P_from_to and P_to_from are erroneously zero in DC power flow

[GabrielKS]

In a power flow output, P_from_to is the active power flowing through the line at its from bus and P_to_from is the active power flowing through the line at its to bus. These are not necessarily the same magnitude due to line losses, but they should at least be comparable in magnitude. In the results of an AC power flow, this holds:

but in the results of a DC power flow, one of the P values for each row seems to be zero:

[rodrigomha]

I'm confused about this implementation. Here is the code that writes this in the DataFrame:

PowerFlows.jl/src/post_processing.jl

Line 491 in 558a337

for i in 1:length(branches)

# get flows on each line
    P_from_to_vect = zeros(length(branches))
    Q_from_to_vect = zeros(length(branches))
    P_to_from_vect = zeros(length(branches))
    Q_to_from_vect = zeros(length(branches))
    for i in 1:length(branches)
        if branch_flow_values[i] >= 0
            P_from_to_vect[i] = branch_flow_values[i]
            P_to_from_vect[i] = 0
        else
            P_from_to_vect[i] = 0
            P_to_from_vect[i] = branch_flow_values[i]
        end
    end

Based on this implementation, if the solution is positive for the branch, it assigns the proper value to the from_to (probably correct). However if the solution is negative, it's assigned the same value to the to_from (probably incorrect). I'm guessing that in the solution of the DC PowerFlow, the solution is always for from_to, so in this case what it needs to happen is the following:

# get flows on each line
    P_from_to_vect = zeros(length(branches))
    Q_from_to_vect = zeros(length(branches))
    P_to_from_vect = zeros(length(branches))
    Q_to_from_vect = zeros(length(branches))
    for i in 1:length(branches)
        if branch_flow_values[i] >= 0
            P_from_to_vect[i] = branch_flow_values[i]
            P_to_from_vect[i] = 0
        else
            P_from_to_vect[i] = 0
            P_to_from_vect[i] = -branch_flow_values[i]
        end
    end

so the flows are always positive with the correct direction.

[rodrigomha]

I'm confused about this implementation. Here is the code that writes this in the DataFrame:

PowerFlows.jl/src/post_processing.jl

Line 491 in 558a337

for i in 1:length(branches)

# get flows on each line
    P_from_to_vect = zeros(length(branches))
    Q_from_to_vect = zeros(length(branches))
    P_to_from_vect = zeros(length(branches))
    Q_to_from_vect = zeros(length(branches))
    for i in 1:length(branches)
        if branch_flow_values[i] >= 0
            P_from_to_vect[i] = branch_flow_values[i]
            P_to_from_vect[i] = 0
        else
            P_from_to_vect[i] = 0
            P_to_from_vect[i] = branch_flow_values[i]
        end
    end

Based on this implementation, if the solution is positive for the branch, it assigns the proper value to the from_to (probably correct). However if the solution is negative, it's assigned the same value to the to_from (probably incorrect). I'm guessing that in the solution of the DC PowerFlow, the solution is always for from_to, so in this case what it needs to happen is the following:

# get flows on each line
    P_from_to_vect = zeros(length(branches))
    Q_from_to_vect = zeros(length(branches))
    P_to_from_vect = zeros(length(branches))
    Q_to_from_vect = zeros(length(branches))
    for i in 1:length(branches)
        if branch_flow_values[i] >= 0
            P_from_to_vect[i] = branch_flow_values[i]
            P_to_from_vect[i] = 0
        else
            P_from_to_vect[i] = 0
            P_to_from_vect[i] = -branch_flow_values[i]
        end
    end

so the flows are always positive with the correct direction.

If we want to add both directions, doing this:

for i in 1:length(branches)
            P_from_to_vect[i] = branch_flow_values[i]
            P_to_from_vect[i] = -branch_flow_values[i]
end

will suffice

[jd-lara]

Yeah, it seems this the post processing code isn't implemented correctly.

[jd-lara]

Let's resolve it to have the P_from_to = -P_to_from and report it like that.

[rodrigomha]

Closed via #45