On Aggregation Requirements for Harmonic Stability Analysis in Wind Power Plants

In harmonic stability studies, stable operation of a power system must be ensured at any possible configuration. This leads to a large number of cases due to the high number of components in a power system. An aggregated model can be used to lower the complexity and to reduce the number of different cases. In other words, several similar converters (e.g. Wind Turbine Generators) can be replaced by a converter with larger ratings. In most cases, aggregated models work well for stability studies, however, in some cases the aggregation might result in a wrong evaluation of stability. The aggregation reduces the complexity of the system by removing some statevariables of the overall system matrices; however, sometimes these removed variables contain some important information about the stability of the system. In this paper this problem is shown by a case study and it is evaluated by different methods, and a solution is also proposed.