Correlation between metrics for primary frequency reserve and frequency quality

As the penetration of renewable, inverter-connected energy sources increases, the relative inertia of the power system decreases. Consequently, there are indications that the frequency quality, the ability to keep the active power balance, is declining. During normal circumstances, primary frequency control is the ancillary service the system operator uses to contain the frequency within a nominal band. Traditionally, the providers of primary frequency control are synchronous generators, but recently, new providers have begun to enter the primary frequency reserve market. Thus, it is essential to study how the service-providing units’ properties affect the power system’s frequency quality. In this study, several performance metrics are defined to describe the step and impulse response, as well as the stability margin, of a power system with a primary frequency control unit and a low inertia power system. These performance metrics quantify the unit’s properties. The correlation between the defined metrics and frequency quality could be calculated by studying the frequency quality when a stochastic power imbalance is added to the power system. The study found significant correlations between metrics derived from the closed-loop system and frequency quality, where metrics for the activation speed correlated with frequency deviation and metrics for oscillation reduction were correlated with the rate of change of frequency.