Improvement of ZVS Range and Current Quality of the Nine-Switch Single-Stage AC–DC Converter

The nine-switch single-stage three-phase ac-dc isolated converter integrates a three-phase active front-end ac-dc converter and a three-phase high-frequency galvanically isolated dc-dc converter in one stage, leading to a device count reduction of 25% compared to an equivalent two-stage configuration. The advantage of the nine-switch converter can be truly realized if it can achieve similar efficiency and input current quality as a two-stage converter. In this article, a design methodology is proposed, which ensures zero-voltage switching of the bottom and the middle switches of the nine-switch converter for the entire line cycle and also reduces its input current total harmonic distortion below 5%. By implementing space vector pulsewidth modulation, the dc-link voltage of the nine-switch converter is reduced to the level of an equivalent two-stage converter. The analytical claims are verified with a 3-kW laboratory prototype operating at 400-V ac input, 800-V dc-link voltage, and 380-V isolated dc output voltage.