As long as you call int2ext() after changing the line status and bus type, so that they actually get removed from the matrices it should be sufficient. I did a little test with a network with two unconnected islands and it does complain of a singular matrix, as I expected. Have you checked if that is what is causing the problem for you?
-- Ray Zimmerman Senior Research Associate 419A Warren Hall, Cornell University, Ithaca, NY 14853 phone: (607) 255-9645 On Feb 29, 2012, at 9:01 AM, Trivik wrote: > Yes. I am making the line status zero and also making the removed buses as > isolated. But apart from that is there anything else that I should change in > the vectors of the mpc struct? I am still getting that warning with a smaller > PTDF matrix generated this time. > > On Tue, Feb 28, 2012 at 5:11 PM, Ray Zimmerman <[email protected]> wrote: > The context of the error message is important. In this case, it has nothing > to do with the ill-conditioning of a matrix encountered by MIPS in the AC OPF > solution, rather the ill-conditioning of a matrix encountered in forming the > PTDF. I suppose it's possible that the same underlying network conditions > could cause both. > > Are you sure that the remaining system is fully-connected? I suspect that the > PTDF calculation may encounter singular matrices if the network is not > connected, though I haven't tested it. > > I suggest converting the indexing to a consecutive internal ordering (and > removing out-of-service branches, buses, etc) by calling ext2int() after > setting the line statuses to zero and before calling makePTDF(). > > -- > Ray Zimmerman > Senior Research Associate > 419A Warren Hall, Cornell University, Ithaca, NY 14853 > phone: (607) 255-9645 > > > > > On Feb 28, 2012, at 7:29 AM, Ravikumar V wrote: > >> Hi Trivik Verma, >> >> This is Matlab error message appears when the matrix inverse is not possible >> because of singular matrix. This shows that the power system becomes >> unhealthy or ill-conditioning because of opening several lines. Kindly >> refer previous posts on this topic. >> >> http://www.mail-archive.com/[email protected]/msg01678.html >> >> >> >> On Tue, Feb 28, 2012 at 4:05 PM, Trivik <[email protected]> wrote: >> Could anyone help me?? >> >> I am viewing a power grid using MATPOWER and for my simulations I need to >> remove a node together with its links. By doing so, I am changing >> mpc.branch(links,:) = 0. After removing the respective links, I am >> calculating PTDFs again. The first time is fine, but in the event of >> redistribution of flows, the next time I am removing about 10 percent of the >> nodes and calculating PTDFs. I get a warning as follows, >> >> Warning: Matrix is close to singular or badly scaled. >> Results may be inaccurate. RCOND = 4.060450e-019. >> >> Do I have to remove something else from the mpc struct as well? >> >> cheers, >> Trivik >> >> >> >> ------------------------------------------------------------- >> WITH REGARDS, >> >> V. Ravikumar Pandi, >> Masdar Institute, Abu Dhabi, >> United Arab Emirates - 54224. >> mobile : +971 5522 78027. >> ------------------------------------------------------------- >> HAVE A NICE DAY >> ------------------------------------------------------------- >> > >
