Mitigation of Voltage Sag and Swell Using Direct Converters with Minimum Switch Count

Abstract

A new simplified topology for a dynamic voltage restorer (DVR) based on direct converter with a reduced number of switches is presented. The direct converter is fabricated using only three bi-directional controlled switches. The direct converter is connected between the grid and center-tapped series transformer. The center-tapped series transformer is used to inject the compensating voltage synthesized by the direct converter. The DVR can properly compensate for long-duration, balanced, and unbalanced voltage sag and swell by taking power from the grid. The switches are driven by ordinary pulse width modulation signals. Simulation and hardware results validate the idea that the proposed topology can mitigate sag of 50% and swell of unlimited quantity.

Voltage Sag, Swell, and Interruption Compensation Using DVR Based on Energy Storage Device

“…The voltage sags are also caused by starting of large motors, switching of large loads, energizing of transformers and equipment faults. Most of these faults (70-80%) will be self-cleared within a few milliseconds as explained in [5][6][7]. IEEE Standard 1100-1992 in IEEE Emerald Book defines voltage sag as, "a rms reduction in the AC voltage from 90% to 10% of nominal supply, at the power frequency, for durations from a half-cycle to a few seconds".…”

“…Many DVR topologies are presented in the literature survey. DVRs based on direct converters are presented in [6,7], in which power required for compensation is taken from the AC supply side and AC/AC direct converters are used to generate compensating voltage for mitigating voltage sag and swell. In this topologies, single phase outage or three phase outages can't be compensated as there is no voltage available at the supply side during outage.…”