Inertia Emulation with the Concept of Virtual Supercapacitor for Islanded DC Microgrid

In recent years, the use of renewable energy sources (RESs) has been increased due to the limited resources of fossil fuels and their environmental issues. The expansion of RESs and advances in power electronics have led to more attention being paid to DC microgrids (DCMGs). DCMGs enable the exploitation of all renewable energy potentials. Along with the advantages of RESs and DCMGs, the use of RESs is associated with the challenges of absence or lack of inherent inertia. Therefore, DCMGs have become more sensitive to disturbances. Rotational inertia is an inherent property of rotating machines that increases stability in the grid. Therefore, by applying energy storage systems (ESSs) in DCMGs, and inertia emulation the mentioned challenges can be overcome. The proposed control scheme is implemented based on the concept of the virtual supercapacitor in the inner control loop of the ESS interface dual-half-bridge (DHB) converter with DCMG to emulate the inertia. Due to the high efficiency, electrical insulation, inherent soft switching, and the need for a smaller filter, the DHB converter has been used. Finally, a DCMG is simulated for the effectiveness of the proposed control strategy in MATLAB/Simulink. The simulation results confirm the validity of the proposed scheme.

I. Introduction

Environmental problems and limitations in fossil fuel sources have led to the use of alternative renewable energy sources (RESs) [1]. Therefore, microgrids (MGs) have been studied as a suitable alternative. DC microgrids (DCMGs) are suitable for using energy sources (e.g., photovoltaic system, batteries, etc.) and DC loads (e.g., data centers, electric vehicle (EV) charging stations, etc.) [2]. Due to the absence or lack of inherent inertia, new challenges have been created for the DCMG. Research on virtual inertia control for DCMGs is limited. A virtual inertia control strategy has been investigated by adding an inertia control loop in [3] to provide inertia for battery-based island DCMGs. However, this method enters voltage differential into the control strategy, which easily leads to high-frequency disturbances. In [4], a virtual DC machine (VDCM) concept is designed to emulate the inertial properties of real DC machines, but this control scheme is very sophisticated. A control strategy under the concept of VDCM has been proposed using the equations governing the separately excited real DC machine, but the dynamic equations governing the synchronous machine have been used [5]. Supercapacitors can also be used to the stability of the DCMG because of its fast response. However, the use of supercapacitors is not recommended due to the limited time of rated power delivery and higher initial costs [6]. In this paper, a new method of creating virtual inertia in DCMG by presenting a virtual supercapacitor control scheme proposed. With further analysis, the dual-half-bridge (DHB) converter has been used as a battery and grid interface power converter. The advantages of this type of converter include high efficiency, high reliability, high power density, electrical insulation, low device stress, low noise, inherent soft switching, and the need for a smaller filter [7]. Therefore, the purpose of presenting this article is as follows: