Study Of Optimization Methods For Robust Power Flow And Reactive Power Based On AC-DC Hybrid System

With the rapid development of high voltage direct current(HVDC)technology,hybrid AC-DC power systems,which are more complex and difficult to model because of the nonlinear and nonconvex parts,have made the power flow optimization and dispatch a tough issue.Moreover,the increasing penetration of intermittent renewable energy sources(RESs)have added additional uncertainties to power system operation,which cannot be modelled using conventional optimal power flow(OPF)method.A possible approach to handle this kind of uncertainty in an AC-DC OPF problem is robust optimization(RO).However,most literatures about robust optimal power flow(ROPF)have considered the DC power flow to model an AC system with no nonlinear or nonconvex constraints,which inevitably neglected some critical variables,such as phase angle,bus voltage and transmission loss.At the same time,with the concept of "Global Energy Internet",the interconnection of regional power grids has become the next trend of grid development.The further expansion of the scale of the grid also poses a challenge to the security of the system,especially the voltage stability,and it needs to be able to coordinate the reactive power optimization methods of the large-scale network.This paper proposes a proper way to model the power flow of AC-DC system using second-order cone relaxation method to eliminate the nonconvex constraints and make the OPF model possible to be solved by interior point method(IPM).And based on the proposed AC-DC OPF model,affinely adjustable robust optimization(AARO)is applied to account for the uncertainty of RESs in the AC-DC system.Numerical results will be obtained on a modified AC-DC IEEE 30-bus to verify the correctness and robustness of the model by using Gurobi Optimizer and YALMIP,which is based on MATLAB.Details of the AAROPF and critical issues are presented as below.Furthermore,aiming at the reactive power optimization of multi-area interconnected AC-DC system,a multi-region reactive power optimization method based on decomposition and coordination algorithm is proposed to solve the problem of collecting difficulty and slow calculation speed of centralized data collection in large-scale system,and the results show that the proposed reactive power optimization based on the decomposition and coordination algorithm can remarkably improve the computational speed and utilize the computational resources rationally.