Dear Professor Zimmerman, Id like to study in more detail the problem of the initial point, so I want to keep on working in this issue in order to obtain a better criterion. In this moment, my single recommendation will be that user should consider a different point.
I think that the PTDF factors can help to improve the convergence of the MIPS algorithm, so I need more time to develop some criterions. Regards, Víctor De: [email protected] [mailto:[email protected]] En nombre de Ray Zimmerman Enviado el: lunes, 16 de septiembre de 2013 13:35 Para: MATPOWER discussion forum Asunto: Re: Reasons for non convergence of optimal power flows Importancia: Alta Thanks Victor for your input. The initial point used by MATPOWER for the MIPS solver was simply an attempt to begin at some interior point, so I'm not surprised at all to hear that selecting a different starting point can sometimes result in convergence of case that ran into numerical problems. What wasn't clear to me was whether your tests suggest a way of selecting a starting point that is likely to be consistently better than the one currently being used. Or is it just an issue of when one doesn't work, try a different one? -- Ray Zimmerman Senior Research Associate B30 Warren Hall, Cornell University, Ithaca, NY 14853 phone: (607) 255-9645 On Sep 13, 2013, at 4:21 PM, Victor Hugo Hinojosa M. <[email protected]> wrote: Dear Professor Zimmerman and Santiago, I had the same problem that Santiago mentioned when I applied an evolutionary algorithm to the static and dynamic transmission expansion planning problem (TEP). The algorithm was based on local random search, so many configurations from the solution space were analyzed. I realized that some configuration didnt converge the Matpower, and I was trying to find out about this problem. For example, in the Garver test system I applied the evolutionary algorithm to the static problem, and I obtained the attached configuration where MIPS algorithm numerically failed. In the same way, I considered virtual generators (bus 2, 4 and 5). The MIPS algorithm dont solve the DC-OPF problem for this configuration mpopt=mpoption; mpopt=mpoption('OPF_ALG',200,'VERBOSE',3); rundcopf(garver_no_CV,mpopt);. This problem occurs due to the initial point that the MIPS algorithm use. In the MIPS solver, the initial point is obtained considering the average power between the minimal and maximal power for each generator. When I changed the initial point to the minimal power generation (x0=[0 0 0 0 0 0]), the MIPS algorithm converges. I had conducted some proofs in order to determine some initial points where the algorithm has convergence problems. Ive divided each generator range, so the MIPS algorithm can consider different initial points. I included three analysis. In first case, I divided the power range in 8 intervals for each generator, so I can combine the power for each generator as initial point. The total points that the algorithm must consider is 531 441 (9^6). For these points, the MIPS algorithm doesnt converge in 15 078 times (2.84%). In the second, I divided in 9 intervals, so the total points is 10^6. In this case, the MIPS algorithm doesnt converge in 14 492 times (1.45%). Finally, I divided in 10 intervals, so the total points is 11^6. In this case, the MIPS algorithm doesnt converge in 42 016 times (2.37%). I attached an excel file where its possible to figure out the initial points that the MIPS algorithm doesnt converge considering 4 intervals. In the row 339, its possible to see the initial point used by Matpower. I had the same problem when I used the MIPS algorithm considering the power generator as decision variable. The solution could be to consider another initial point, but Id like to study again the problem. I hope your comments and ideas about the analysis carried out. Regards, Víctor De: [email protected] [mailto:[email protected]] En nombre de Ray Zimmerman Enviado el: martes, 28 de mayo de 2013 11:34 Para: MATPOWER discussion forum Asunto: Re: Reasons for non convergence of optimal power flows Islands should not be a problem as long as there is a REF bus in the island and the available generation is sufficient to meet the load in each island. So (1) is a definite possibility, but (2) shouldn't be an issue. Insufficient reactive power range to keep voltage magnitudes within range, and overly restrictive branch flow limits could be other causes of an infeasible OPF problem. Aside from things that can cause the problem to actually be infeasible, there are also numerical issues that can affect feasible problems. These can be the result of large ranges in parameters (branch impedances, generator costs, etc.). In these cases, often a different solver or algorithm may be able to solve the problem successfully. Hope this helps, -- Ray Zimmerman Senior Research Associate 419A Warren Hall, Cornell University, Ithaca, NY 14853 phone: (607) 255-9645 On May 20, 2013, at 1:21 PM, Santiago Torres <[email protected]> wrote: Dear Ray, I my resarch work I am using many transmission topologies and also I am using ficticious generators in order to get optimal power convergence for those different transmission topologies. Using those artificial or ficticious generators in all exclusive load buses is suposed to help for convergence, however in practice I am getting some transmission configurations that do not achieve convergence. I am thinking in the following reasons: 1) Too strict power generation limits of ficticious generators. 2) Some topologies with islanded nodes. Can you think in other reasons? Islanded nodes is a non convergence cause in Matpower? Best Regards, Santiago -- Dr.-Ing. Santiago Torres IEEE Senior Member Post-Doctoral Fellow School of Electrical and Computer Engineering University of Campinas, Campinas, SP, Brazil http://www.dsee.fee.unicamp.br/ Albert Einstein, 400 13083-852, Campinas, SP, Brazil <garver_no_CV.m><No_CV_analysis.xlsx>
