The Assessment Of Power System Random Voltage Stability Based On Impedance Modulus Margin Index

Power system is a highly complex system of random nature.In the study of voltage stability,using deterministic stability margin index to evaluate,the conclusion must be too optimistic.It is necessary to consider the influence of random factors on the system.Voltage stability assessment of considering stochastic trend in power system,can more accurately reflect the effect of random interference on the system voltage stability.The present study firstly describes the main contents and various analysis methods of the static voltage stability and introduces the research of voltage stability mechanism and evaluation index.In order to achieve the distributed and control of node voltage of the power system stability assessment of,the proposed method application for power system dynamic voltage stability equivalent circuit analysis.By analyzing the nonlinear complex circuit transmission power limit conditions,seen from a load node of power system comprehensive dynamic equivalent circuit and its parameters calculation method,according to the comprehensive dynamic equivalent circuit parameters can easily calculate the PQ node voltage stability impedance modulus margin index.Impedance modulus margin index and the various specific nodes in the network has one corresponding relationship,which is the most intuitive evaluation index of node voltage stability.According to the impedance modulus margin size of the PQ node voltage stability of pecking order,we can quickly find the weakest node of the voltage stability,which is conducive for the dispatcher to monitor and control the voltage stability weak nodes.When the stochastic power flow calculation is carried out,the Monte Carlo method and the semi invariant method are used for analysis.Modeling and data collection phase using Monte Carlo sampling method with important principles of sampling,In the data analysis and processing stage probability density function use Gram-Charlier series expansion coefficients and,ultimately,the node voltages and branch distribution function of the trend.On the basis of stochastic load flow and voltage stability index,the paper proposes a new method of analysis of stochastic voltage stability index based on mean impedance modulus margin.In solving the mean impedance modulus margin index,the load of uncertainty and randomness slip faults are equivalent to nodal injection power to deal with stochastic volatility,define different variances power to simulate the injection of random variation and semi invariant method determined impedance modulus margin and its semi-invariant order to obtain the probability density,finally get mean impedance modulus margin of each node PQ under different operating conditions.Simulation calculations of IEEE30 and IEEE 14 nodes system,verify the correctness of the random flow impedance analog voltage stability margin index of evaluation.Compared with the voltage stability index under deterministic trend,considering the random factors can reduce the overall voltage stability index,indicating that random trend is more conservative in assessing the system voltage stability with good reliability.