Abstract
When the growing number of distributed energy resources (DERs) which are connected to the utility through grid-connected converters, electric power company defines low-voltage ride-through (LVRT) requirements to ensure the stability of utility grids. LVRT requirements demand grid-side converters to remain connected to the network in presence of grid-voltage sags. At the time of our interface transformer between converter and grid under grid faults, magnetizing inrush current generated when voltage recovers, which contains a large amount of harmonic components and high current magnitude, reduce power quality on the system and transformer’s residual life due to the high mechanical stresses. In this paper, transformer inrush reduction techniques developing for mitigating the inrush current phenomenon, we propose virtual impedance method. By uses virtual impedance control term to adjust the converter output impedance that produce virtual resistors insert in transformer iron core or transformer winding. That is capable of reducing the inrush current effectively when voltage recovers. This strategy is easier to implement because it has simple control method and requires no information about the transformer model parameters, angle when voltage sags and flux linkage of transformer.