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 λ factor that incorporates the converter output voltage and power information. The secondary control computes the average λ locally and the controller generates an unique voltage-shifting term that modifies the converter output voltage reference. When all converters' λ 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.

I. Introduction

The microgrid (G) concept is a solution for the integra-tion of multiple renewable energy sources and energy storage systems into the grid, enabling local resources to be clustered together and operate either islanded or grid-tied, thus providing more flexibility and resilience to the electrical system [1]–[3]. Recently, dc-Gs have become more prominent due to their advantages over ac-Gs [4], e.g., simplified power control, since there is no reactive power flow, phase synchronization, and ac power quality issues [5], [6]. Moreover, since most renewable sources and storage devices exhibit a dc output, interfacing them to the main bus of a dc-G requires less power conversion stages, thus leading to a more efficient approach [4], [5], [7], [8].