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Top1. Introduction
The conventional HFIB-DAB DC-DC converter proposed earlier (Doncker, R. De. et al (1991)) has many attractive features like galvanic isolation, efficient power conversion, ease of control, soft-switching capability, bidirectional power transfer capability, and high-power density. It has been used in different applications which require higher power density along with some energy storage systems like batteries and super-capacitors. A typical distributed generation (DG) system including solar photo-voltaic panel, permanent magnet synchronous generator (PMSG), battery bank and HFIB-DAB DC-DC converter is shown in Fig.1.
This HFIB-DAB DC-DC converter has the drawback of reduction in power conversion efficiency during low power transfer as well as non-unity voltage gain conditions. But, due to the advancements in semiconductor switching devices (Biela, J. et al (2011)), magnetic materials (Lee, M.C. et al (2008)) and microelectronic technologies; this conventional HFIB-DAB DC-DC converter has evolved in terms of its power transfer efficiency, thereby posing a great challenge for power electronic scientists and engineers to put them in real life applications.
Figure 1. Distribution Generation (DG) System
There are various modifications in the topological structure (Li, X. et al (2010), Chen, C. et al (2010), & Jung, J. H. et al (2013)) as well as modulation technique for its improvement in power transfer efficiency. The different power modulation techniques include single-phase-shift (SPS) modulation (Mishima, T. et al (2011)), extended-phase-shift (EPS) modulation (Wen, H., et al (2016)), dual-phase-shift (DPS) modulation (Bai, h. et al (2008)), and triple-phase-shift (TPS) modulation with respective one, two, two and three control degrees of freedom. A modulation scheme with four control degrees of freedom including two internal and one external phase-shift angles along with switching operational frequency (Yaqoob, M., et al (2019)) achieves various features like zero value of reactive power, least tank current which reduces the capacity of current carrying semiconductor switching devices and full soft-switched operation for a series-resonant HFIB-DAB DC-DC converter over wide range variations in output power transfer and voltage gain.
The power conversion efficiency increases in HFIB-resonant DAB DC-DC converter due to reduction in AC bridge currents as well as improvement in bridge power factors which lowers both conduction loss as well as switching loss respectively (Twiname, R. P., et al (2014), & Twiname, R.P., et al (2015)). It mainly consists of two full-bridge converters which are linked by either tuned inductor-capacitor-inductor (LCL) resonant tank network (Twiname, R. P., et al (2014)) or tuned capacitor-inductor-capacitor (CLC) resonant tank network (Twiname, R.P., et al (2015)) along with high frequency transformer. A tuned capacitor-inductor-inductor-capacitor (CLLC) resonant tank network with phase-controlled HFIB-resonant DAB DC-DC converter is presented in (Malan, W.L., et al (2016)).
This HFIB-resonant DAB DC-DC converter with tuned LCL resonant tank network in (Twiname, R. P., et al (2014)) uses DPS power modulation technique with only one control degree of freedom. In this, the reactance of all reactive components in the LCL resonant tank network is required to be equal and this is possible only under ideal conditions. In actual practice, it is hardly possible to procure the components of required value as per calculation (Twiname, R. P., et al (2014)). Moreover, the power transferred by the DPS power modulation technique like PWM modulation is only in fraction of given voltage with reduced duty cycle which results in increase of circuit peak current with increased stress on the semiconductor switching devices and thus requiring these devices of higher rating.