Linear and Nonlinear Coordinated Droop Control Strategies to Address Current Sharing and Voltage Regulation Challenges for the Parallel Operation of DC-DC Converters in DC Microgrid

Abstract

In the field of DC microgrids (MGs), ensuring both optimal load sharing and voltage regulation poses a significant challenge due to unequal rating of distributed generations (DGs), sensor inaccuracies, and cable resistances. To cope with the same decentralized method based on a linear droop control approach proves to be a very efficient control technique for DC MG. However, the conventional linear droop control approach suffers from current sharing error and voltage regulation with increased loading conditions. Thus, to improve the above issues, this paper proposes the design aspects of coordinating three droop curves in the controller, which consists of two nonlinear (NL) and one linear for parallel operation of DC-DC converters working under varying loading conditions. The designed controller automatically switches between different droop curves with load variations. Further, through proper analysis, droop coefficients for different curves under varying loading conditions are derived for optimal performance of the parallel-operated DC-DC converter with better current sharing accuracy and voltage regulation, even under line resistance. To gauge the improvement in current sharing accuracy and voltage regulation by coordinating multiple droop curves vis-a-vis only a single droop curve from light load to heavy load conditions, a MATLAB-based simulation has been performed, and current sharing error and voltage regulation have been compared. Further hardware prototypes of 300 W have also been developed to validate the proposed control logic.