Probabilistic Study On Voltage Stability For Power System With Wind Power Integration

With the continuous development of wind power generation technically,the proportion of wind farms in the power system is increasing. The impact onvoltage stability for the power system with wind power integration is becomingserious increasingly. Because of intermittence and randomness of wind power,the power system has been in multi-operation conditions. However, theconventional voltage stability analysis methods are often based on a singlesystem operation. In this paper, a probabilistic methods approach is applied tostudy the small disturbance voltage stability for the power system with windpower integration.Probability flow calculation for the power system with wind powerintegration is the basis for the probability study of the system voltage stability.Taking into account the uncertainties of system multi-operating conditions, theprobability distribution of the power flow can be obtained by flow calculationonce. In the IEEE three-generator systems, the equivalent doubly-fed windturbine wind farm replacing the same power output synchronous generators,semi-invariant probability flow calculation method is applied to calculateprobability flow in the paper. At the same time, the calculated result iscompared and analyzed with Monte Carlo simulation calculation method.The small disturbance analysis method is applied to study the voltagestability for the power system with wind power integration. The linearizedmodel of network, load, synchronous generators, DFIG (Doubly fed inductiongenerator) wind turbines are established based on plugging modelingtechnology (PMT). Especially the DFIG, which includes aerodynamic model,shaft system model, pitch control systems model, doubly-fed inductiongenerator model, the converter and its control systems model, is described withelectromechanical transient model which is suitable for small disturbancestability. The maximum power point tracking in aerodynamic model and the complete control model for the converter is shown in this paper.Based on the small disturbance stability analysis, the probabilitydistribution of the system characteristic eigenvalues corresponding to thesystem state matrix is calculated with the probabilistic method. Then the systemprobability unstable modes are determined. Voltage stability correlation ratio isreferred as a criterion to distinguish voltage instability from angle instability,which expands probabilistic eigenvalue analysis method to study voltagestability. The weak points of power system voltage can be founded by voltageinstability mode coefficient. The robust SVC is installed to improve the voltagestability of the power system at the weak point.At last, the above methods are validated in the three-generator system andeight-generator test systems. The results show that the probability of the smalldisturbance voltage instability of the power system is larger with wind powerintegrated, and adding SVC at the weak point can improve the voltage stabilityof power system at some extent.