Passivity-Based Synchronization Stability Analysis for Power-Electronic-Interfaced Distributed Generations

Distributed generations (DGs) have been increasingly employed in AC microgrids to provide carbon-free power supply. To coordinate multiple DGs, careful attention must be paid to the synchronization stability of their interfaced inverters. Otherwise, low-frequency oscillations and even loss of synchronism may occur and pose a great threat to the system. The conventional solutions towards this issue are to derive the microgrid state-space model and evaluate its stability based on the roots of the characteristic equation. However, tremendous efforts shall be spent on modeling as the number of DG increases. This paper provides an alternative way, which localizes the target of system synchronization stability into individual inverters. It is revealed and proven that microgrid synchronization stability can be guaranteed if all the inverters are designed to have passive synchronization behaviors. To fulfill this requirement and achieve a satisfactory phase margin, an auxiliary controller is designed to reshape frequency-power characteristics of inverters. Finally, case studies of a three-DG microgrid verify the theoretical findings as well as the effectiveness of the auxiliary controller.