A Review and Modeling of Different Droop Control Based Methods for Battery State of the Charge Balancing in DC Microgrids

Abstract

Nowadays, DC microgrids by linking DC sources such as renewable resources directly to the DC loads and offering higher efficiency due to the elimination of conversion stages are gaining more and more popularity. In DC microgrids with renewable resources, there are stochastic behavior and uncertainties. Thus, energy storage use is unavoidable. Droop control as a well known method is used as the basis of the power sharing among different parallel voltage sources and battery energy storage systems (BESSs). In order to extend the lifetime of BESSs and avoid the overuse of a certain battery, the State of the Charge (SoC) of BESSs should be balanced. This paper presents a review on three different droop control based methods for balancing SoCs of different BESSs in DC microgrids. Moreover, the paper proposes a new droop control method for SoC balancing to overcome the drawbacks of the mentioned methods. The mathematical model of these different methods are derived using small signal state space modeling for a Photovoltaic (PV) grid-interactive DC microgrid consisting of two BESSs. Then, a comparison study has been performed for the mentioned four methods using MATLAB/Simulink.