Dear Dr. Zimmerman, I think your method is correct, it is converged and the same results of 'runopf' and 'runpf' can be got when I tried it with original 'case24_ieee_rts' data . However, when I use my own bus PD data, it can not converge. But, With the PD increase, it began to converge. So, I think maybe QD at each bus is the problem. I revised the QD to follow the PD curve at each bus, but the situation even worse, the converge times is even fewer. What should I do next? Can you give me hint?I really can not figure out what is wrong, maybe the constraint VMAX=VMIN=VG is too strict, because it converged when I use 'runopf(my data)' with all default constraint.
Thank you for your time to consider my question. Difei ________________________________ 发件人： Ray Zimmerman <[email protected]> 收件人： MATPOWER discussion forum <[email protected]> 发送日期： 2013年3月14日, 星期四, 2:56 上午 主题: Re: new question about ref bus Pg when reduce and increase load Running an OPF with all generator costs set to zero essentially gives you an arbitrary feasible solution to the problem, which could vary in arbitrary ways from one run to another. I don't think this is probably what you want. If you don't have actual generator costs, at least choosing them to be equal and non-zero will minimize losses. Difei, I think your idea of removing constraints was close to what you want. However, you can't remove all voltage constraints. MATPOWER's OPF allows generator voltages to be redispatched within its limits as well as generator power. Power flow, on the other hand, fixes generator voltages at a specified set-point. What you probably want is to remove the voltage limits for the PQ buses, and set VMIN=VMAX=VG for the generator buses. If you also remove the line limits, then I think the output of runopf() will be equal to the output of runpf() with the redispatched generators. You can try it to check … something like this … define_constants; mpc.bus(, VMAX) = 2; % set VMAX of all buses to 2 mpc.bus(:, VMIN) = 0; % set VMIN of all buses to 0 gbus = find(mpc.bus(:, BUS_TYPE) == PV | mpc.bus(:, BUS_TYPE) == REF); % gen buses for i = gbus % for each generator bus ig = find(mpc.gen(:, GEN_BUS) == mpc.bus(i, BUS_I), 1); % 1st gen at bus mpc.bus(i, VMAX) = mpc.gen(ig, VG); mpc.bus(i, VMIN) = mpc.gen(ig, VG); end mpc.branch(:, RATE_A) = 0; % set RATE_A of all branches to 0 r1 = runopf(mpc); r2 = runpf(r1); In this case, r1 and r2 should contain the same solution. -- Ray Zimmerman Senior Research Associate 419A Warren Hall, Cornell University, Ithaca, NY 14853 phone: (607) 255-9645 On Mar 13, 2013, at 1:15 PM, iman <[email protected]> wrote: Dear Difei, >As far as I follow, you are trying to study the system without generation >cost.If this is the case,please put the cost of generators equal to zero and >runopf. Now Optimal power flow will be regardless of the price of the >generation. >Best regards >Iman > > > > >On Wed, Mar 13, 2013 at 5:08 PM, TANG Difei <[email protected]> wrote: > >Dear Dr. Zimmerman and Shiyang, >> >> >>Thank you again for the prompt reply. >> >> >>Yes. As Dr. Zimmerman said, to make the re-dispatch of generator more >>reasonable, running 'runopf' function is a good choice. >>I tried and here comes the problems. >>First, I run 'runopf' with all constraints, although all 24 runs converged, >>none of branch flows nor bus voltage became overload or drop. I noted this >>because my aim is to see how branch flow and bus voltage changes. So, I >>realized that the constraints are the reason. >>Then, to see how branch flow and bus voltage changes, I remove all the >>constraints except Pmax Pmin, Qmax Qmin and equality nonlinear constraints as >>follows: >> >> >>mpopt = mpoption('OPF_IGNORE_ANG_LIM', 1); % ingnore branch voltage angle >>difference limits >>mpc.bus(:, 12) = ones(24, 1) .* 2; % set VMAX of all buses to 2 >>mpc.bus(:, 13) = zeros(24, 1); % set VMIN of all buses to 0 >>mpc.branch(:, 6) = zeros(38, 1); % set RATE_A of all branches to 0 >> >> >>The results shows all bus voltage increase to 1.6~1.9 while branch 10 exceed >>flow_max. I realized that in this unconstrained situation, all unconstrained >>variables are adjusted to minimize the system gen cost, so the results are >>not reasonable. >> >> >>(1) In conclusion, if I want to see how branch flow and bus voltage changes >>due variable load, I must run 'runpf' rather than 'runopf', but I have to >>re-dispatch gens first. If I use 'runopf' to re-dispatch the gens, do I need >>to activate all constraints or not? >> >> >>(2) After the re-dispatch, I use the dispatched gens Pg instead of the >>original data to run 'runpf', is that reasonable? >>In my opinion, it is not because the system is power balanced when the >>optimal solution achieved. If I use the gen Pg from 'runopf' to run 'runpf', >>the results totally changes, eg. all the bus voltage no longer between 1.6 >>and 1.9, the system is then in a new power balance state, not the previous >>gen_cost minimization state. Please correct me if I am wrong. >> >> >> >> >>Thanks in advance. >>Difei >> >> >> >> >> >>________________________________ >> 发件人： Ray Zimmerman <[email protected]> >>收件人： MATPOWER discussion forum <[email protected]> >>发送日期： 2013年3月13日, 星期三, 10:48 下午 >>主题: Re: 回复：new question about ref bus Pg when reduce and increase load >> >> >>As Shiyang says, yes, it's ok to change the generator dispatches. In fact, as >>the load changes throughout the day, you will have to re-dispatch your >>generators to follow the load. There are many