Implementation of MPPT+PID for a BUCK Converter

Hello,

The goal of my project is to aliment 48V batteries with a photovoltaic source

Because the input is variable, I have to implement a regulation loop to make sure I can obtain a 48V output.

Here is my Simulink model

I really don't understand why I have such weird results when I simulate my model (it's the scope for Vout):

Here is my MPPT algorithm:

function Vref= RefGen (V_PV, I_PV)

Vrefmax=140;
Vrefmin=0;
Vrefinit=112;
deltaVref=0.5;

persistant Vol Pold Vrefold;

if isempty (Vold)
    Vold=0;
    Pold=0;
    Vrefold=Vrefinit;
end
P= V_PV*I_PV;
dV=V_PV-Vold;
dP=P-Pold;

if dP~=0
    if dP>0
        if dV>0
            Vref= Vrefold - deltaVref;
        else
            Vref=Vrefold + deltaVref;
        end
    else
        if dV> 0
            Vref= Vrefold + deltaVref;
        else
            Vref= Vrefold - deltaVref;
        end
    end
else
    Vref= Vrefold;
end

Vrefold = Vref;
Vold = V_PV;
Pold = P;
end

Please find also attached my Matlab model.

Thanks in advance for your help

[Sam Chak]

Do you have the mathematics that describes the Buck Converter system?

When you have the full mathematics, you can do wonders most of the time.

[Thibaut C]

I'm not sure to understand what you want, do you want to see my calculations for dimensioning the components ?

[Pat Gipper]

This question looks similar to the question below. I wonder if my answer there might help?

PV MPPT Tracking Failing PV Array Current or Volatge Goes negative - (mathworks.com)

[Tony Castillo]

Dear @@Thibaut C I have try your model and I can see two drawbaks.

1. It is not properly designed. You better redisign it using the correct formulas. Try the model that I shared in this email with you.
2. The MPPT is entering an undesired perturbation to your control, I have detected removing it and introducing a PWM block plus a constant value. You have an example of MPPT in MATHLAB https://es.mathworks.com/solutions/power-electronics-control/mppt-algorithm.html

[Sam Chak]

Hi @Thibaut C

If you have the mathematical model that describes the behavior of the Buck Converter such that

where u is the PID control input, then you can possibly apply some control design methods to tune the gains, in a way that yields the desired output 48V consistently.

Moreover, having the mathematical model allows the Engineers, Researchers, Scientists, and Experts like @Pat Gipper and @Tony Castillo to check if your Buck Converter is correctly modeled in Simulink or not.

As a trained Engineer, you must have a "blueprint" that serves a system template for you to follow when designing similar systems. If the Buck Converter is incorrectly modeled in Simulink in the first place, then any PID controller you design later would become meaningless, as the controller cannot be practically implemented in the real world.