Under-Frequency Load Shedding Schemes Optimal Research With Real Power Systems Considered

The power system operation condition becomes more complicated with the development of net and the appearance of power market recently. Meanwhile, the net's security and stability need to be improved. The dynamic frequency responses of large interconnected power system show space-time distribution features with the input of various components which make the dynamic act of power system get more and more complex. The actual single-machine model is proposed by power system automatic load-shedding technical scheme. This model can't reflect the dynamic frequency characteristic of power system, so it's necessary to study the power system frequency's space-time features and design the appropriate under-frequency load shedding scheme.According to power system automatic load-shedding technical scheme, the final stable frequency should not be less than 49.5Hz and appropriate over-shedding is permitted. To improve the precision of the setting of under frequency load shedding equipment, eliminate over shedding or under shedding, correspond the equipment of the under frequency load shedding in system, this paper presents a under frequency load shedding model based on evolutionary and traditional optimal algorithms to solve the setting. The power system simulation softwares PSS/E and PSASP are used to get the dynamic frequency response of system and different optimal methods are compared in a real power system and Pan Zhihua power system.Based on the compared results, evolutionary optimal algorithm has better performance than non-evolutionary (traditional) optimal algorithm on this proposed model. The results meet automatic load shedding power system technical requirements for the final frequency not less than 49.5Hz and maximally limiting the frequency overshoot. All the final frequencies for the real power system are between 49.5-50.2Hz, and ones for Pan Zhihua are between 49.5-50.0Hz. The results for both power systems are satisfying. This dissertation provides the new method and means of setting for UFLS in large power system. It has great theoretical significance and practical reference value to configure the reliable third line of defense for power grid safe and stable operation.