SPACE VECTOR CONTROL AND CURRENT HARMONICS IN QUASI-RESONANT SOFT-SWITCHING PWM CONVERSION

The paper presents an analysis of the behavior of the modulation schem es useful for the soft-switched, quasiresonant VSI power inverter in c omparison with standard PWM techniques (sine-triangle and space-vector ). Although the presence of a purely capacitive snubber across each po wer device in such kind of converters allows true PWM, this is affecte d by some constraints in the switching sequence depending on the load current polarities, which result in a ripple content much higher than that obtained from conventional PWM schemes with the same switching fr equency. However, it is also shown that the location and duration of t he zero-vector state is a degree of freedom which can be useful to obt ain different switching sequences, so reducing substantially the rippl e; The above criteria have been adopted in developing a PWM technique based on space vectors, which is also described in the paper, Such tec hnique determines the optimum vector sequence which gives the wanted v oltage vector, while reducing the ripple content, Results of simulatio ns are reported, illustrating the differences between the various sche mes and validating the effectiveness of the proposed modulation method .