The Calculating Method Study Of Critical Voltage Collapse In Power Systems Based On Stochastic Optimal Power Flow

Voltage collapse critical point can reflect the ability of electrical power system to maintain its steady-state viability, so it stands an important position in the voltage stability research of electrical power system, it can be solved based on power flow, continuation power flow(CPF) and optimal power flow(OPF) and so on, and these method are usually built on fixed system network, parameters and constant power demand, but the electrical power system is a multidimensional non-linear stochastic system,the traditional power flow method has its boundedness in solving problem of this kind, while probabilistic power flow is an efficient way, for it can give the statistic characteristic of nodal voltage and branch power flow, reflect the operation conditions, the existing problem and the weakness of electrical power system more deeply, and then provide comprehensive information for system programming, operation and decision-making, thus there by sequentially improve the secure operation level in power system.Firstly, this paper introduces the research background of this project, and also focuses on main research method on static voltage stability, , establishes the basic model of stochastic optimal power flow, based on this, the uncertainty of load forecasting and load static voltage characteristics are taken into account, an approach for determining voltage collapse critical point considering the uncertainty and static voltage characteristic of load based on stochastic optimal power flow is presented in this paper. Use the information of load uncertainty based on load forecast and ZIP(constant impedance-constant current-constant power) load model obtained from load modeling, take the maximum load that the system can afford as the objective function, build the corresponding chance-constrained programming of variables randomness caused by load uncertainty, and solve it by the nonlinear programming algorithm, with the purpose of obtaining the maximum load that subject to a certain probability constraint, and obtain the corresponding optimal power flow operation state under the maximum load. Finally, use the IEEE 39-bus system and 57-bus system and 118-bus system as the example and simulate, mainly study the influence of the load probability distribution and load static characteristic on voltage collapse critical point, calculate voltage collapse critical point of different method,and show the validity of the proposed approach.Secondly, takes the disconnection fault into consideration, deals with the disconnection fault using stochastic line-selection model based on Monte Carlo method, and integrates stochastic line-selection model based on Monte Carlo method to voltage collapse critical point model considering the uncertainty and static voltage characteristic of load based on stochastic optimal power flow, forms an Approach for determining voltage collapse critical point based on Monte CarLo stochastic optimal power flow method, and then simulates in IEEE 3-bus-9-generators systems , figures out the maximum load when different branches are removed, so as to test the validity of the proposed approach.Finally, given the realistic situation, wind farm model with the stochastic wind speed being considered is joined in, according to Wei-bull distribution based on wind speed, derived from the average wind turbine mechanical power. The slip of the wind turbines is added in the probabilistic OPF formulation as a new state variable, and the average wind turbine mechanical power, electromagnetic power balance equality constraints, bound, slip upper and lower limits are increased in order to construct a probabilistic optimal power flow model. Study the change of maximum load that system can afford after the wind farm model is joined, Test results on IEEE 39-node system illustrate that the algorithm is effective and practicable.