650V GaN Based 3.3kW Bi-Directional DC-DC Converter for High Efficiency Battery Charger with Wide Battery Voltage Range

This paper presents an isolated bi-directional DC-DC converter built with 650V Cascode GaN FETs for high efficiency battery chargers. The converter adopts the classic dual active bridge (DAB) topology to achieve voltage regulation over a wide battery voltage range. Benefiting from the topology, the converter does not need either variable switching frequency or variable DC-link voltage, which resonant converters, such as CLLC, do require. The prototype switching frequency is fixed at 100 kHz and its DC-link voltage can be chosen between 380V and 410V, which makes it a superior choice in terms of design for manufacturability (DFM). Additionally, it offers consistently high efficiency, over 97%, at rated power over a wide battery voltage range from 250V to 450V. This combined advantage is enabled by the ability of GaN devices to handle both hard and soft switching efficiently, which makes the classic DAB topology more competitive than ever. When combining the prototype and a totem pole active front end, system efficiency of a 3.3kW bi-directional battery charger is estimated around 96.7% for rated power and 97.7% for half power at 230Vrms input and 350V battery voltage. The maturity of DAB and Cascode GaN FETs is bringing high efficiency bi-directional chargers into real world.