Hello Jaroslaw, I may be completely off, as I do not know the RTDS system you're using, but I couldn't help noticing this sounds as if RTDS is using the "ZIP" (in your case just Z,P) load model components *only for transients*, not for static powerflow. But this is to be expected, because using load modeling schemes such as ZIP usually does not make much sense in static powerflow studies.
-- Jose L. Marin Grupo AIA On Tue, Apr 12, 2016 at 6:47 AM, Jaroslaw Krata <j.kr...@uq.edu.au> wrote: > Dear Ray, > > > thank you for your reply. > > I have updated shunt load with voltage coefficient. > > However, I am still finding some issues with final results. > > > I have replicated my system in two independent software platforms. > > One is the Matpower and the second is the RTDS (real-time digital power > system simulator). > > > When I set my system loads to be 100% constant power loads, the power flow > results from both simulators are nearly identical. > > Newton's method power flow converges in 4 iterations and the voltages > differences between RTDS and Matpower is only approx. 0.1% and it is > consistent at all buses. > > I consider it as an extremely good result and I am very happy with it. > > > However, when I add some portion of a constant impedance loads (ratio > 70/30 or 80/20), the voltage error increase to 0.6%-0.8% (and shunt power > accordingly). > > It is 7x bigger error caused only by changing the proportions of constant > impedance to constant power loads. > > At the each investigated case, Matpower calculated higher value of > voltages. > > > Do you have any idea what might the source of the error (bearing in mind > that for fully constant power loads the error is almost non-existent)? > > How can I possibly eliminate the issue? > > > BR, > > Jaroslaw > > > ------------------------------ > *From:* bounce-120338215-75504...@list.cornell.edu < > bounce-120338215-75504...@list.cornell.edu> on behalf of Ray Zimmerman < > r...@cornell.edu> > *Sent:* 06 April 2016 00:27 > *To:* MATPOWER discussion forum > *Subject:* Re: Matpower 5.1 and constant impedance loads > > Hi Jarek, > > I don’t think any code changes should be necessary for solving the problem > you want to solve. That is, if you put the constant impedance loads in the > GS and BS columns of the bus matrix, the calculations should be correct, > including all of the resulting voltages and flows. The only issue is that > the power delivered to these elements is not reported anywhere as “load”, > so you’ll have to do that manually after the fact, but that is a trivial > calculation once you have the bus voltages. For example, if the nominal > (i.e. at 1 p.u. voltage) active and reactive constant impedance loads are > given in the nb x 1 vectors Pdz0 and Qdz0, then you can calculate the > constant impedance loads at the solution as follows ... > > define_constants; > mpc = loadcase(...); > mpc.bus(:, GS) = mpc.bus(:, GS) + Pdz0; > mpc.bus(:, BS) = mpc.bus(:, BS) - Qdz0; > > r = runpf(mpc); > > Pdz = Pdz0 ./ r.bus(:, VM) .^ 2; > Qdz = Qdz0 ./ r.bus(:, VM) .^ 2; > > The constant power loads can be found using total_load() … > > [Pds, Qds] = total_load(r.bus, r.gen, 'bus'); > > So, no need for any of your steps beyond a) under #2, except I suppose f) > could be done by simply doing … > > r.bus(:, PD) = r.bus(:, PD) + Pdz; > r.bus(:, QD) = r.bus(:, QD) + Qdz; > > > Ray > > > > On Apr 5, 2016, at 1:43 AM, Jaroslaw Krata <j.kr...@uq.edu.au> wrote: > > Dear Matpower authors, > > I wish to use the Matpower software in my PhD research. > I need to calculate power flow for the distribution system that consists > of many constant impedance and constant power loads. > > After I read in the manual that " (...) the constant impedance portions > can be modeled as a shunt element (...)", > I thought naively that it's gonna be easy ;-). > I went through other messages from this mailing list and I understand that > I need to changes the code of the Power Flow calculation. > > In particular, I was trying use this advise > https://www.mail-archive.com/matpower-l%40cornell.edu/msg03254.html > but it seems that since 2014 the code of Matpower has changed and this > advice is not easy applicable to the newest version of the Matpower. > > Thus, I would like to ask you for help of the required code changes in the > Matpower 5.1. > I wish to achieve two targets: > 1. correct power flow calculation assuming const P and const Z loads > 2. output branch and power matrices showing updated (real) values of power > from const Z loads. > > I started as follows: > a) I assume that whole constant power loads are assigned to the bus matrix > - Pd and Qd columns > while all constant impedance loads are assigned to Gs and Bs columns > > b) I modified makeSbus() function by adding lines related to const P and Z > line1: [Sbus, Sbus_gen, Sbus_constP, Sbus_constZ] = makeSbus(baseMVA, > bus, gen) %adding Sbus_gen, Sbus_consP and Sbus_constZ vectors > line36 to 38: > Sbus = ( Cg * (gen(on, PG) + 1j * gen(on, QG)) ... %% power injected by > generators > - (bus(:, PD) + 1j * bus(:, QD)) ... %% plus power > injected by const P loads > ) / baseMVA; %% converted to > p.u. > > replaced by: > Sbus = ( Cg * (gen(on, PG) + 1j * gen(on, QG)) ... %% power injected by > generators > - (bus(:, PD) + 1j * bus(:, QD)) ... %% plus power > injected by const P loads > - (bus(:, GS) + 1j * bus(:, BS)) )/ ... %% plus power > injected by const Z loads > baseMVA; %% converted to p.u. > > Sbus_gen = (Cg * (gen(on, PG) + 1j * gen(on, QG))) / baseMVA; > Sbus_constP = (bus(:, PD) + 1j * bus(:, QD)) / baseMVA; > Sbus_constZ = (bus(:, GS) + 1j * bus(:, BS)) / baseMVA; > > c) I pass all Sbus vectors to newtonpf() function > [V, converged, i] = newtonpf(Ybus, Sbus, Sbus_gen, Sbus_constP, > Sbus_constZ, V0, ref, pv, pq, mpopt) > > d) In newtonpf(), I calculate 'mis' variable as > line 54 and line 106: mis = V .* conj(Ybus * V) - (Sbus_gen - Sbus_constP > - Sbus_constZ.*(Vm.^2)) > (replacing the default mis = V .* conj(Ybus * V) - Sbus;) > > e) How should I change the dSbus_dV() function?? > f) How to update bus matrix to show updated value of const Z power? > g) Should I change other functions as well (e.g. makeYbus() function)? > > > I will be grateful for your help and suggestions, > BR, > Jarek > > > >
