A Bidirectional Three-phase Unfolding Based High Efficiency EV Charger Featuring Partial Power Operation

This paper proposes a three-phase unfolding based bidirectional electric vehicle (EV) charger with partial power processing dc-dc stage that offers high efficiency operation along with significant passive size reduction. The ac-dc stage comprises a three-level T-type neutral point clamped (TNPC) converter switched at grid frequency with inherent zero voltage switching (ZVS) capability. This leads to zero switching loss in this power conversion stage. Due to grid frequency switching, the grid filter size reduces drastically. A pulsating dc-link voltage is maintained by DAB based partial power processing stage to reduce the dc-link capacitor requirement. Another partial power processing buck-boost based third-harmonic current injection circuit is incorporated for power factor correction (PFC). The paper contains the detailed operational principles and control strategies of the proposed topology. To validate the performance, a 5 kW prototype is developed and tested, achieving a peak efficiency of 97.2%.