Research On Evaluation And Optimization Of Power System Flexibility With Large Scales Of Renewable Energies

With the development of large scales of renewable energies, the power system is strongly affected by uncertain factors, which will bring many negative effects on the safety and reliability of power system. It is necessary for power system to possess a certain flexibility and response capability to cope with or eliminate and reduce the negative effects. As the evaluation of the uncertain factors and strain capacity of power system, power system flexibility, which is closely related to power system safety, reliability and economy, is the internal demand of modern power system and is one of the most important indices that cannot be ignored. Therefore, the research on evaluation and optimization of power system flexibility is far-reaching for power system planning, operation and optimization.With the integration of large scale of renewable energies in power system, the evaluation method and optimization method is proposed in this paper. Based on the current research, the definition, characteristics and properties of power system flexibility are analyzed. The relations and the advantages and disadvantages among kinds of flexibility resources are presented, which will be the foundation for flexibility index and optimization. With the characteristics of flexibility, the flexibility model and comprehensive assessment system are proposed based on the analysis of characteristics of power system flexibility. Flexibility model considers the maximum mutation of renewable energy generation, while the constraints are divided into two parts, namely traditional constraints and flexibility constraints. In comprehensive assessment system, the assessment table which can reflect the states, changes and trends of flexibility, is established according to controls methods and objects. The inherent flexibility index can compare the flexibility between different operation states and different power systems. The optimization of flexibility is divided into two parts in this paper, namely flexibility resource optimization and flexibility operation optimization. The flexibility resource optimization considers the characteristics of flexibility demand to formulate the sets of flexibility resources. The response costs of variable flexibility resources are analyzed. The flexibility resource optimization model is established under the condition that the flexibility demand is satisfied first. The flexibility operation optimization considers the demand of flexibility and economy together and the model is established. The Pareto optimal frontier curve, which will provide a theoretical reference for operating personnel or dispatcher, is presented via multi-object particle swarm algorithm. Finally, the flexibility evaluation model, flexibility resource optimization model and flexibility operation optimization model are verified through IEEE-30 node grid and IEEE-118 node grid. The results show the models which fully consider the characteristics of flexibility can reflect the important functions and practical uses of the power system flexibility. It is also proved that the evaluation index and optimization method is valid and significance.