I agree. In the OPF, the reference is only for the angle. If you want to set a specific voltage magnitude it must be done via VMIN and VMAX columns in the bus matrix.
And there is nothing about the OPF problem formulation or MATPOWER's solvers that would require the voltage magnitude of generator buses to be >= 1pu. That is purely a matter input data and how you want to constrain the problem. -- Ray Zimmerman Senior Research Associate B30 Warren Hall, Cornell University, Ithaca, NY 14853 phone: (607) 255-9645 On Jul 23, 2013, at 4:54 PM, spyros gian <[email protected]> wrote: > Thank you Dr Zimmerman. > > I am running an ACOPF in matpower. In the mpc.bus I set for bus 13: Vm=1 , Va > = 0, type = 3. > So bus 13 is my reference bus. This means that in the results I will take > that voltage at bus 13 has an angle of 0 degrees, and a magnitude of 1 pu? > Ie , in your reply you wrote that in ACOPF, the reference bus determines the > voltage reference for the system. Does this mean, only the voltage_angle or > also the voltage_magnitude are determined ? > > After running the ACOPF, I get for bus 13: Voltage angle = 0 , > Voltage_magnitude = 1.05 pu. > This shows me that bus13, being the reference bus in the ACOPF, only means > that its angle is equal to > the Va parameter in the mpc.bus matrix. And that its voltage magnitude is > determined in the ACOPF. > > Do you agree with this? > > Secondly, I would like to ask you : Is it compulsory that a bus equipped with > generators, has voltage magnitude >=1 pu in the ACOPF results? > > Thank you > > From: [email protected] > Subject: Re: OPF on matpower > Date: Tue, 23 Jul 2013 13:44:09 -0400 > To: [email protected] > > 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 <[email protected]> wrote: > > > > On Jul 23, 2013, at 9:42 AM, spyros gian <[email protected]> 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 > > > >
