I agree. Having the warnings for all generators, voltages, etc. would be helpful for the cases when users are also varying the generation on PV buses. I would even like MATPOWER fixing the active power at PV buses to the max. or min. limit, if the generation exceeds these limits, and informing the users via a warning.
Shri From: Ray Zimmerman <r...@cornell.edu<mailto:r...@cornell.edu>> Reply-To: MATPOWER discussion forum <matpowe...@list.cornell.edu<mailto:matpowe...@list.cornell.edu>> List-Post: matpower-l@cornell.edu Date: Thursday, February 18, 2016 at 10:34 AM To: MATPOWER discussion forum <matpowe...@list.cornell.edu<mailto:matpowe...@list.cornell.edu>> Subject: Re: power flow question 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 <jovan.i...@gmail.com<mailto: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<mailto: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<mailto: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<mailto: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<mailto: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
