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 <[email protected]> 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 <[email protected]> > 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 <[email protected]>: >> >>> 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 <[email protected]> >>> 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 >>> >>> >>> >> > >
