First of all, using small identical *quadratic* cost functions for generators
is not strictly the same as minimizing losses. If the costs are identical
*linear* costs, then it is strictly the same as loss minimization, since it is
essentially trying to minimize the sum of the real power dispatch.
If you start putting costs on the reactive power outputs of the generators, it
will affect the dispatches (real and reactive) and therefore will increase the
total real power losses relative to the optimum obtained by the problem
describe above.
Ray
On Sep 6, 2014, at 4:02 AM, vids <vidaj...@gmail.com> wrote:
> Hi Dr Zimmerman,
>
> I have another question on the generator cost and objective function
> formulation. I read in the previous messages that in order to change
> the objective function from total cost minimization to real power loss
> minimization, the gencost function must be modified to specify small
> quadratic cost functions identical for all generators.
>
> What is the expected behavior of MATPOWER when (a) small identical
> quadratic cost functions will also be specified for the generator
> reactive power output as opposed to (b) the default setting wherein
> there are no costs specified for reactive power?
>
> If I want my objective to be irrelevant of the cost of reactive power,
> I just want to minimize the losses, which option do I choose, option a
> or b? Thank you very much.
>
> Vids
>
>
> On Tue, Sep 2, 2014 at 10:39 PM, Ray Zimmerman <r...@cornell.edu> wrote:
>> Both cases have a all generator cost functions equal to zero, so all
>> feasible power flow solutions are optimal. That is, there isn’t even a
>> unique *local* optima, let alone a global optima. Under such circumstances,
>> numerical optimization routines such as those used by MATPOWER, should not
>> be expected to produce anything unique or consistent. Adding a small
>> quadratic real power cost for each generator does result in consistent
>> solutions for the two cases (to numerical accuracy of the algorithms).
>>
>> --
>> Ray Zimmerman
>> Senior Research Associate
>> B30 Warren Hall, Cornell University, Ithaca, NY 14853 USA
>> phone: (607) 255-9645
>>
>> On Sep 1, 2014, at 10:42 AM, vids <vidaj...@gmail.com> wrote:
>>
>> Hi Matpower Community,
>>
>> I was testing the application of reactive capability curve limits. I
>> defined a generator operating region by using the points described in
>> section 6.4.3 in the manual.
>> I first performed the OPF without including the parameters, and then
>> compared it with the results when the PQ curve limitation was
>> included. I was expecting the same results because the operating point
>> is very well within the operating region defined by the limits. But
>> the results were two slightly different operating points. Is this
>> really how Matpower behaves? I am attaching the two case files, in
>> case. Thank you very much!
>>
>> Vids
>> <capabilitytests_1.m><capabilitytests_2.m>
>>
>>
>
>
>
> --
> 2 Cor 12:9
> Each time he said, "My grace is all you need. My power works best in
> weakness." So now I am glad to boast about my weakness, so that the
> power of Christ can work through me.
>
>
