Let me see if I get this rightt:
1) You define real power dispatches of non-slack generators in a test
case, perhaps also change the amount of load, and then
2) you run a power flow, ostensibly with runpf. But then,
3) you find that the dispatch values that you had defined in step (1)
for generators other than the slack have been changed by runpf.
It should not happen normally. The only mechanism for this to happen is
if a) you have ENFORCE_Q_LIMS set to 1 (default is 0), and b) The slack
generator happens to hit a Q limit, in which case the the slack bus is
treated as a PQ bus with Qg set to the limit, and then the next PV
generator is treated as the slack bus, which might cause this generator
to have a slightly different Pg dispatch than what you originally
specified. Could this be what you are seeing?
Carlos.
Hanie Sedghi wrote:
I think I should explain the problem more briefly.
The thing is that when I input some load to a grid in MATPOWER, the
final value of power injections at buses are not exactly equal to the
initial values I assigned them.
I now know this happens in a real grid due to the branch data (line
and/or transformer impedance data), and other loads in the system (if
any) that can consume power at each bus when running power flow.
So my question is, is it ok to get this result if I run DC power flow
in MATPOWER? and I am wondering why this happens.
I just want to justify the results.
Thank you so much,
Hanie
On Fri, Aug 17, 2012 at 9:51 AM, Hanie Sedghi <[email protected]
<mailto:[email protected]>> wrote:
Hello sir,
Hope you are doing great.
For my research, I need to feed the grid with independent demands
and follow the outputs. I solve for DC power flow
For changing the demand I use
mpc = loadcase('case9');
define_constants;
Nominal_PD =[0;0;13;21.97;0;0;0;0;52.42;0] %something random
So I expect that Pload in MATPOWER's output be the same as my
given Nominal_PD
which is not always true.
for example I have used case 9 with above Nominal_PD, which is
less than sum of Nominal generations for bus 2,3 (that is 163, 85
respectively)
now Pload=[-3.68;1.83 ;20.53 ;33.52;4.44;3.55 ;4.92
; -0.56;44.83;-3.02]
or even when Nominal_PD is such that sum of demand exceeds the
generation in 2,3 (and slack bus compensates for the rest) I have
the same problem that Pload is not equal to Nominal_PD (I assign
this value randomly)
It seems like the grid satisfies demand partially for some nodes
and induces some gen/demand at nodes when there is no demand(when
I run DC power flow)
So I was wondering what is going on here. Is it what in fact
happens in the grid or I am missing an assumption in MATPOWER or
is it something else?
I would truly appreciate your response.
Best Regards,
Hanie
