Design and implementation of a transformerless dynamic voltage restorer by using bidirectional DC-DC converter

In this thesis, a new bidirectional DC-DC converter based transformerless dynamic voltage restorer topology (DVR) is developed and presented. The proposed topology can compensate balanced and unbalanced voltage sag/swell that are the most common electrical power quality problems and can provide the isolation of the series converter and the grid by a high frequency transformer (HFT) rather than bulky injection transformers. The improved voltage compensator is composed of a H bridge DC-DC converter equipped with a HFT with 1 primary and 3 secondary windings and transformerless DVR. The single phase shift (SPS) control method is used for each series converters independently to provide the bidirectional power flow of DC-DC converter while in-phase compensation method is used to correct the missing and excessive voltage of load. LC filter is employed to attenuate the switching ripple harmonics on the output of the DVR. An experimental prototype has been implemented for 380 V three phase / three wire, 10 kVA ratings to validate the performance of the proposed system. In order to test the performance of the proposed voltage compensator, 3 phase, 20kVA voltage disturbance generator prototype is also desinged. The performance of the system is verified with experimental results.