Coordinated dual-mode inverter control with NF–ROCOF-based islanding detection for enhanced power quality and seamless transition in DC–AC hybrid microgrids

This article describes a unified DC-AC microgrid system based on photovoltaic PV batteries that offers coordinated parallel inverter operation in both grid-following and autonomous modes of operation. The developed system is intended to transition seamlessly between these operating modes to create the required enhancement in power quality PQ, reactive power support, utility needs, and local load demand. A dual-controller strategy is employed to allow realization of these features. In the grid-following mode, dual-tree complex wavelet transform (2TCWT) is coupled with DC-link voltage regulation and maximum power-based current control for properly executing real and reactive power operation. A synchronous reference frame SRF-based voltage control scheme is utilized to guarantee steady operation and voltage regulation among parallel inverters in the autonomous mode. On the other hand, to ensure the gridded performance and reliable operation, a hybrid islanding detection (HID) method is applied. The system combines a robust notch filter (NF) and a rate of change of frequency (ROCOF)-based phase-locked loop PLL which have good performance in grid monitoring, fast disturbance recognition, and resynchronization. The proposed HID method is in accordance with IEEE 2030.7 standards, thereby ensuring compliance with practical implementation requirements. The performance of the proposed unified microgrid architecture is validated by performing detailed simulation studies and experimental evaluation on the PV battery in a lab-scale prototype. Various operating scenarios, including grid-connected, islanded, and transition conditions were tested to prove the robustness of the design. The results confirm that coordinated parallel inverter operation improves power quality and reactive power support while guaranteeing seamless resynchronization and reliable autonomous operation. The extensive software-hardware validation reinforces the proof of concept and demonstrates the ready applicability of the DC-AC unified microgrid system toward future resilient energy networks.