Research On Random Prediction Of Voltage Sags Based On Sequential And Nonsequential Monte Carlo Method

With the development of science and technology and the wide use of modern electrical equipment, the problems of power quality have been paid more and more attention. Voltage sags is one of the most frequent and serious power quality problems. Voltage sags is usually caused by the short-circuit fault of line, and has a strong randomness.In addition, with the large number of sensitive equipment put into use, the problems of equipment failure caused by voltage sags is also becoming more and more serious. Therefore, researching on the method of stochastic assessment and the influence of voltage sags has a important scientific significance and practical value.The thesis first introduces several classical methods of voltage sags stochastic estimation, such as fault point method, the critical distance method, the direct method and so on. Then focuses on the specific steps and procedures using the Monte Carlo method to estimate when the voltage drops random. The Monte Carlo method in the stochastic assessment of voltage sags suffers from low computing efficiency, long time consuming and large memory. According to those defects, the thesis presents a stochastic assessment based on Nonsequential and Sequential Monte Carlo method, and sets up a mathematical model study fault lines, fault types and fault location of fault state variables.The thesis established an IEEE-9-bus test system model on the MATLAB/Simulink platform, and state variables of the fault model are obtained. By using the pseudo-random number generator to get a large number of sampling system state samples, and based on the Sequential and Nonsequential Monte Carlo method for stochastic estimation of voltage sags is studied. Probability distribution of each node voltage drop amplitude and drop index assessment is adopted in this thesis, and verified the Sequential and Nonsequential Monte Carlo method for stochastic estimation of voltage drop research the feasibility and correctness. Through the comparison of the stability and convergence of the Monte Carlo method and the Nonsequential Monte Carlo method, Sequential Monte Carlo method and the Nonsequential Monte Carlo method analysis, the convergence speed of the Nonsequential Monte Carlo method is faster, more stable.And compared with the Sequential Monte Carlo method and Monte Carlo method two kinds of methods, the application of Nonsequential Monte Carlo method to estimate the voltage drop randomly, just for a small number of samples can obtain more accurate results, reduced the sampling time, accelerates the calculation speed.