A New Virtual Oscillator-Based Grid-Forming Controller with Decoupled Control Over Individual Phases and Improved Performance of Unbalanced Fault Ride-Through

Abstract

Virtual Oscillator (VO) control is the latest and promising control technique for grid-forming inverters. VO Controllers (VOCs) can simultaneously provide time-domain synchronization and steady-state droop functionalities. In recent developments, VOCs have been integrated into system-level control architecture to provide additional functionalities such as capacitor voltage regulation and overcurrent protection. This article has further refined the existing VO-based system-level grid-forming control architecture with two essential and specific research contributions. The first contribution is to improve the decoupling in control over individual phases, which is achieved by combining Symmetrical Component based VOC (S-VOC) with nested voltage and current controls. The proposed phase decoupling control feature improves the grid-forming performance of existing VOCs in the presence of unbalanced grid voltages. The second contribution is to improve the fault ride-through performance under unbalanced faults by modifying the feedback of the existing VOC. Systematic development of the proposed grid-forming control architecture with analytical reasoning is presented. The proposed controller is successfully validated using simulations and experiments.