A Direct Power Synchronization Based Control of Grid-Connected Converter for EV Charging Station With Hybrid Energy Source under Non-Ideal Grid

This study investigates the stability of a voltage source converter (VSC) employed in fast-charging station for an electric vehicle (EV) connected to weak grid conditions utilizing a hybrid energy source. The digital control delay induces instability challenges in VSCs equipped with LCL filters. This phenomenon transpires when the resonance frequency descends below the critical frequency (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$f_{s}/6$</tex-math></inline-formula>) as a result of grid impedance variations in a weak grid. An RC-damped LCL filter is designed for VSC to attenuate high-frequency instability. A direct power synchronization (DPS) technique is utilized to enhance low-frequency stability in comparison to PLL synchronization methods. To augment the efficacy of DPS, a frequency adaptive double third-order generalized integrator (FA-DTOGI) filter is incorporated into the system. The EV charging converter, with bidirectional power capabilities, and a photovoltaic (PV) system are connected at the DC link. The VSC outer power loop controller regulates the DC link to maintain a set reference, ensuring consistent operation of the EV charging station despite variations in photovoltaic power output. The proposed control method is validated through simulation studies and laboratory experiments, addressing scenarios such as unbalanced voltages, variations in PV and EV power, and both V2G and G2V operations.