Complex Power System Frequency Dynamic Process Analysis Based On The Trajectory

Under-frequency load shedding (UFLS) is widely used in complex power system, which serves as the last defense line of power system security. The basic work for proper UFLS strategy is to get hold of the dynamic characteristics of frequency. Although, design of single machine with centralized load model and multiple machines checking method have been carried out for the setting work of UFLS in most complex power system, this method has its application limit. And it is also hard to achieve any information of the capability to keep frequency stability from the UFLS scheme. Under the situation that the parameters'accuracy is not certified in the dynamic process of frequency, the checking results'acuracy of UFLS scheme can not be guaranteed.In this paper, theoretical analysis and time domain simulation methods were combined to research the frequency regulation effect problem of single-load and single-machine system. The practical use of dynamic frequency process research on complex power system was analyzed, on the basis of which, the keep capability of frequency stability by UFLS scheme for complex power system was researched.In the research on the frequency regulation effect problem of single-load and single-machine system, analytical method was researched on the dynamic frequency process of single-load and single-machine system from its mathematical model aspects. The analytic solution errors of the former research were corrected on the dynamic frequency process problem of single-load and single-machine system. The coefficients calculation method of frequency regulation effect based on the frequency trajectory was put forward for the first time. The frequency regulation effect under different situations was also researched, which improved the setting work of UFLS scheme in single machine system with centralized load model.In order to make it practical for the dynamic frequency process research for complex power system, research was carried out on the problems of the acquisition of practical models and parameters, error evaluation index, the key factors of operation, the adjustment principle of parameters and so on. The practical parameters have been achieved according to a large number of actual trajectories of frequency fluctuation events of complex power system, which reflected the principal character of the dynamic frequency process in real complex power system. And this work has laid the technical and method foundation for UFLS scheme checking of complex power system.To check the capability of keeping frequency stability by UFLS scheme, a checking method was proposed for the first time, which used the centralized power shedding mode to check the defense ability of UFLS scheme for complex power system. And the test work was also carried out on the capability problem of keeping frequency stability in a real complex power system. All of above fully verified the effectiveness of the whole research method based on frequency trajectory on the dynamic frequency process problem for complex power system.