IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL. 48, NO. 1, JANUARY/FEBRUARY 2012 161 High-Efficiency Modular High Step-Up Interleaved Boost Converter for DC-Microgrid Applications Ching-Ming Lai, Member, IEEE, Ching-Tsai Pan, Member, IEEE, and Ming-Chieh Cheng, Student Member, IEEE Abstract—In this paper, a modular interleaved boost converter is first proposed by integrating a forward energy-delivering circuit with a voltage-doubler to achieve high step-up ratio and high ef- ficiency for dc-microgrid applications. Then, steady-state analyses are made to show the merits of the proposed converter module. For closed-loop control design, the corresponding small-signal model is also derived. It is seen that, for higher power applications, more modules can be paralleled to increase the power rating and the dynamic performance. As an illustration, closed-loop control of a 450-W rating converter consisting of two paralleled modules with 24-V input and 200-V output is implemented for demonstration. Experimental results show that the modular high step-up boost converter can achieve an efficiency of 95.8% approximately. Index Terms—DC microgrid, high step-up converter, modeling and parallel operation control. I. I NTRODUCTION I N RECENT years, due to the public concern about global warming and climate change, much effort has been focused on the development of environmentally friendly distributed generation (DG) technologies [1]–[4]. It is well known that when many DGs are connected to utility grids, they can cause problems such as voltage rise and protection problem in the utility grid [5]–[8]. To solve these problems, new concepts of electric power systems are proposed, and dc microgrid is one of the solutions [9]–[12]. DC microgrid is suitable to use where most of the loads are sensitive dc electronic equipment. The ad- vantage of a dc microgrid is that loads, sources, and energy stor- age can be connected through simpler and more efficient power electronic interfaces. Moreover, it is not necessary to process ac power quality issues. So far, dc microgrids have been used in telecom power systems, data centers system, generating sta- tions, traction power systems, and residential houses [13]–[15]. Manuscript received April 25, 2011; revised June 25, 2011; accepted September 8, 2011. Date of publication November 9, 2011; date of current version January 20, 2012. Paper 2011-IPCC-148.R1, presented at the 2010 IEEE International Conference on Sustainable Energy Technologies, Kandy, Sri Lanka, December 6–9, and approved for publication in the IEEE TRANSAC- TIONS ON I NDUSTRY APPLICATIONS by the Industrial Power Converter Com- mittee of the IEEE Industry Applications Society. This work was supported by the National Science Council of Taiwan under Grant NSC-100-2218-E-007- 001, and by the Ministry of Education under Grant 100N2026E1. C.-M. Lai is with Power SBG, Lite-ON Technology Corporation, Taipei 235, Taiwan (e-mail: pecmlai@gmail.com). C.-T. Pan and M.-C. Cheng are with the Center of Advanced Power Technologies (CAPT), Department of Electrical Engineering, National Tsing Hua University, Hsinchu 30013, Taiwan (e-mail: ctpan@ee.nthu.edu.tw; mjay.cheng@gmail.com). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TIA.2011.2175473 Briefly speaking, the output voltages of most distributed energy resources such as fuel cells and photovoltaic (PV) are usually relatively low, requiring a high step-up converter for practical applications [16]–[19]. Recently, an interleaved boost converter extended by mag- netically coupling a ´ Cuk-type auxiliary step-up circuit that charges a voltage-doubler in the output was proposed to achieve the required voltage gain [18]. As a similar solution, a sepic- integrated boost converter which provides an additional step-up gain with the help of an isolated sepic-type auxiliary step-up circuit was also proposed [19]. Nevertheless, the circuit struc- tures of the ´ Cuk/sepic integrated high step-up converters are relatively complex and expensive; thus, they might be difficult to mass manufacture. In addition, considering the practical sit- uation, the maximum output voltage and power efficiency will be affected by the parasitic effects such as winding resistances of inductors for the ´ Cuk/sepic integrated circuits. For small to medium power capacity (25 W ∼ 250 W), the forward circuit topology has less components and smaller volume than that of the ´ Cuk/sepic auxiliary step-up circuits, which makes the forward-type circuit another choice to implement the auxiliary circuit scheme. The main objective of this paper is to develop a modular high-efficiency high step-up boost converter with a forward energy-delivering circuit integrated voltage-doubler as an in- terface for dc-microgrid system applications. In the proposed topology, the inherent energy self-resetting capability of auxil- iary transformer can be achieved without any resetting winding. Moreover, advantages of the proposed converter module such as low switcher voltage stress, lower duty ratio, and higher volt- age transfer ratio features are obtained. Steady-state analyses are also made to show the merits of the proposed converter topology. For further understanding the dynamic characteristic, small-signal models of the proposed converter are derived by using state-space averaging technique. For higher power appli- cations, modules of the high step-up converters are paralleled to further reduce the input and output ripples. Analysis and control of the overall system are also made. Finally, a 450-W rating prototype system is constructed for verifying the validity of the operation principle. Experimental results show that the highest efficiency of 95.8% can be achieved. II. OPERATION PRINCIPLE The proposed interleaved converter topology with high volt- age transfer ratio is proposed as shown in Fig. 1. It can be seen from Fig. 1, the proposed converter consists of two-phase circuits with interleaved operation. The first phase is a boost 0093-9994/$26.00 © 2011 IEEE