Enhanced Frequency Droop Method for Decentralized Power Sharing Control in dc Microgrids

This article proposes two novel approaches to improve the superimposed frequency droop scheme for the control of dc microgrids (MGs). Conventional voltage-based control strategies suffer from issues such as undesirable voltage regulations, poor power sharing among the sources, and negative effects of line resistances on the equivalent droop characteristics. To overcome these challenges, a superimposed frequency droop scheme has been introduced. However, this method suffers from three major issues: 1) instability in terms of load variation, which is due to the location of system dominant poles; 2) limitation in system loading due to the limitation in the transferred reactive power; and 3) poor voltage quality caused by injection of the ac voltage. In this article, two methods are presented to stabilize the system and enhance its loading condition, consequently improving its viability for control of the dc MG. Furthermore, the system voltage quality is improved by limiting the amplitude of the injected ac voltage. The effectiveness of the proposed schemes is shown by different simulations and is further validated by experiments.