A New Family of ZCT-PWM Isolated DC-DC Converters with the Optimized Control Strategy ZCT Cell On Secondary Side
ABSTRACT To overcome the complicated strategy and circuit implementation issue for control of the conventional ZCS converter to derive the driving signal for the auxiliary switch, a novel ZCT cell which greatly simplifiers the control strategy by directly extending the duty duration to be the whole off-time of the primary switch is proposed in this paper, where the control circuit is implemented only by a logic inverter and two sets of RC combinations with the same parameters. When preferably placed on the secondary side, the proposed ZCT cell can not only help the converter to achieve ZCS for the primary switches and the ZCT for auxiliary switch wherein itself but also soften the communication of the secondary rectifiers. In addition, the behavior of ZCS has no interaction with primary side ZVS process, therefore a fully soft-switching (ZVS on and ZCS off) converter can be easily obtained. The detail operation principles and design considerations, as well as the family of the new ZCS converters, were presented. A prototype with the fully soft-switching dual switch active-clamped forward topology suitable for being the front-end dc-dc converter in the server system, whose highest conversion efficiency is 95.5%, was built to verify the validity and applicability of this proposed ZCT cell.
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ABSTRACT: A new concept of high-voltage dc-dc power conversion is presented in this paper. Its distinctive feature lies in distributing the high input voltage asymmetrically between two primary-side series-connected switch pairs. This allows using switches of optimal ratings in their respective class: the low-voltage switch pair implemented with MOSFETs only, and the high-voltage switch pair implemented with insulated gate bipolar transistors (IGBTs) only. As the switches in a switch pair are of the same type and voltage rating, they are maximally utilized. With an active snubber on the secondary side of the isolation transformer, a hybrid zero-voltage-switching-zero-current-switching (ZCS) scheme, which is different from the zero-voltage and zero-current-switching technique, is realized and makes all IGBTs be zero-current-switched and all MOSFETs be zero-voltage-switched from very light load to full load condition with minimal circulating energy. The ZCS snubber energy is completely released to the load, leading also to a duty-cycle gain. The operating principles, dc analysis, and design guidelines will be given. A 2-kW, 1500/48-V experimental prototype has been built and evaluated. The measured efficiency of the converter is found to be 92.4% at the rated condition.IEEE Transactions on Power Electronics 01/2012; 27(5):2242-2259. · 4.08 Impact Factor