An 18 kW Battery Charger Module for Extreme Fast Charging Applications Using an Unfolding-Based AC-DC Topology

This paper proposes a high-performance Unfolder-based single-stage ac-dc converter for electric vehicle battery charging applications. The dc-dc converter utilizes a T-type bridge structure to process the soft dc-link voltage generated from an Unfolder. The converter is designed to operate efficiently over a wide range of variations in the output and input voltages. A leading-edge aligned modulation technique is used to increase the soft switching range of the primary bridge switching devices. Coupling between two input ports of the dc-dc converter due to the unique modulation technique is discussed and a decoupling control strategy is introduced to achieve the two control objectives of power factor control and output current control. The proposed 18kW module serves as a scalable building block for a modular extreme fast charging system. Hardware results from an 18kW module are presented with 96.3% ac-dc and 97.3% dc-dc efficiency for rated operating conditions.