Large Signal Stability Analysis of AC Microgrids Considering the Storage System

Many urban communities are increasingly turning to AC Microgrids (AC MGs) as an alternative source of electricity. Distributed energy sources, different loads, and energy storage systems are all interfaced with AC MGs through power electronic converters. These tightly regulated loads could be regarded as constant power loads (CPLs), usually inducing negative impedance instability problems. Unfortunately, most stability studies have been based on small signal linearization techniques. This paper investigates the large signal stability of AC MGs based on mixed potential theory, and considers the influences of the storage system and CPLs. Firstly, the AC MGs are converted to DC systems in dq rotating frame. Then the mixed potential models are constructed and analyzed, and large signal stability criteria are derived. The criteria give important constraints on control parameters of the storage system, and the characteristics of CPLs are also taken into account. Simulation results indicate the criteria could guarantee the whole AC system stable during large disturbances.