# Re: AC OPF Convergence Issue

```Making Vm = 1 means that the voltage is equal to its nominal value specified in
the BASE_KV column of the bus matrix.```
```
Regarding relaxing line limits, first this is the one case where setting them
to zero is interpreted as completely unconstrained. That is a reasonable thing
to try in the process of trying to get a convergent case. The question of what
sort of violations of the original limits are acceptable depends of course on
the particular system and scenario you are trying to analyze/optimize.

Ray

> On Mar 7, 2018, at 10:21 PM, Aakanksha Dubey <aad...@lehigh.edu> wrote:
>
> Thank You, Mirish and Shri for the guidance.
>
> Shri, the model is converging now. I understand that Vmax and Vmin limits
> should have been more relaxed. I have a couple of quick follow-up questions:
> I had set the voltage magnitudes on per unit basis since the network voltages
> range from 69kV to 500kV. By now making Vm=1, wouldn't all voltages be set
> equal to 500kV?
> Also, while relaxing line limits, what is the maximum acceptable percentage I
> should be increasing those values to?
>
> sincerely,
> Aakanksha Dubey
>
>
> On Wed, Mar 7, 2018 at 7:25 PM, Abhyankar, Shrirang G. <abhy...@anl.gov
> <mailto:abhy...@anl.gov>> wrote:
> The voltage magnitudes in MATPOWER data files, (bus(:,VM)), are given in per
> unit and are generally close to 1.0. You have very low voltages for many of
> the buses. Similarly, the VMAX and VMIN values are also in per unit and
> generally they are 1.0 and 0.95, respectively. The following code results in
> convergent OPF.
>
>
>
>
> define_constants;
>
> mpc.bus(:,VM) = 1.0;
>
> mpc.bus(:,VA) = 0.0;
>
> mpc.bus(:,VMAX) = 1.1;
>
> mpc.bus(:,VMIN) = 0.9;
>
> runopf(mpc);
>
>
>
> Also, note that when relaxing the limits set them to large values, not zeros.
>
>
>
> Thanks,
>
> Shri
>
> Ph: (630) 252 0219 <tel:(630)%20252-0219>
> www.mcs.anl.gov/~abhyshr <http://www.mcs.anl.gov/~abhyshr>
> From: <bounce-122357558-73493...@list.cornell.edu
> <mailto:bounce-122357558-73493...@list.cornell.edu>> on behalf of Aakanksha
> Reply-To: MATPOWER discussion forum <matpowe...@list.cornell.edu
> <mailto:matpowe...@list.cornell.edu>>
> Date: Wednesday, March 7, 2018 at 4:23 PM
> To: "MATPOWER-L@cornell.edu <mailto:MATPOWER-L@cornell.edu>"
> <MATPOWER-L@cornell.edu <mailto:MATPOWER-L@cornell.edu>>
> Subject: AC OPF Convergence Issue
>
>
>
> Hi All,
>
>
>
> I am developing a model for transmission grid at Lehigh Valley. My model
> seems to converge for DC OPF but is unable to converge for AC. I have tried
> the following to make it converge but nothing works:
>
>
>
> ·         Relaxed Vmax, Vmix, BR_R, Rate_A,Rate_B,Rate_C
>
> ·         Checked the tap ratio, Qmax, Qmin,Pmax,Pmin
>
> ·         Tried to change the OPF options by using opf.init_from_mpc
>
> ·         Using mpoption I tried to change the solver to IPOPT& MINOPF but
> and connecting the path to MATLAB it gives me the same error.
>
> I have attached my casefiles to this email. Please let me know if anyone can
> find an issue with the model.
>
>
>
> Thank you!
>
>
>
> Aakanksha
>
>
>
>

```