An Optimal Thevenin Equivalent Estimation Method and its Application to the Voltage Stability Analysis of a Wind Hub

A simplified voltage stability analysis method is to use a static Thevenin equivalent to represent the electrical connection to a load center. Assuming fixed values of the Thevenin voltage and reactance, a power-voltage (PV) curve analysis can be performed to find the voltage collapse point and stability margin. This paper proposes a method to compute the static Thevenin equivalent voltage and reactance of a power system using measured data. The method is validated with simulated PMU data and with 24-hour SCADA data at a wind hub on a medium voltage transmission system in the US western system. For the wind hub, the Thevenin equivalent parameters are used to compute the maximum power transfer capability of the wind hub as constrained by voltage stability. Then the method is extended to online application by using short data windows and forgetting factors.