Determining a critical number of similar units in a power network

The method involves performing a robust stability analysis of a combined system consisting of all similar units (1,1') and a power grid (3) using the frequency domain representation as parameter. An upper bound of similar units for which the combined system is stable is determined from the analysis result. DEPENDENT CLAIMS are also included for the following: (1) computer program for determining a critical number of similar units in a power network; and (2) data processing system.