Seite - 218 - in Emerging Technologies for Electric and Hybrid Vehicles

Energies 2016,9, 410 3RLQW RI FRPPRQ FRXSOLQJ 3&& 667 %LGLUHFWLRQDO *ULG &RQQHFWHG &RQYHUWHU *&& '& %XV %LGLUHFWLRQDO '& '& &RQYHUWHU 39 '& '& &RQYHUWHU :LQG 7XUELQH $& '& &RQYHUWHU %DWWHU\ 6WRUDJH '*V %(6 (9 '& KRPH DSSOLDQFHV %LGLUHFWLRQDO '& '& &RQYHUWHU (OHFWULF 8WLOLW\ Figure1.Atypicaldc-microgridstructure [4]. Comparedwithisolatedtypes,BDCswithcoupled-inductorsfornon-isolatedapplicationspossess simplerwindingstructuresandlowerconduction losses [12–17]. Furthermore, thecoupled-inductor techniques can achieve easily the highvoltage conversion ratio by adjusting the turn ratio of the coupled-inductor. However, the energy stored in the leakage inductor of the coupled inductor causes a highvoltage spike in the powerdevices. Wai et al. [12,13] investigated a high-efficiency BDC,whichutilizesonly three switches toachieve theobjectiveofbidirectionalpowerflow. Also, thevoltage-clamped techniquewasadopted to recycle the leakage energy so that the low-voltage stressonpowerswitchescanbeensured. Toreduce theswitching losses,Hsieh et al.proposedahigh efficiencyBDCwithcoupled inductorandactive-clampingcircuit [16]. In this reference,a low-power prototypewasbuilt toverify the feasibly. AsshowninFigure2,Liang et al. [17]proposedabidirectionaldouble-boostcascadedtopology fora renewableenergyhybridsupplysystem, inwhich theenergy is transferred fromonestage to anotherstage toobtainahighvoltagegain.Hence theirconduction lossesarehighandit requiresa largenumberofcomponents. Chen et al. [18]proposedareflex-basedBDCtoachieve theenergyrecovery functionforbatteries connectedtoa low-voltagemicrodc-bussystem. In [18],a traditionalbuck-boostBDCwasadopted, however, thevoltageconversionratio is limitedbecauseof theequivalent series resistance (ESR)of the inductorsandcapacitorsandeffectof theactiveswitches [19]. CL Np+ VL - S2 S1 C2 Ns S3 + VH - CHD4 Discharge StateCharge State Figure2.Circuit structureof thebidirectionaldouble-boostcascadedtopology[17]. 218