Re: power flow

[Mounika Vanjarapu]

thank u

On Tue, Apr 12, 2016 at 2:45 PM, Deep Kiran  wrote:

> Dear Mounika,
>
> for example of case5.m
>
> Write the code as:
>
> mpc = loadcase(case5);
> mpc.branch('branch number',6) = 'specify your line limit for the branch of
> your choice';
>
> I hope this helps!
>
> Regards,
> Deep Kiran
>
>
>
> On 12 April 2016 at 14:15, Mounika Vanjarapu 
> wrote:
>
>> can anyone say how to change the power flow limits by writing the code
>> but not by editing the limits.like setting the limits to my wish for some
>> branches
>>
>
>

Re: Query for Lagrange multiplier correspond to Qg limits

[Deep Kiran]

Wow, its been 2 years of using Matpower and I was unaware of this setting.
Thank you Sir.

Best regards,
Deep Kiran

On 8 April 2016 at 19:37, Ray Zimmerman  wrote:

> Your understanding is correct. However, with numerical algorithms such as
> the primal-dual interior point method used by MATPOWER’s default OPF
> solver, depending on the numerical termination criteria for the algorithm,
> some non-binding constraints may still have small non-zero values for their
> multipliers. MATPOWER attempts to screen these out with a threshold of 1e-4
> required to display a constraint, but in this case that threshold is too
> small.
>
> Decreasing the termination tolerance eliminates the problem.
>
> mpopt = mpoption('opf.ac.solver', 'MIPS', 'mips.comptol', 1e-7);
> r = runopf(m,mpopt);
>
> Best regards,
>
> Ray
>
>
>
> On Apr 8, 2016, at 3:50 AM, Deep Kiran  wrote:
>
> Dear Matpower community,
>
> I was doing some interpretation for pattern of Lagrange multiplier
> correspond to Qg limits on case5.m.
>
> I have done some modification on the network which are as follows:
>
> m = loadcase(case5);
> m.bus(:,[3,4]) = m.bus(:,[3,4])*0.65;
> m.bus(:,[4]) = m.bus(:,[4])*-2;
> r = runopf(m);
>
> With the above modification, I get the following result for reactive power
> limit of generator at bus 4.
>
> Gen   Bus Reactive Power Limits
>   # # Qmin mu Qmin   Qg   QmaxQmax mu
>   -   ---         ---
>4 4  0.001   -150.00   -145.20150.00  -
>
> From the above result, Qg(=-145.20)  is still within its limits
> [-150,150]. My understanding of Lagrange multiplier is that it remains zero
> for the inequality constraint that is < or > 0. Its value will be non-zero
> only if the inequality constraint is = 0. Although, the Qmin mu(=0.001) is
> small, however, Qg is 4.8 off from its lower bound.
>
> Am I missing some obvious link here?
>
> Thank you in advance.
>
> Best regards,
> Deep Kiran
> Research Scholar,
> IIT Delhi,
> India
>
>
>

Re: power flow

[Deep Kiran]

Dear Mounika,

for example of case5.m

Write the code as:

mpc = loadcase(case5);
mpc.branch('branch number',6) = 'specify your line limit for the branch of
your choice';

I hope this helps!

Regards,
Deep Kiran



On 12 April 2016 at 14:15, Mounika Vanjarapu 
wrote:

> can anyone say how to change the power flow limits by writing the code but
> not by editing the limits.like setting the limits to my wish for some
> branches
>

power flow

[Mounika Vanjarapu]

can anyone say how to change the power flow limits by writing the code but
not by editing the limits.like setting the limits to my wish for some
branches

Re: Matpower 5.1 and constant impedance loads

[Jose Luis Marin]

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  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  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:
>