  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.
