An inrush current mitigation method for the grid-connected converters in the low-voltage ride-through operation

With more and more renewable and other distributed energy resources (DERs) being adopted, the utility requires these DERs systems have low voltage ride-through (LVRT) capability, which means the DERs converters must remain grid-connected and to provide reactive or active power for grid support during low voltage situations caused by faults. As such voltage sags occur, the deformed grid voltages often result in magnetic flux deviations in the grid-side transformer of the DERs converter. When the fault clears and the voltages restore to normal level, the flux deviation can easily result in inrush current of the transformer. This paper proposes an inrush current mitigation method for the grid-connected converters in the LVRT operation. The proposed method reduces the risk of inrush current by compensating the magnetic flux deviation during the LVRT operation. A pre-defined ampere constraint is imposed upon the LVRT and flux compensation to avoid burdening the power semiconductor devices. The proposed method can reduce the the stress of the converter and its grid-side transformer while performing the LVRT operation.