Study On Interface Power Control And Static Voltage Stability Region Of Power Systems

In recent years, voltage instability has aroused several blackouts. It is mainly dueto long distance transmission lines and heavy loads, loss of electrical source at sink.Inaddition, with the development of word-wide electric deregulation, power systems aremore often operating near their stability limits and there is large probability of voltageinstability. Operators usually supervise the power flow on some critical interfaces inorder to guarantee the system stability. So, effective interface power control methodand voltage stability region in cut-set power space (CVSR) have become theirpowerful tool for power system monitoring and control. Considering the factorsmentioned above, this thesis focuses on the following content:Firstly, interface power control method of power system is studied in this thesis.A new interface power control method based on DC factor table is presented. Powerflow is firstly used to determine the correlation coefficients among differentgenerators and branches in the interface in order to get the DC factor table which isused in the optimization to the interface power control. Further, we combine theinformation given by DC factor table with the nonlinear optimization to get thecontrol scheme.Secondly, method to determine the local boundary of CVSR is studied in thisthesis. A new approach to determine the local boundary of CVSR is presented. Powerflow tracing is first used to determine the generator-load pair sensitive to each branchin the interface. The generator-load pairs are then used to exactly control the powerflow on the branches in increasing and decreasing directions to get new equilibriumpoints around the initial point. And, continuous power flow is used starting from suchnew points to get the corresponding critical points around the initial critical point onthe CVSR boundary. Then a hyper-plane cross the initial critical point can be gottenby solving a set of linear algebraic equations.Then, the presented methods above are applied to the New England-39bussystem, IEEE-118bus system. Based on the case studies, it can be found that theapproach based on DC factor table not only can exactly control the total power flowof the interface, but also can meet the restrictions of the power change in each branch.The approach to determine local boundary of CVSR based on small disturbance ismore quickly and has less approximation error. So it is more helpful to power systemonline voltage stability monitoring and assessment.Finally, three methods commonly used to control power flow on branches are summarized and compared: method based on sensitivity information, method basedon power flow tracing and method based on DC factor table. Based on some casestudies, the thesis analyses the application scope of the three methods in depth. It ishelpful to the engineering and technical personnel to select accordingly.