Hi Sayandev,

As you know, iterative methods need an initial guess.  But this is the
user's *choice*: you can use a flat start as you mention, or any other
information you may have (for instance, from previously solved cases that
are similar to the one at hand---as it happens when solving N-1 contingency
analysis cases).  MATPOWER cannot make this choice for you; so it will just
take the values of bus(:,[VM VA]) present in the input file as the initial
guess (except for VM in PV buses, where the value is replaced by the
regulation voltage VG of the corresponding generators).

So, if you want to test a "flat start", you have to explicitly set the
values of VM and VA before you call runpf().  By the way, setting the VM to
the swing's Vref is (arguably) slightly better than setting them to 1.  In
any case, note that "flat start" is by no means a guaranteed way to obtain
the correct solution (or a solution at all).

Jose L. Marin
Grupo AIA

2017-08-08 10:11 GMT+02:00 Sayandev Ghosh <sayande...@gmail.com>:

> Beg your pardon the missing snippet from the previous mail is as follows:
> %% initial state
>     %V0    = ones(size(bus, 1), 1);            %% flat start
>     V0  = bus(:, VM) .* exp(sqrt(-1) * pi/180 * bus(:, VA))
>     vcb = ones(size(V0));           %% create mask of voltage-controlled
> buses
>     vcb(pq) = 0;                    %% exclude PQ buses
>     k = find(vcb(gbus));            %% in-service gens at v-c buses
>     V0(gbus(k)) = gen(on(k), VG) ./ abs(V0(gbus(k))).* V0(gbus(k));
> Assistant Professor
> Electrical Engineering Department
> Chaibasa Engineering College, Chaibasa, Jharkhand
> Mob. No. - 7292880077 / 9748509620
> On Tue, Aug 8, 2017 at 1:31 PM, Sayandev Ghosh <sayande...@gmail.com>
> wrote:
>> Hello,
>> I am Sayandev Ghosh, presently teaching power system in an undergraduate
>> engineering college. I have done my M.Tech on Energy Science from Jadavpur
>> University. I have been using MATPOWER for load flow analysis of till 118
>> bus by Newton Raphson method. While doing that I am not able to understand
>> the following area:-
>>  In the runpf() function while using Newton Raphson method  the initial
>> values of voltage magnitude and voltage angle have been assigned by the
>> following lines (line 177 - 183):
>>                               [image: Inline image 2]
>>     I am having a bit problem in understanding this section. Why are we
>> considering the final values of Voltage magnitude and Voltage angle as the
>> initial guess? In the case files for eg. 'case57' the Vm and Va are
>> probably the final voltage magnitudes and voltage angles.
>> Shouldn't it be like assigning all the voltage magnitudes of PQ bus as 1.0
>> pu and voltage angles of all PV and PQ bus as 0 degree for a flat start.
>> Depending on the answer of this question I would like to convey my other
>> doubts/questions.
>> Thanks in advance.
>> Assistant Professor
>> Electrical Engineering Department
>> Chaibasa Engineering College, Chaibasa, Jharkhand

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