Dynamic mater-slave control strategy for transient coordination of inverter based microgrids under asymmetric faults

• A DVRU is defined to grasp the communication right and act as a master to maintain the system voltage under faults. The other DERs will follow after the DVRU to form a dynamically master–slave architecture to avoid phase conflict and realize proper transient power sharing among grid-forming DERs. • A local FCDDM is proposed to realize the autonomous selection of the DVRU among various DERs under real-time faults. Moreover, when the current DVRU undergoes communication failure, a new one will automatically replace it to enhance the transient reliability. • Compared with conventional methods, it is the switching signals rather than the phase signals that transferred by the communication bus. Therefore, the low-bandwidth communication can meet the timeliness and accuracy requirements under transient state. • The system mathematical mode is developed to optimize the voltage tracking control parameters to avoid the PCC over-voltage during the recovery stage, where the adaptive capability to various fault situations is considered. Additionally, compatibility with MG protection is also discussed by referring to the existing protection configurations. The ever-expanding inverter-based microgrids (MGs) require the grid-forming distributed renewable energy resources (DERs) to enhance the system safety. However, the different types of grid-forming DERs are prone to have transient conflicts with each other under short circuit faults, leading to unexpected outage or even system collapse. The fast response and poor overcurrent capability of DERs make transient coordination a challenge. This paper proposes a dynamic master–slave architecture for transient coordination control in islanded MGs under asymmetric faults. A dynamic reconfigurable voltage reference unit (DVRU) is designed according to the real faults. In this manner, the other DERs could comply with this DVRU to achieve both system voltage support, inrush current restraining, and power oscillation suppression. It is action signals instead of phase signals need to be transferred by the communication bus with the proposed local fault current differential time delay method (FCDDM). Thus, the low-bandwidth and the enhanced robust communication could be met under transient state. Additionally, the feasibility of the proposed method to combined with relay protection is analyzed. Finally, case study results on islanded MGs consisting of various grid-forming and grid-following DERs demonstrate the effectiveness and robustness of the proposed method under short circuit faults as well as communication failures.