Dynamic voltage restoration with minimum energy injection

Voltage sag is one of the most important power quality problems challenging the utility industry. Voltage sags can be compensated for by voltage and p ower injection into the distribution system. By injecting voltage with a ph ase advance with respect to the sustained source-side voltage, reactive pow er can be utilized to help voltage restoration. Hence, the consumption of r eal power, from the perspective of the energy supply device, can be reduced . This energy-saving voltage injection comes at the expense of an increased voltage injection magnitude, load power swing, phase shift, and discontinu ity of voltage wave-shape. For this reason, several proposed compensation s trategies are examined, in terms of satisfying custom power while taking in to consideration the capacity of the energy-storage device and the voltage injection constraint of dynamic voltage restorer, Numerical examples are in cluded to illustrate the efficacy of the proposed control strategies.