Dynamic Microgrids With Self-Organized Grid-Forming Inverters in Unbalanced Distribution Feeders

• Published in: IEEE journal of emerging and selected topics in power electronics 2020-06, Vol.8 (2), p.1097-1107
• Main Authors: Du, Yuhua, Lu, Xiaonan, Tu, Hao, Wang, Jianhui, Lukic, Srdjan
• Format: Article
• Language: English
• Subjects: Control stability; Control systems; Control systems design; Distributed control; Distributed generation; dynamic microgrids (MGs); Electric potential; Feeders; Hardware; Inverters; Microgrids; network reconfiguration; Network topology; Reconfiguration; secondary control; Stability analysis; Strategy; Topology; Transient analysis; Unbalance; unbalanced system; Voltage; Voltage control
• ISSN: 2168-6777; 2168-6785
• DOI: 10.1109/JESTPE.2019.2936741

In contrast to conventional static microgrids (MGs), MGs with dynamic and adjustable territories (i.e., dynamic MGs) are proposed and implemented in this article. Dynamic MGs are commonly dominated by grid-forming inverters and nested in unbalanced distribution feeders. Unlike balanced systems where only positive-sequence components exist, proper operation of unbalanced dynamic MGs presents additional challenges. A distributed secondary control strategy is developed in this article for distributed generators (DGs) interfaced with grid-forming inverters in unbalanced dynamic MGs by providing coordinated regulations on both positive- and negative-sequence system models. System frequency and voltage are under constant regulation, along with voltage unbalance (VU) management for multiple critical load buses (CLBs). The proposed control strategy enables seamless system transition during unbalanced dynamic MGs reconfiguration and guarantees proportional positive- and negative-sequence power-sharing among connected DGs with respect to system topology variation. Detailed controller designs are provided and stability analyses are derived. The proposed control strategy is fully implemented in hardware controllers and validated on a hardware-in-the-loop (HIL) MG testbed.