Soft curtailment for voltage limiting in low-voltage networks through reactive or active power droops

Abstract

The increasing share of small-scale distributed generation (DG) units can lead to over-voltage problems in low-voltage networks. In order to solve this issue, the DG units are sometimes equipped with Q/V droops, which is analogous as in the transmission network. This paper shows that the impact of reactive power on the voltage profile is limited in the considered low-voltage networks. The main reason is that in resistive networks the voltage is mainly linked with active power, not reactive power. Another, indirect, effect comes from the Q/V linkages in the overlaying networks, which is unknown and often counteracted by designated devices. Therefore, an effective way to avoid voltage limit violation in low-voltage networks is by implementing P/V droops in the DG units. A special variant of this is the voltage-based droop control that enables, without communication, to firstly change the output power of the dispatchable DG units and, only when necessary, also that of the renewable energy sources.