A transformer inrush reduction technique for low-voltage ride-through operation of renewable converters

The low-voltage ride-through (LVRT) capability has become one of the most important issues since more renewable and distributed energy resource are installed in the grid. The LVRT capability means the converter should remain grid-connected and inject required current to support gird voltage. On the other hand, the sudden reduction of grid voltage may result in magnetic flux deviation in the step-up transformer as grid voltage sag occurs. The deviation of magnetic decays very slowly due to the high efficiency transformer, and it would lead to inrush current as grid voltage restores to normal level. This paper proposes a method to mitigate the magnetic flux deviation and limit the peak current without excelling the current capability of semiconductor devices by using a close-loop current control during LVRT operation. The proposed method can manage the converter´s output peak current and reduce the risk of inrush current as grid voltage restores.