Seamless Power Management for a Distributed DC Microgrid with Minimum Communication Links under Transmission Time Delays

To maintain voltage stabilization under transmission time delays, this paper proposes a seamless power management scheme for a distributed DC microgrid (DCMG) with minimum digital communication links (DCLs). First, a DCL topology with minimum communication data is presented for the construction of distributed DCMG system not only to mitigate the communication burden but also to enhance the system’s flexibility and reliability. In addition, based on information gathered from nearby agents and local measurements, the operating modes of local agents in a DCMG system are determined properly to ensure a proper power balance under various conditions. During normal operation, the proposed scheme works as a distributed control scheme either in the grid-connected or islanded mode to take advantage of the distributed control method. To maintain seamless power management even under transmission time delays such as grid fault detection delays and grid recovery detection delays, the operating modes of each agent in a DCMG system are switched to a decentralized scheme based on the droop control method. When the utility grid information is properly identified by all power agents after a transmission time delay, the DCMG system returns to the distributed control scheme based on DC-link voltage (DCV) control to guarantee voltage stabilization. Furthermore, the scalability issue of a distributed DCMG system is also considered in this paper when an additional energy storage system (AESS) agent is involved in the DCMG system. For this purpose, a DCL topology with minimum communication data is designed for the AESS, which enables power units to participate in or to leave the distributed DCMG system easily. Simulation and experimental results under various conditions demonstrate the effectiveness and reliability of the proposed seamless power management strategy.