High-frequency series-resonant DC link power conversion

An AC/AC conversion scheme that eliminates the need for self-commutated devices and requires only 12 thyristors for full double bridge AC-to-AC power conversion is presented. The system utilizes a series-resonant DC link between the AC/DC and DC/AC converters. This series-resonant scheme is, in effect, the dual of the parallel DC resonant converter. The DC resonant circuit can be essentially considered as a commutating circuit that ensures turnoff of all 12 thyristors by providing the necessary zero-current instants. A significantly improved sinusoidal current waveform can be obtained at both the input and outputs, compared with conventional high-power converters by the use high-frequency pulse density modulation