Online Evaluation Method of Power System Frequency Strength and Its Application

The substitution of large-scale renewable energy for traditional synchronous generators reduces the frequency strength of the power system and increases the risk of frequency instability. Currently, online evaluation of system frequency strength and monitoring system frequency stability margin are of great significance to the safe and stable operation of the system. Therefore, this paper proposes an online evaluation method of frequency strength suitable for the actual provincial asynchronous power grid. The system includes three parts: data acquisition and preprocessing, system frequency modulation model simplification and system frequency strength evaluation. Firstly, based on the monitoring operation control system, the operating condition information such as the start-up and output of each equipment in the system is obtained. And through data in BPA and the wide area measurement system, the dynamic model library of equipment frequency modulation in the system can be established. Secondly, the equipment running in the system can be reduced by the method of unified transfer function structure (UTFS) approximation. Furthermore, based on the UTFS parameters of the system, the frequency drop depth coefficient and slope coefficient are calculated to evaluate the frequency strength of the system. Finally, the effectiveness of the proposed evaluation method is verified by simulation.