Optimized control for a DVR to compensate long duration voltage sag with low distortion at the load

The dynamic voltage restorer (DVR) is designed to protect sensitive loads from the effects of voltage sags on the distribution feeder. The capability of DVR in compensating long-duration voltage sags is largely depended on the amount of stored energy within the restorer which is very expensive. In order to reduce the price of DVR, many control strategies have been implemented to make better use of the stored energy. Unfortunately, the traditional voltage compensation strategies are merely designed to minimize the needed compensation voltage to extract more energy from the DC-link or to decrease the output active power of DVR or to reduce the distortions at the load. To combine the advantages and avoid the drawbacks of the traditional strategies, an optimized control strategy has been designed and tested by MATLAB simulation. The new strategy can dramatically increase the compensation time with low distortion at the load and without enlarging the energy storage of the DC-link.