Unified Virtual Oscillator Control for Synchronization Under Ultra-Weak Grid Conditions

A unified virtual oscillator controller (uVOC) with fast power control response is proposed for enhanced synchro-nization under ultra-weak grid conditions. The recently proposed uVOC offers a unified analysis, design, and implementation framework for both grid-following and grid-forming converters; leveraging its superior synchronization capability, enhanced fault ride-through response is achieved without the need for a back-up controller during faults. In this work, we propose an improved uVOC design and implementation which enables fast power-flow control. Through analysis, we demonstrate that the proposed controller retains synchronization as long as a feasible equilibrium exists. Furthermore, using dynamic reactive power control the feasible power-flow range is extended under ultra-weak grid conditions. Systematic design guidelines for controller parameters are presented. The analysis and design are validated through hardware experiments.