I am doing some analysis with load redistribution. So when I remove certain high load nodes, there are of course islands because I eventually end up removing half the network and the average degree is about 3.2. The reason surely could be the islanding effect.
On Wed, Feb 29, 2012 at 3:23 PM, Ray Zimmerman <[email protected]> wrote: > 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 >> ------------------------------------------------------------- >> >> >> > >
