Method for calculating voltage stability margin of regional power grid by considering outer network equivalence

The invention discloses a method for calculating a voltage stability margin of a regional power grid by considering outer network equivalence and belongs to the technical field of analysis of static voltage stability of a power system. The method comprises the following steps of: adding a ground branch circuit into a conventional David south model to make an outer network equivalent; calculating outer network equivalence reactance and ground admittance by using a computer through a program according to outer network information under a typical running mode; calculating equivalent power supply electric potential according to inner network measured data and finally calculating an index of the static voltage stability margin of the regional power grid. By the method, the influence of the outer network on the ground branch circuit can be considered effectively and the problem of parameter drift in the conventional David south equivalence method can be solved effectively; therefore, the calculation precision of the stability margin index is high. In the method, only the information under the typical running mode of the outer network is needed and the data under all the running modes of the outer network is not needed, so that the requirement on the data of the outer network is low, the engineering practicability is high and the popularization and application are facilitated. The method can be widely applied to calculation and analysis of the index of the static voltage stability margin of the regional power grid which is connected with the outer network through a single point.