An Improved Voltage-Shifting Strategy to Attain Concomitant Accurate Power Sharing and Voltage Restoration in Droop-Controlled DC Microgrids

This article proposes a distributed secondary level control strategy for dc microgrids, which achieves accurate and proportional power sharing and dc-bus voltage deviation restoration based on voltage shifting. In contrast to similar approaches, only one variable per converter is transmitted in the low-bandwidth communication link and with a simple integrator as the secondary level controller both objectives are achieved simultaneously. The information state shared between converters is a lambda factor that incorporates the converter output voltage and power information. The secondary control computes the average lambda locally and the controller generates an unique voltage-shifting term that modifies the converter output voltage reference. When all converters' lambda converge to the average value, both proportional power sharing and dc-bus voltage restoration are attained. The proposed technique suppresses the need for a complex control structure and large amount of converter variables. The proposed control is evaluated through PLECS simulation and it is validated in a 6.4 kW dc microgrid setup.