Thanks for referencing the subject section as i have apparently overlooked it.
I agree with you about the AC OPF but i have decided to use DC OPF for the
large system. I have a particular question about step-3 and step-4 in
particular. If i understand correctly from the code, step-3 selects candidate
generators with high average cost at Pmin that makes the sum of minimum gen
limits is not anymore higher than served load. However, i do not understand
step-4 because i thought we should turn off all generators that creates
infeasibility when sum of Pmin is higher than served load. So, i expected that
all the expensive generators at Pmin should be turned off and we should solve
one time and check the total cost then. So, i appreciate a feedback about the
situation or the reason for solving for each generator in the candidate list
instead of doing them all at once. Note that for my case, i am using DC OPF and
i know the case of light loading, we have the expensive generators to be close
to each others cost. So, if i use a priority list for the candidate generators
and turn them off till we have Pmin total less than served load. In this case,
we only run one DC OPF instead of multiple DC OPF. This would be very helpful
especially for larger systems. Also, i have tried to do some modifications to
uopf.m and run duopf which i believe when i traced it that it calls uopf, i did
not see any change in my output. So, i also appreciate confirming my
understanding about that as well. My final objective is simple and i know that
it can be done which is run DC OPF only once after all expensive units based on
priority list satisfies the feasibility check of having total Pmin less than
the served load.
Thanks again for your cooperation and take care.
Kindly,
From: r...@cornell.edu
Subject: Re: dealing with unit de-commitment
Date: Tue, 18 Nov 2014 12:18:50 -0500
To: matpowe...@list.cornell.edu
Hi Mans,
Yes, the unit-decommitment is handled in uopf.m. And, yes, it can be very, very
slow, especially for large systems. It is a very brute-force method. The basic
algorithm is as described in Chapter 8 in the User’s Manual, with the exception
that it actually does as you proposed in (1) before attempting the first OPF in
Step 2. (I guess I need to update that in the manual)
You could certainly code your own commitment algorithm using any number of
heuristics. For the AC OPF the problem is mixed-integer non-linear program, so
finding the optimal value is non-trivial, but I’m sure you can find a pretty
good heuristic that is much faster than uopf.m.
Ray
On Nov 17, 2014, at 4:04 PM, mohd <mansour1...@hotmail.com> wrote:Dear all,
I was recently faced with a system that experiences a negative lambda. Upon
further analysis, this happens when minimum generation exceeds load, which is
typical in a Winter season. So, i have tackled it by using the unit
de-commitment algorithm provided by matpower. However, i was faced with an
expensive computational time that takes almost 30 minutes to solve one instance
of DCOPF. So, i have several ways to resolve the issue and i am wondering about
the possibility of implementing these possibilities into the unit de-commitment
scheme to save some computational time even if that means a less optimal
solution for my case. The following are the approaches:
1) De-commit units and check against the sum of the minimum of generators till
the issue is resolved without running the DCOPF each time.2) Turn units
sequentially using a priority list without looking into different combinations.
I am not sure how matpower does that but i suspect that matpower tries
different combinations of generators that are turned ON and OFF and saves only
the cheapest objective function (the minimum total cost). If so, this is
computationally expensive, especially for large systems and can create
computational infeasibility.
So, what is the case file that performs the unit de-commitment. Is it the
uopf.m? If so, i need someone to explain to me the algorithm because some
commands that are used for the de-commitment decision are not familiar to me.
Also, I appreciate any feedback in regard to the subject issue. Thanks for your
cooperation in advance and take care.
Kindly,
