SIMULINK dynamic response versus root loci

I am new to the SISO tool, but used it to compare, not design, the response of 2 systems I constructed in SIMULINK. I have included the 2 SIMULINK models. As far as I know the 2 models represent a 3 DOF system constructed by linking 3 spring mass systems in series. One is represented by SIMSCAPE mechanical elements & the other by SIMULINK Continuous System elements. I constructed the 2 models. I made sure gain values in the Continuous model corresponded to the stiffness, damping, and mass values in the SIMSCAPE model.

I generated the step response of the 2 systems with the SISO tool. Note that I changed the low frequency gain by 14% so that the 2 systems can be discerned in the plots. The BODE & the time response plots show the 2 systems appear to behave identically; however, examination of the root loci show the locations of the poles are not the same. The poles of the SIMSCAPE model are in GREEN & the other is BLUE. Assuming my gain values are correct in the Continuous model I speculate that my connections in the Continuous model are not the same as those in the SIMSCAPE model, but I am at a loss as to how or why.

Does anyone out there see why this is the case & what needs correction? If you are missing any vital information in the .mat file let me know & I will try to provide it. Disregard the SISO project2.mat file.

[Jeff]

Additional consideration, the SIMSCAPE poles are mathematically correct. I confirmed this via MAPLE through the equations of motion for the systems linked in series.

[Jeff]

I forgot to include the gain values to use for the blkdiag1.slx.

a=1; b=[2*1/4*1*200 19700/3 17800/3]; c=[200^2 24960000 75040000];

[Sudarshan Kolar]

I would recommend trying with a very simple model first. A simple spring mass damper system and check if you still see the issue.

Answer 1

[Jeff]

I have since resolved this issue. It turned out that my feedback path was not correct. I have included the correct SIMSCAPE & Simulink block diagram models in the .zip file.