Brenda: That is exactly what the slack generator is expected to do in a
traditional load flow. I suggest that you look up any classic textbook
(Bergen, Wood & Wollenberg, etc.) and learn about the load flow problem
and its standard assumptions.
carlos.
BRENDA ROJAS DELGADO wrote:
Hi, everyone:
I was running a power flow for case9 and I noticed that the slack bus
gives some wrong behavior. I give two examples:
1. Running first PF with Matlab 2015a and Matpower 5.0.b1 and later
with Matlab 2016a and Matpower version 6.
mpc=loadcase('case9');
mpc.gen(1,9:10)=[10 0];
mpc.gen(3,9)=300;
results=runpf(mpc);
MATPOWER Version 5.0b1, 01-Jul-2014 -- AC Power Flow (Newton)
MATPOWER Version 6.0, 16-Dec-2016 -- AC Power Flow (Newton)
Newton's method power flow converged in 4 iterations.
Converged in 0.01 seconds
================================================================================
| System Summary |
================================================================================
How many? How much? P (MW) Q (MVAr)
--------------------- ------------------- -------------
-----------------
Buses 9 Total Gen Capacity 610.0 -900.0 to 900.0
Generators 3 On-line Capacity 610.0 -900.0 to 900.0
Committed Gens 3 Generation (actual) 320.0 34.9
Loads 3 Load 315.0 115.0
Fixed 3 Fixed 315.0 115.0
Dispatchable 0 Dispatchable -0.0 of -0.0 -0.0
Shunts 0 Shunt (inj) -0.0 0.0
Branches 9 Losses (I^2 * Z) 4.95 51.31
Transformers 0 Branch Charging (inj) - 131.4
Inter-ties 0 Total Inter-tie Flow 0.0 0.0
Areas 1
Minimum Maximum
-------------------------
--------------------------------
Voltage Magnitude 0.958 p.u. @ bus 9 1.003 p.u. @ bus 6
Voltage Angle -4.35 deg @ bus 9 9.67 deg @ bus 2
P Losses (I^2*R) - 2.46 MW @ line 8-9
Q Losses (I^2*X) - 16.74 MVAr @ line 8-2
================================================================================
| Bus Data |
================================================================================
Bus Voltage Generation Load
# Mag(pu) Ang(deg) P (MW) Q (MVAr) P (MW) Q (MVAr)
----- ------- -------- -------- -------- -------- --------
1 1.000 0.000* 71.95 24.07 - -
2 1.000 9.669 163.00 14.46 - -
3 1.000 4.771 85.00 -3.65 - -
4 0.987 -2.407 - - - -
5 0.975 -4.017 - - 90.00 30.00
6 1.003 1.926 - - - -
7 0.986 0.622 - - 100.00 35.00
8 0.996 3.799 - - - -
9 0.958 -4.350 - - 125.00 50.00
-------- -------- -------- --------
Total: 319.95 34.88 315.00 115.00
================================================================================
| Branch Data |
================================================================================
Brnch From To From Bus Injection To Bus Injection Loss
(I^2 * Z)
# Bus Bus P (MW) Q (MVAr) P (MW) Q (MVAr) P (MW)
Q (MVAr)
----- ----- ----- -------- -------- -------- -------- --------
--------
1 1 4 71.95 24.07 -71.95 -20.75 -0.000
3.32
2 4 5 30.73 -0.59 -30.55 -13.69 0.174
0.94
3 5 6 -59.45 -16.31 60.89 -12.43 1.449
6.31
4 3 6 85.00 -3.65 -85.00 7.89 -0.000 4.24
5 6 7 24.11 4.54 -24.01 -24.40 0.095
0.81
6 7 8 -75.99 -10.60 76.50 0.26 0.506 4.29
7 8 2 -163.00 2.28 163.00 14.46 0.000 16.74
8 8 9 86.50 -2.53 -84.04 -14.28 2.465
12.40
9 9 4 -40.96 -35.72 41.23 21.34 0.266 2.26
-------- --------
Total: 4.955 51.31
The results are exactly the same, but what is not normal is that if I
am forcing both active and reactive power on the slack bus to be 10 MW
and 0 MVAr respectively, slack bus power is 72 MW, which by far bigger
than the initial value I impossed it.
So, why is this happening?
Thanks in advance for any reply. Best regards.
