On Mar 14, 2007, at 10:12 PM, Sarina Adhikari wrote:
I have a small query on Matpower. I noticed that in an optimal
power flow program (fmincopf), all the variables are sent as the
parameter
and there is no distinction between PV and PQ buses. In traditional
Power
flow, we have to make a distinction between PQ and PV bus. The
limits on
reactive power of the PV bus needs to be checked. If it hits the
limit,we
treat it as the PQ bus. But, in OPF of Matpower, I didnot notice these
things. Are there any assumptions or modificatiions made to take
care of this which I
have overlooked?
Specifying buses as PV or PQ is done in a traditional n-bus power
flow problem, because there are 4*n unknowns (P, Q, V, theta at each
bus) but only 2*n equations (P and Q power balance at each bus). So
in order to solve the equations we must specify values for half of
the variables. We traditionally pick those that we either already
know (reference theta, P and Q at load buses) or are able to control
(V and P at generator buses).
In the context of an optimal power flow, the power balance equations
are simply constraints in an optimization problem and it is not
necessary to make the PV / PQ distinction for the purpose of finding
a solution. If, for example, one would like to hold the voltage
constant, it can be done using the voltage constraints. Similarly,
for any of the other variables.
I hope this answers your question.
--
Ray Zimmerman
Senior Research Associate
428-B Phillips Hall, Cornell University, Ithaca, NY 14853
phone: (607) 255-9645
