Voltage Sag Compensation Through Dynamic Voltage Restorer Under Non-Sinusoidal Electrical Grid Condition

This work presents a method of voltage insertion into the grid with harmonic distortions through a dynamic voltage restorer (DVR) for protection of sensitive loads to short-term voltage sags. The aim is to recover the nominal voltage level at the load by restoring only the fundamental frequency component without compensating the harmonic contents. Corrections carried out in this manner are justified as the DVR is a device dedicated to restore the amplitude of the sensitive load to its rated value, based on rapid variations from the power grid. The correction of distortions is not suitable for this equipment as harmonics are permanent problems and originate from nonlinearities of electrical loads. Therefore, the batteries that supply the DVR do not support the correction of permanent problems, only for rapid variations. Thus, it allows an extension in the lifespan of the batteries (needed in this type of compensator). Collaterally, restoring only the fundamental decreases the total harmonic distortion of the load, thus allowing this method to make a double contribution to improving the system's power quality. For this purpose, a recursive least-square estimation is developed, suitable for voltages with harmonic content, here called HRLS. The construction of the reference voltage to be produced by the DC-AC converter also considers the synchronism with the fundamental component of the grid, which allows an optimization of the voltage level used on the DC-link. Correction scenarios only inserting the fundamental, as well as with harmonic content, are tested in simulation to compare performance in the use of the compensator power. The same scenarios are also tested on an experimental platform developed in the laboratory to confirm the proposal.