A Robust and Flexible Controller Based on Minimum Active Power Injection to Precise Tracking of Load Variation to Compensate Voltage Sag

In viewpoint of technology-driven custom power apparatus, dynamic voltage restorer (DVR) is recognized as a most prominent device which can be implemented to compensate the voltage sag. On the other hand, this device has been customarily used in power distribution system to protect sensitive loads from sudden voltage sag. Owing to the restriction of energy storage in DVR's capacitors, it is essential that the active power injection by DVR to be reduced. As a consequence, this energy-saving strategy leads to the injecting the larger voltage magnitude and reactive power, shifting the phase, and cluttering the voltage wave shape. Meantime, this strategy is very sensitive respect to variation in load’s power factor, so that the compensating operation will not be properly performed. In this regard, this paper suggests a flexible controller based on minimum active power strategy in order to perfectly correct the voltage sag notwithstanding variation in load’s power factor. Likewise, the under-study DVR has been structured according to the cascaded H-bridge multilevel inverter topology.