Abstract
The growing integration of electric vehicles (EVs) into modern energy systems presents an urgent need
for innovative charging solutions that enable bidirectional energy flow and enhance grid stability,
energy management, and the role of vehicles as distributed energy resources. This paper presents the
design and analysis of an onboard bidirectional charging (OBD) system for vehicle-to-grid (V2G) and
Vehicle-to-Load (V2L) applications. The system, rated at 50 kW, facilitates dynamic energy exchange
between the EVs, grid, and local loads. A series-connected 43-cell lithium-ion battery with a nominal
voltage of 3.7 Vand 120 Ah capacity, a 230 V, 50 Hz grid supply, power electronics such as buck-boost
converters, an Inductor-Capacitor-Inductor (LCL) filter, and a mode selector controller, designed in
MATLAB/Simulink using dual Stateflow, governs battery state-of-charge (SoC) based operations.
The simulation results indicate robust V2G and V2L mode performance when the SoC exceeds 40%.
The system maintained a stable 400 VDCbus (pm5V) and provided consistent 12 Vand 24 V
outputs. The grid interaction demonstrated high power quality with sinusoidal voltage and current
peaks of 325 Vand 20 A, respectively. The battery voltage stabilised at 158.6 Vwith minimal
oscillations, and smooth transitions between the V2G, V2L, and Grid-to-Vehicle (G2V) modes were
observed. The proposed design facilitates efficient bidirectional power transfer by utilising a fourquadrant
full-bridge inverter to enable both V2L and V2V energy exchange, with the mode selection
governed by an SoC threshold of 40%. Key findings include rapid transient responses in voltage
stabilisation with the V2L mode supplying power linearly with increasing load current, reaching
2100Wat 10 A, and low ripple inDCvoltages, ensuring reliable performance under variable load
conditions. In this study, the designed onboard bidirectional converter in the V2G mode has a power
transfer efficiency of 84%–93% and a stabilisation voltage within±4.7% of the nominal grid voltage,
whereas in the V2L mode, it has a wider voltage fluctuation range of±9%and a slightly lower
efficiency of 78%–88%. The findings of this study reveal the viability of the system in enabling the
integration of EVs as distributed energy resources in smart grid applications for energy management
and grid support services, and provide important insights into the design of bidirectional charging
systems with potential implications for improving control strategies and power quality in future grid
scenarios.