That will be great. I have to simulate the European power grid in case of cascading failures and it soon separates out into Islands. Your code will be very helpful. Thanks a lot.
Best, Trivik On Thu, Mar 1, 2012 at 2:44 PM, Ray Zimmerman <[email protected]> wrote: > If there are islands, and you get the singular matrix warning, I suspect > the PTDF returned could be incorrect. If there are no islands, then maybe > it is due to some strange line parameters (zero reactance lines or > something). In that case, I really don't know what to make of the PTDF. > > If you are interested I have some code that I'll be including in the next > release of MATPOWER that detects the islands in a network (and extracts > them into separate cases). I could send it to you off-list. > > -- > Ray Zimmerman > Senior Research Associate > 419A Warren Hall, Cornell University, Ithaca, NY 14853 > phone: (607) 255-9645 > > > > > On Mar 1, 2012, at 7:46 AM, Trivik 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 4:39 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 >>>>> ------------------------------------------------------------- >>>>> >>>>> >>>>> >>>> >>>> >>> >> > >
