Ramp-Rate Limitation of Renewable Energy Sources for Voltage Quality Improvement in Distribution Networks: An Experimental Study

The continuously increasing penetration of Converter-Interfaced Renewable Energy Sources (CI-RES) has posed various challenges to the electric grids, e.g., frequency instability, reverse power flows, power quality issues, etc. Regarding CI-RES connected to transmission systems, several regulations exist for limiting the CI-RES high active power ramp-rates (RRs), so as to reduce the conventional unit commitment and its associated, with the frequency-related Ancillary Services, costs. In Distribution Networks (DNs), no such specifications exist, even though high RRs, caused by the distributed CI-RES (CI-DRES), have been linked to rapid voltage changes (RVCs) and flickering phenomena, resulting in the reduction of voltage quality within DNs. In this paper, an RR limitation (RRL) method is incorporated in CI-DRES lab prototypes, equipped with Supercapacitors at their DC-link. These prototypes operate in a scaled-down version of the CIGRE Benchmark MV DN. The effect of the RRL on RVCs is studied with respect to two different RVC definitions, described in the IEEE 1547:2018 and IEC 61000-4-30:2015 Standards. The experiments reveal that the operation of CI-DRES, when incorporating a fast-acting energy storage system, can improve the voltage quality by mitigating the RVCs, considering both Standards' definitions.