A Fuzzy Clustering Based Method For Secondary Voltage Control Partitioning

With the development of interconnected power network, the problem on voltage stability has become increasingly important. Consequently, coordinated voltage control system that guarantees the security and stability of power system is crucial. In this situation, hierarchical voltage control system emerged as the times require. Commonly, hierarchical voltage control consists of three levels, they are tertiary voltage control (TVC), secondary voltage control (SVC) and primary voltage control (PVC). TVC setting on dispatching center is based on the whole system. SVC setting on system hub node is based on the region. It receives the control signal from TVC and maintains voltage amplitude of pilot node in the area nearby the set value. If the voltage amplitude of pilot node has deviated from the set value, PVC setting on power station and load must be started. In the secondary voltage control, how to divide the whole system into some approximate decoupling regions, which largely enhances the efficiency of voltage control, is an important subject.Based on the characteristic of reactive power voltage control, this paper researches the function and assignment of each level in hierarchical voltage control system. And then come to the conclusion that SVC is the key link of voltage control in power system for keeping voltage stability. By summarizing the reports and achievements in the secondary voltage control system, this paper analyzes the implementation secondary voltage control which involved the selection of pilot nodes and control strategy. And then the methods solving the problem of voltage control decomposition by fuzzy clustering are proposed. Based on the control of reactive power source, each PQ bus in electric network is regarded as a single object whose characteristic index is the control of each reactive power source. Because this method considers the specific process of secondary voltage control adequately, it is more superior comparing with the normal electrical distance.A New England 39-bus system is used to verify the procedures of power network partitioning by fuzzy clustering. The result shows that both methods presented in this paper are effective and feasible. By comparing the proposed two methods, we can know that FCM arithmetic has more advantages such as good convergence, less isolated point and appropriate scale of subarea, etc. Accordingly, the fuzzy c-means clustering is suit to solve secondary voltage control partitioning problem.