Problems building up a simple DCDC converter in Modelica - modelica

Question

I want to write a very simple model for a DCDC converter. For some reason, Dymola tells me that the "model is not well-posed" and overdetermined for Real elements.
It might be a quite simple problem but I can't see it!
Here's my code:
model DCDC
extends Modelica.Electrical.Analog.Interfaces.TwoPort;
parameter Real demandedVoltage;
Modelica.Electrical.Analog.Sensors.VoltageSensor sekVolt annotation (
Placement(transformation(
extent={{-10,-10},{10,10}},
rotation=270,
origin={80,0})));
Modelica.Electrical.Analog.Sensors.CurrentSensor currentSensor annotation (
Placement(transformation(
extent={{-10,10},{10,-10}},
rotation=270,
origin={-50,-30})));
Modelica.Electrical.Analog.Sources.SignalCurrent signalCurrent annotation (
Placement(transformation(
extent={{-10,-10},{10,10}},
rotation=270,
origin={-50,30})));
Modelica.Electrical.Analog.Sources.ConstantVoltage constantVoltage(V=
vehicleVoltage)
annotation (Placement(transformation(
extent={{-10,10},{10,-10}},
rotation=270,
origin={50,30})));
Modelica.Electrical.Analog.Sensors.CurrentSensor currentSensor1 annotation (
Placement(transformation(
extent={{-10,-10},{10,10}},
rotation=270,
origin={50,-30})));
Modelica.Blocks.Math.Division division
annotation (Placement(transformation(extent={{6,22},{-10,38}})));
Modelica.Blocks.Math.Product product
annotation (Placement(transformation(extent={{8,-8},{-8,8}},
rotation=270,
origin={30,8})));
Modelica.Blocks.Math.Gain gain(k=-1)
annotation (Placement(transformation(extent={{-20,22},{-36,38}})));
Modelica.Electrical.Analog.Sensors.VoltageSensor primVolt
annotation (
Placement(transformation(
extent={{-10,10},{10,-10}},
rotation=270,
origin={-80,0})));
equation
connect(currentSensor.p, signalCurrent.n) annotation (Line(
points={{-50,-20},{-50,20}},
color={0,0,255},
smooth=Smooth.None));
connect(constantVoltage.n, currentSensor1.p) annotation (Line(
points={{50,20},{50,-20}},
color={0,0,255},
smooth=Smooth.None));
connect(signalCurrent.p, p1) annotation (Line(
points={{-50,40},{-50,50},{-100,50}},
color={0,0,255},
smooth=Smooth.None));
connect(currentSensor.n, n1) annotation (Line(
points={{-50,-40},{-50,-50},{-100,-50}},
color={0,0,255},
smooth=Smooth.None));
connect(constantVoltage.p, p2) annotation (Line(
points={{50,40},{50,50},{100,50}},
color={0,0,255},
smooth=Smooth.None));
connect(currentSensor1.n, n2) annotation (Line(
points={{50,-40},{50,-50},{100,-50}},
color={0,0,255},
smooth=Smooth.None));
connect(primVolt.n, n1) annotation (Line(
points={{-80,-10},{-80,-50},{-100,-50}},
color={0,0,255},
smooth=Smooth.None));
connect(primVolt.p, p1) annotation (Line(
points={{-80,10},{-80,50},{-100,50}},
color={0,0,255},
smooth=Smooth.None));
connect(sekVolt.p, p2) annotation (Line(
points={{80,10},{80,50},{100,50}},
color={0,0,255},
smooth=Smooth.None));
connect(sekVolt.n, n2) annotation (Line(
points={{80,-10},{80,-50},{100,-50}},
color={0,0,255},
smooth=Smooth.None));
connect(gain.y, signalCurrent.i) annotation (Line(
points={{-36.8,30},{-43,30}},
color={0,0,127},
smooth=Smooth.None));
connect(division.y, gain.u) annotation (Line(
points={{-10.8,30},{-18.4,30}},
color={0,0,127},
smooth=Smooth.None));
connect(currentSensor1.i, product.u2) annotation (Line(
points={{40,-30},{25.2,-30},{25.2,-1.6}},
color={0,0,127},
smooth=Smooth.None));
connect(sekVolt.v, product.u1) annotation (Line(
points={{70,0},{62,0},{62,-10},{34.8,-10},{34.8,-1.6}},
color={0,0,127},
smooth=Smooth.None));
connect(product.y, division.u1) annotation (Line(
points={{30,16.8},{30,34.8},{7.6,34.8}},
color={0,0,127},
smooth=Smooth.None));
connect(primVolt.v, division.u2) annotation (Line(
points={{-70,0},{14,0},{14,20},{14,20},{14,25.2},{7.6,25.2}},
color={0,0,127},
smooth=Smooth.None));
