Primary and secondary frequency control in a small power system (SPS) with rotating and static sources after islanding

The aim of this paper is to present mathematical relation between frequency and both generated and consumed active power balance in a small power system (SPS) during and after its islanding. The paper also offers a method for frequency control in an autonomously operating SPS. Active power and frequency measured and registered during switching from operation synchronous with external power system to island operation served as means to identify SPS´s equivalent inertia constant and primary frequency control parameters. These values in turn served as the basis for selecting secondary frequency control parameters. The proposed idea of frequency control in SPS is illustrated with an example based on power and frequency changes registered during an experiment that consisted in the islanding of a small industrial CHP plant with an 11.5 MW synchronous turbo generator.