Problem using "pidtool" and "pidtune"

I tried using "pidtool" for tuning the controller. But the tuned values showed negative values of Kd and Ki. Kd and Ki values should always be positive as Kd = Td and Ki = 1/Ti

why does Kd and Ki show negative values?

Same problem occured while using "pidtune"

pA =

                   -3.802 s^2 - 0.175 s - 0.08049
  ----------------------------------------------------------------
  s^5 + 4.307 s^4 + 1.257 s^3 + 0.1188 s^2 + 0.04301 s + 0.0007226

[C_pid,info] = pidtune(pA,'pid')

C_pid =

             1          
  Kp + Ki * --- + Kd * s
             s          

with Kp = -0.869, Ki = -0.0225, Kd = -1.71

Answer 1

[Arkadiy Turevskiy]

Kd=Kp*Td and Ki=Kp/Ti.

As Kp, Ki, and Kd are all negative, Td and Ti are positive.

Take a look at pidstd reference page. If you want to get PID in standard from, in PID Tool select "Standard" in the "Form" drop down menu.

If you you are using pidtune, the do

C_pidstd=pidstd(C_pid);