This Letter proposes a novel control and optimisation strategy for a bi-directional, three-stage, on-board battery charger (OBC) achieving 80 PLUS Titanium efficiency. The proposed strategy utilises the benefits of silicon carbide (SiC) devices and is based on direct current hysteretic control (DCHC) with optimisation of switching patterns and dead time. The OBC first stage is a solid-state transformer that provides the isolation barrier and is operated under zero-current switching/zerovoltage switching (ZVS) conditions. The second stage is a bi-directional buck-boost converter that operates in critical conduction mode (CRM) with automatic dead time optimisation to achieve ZVS operation. The third stage is an H-bridge inverter with a DCHC controlled current loop to optimise dynamic and steady-state performance and provide a smooth transition between CRM and continuous conduction mode. The DCHC is implemented using a hybrid software/hardware approach. The experimental results show that the OBC can not only change the power flow direction within a few milliseconds but can also provide reactive power support for the grid. Additionally, the OBC achieves a peak efficiency of 96.65% and a minimum total harmonic distortion equal to 1%.

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