Simulation Of Dual Active Bridge Converter For Energy Storage . - IJETT
International Journal of Engineering Trends and Technology (IJETT) – Volume 27 Number 2- September 2015Simulation of Dual Active Bridge Converter for EnergyStorage SystemVuppalapati Dinesh1, E.Shiva Prasad21M.Tech Scholar, 2Assistant Professor, EEE Dept, VNR VJIET, Telangana, IndiaAbstract: The increased demand of an intermediatestorage of electrical energy in battery systems, inparticular due to use of renewable energy, hasresulted in the need of dual active bridge convertersor bidirectional DC to DC power converters. Themost cost effective solution for electrical energystorage is battery. The battery output is converted toAC for connecting to electrical loads. Charging anddischarging of the battery can be carried out bybidirectional power converters. DAB converter can beused for battery charging and uninterruptable powersupply for hybrid vehicles, telecommunication,industrial, space and defence applications. This thesisinvestigates different isolated bidirectional DC–DCconverters with a rating of voltage 220V, frequency 1kHz and power of 1600W. Closed loop control blocksfor various applications of DAB circuit have beenproposed and validated by simulation.Keywords — Dual Active bridge (DAB) Converter,bidirectional DC–DC converters.I.INTRODUCTIONIn order to reduce the dependence on non-renewablefossil fuel and the amount of greenhouse gasemission, the demand for higher penetration ofrenewable energy has been growing rapidly duringthe last two decades. The major sources of renewableenergy include wind energy, photovoltaic energy,hydrogen fuel cell energy, tidal energy, andgeothermal energy. Most of these energy resourcesare utilized in the form of electric energy. Because ofthe unpredictable, and distributed nature of mostrenewable energy resources, the higher penetration ofrenewable energy will bring some challenges to theexisting electric power system.Fig: 1 Typical application of bidirectional DC-DCconverter for power distributionISSN: 2231-5381Global climate change and depleting fossil fuelreserves are driving society’s quest for a sustainableenergy infrastructure. The incorporation of renewableenergy is limited in many ways due to the variableand intermittent nature of its output. Hence, energystorage systems such as lithium ion batteries, supercapacitors and electric vehicles have to be used tocompensate the source variations.The increasedemand of an intermediate storage of electricalenergy in battery systems, in particular due to the useof renewable energy, has resulted in the need of dualactive bridge converters or bidirectional DC-DCpower converters.Therefore these applicationsintroduce power converter with bi-directional powertransfer property. Bidirectional DC-DC convertersrecently gates awareness due to application ofbidirectional power transfer between different dcsources buses. The demand for development ofcomplex, compact and efficient power systemimplementation has encouraged scientists in bidirectional converter development. This paper isorganized as follows. Section II analysis the DABcircuit configuration. Section III presents thegeneralized analysis based on per unit system. PIDcontroller is analysed in section IV. Section V showsthe simulation results of battery charging anddischarging. Section VII summarizes the contributionof this work.II.DUAL ACTIVE BRIDGE CONVERTERSCircuit ConfigurationA DAB converter consists of two switching bridgesand one high-frequency transformer. Each switchingbridge is made up of four high-frequency activecontrollable switching device( IGBTs) in an H-bridgeconnection. However, instead of using uncontrollableswitching devices (such as diodes) bridge in the otherside of transformer, DAB converters use two activebridges formed by active controllable devices. This iswhy the name “Dual Active Bridge” is given to thiskind of converters.A transformer is used to provide galvanic isolationbetween the input side and the output side of a DABconverter. A high-frequency transformer is preferredto reduce the weight and volume of the magnetic core.The leakage inductance has two purposes: (1) it isused as energy storage components in DAB convertersand (2) it reduces the dv/dt across switching devicesduring commutation transients, facilitates softswitching, and reduces switching losses.http://www.ijettjournal.orgPage 79
