A Novel Isolated Connector for Bidirectional Direct V2V Charging Using Onboard Chargers

This paper presents a novel isolated connector designed for battery charging between two electric vehicles (EVs), To reduce costs and eliminate the need for a complex interfacing, it utilises the onboard chargers of both EVs while requiring two additional capacitors and a high frequency transformer (HFT). With the latter, the proposed connector provides gal-vanic isolation for safe vehicle-to-vehicle (V2V) charging process. Because it involves a single-stage power conversion, the losses in the power devices are potentially low compared to other isolated topologies. In each charging cycle, not all devices of the existing chargers are utilised. Different set of switches can be selected for different charging cycle allowing each switch to experience an idling state, thus minimising its voltage and current stresses. The voltage regulation can be done in a similar way to a non-isolated pulse-width-modulation (PWM) controlled DC-DC converters making the conventional control schemes can still be applied. This paper describes in detail the operating principles of the connector, the derivation of its input-output voltage relationship and its application in charging the lithium-ion battery packs of either EVs. MATLAB/Simulink simulation results validate its functionality, demonstrating well-controlled transient performance. This connector has also been tested with the operation when constant-current control is required for charging a battery under different initial states-of-charge (SOCs).