The VG column in the gen matrix is only for the power flow problem. It has no effect on the OPF problem.
-- Ray Zimmerman Senior Research Associate B30 Warren Hall, Cornell University, Ithaca, NY 14853 phone: (607) 255-9645 On Jul 23, 2013, at 5:16 PM, Yi Liang <[email protected]> wrote: > From my understanding, > > For the AC electricity, the matter is not the absolute value of the voltage > angle, the differences between different bus voltage angles are what you want > to know. So people set one bus as the reference bus and usually set the angle > as 0. > > I believe that Vm here is from the mpc.bus, which I assume is the start point > value. > However, in mpc.gen, there is a column (column 6) indicates the voltage > magnitude setpoint (p.u.). It's in a file called caseformat. Or you can find > it in the manual. > > for the additional questions, usually, in real world, people are going to > control the voltage magnitudes. So, in matpower, you can go and check the > mpc.gen mentioned above to check the setpoints of generator voltages. > > Hope it helps, Correct me if I made any mistakes. > > Thanks, > Yi Liang > > > On Tue, Jul 23, 2013 at 3:54 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 > > > > > > > -- > Yi Liang, Master Candidate > > Room 403, Coordinated Science Laboratory > Department of Electrical and Computer Engineering > University of Illinois at Urbana Champaign > 1308 W Main Street, Urbana, IL, 61801-2307 >
