Static Voltage Security Assessment And Reactive Power Optimization In Joint Power Transmission And Distribution Systems

In recent years, a large number of distributed generations have been connected to the power system. On the one hand, the distributed generations can save investment and reduce the operation energy loss because of the renewable and non-polluting characteristics, so the distributed generations have broad development prospects. On the other hand, the distributed generations have brought new problems to the operation and analysis. Transmission system and distribution system are analyzed independently in the traditional research methods. With the accession of a large number of distributed generations to the distribution system, the allocation pattern of power supply has been changed, there is interaction between the transmission and distribution systems so it is difficult to delimitate clearly. Therefore the traditional methods are no longer applicable, global analysis of transmission and distribution network is needed. This paper concretes on static voltage security assessment and reactive power optimization decision in joint transmission and distribution systems from the joint view.Static voltage security assessment methods carry on prevention and control through contingency analysis, then the system can not only remain stable in the current operating state, but also maintain stability and a certain static voltage stability margin in a contingency state. This paper establishes a static voltage security assessment model aiming at a minimum control cost while taking into account the mutual influence of transmission and distribution systems. Therefore a certain static voltage stability margin can be maintained in the transmission and distribution systems before and after the expected failure. The simulation results of the corresponding examples verify the correctness of the model.With the accession of a large number of distributed generations to the distribution system, it is necessary to consider the self-regulation of distribution system. The master-slave method is used in this paper to implement static reactive power optimization in joint transmission and distribution systems. Static reactive power optimization mode is established and the iteration between transmission and distribution systems is taken through the interaction of the boundary nodes.The dynamic reactive power optimization with distributed generations is established based on the static reactive power optimization considering the randomness of distributed generations and the times constraints of reactive equipments. Sub-time strategy is used to solve the randomness of the distributed generations. First divide the research time into several reasonable period, then calculate the output of each period which is used for reactive power optimization. The control variables of the reactive power optimization in the transmission and distribution network with distributed generations includes continuous variables such as generator output and discrete variables such as transformer tap, reactive power compensation capacitor bank. When optimizing, the discrete control variables need to meet the constraints of action times. While there are no constraints of action times to the continuous control variables, and there is no interaction between the various sub-periods. Therefore we need to use different approach for continuous and discrete variables. In this paper, a combination algorithm of PSO and interior point method based on the overall nesting strategy is used. The continuous variables are optimized by interior point method and the discrete variables are optimized by PSO. The interior point method is embedded PSO as the part of fitness evaluation, and the respective advantages of PSO and interior point method are utilized full in this algorithm.The proposed models and methods are simulated in the corresponding examples of transmission and distribution systems. The results show that the proposed algorithm considers the impact of the regulation of the distribution system to the transmission system and the joint reactive power optimization can be achieved effectively.