Comparative Analysis of the Dynamic Properties of Variants of Automatic Frequency and Power Control Systems for Steam Power Plants Equipped with Once-Through Boilers

Abstract

Considerably complicated power-system problems that have to be solved by the Russian power-generating units and, consequently, the need to ensure the fully automated operation of the power-generating units under working loads necessitated improving the structure of the automatic frequency and power control systems (AFPCSs). Not all solutions adopted in the 1980s, in particular, the use of the classical variants of the automatic power control systems (APCS-1 and APCS-2), ensure the required quality of suppressing power-system disturbances. In this work, the authors performed comparative analysis of six AFPCS variants that correspond to both the classical APCS-1 and APCS-2 and their combinations. The research was carried out using a mathematical model under disturbances of characteristic types, viz., those caused by network frequencies, unit power settings, and boiler loads. The model was developed by approximating experimental step response curves of the 300-MW power-generating unit 3 equipped with a once-through boiler at Kashirskaya State District Power Station. The quality of control was analyzed by comparing the amplitude-frequency characteristics and the curves of the transient processes of the compared AFPCS variants and the integral quadratic criterion values and the maximum deviations of the controlled variables and control actions in the course of the above processes. The combined AFPCS and advanced APCS-2 proved to be the most preferable. The combined AFPCS variants offer advantages in terms of maintaining the steam pressure, while the advanced APCS-2 has an advantage as a means for controlling the unit power with the gain in the first case being somewhat greater than that in the second case. Both variants have been successfully used for a long time at numerous power-generating units of the country.