Patrick, The first thing that I would try to do is to make sure 1. and 2. give similar solution. I would do this by imposing the cross-border flows in 1 as constraints on the tie-lines in 2. So Smax and Smin of the tie-line would be set to the cross-border flow value. The OPF may not converge if you set Smax=Smin=cross-border-flow so allow a little margin for the flow to vary. Also, instead of running the OPF on n countries at once, I would start with just 2 countries first. This would help to identify any problems relatively easily. Another thing to consider are your cost function coefficients. If the countries have different currencies then you'll have to convert the coefficients accordingly. Good luck, Shri ________________________________________ From: bounce-117288115-33970...@list.cornell.edu [bounce-117288115-33970...@list.cornell.edu] on behalf of Eser Patrick [es...@student.ethz.ch] Sent: Monday, July 14, 2014 8:34 AM To: MATPOWER-L@cornell.edu Subject: Convergence issues: OPF simulation of several interconnected countries
Dear MATPOWER Community, I am trying to solve a relatively large (>1000 buses) AC OPF problem. It consists of several individual countries (200-300 buses each). Please allow me to describe my procedures, to paint the full picture. 1. In a first study, I simulated all countries individually. The cross-border power flows to the neighboring countries is known to me from a database. I include these cross-border flows by implementing "pseudo-generators" of zero production cost or "pseudo-demand" at the borders. This procedure works nicely, I get convergence in almost every case I run. 2. Now I would like to simulate not only one country, but all my countries interconnected as one large system. I have "stitched" the transmission grids of the individual countries together in a realistic manner. If I run the OPF without further constraints, I receive converging simulations. But unfortunately, the flow between my countries is massively too high, probably due to price level differences between my countries. I would like to prevent these high cross-border flows, which leads to point 3. 3. I would like to limit the power flow (especially the real power flow) between my countries (so on individual branches in my full system), but am not able to get a converging simulation. I have played around extensively the MVA ratings of the lines (long and short term), but as soon as I impose realistic line ratings, I only get "infeasible solution" problems. As a workaround, I tried replacing the AC cross-border transmission lines with DC lines (and limiting real power flow in those DC lines). This does converge sometimes, but not always. I am using MIPS and/or IPOPT. I would massively appreciate any help in this regard. Some questions about the problem: What is the best ways to limit the power flow in an individual branch? Why are my simulations never converging, if I impose MVA ratings? Has anybody solved such a problem before? It seems quite straightforward, I am sure someone has already done something like this with MATPOWER. What would you suggest me to do? Should I rather use other solvers than MIPS or IPOPT? As I am not an expert of transmission system, what indicators should I be looking at to find out, where my simulations are going wrong? Thanks a lot for your comments. Best Regards, Patrick
