Study of the Dynamic Operating Modes of Thermal Power Plants Under the Load Frequency Control in Electric Energy System

Abstract

The performance of the Interconnected Power System (IPS) of Ukraine during emergency events was analyzed particularly in the events when the nuclear power plant (NPP) becomes disconnected. Mainly, the analysis revealed significant frequency oscillations and excessive control actions that are applied to the regulating equipment of thermal power plant (TPP) units. Those events impose additional mechanical stress on servo drives and the mechanisms of turbine control, thereby resulting in the reduced service life and an increased probability of failure during load frequency control. Current study was carried out using simulation in the DigSilent PowerFactory software with the usage of the comprehensive model of the Ukrainian IPS that incorporates transmission networks, generators, load nodes, and intersystem transmission lines. The participation of a 300 MW TPP unit in normal primary load frequency control (NPLFC) during an emergency shutdown of an NPP unit was examined. It was established that during frequency deviations, alternating fluctuations are observed in the control signal that is applied to the servomotor, which are not accompanied by corresponding changes in turbine power output but cause increased wear of the regulating equipment. In order to reduce the amplitude of these fluctuations, the authors proposed the usage of a first-order Butterworth filter and a moving average filter for smoothing the regulation error signal. Simulation demonstrated that the application of the Butterworth filter reduces the amplitude of the control signal by a factor of 7,8, while the moving average filter reduces it a factor of 1,54 thereby maintaining frequency regulation accuracy within the required standards. Proposed approach minimizes redundant control actions of the TPP unit servomotor, thereby improving the reliability and extending the lifetime of the regulating equipment, while preserving the unit’s maneuverability and compliance with the established frequency and active power control requirements.