Computing measurement-based voltage stability margins for a wind power hub using the AQ-bus method

In PV-curve-based voltage stability analysis, it is known that the Newton-Raphson power flow Jacobian matrix becomes increasingly ill-conditioned as the maximum loading condition is reached. In many cases, the power flow diverges before the maximum loading condition is reached. In previous work, we proposed a novel method to alleviate the ill-conditioning issue in the power flow by reformulating the problem using a new AQ bus type [1]. For an AQ bus, the voltage angle and reactive power consumption are specified. For steady-state voltage stability analysis, the angle separation between the swing bus and AQ bus is adjusted to indirectly control power transfer. This reformulation alters the Jacobian matrix such that it is nonsingular at the critical voltage point. In this work, we use the AQ-bus method to compute the PV curves for a real power system including a wind power hub with multiple wind power plants. The network has two transfer paths and reactive power compensation from switched shunts. We use measurements to construct voltage stability models for the wind power plants and external system. The switched shunts are modeled in the AQ-bus power flow according to their operational guidelines. Using this real system, we demonstrate the capability of the AQ-bus method to compute voltage stability margins for multiple transfer paths and complex injections.