Operation and control of dynamic voltage restorer using single-phase direct converter

Abstract

In this paper, a new topology based on a direct ac/ac converter is proposed for a single-phase dynamic voltage restorer (DVR). This topology uses the minimum switches (i.e. two switches) and does not require dc-link energy storage elements. As a result of elimination of the energy storage elements, the cost and the physical size of the proposed topology is reduced. A new control method is also proposed for direct ac/ac converter in the proposed topology. The proposed topology is properly able to compensate voltage sag and swell in the desired range according to the turn ratio of the injection transformer and is also able to eliminate harmonics and flickers. Considering these capabilities, the proposed topology is a several purpose device with a simple topology. It is worth noting that all of these capabilities are not integrated in the conventional DVR topologies. It is obvious that the proposed topology would not face any problems in long time compensation due to the fact that it provides the required energy directly through the grid. The proposed topology can be easily extended to n-phase systems such as three-phase based on the same principle of the operation. In n-phase systems, the voltage sags and swells can be properly compensated regardless of the balanced or unbalanced operation. The experimental and simulation results are presented to validate the capabilities of the proposed topology.