Tracking of Thevenin equivalent parameters on weak voltage load bus groups

In this paper, a scheme is proposed to monitor the weak voltage load bus groups with Thevenin equivalent parameters. First, continuation power flow solves V-lambda curves of the load buses. Then weak voltage buses are selected with voltage magnitude variation under similar load variation rate. The buses of bigger normalized Delta V are chosen as weak voltage ones. The rate of voltage magnitude variation is used as grouping standard and an index is constructed for weak voltage load bus group similarity. A fuzzy maximal tree is established to group the weak voltage load buses according to their similarities and simultaneously the geographic factors are taken into consideration. We track network side Thevenin equivalent parameters on each typical bus of weak voltage load bus group and analyze the problems of Thevenin equivalent parameters computing based on local measurements. Therefore, a power flow data based simulation method to track Thevenin equivalent parameters is presented, which can observe the voltage stability margin of weak voltage load bus group. The simulations on IEEE 118 bus system show our scheme is effective.