Switching minimization and reduction of power loss in a Dynamic Voltage Restorer

The Dynamic Voltage Restorer (DVR) is a custom power device connected in series with the load, which can control the voltage applied to the load by injecting a voltage of arbitrary amplitude, phase and harmonic component into the line. 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 using hysteresis. This paper deals with reducing the switching losses in a DVR. Here two switching minimization control algorithms for a three-phase four-leg VSI topology of DVR are presented to minimize the switching frequencies, while protecting the sensitive loads against sag/swell. This paper also presents a virtual resistance concept in order to reduce the losses in the VSI. The effectiveness of both the control algorithms is illustrated through simulations using PSCAD 4.2.1.