Output Impedance Shaping schemes for Enhanced Power Sharing amongst Distributed Energy Resources in DC Microgrids

Abstract

DC power supply systems are gaining increased importance as most electronic loads and renewable sources are of direct power in nature. Several DC distributed generators (DGs) are typically connected in parallel to supply local and common DC loads. These DC microgrid systems are being proposed to be connected to the AC smart distribution networks to form hybrid systems. The non-uniform physical (and electrical) distances of sources in the network cause voltage drops and lead to mis-matches in the load power sharing between the sources. This issue in de-centralized droop controlled DGs in DC microgrids can be addressed using virtual impedance (VI) as in the case of AC counterparts. This paper proposes two simple control schemes to change the virtual resistance (VR) value in a self-regulating fashion to achieve better proportional load power sharing amongst the distributed energy resources (DERs). Validations of the control schemes considering solar photovoltaic (PV) power output fluctuations, with different types of DC loads (constant resistance, constant current, constant power and dynamic load (motor)), and in meshed networks with three DERs using off-line simulations (on Matlab Simulink) have been performed and the results are presented.