Hi everyone,

I'm new to the Modelica,
I'm trying to make a simple model for two connected liquid tanks (from tank1 to tank2). In this model, we can only open or close the output valve of a tank, according to the liquid level in the relevant tank. here is the model.

package SimplefiedTwoTanks
block Tank
  parameter Real area(unit="m2");
  parameter Real capacity(unit="m3");
  parameter Real max=80;
  parameter Real min=20;
  Real h(start=0,unit="m");
  FlowConnector rateIn;
  FlowConnector rateOut;
equation
  if h>= max then rateIn.rate=0;
  elseif h<=min then rateIn.rate=1;
  else rateIn.rate=1; end if;
  der(h)=(rateIn.rate - rateOut.rate)/area;
end Tank;

block Source
  FlowConnector rate;
end Source;

connector FlowConnector
  Real rate; //flow rate of the connector
end FlowConnector;

block TwoTanks
  Tank tank1(area=10,capacity=100,h=0); // the first tank (the provider tank)
  Tank tank2(area=10,capacity=100,h=0,rateOut.rate=0.5,rateIn.rate=1); // the second tank (the receipient tank)
  Source source(rate.rate=1); // the liquid source
equation
  connect(source.rate, tank1.rateIn);
  connect(tank1.rateOut, tank2.rateIn);
end TwoTanks;

I received error :
Too many equations, over-determined system. The model has 11 equation(s) and 7 variable(s).
as well as, warning that the first (of two) equation in the tank block is not enough big enough to solve for enough variables.

- What am I doing wrong?.
- What are the changes to do to make it works?.

Thank you.