Comparison of 2-stage isolated converters for fast EV charger, using partial power

In this publication, specifications of a modular fast EV charging converter are selected based on standards and the state-of-the-art. According to these specifications, a 2-stage cascaded conversion approach is proposed, with separated isolation and charging regulation stage. This enables the design optimization of the each stage for different functionality. Furthermore, a partial power (PP) processing is implemented in the regulation stage to improve the efficiency. Two different 2-stage isolated topologies using PP structure are proposed, employing either 2 or 3 voltage levels. The converters use SiC or Si devices, depending on the voltage stress on the devices for each topology. Additionally, the gain of the PP converter of the regulation stage and the turns ratio of the transformer are analyzed and optimized to reduce the RMS of inductors and switches, as well as the inductor peak energy. The design calculations are done considering full-ZVS condition on all switches, except for the balancer switches with applied ZCS instead. Finally, the two topologies are compared and discussed.