Modelica Example - Discrete Events

//50% duty cycle pulse generation

within ModelicaByExample.DiscreteBehavior.PulseGenerator;

model PulseGenerator "A model that produces pulses at a fixed interval"

  type Time=Real(unit="s");

  parameter Time width=100e-3;

  Boolean pulse;

initialequation 

  pulse = false;

equation

  when sample (width,width) then//form a pulse with 50% duty cycle 

    press = not pre (press); 

  endwhen; 

end PulseGenerator;

//counter

within ModelicaByExample.DiscreteBehavior.Counter;

model Counter "Counting samples"

  type Time = Real(unit="s");

  parameter Time interval=100e-3;

  Integer count;

initialequation 

  count = 0;

equation

  whensample(interval, interval) then 

    count = pre(count)+1;

  endwhen; 

end Counter;

// sample and hold

within ModelicaByExample.DiscreteBehavior.SpeedMeasurement;

model SampleAndHold "Measure speed and hold"

  extends BasicEquations.RotationalSMD.SecondOrderSystem;

  parameterRealsample_time(unit="s")=0.125;  

  discreteReal omega1_measured; 

equation

  whensample(0,sample_time) then 

    omega1_measured = omega1;

  endwhen; 

end SampleAndHold;

//Bang-Bang control

within ModelicaByExample.DiscreteBehavior.Hysteresis;

model HysteresisControl "A control strategy that doesn't chatter"

  type HeatCapacitance=Real(unit="J/K");

  type Temperature=Real(unit="K");

  type Heat=Real(unit="W");

  type Mass=Real(unit="kg");

  type HeatTransferCoefficient=Real(unit="W/K");

  Boolean heat(start=false) "Indicates whether heater is on";

  parameter HeatCapacitance C=1.0;

  parameter HeatTransferCoefficient h=2.0;

  parameter Heat Qcapacity=25.0;

  parameter Temperature Tamb=285;

  parameter Temperature Tbar=295;

  Temperature T;

  Heat Q;

initial equation

  T = Tbar+5;

  heat = false;

equation

  Q = if heat then Qcapacity else 0;

  C*der(T) = Q-h*(T-Tamb);

  when {T>Tbar+1,T<Tbar-1} then

    heat = T<Tbar;

  end when;

end HysteresisControl;