Hi Jovan, Sorry, I see I misundertood. I had read your proposal as consisting in adding an *equality* constraint, instead of an *inequality* constraint.
But as you say, I suspect that such thing would be equivalent to just adding a simple post-calculation check and a warning to the user when PG is out of bounds (PMIN, PMAX). -- Jose L. Marin Grupo AIA On Thu, Feb 18, 2016 at 2:05 PM, Jovan Ilic <jovan.i...@gmail.com> 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 <mari...@gridquant.com> > 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 <jovan.i...@gmail.com> >> 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 < >>> santiago.i...@gmail.com> 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" <wenlei_...@baylor.edu> >>>> 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 >>>>> >>>>> >>>>> >>>> >>> >> >
