>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 <sp.g...@hotmail.com> 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: r...@cornell.edu > > Subject: Re: OPF on matpower > Date: Tue, 23 Jul 2013 13:44:09 -0400 > To: matpower-l@cornell.edu > > > 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 > > > > > -- 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
