Transmission Expansion Planning Optimization Strategy And Assessment Of The Value Of Security

The traditional power system planning faces new challenges due to the integration of large-scale renewable energy and the construction of ultra high voltage power grids. The development and evaluation of planning schemes should not just rely on the planners'experience, whereas the efficient and systematic approaches must be adopted to assist planners to make decisions. With a view to the several major power blackouts in the world in recent years, how to systematically assess the security of power system planning schemes becomes an urgent problem. Therefore, this dissertation designs an optimization strategy for transmission network expansion planning from two aspects of global and local, and studies the evaluation of the value of security of power system planning schemes thoroughly.Firstly, in view of the features of transmission expansion planning (TEP), discrete monkey algorithm (DMA) is proposed as the global optimization strategy for solving the TEP problem, which can be used as the core algorithm in the decision support tools for planners. It includes climb process, watch-jump process, cooperation process, somersault process and termination criteria. Large-step and small-step climb processes are designed to avoid invalid climb process when solving optimization problems with discrete variables by primary monkey algorithm. Cooperation process and stochastic perturbation mechanism are also introduced to improve the computational efficiency. Numerical results demonstrate that DMA has strong robustness and is capable of solving large-scale TEP problems rapidly.Secondly, a local search strategy is proposed for the TEP problem. Removing one circuit in the current transmission planning scheme may make some components overloaded, some buses isolated or the remained system intact. Based on the three situations, three sets known as local bus, local circuit and effective local circuit are defined, and thus the neighborhood of current transmission planning scheme is presented. Then, the local search (LS) in the neighborhood is transformed into a 0-1 programming problem by variable transformation and the zero-one implicit enumeration method is employed to solve the problem, in which pruning strategies concerning the characteristics of TEP are designed to reduce the number of nodes to be assessed in enumeration process and improve search efficiency. The local search strategy, on the one hand can significantly improve the local search capability in global optimization algorithm, and on the other hand can help the planners adjust the planning schemes.Finally, concerning the integration of large-scale wind power, the integrated model of generation and transmission expansion is proposed based on the assessment of the value of static and dynamic security. Based on the predicted hourly load and wind power output data in the planning horizon, the unit commitment is used to evaluate the costs of preventive control, emergency control and social loss due to the uncertainty of load and wind power. The cost of preventive control consists of power generation fuel cost, the environmental cost and the load shedding cost. This not only provides a systematic method of secutity assessment of power system expansion plans, but also broadens the perspective of power system planning from the technology and economic assessment to the measure of the value of the whole society. In the assessment process, the preventive control and emergency control of cascading failures are also presented, which provides a powerful tool for cascading failure analysis of planning schemes and makes the security assessment more comprehensive and reasonable.