Switching minimization of three-phase four-leg dynamic voltage restorer

Dynamic Voltage Restorers are utilized to protect sensitive loads from voltage disturbances which take place in the distribution systems. The three-phase four-leg topology of DVR is more advantageous over the other topologies. But it requires higher switching operations of the VSI for tracking the reference voltages through hysteresis. This paper presents two switching minimization control algorithms for a three-phase four-leg VSI topology of DVR to minimize the switching frequencies, while protecting the sensitive loads against sag / swell. The effectiveness of both the control algorithms is illustrated through detailed simulation study using PSCAD 4.2.1.