I agree that checking for exceeded limits and warning about them would be a nice feature to add to the the power flow. I see no reason, though, why it should be limited to the swing bus power injection … why not include all of the other generator, voltage and branch flow limits, all of which can be violated in a converged power flow solution.
I’ll put it on the “to do” list. Ray > On Feb 18, 2016, at 8:05 AM, Jovan Ilic <[email protected]> wrote: > > > Jose, > > I did not suggest to turn the swing bus into a PV bus. There should be at > least one swing bus > in the system unless you formulate your PF problem as ACOPF problem which > does not need > any slack buses. > > I understand what you are saying and you are right. I'd keep the swing bus as > it is just > to provide the angle reference (admittance matrix is rarely singular) and add > to Jacobian a > constraint on the sum of P and Q flows on the lines connected to the swing > bus. The sum > of all these lines out flows must be less than the power injection capability > of the swing bus, > both P and Q. If the constraint is violated the power flow does not converge. > The original > poster was concerned with the convergence when there is not enough > generation, so > no convergence would give them a really stern "warning" and leave them > guessing what went > wrong. Or you can just keep it simple and have PF implementation just print > out a warning > that the slack bus exceeded its capacity. Modifying the Jacobian was the > first thing that > came to my mind but I am not sure if it provides anything in addition of a > warning to user. > > Jovan > > > On Thu, Feb 18, 2016 at 3:25 AM, Jose Luis Marin <[email protected] > <mailto:[email protected]>> wrote: > But you did that, it would no longer be a powerflow calculation. There are > good mathematical reasons why the standard powerflow calculation is > formulated so that there should be at least one swing bus (where you specify > both V and A, leaving P and Q "free"). If you specified V, A, and Pgen at > the swing, this would yield an overdetermined system. You could > theoretically formulate a powerflow in which the swing bus specified only A > (the global angle reference) and Pgen, leaving Vref and Qgen free, but this > would yield a system of equations with a severe pathology, namely a > near-singular Jacobian (this originates from the fact that the full > transmission admittance matrix, being a Laplacian matrix, always has a zero > eigenvalue, which corresponds to a translation symmetry consisting in > uniformly shifting all voltages; pinning down at least one voltage is what > breaks this symmetry and recovers invertibility). > > However, I think you're right it would be a good idea to *warn* the user when > the swing generator(s) have gone over their PMAX (or below their PMIN!). > > -- > Jose L. Marin > Grupo AIA > > > On Thu, Feb 18, 2016 at 12:08 AM, Jovan Ilic <[email protected] > <mailto:[email protected]>> wrote: > > Good point, maybe we should trow a Pgen constraint on the swing buses in the > Jacobian. > > > > On Wed, Feb 17, 2016 at 5:30 PM, Santiago Torres <[email protected] > <mailto:[email protected]>> wrote: > Because the exceding generation is supplied by the swing bus. Normal power > flow does not check power generation limits. > > El 17 feb. 2016 1:58 PM, "Bai, Wenlei" <[email protected] > <mailto:[email protected]>> escribió: > Dear Ray, > > I tried to modified load of ‘case9’ to exceed the total generation capacity > purposely. > > To my surprise, power flow still converges. More specifically, the total > generator ‘on-line capacity’ is 820MW, while the ‘actual generation’ is > 920.8MW > > Why the actual generation can be larger than its capacity? > > > > Blessings, > Wenlei > > > > > >
