Experimental verification of an optimized control strategy for a medium-voltage DVR

Voltage sags are a major problem in present distribution systems. Therefore, different solutions have been examined to compensate these sags to avoid production losses at sensitive loads. In particular, Dynamic Voltage Restorers (DVRs) can realize this goal. Presently, a system wide integration of DVRs is hampered because of their high cost, in particular, due to the expensive DC-link energy storage devices. The cost of these DC-link capacitors remains high because the DVR requires a minimum DC-link voltage to be able to compensate a sag. As a result, only a small fraction of the energy stored in the DC-link capacitor can be used, which makes it almost impossible for the DVR to compensate relatively long voltage sags. Present control strategies are only able to minimize the distortions at the load or to allow a better utilization of the storage system by minimizing the needed voltage amplitude. To avoid this drawback an optimized control strategy is presented in this paper, which is able to reduce the needed injection voltage of the DVR and concurrently to mitigate the transient distortions at the load side. In the following paper a brief introduction of the basic DVR principle will be given. After this, an optimized control strategy will be briefly described. Finally, experimental results using a medium-voltage 10 kV DVR setup will be shown to verify and prove the functionality of the presented control strategy in both symmetrical and asymmetrical voltage sag conditions.