Study On Safety And Stability Assessment Of AC/DC Hybrid Power Grid Considering The Uncertainty Of Loads And New Energy Generator Outputs

With the development of power grid construction,many AC/DC hybrid power grids have been formed.The interaction of AC and DC system faults enlarges the insecurity degree and scope of power grid disturbance,threatens the safe and stable operation of power grid.Power loads and new energy outputs are volatile and uncertain.It is necessary to consider these uncertainties in the security and stability analysis of power grid.Among the methods of expressing uncertainty,scenario-based decision making method can reflect uncertain information with limited scenarios.How to determine the scenario and its corresponding probability is the primary problem to be solved.Based on this background,safety and stability analysis of AC/DC hybrid power grid considering uncertainties of loads and new energy outputs based on sampled-blind-number(SBN)method and PSASP simulation software is carried out in this paper.The uncertainty of loads and new energy outputs in power grid is expressed by sampled-blind-number.A fixed order non-equal interval sampling method is proposed to minimize the error of blind number in order sampling.Considering the strong correlation among loads and new energy outputs,a space generation method considering the correlation coefficients between random variables was proposed.A sampled-blind-number generation program based on the given order non-equal interval sampling method and a sample space generation program considering correlation are developed by MATLAB.A method of N-1 static security assessment for AC/DC hybrid power system is proposed,in which sampled-blind-number is used to reflect the uncertainty of loads and new energy outputs.Static security indexes considering uncertainty are established.The assessment results are divided into three categories: fully satisfying N-1 criterion,basically satisfying N-1 criterion and not satisfying N-1 criterion.The static security margin is used to reflect the security margin when the N-1 criterion is fully satisfied,and the probability of not meeting the N-1 criterion for a period of time is used to reflect the degree of insecurity when the N-1 criterion is basically satisfied or not.The characteristics of transformer N-1 static security analysis,transmission line N-1 static security analysis and distribution network N-1 static security analysis are illustrated in detail with examples.The results show that the proposed method is feasible.A method of transient stability assessment for AC/DC hybrid power system is proposed,which sampled-blind-number is used to reflect the uncertainty of loads and new energy outputs.The transient stability indexes considering uncertainty is established.The indexes include The probability of not satisfying the transient stability requirement at a given time under a given fault,the probability of not satisfying the transient stability criterion at a given time,the probability of not satisfying the transient stability criterion in a period of time,the average probability of not satisfying the transient stability for a given fault in a period of time,the transient stability margin,etc.The transient stability analysis of EPRI36 bus is carried out,and the results show that the proposed method is feasible.Repeatedly calling of the power flow calculation and transient calculation core modules of PSASP is needed for power system security and stability analysis based on sampled-blind-number.In order to improve the efficiency of analysis,software is designed to interface with PSASP and automatically call its functions to assess power grid security and stability considering uncertainty.It mainly includes data import and display module,data management module,power flow calculation and transient calculation module,security and stability indexes calculation module and other major functional modules.The software has been successfully developed by professional software companies and applied in this research work.