Research On Power System Under-Frequency Load Shedding Algorithm

Power system has entered the age of large power grid, high voltage and large units, and the development of grid interconnection and power market makes the dynamic act of power system get more and more complex. Which make the requirements of safe and stable operation of power system get higher and higher. Under-frequency load shedding (UFLS) is the earlyest control means for the frequency stability. Now, it is still the last line of defense for power grid safe and stable operation, and one of the main means, which prevent the accident from becoming more serious, and prevent large area outage, when power system undergoes a serious disturbance. In factual running, power system has appeared the situations of UFLS being failure to run for the system voltage decline with the disturbance, or the system collapse for the lack of active power which results in UFLS running too late. In this paper, the principle and algorithm of UFLS are researched in-depth. The purpose is heightening the stability of frequency, when power system undergoes disturbances. The paper's main contents include the following aspects:1. Traditional UFLS algorithm based on frequency absolute value and adaptive UFLS algorithm based on frequency rate of change are analyzed in-depth. Adaptive UFLS algorithm based on local frequency rate of change is improved. An adaptive UFLS new algorithm based on wide area information, which heightens the shedding effects by the measuring of system frequency rate of change, is proposed.2. Using the function of PSS/E user-defined model, and according to the flow of PSS/E dynamic simulation, adaptive UFLS model and the governor model used by practical power system are built with FLECS language by calling internal dynamic simulation arrays, paramitres and ralated function of PSS/E. On this basis, IEEE's 145-bus 50-generator system with some modification is built, Sichuan Panzhihua power system and its UFLS system are built.3. On IEEE modified test system and practical Panzhihua power grid, respectively, traditional UFLS scheme and adaptive UFLS scheme with different accidents are analyzed and compared. The adaptive UFLS scheme proposed by this paper, acquires a batter UFLS effect compared with other UFLS schemes.