Active suspension PID controller

Hello

I need some help to design pid control for active suspension system. The following link has .mdl file for active suspension system. I am trying to send acceleration of x_s to be the error

http://www.sendspace.com/filegroup/ktDFOw7%2B3Wrs5XvJMoZ93g

There is a pdf file that I'm reading right now, and it says that using the same parameters, the system has unstable output when K_d is increased higher than 4.915 using Ziegler-Nichols method. But the system output barely changes when I only increase K_d term(using ZN method) I have a problem tuning this pid controller.

Would you please check if I have right set-up? And why the system does not respond to increasing K_d term(While setting Ki=kd =0) ?

System parameters are: M_s = 300 M_u = 60 K_s = 16850 K_t = 190000 B_s = 1000

[Arkadiy Turevskiy]

can you attach the files here directly?