636 Journal of Power Electronics, Vol. 13, No. 4, July 2013 http://dx.doi.org/10.6113/JPE.2013.13.4.636 JPE 13-4-15 Analysis and Design of a Single-Phase Tapped-Coupled-Inductor Boost DC–DC Converter Michael Njoroge Gitau * , Fredrick Mukundi Mwaniki † , and Ivan W. Hofsajer ** †* Dept. of Electrical, Electronic and Computer Eng., University of Pretoria, Pretoria, South Africa ** School of Electrical and Information Eng., University of Witwatersrand, Johannesburg, South Africa Abstract A single-phase tapped-inductor boost converter has been proposed previously. However, detailed characterization and performance analysis were not conducted. This paper presents a detailed characterization, performance analysis, and design expressions of a single-phase tapped-coupled-inductor boost converter. Expressions are derived for average and RMS input current as well as for RMS input and output capacitor current ripple. A systematic approach for sizing the tapped-coupled inductor, active switch, and output diode is presented; such approach has not been reported in related literature. This study reveals that sizing of the inductor has to be based on current ripple requirement, turns ratio, and load. Conditions that produce discontinuous inductor current are also discussed. Analysis of a non-ideal converter operating in continuous conduction mode is also conducted. The expression for the voltage ratio considering the coupling coefficient is derived. The suitability of the converter for high-voltage step-up applications is evaluated. Factors that affect the voltage boost ratio are also identified. The effects of duty ratio and load variation on the performance of the converter are also investigated. The theoretically derived characteristics are validated through simulations. Experimental results obtained at a low power level are included to validate the analytical and simulation results. A good agreement is observed among the analytical, simulation, and experimental results. Key words: Battery, Bidirectional, Isolated, Modeling, Startup, Supercapacitor I. INTRODUCTION Many applications demand the use of a DC–DC converter with high voltage gain. Full utilization of renewable sources requires a converting stage to match the demanded voltage for effective grid connection. The start-up voltage for high-intensity discharge lamp ballasts utilized in automotive headlamps is as high as 400 V. During steady-state operation, a DC–DC converter has to boost the 12 V of battery voltage to 100 V [1]. Electric and hybrid electric vehicles require high-voltage DC bus voltage from energy storage elements such as fuel cells, batteries, and ultracapacitors [2]. The 48 V nominal telecom DC bus voltage should be boosted to the intermediate 380 V DC bus voltage with the convergence of computer and telecommunication industries. Theoretically, conventional boost converters can achieve high step-up voltage gain at heavy-duty load conditions. However, voltage gain is limited in practice because of losses generated in the inductor, filter capacitor, active switch, and output diode. Given these losses, high voltage gain in a conventional boost converter can only be achieved with an extreme duty ratio. The output diode conducts for only a short time during each switching cycle with a high duty ratio, thereby resulting in serious reverse-recovery problems and an increase in the rating of devices [3]. Tapped inductors provide high step-up and step-down ratios with good efficiency without the need for isolation [4–14]. The two windings, N 1 and N 2 , of the tapped inductor are on the same core and are therefore magnetically coupled as Manuscript received Jan. 25, 2013; revised May 19, 2013 Recommended for publication by Associate Editor Honnyong Cha. † Corresponding Author: fredmukundi@gmail.com Tel: +27-12-420-3111, University of Pretoria * Dept. of Electrical, Electronic and Computer Eng., University of Pretoria, South Africa ** School of Electrical and Information Eng., University of Witwatersrand, South Africa Fig. 1. Tapped-coupled inductors.