevents the circuit fromresonating continuously. This period is allowedto complete fully before the primary sideswitches change states. If both resonantperiods are allowed to complete, there is noother method to control the output, and theoutput is simply a reflection of the input. Hencea “regulating element” in this case a boostconverter is added to the circuit as shown inFigure 3. The cost is two additional transistors,with their associated gate drive requirementsand some additional switching and conductionloss.

This circuit is simplified by integrating thesystem so that the boost converter function is

implemented by the original two MOSFETs. Inthis circuit the input inductor is directlyconnected to the midpoints of both activeswitching legs at the same time. This changedirectly connects the inductor to one terminalof the transformer. Thus, the circuit simplifies,with the additional connection and the removalof Qx and QY, into the topology shown in Figure4. Now single upper and lower FETs (Q1 andQ2) are effectively replacing two parallel FETs,they carry the combined current from theoriginal four switches.

Figure 3: Resonant Half-Bridgewith Separate Boost Input Stage

Figure 4: IBR Converter

The new topology can be effectively brokendown into four distinct operating modes.

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Mode 1: At the beginning when Q2 is turnedoff, the current in the input inductor L flows intothe body diode of Q1. This allows Q1 to beturned ON as shown in Figure 5.

D1 prevents the continued resonating in thereverse direction, ending mode 1.

Mode 2: Q1 is still active, yet it is onlyconducting the input inductor current, which isstill decreasing, a pathway which is shown inFigure 6. The resonant elements all conductzero current. Only C5 continues discharging intothe load. Mode 2 ends with the turn-off of Q1

and the subsequent turn on of Q2.

Mode 3: After the turn-off of Q1, but prior theturn-on of Q2, the inductor current is still forcedinto charging the series combination of C1 andC2, through the body diode of Q1, anddecreasing almost linearly. When Q2 is turnedON, the body diode of Q1 is hard-commutated,causing some switching loss. C2 begins toresonate with Lk and the parallel combinationof C3 and C4, through the diode D2.Simultaneously, the inductor current also flowsthrough Q2, increasing linearly as shown inFigure 7 of the transformer current and theinductor current. Thus, the rms current throughQ2 is significantly larger than that of Q1, whichcarries the difference of the two currents. Oncethe transformer current resonates back to zero,D2 blocks the continued oscillation, markingthe end of mode 3.

Figure 5: IBR Converter OperatingMode 1

At this time, the upper input-side capacitorC1 begins resonating with the transformerleakage inductance Lk and the output-sidecapacitors, C3 and C4, through D1.Instantaneously, the input current charges theseries combination of C1 and C2. Q1 carriesthe difference between the transformer current,flowing from C1 through the positive terminalof the transformer and the input current. Oncethe transformer current resonates back to zero,

Figure 6: IBR Converter OperatingMode 2 Figure 7: IBR Converter Operating

Mode 3

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Mode 4: The inductor current continues to flowthrough the lower device, increasing until Q2 isturned OFF as shown in Figure 8 and the circuitreturns to mode 1. Also, during both modes 3and 4, Q1 effectively isolates the uppercapacitor from charging or discharging.

are obtained from the datasheet. Figure 9shows the output voltage obtained from theMatlab simulation.

CONCLUSIONFrom the simulated results it can be seen thatthe proposed circuit works as expected. Thesystem is a hybrid between a traditional CCMboost converter and a series-resonant half-bridge, employing only two active switches.The synthesis of the converter was describedalong with the circuit operating modes. Theproposed topology has the advantage of highefficiency, reduced complexity.

REFERENCES1. Gao L, Dougal R A, Liu S and Iotova A P

(2009), “Parallel-Connected Solar PVSystem to Address Partial and RapidlyFluctuating Shadow Conditions”, IEEETrans. Ind. Electron., Vol. 56, No. 5,pp. 1548-1556.

2. Gules R, De Pellegrin Pacheco J, Hey HL and Imhoff J (2008), “A Maximum PowerPoint Tracking System with ParallelConnection for PV Stand-AloneApplications”, IEEE Trans. Ind. Electron.,Vol. 55, No. 7, pp. 2674-2683.

3. Lazar J F and Martinelli R (2001), “Steady-State Analysis of the LLC SeriesResonant Converter”, in Proc. Appl. PowerElectron. Conf., Vol. 2, pp. 728-735.

4. Li Q and Wolfs P (2006), “RecentDevelopment in the TopologiesPhotovoltaic Module IntegratedConverters”, in Proc. IEEE PowerElectron. Spec. Conf., pp. 1-8.

5. Li Q and Wolfs P (2008), “A Review of

Figure 8: IBR Converter OperatingMode 4

SIMULATION RESULTSThe simulation of this proposed new topologyis carried out using a computer-aidedsimulation tool to verify the validity of the circuit.The simulation is done using Matlab/Simulink.Simulation has been carried out for 150 W BPSX150S module with the switching frequencyof 20 Khz. The parameters of the PV module

Figure 9: Output Voltage Waveform

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the Single Phase Photovoltaic ModuleIntegrated Converter Topologies withThree Different dc Link Configurations”,IEEE Trans. Power Electron., Vol. 23,No. 3, pp. 1320-1333.

6. Lopez O, Teodorescu R, Freijedo F andDoval Gandoy J (2007), “LeakageCurrent Evaluation of a Single-PhaseTransformerless PV Inverter Connected tothe Grid”, in Proc. IEEE Appl. PowerElectron. Conf., pp. 907-912.

7. Lu B, Liu W, Liang Y, Lee F C and vanWyk J D (2006), “Optimal DesignMethodology for LLC ResonantConverter”, in Proc. Appl. Power Electron.Conf., p. 6.

8. Masoum A S, Padovan F and MasoumM A S (2010), “Impact of Partial Shadingon Voltage- and Current-BasedMaximum Power Point Tracking of SolarModules”, in Proc. IEEE PES GeneralMeet., pp. 1-5.

9. Xiao W, Ozog N and Dunford W G (2007),“Topology Study of Photovoltaic Interfacefor Maximum Power Point Tracking”, IEEETrans. Ind. Electron., Vol. 54, No. 3,pp. 1696-1704.

10. Zhang L, Sun K, Xing Y, Feng L and Ge H(2011), “A Modular Grid-ConnectedPhotovoltaic Generation System Basedon dc Bus”, IEEE Trans. Power Electron.,Vol. 26, No. 2, pp. 523-531.

a novel boost resonant converter for solar … · 2017. 8. 17. · these make the single-panel pv...

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