Splitting control for large scale power systems

In this thesis, a new two-stage splitting control design method is proposed. The new method is based on the concept of critical machines and the method of trajectory analysis. The first stage focuses on the stability issues to guarantee the stability in each island alter the splitting, and the second stage is used to deal with the system viability issues to prevent the possible island collapse and to improve the power quality after the splitting. Appropriate design makes the system splitting a competitive emergency control scheme but not just the last resort of the security control.; The advantages and effectiveness of the new method are justified through various test cases in the IEEE 118 bus system. The appropriately designed splitting control can be treated as qualified emergency control candidate in 24 out of total 33 unstable cases for a particular operating scenario. The detailed simulations show that, under the new splitting strategy, not only the island stability, but also the frequency and voltage deviation issues have been solved satisfactorily.; Further, the implementation of the splitting control in a power system is discussed in detail. The focus is how to include the new proposed splitting scheme into the existing power system security control framework. The new splitting scheme is implemented in an online analysis, real-time matching mode. The contingency screening module decreases the online computational burden and the "line matching" scheme simplifies the matching process. The online unstable prediction module guarantees that the splitting will be only applied when it is necessary. In addition, the mismatching problems under some extreme operating situations are also discussed and the corresponding real-time splitting control module is proposed.; Some important protection issues related to the splitting control are also included in this thesis. Due to the significant changes in power grid structure and the fluctuation of the related electrical quantities accompanying the system splitting, some relays may be inappropriately picked up and their operation may bring negative effects to the predesigned splitting control. The methods used to identify these vulnerable relays are presented and the possible solutions are proposed. The objective is to make the splitting control one of the qualified candidates of the power system emergency control measure without compromising the objectives of the protection system.; Keywords. critical machine; emergency control; splitting control; transient stability; transient stability margin index; viability control.