I suppose this is a bit unusual, but I don’t think you are doing anything wrong. The most likely explanation is simply that adding a dispatchable DC line where you did somehow makes the problem numerically much more difficult to solve. You might try changing the from and to bus parameters for the line (i.e. moving it around the network). My guess is that you’ll find some cases solve just as quick as the original and some (like your original location) take much longer. I’d be curious to know whether you see the same sort of variation in solve times when using a different solver (such as MIPS, fmincon or Knitro).
-- Ray Zimmerman Senior Research Associate B30 Warren Hall, Cornell University, Ithaca, NY 14853 USA phone: (607) 255-9645 > On Apr 13, 2015, at 7:51 AM, Eser Patrick <[email protected]> wrote: > > Dear MATPOWER community, > > I have a question regarding adding DC lines to an AC system with the > “toggle_dcline" command. > > I am running a 1100-bus system, using IPOPT as solver. When I solve the > standard ACOPF system, the simulation converges within 7 seconds (40 > iterations). Now when I add one DC line of 10 MW capacity, applying the > “toggle_dcline” command, the system needs 38 seconds (310 iterations) to > converge. Since I have not really changed the system with adding one single > 10 MW DC line, the results between both cases are 99.99% identical. > > So why is it, that the DC-line case needs so much more iterations to converge > (factor 5 more)? The parameters of my fictitious DC line are: > > PMAX = +10 MW > PMIN = -10 MW > QMINF, QMINT both = -10 MVAr > QMAXF, QMAXT both = +10 MVAr > VF, VT both = 1.0 p.u. > LOSS0 = 0.1 > LOSS1 = 0 (since I want to enable the code to use the DC in both directions, > following a comment in the MATPOWER manual) > > Have I messed up the definition of the DC line? If not, is there a workaround > to bring individual DC lines into a predominantly AC system without having a > runtime penalty of factor of 3-5? Or do I just need to re-adjust several > parameters of the IPOPT solver to set it up for new constraints of the type > “lower bound only”? In the AC-only system, I only have “both lower and upper > bound” constraints, so maybe my IPOPT is set up to handle only those > constraints properly? > > Any hints would appreciated. Thanks a lot. > > Best, > > Patrick Eser
