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In a large-scale wind farm, under the influence of the wake effect, the single-machine maximum power extraction control strategy would not be able to function at the ideal optimal value. It is important to study the coordinated operation strategy of the wind farm under the wake effect to improve the output power of wind farms and improve the economic benefit. In this paper, a practical wake model called the PARK model is used and a wake superposition model based on energy balance is derived. Based on these models, an optimization problem is formulated to maximize the output power of the wind farm considering the wake effect. Taking the Horns Rev offshore wind farm as an example, the stochastic points method, particle swarm optimization, and the pattern search algorithm are implemented and compared with the single-machine maximum power extraction algorithm. Test results show that the particle swarm optimization and the pattern search algorithm have better performance. The output power of the wind farm increases by about 10 percent. The particle swarm optimization requires less computation while the pattern search algorithm obtains better and more practical results. Finally, the pattern search algorithm is used to improve economic benefits under different wind conditions.

In many China's enterprise-owned power grids (EPGs), the frequently changing operation state and the poor reliability of some outdated facilities may lead to inaccuracy or even malfunctions of the traditional pre-decision-making emergency control systems, which have already caused several blackouts in EPGs. To solve this problem, a real-time decision-making emergency control system based on the detailed time-domain transient stability simulation is designed. Based on the trajectory characteristics of the stability restoration process of EPGs, the stability restoration criteria are proposed to significantly shorten the simulation time needed to judge the elimination of a certain stability problem. Fast decision-making algorithms for frequency instability, rotor angle instability and branch overload with relatively low computational cost are introduced. Control strategies can be determined within a specific time after faults are detected. The corresponding countermeasures are directly executed when the strategy is obtained. The system configuration is designed to be capable of dealing with complicated and unanticipated faults, such as cascading outages and unexpected grid splitting. The test results of a 31-node practical EPG show that the proposed algorithms and the system configuration are practical and efficient. This work is a meaningful exploration of the real-time decision-making emergency control system.

Parallel computing is an effective tool to improve the efficiency of transient stability simulations. The method of forming the bordered block diagonal form matrix (BBDF method) is widely used. However, as the number of subnets increases, the computational complexity of the cut-node network and the communication overhead become large quickly, which limits the efficiency of the method. A new fully parallel BBDF (FBBDF) method is proposed to solve this problem. During the iterative solutions of network equations, the FBBDF method parallelizes the solutions of subnets and the solution of the cut-node network by utilizing the result of the cut-node network at previous iteration step for the solutions of subnets at current iteration step. The calculation time can be reduced from the total solution time of the largest subnet and the cut-node network to the largest solution time of subnets and the cut-node network. The whole network is divided via the factorization path graph. The test results show that the FBBDF method requires less computing time than the classic BBDF method and can increase the speedup of parallel computing to more than 16x with 40 threads in a 24886-node actual power system.

In the power system parallel transient stability simulation (TSS), the parallel overhead will rise significantly with the increase in concurrency, which will seriously affect the efficiency of parallel computing. However, there are relatively few studies on the parallel overhead in the power system research field at present. In this paper, the geneses of the parallel overhead are introduced from the point of view of computer technology. The composition of the parallel overhead of the bordered block diagonal form (BBDF) method and the nested BBDF (NBBDF) method of the power system parallel TSS is analyzed. The time consumption of computing tasks and the parallel overhead of the BBDF method and the NBBDF method implemented by message passing interface (MPI) and OpenMP under different thread scheduling patterns are tested in detail in the 2383wp system and two practical power systems (13 490 node and 24 886 node). On this basis, an efficient implementation of the NBBDF method based on subnet-core mapping and mixed programming of MPI and OpenMP is suggested, which can further reduce the parallel overhead and increase the speedup ratio to more than 17x with 64 cores in the 24 886-node system. At last, some rules are summarized based on the test results.

To simplify the transient stability analysis of a large-scale power system and realize real-time emergency control, a fast transient stability simulation algorithm based on real-time dynamic equivalence is proposed. Generator models are grouped and aggregated according to a fast numerical integration. A fast calculation method of the admittance matrix is then proposed to calculate the parameters of an equivalent system, and numerical integration is performed using the obtained equivalent system. Then, based on integral sensitivity, a new fast emergency control strategy is proposed for the equivalent system. The final emergency control strategy is obtained by mapping the control strategy for the equivalent system back to the original system. The results of a simulation on an East China Power System that includes 496 generators and 5075 buses show that the suggested algorithm can output an accurate transient stability simulation result and form an effective emergency control strategy. The proposed algorithm is much faster than the existing solutions and has the potential to be used for online pre-decision.

When solving network algebraic equations during power system transient stability simulations, the nonzero elements in the independent vector and the elements needed in the solution vector are determined by the location of source nodes. Different kinds of source nodes will have a different influence on the solution process of the network equations. According to these features of source nodes, sparsity techniques, more specifically, the node ordering algorithm and sparse vector method, are improved in this paper. A new heuristic ordering algorithm is proposed to enhance the efficiency of the sparse vector method by reducing the number of nodes in the factorization path set of source nodes while maintaining the sparsity of the factorized matrix. A multipath sparse vector method is proposed to avoid the unnecessary computation in the iterative solution process of the network equations, whereby the idea of the method is to form different paths for different types of source nodes. Different paths are used to solve different elements in the solution vector. The correctness and effectiveness of these improvements is proven by the simulation results of three practical power systems (up to 13 490 nodes) and six IEEE examples (up to 162 nodes).