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ABSTRACT
In this paper, two new control methods have been proposed for a three-phase dynamic voltage restorer (DVR) based on direct converters. Three-phase to single-phase direct converters are used to regulate the voltage at each phase. The converter is constructed using four bi-directional controlled switches. As each converter operates independently the DVR can properly compensate unbalanced, long-time voltage sags and swells. Two procedures have been considered. In the first method, voltage sag compensation is achieved by feeding power from the same phase and voltage swell compensation is done by using the other two phases, enabling the compensation of maximum sag of 50% and swell of 100%. In the second method, the voltage swell can be compensated by feeding power from the same phase while the sag compensation is performed by using the other two phases, leading to the maximum sag compensation of 33% and swell of 100%. The switches are controlled by a combination of the plain pulse-width modulation (PWM) as well as sinusoidal PWM techniques. The simulation studies substantiate the voltage compensation capabilities of the proposed methods.