Dear Carlos, Thank you so much for your consideration,
Actually No. I am not changing the generators. PD_Nominal as I understand it is the demand at each bus. There is a generator part in the case file that I do not change. What I am saying is that I am setting the power demand at each bus and then run the DCpower flow. afterwards, the values of injected demand or Pload(as stated in output) are not exactly the same as the initial demand but in a range of it. So my question is what is MATPOWER doing for solving the DC power flow that causes this. It would be of great help to me if you answer this. All the best, Hanie On Tue, Aug 21, 2012 at 2:46 PM, Carlos E Murillo-Sanchez < [email protected]> wrote: > Let me see if I get this rightt: > > 1) You define real power dispatches of non-slack generators in a test > case, perhaps also change the amount of load, and then > 2) you run a power flow, ostensibly with runpf. But then, > 3) you find that the dispatch values that you had defined in step (1) for > generators other than the slack have been changed by runpf. > > It should not happen normally. The only mechanism for this to happen is > if a) you have ENFORCE_Q_LIMS set to 1 (default is 0), and b) The slack > generator happens to hit a Q limit, in which case the the slack bus is > treated as a PQ bus with Qg set to the limit, and then the next PV > generator is treated as the slack bus, which might cause this generator to > have a slightly different Pg dispatch than what you originally specified. > Could this be what you are seeing? > > Carlos. > > Hanie Sedghi wrote: > >> I think I should explain the problem more briefly. >> The thing is that when I input some load to a grid in MATPOWER, the final >> value of power injections at buses are not exactly equal to the initial >> values I assigned them. >> I now know this happens in a real grid due to the branch data (line >> and/or transformer impedance data), and other loads in the system (if any) >> that can consume power at each bus when running power flow. >> So my question is, is it ok to get this result if I run DC power flow in >> MATPOWER? and I am wondering why this happens. >> I just want to justify the results. >> >> Thank you so much, >> Hanie >> >> On Fri, Aug 17, 2012 at 9:51 AM, Hanie Sedghi <[email protected]<mailto: >> [email protected]**>> wrote: >> >> Hello sir, >> >> Hope you are doing great. >> >> For my research, I need to feed the grid with independent demands >> and follow the outputs. I solve for DC power flow >> For changing the demand I use >> >> mpc = loadcase('case9'); >> define_constants; >> Nominal_PD =[0;0;13;21.97;0;0;0;0;52.42;**0] %something random >> >> So I expect that Pload in MATPOWER's output be the same as my >> given Nominal_PD >> which is not always true. >> for example I have used case 9 with above Nominal_PD, which is >> less than sum of Nominal generations for bus 2,3 (that is 163, 85 >> respectively) >> now Pload=[-3.68;1.83 ;20.53 ;33.52;4.44;3.55 ;4.92 >> ; -0.56;44.83;-3.02] >> >> or even when Nominal_PD is such that sum of demand exceeds the >> generation in 2,3 (and slack bus compensates for the rest) I have >> the same problem that Pload is not equal to Nominal_PD (I assign >> this value randomly) >> >> It seems like the grid satisfies demand partially for some nodes >> and induces some gen/demand at nodes when there is no demand(when >> I run DC power flow) >> So I was wondering what is going on here. Is it what in fact >> happens in the grid or I am missing an assumption in MATPOWER or >> is it something else? >> >> I would truly appreciate your response. >> >> Best Regards, >> Hanie >> >> >> > >
