Secondary Voltage and Frequency Regulation for Grid Re-Synchronization in Microgrid with Unified Virtual Oscillator Controlled Multi-port Converters

Unified Virtual Oscillator Controller (uVOC) is a type of oscillator based nonlinear time domain controller that achieves faster primary control response than conventional droop control as no phase-locked loop (PLL) is required. uVOC can be used effectively for either grid following or grid-forming voltage source converters. Grid-forming converter is essential for a microgrid to operate in islanded mode in addition to the more common grid-connected mode. In this paper, a secondary regulation scheme is proposed to augment the capability of uVOC based on a Multi-port Converter (MPC) by adding voltage and frequency regulation for grid re-synchronization. With this method, changing primary controller is not required and seamless transition is achieved. To implement this secondary regulation, communication or data exchange between different components is required. The network connectivity is implemented based on the RIAPS platform, an open-source distributed operating system developed for real-time control of microgrid/smartgrid systems. Finally, the suitability of proposed secondary regulation with uVOC based MPC was verified through simulation and experiment on a microgrid testbed.