A novel three-phase unbalanced power flow solution for islanded microgrids with distributed generations under droop controls

Abstract

With the increasing penetration rate of distributed generations (DGs) in the distribution network, microgrids are widely applied for the benefits of efficiency and flexibility. The demands of power flow analysis for microgrids are increasing. However, the traditional power flow algorithms cannot be utilized directly when microgrids operate in islanded modes and the DGs are adjusted by a droop control scheme. To increase the effectiveness and generalization of the power flow, a novel two-layer iteration method for microgrids is proposed. First, the three-phase unbalanced power flow is calculated by the power-injection algorithm in the inner iteration. Then, the node admittance matrix of the transmission line, the loads, the power generations and voltage of DGs are updated directly through the power flow results in the outer iteration. Finally, the processes of calculating convergence solutions with inner and outer iterations are presented. The proposed method was implemented on the CloudPSS platform and tested with a modified IEEE-13 bus microgrid system. The power flow results of the proposed method are compared with the electromagnetic transient (EMT) simulation. The comparison results demonstrate the practicability and effectiveness of the proposed algorithm.

Keywords

• Distributed generations
• Droop control
• Islanded microgrids
• Three-phase power flow