annotation (
Diagram(coordinateSystem(preserveAspectRatio=false, extent={{-100,-100},{100,
100}}), graphics), Icon(coordinateSystem(preserveAspectRatio=false,
extent={{-100,-100},{100,100}}), graphics={
Rectangle(
extent={{-100,100},{100,-100}},
lineColor={0,0,127},
lineThickness=0.5,
fillPattern=FillPattern.Solid,
fillColor={215,215,215}),
Line(
points={{-100,100}},
color={0,0,255},
smooth=Smooth.None),
Line(
points={{-100,100},{-100,-100},{100,-100},{100,100},{-100,100}},
color={0,0,127},
thickness=0.5,
smooth=Smooth.None),
Line(
points={{-100,-100},{100,100}},
color={0,0,127},
thickness=0.5,
smooth=Smooth.None),
Text(
extent={{-60,80},{0,20}},
lineColor={0,0,0},
lineThickness=0.5,
textString="DC"),
Text(
extent={{0,-20},{60,-80}},
lineColor={0,0,0},
lineThickness=0.5,
textString="DC")}));
end DCDC;
Hopefully someone may figure out my problem here.
Thank you in advance!
EDIT:
After the answers I decided to change my model a bit since I need the converter for a hybrid (energy/power) supply. The resulting converter is given in the following code:
model DCDC2 "Component with two electrical ports, including current"
Real v_energy "Voltage drop over the energy port";
Real v_power "Voltage drop over the power port";
Real v_output "Voltage drop over the output port";
Real i_energy "Current flowing from pos. to neg. pin of the energy port";
Real i_power "Current flowing from pos. to neg. pin of the power port";
Real i_output "Current flowing from pos. to neg. pin of the output port";
Real p_energy;
Real p_power;
Real p_output;
parameter Real demandedVoltage;
parameter Real efficiency = 1;
Modelica.Electrical.Analog.Interfaces.PositivePin pinP_Energy
annotation (Placement(transformation(extent={{-110,50},{-90,70}})));
Modelica.Electrical.Analog.Interfaces.NegativePin pinN_Energy
annotation (Placement(transformation(extent={{-110,-70},{-90,-50}})));
Modelica.Electrical.Analog.Interfaces.PositivePin pinP_Power
annotation (Placement(transformation(extent={{90,50},{110,70}})));
Modelica.Electrical.Analog.Interfaces.NegativePin pinN_Power
annotation (Placement(transformation(extent={{90,-70},{110,-50}})));
Modelica.Electrical.Analog.Interfaces.PositivePin pinP_Output
annotation (Placement(transformation(extent={{-20,80},{20,120}})));
Modelica.Electrical.Analog.Interfaces.NegativePin pinN_Output
annotation (Placement(transformation(extent={{-20,-120},{20,-80}})));
equation
v_energy = pinP_Energy.v - pinN_Energy.v;
v_power = pinP_Power.v - pinN_Power.v;
v_output = pinP_Output.v - pinN_Output.v;
0 = pinP_Energy.i + pinN_Energy.i;
0 = pinP_Power.i + pinN_Power.i;
0 = pinP_Output.i + pinN_Output.i;
i_energy = pinP_Energy.i;
i_power = pinP_Power.i;
i_output = pinP_Output.i;
p_energy = v_energy * i_energy;
p_power = v_power * i_power;
p_output = v_output * i_output;
p_output = efficiency*(p_energy + p_power);
i_output = i_energy + i_power;
v_output = demandedVoltage;
annotation (
Diagram(coordinateSystem(preserveAspectRatio=false, extent={{-100,- 100},{100,
100}}), graphics), Icon(coordinateSystem(preserveAspectRatio=false,
extent={{-100,-100},{100,100}}), graphics={
Rectangle(
extent={{-100,100},{100,-100}},
lineColor={0,0,127},
lineThickness=0.5,
fillPattern=FillPattern.Solid,
fillColor={215,215,215}),
Line(
points={{-100,100}},
color={0,0,255},
smooth=Smooth.None),
Line(
points={{-100,100},{-100,-100},{100,-100},{100,100},{-100,100}},
color={0,0,127},
thickness=0.5,
smooth=Smooth.None),
Text(
extent={{-68,60},{70,-66}},
lineColor={0,0,0},
textString="Hybrid
DC
Converter")}));
end DCDC2;
If I test the converter using two simple constant current sources and one constant current load, I get again a singularity error. Dymola 2015 tells me, that there might be a not determinable ground, which shouldn't be the case.
