Matlab Function block changes input values by order of magnitude

Hello!

I'm trying to implement a basic MPPT P&O Algorithm in Simulink. For this I have a Matlab Function block that takes in the current, voltage, and power. It then applies the P&O algorithm and outputs a desired dutycycle which is feed into a PWM generator.

The system was not behaving as I expected so I added a output form the Function Block

StateVector = [Ppv, Pprev, Vpv, Vprev, Dprev];

When then viewing the output from the StateVector with a scope I found that Ppv (INPUT) =/= Ppv (OUTPUT)

The full code (Incorrect Algorithm) is as follows:

function [D,DeltaP,StateVector] = fcn(Vpv,Ipv,Ppv)
persistent Dprev Pprev Vprev
if isempty(Dprev)
    Dprev = 0.1;
    Vprev = 48;
    Pprev = 380;
end
%Ppv = Vpv*Ipv;
DeltaP = Ppv-Pprev;
deltaD = 0.1;
if (Ppv-Vprev) > 0
    if (Vpv-Vprev) > 0
        D = Dprev-deltaD;
    else
        D = Dprev+deltaD;
    end
else
    if (Vpv-Vprev) > 0
        D = Dprev + deltaD;
    else
        D = Dprev - deltaD;
    end
end
Dprev = D;
Vprev = Vpv;
Pprev = Ppv;
StateVector = [Ppv, Pprev, Vpv, Vprev, Dprev];

As you can see at no point is Ppv changed. At first it was calculated internally, but when I found this error I moved the computation outside making use of a product block.

The input Ppv can be seen below:

And the output:

I do not understand what could cause this. These signals are pulled directly at the input and output.

I appreciate any suggestions :)

EDIT: Ops the algorithm was very wrong. But ignoring the incorrectly formulated P&O Algorithm, why would the input-output relation be so strange?

[Yifeng Tang]

Attaching the model will be helpful for the community to diagnose the issues.

[Adarsh]

Hi @Lillebror Sagmen-Andersson,

I have tried to reproduce the issue that you are facing using an example model, in which i have used the given code in the "MATLABFcn" block and provided the input ports with data generated by different signal generators, each having different frequencies (so that i can verify where exactly the issue is occuring). when I inspected the Input and the output "Ppv" signals in a "scope" block I see that both the signals are same, pointing no issue with the given function.

Here is an image of the example model that I have tested:

Here is the output of the "scope" block:

Attaching the exact model will be helpful to find out the exact issue.