International Journal of Engineering Trends and Technology (IJETT) – Volume 27 Number 2- September 2015Figure:2 shows the circuit schematic of a dc-dc DABconverter. The IGBT- diode pairs can conduct currentbidirectional. Therefore, the circuit shown in Figure: 2is able to conduct bidirectional current. Furthermore,DAB converters have symmetrical dual active Hbridge configuration, which help achieve bidirectionalpower flow. On the other hand, such configuration canonly block positive voltage. Therefore, the topologyshown in Figure:2 is only for dc-dc DAB converters.Fig: 2 DAB converter schematicconverters and ac-ac DAB converters. By using a perunit model, the parameters of both bridges of an DABconverter can be scaled up/down easily.Steady-State Model of DC-DC DAB ConvertersLet , ,andbe the input voltage, outputvoltage, transformer primary winding voltage andtransformer secondary voltage, respectively ( asshown in fig:2.1). and are the transformer leakage impedances due to leakageinductance at primary and secondary winding,respectively, whererepresents switching frequency.Assume that DAB converter is operating in Q1.During interval 1 the current at transformer primaryside is . (1)Whereandare the primary side current attime t and t 0, respectively. Similarly, theA DAB converter is controlled by Phase-ShiftModulation (PSM). Both the direction and the amount current at transformer secondary side isof power flow is regulated by controlling the phaseshift between the those H-bridges. Power flows from .(2)the leading bridge to the lagging bridge. Twooperating modes, corresponding to two directions ofpower flow of a DAB converter, respectively, aregiven in Figure 3.(a) and Figure 3.(b). In Figure 3.(a),Whereandare the secondary sidepositive power flow is defined as power transfer fromthe left to the right for the converter shown in Figure 2,current at time t and t 0, respectively.while in Figure 3.(b), negative power flow is definedA per unit system at both windings can be definedas power transfer from the right to the left.as.(3).(4)(5)(a) Positive power flow.(b) Negative power flowFig: 3 Operation modesIII. Steady State AnalysisThis work derives a per-unit steady-state model of aDAB converter for circuit analysis and converterdesign. This model works for both dc-dc DABISSN: 2231-5381(6)Whereis base apparent power,andare base voltage at primary and at secondary side,respectively, Ib,pri and Ib,sec are base current at primaryand at secondary side, respectively, and Zb,pri and Zb,secare base impedance at primary and at secondary side,respectively.By using eq (3), (4), (5) and (6) all voltage andcurrent variables, Vi, Vo, Vpri , Vsec, i0,pri, i0,pri i0,sec iΦ,priiΦ,sec can be converted into their corresponding perunitvariables,respectively. It is also intuitive thathttp://www.ijettjournal.orgPage 80
International Journal of Engineering Trends and Technology (IJETT) – Volume 27 Number 2- September 2015 . (7) . (15)( (8)Ideally, when the loss of a converter is insignificant,output power is equal to input power . .(9)The transformer leakage reactance can be lumped asXpu Xpri / Zb,pri Xsec / Zb,sec. Using the per unitsystem defined above and substituting all per unitvariables into (1) and (2), the per unit transformercurrent is . (16)Where Rpu R / Zb,sec and R is load resistance.Using per unit notation the ideal dc voltage transfer . (10)ratio isto π, theSimilarly during second interval i.e fromtransformer current is))Insteadystatethe (11)transformercurrentis . (17)The above equation shows the voltage transferratio of DC to DC DAB converter.symmetrical every half switching periodIV.PID CONTROLLERThereforeandare calculated as . (12)PID controllers typically use control loop feedback inindustrial and control systems applications. Thecontroller first computes a value of error as thedifference between a measured process variable andpreferred set-point. It then tries to minimize the errorby increasing or decreasing the control inputs to theprocess, so that process variable moves closer to theset . (13)From eq (12) and (13) the input current averagedover one switching period is) . (14)Fig: 4.PID controller block diagramThe amount of power transferred to the load iscontrolled by phase shift angle between twobridges, the input voltage, and the outputvoltage as described in below equationISSN: 2231-5381point. To increase performance, for example toincrease the responsiveness of the system, PIDparameters must be adjusted according to the specificapplication. An open-loop controller, also called anon-feedback controller, is a type of controller whichcomputes its input into a system using only the currentstate and its model of the system. The controller doeshttp://www.ijettjournal.orgPage 81
