A method for computing minimum voltage stability margins of power systems

A new and fast method for computing the minimum voltage stability margin (VSM) of power systems is presented. The computation of the VSM is required for power systems planning and operation. Usually, it is assumed that loads increase along a predefined direction (e.g. with constant power factor, followed by a proportional MW generation increase) up to the system´s maximum loading point is reached. Situations may occur where variations from the predefined load increase direction, for example an unexpected load increase at some bus or area may result in smaller VSM, taking the system to an insecure state. The computation of the minimum VSM (mVSM) allows forecasting the load increase worst scenario. The information regarding the mVSM and the corresponding load increase direction for which it occurs, along with the usual VSM, allows operators to take measures like preventive control actions to move the system to securer operating points. Simulation results for IEEE test systems and for realistic systems are shown. Also, the proposed method is compared with other methods found in the literature.