Hi Aaqib,

Let me give you a few different answers, and you can pick the one you like 
based on your real ultimate goal.

1. If you just want to run a power flow that respects the reactive power 
limits, simply call runpf() with the 'pf.enforce_q_lims' option set.

2. If you want to change the PV bus to a PQ bus during the power flow solution 
(as opposed to afterward, and re-running, like 'pf.enforce_q_lims' does), 
you’ll have to modify newtonpf() 
<http://www.pserc.cornell.edu/matpower/docs/ref/matpower6.0b1/newtonpf.html> to 
update the pv and pq vectors and the corresponding j1–j6 indexes on the fly. 
This has no effect on Ybus, however, and I don’t think of it as a topology 

3. If you really want to modify Ybus during the power flow solution, by adding 
some synchronous reactance, then I’m afraid you’ll have to probably do some 
more substantial modifications to make sure that newtonpf() 
receives all of the information needed to make the Ybus modifications you want. 

Hope this at least points you in the right direction,


> On Oct 17, 2016, at 4:20 PM, Aaqib Peerzada <peerz...@tamu.edu> wrote:
> Dear Dr. Zimmerman and Friends
> I have a query about updating the Ybus matrix. While running the power flow 
> on any system, it is possible that some of the generators will hit their 
> respective reactive limits, and change from a PV to a PQ bus. When this 
> happens, how can I update the Ybus matrix which will factor in, this topology 
> change? (Adding the synchronous reactance!!)
> Thanks
> -- 
> Aaqib Ahmad

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