Design Of Under-Frequency Load Shedding Schemes Using Combinatorial Optimization

With the development of power system, the increasing scale of power grids, and the input of various dynamic components which make the dynamic act of power system get more and more complex. The dynamic frequency responses of large interconnected power system show space-time distribution features. The Single Generator Single Load Analysis method which is commonly used in the current power system doesn't suit to the needs of setting for the Under-frequency load shedding (UFLS). The study of dynamic frequency responses in multi-machine power system and design the UFLS shemes which adapt to it are particularly important. However, so far the analytical solution of power system dynamic behavior (including frequency) can't be getted. In this paper, the dynamic frequency responses of system are getted by the power system simulation software, and the combinatorial optimization algorithms is used to achieve UFLS optimal shemes.The present status of UFLS research is summarized and analyzed, and the key problems are pointed out in this paper. The requirements, principles and methods of setting for the traditional UFLS sheme are also introduced and analyzed. Mathematical model and its solution of optimal setting for UFLS are proposed based on the combinatorial optimization method under various operating conditions and fault. So the algorithm has strong adaptability.By means of user-defined function, excitation system and governor model which are used widely in china, and the traditional UFLS model are built in PSS/E. On this basis, a certain actual power system in china is built, which realizes the data conversion from the BPA to PSS/E. The possible power-load unbalance contingencies of four typical operating conditions are setted for the power grid. Then the optimal setting for UFLS shemes are established in two cases which consider the probability of failure and don't respectively. Compared with the current sheme, the optimal sheme which proposed by this paper can effectively control the amount of load shedding, the over-shedding or under-shedding phenomena can be avoided, so the the system frequency can restore to the good state, and the amount of load shedding reduce significantly. This dissertation provides the new method and means of setting for UFLS in large power system, which consistent with the actual situation. It has great theoretical significance and practical reference value to configure the reliable third line of defense for power grid safe and stable operation.