A Modified T-Type Based Single-Stage 3-Level Isolated Bidirectional Off-Board Charger for Electric Vehicles

Traditional AC-DC isolated converters typically follow a design approach by integrating the two stages. The primary stage involves an AC-DC power factor correction (PFC) stage. The Secondary stage is a resonant converter with regulated output DC voltage. Existing topologies mainly comprise the boost-PFC stage which is integrated with either side of the switch network of the resonant converter, with the benefit of 25% reduction in switching devices. These topologies allow for soft switching at high frequencies, enabling the use of smaller magnetic components and capacitors for higher power density. Despite that, they are unipolar voltage-fed resonant systems with unidirectional power flow (AC-to-DC) and high switch voltage stress. To embark on the drawbacks of conventional converters, this paper proposes a novel 3-level T-type isolated bidirectional AC-to-DC converter. The voltage generated across the secondary side of the resonant tank corresponds to the proposed converter is bipolar in nature, which leads to advantageous G2V and V2G operation. It is an extended version of the T-type 3-level converter. Simulations and experiments demonstrate successful power transfer (6.6 kW) at a 126 kHz switching frequency, with a 415V AC input grid and 800V DC battery.