A grid forming controller with integrated state of charge management for V2G chargers

Abstract

Vehicle-to-grid (V2G) technology offers an innovative solution to provide grid services using electric vehicle (EV) batteries. This work proposes a novel grid forming (GFM) controller for V2G applications which can ensure the voltage source behaviour and provide support to the grid, regardless of the state of charge (SoC) and the charging requirements of the battery. This is achieved by integrating a SoC controller that modifies the classical GFM algorithm. The controller only relies on the SoC and power measurements, achieving a decentralized without the need of communication. With the proposed approach, the V2G charger will always behave as a voltage source that provides inertial response and voltage support to the grid. The primary frequency regulation, on the other hand, will depend on the battery status and charging needs. Frequency regulation could be enabled, disabled or it could be limited to some perturbations (under/over frequencies). Moreover, the SoC controller provides freedom to tune the frequency support of the device, limiting it to inertial response or extending its contribution along the time. The tuning of the system parameters is addressed in detail to ensure a damped response under all the operation scenarios provided by the SoC controller. Its performance and stability is evaluated using small signal transfer functions. Finally, it is validated both in simulation and experimentally.