Dynamic Voltage Restorer Based on High Frequency Link Direct Ac-Ac Converter

Abstract

Power quality has been a concern for last decade with increase in sensitive loads. Power quality issues affect the quality of production, reduce production efficiency and increases the production cost. Dynamic voltage restorer(DVR) is a power quality improving device used for improving voltage quality to a sensitive load. DVR is connected in series with the supply and injects a voltage in series with the supply voltage to correct the voltage quality problems. The major voltage quality problems identified are voltage sag, voltage swell, voltage harmonics, flicker and voltage imbalance. DVR is identified to be cost effective solution for protecting sensitive loads from voltage related power quality issues. Conventional DVR is using either energy storage based or two stage ac-dc-ac converter based system. These topologies are bulky and costly due to the big line frequency isolation transformer and bulky dc-link capacitor. The extend of cost reduction and efficiency can be improved by eliminating the injection transformer. A new DVR topology based on high frequency link direct ac-ac converter is proposed in this work. This topology does not require a line frequency transformer. Instead it uses a high frequency link transformer. High frequency transformer is very small compared to a line frequency transformer. The dc-link capacitance is not required for this topology. A fictitious dclink is maintained. Since the DVR does not have an injection transformer, it has lower loss, lower cost and it is less bulky.