A Multiport EV-Fleet Charging Station Based on Modular Multilevel Converter

This paper proposes a multiport electric vehicle battery fleet charging station (EVBFCS) based on modular multilevel converter (MMC). This structure uses a medium frequency AC-link transformer, which provides isolation between the electric vehicle batteries and the source. With a modular structure, the structure has two conversion stages i.e DC-AC-DC with one MMC-leg on the primary-side and two MMC legs on the secondary-side of the isolation transformer. Each sub-module (SM) on the secondary-side of the transformer has EV batteries connected to it. The SM’s connected on both sides of the transformer, employ level-shifted PWM (LS-PWM) modulation strategy. In this paper, a detailed design and control of EVBFCS with the consideration that all the EV’s are connected to the charging system is given. A vector control scheme is implemented to adjust the power flow to MMC connected EV’s in this system. A second-order generalized integrator- frequency locked loop (SOGI-FLL) with a pre-filter is used to generate stationary frame references which possess DC-offset, harmonics and sub-harmonic rejection capabilities. A coordinated controller also ensures the power balance between the arms and legs, is maintained. Finally, the viability of this system along with the effectiveness of the the controller is verified by the simulation results in both steady-state and dynamic conditions.