Improved low voltage solution calculation method for voltage stability assessment of electric power systems

In this paper a method for calculating low voltage solutions (LVS) of the load flow (LF) equations is proposed. It is based on a state space search approach and it has the following features: (a) it is fully derived with voltages in polar coordinates, making its insertion in existing production grade LF programs a very easy task; (b) a special procedure is proposed so that it is always possible to obtain a state space search direction and an initial state estimate for the LVS calculation; (c) nonconvergent and divergent cases are easily and efficiently detected and handled through the use of step size optimization techniques; (d) it correctly identifies the desired LVS in case several close solutions exist (as it is often the case for real life systems); and (e) the LVS can be found regardless of its distance to the stable (high voltage) solution. Test results have shown that the method is robust and efficient. Finally, a very simple maximum loading point proximity index is proposed and its characteristics are discussed.