Accurate power sharing for islanded DC microgrids considering mismatched feeder resistances

Accurate load power sharing and bus voltage regulation are two critical control objectives for ensuring power quality and reliable operation of DC microgrids. Although regulating the DC Bus voltage can be achieved by adopting an external secondary control loop, inaccurate load power/current sharing among converters is a prominent issue due to feeder resistances mismatch. This can lead to undesired overloading of converters, triggering over-current protection relays, and potentially resulting in cascading failure of the whole system. Existing literature uses virtual resistance techniques to improve the power sharing accuracy; however, so far, no explicit relation between the values of the virtual resistances and the feeder resistances mismatch has been formulated, opening the possibility to enhance power sharing even further. Therefore, this paper proposes an accurate power sharing strategy in which the virtual resistances are chosen to account for the feeder resistances mismatch. The proposed technique relies on the optimal tuning of the virtual resistance assigned to the local controller of each converter. An online estimation algorithm of the physical feeder resistances, required for virtual resistance tuning, is embedded into the control loop of each converter. Thus, prior information about the feeder resistances in the design stage is not required. The proposed approach is validated through simulation and experimental results from a Hardware-in-the-Loop setup of a typical islanded DC microgrid. The results demonstrate the approach merits, achieving accurate power sharing among converters and ensuring robust operation, even in scenarios involving communication failures.