Problem Occurred While Using MATLAB System Identification Toolbox

Hello, I am currently performing system identification using the System Identification Toolbox after extracting the response data of an aircraft by applying control inputs in the trim state of a FlightGear aircraft to estimate a linear model.

However, I have encountered a problem. I set the InitialCondition = 'zero' option in the n4sid estimation, but as shown in the figure below, many outputs are not starting at zero.(you can see that all initial conditions of outputs are 0.) If anyone knows how to resolve this issue, I would appreciate your help.

<options>

Options = n4sidOptions;

Options.Display = 'on';

Options.InitialState = 'zero';

Options.N4Horizon = [20 0 10];

ss2 = n4sid(mydata, 13, 'Form', 'canonical', 'DisturbanceModel', 'none', Options); nx = 13 (output vectors = states vectors)

(y1 : v(lateral velocity), y2 : p, y3 : r, y4: phi, y5: psi, y6 ~ y13 : F1(first engine's thrust) ~ F8(eighth-engine's thrust)

[Aquatris]

The identified model might have a feedthrough term? What is the resulting D matrix?

[준호]

Hi Aquatris,

D matrix is 0

Answer 1

[M.]

What type of data is 'mydata' ?

You may have a look at this discussion.

[준호]

Hi,

mydata is iddata type and it was used for system identification with ssest function.