Dear Dr. Zimmerman,
the "Bus types play no role" confused me a bit, so I tried declaring some
previous generator nodes as PQ buses.
It seems to me the only effect is, that the voltage now is not longer fixed to
the generator set point during a normal Power Flow calculation.
Do you know if that's correct or has it any further consequences?
thanks in advance
Simon
>>> Ray Zimmerman <r...@cornell.edu> 23.07.2013 19:44 >>>
Shri is correct with some *very* minor tweaks the only bus type that matters is
the REF bus which determines the voltage reference for the system, and the
voltage angle at that bus is set to the corresponding value in the bus matrix,
which is usually set to 0, but need not be.
And, yes, the OPF solvers in MATPOWER do find locally optimal solutions that
are not guaranteed to be globally optimal. Theoretically, MATPOWER could find
different solutions depending on the algorithm, starting point, algorithm
parameters, etc. However, in my experience, it has been very difficult to find
multiple local optima. The one example I have been able to confirm has nearly
identical objective values and active power dispatches, with some differences
in voltage profile and reactive dispatch in a few buses.
My conjecture is that in most cases, especially for relatively small systems,
the solution found by MATPOWER is likely the global optimum or else something
extremely close to it. I hope to include in an upcoming version some
contributed code that will be able to confirm in some cases that a solution is
a indeed a global optimum.
--
Ray Zimmerman
Senior Research Associate
B30 Warren Hall, Cornell University, Ithaca, NY 14853
phone: (607) 255-9645
On Jul 23, 2013, at 1:05 PM, Shri <abhy...@mcs.anl.gov> wrote:
On Jul 23, 2013, at 9:42 AM, spyros gian <sp.g...@hotmail.com> wrote:
Dear Dr Zimmerman,
Running an OPF in matpower means that
1. Bus types play no role (eg slack, PV, PQ etc)
Yes.
2. All values for Real Power generation and reactive power generation are
unknown
Yes.
3. All values for bus_voltages and voltage phase angles in buses, are unknown
as well
The voltage angle of the reference bus is fixed and set to 0.
4. As a result, all values for real and reactive power flows are unknown.
Yes.
5. Losses are unknown.
Yes.
What is known :
1. The resistance, reactance, admittance per unit / per conductor
2. Values for Real and Reactive demand at each bus
3. Limits on voltage magnitude , limits on real and reactive power generation
4. MVA limits on each line
5. Fuel cost for each generator.
Yes for all
So my question is
a. Are the above correct for matpower ?
b. Since matpower uses a non-linear optimisation, is the result a local minimum
or a global minimum?
(for the case of a cost-minimization OPF) ? i.e. the values for voltages,
reactive powers etc, are
globally optimum or perhaps other optimum values for all the unknown
quantities exist ?
I believe most of the optimization tools, such as fmincon in Matlab, find a
local minimum.
Shri
Thank you,
Spyros Gian