ways to re-dispatch the >>generators, and each option results in a different set of line flows and a >>different set of bus voltages. Simply re-running the PF without changing >>inputs means that the slack bus handles all of the redispatch to follow load >>(even if it has to absorb, rather than generate power) … probably not what >>you intend. >> >> >>My suggestion, if you want to have something that approximates typical >>operation, would be to choose some reasonable costs for the generators and >>then use runopf() to compute the dispatch based on minimizing generation cost. >> >> >>-- >>Ray Zimmerman >>Senior Research Associate >>419A Warren Hall, Cornell University, Ithaca, NY 14853 >>phone: (607) 255-9645 >> >> >> >> >>On Mar 13, 2013, at 12:48 AM, [email protected] wrote: >> >>Hi Difei, >>>(1). See (2). >>>(2). Yes, it is. >>>(3). Why not? It's authorized. But I think your question is on dispatching >>>when loads increase, not the base case defined in case file. >>> >>> >>>Shiyang Li >>> >>> >>> >>> >>>----- 原始邮件 ----- >>>发件人：TANG Difei <[email protected]> >>>收件人：MATPOWER discussion forum <[email protected]> >>>主题：new question about ref bus Pg when reduce and increase load >>>日期：2013年03月13日 11点16分 >>> >>> >>>Dear all, >>> >>> >>>Thank you for Dr. Zimmerman and Li Shiyang 's help about my previous >>>question. I appreciate it. >>> >>> >>>Here is a new question about ref bus Pg reduce and increase load. >>>I use runpf function for the power flow calculation for variable load in 24 >>>hours. My aims is to see how branch flow and bus voltage change when the bus >>>load change. So, I revised the bus load data to classify the buses into 3 >>>types of load: residential, industrial and commercial, which means the load >>>at each bus is different from the original case data. Please be noted that >>>the load is changed but the generator output (Pg) is not changed. >>>Then, the problem comes. >>>Although all 24 PF calculations converged successfully, the Pg of ref bus is >>>negative when the system load is low in the morning, while the Pg of ref bus >>>is very high (much higher than other gen) when the system load is high in >>>the evening. This result can not reflect the real world power system >>>operation. I know the problem is from the Pg of ref bus must archive system >>>power balance. >>>(1)So, I want to know, how can I see the branch flow and bus voltage change >>>when all the generator Pg is between PMIN and PMAX? >>>(2)I refer to iman's thread about limits on the branch. >>>http://www.mail-archive.com/[email protected]/msg01475.html >>> >>> Is it a good solution that I change the other generator Pg so the ref >>>bus Pg is kept in a reasonable scale? >>>(3) Is that OK if I change the original case data (bus load) to my own data? >>> >>> >>>Thanks in advance. >>> >>> >>>Difei >>> >>> >>> >>> >>> >>>________________________________ >>> 发件人： Ray Zimmerman <[email protected]> >>>收件人： MATPOWER Discussion List <[email protected]> >>>发送日期： 2013年3月1日, 星期五, 5:04 上午 >>>主题: Re: slack bus real power output (PG) is negative? >>> >>> >>>(1) It depends what you mean by reasonable. Yes, this a perfectly reasonable >>>(i.e. correct) answer to this power flow problem. No, it is not reasonable >>>to operate this power system at this set-point, other generator set-points >>>should be reduced to make it feasible. >>> >>> >>>(2) Again, it depends what you mean. What the result says, is that given >>>that network, under that loading condition, with those generator set-points, >>>you would need about 3 MW of load at that bus to achieve power balance. >>> >>> >>>(3) You should not expect flows to increase uniformly throughout the system >>>as you scale loads at all buses and generation only at the slack bus. Some >>>may increase, some may decrease, some may even switch direction. >>> >>> >>>-- >>>Ray Zimmerman >>>Senior Research Associate >>>419A Warren Hall, Cornell University, Ithaca, NY 14853 >>>phone: (607) 255-9645 >>> >>> >>> >>> >>>On Feb 28, 2013, at 10:02 AM, TANG Difei <[email protected]> wrote: >>> >>>Dear all, >>>> >>>> >>>>I ran 'results=runpf('case24_ieee_rts')' and found that >>>>results.gen(12,2)==-2.9536 MW, which means the real power slack bus (Bus >>>>13) is a negative value. >>>>(1) Is that result reasonable? >>>>(2) Can the slack bus with negative PG be looked as a load? >>>>By checking the previous thread, I knew that PG of slack bus = all loads + >>>>all losses - all other generator real power outputs >>>> >>>> >>>>In my opinion, it is not reasonable. For example, I used function >>>>'scale_load' to scale all the real and reactive loads from 10% to 100% of >>>>original value (I did not scale the generator output), by using >>>> >>>> >>>>mpc = loadcase('case24_ieee_rts'); >>>>for i = 1 : 10 >>>> multiple = i/10; >>>> mpc_m(i) = mpc; >>>> mpc_m(i).bus = scale_load(multiple, mpc_m(i).bus); >>>> [results_m(i), success_m(i)] = runpf(mpc_m(i)); >>>>end >>>> >>>> >>>>Then, I found that, for example, in the scenario of the multiple value from >>>>0.1 to 1, the real power injected at "to" bus end (PT) of Branch 1 is >>>>reduced from 25.2679 MW to 11.9363 MW, and the PG of slack increase from >>>>-2322 MW to -2.9536 MW , which is not reasonable, because with the loads >>>>increase from 0.1 to 1, the power of each branch will increase too. >>>>(3) Am I correct? >>>> >>>> >>>>Any advice from anyone will be very much appreciated. >>>> >>>> >>>> >>>> >>>>Best wishes, >>>>Difei Tang >>> >>> >>> >> >> >> > > >-- >Best regards >Iman >
