Sorry, one mistake in my example: the BUS_TYPE in the second case should obviously be 2 (PV), not 1.
-- Jose L. Marin Grupo AIA On Thu, Apr 28, 2016 at 11:48 PM, Jose Luis Marin <mari...@gridquant.com> wrote: > > Looking at those records I think I may have misunderstood what you're > doing. I thought you were converting a given PQ bus (BUS_I=246) into PV, > but the generator record you're showing is attached to BUS_I=1 instead. > > To be precise, I thought you were starting from (numbers made up for this > example): > > bus_i type Pd Qd Gs Bs area Vm Va > baseKV zone Vmax Vmin > 246 1 15.37 1.12 0 0 3 1 0 > 20 4 2 0.6; > > And, assuming that the solution for that starting case gave for instance > V=1.0375 on BUS_I=246, then making these changes to the case: > > bus_i type Pd Qd Gs Bs area Vm Va > baseKV zone Vmax Vmin > 246 1 0.0 0.0 0 0 3 1 0 > 20 4 2 0.6; > > plus adding this generator to the bus: > bus Pg Qg Qmax Qmin Vg mBase > status Pmax ... > 246 -15.37 0 999.99 -999.99 1.0375 100 > 1 1.3 ... > > Then, provided you are not enforcing MVAR limits (which may change a lot > of things), you should obtain the same powerflow solution in this second > case (with Qg near -1.12, in this example), > > > Did I miss something? > > > -- > Jose L. Marin > Grupo AIA > > > > On Thu, Apr 28, 2016 at 7:26 PM, Chris Prokop <christophprok...@gmail.com> > wrote: > >> Hi, >> >> @ Jose L. Marin: >> I used a generator in both cases, hence it should be the correct sign >> (should result in the same I guess). Anyway P was very small, around 1e-6 >> MW. >> >> I'm not sure if I've modelled something wrong: S_base is 100, my >> generator is at bus 1 (at the end zeros(1,12)): >> bus Pg Qg Qmax Qmin Vg mBase >> status Pmax ... >> 1 0.4 0 0.7 -0.45 1.04 >> 100 1 1.3 ... >> >> And the PQ-bus: >> bus_i type Pd Qd Gs Bs area Vm >> Va baseKV zone Vmax Vmin >> 246 1 2.64e-06 -30 0 0 3 1 >> 0 20 4 2 0.6; >> >> I've tried another thing: I changed the PQ-bus from -30 to +30 Mvar (e.g. >> mpc.bus(1, 4) = 0) and for another time I did the same with the generator >> from +30 to -30 Mvar (e.g. mpc.gen(1, 3)=30), the other part (gen vs. load) >> was always set to 0. The result was not (!) the same... hm? - I guess this >> is the reason for the problem. >> With the bus I get results from -8 Mvar up to 30 Mvar with v=0.635 to >> 1.46 whereas with the generator the voltage varies only within -1 Mvar and >> +1 Mvar (appr. 1.01 pu to appr. 1.04 pu), for other Q-injections the >> voltage doesn't change. >> >> I uploaded the plot under: http://de.tinypic.com/r/350pk02/9 >> >> Do you have any idea why? >> >> Thanks for your help, nice regards, >> Chris >> >> >> >> >> Am 28.04.2016 um 17:41 schrieb Jose Luis Marin: >> >> >> Those are certainly some crazy Mvar injections! Just checking: are you >> sure you reversed the signs of P properly when switching the type of that >> bus from PQ (load) to PV (gen with neg real power), also taking care of >> making the corresponding changes in the bus row and adding a new gen row? >> >> If you could share your case file I could try to give you a quick >> diagnostic. >> >> -- >> Jose L. Marin >> Grupo AIA >> >> >> >> On Thu, Apr 28, 2016 at 5:19 PM, Chris Prokop <christophprok...