model test2
Modelica_EnergyStorages.Sources.Loads.BooleanConstantCurrent
booleanConstantCurrent(I=40)
annotation (Placement(transformation(extent={{46,0},{26,20}})));
Modelica.Electrical.Analog.Basic.Ground ground
annotation (Placement(transformation(extent={{-84,-40},{-64,-20}})));
Modelica.Blocks.Sources.BooleanConstant booleanConstant
annotation (Placement(transformation(extent={{66,0},{46,20}})));
Modelica.Electrical.Analog.Basic.Ground ground1
annotation (Placement(transformation(extent={{26,-86},{46,-66}})));
ElectricalEnergyStorageSystem.Components.DCDC2 dCDC2_1(efficiency=1,
demandedVoltage=15)
annotation (Placement(transformation(extent={{-44,0},{-24,20}})));
Modelica.Electrical.Analog.Sources.ConstantCurrent constantCurrent(I=5)
annotation (Placement(transformation(
extent={{-10,-10},{10,10}},
rotation=270,
origin={-74,10})));
Modelica.Electrical.Analog.Sources.ConstantCurrent constantCurrent1(I=15)
annotation (Placement(transformation(
extent={{-10,-10},{10,10}},
rotation=270,
origin={6,10})));
Modelica.Electrical.Analog.Basic.Ground ground2
annotation (Placement(transformation(extent={{-4,-40},{16,-20}})));
equation
connect(booleanConstantCurrent.on, booleanConstant.y) annotation (Line(
points={{45,10},{45,10}},
color={255,0,255},
smooth=Smooth.None));
connect(booleanConstantCurrent.pin_n, ground1.p) annotation (Line(
points={{36,0},{36,-66}},
color={0,0,255},
smooth=Smooth.None));
connect(dCDC2_1.pinP_Output, booleanConstantCurrent.pin_p) annotation (Line(
points={{-34,20},{-34,76},{36,76},{36,20}},
color={0,0,255},
smooth=Smooth.None));
connect(booleanConstantCurrent.pin_n, dCDC2_1.pinN_Output) annotation (Line(
points={{36,0},{36,-54},{-34,-54},{-34,0}},
color={0,0,255},
smooth=Smooth.None));
connect(constantCurrent1.p, dCDC2_1.pinP_Power) annotation (Line(
points={{6,20},{-24,20},{-24,16}},
color={0,0,255},
smooth=Smooth.None));
connect(constantCurrent1.n, dCDC2_1.pinN_Power) annotation (Line(
points={{6,0},{-24,0},{-24,4}},
color={0,0,255},
smooth=Smooth.None));
connect(constantCurrent.p, dCDC2_1.pinP_Energy) annotation (Line(
points={{-74,20},{-44,20},{-44,16}},
color={0,0,255},
smooth=Smooth.None));
connect(constantCurrent.n, dCDC2_1.pinN_Energy) annotation (Line(
points={{-74,0},{-44,0},{-44,4}},
color={0,0,255},
smooth=Smooth.None));
connect(constantCurrent1.n, ground2.p) annotation (Line(
points={{6,0},{6,-20}},
color={0,0,255},
smooth=Smooth.None));
connect(ground.p, constantCurrent.n) annotation (Line(
points={{-74,-20},{-74,0}},
color={0,0,255},
smooth=Smooth.None));
annotation (uses(
Modelica_EnergyStorages(version="3.2.1"),
Modelica(version="3.2.1"),
Buildings(version="2.0.0")), Diagram(coordinateSystem(preserveAspectRatio
=false, extent={{-100,-100},{100,100}}), graphics));
end test2;
And the code results in the following model. (Constant current load is from the Modelica_EnergyStorages library)
Hope you can somehow help me with that issue! Thanks in advance!

