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

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 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.