An efficient and compact voltage feed-forward DAB-based bidirectional DC-DC converter for onboard EV charger

An efficient and compact bidirectional DC-DC converter is essential for onboard Electric Vehicle(EV) chargers to adopt the Grid-to-Vehicle(G2V) and Vehicle-to-Grid(V2G) power transfer features. In this context, this paper proposes a simple, efficient voltage feed-forward Dual Active Bridge(DAB) based bidirectional DC-DC converter. In this converter, the power from the DC source to the battery flows through a direct lossless path and a partial lossy path through the DAB. Analytical expressions of the power-sharing ratio between partial and direct paths are derived and analysed for charging and discharging. Based on the analysis, a MATLAB/Simulink converter model with a power rating of 2.45 kW is developed along with a battery of 240 V, 12 Ah. Also, a hardware prototype of the converter with the same rating is developed, and its performance for various operating conditions and its ability to adapt to step change in the phase shifting ratio is demonstrated. The experimental results show that the power flow through the partial path is nearly 50%. Accordingly, all the components' ratings and sizes can be reduced on the partial path. The converter achieves an efficiency of 95.5% during charging and 94.2% during discharging. Furthermore, the proposed DC-DC converter is considered part of an onboard EV charger, and its impact on overall charger efficiency is evaluated iteratively. The estimated overall onboard charger efficiency is 93.8% in G2V and 93.3% in V2G. This performance is comparable to commercial onboard EV chargers. Thus, the proposed DC-DC converter will be one of the solutions for an efficient and compact onboard charger.