1132 / 2019-05-21 09:18:16

Holomorphic Embedding Load Flow Method for Islanded Droop-Controlled Microgrids

droop-controlled islanded microgrid;,power flow calculation;,holonmorphic embedding method;

In droop-controlled islanded microgrids (IMGs), the voltages and frequency are regulated by cooperation of controllable distributed generations (DGs). There is no such DGs serving as slack buses and the frequency is not const. Consequently, traditional load flow modelling method is not suitable for droop-controlled IMGs. Besides, convergence is a major challenge for Newton-type iterative methods, and the case with droop-controlled IMGs is even worse. Therefore, a non-iterative holomorphic embedding load flow method (HELM) for droop-controlled IMGs is proposed in this paper. Firstly, taking voltage of each node and frequency as variables, the load flow model of IMGs is built considering the static voltage/frequency characteristics of droop-controlled DGs. Then HELM formulations for droop-controlled IMGs are developed in such a way that the equations are holomorphic, with the unknown variables represented by power series. The coefficients of power series for unknown variables are determined by recursive formulas according to germ solutions. Finally, the numerical values of unknown variables are obtained by Padé approximants. The proposed method is tested on a droop-controlled IMG based on IEEE 33-node distribution system. Numerical examples demonstrate the correctness and effectiveness of the proposed model and method.