Answer 1

The only small problem is that you have declared demandedVoltage but you use vehicleVoltage. Nothing else is wrong with your model.
Note: It would be better to include a minimal top-model for testing in the question.
I tested your model in a top-model TestDCDC together with a capacitor as power supply and a resistor as load in SimulationX 3.6.5.
The following picture shows the schematic of the test model.
The results obtained with SimulationX are depicted in the following figure.
I also checked the equation system generated by SimulationX. It looks fine.
Dymola 2015 generates a wrong error message saying that there are two more variables than equations. You should issue a bug-report for this model to the producer of Dymola. Note, that the symbolic analysis of Modelica models is quite complicated and problems like that may happen. Usually the maintainer of the tool is grateful for a bug-report in this case.
Discussion of the solution:
The DCDC converter demands a constant power of P=100W from the capacitor and the initial voltage of the capacitor is capacitor1.v.start=10 V.
This gives an energy-time signal of
W = C/2*(v.start)^2-P*time = 50Ws - 100W*time
and the capacitor voltage signal results to
capacitor1.v = 2*sqrt(W)/C = 2V/As * sqrt(50Ws-100Ws*time)
At time = 0.5s the capacitor is empty and the current diverges.
SimulationX stops correctly with an error message at time=0.5.
Complete model for reproducing the results:
model TestDCDC
model DCDC
extends Modelica.Electrical.Analog.Interfaces.TwoPort;
parameter Real demandedVoltage;
Modelica.Electrical.Analog.Sensors.VoltageSensor sekVolt annotation(Placement(transformation(
origin={80,0},
extent={{-10,-10},{10,10}},
rotation=270)));
Modelica.Electrical.Analog.Sensors.CurrentSensor currentSensor annotation(Placement(transformation(
origin={-50,-30},
extent={{-10,10},{10,-10}},
rotation=270)));
Modelica.Electrical.Analog.Sources.SignalCurrent signalCurrent annotation(Placement(transformation(
origin={-50,30},
extent={{-10,-10},{10,10}},
rotation=270)));
Modelica.Electrical.Analog.Sources.ConstantVoltage constantVoltage(V=demandedVoltage) annotation(Placement(transformation(
origin={50,30},
extent={{-10,10},{10,-10}},
rotation=270)));
Modelica.Electrical.Analog.Sensors.CurrentSensor currentSensor1 annotation(Placement(transformation(
origin={50,-30},
extent={{-10,-10},{10,10}},
rotation=270)));
Modelica.Blocks.Math.Division division annotation(Placement(transformation(extent={{6,22},{-10,38}})));
Modelica.Blocks.Math.Product product annotation(Placement(transformation(
origin={30,8},
extent={{8,-8},{-8,8}},
rotation=270)));
Modelica.Blocks.Math.Gain gain(k=-1) annotation(Placement(transformation(extent={{-20,22},{-36,38}})));
Modelica.Electrical.Analog.Sensors.VoltageSensor primVolt annotation(Placement(transformation(
origin={-80,0},
extent={{-10,10},{10,-10}},
rotation=270)));
equation
connect(currentSensor.p,signalCurrent.n) annotation(Line(points={{-50,-20},{-50,-15},{-50,15},{-50,20}}));
connect(constantVoltage.n,currentSensor1.p) annotation(Line(points={{50,20},{50,15},{50,-15},{50,-20}}));
connect(signalCurrent.p,p1) annotation(Line(points={{-50,40},{-50,45},{-50,50},{-95,50},{-100,50}}));
connect(currentSensor.n,n1) annotation(Line(points={{-50,-40},{-50,-45},{-50,-50},{-95,-50},{-100,-50}}));
