Résumé

This paper proposes an enhanced modulation for the isolated and bidirectional single-stage three-phase Quad-Active-Bridge (QAB) AC-DC converter. In the QAB AC-DC converter, a DC OFFSET is controlled at the neutral point, allowing grid voltages to be modulated using unipolar voltage switches. In the proposed modulation, the offset grid voltages are modulated by a symmetrical duty ratio whose angle changes according to the instantaneous grid frequency, whereas the DC source is modulated by a 50% symmetrical duty ratio (DR) and a phase-shift (PS) to control the bidirectional power transfer. Hence, the command signals can be easily calculated. Converter design, simulation, and experimental results are presented. Grid currents with very low THD (2.8 %) are obtained in open-loop operation.