The power flow algorithm is not affected by generators ability to supply extra reactive power at all. It would be affected if a generator was not able to provide enough reactive power and in that case its reactive output would be set to one of the limits and the bus would become a PQ bus. If you check the code, you should find a section where the generator's reactive output is calculated to balance Q at a node and keep the voltage as set, after everything else is calculated. Remember, dQ/dV for PV buses is not part of the Jacobian. In real life, the field current is controlled to keep the voltage constant or supply ISO requested Vars. I think Matpower is a little bit more realistic, Ray can correct me. A few years ago I was at a conference where somebody was questioning presenter's results obtained from Matpower because he assumed that Matpower does not use generator capability curve. I think that it can, right Ray?
You should use capacitor shunts to get the answer to your question although it should be obvious. If you have too much reactive power you should see overvoltages and if you do not have enough you should see undervoltages. You probably want quantitative results for a particular case. I just reread your e-mail, it seems that you are using ACOPF. The above comment still holds with just one addition. If the generator's Q limits are not binding you should not see any change in the solution after changing Q limits. This would be true only if the ACOPF is not using any penalty functions (Newton-Raphson) implicitly or explicitly. If it does, you can change relevant inequality constraints and you will get small, unpredictable, changes in the result even if the constraints are not binding. Jovan Ilic On Fri, Jun 28, 2013 at 5:52 PM, Ray Zimmerman <[email protected]> wrote: > I was not able to use your data without manual editing, due to the way the > text wrapped, but you can try relaxing the Qmin constraint a bit and see > how the solution changes to understand the tradeoffs the optimization is > making in order to accommodate the Q injection. > > -- > Ray Zimmerman > Senior Research Associate > B30 Warren Hall, Cornell University, Ithaca, NY 14853 > phone: (607) 255-9645 > > > > > > On Jun 19, 2013, at 6:27 AM, Jiashen Teh <[email protected]> > wrote: > > Dear Dr Ray, > > I am trying to find out what will happen if I have excessive reactive > power supply on a 3 bus network. > > I did that by forcing synchronous generator to have max and min VAR supply > of 100 MVAR. > > When I do that, I expect bus voltages to increase (done by relaxing bus > voltage limits). However, from MATPOWER simulation shows me that bus > voltages drop instead. > > Could you please explain why this is happening? I attached here are my > network data. Thanks in advance. > > %% bus data > % bus_i type Pd Qd Gs Bs area Vm Va baseKV zone Vmax Vmin > mpc.bus = [ > 1 2 0 0 0 0 1 1 0 > 230 1 5 0 > 2 2 0 0 0 0 1 1 0 230 1 > 5 0 > 3 3 0 0 0 0 1 1 0 230 1 > 5 0 > ]; > %% generator data > % bus Pg Qg Qmax Qmin Vg mBase status Pmax > Pmin > mpc.gen = [ > 1 0 0 100 0 1.00 100 1 > 400 0 > 2 0 0 50 0 1.00 100 1 > 200 0 > 2 0 0 50 0 1.00 100 1 > 200 0 > 3 0 0 100 100 1.00 100 1 > 0 0 % SG > 2 0 0 0 -20 1.00 100 1 > 0 -100 % Dispatchable load > 3 0 0 0 -33 1.00 100 1 > 0 -165 % Dispatchable load > ]; > %% branch data > % fbus tbus r x b rateA rateB rateC ratio > angle status angmin angmax > mpc.branch = [ > 1 3 0.0342 0.180 0.0106*2 150 85 85 > 0 0 1 -360 360 > 1 2 0.0912 0.480 0.0282*2 100 85 85 > 0 0 1 -360 360 > 2 3 0.1140 0.600 0.0352*2 200 71 71 > 0 0 1 -360 360 > 1 3 0.0342 0.180 0.0106*2 150 85 85 > 0 0 1 -360 360 > 1 2 0.0912 0.480 0.0282*2 100 85 85 > 0 0 1 -360 360 > 2 3 0.1140 0.600 0.0352*2 200 71 71 > 0 0 1 -360 360 > ]; > %% generator cost data > % model Startup Cost Shutdown Cost Coefficient number Coefficient > mpc.gencost = [ > 2 10 0 3 10 > 100 1000 > 2 10 0 3 2.5 > 5 10 > 2 10 0 3 2.5 > 5 10 > 2 10 0 3 0 > 0 0 % SG > 2 10 0 2 5000 > 2500 0 % Dispatchable load > 2 10 0 2 5000 > 2500 0 % Dispatchable load > ]; > > Yours sincerely, > > Jiashen Teh > PhD Student > Electrical Energy & Power Systems Group, School of Electrical & Electronic > Engineering > Ferranti Building (B18), The University of Manchester, M13 9PL, United > Kingdom > Tel: +44 (0) 161 306 2263; Mobile: +44 (0) 792 322 4864 > > >
