Determination of the transformer turns ratio in a DVR to reduce the switches voltage rating

Dynamic voltage restorer (DVR) as one of the most effective custom power devices for voltage sag and swell compensation attracted growing attention in recent years. Various topologies have been presented for DVRs. The topologies are based on both dc/ac inverters and ac/ac direct converters. The ac/ac converter based DVRs address some problems arise in the conventional dc/ac inverter based DVRs. These problems include compensation time limit due to the limited capacity of the energy storage used in the conventional DVR topologies and costly and bulky dc link capacitors. Therefore, in the ac/ac converter based DVRs the installation area and cost can be reduced and compensation time limitation is eliminated. In this paper, a new algorithm to determination of the transformer turns ratio is given so that the voltage rating of the switches is reduced. On the other hand, as the switches operate with lower voltage, the switching losses and also stress on the switches is mitigated. Moreover, the reduction in the voltage rating as well as required copper for transformer winding leads to reduction in the overall cost of the system. The operation validity of the system is verified through simulation with the PSCAD/EMTDC software.