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] <mailto:[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]
<mailto:[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]
<mailto:[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
