Parameters Design and Stability Analysis of Weak-Grid Interfaced Inverter with Droop Control

Droop-controlled inverter (DCI) is known for appealing characteristics in load sharing and stability enhancing. By simulating the external droop feature of synchronous generator, the DCI can also naturally offer necessary frequency/voltage regulation or provide active/passive power support when interfaced to the utility grid. However, with the growing penetration of distributed power generation system (DPGS), the large impedance in weak grid may arouse unexpected oscillation problem. In order to evaluate the stability performance of the DCI when it is interfaced to weak grid, the sequence- impedance model of DCI is established for the first time in this paper. The controller parameters of DCI are designed step by step under the theoretical guide. On this basis, the interactive oscillation risk between DCI and weak grid is analyzed in detail through Nyquist criteria. The results show that DCI exhibits excellent adaptability in weak grid integration. All these theoretical conclusions are tested and verified via simulations and experiments eventually.