Research on the critical point of steady state voltage stability

The traditional method of the static voltage stability analysis is to take the inflection point of the P-V curve as the critical point for the system voltage instability. But as this point reflects the transmission power limit of the electrical power system and it´s corresponding running voltage, and the system dynamic characteristic is neglected, the above method may result in a certain error. In the small disturbance analysis, the dynamics of generators, excitation systems, speed governors and so on were considered, and the point corresponding to the operating point when the eigenvalue of the system state matrix passes through the vertical axis is regarded as the real collapse point of system. This paper introduces the concepts of load power deviation coefficient and the voltage deviation and compares the maximum load power and the voltage value corresponding to the P-V curve´s inflection point with the load power and the critical voltage value corresponding to the point when the eigenvalue of the system state matrix passes through the vertical axis. As a result of taking the inflection point of the P-V curve as the static voltage stability limit in the static voltage stability analysis, the error of the maximum load power and the voltage value is calculated quantitatively. Standard IEEE9 system is analyzed and explained as an example