Control Strategy for Three-Phase Four-Leg Dynamic Voltage Restorer Based Third-Harmonic Injection

To achieve the voltage compensation of dynamic voltage restorer in the case of three-phase voltage amplitude unbalanced sag, the control strategy for the three-phase four-leg dynamic voltage restorer based third-harmonic injection has been proposed in this paper. To analyze the principle of third-harmonic injection modulation, the dynamic voltage restorer topology of three-phase four-leg has been established. Because the third-harmonic injection modulation can independently regulate each phase, the double closed-loops control strategy with proportional-resonant controllers and the detection method with band-stop filter have been designed for single-phase voltage. The simulation experiments under the circumstance of three-phase voltage amplitude balanced and unbalanced sag have been built respectively, the simulation results have proved that the dynamic voltage restorer system has fantastic capability of voltage compensation.