Coupling transformer with a virtual air gap for the protection of dynamic voltage restorers

The dynamic voltage restorers are efficient series compensation devices to improve power quality. Indeed, they are composed of a coupling transformer and power electronics to provide fast voltage sag correction and harmonics compensation. This paper focuses on a new topology of a coupling transformer for the dynamic voltage restorers which improves the protection of the voltage source converter against grid fault including short-circuits, by changing the magnetic state of the transformer core. In this paper, the operating modes in steady state of the proposed coupling transformer equipped with a virtual air gap are studied by both Finite Element simulations and experimental measurements.