Stability Analysis of a Grid-Connected DC Microgrid with Hybrid Renewable-Energy Systems and EV Loads

This paper presents a stability analysis of a grid-connected DC microgrid (MG) consisting of hybrid renewable-energy systems (RESs) and electric vehicles (EVs) fed to a railway station. The hybrid RESs including a wind-turbine generator (WTG) and a PV array are connected to the DC MG through an AC/DC power converter and a DC/DC boost converter, respectively. The prospective spread of EVs and plug-in hybrid EVs raises the need for fast charging rates while the required high charging rate also leads to high power demands that may not be directly supported by the power grid. Due to the intermittent features of EVs' charging/discharging operations and/or RESs' power generation, it is necessary to add energy storage systems (ESSs) to smooth power imbalances and fluctuations. Thus, the supercapacitor (SC)-ESS is the most suitable one due to its high energy-density characteristics. To investigate the uncertainty and intermittent characteristics of the studied system, both frequency-domain study and time-domain analysis are conducted under various operating conditions. Simulation results are performed to show the effectiveness of the proposed ESS and the impacts of the fast EV charging stations on the DC MG.