If you run a power flow or continuation power flow on a case that has no slack
bus, it will automatically select the first PV bus to use as a slack.
Regarding your question about introducing a slack bus vs. increasing PG … in
general, no, they are not the same, and not defining a slack is not an option
for power flow. But either I’m not understanding your question (in which case,
please clarify) or else you lack a basic understanding of what a slack bus is
in the context of the power flow problem (in which case, please consult a good
power systems textbook).
Ray
> On Mar 3, 2015, at 5:35 PM, Bijay Hughes <[email protected]> wrote:
>
> Sometimes it looks like matpower automatically chooses the reference bus
> (slack bus). Is it true? For instance, if I increase the power demand of one
> of the buses in my two-bus island, the generator increases its power
> generation as well, even though it is not marked as slack bus. Please look at
> the two cases, in the second case I increased the power demand, and hence
> generation increased too to reduce the imbalance. Another question: does
> slack bus substitute for increasing PG. In other words, is it the same when
> one introduces slack bus or increases the PG to meet the PD? If not, which
> one is better?
>
>
> Summary 1:
>
>
> Bus Voltage Generation Load
> # Mag(pu) Ang(deg) P (MW) Q (MVAr) P (MW) Q (MVAr)
> ----- ------- -------- -------- -------- -------- --------
> 1 1.000 0.000 436.05 158.45 - -
> 2 0.950 -7.136 170.00 0.00 600.00 98.61
> -------- -------- -------- --------
> Total: 606.05 158.45 600.00 98.61
>
> ================================================================================
> | 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 2 436.05 158.45 -430.00 -98.61 6.052 60.52
> --------
> --------
> Total: 6.052 60.52
>
>
>
>
>
> Summary 2:
>
> Bus Voltage Generation Load
> # Mag(pu) Ang(deg) P (MW) Q (MVAr) P (MW) Q (MVAr)
> ----- ------- -------- -------- -------- -------- --------
> 1 1.000 0.000 747.87 276.69 - -
> 2 0.924 -12.657 170.00 0.00 900.00 98.61
> -------- -------- -------- --------
> Total: 917.87 276.69 900.00 98.61
>
> ================================================================================
> | 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 2 747.87 276.69 -730.00 -98.61 17.873 178.73
> --------
> --------
> Total: 17.873 178.73
>
>
> Thanks,
>
> Bijay
>
>
> On Mon, Mar 2, 2015 at 10:24 PM, Ray Zimmerman <[email protected]
> <mailto:[email protected]>> wrote:
> It appears you are using an older version of MATPOWER. Could you try it with
> the latest released version and see if you still get an error.
>
> Ray
>
>> On Mar 1, 2015, at 3:46 PM, Bijay Hughes <[email protected]
>> <mailto:[email protected]>> wrote:
>>
>> Hi All,
>>
>> When I remove some branches in case5, two islands are formed. First island
>> with slack bus (bus_type 3) and second island with no slack bus. I want to
>> extract the second island extract_islands(mpc,2) and run power flow. It
>> doesn't work obviously because there is imbalance in load and supply due to
>> the lack of slack bus. However, I try to change the bus type of one of the
>> busses in second island to 3 to have the slack bus, but my power flow still
>> doesn't work. It gives me the following error message:
>>
>> Subscript indices must either be real positive integers or logicals.
>>
>> Error in ext2int (line 185)
>> as = bs(n2i(mpc.areas(:, PRICE_REF_BUS)));
>>
>> Error in runpf (line 130)
>> mpc = ext2int(mpc);
>>
>> Error in rough (line 12)
>> results=runpf(ccr)
>>
>> Am I missing something here? Does all islands need to have slack bus
>> (bus_type 3) to run power flow? Why does my island still not run power flow
>> even though I made one of the buses into the slack bus? Could anyone please
>> help me out?
>>
>> Thanks,
>>
>> Bijay
>
>
