With regard to that zero at +13333.33, I am not familiar with rlocus, but I
have plotted it without finding this zero at +13333 in the plot that would
make the system unstable I guess, if located on the right side of the plane.
Attached I send the plot. Anyway, I also wrote the command [r,k] =
rlocus(sys_1_vd), to see the exact numerical value of the roots, but did not
find any +13333.33 location.
On the other hand, by obtaining the eigenvalues of the system, they all
have negative real part, except for 2 with a very small positive real part,
which it may be due to inaccuracies of the calculation. But I think, this
has no relationship with the zero you have pointed out to be located at
-757.69960 + 0.00000i
-1487.09047 + 0.00000i
-28.89898 + 318.89945i
-28.89898 - 318.89945i
-25.27902 + 323.48505i
-25.27902 - 323.48505i
-0.00207 + 314.16966i
-0.00207 - 314.16966i
0.01004 + 314.15586i
0.01004 - 314.15586i
-0.00797 + 314.15227i
-0.00797 - 314.15227i
How can I see this zero at +13333.33?
This will convert your transfer function to num/den form then looks at the roots of the numerator.