Impedance-based adaptive droop method in islanded microgrids with three-phase and single-phase converters for line loss reduction

Abstract

During the last decade, the integration of Distributed Energy Resources (DERs) has considerably increased, establishing the microgrid concept. A common power sharing methodology applied in converter-dominated microgrids without physical communication among the DERs is the droop control method. According to this method, the active power-frequency and the reactive power-voltage droop curves are adopted, in order to fulfil the load demands with power of high quality and reliability. Conventionally, the droop coefficients are fixed and predetermined, according to the nominal apparent power of the converter. However, this power sharing may not be the optimum, regarding the line losses. This paper proposes a novel adaptive droop control method, where the droop coefficients are adjusted based on the indirect measurement of the microgrid impedance, aiming at operation with reduced line losses. The sensed microgrid impedance is different for each DER, since the line impedances between the DER and the loads are different. The proposed control strategy can be implemented in both three-phase and single-phase converters, while the location and the size of the loads can be arbitrary within the microgrid. The effectiveness of the proposed control strategy is validated by analytical simulation tests.