A. a Novel Two-quadrant Soft-switching Converter with One Auxiliary Switch for High Power Applications

There has been an increasing interest in the soft-switching power conversion technologies in order to overcome the limitations of the hard-switching technologies [1]-[7]. Soft-switching (SS) converters had many advantages over hard-switching (HS) converters. For example, SS converters lower switching losses, reduce voltage/current stress, reduce EMI, and allow a greater high switching frequency in high power applications [1]. Despite the advantages of SS converters, its applications have been so far limited due to complexity in the design of SS circuits, and difficult in control realization. There has been a growing demand for a simple design that provides reliable control in a wide-range of operational condition. Several SS techniques have been developed such as the auxiliary resonant snubber inverter (RSI) [1], the auxiliary resonant commutated pole inverter (ARCP) [3], [6], the inductor coupled zero-voltage transition inverter (ZVT) [4]-[5], and the resonant dc link inverter (RDCL) [2], [7]. The RSI is suitable for single or three-phase inverters with multiple branches of auxiliary circuits but needs modification of space vector modulation to ensure zero voltage switching. The ARCP requires large split capacitors to achieve a zero-voltage switching. The ZVT requires bulky coupled inductors to reset the resonant current. The RDCL needs a device voltage rating higher than that which has been used in other converters. This study found that the RSI can easily be extended to two-quadrant chopper applications, but it must use a variable boost current to meet different load current conditions. In a two-quadrant soft-switching (TQSS) converter, there are no switches available for current