| Under deregulation environment, power systems are operated even more close to its stability limit so as to obtain more profit, which increases the possibility of voltage instability. So, it is necessary to consider the voltage stability constraints in the traditional optimal power flow (OPF). This problem is usually denoted as Voltage Stability Constraint Optimal Power Flow (abbr. VSCOPF). Some researches have been done on this topic in the past. However, up to now, there is no mature theory on VSCOPF and no successful application of VSCOPF in real power system operations. So more studies on this problem should be given. This thesis mainly focus on some aspects on the studies of optimal power flow with considering the constraints of voltage stability and small signal stability.Firstly, we established four types of voltage stability constraint optimal power flow model based on a local voltage indicator named L. They are 1) maximum voltage stability margin model, 2) fixed voltage stability margin model, 3) linear combination model and 4) hybrid model. Then, some testing systems, such as WSCC 9-bus, New England 39-bus system, IEEE 57-bus and 118-bus system are employed to validate the proposed models. Based on the case studies, some comparisons and discussions are performed to the models.Secondly, some tentative studies on the optimal power flow with considering small-signal stability constraints are performed. An optimal-based approach to trace small signal stability region's boundaries and extended small signal stability region's boundaries is first brief reviewed. Then new models of optimal power flow with considering the small-signal stability constraints are introduced based on eigenvalue analysis and the system damp factor. Simulation results based on the WSCC 9-bus system show that the proposed models can satisfy the security and economical demand of power systems well.Studies in this thesis are helpful to find more useful and appropriate optimal power flow model with considering the constraints of voltage stability and small- signal stability. |
