Re: MILP solver 'GUROBI' failed with exit flag

[Ray Zimmerman]

According to …

http://www.gurobi.com/documentation/8.0/refman/optimization_status_codes.html

… Gurobi exit flag 4 means that the problem is infeasible or unbounded. The 
other errors are a result of attempting to continue after the solver failed to 
find a solution.

   Ray


> On May 7, 2018, at 9:07 PM, sergio valencia ocampo  
> wrote:
> 
> Hello all,
>  
> I am trying to run the most and the basic conditions with the gurobi solver 
> but I get this warning
>  
> - MOST: MILP solver 'GUROBI' failed with exit flag = -4
>   You can query the workspace to debug.
>   When finished, type the word "return" to continue.
>  
> Then i get the next error:
>  
> - Post-processing results.
> NaN's cannot be converted to logicals.
>  
> Error in most (line 2102)
>   mdo.UC.CommitSched(:, t) = mdo.QP.x(vv.i1.u(t):vv.iN.u(t));
>  
> Error in most_ex7_suc2 (line 111)
> mdo = most(mdi, mpopt);
>  
>  
> I have no idea why the warning or the error should be
>  
> Thanks for any hints.
> Best regards, Sergio

Re: Branch model - switch FROM and TO bus?

[Jose Luis Marín]

Hello Elis,

The ordering matters for the correct specification of the *tap ratio*.
>From the manual (p. 21--22):

"The transformer, whose tap ratio has magnitude $\tau$ and phase shift
angle $\theta_{shift}$, is *located at the from end of the branch*, as
shown in Figure 3-1".

If, for whatever reason, you wanted to swap FROM and TO labels, then the
values of the tap ratio would have to change accordingly (it's not hard to
figure out the formulas for this transformation).

Note also that the manual defines N as the *complex* value of the tap
ratio, so when you say N>1 or N<1, I assume you're thinking about its
modulus, tau.  This value can be greater or less than 1, either way.  And
MATPOWER doesn't care which side is the high-voltage or low-voltage one, as
long as your tap ratio is correctly modeled.

Hope it helps,

-- 
Jose L. Marin
Grupo AIA



2018-05-09 14:17 GMT+02:00 Elis Nycander :

> Hi,
>
> In the matpower branch model (Fig 3.1) the impedance is on the TO-bus
> side. However, since the impedance is in pu, for an ideal transformer we
> might as well move the pu impedance to the FROM-bus right? So in this case
> we can exchange the TO-bus and FROM-bus for any branch without effecting
> the results of a load flow.
>
> Q1. So when does the the ordering of the FROM and TO bus actually matter?
> Is there any case when we cannot swich the TO and FROM bus of a branch and
> still get the same result from a load flow or opf?
>
> Q2. From Figure 3.1 it looks as if the FROM bus is the high voltage bus
> (assuming N > 1). Is this always the case or can we have N < 1 just as well?
>
> Regards,
> Elis
>

Branch model - switch FROM and TO bus?

[Elis Nycander]

Hi,

In the matpower branch model (Fig 3.1) the impedance is on the TO-bus side.
However, since the impedance is in pu, for an ideal transformer we might as
well move the pu impedance to the FROM-bus right? So in this case we can
exchange the TO-bus and FROM-bus for any branch without effecting the
results of a load flow.

Q1. So when does the the ordering of the FROM and TO bus actually matter?
Is there any case when we cannot swich the TO and FROM bus of a branch and
still get the same result from a load flow or opf?

Q2. From Figure 3.1 it looks as if the FROM bus is the high voltage bus
(assuming N > 1). Is this always the case or can we have N < 1 just as well?

Regards,
Elis