New soft-commutated PWM inverter with ac current transformer

The soft-commutated PWM inverter is very attractive for high-power applications. In the conventional soft-commutated PWM inverter, however, there exist some deteriorative problems such as high voltage and/or high current stresses on the switches, the necessity of additional switches for realizing soft-commutated PWM, and the relatively large power loss caused by the large circulating current composed of the load current and the resonant current. This paper presents a new soft-commutated PWM inverter, in which an ac current transformer and a main resonant capacitor are used to detect the value and the polarity of the ac load current, and to realize soft commutation of the switches without causing the above deteriorative problems. The operation and the characteristics of this soft-commutated PWM inverter are analyzed and its usefulness is confirmed by experiments.