International Journal of Engineering Trends and Technology (IJETT) – Volume 27 Number 2- September 2015OUTPUT CURRENT654CURRENTnot receive a feedback signal from the process and itonly has a set-point and a fixed output signal. In aclosed-loop system, also called a feedback system, thecontroller has a feedback signal from the process. Thecontroller has a set-point, a feedback input signal, anda varying output signal. The output signal increases ordecreases proportionally to the error of the set-pointcompared to the input signal.321000.20.40.60.811.21.41.61.82Time (seconds)V.SIMULATIONfig.(7)The result of the galvanic isolated dual activebridge DC-DC (DAB) converter. The simulationcircuit and its corresponding waveforms are asfollows:OUTPUT 5TIME (seconds)Fig.(8)(i) DAB for energy storage systemThe phase shift between primary voltage(V1) andsecondary voltages(V2) is shown in the fig (6). Thephase shift between the two voltages is 20 degree.PHASE SHIFT BETWEEN PRIMARY AND SECONDARY VOLTAGES250200150Battery charging circuitFig: 9 (a) shows the battery charging circuit for theDAB converter. In this circuit we are using aLithium Ion battery for energy storage purpose.Power flows from primary side to secondary sideand thus the battery charges. Simulation results aregiven in fig 40.0060.0080.01TIME (SEC)0.0120.0140.0160.0180.02Fig (6)The output voltage and current is show in the fig(7).The output voltage is 220V and output current is3.6 A. The output power is shown in fig (8). Theoutput power is 1600 wattsOUTPUT VOLTAGE400350VOLTAGE300250200Fig:(9) Battery charging circuit for DAB converter15010050000.51ISSN: 2231-53811.52Time (seconds)2.533.54http://www.ijettjournal.orgPage 82
International Journal of Engineering Trends and Technology (IJETT) – Volume 27 Number 2- September 2015Simulation ResultsBATTERY DISCHARGINGVOLTAGE,PERCENTAGE,CURRENT12000BATTERY EC)600070008000900010000Fig.(11)Fig.(10)VI. CONCLUSIONSThe above shown fig: 10 is the output waveform ofbattery. The first waveform is the charging outputvoltage of DAB converter, second waveform is thestate of charge (SOC) and the third waveform is thecharging current.Battery discharging circuitFig: 11 shows the battery discharging circuit for theDAB converter. In this circuit we are using a LithiumIon battery and this battery provides the voltage toflow from secondary to primary. Thus the batterydischarges to provide the Power flow from secondaryside to primary side.The main objective of this paper is to analyse differentaspects of DAB converters and to provide a set oftools to design DAB converters for energy storagesystem application. This work presents a proof-ofconcept study of applying dc-dc DAB converters. Thisthesis investigates different isolated bidirectional DC–DC converters with a rating of voltage 220V,frequency 1 kHz and power of 1600W.In this project, a DAB converter is simulated by usingMATLAB Simulink. Bidirectional power flow i.e.power flow from primary side to secondary side andfrom secondary side to primary side of the DABconverter circuit is simulated. The application of DABconverter for energy storage application has beendemonstrated by simulation of DAB along withbattery in charging and discharging mode. Thesimulation studies on DAB converter for variousapplications have been performed.REFERENCESFig:11 Battery discharging circuit for DAB converterSimulation ResultsThe below shown fig: 12 is the output waveform ofbattery. The first waveform is the charging outputvoltage of DAB converter, second waveform is thestate of charge (SOC), third waveform is thedischarging current and fourth waveform is the outputcurrent of DAB converter.ISSN: 2231-5381[1] A. Huang, M. Crow, G. Heydt, J. Zheng, and S. Dale, “TheFuture Renewable Electric Energy Delivery and Management(FREEDM) System: The Energy Internet,”Proceedings of theIEEE, vol. 99, pp. 133–148, Jan. 2011.[2] F. Krismer, S. Round, and J. Kolar, “Performance optimizationof a high current dualactive bridge with a wideoperating voltage range,” in IEEE Power ElectronicsSpecialists Conference (PESC), 2006, pp. 1–7, Jun. 2006.[3] H. Qin and J. W. Kimball, “Ac-ac dual active bridge converterfor solid state transformer,” in IEEE Energy ConversionCongress and Exposition (ECCE),2009, pp. 3039–3044, 2009.[4] Kheraluwala, M. N., Randal W. Gascoigne, Deepakraj M. Divan,and Eric D. Baumann. "Performance characterization of ahigh-power dual active bridge dc-to-dc converter." IndustryApplications, IEEE Transactions on 28, no. 6 (1992).[5] D. Xu, C. Zhao, and H. Fan, “A PWM plus phase-shift controlbidirectional dc- dcconverter,” IEEE Transactions onPower Electronics, vol. 19, pp. 666–675, Mar. 2004[6] S. Inoue and H. Akagi, “A bidirectional dc-dc converter for anenergy storagesystem with galvanic isolation,” IEEETransactions on Power Electronics, vol. 22, pp. 2299–2306,Nov. 2007.[7] Inoue, S.; Akagi, H. A bidirectional DC TO DC converter for anenergy storage system with galvanic isolation. IEEE Trans.Power Electron.2007[8] D. Xu, C. Zhao, and H. Fan, “A PWM plus phase-shift controlbidirectional dc- dcconverter,” IEEE Transactions onPower Electronics, vol. 19, pp. 666–675, Mar. 2004http://www.ijettjournal.orgPage 83
design. This model works for both dc-dc DAB converters and ac-ac DAB converters. By using a per-unit model, the parameters of both bridges of an DAB converter can be scaled up/down easily. Steady-State Model of DC-DC DAB Converters Let , , and be the input voltage, output voltage, transformer primary winding voltage and
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