@gmail.com >> > wrote: >> >>> Thanks for your responses. >>> >>> @ Ray Zimmerman: >>> I can't find the problem here. If I set Q=+0.7 Mvar (cap.), the voltage >>> at this bus is about 1.04 p.u., with Q=-0.7 Mvar (ind.) it decreases to >>> 1.02 p.u., the power flow converges as expected (+the result is as >>> expected). Only converting this bus into a PV-bus results in the problem >>> mentioned above (with or without limits). I don't get why the Newton Power >>> Flow returns for example 1e3 Mvar for this bus as a result, as only <1 Mvar >>> should have been enough reactive power. >>> Before solving the case the reactive power of the generators at the >>> PV-buses are (variable gen in runpf): >>> - Reference bus: 0 Mvar >>> - PV-Bus1: 0 Mvar >>> - PV-Bus2: 64.4 Mvar >>> - PV-Bus3 (the problematic one): 0.1 Mvar >>> after solving it (after pfsoln), the variable gen is filled with: >>> - Reference bus: 1e6 Mvar >>> - PV-Bus1: 2.7e4 Mvar >>> - PV-Bus2: 9.6e3 Mvar >>> - PV-Bus3 (the problematic one): -600 Mvar >>> whereas the next most reactive power intensive gen&bus has less than 5e2 >>> Mvar. I don't understand where the power comes from/goes to... >>> >>> @ Jose Luis Marin: >>> If I use the voltage from the PQ-calculation (e.g. 20.6668/20 >>> p.u.) there remains the same problem. Also without Q-limits I get the the >>> problem... >>> Vg=1 p.u. actually works as a PV-bus, Vg=1.01 or Vg=1.02 etc. don't. >>> >>> >>> Nice regards, >>> Chris >>> >>> 2016-04-28 16:04 GMT+02:00 Ray Zimmerman <r...@cornell.edu>: >>> >>>> It sounds like the voltage at that bus may be very sensitive to the >>>> reactive power injection. One thing you might try to get some idea of this >>>> is to change that bus back to PQ with the reactive at the lower limit, then >>>> try running a few cases with slightly perturbed values of the reactive >>>> power at that generator and see how the voltage at the bus changes. >>>> >>>> Ray >>>> >>>> >>>> On Apr 28, 2016, at 8:40 AM, Chris Prokop <christophprok...@gmail.com> >>>> wrote: >>>> >>>> Hi, >>>> >>>> >>>> I'm using Matpower (v5.0b1, but the same holds for v5.1) for a 220 >>>> kV/110 kV/20 kV-grid quite a while. The grid has 1 reference bus (220 kV), >>>> 2 PV-buses (220 kV) and >100 PQ-buses (110 kV & 20 kV). So far calculating >>>> the grid using runpf with Newton has never been a problem. >>>> >>>> Now I've tried to change a 20 kV PQ-bus to a PV-bus with the Q-limits >>>> +0.7 for Q_max and -0.45 for Q_min (considering mpopt = >>>> mpoption('pf.enforce_q_lims', 1)). If I set Vg of the generator to >>>> 1.05 I get the error: >>>> "All 4 remaining gens exceed their Q limits : INFEASIBLE PROBLEM" >>>> whereas when using 1.00 as Vg there is no problem (then the generator >>>> is at its lower Q-limit, hence converted to PQ). If the problem is >>>> infeasible the result of pfsoln in runpf are Q-values of all 4 >>>> PV generators (Slack+3 PV) that are out of their limits. Why is there such >>>> a big difference between the case V=1.05 and V=1.00? >>>> >>>> As a info: the Slack has a Q-Limit of +-10000, both of the already >>>> existing PV buses +720/-290, according to case_info the total generation is >>>> -300 MW+j10 Mvar, the total load 300 MW-j50 Mvar, but I've tried several >>>> scenarios which are no problem when using the PQ instead of the PV-bus (or >>>> the Vg=1). >>>> >>>> >>>> Does anybody experience a similar problem/has an idea how to fix it? >>>> >>>> Nice regards, >>>> Chris >>>> >>>> >>>> >>> >> >> >
