I have a state space model and am getting different responses between using compare and sim command. I want to be able to model correctly with just input data, but I cannot get an accurate response.

Below is my state space model. When I use the compare command with input/output data I get a response very close to the actual output. However when I use the sim command with only input data, my response is does not match the measured output. I tried setting initial conditions with the sim command but still fail to get an accurate response. Why does the sim command not give the same answer? I need to be able to accurately model using only input and cannot at this point.

ys3_L1 = Discrete-time identified state-space model: x(t+Ts) = A x(t) + B u(t) + K e(t) y(t) = C x(t) + D u(t) + e(t)

A = 
            x1         x2         x3         x4         x5
 x1      1.022   -0.00318   0.005019   -0.01857   -0.01896
 x2    0.01044     0.9989    0.01821   -0.04077   -0.03857
 x3  -0.003853    -0.0198     0.9973  -0.007014   -0.05084
 x4    0.01359     0.0237     0.0235     0.9923   -0.05736
 x5     0.0325    0.02983    0.04684    0.06782      1.002
 x6  -0.008547   -0.04397    0.05131    0.03622   -0.03691
 x7   0.003606    0.04205   -0.03639    0.02476    -0.0576

              x6         x7
   x1   0.009543   -0.02097
   x2    0.06469   -0.06807
   x3    -0.0612    0.02442
   x4   -0.03271   -0.02684
   x5    0.02944    0.04288
   x6     0.9943  -0.009728
   x7   0.006838     0.9974

B = 
            u1
 x1  -0.001269
 x2  -0.005218
 x3  0.0009404
 x4  -0.001774
 x5  -0.007058
 x6  -0.007754
 x7  0.0001633

C = 
          x1       x2       x3       x4       x5       x6       x7
 y1   -46.98    14.22    7.889   -2.671  -0.9139    0.484   -3.026

D = 
     u1
 y1   0

K = 
         y1
 x1  -27.77
 x2     531
 x3   -1145
 x4    1419
 x5    1208
 x6   986.2
 x7   -1520

Sample time: 1e-06 seconds

Parameterization: FREE form (all coefficients in A, B, C free). Feedthrough: none Disturbance component: estimate Number of free coefficients: 70

[M]

How do you use the sim command ?

[Andrew Felber]

I am using the compare command as

[L1,~,~] = compare(data_L1,sys3_L1);

which matches my output well. For the sim command I am using sim

(sys3_L1,data_L1.u);

Attached is my input/output data. With the sim command I also tried executing it with the initial states estimated using

% Estimate the initial states

X0est = findstates(sys3_L1,data_L1);

% Simulate the response using estimated initial states

opt = simOptions('InitialCondition',X0est); sim(sys3_L1,data_L1.u,opt)

Using the initial states changed my response but it is still inaccurate.

[WenYong Zhang]

hello, have you figure out this problem yet?

[alok dhaundiyal]

Try to incorporate the initial states.

It will work.