IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 23, NO. 4, JULY 2008 1743 A Full-Bridge DC–DC Converter With Zero-Voltage-Switching Over the Entire Conversion Range Mangesh Borage, Sunil Tiwari, Shubhendu Bhardwaj, and Swarna Kotaiah Abstract—A new topology of full-bridge dc–dc converter is pro- posed featuring zero-voltage-switching (ZVS) of active switches over the entire conversion range. In contrast to conventional tech- niques, the stored energy in the auxiliary inductor of the proposed converter is minimal under full-load condition and it progres- sively increases as the load current decreases. Therefore, the ZVS operation over the entire conversion range is achieved without significantly increasing full-load conduction loss making the converter particularly suitable in applications where the output is required to be adjustable over a wide range and load resistance is fixed (e.g., an electromagnet power supply). The principle of operation is described and the considerations in the design of converter are discussed. Performance of the proposed converter is verified with experimental results on a 500-W, 100-kHz prototype. Index Terms—DC–DC power conversion, soft-switching, zero- voltage-switching (ZVS). I. INTRODUCTION T HE full-bridge (FB) zero-voltage-switching (ZVS) con- verter (FBZVS converter), [1]–[5], is the most popular topology for dc–dc converters due to fixed switching frequency, ZVS operation, high efficiency, low circulating reactive energy and moderate device stresses. By using a dc blocking capac- itor and a saturable inductor in series with primary winding, the primary current during the free-wheeling interval can be reduced to zero. This circuit is called as the zero-voltage and zero-current-switching (ZVZCS) FB converter [6] wherein the lagging-leg switches operate at ZCS and leading-leg switches operate with ZVS. The major limitation of the FBZVS con- verter has been the limited range of operation over which ZVS can be achieved. When the load current is low, the ZVS of the lagging-leg switches is lost as the energy stored in the leakage inductance of the transformer is insufficient to discharge the switch and transformer capacitances. The loss of ZVS results in increased switching losses and electromagnetic interference (EMI). In the case of high-power converters using insulated gate bipolar transistor (IGBT), an external snubber capacitor is con- nected to reduce the rate of rise of voltage and turn-off losses. Manuscript received September 29, 2007; revised January 14, 2008. Pub- lished July 7, 2008 (projected). Recommended by Associate Editor H. Chung. M. Borage, S. Tiwari, and S. Kotaiah are with the Power Supplies Division, Raja Ramanna Center for Advanced Technology, Indore 452013, India (e-mail: mbb@cat.ernet.in). S. Bhardwaj is with the Department of Electronics Engineering, Indian School of Mines-University, Dhanbad, India. 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/TPEL.2008.925203 Therefore, in high-power converters, the loss of ZVS addition- ally results in the discharge of snubber capacitor in IGBT. The resulting surge current can be detrimental to IGBT and capacitor in the long run and it increases EMI problem. Further, the reso- nant voltage overshoots due to resonance between the snubber capacitor and wiring/lead inductance can exceed IGBT voltage rating. Therefore, it is important to maintain ZVS operation over the entire range of operation or the conversion range. The fol- lowing solutions have been proposed in the past. 1) Using higher series inductance increases the ZVS range but results in increased loss of duty cycle and ringing across secondary-side rectifier diodes. With consequent reduction in transformer turns ratio, primary reflected current and switch conduction loss increases [2], [5]. 2) Using saturable inductor instead of a linear inductor, ZVS range can be increased without significantly losing the duty ratio [7], [8]. However, a large-size core is required to im- plement the saturable inductor. 3) The energy stored in the magnetizing inductance can also be used to aid the ZVS operation. The switch current and the conduction loss is significantly increased [9]. In the converter proposed in [10] and [11], the stored energy in the magnetizing inductance of auxiliary transformer (which is independent of load) is used to extend the ZVS range. 4) Using a passive auxiliary “pole” circuit, full-range ZVS operation can be achieved [12] but the fixed circulating current results in additional conduction loss. In the above listed techniques, except for (2), the range of ZVS operation can be extended at the expense of increased full-load conduction loss. Ideally, additional energy storage is not required under full-load condition since the energy stored in transformer leakage inductance is sufficient for ZVS oper- ation. The additional stored energy is required only when the load current is less. FBZVS converters featuring this kind of adaptive energy storage using coupled inductors are reported in [13] and [14]. A passive auxiliary add-on circuit for conven- tional FBZVS converter using a transformer and an uncoupled inductor to achieve ZVS operation over the entire conversion range is recently proposed [15]. In this paper a new topology of FBZVS converter is proposed to achieve ZVS over entire con- version range with minimum additional conduction loss. The proposed converter does not use auxiliary coupled inductor or transformer, rather, the main power transformer is divided into two half-rated transformers and an uncoupled inductor is used to achieve ZVS over entire conversion range. It is particularly suitable in applications where the output is required to be ad- 0885-8993/$25.00 © 2008 IEEE Authorized licensed use limited to: ULAKBIM UASL - YILDIZ TEKNIK UNIVERSITESI. Downloaded on April 22, 2009 at 13:00 from IEEE Xplore. Restrictions apply.