Simulink Control Design 3.0

Linearization of an Engine Speed Model

Contents

This demonstration introduces the linearization of an engine speed model.

The model can be opened using the command:

scdspeed

Generation of Operating Points

This example generates linear models of the output engine speed and between the inputs the Spark Advance and the Throttle Angle. The FINDOP command computes the operating points at steady state conditions at 2000, 3000, and 4000 RPM.

Create an operating point specification object using the command

opspec = operspec('scdspeed')

 Operating Specification for the Model scdspeed.
 (Time-Varying Components Evaluated at time t=0)

States:
----------
(1.) scdspeed/Throttle & Manifold/Intake Manifold/p0 = 0.543 bar
      spec:  dx = 0,  initial guess:         0.543
(2.) scdspeed/Vehicle Dynamics/w = T//J w0 = 209 rad//s
      spec:  dx = 0,  initial guess:           209

Inputs:
----------
(1.) scdspeed/Throttle  perturbation
      initial guess: 0

Outputs: None
----------

Next, specify the desired operating conditions. Fix the first output port of the Vehicle Dynamics to be 2000, 3000, and 4000 RPM. Use the command ADDOUTPUTSPEC to do this.

opspec = addoutputspec(opspec,'scdspeed/rad//s to rpm',1);

Set the first operating specification

opspec.Output.Known = 1;
opspec.Outputs.y = 2000;

Search for the operating point that meets this specification

op(1) = findop('scdspeed',opspec);

 Operating Point Search Report:
---------------------------------

 Operating Report for the Model scdspeed.
 (Time-Varying Components Evaluated at time t=0)

Operating point specifications were successfully met.

States:
----------
(1.) scdspeed/Throttle & Manifold/Intake Manifold/p0 = 0.543 bar
      x:         0.544      dx:     2.66e-013 (0)
(2.) scdspeed/Vehicle Dynamics/w = T//J w0 = 209 rad//s
      x:           209      dx:    -8.48e-012 (0)

Inputs:
----------
(1.) scdspeed/Throttle  perturbation
      u:       0.00382    [-Inf Inf]

Outputs:
----------
(1.) scdspeed/rad//s to rpm
      y:        2e+003    (2e+003)

Now, search for the remaining operating points at 3000 and 4000 RPM

opspec.Outputs.y = 3000;
op(2) = findop('scdspeed',opspec);
opspec.Outputs.y = 4000;
op(3) = findop('scdspeed',opspec);

 Operating Point Search Report:
---------------------------------

 Operating Report for the Model scdspeed.
 (Time-Varying Components Evaluated at time t=0)

Operating point specifications were successfully met.

States:
----------
(1.) scdspeed/Throttle & Manifold/Intake Manifold/p0 = 0.543 bar
      x:          0.49      dx:    -5.14e-015 (0)
(2.) scdspeed/Vehicle Dynamics/w = T//J w0 = 209 rad//s
      x:           314      dx:     4.57e-013 (0)

Inputs:
----------
(1.) scdspeed/Throttle  perturbation
      u:          2.94    [-Inf Inf]

Outputs:
----------
(1.) scdspeed/rad//s to rpm
      y:        3e+003    (3e+003)


 Operating Point Search Report:
---------------------------------

 Operating Report for the Model scdspeed.
 (Time-Varying Components Evaluated at time t=0)

Operating point specifications were successfully met.

States:
----------
(1.) scdspeed/Throttle & Manifold/Intake Manifold/p0 = 0.543 bar
      x:         0.473      dx:     1.13e-011 (0)
(2.) scdspeed/Vehicle Dynamics/w = T//J w0 = 209 rad//s
      x:           419      dx:    -1.49e-010 (0)

Inputs:
----------
(1.) scdspeed/Throttle  perturbation
      u:          5.83    [-Inf Inf]

Outputs:
----------
(1.) scdspeed/rad//s to rpm
      y:        4e+003    (4e+003)

Model Linearization

The operating points are now ready for linearization. First specify the input and output points using the commands:

io(1) = linio('scdspeed/throttle (degrees)',1,'in');
io(2) = linio('scdspeed/Spark Advance',1,'in');
io(3) = linio('scdspeed/rad//s to rpm',1,'out');

Linearize the model and plot the Bode magnitude response for each condition.

sys = linearize('scdspeed',op,io);
bodemag(sys)

Close the model.

bdclose('scdspeed')