The widespread integration of renewable energy sources (RESs) into the grid through inertia-less power converters is reducing the overall system inertia leading to large frequency variations. To mitigate this issue, grid-forming (GFM) control strategies in bidirectional battery chargers have emerged as a promising solution, since the inertial response of synchronous generators (SGs) can be emulated by power converters. However, unlike SGs, which can withstand currents above their rated values, the output current of a power converter is limited to its nominal design value. Therefore, the estimation of the power delivered by the GFM power converter during frequency events, called Virtual Inertia (VI) support, is essential to prevent exceeding the rated current. This article analyzes the VI response of GFM power converters, classifying the dynamic behavior as underdamped, critically damped, or overdamped according to the selected inertia constant and damping coefficient, parameters of the GFM control strategy. Subsequently, the transient power response under step-shaped and ramp-shaped frequency deviations is quantified. The proposed analysis is validated using a 1.2 KW single-phase power converter. The simulation and experimental results confirm that the overdamped response under a ramp-shaped frequency event shows higher fidelity to the theorical model.

The increasing penetration of renewable energies into the power grid, predominantly interfaced through power electronic converters that lack inherent inertia, has led to significant challenges, including inertia reduction and transient voltage deviations. To address these concerns, the configuration of single-phase bidirectional electric vehicle chargers (BEVCs) into a three-phase arrangement, incorporating vehicle-to-grid (V2G) functionalities, has been identified as a promising solution. This paper presents a novel control strategy to enable the provision of V2G services—including virtual inertia (VI), long-term frequency-watt support, and voltage-var regulation—in a single-phase BEVC architecture powered by a hybrid energy storage system (HESS). The proposed BEVC topology consists of a dual active bridge (DAB) resonant-type DC-DC converter linked to a voltage source inverter (VSI). The HESS comprises DCL capacitors and a lithium-ion battery, enabling the decoupling of the BEVC's active power response from grid frequency disturbances. Specifically, the fast dynamic response required for VI emulation is handled by the DC-link capacitors, while the slower response associated with long-term frequency support is provided by the EV battery. As a result, the virtual inertia support is delivered without adversely affecting battery lifespan. Experimental validation using a 1.2 kW prototype demonstrates the effectiveness of the proposed control strategy.