Network Analysis Based Methods For Pilot Node Selection And Voltage Control

Secondary Voltage Control(SVC) is beneficial to improve the power system’s voltage stability in Hierarchical Voltage Control. The whole power system is divided into several relatively independent parts by SVC, and the specific pilot node which positively influences the voltage can be found in each part. Making each pilot node’s voltage remain unchanged by the established control laws will maintain regional voltage level in a good condition.A rational selection of pilot node would play an important role in secondary voltage control’s effectively working. In this paper, questions that might exist in the system would be analyzed through methods of pilot node selection. Starting from the definition of pilot nodes, with the tools of network impedance matrix, by analyzing the voltage sensitivity of generator to load and the coupling relationship among load nodes, this paper could note that regional structural controllability and observability are the theoretical basis of pilot node selection, and could design the parameter of pilot node selection considering the generator working condition by the analyzing above. Considering regional structure controllability indicators and regional structural observability indicators, this paper proposed pilot node selection function. The result of numerical example and the actual system simulation showed that this method could effectively select the pilot node and has certain robustness. This method is based on coupling among nodes, and the direct use of the measurement information of the network impedance matrix and the generator nodes achieves quick selection of pilot node, which could avoid the incorrect selection of pilot nodes caused by ignoring the generator reactive power margin.The access of wind power has brought challenges to secondary voltage control, the influence of wind power access needs to be considered when choosing the pilot node. Through theoretical analysis of typical systems and numerical examples simulation of complex systems, the paper points out that: such factors as the type of wind turbines, the access position and output volatility of wind farms will affect the selection index of pilot node, and the original state variables can’t be ignored. To solve above-mentioned problems, this paper put forward selection index of pilot node considering regional operation state. According to different scene of the farm output, a pilot node selection function considering scene probability is designed. The simulation results showed that, the method could reasonably reflect the effects of wind power access to the pilot node selection, relevant examples revealed the change law of pilot node selection results after wind power access.A secondary voltage control law is the most critical issue of secondary voltage control. In this paper, the voltage sensitivity of generator to load was presented, and the selection method of the generators those participate in secondary voltage control was presented. By analysing the coupling relationship among generator nodes, using existing objective function and constraint conditions of secondary voltage control, transforming the original objective function, the control law was solved by the least square method. Simulation results show that the secondary voltage control based on the network analysis can eliminat e the voltage shift of the pilot nodes in the control region, which leaves enough reactive power reserve to extend the process of voltage instability and improves the voltage stability of the system.