Patrick,
I'm afraid setting Smin limit on tie line flow is not as
straightforward as I initially thought. The reason being that with
MATPOWER's optimal power flow, the flow constraint for a transmission line
is set as
|S_flow| - Smax^2 \le 0. MATPOWER uses rate_A limit as the flow limit
(Smax) for branches. So, while a Smax can be set for the line flow, Smin
is not implemented.
You'll have to do a little bit of hackery to do what you want. Here are
the steps:
i) Set the Smin values for branches in branch RATE_B column (RATE_B is not
used anyways for the OPF so this should be fine). Only tie lines will have
a non-zero Smin, others will be zero. This will help
you to identify the tie lines and set constraints only for them.
ii) Modify the file opf_consfcn.m (the routine sets up the equality and
inequality constraints for the OPF) to include additional inequality
constraints for the tie lines in the h vector. Note that the optimization
expects the inequality
constraints in the standard form h(x) \le 0. So your additional
inequality constraints should be Smin(tie_line_idx).^2 - |
S_flow(tie_line_idx)) |
Shri
-----Original Message-----
From: Eser Patrick <es...@student.ethz.ch>
Reply-To: MATPOWER discussion forum <matpowe...@list.cornell.edu>
Date: Mon, 14 Jul 2014 17:30:48 +0000
To: MATPOWER discussion forum <matpowe...@list.cornell.edu>
Subject: AW: Convergence issues: OPF simulation of several interconnected
countries
>Ray, Carlos, Shri,
>
>Thanks for your inputs, I really appreciate your help.
>
>With regard to your responses:
>
>@Shri: How would I impose the Smin and Smax of the tie-line in the
>MATPOWER intput? I can't see anything alike in the mpc.branch struct, as
>PF, QF, PT and QT are ignored as inputs according to the manual. Fixing
>the S-value to the cross-border flow value would definitely help me!
>
>@Carlos: No, there are no phase shifters in the system. Would including
>phase shifters at crucial points help me?
>
>@Ray,Shri: I have already cooked the problem down to two countries, so I
>totally agree to your boiling-down approach. I will have to look at each
>line in detail, but I wanted to make sure first, that I am not making a
>general mistake that completely prevents convergence.
>
>Thanks again!
>________________________________________
>Von: bounce-117289979-69334...@list.cornell.edu
>[bounce-117289979-69334...@list.cornell.edu]" im Auftrag von
>"Abhyankar, Shrirang G. [abhy...@mcs.anl.gov]
>Gesendet: Montag, 14. Juli 2014 17:40
>An: MATPOWER discussion forum
>Betreff: RE: Convergence issues: OPF simulation of several interconnected
>countries
>
>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
>
>
>
>
>
