Hi Waqquas I will try to explain your question
For a power flow, is used, form example the Newton's method, (according the wikipedia) "the best known method for finding successively better approximations to the zeros (or roots) of a real-valued function. Newton's method can often converge remarkably quickly, especially if the iteration begins "sufficiently near" the desired root." In a PF, the method in each iteration, use the derivate of the equations (approximation), to find a feasible solution of the equations systems. On the other hand, an optimization problem can be described in three parts, the objective function, the equality constraints and the inequality constraints. An OPF, you must to have an objective that you want to optimize, for example the cost of the energy, "Economic dispatch. The equality constraint are the power flow equations, g(x) = 0. The inequality constraint are the limits of the elements and variables: generations, lines charge and voltages, h(x) ≤ 0 and xmin ≤ x ≤ xmax. In a OPF, all the variables can change, P, Q, V and Theta. Because the method used, look for the best solution according the objective function, also satisfying all the constraints. A feasible solution is different that an optimal solution. I hope these clarify your doubt. -- Álvaro On Fri, Oct 1, 2010 at 12:23 PM, Waqquas Bukhsh <[email protected]> wrote: > Dear All, > > I have a general query which naturally popped up after running simulations > on Matpower. I shall be great full if some can answer the question: > > > > Load flow gives us the knowledge of the vector (V,delta,P,Q) at each bus of > the network. In load flow analysis we fix two of them and calculate other > two. > > > > So at PV bus voltage is fixed and it can not change. *But why in OPF the > voltage even at the PV bus changes?* I know optimization is performed on a > bigger space but even then the power flow equations have to be satisfied in > OPF. And what are the variable quantities at the buses? > > Thanks. > > > Kind regards, > > Waqquas > >
