Improved zero-current transition converters for high-power applications

Existing zero-current 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 auxiliary switches to be turned on and off under zero-current conditions, The zero-current switching at both turn-on and turnoff not only reduces switching losses significantly, but also eliminates the need for passive snubbers, due to the much reduced switch stress. The cost of the auxiliary switches can be reduced compared to the existing ZCT schemes, due to their zero-current turnoff. The proposed technology is well suited for de-de and three-phase converters with insulated gate bipolar transistors (IGBT's), MOS-controlled thyristors (MCT's), and gate-turnoff switches (GTO's), Theoretical analysis, computer simulation, and experimental results are presented to explain the proposed schemes.