On Optimization Control Of Coordination Of Emergency Load Shedding And Corrective Line Switching

The expansion of the UHVAC\DC (Ultra-High-Voltage AC\DC) transmission system leads to the increase in the proportion of receiving power of the eastern power system. The increase in pene-tration of the renewable energy resources, like wind power and solar power, seriously changes the power system dynamics. New problems and challenges are brought about, like a sudden loss of a bulk power. It is crucial to study power system security and stability control system to deal with these problems and challenges for the purpose of secure, reliable and economic operation. Ordi-nances of Electrical Security Accident Emergency Disposal and Investigation define the accident level and cost related to the load to be shed, imposing limitation on load shedding scheme. To de-crease the load to be shed and thus decrease the accident level and cost, electric companies are forced to adjust their original security and stability control system, especially optimizing the load shedding scheme and study other measures like corrective line switching. This study focuses on emergency load shedding and corrective line switching, and the results can help guide the power system opera-tion and control.The main content is listed below:(1) An optimization algorithm for emergency load shedding considering transient security and stability constraints is proposed. An emergency load shedding model, whose objective function is to minimize the total load shedding cost, is proposed. The constraints include transient angle stability, transient voltage and frequency deviation security, and load shedding amount. The assessment of se-curity and stability are all calculated on the basis of full time-domain simulation of the power system. By analyzing the characteristics of the optimal solution of this model, a trajectory sensitivity-based solution approach is presented, which converts the non-linear programming model into linear pro-gramming one and approaches the optimal results with iterations. A parallel computation approach scheme is implemented in obtaining the trajectory sensitivities to accelerate the solving process. The validity of this algorithm and parallel computation is tested and verified using two different power systems.(2) A corrective line switching assessment indexes framework is constructed. The feasible im-plementation measures of corrective line switching is analyzed, namely, the lines and transformers that are not in service after maintenance and the reserved line due to the open loop. On the basis of this analysis, the problems or scenes that can implement corrective line switching are clarified, namely, the equipment overload and under-voltage of load bus. The impact of corrective line switch-ing to power system economics, security and reliability is analyzed, and thus construct the assess-ment framework, which could support to design the corrective line switching scheme.(3) An optimization algorithm for corrective line switching is proposed. The mathematical na-ture of the corrective line switching problem is analyzed based on its characteristics. Then this prob- lem is transformed into a multi-objective optimization problem through the quantitative assessment indexes set, concerning economics, security and reliability aspects. Firstly the candidate schemes are filtered out based on sensitivity, all of which can satisfy the operation requirement. The mul-ti-objective optimization is carried out through TOPSIS based on the assessment indexes set. The validity of this algorithm in solving emergency states and decreasing load shedding cost is testified on the actual power systems.(4) An optimization algorithm for load shedding and corrective line switching coordination is proposed. The coordination model is constructed. Due to the key characteristic that the higher sever-ity of the emergency state is related to more loads to be shed, this optimization is divided to two stages. The first one is corrective line switching stage, in which the corrective line switching scheme that can best solve the emergency state is selected. The second one is load shedding stage, in which the load shedding scheme with least load to be shed is selected to optimize the load to be shed. The validity of this algorithm in solving emergency states and decreasing load shedding cost is testified on the actual power systems.