Modal estimation in distributed synchronous generation systems under three-phase unbalanced conditions

Underdamped electromechanical oscillations (EMO), which are a typical problem of transmission systems, can also appear in power distribution systems (PDS) where synchronous generators are present. The tools to study EMO in bulk power systems are well established. Nevertheless, distributed synchronous generators have a different behavior from the ones connected to balanced three-phase bulk power systems. In these cases, some well-consolidated tools used to study EMO in bulk power systems are not adequate, since in distributed generation systems the load fluctuation is proportionally much higher and, therefore, it is not possible to define a good approximation for an equilibrium point. In this paper, a set of appropriate tools, which does not depend on the system model, is utilized to assess the presence of EMO in unbalanced PDS with synchronous generators. The obtained results show that the measurement-based methods which use ambient and ringdown responses can be applied to estimate the parameters of EMO in unbalanced PDS with high accuracy.