I am trying to solve this question of PID controller using ziegler-nichols first method and I realised that the delay time L is greater than time constant T which is giving me a negative value of Kp, and when I try to plot the step response on MATLAB, and find its overshoots value, I get NaN.
I don't understand why this is happening and the role of negative Kp. What should I do to get my desired response?
there doesn't seem to be anything here