Improved zero-current transition converters for high power applications*

Improved Zero-Current Transition Converters For High Power Applications*
Hengchun Mao, Fred C. Lee, Xunwei Zbou, and Dushan Boroyevich
Virginia Power Electronics Center
The Bradley Department of Electrical Engineering
Virginia Polytechnic Institute and State University
Blacksburg, VA 2406 1-0 111
Fax: [phone], Email: hmao@vtvml .cc.vt.edu

Abstract - Existing Zero-Currenit Transition (ZCT) converters do not solve main switch turn-on problems and require auxiliary switches to be turned off with high current, and therefore are not suitable for high power applications. Novel
ZCT schemes proposed in this paper enable all main switches and auxiliavy switches to be turned on and off under zero current conditions. The zero-current switching at both turnon and turn-off not only reduces switching losses sign@cantly, but also eliminaires the necessity of passive snubbers due to the much reduced switch stress. The cost o f the auxiliary switches can be reduced compared to the existing ZCT schemes due to their zero-current turn-ofl The proposed technology is well suited for dc-de and three-phase converters with IGBTs, MCTY and GTOs. Theoretical analysis, computer simulation and experimental results are presented to explain the proposed schemes.

I. INTRODUCTION
Power semiconductor switches in high power applications are subject to high switching stresses and switching losses.
In conventional designs, significant derating of device voltage and current ratings and elaborate passive snubbers have to be used due to the switching stresses, and the switching firequency is limited to low frequency ranges. In recent years, various soft-switching techniques have been proposed to alleviate these problems.
Significant performance improvements as well as cost, size and weight reduction can be achieved with the help of soft switching. A successful s oft swlltching scheme for high power applications should reduce the switching losses, diode