There are a few things that I think make your case below behave in non-intuitive ways. First, you are reducing only a few of the loads from one base case to the next, but each time you are setting the target to be a scaled version of that new base (exaggerating the differences from the original base load pattern). Second, you allow these few loads to go negative. This means that in the target case, they are even more negative, meaning that you have to increase the other loads much further before you get to the same total load (which is what you are basing the load margin on).
So, I think sticking to positive loads and using a fixed target case might yield much more intuitive results. Ray > On Feb 16, 2017, at 1:16 PM, Majid Mehdizadeh <majidmeh....@gmail.com> wrote: > > I have tried the same load reduction in other ieee cases and again i have got > the same answer. It is a big question in matpower cpf function that when the > load of system reduces, why the load margin becomes lower? May be we should > use a same target loading and generation in every cases. It means that as the > system load reduces, the target load and generation remains the same and then > the cpf is performed with the base and target loading and generation > condition. Is this reasonable? I did it for the mentioned problem. The load > margin increased in this case! > > > On Feb 16, 2017 7:41 PM, "Abhyankar, Shrirang G." <abhy...@anl.gov > <mailto:abhy...@anl.gov>> wrote: > I agree with Ray. The base case dispatch being updated by OPF causes a > reduction in generation, commensurate to the load reduction, and hence you > are seeing a decrease in the load margin. What happens when you decrease the > load at some other buses? Do you get the same behavior? > > Shri > > From: Ray Zimmerman <r...@cornell.edu <mailto:r...@cornell.edu>> > Reply-To: MATPOWER discussion forum <matpowe...@list.cornell.edu > <mailto:matpowe...@list.cornell.edu>> > Date: Thursday, February 16, 2017 at 8:28 AM > To: MATPOWER discussion forum <matpowe...@list.cornell.edu > <mailto:matpowe...@list.cornell.edu>> > Subject: Re: load reduction in continuation power flow (CPF) > > The code looks correct to me. I’m not sure why the load margin decreases, but > the changes in load (from positive to equally negative) may be forcing the > OPF solution into generator dispatch solutions that somehow reduce the load > margin. > > Ray > > >> On Feb 15, 2017, at 10:45 PM, Majid Mehdizadeh <majidmeh....@gmail.com >> <mailto:majidmeh....@gmail.com>> wrote: >> >> Dear sir and matpower committee >> It is very strange for me that when the load of some PQ buses in IEEE 39 bus >> test system are reduced and then cpf is performed then the load margin of >> the system is becoming lower . It should be noted that i use the following >> code to estimate the load margin of the system using maximum lambda.: >> clc >> clear all >> a=0; >> for ii=1:20 >> mpcb = loadcase(case39); % load base case >> for v=[1 3 4 7]; >> mpcb.bus(v,3)=mpcb.bus(v,3)-a*mpcb.bus(v,3); >> end >> mpopt = mpoption('verbose',0,'out.all',0); %default >> result=runopf(mpcb,mpopt);%bayad print ro disable koni >> mpcb.gen(:,2)=result.gen(:,2); >> load=sum(mpcb.bus(:,3)) >> generation=sum(mpcb.gen(:,2)) >> mpopt = mpoption('out.all',0,'verbose',0); >> mpopt = mpoption(mpopt,'cpf.stop_at','NOSE','cpf.step', 0.2); >> mpopt = mpoption(mpopt,'cpf.plot.level',0,'cpf.plot.bus',8); >> mpct = mpcb; % set up target case with >> mpct.gen(:,[2 3]) = mpcb.gen(:,[2 3]) * 3.5; % increased generation >> mpct.bus(:,[3 4]) = mpcb.bus(:,[3 4]) * 3.5; % and increased load >> results = runcpf(mpcb, mpct, mpopt); >> landa(ii)=results.cpf.max_lam;% >> Pf= mpcb.bus(:,3) +landa(ii)*(mpct.bus(:,3)-mpcb.bus(:,3)); >> Pinitial(ii)=sum(mpcb.bus(:,3)); >> Pfinal(ii)=sum(Pf); >> loadmargin(ii)=Pfinal(ii)-Pinitial(ii); >> a=a+0.1; >> end >> bar(loadmargin) >> >> >> >> Is there any wrong calculation of final or initial load with maximum lambda? >> as you see, the load margin is final load minus the initial load: >> Pf= mpcb.bus(:,3) +landa(ii)*(mpct.bus(:,3)-mpcb.bus(:,3)); >> Pinitial(ii)=sum(mpcb.bus(:,3)); >> Pfinal(ii)=sum(Pf); >> loadmargin(ii)=Pfinal(ii)-Pinitial(ii); >> >> -- >> >> Best Regards >> Majid Mehdizadeh >> >> Ph.D Student of electrical engineering, Power Department, >> Ferdowsi University of Mashhad >> >> Substation and Transmission Line Expert, Engineering office, >> Khorasan Regional Electric Co. >> >> http://mehdizadeh.majid.student.um.ac.ir >> <http://mehdizadeh.majid.student.um.ac.ir/> >> >> >
