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 and grid-supporting inverters. VO Controllers (VOCs) provide time-domain synchronization with a connected electrical network. At the same time, a VOC can incorporate additional nested control loops to meet the system-level requirements such as fault ride-through capability. However, existing VOCs have two limitations. Firstly, the existing VOCs do not have decoupled control over individual phases. As a result, the performance of the existing VOCs is not satisfactory in presence of unbalanced grid voltages. Secondly, the fault ride-through performance of the existing VOCs under unbalanced faults is not satisfactory. The power operation at a healthy phase is badly affected by a faulty phase. This paper has introduced a modified VO based system-level grid-forming controller to overcome the limitations mentioned above. Systematic development of the proposed control architecture with analytical reasoning is presented. Simulation studies and hardware experiments are conducted for validation.