Voltage Restoration and Adjustable Current Sharing for DC Microgrid With Time Delay via Distributed Secondary Control

As a key part of modern power systems, DC microgrid is becoming increasingly important. Among different control methods for DC microgrid, secondary control has been widely investigated since it can guarantee both current sharing and DC bus voltage restoration. However, the existing secondary control results only consider fixed current sharing ratio among DC converters, and thus they cannot be applied to the case where an adjustable current sharing ratio is desired. Motivated by this observation, this paper presents a new distributed secondary control strategy. By imposing a time-varying droop gain and specifying the “virtual voltage drop,” this strategy is able to ensure adjustable current sharing ratio among DC converters. Moreover, the effects of time delay on the control performance is also analyzed. Three case studies and two hardware-in-the-loop (HIL) tests are provided to verify the efficacy of the presented strategy.

I. Introduction

With the rapid development of distributed energy resources (DERs), modern power system is under transformational changes where more distributed and highly-automatous system structures, i.e. microgrid, are emerging [1]–[3]. Compared to AC microgrid, DC microgrid is able to connect DERs (e.g. photovoltaics and batteries) and DC-type loads directly without AC/DC conversion [4]. Therefore, DC microgrid is increasingly drawing attention due to its high control reliability, flexibility and efficiency [5]–[7].