modelica - How to increase a value and check if the increment has led to a increment of another variable? - Stack Overflow

I want to implement a Controller which has an electrical OnePort. The controller should regulates the voltage of the input, to get the maximum power input. The current of the input is constant as long as the voltage is kept under a specific value. If the voltage gets higher than this value, the current is exponentially decreasing. This (voltage-)value is unknown and should be iteratively discovered by the controller by incrementing the voltage, measuring the power and comparing it to the previously measured power.

How can I implement that in OpenModelica?

I tried the following code. I set the Vstart(start = 30).

algorithm
  Vpv := Vstart;
  if P_pv_current > (P_pv_prev + dPthreshold) then
    P_pv_prev := P_pv_current;
    if increase then
      Vstart := Vstart + stepSize;
    else
      Vstart := Vstart - stepSize;
    end if;
  elseif P_pv_current < (P_pv_prev-dPthreshold) then
    P_pv_prev := P_pv_current;
    increase := not increase;
    if increase then
      Vstart := Vstart + stepSize;
    else
      Vstart := Vstart - stepSize;
    end if;
  end if;
  Vpv := Vstart;
equation
  v1 = Vpv;
  i1 = Ipv;
  
  P_pv_current = Vpv * Ipv;

It seems like while simulating it jumps into the if 1 time but after that not anymore. So at the simulation Vpv, Vstart have the value 30.01 and the P_pv_current = P_pv_prev.

I want to implement a Controller which has an electrical OnePort. The controller should regulates the voltage of the input, to get the maximum power input. The current of the input is constant as long as the voltage is kept under a specific value. If the voltage gets higher than this value, the current is exponentially decreasing. This (voltage-)value is unknown and should be iteratively discovered by the controller by incrementing the voltage, measuring the power and comparing it to the previously measured power.

How can I implement that in OpenModelica?

I tried the following code. I set the Vstart(start = 30).

algorithm
  Vpv := Vstart;
  if P_pv_current > (P_pv_prev + dPthreshold) then
    P_pv_prev := P_pv_current;
    if increase then
      Vstart := Vstart + stepSize;
    else
      Vstart := Vstart - stepSize;
    end if;
  elseif P_pv_current < (P_pv_prev-dPthreshold) then
    P_pv_prev := P_pv_current;
    increase := not increase;
    if increase then
      Vstart := Vstart + stepSize;
    else
      Vstart := Vstart - stepSize;
    end if;
  end if;
  Vpv := Vstart;
equation
  v1 = Vpv;
  i1 = Ipv;
  
  P_pv_current = Vpv * Ipv;

It seems like while simulating it jumps into the if 1 time but after that not anymore. So at the simulation Vpv, Vstart have the value 30.01 and the P_pv_current = P_pv_prev.

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Share Improve this question Follow edited Feb 7 at 15:22 Clement44 79411 gold badge33 silver badges2121 bronze badges asked Jan 18 at 16:43 REvLo123REvLo123 1111 bronze badge 2

• 1 From the variables, I am assuming you are building a maximum power tracker for a photovoltaics system? Did you have a look at github.com/christiankral/PhotoVoltaics ? Especially PhotoVoltaics.Components.Blocks.MPTrackerSample could be of interest... – Markus A. Commented Jan 20 at 7:37
• @MarkusA. Thank you. I didn't want to search for MPPT Controller, because I did not want a perfect modulated Controller with IGBT. But the repo you send me is perfect. – REvLo123 Commented Jan 21 at 13:10

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2 Answers 2

Sorted by: Reset to default 0

The solution is that I need to implement a when sample(starttime, timesteps) then because Openmodelica does not do it on its own.

It would help with a complete model, but it is clear that the model code has an algorithm with an if-statement of the kind:

algorithm
 if a>f(b) then
   b:=...
 ...

That is rarely correct in models in Modelica.

Instead you should use when-statements - the difference is that it is only triggered when true - and otherwise keep the value of variables. To make it clearer I would also use pre(b) giving something like:

  when P_pv_current > (pre(P_pv_prev) + dPthreshold) then
    P_pv_prev = P_pv_current;
    if increase then
      Vstart = pre(Vstart) + stepSize;
    else
      Vstart = pre(Vstart) - stepSize;
    end if;
  elsewhen P_pv_current < (pre(P_pv_prev)-dPthreshold) then
    P_pv_prev = P_pv_current;
    increase = not pre(increase);
    if increase then
      Vstart = pre(Vstart) + stepSize;
    else
      Vstart = pre(Vstart) - stepSize;
    end if;
  end when;
  Vpv = Vstart;

You could have it as an algorithm, but it very rare that an algorithm is needed in model code in Modelica.