Design of dynamic voltage restorer for voltage sag and swell compensation using high-frequency-isolated direct AC-AC converter without commutation problem

In this paper, a dynamic voltage restorer (DVR) is presented based on a novel buck type PWM direct ac-ac converter topology. The ac-ac converter used in proposed DVR has no commutation problem because of using switch cell structure and coupled inductors, and therefore, it does not need to sense the input voltage polarity for safe commutation, which saves the cost of input voltage sensor. The proposed DVR also utilizes high-frequency-isolation in the direct ac-ac converter, to avoid the need of the bulky line frequency (60 Hz) transformer. Although the proposed converter adds two coupled inductors to solve the commutation problem, however, the size of the transformer and output inductor can be reduced significantly. All the passive components in proposed DVR also experience twice the switching frequency, and the use of external fast recovery diodes allow to further increase the switching frequency, which can significantly reduce the passive component sizes. Moreover, the ac-ac converter used in proposed DVR has both inverting and non-inverting operation and therefore, can compensate both voltage sags and swells. A detailed analysis of the proposed DVR is given, followed by the experimental results.