Even after removing links and generators from the struct I get *this* warning. Do you think the PTDF is reliable enough once I have removed all the malfunctioning links and nodes from the network? It is a huge network (N = 1254, L = 1822). It is difficult to analyse by hand.
On Wed, Feb 29, 2012 at 4:39 PM, Trivik <[email protected]> wrote: > Even after removing links and generators from the struct I get *this* > warning. Do you think the PTDF is reliable enough once I have removed all > the malfunctioning links and nodes from the network? It is a huge network > (N = 1254, L = 1822). It is difficult to analyse by hand. > > > On Wed, Feb 29, 2012 at 4:06 PM, Trivik <[email protected]>wrote: > >> 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 >>>> ------------------------------------------------------------- >>>> >>>> >>>> >>> >>> >> >
