Hanie, I do not understand how this could be possible. I think that we
should move the discussion offline and when we have a resolution to this
riddle we will post it back for others to see. Please email me
privately at [email protected] and describe in detail the steps
that you are taking; include scripts/functions if necessary. But what
you are describing should not happen.
Carlos.
Hanie Sedghi wrote:
Dear Carlos,
Thank you so much for your consideration,
Actually No.
I am not changing the generators. PD_Nominal as I understand it is the
demand at each bus.
There is a generator part in the case file that I do not change.
What I am saying is that I am setting the power demand at each bus and
then run the DCpower flow. afterwards, the values of injected demand
or Pload(as stated in output) are not exactly the same as the initial
demand but in a range of it.
So my question is what is MATPOWER doing for solving the DC power flow
that causes this.
It would be of great help to me if you answer this.
All the best,
Hanie
On Tue, Aug 21, 2012 at 2:46 PM, Carlos E Murillo-Sanchez
<[email protected] <mailto:[email protected]>> wrote:
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]>
<mailto:[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