connect(constantVoltage.p,p2) annotation(Line(points={{50,40},{50,45},{50,50},{95,50},{100,50}}));
connect(currentSensor1.n,n2) annotation(Line(points={{50,-40},{50,-45},{50,-50},{95,-50},{100,-50}}));
connect(primVolt.n,n1) annotation(Line(points={{-80,-10},{-80,-15},{-80,-50},{-95,-50},{-100,-50}}));
connect(primVolt.p,p1) annotation(Line(points={{-80,10},{-80,15},{-80,50},{-95,50},{-100,50}}));
connect(sekVolt.p,p2) annotation(Line(points={{80,10},{80,15},{80,50},{95,50},{100,50}}));
connect(sekVolt.n,n2) annotation(Line(points={{80,-10},{80,-15},{80,-50},{95,-50},{100,-50}}));
connect(gain.y,signalCurrent.i) annotation(Line(
points={{-36.7,30},{-41.7,30},{-38,30},{-43,30}},
color={0,0,127}));
connect(division.y,gain.u) annotation(Line(
points={{-10.7,30},{-15.7,30},{-13.3,30},{-18.3,30}},
color={0,0,127}));
connect(currentSensor1.i,product.u2) annotation(Line(
points={{40,-30},{35,-30},{25.3,-30},{25.3,-6.7},{25.3,-1.7}},
color={0,0,127}));
connect(sekVolt.v,product.u1) annotation(Line(
points={{70,0},{65,0},{65,-6.7},{34.7,-6.7},{34.7,-1.7}},
color={0,0,127}));
connect(product.y,division.u1) annotation(Line(
points={{30,16.7},{30,21.7},{30,34.7},{12.7,34.7},{7.7,34.7}},
color={0,0,127}));
connect(primVolt.v,division.u2) annotation(Line(
points={{-70,0},{-65,0},{12.7,0},{12.7,25.3},{7.7,25.3}},
color={0,0,127}));
annotation(
Icon(
coordinateSystem(preserveAspectRatio=false),
graphics={
Rectangle(
lineColor={0,0,127},
fillColor={215,215,215},
fillPattern=FillPattern.Solid,
lineThickness=0.5,
extent={{-100,100},{100,-100}}),
Line(
points={{-100,100}}),
Line(
points={{-100,100},{-100,-100},{100,-100},{100,100},{-100,100}},
color={0,0,127},
thickness=0.5),
Line(
points={{-100,-100},{100,100}},
color={0,0,127},
thickness=0.5),
Text(
textString="DC",
lineThickness=0.5,
extent={{-60,80},{0,20}}),
Text(
textString="DC",
lineThickness=0.5,
extent={{0,-20},{60,-80}})}),
Diagram(coordinateSystem(preserveAspectRatio=false)));
end DCDC;
DCDC dcdc(demandedVoltage=10) annotation(Placement(transformation(extent={{-30,30},{-10,50}})));
Modelica.Electrical.Analog.Basic.Ground ground1 annotation(Placement(transformation(extent={{-85,-5},{-65,15}})));
Modelica.Electrical.Analog.Basic.Resistor resistor1(R=2) annotation(Placement(transformation(
origin={35,40},
extent={{-10,-10},{10,10}},
rotation=-90)));
Modelica.Electrical.Analog.Basic.Ground ground2 annotation(Placement(transformation(extent={{0,-5},{20,15}})));
Modelica.Electrical.Analog.Basic.Capacitor capacitor1(
v(
start=10,
fixed=true),
C=1) annotation(Placement(transformation(
origin={-75,40},
extent={{-10,-10},{10,10}},
rotation=-90)));
equation
connect(resistor1.p,dcdc.p2) annotation(Line(
points={{35,50},{35,55},{15,55},{15,45},{-5,45},{-10,
45}},
thickness=0.0625));
connect(resistor1.n,dcdc.n2) annotation(Line(
points={{35,30},{35,25},{15,25},{15,35},{-5,35},{-10,
35}},
thickness=0.0625));
connect(ground2.p,dcdc.n2) annotation(Line(
points={{10,15},{10,20},{10,35},{-5,35},{-10,35}},
thickness=0.0625));
connect(dcdc.p1,capacitor1.p) annotation(Line(
points={{-30,45},{-35,45},{-35,55},{-75,55},{-75,50}},
thickness=0.0625));
connect(dcdc.n1,capacitor1.n) annotation(Line(
points={{-30,35},{-35,35},{-35,25},{-75,25},{-75,30}},
thickness=0.0625));
connect(ground1.p,capacitor1.n) annotation(Line(
points={{-75,15},{-75,20},{-75,25},{-75,30}},
thickness=0.0625));
end TestDCDC;