Hello Asma,
I thank you very much for your help, I understood the solution that you > proposed. I decreased the cos phi to finally have a max_lambda> 1, after > I saw the > value of Q which corresponds to the value of max lambda > 1 and I put the > Q for each turbine in negative like you did for P. > Please keep in mind that you probably cannot choose cos_phi freely for wind turbines. You will have to investigate what kind of technology (inverters?) they're using, and then find out how much reactive power they can really absorb/inject. I'm not an expert in such models, but I bet their operating range is not much wider than cos_phi 0.95 either way (lagging/leading). Additionally, if you trust your values of P to be correct, I think the only way you can "torture your case until it solves" is by lowering the line reactances. > my questions are: > > 1/ why did you put the P and Q in negatives because I try to put them in > positive and the calculation diverges, > Because the columns bus(:, [PD QD]) are power injection *demand* (see http://www.pserc.cornell.edu//matpower/docs/ref/matpower6.0/idx_bus.html). So they're supposed to be positive when they're loads, and negative when they're generation. > 2/ with max_lambda> 1 I got also mean voltage> Vmax = 1.1, is that > logical, so I increased Vmax to 1.5 and it did not change the results > The columns bus(:, [VMAX VMIN]) play absolutely no role in *powerflow*; they're only used for OPF. > 3/ in my current case (see image and mfile) I have 2 transmission lines > between 1002 and 3001 and between 1001 and 3001, my problem is when I > increase the transmission distance (beyond 130 km) so I increase the > values of r x and b between these branches, the calculation diverges > knowing that it worked for distances <130 km. and I also noticed that the > Q losses decrease by increasing the transmission distance which is not > logical. what is the problem in your opinion? > > the solution that i did: I changed the value of system MVA base = 8MW * > 100 (which was set to 100) so here my program converges without even > injecting reactive power for the turbines and the value of Q increases by > increasing the transmission distance. > I thought to do that because I saw in other load flow calculation code > that the basic value of the system = the production of each wind turbine > (8MW) * nb of wind turbines (100) is my logic true and what is the effect > of the base MVA value? > Increasing the values of X (while maintining everything else fixed) will eventually lead to an infeasible case, that's no surprise. But the value of net reactive losses (I^2 X) may vary in non-monotonic ways because it also depends on other factors such as the line susceptances (Bshunt). Now, did you change the MVAbase without making the corresponding change in all of your R, X, B parameters? If so, this is simply wrong. The MVA base is just a choice of units for power; so if your case is infeasible in one choice of units, it will still be infeasible in any other. I'm guessing you're obtaining convergence simply because the values of R, X, B are not expressed correctly in the new MVAbase (they are 8 times lower), so you are changing the case altogether! If I were you I would first double check that your branch parameters R, X, B are correct for the choice of MVAbase and the corresponding Voltage level. and my last question: > 4/how can I do the compensation of the reactive power at nodes 1002 and > 1001 (the 2 substations) and at pdl node 3001 and how can i see the > intermediate calculation of the reactive losses for each node because > matpower gives us directly the results without seeing the details of the > calculations. > I'm not sure I understand your question. To find out the amount of reactive compensation you need, here's one very simple thing you can do in MATPOWER: introduce a new generator at the desired bus, with PG=0 (no real power), and choose some sensible value for the desired voltage setpoint, VG. This will act as a "synchronous condenser", injecting or absorbing just the right amount of reactive power Q so that the bus reaches the voltage setpoint. Solve the case and look at the solution. The Q injected by this generator will give you exactly the amount of (local) reactive support you need. You can later convert this generator into a static capacitor bank, if you prefer. I mean, a bus capacitor whose BS value would yield the same injection Q when the bus voltage is VG (BS = Q / VG^2). -- Jose L. Marin Grupo AIA
