Ziegler Nichols Tuning Method - Danfoss FC 300 Design Manual

3. Introduction to FC 300
Optimization of the process regulator
The basic settings have now been made; all that needs to be done is to optimize the proportional
gain, the integration time and the differentiation time (par. 7-33, 7-34, 7-35). In most processes,
this can be done by following the guidelines given below.
1.
3
2.
3.
4.

3.3.5. Ziegler Nichols Tuning Method

In order to tune the PID controls of the adjustable frequency drive, several tuning methods can
be used. One approach is to use a technique which was developed in the 1950s, but which has
stood the test of time and is still used today. This method is known as the Ziegler Nichols tuning
method.
The criteria for adjusting the parameters are
based on evaluating the system at the limit of
stability rather than on taking a step response.
We increase the proportional gain until we ob-
serve continuous oscillations (as measured on
the feedback), that is, until the system be-
comes marginally stable. The corresponding
gain
od of the oscillation
period) is determined as shown in Figure 1.
P should be measured when the amplitude of oscillation is quite small. Then we "back off" from
u
this gain again, as shown in Table 1.
40
Start the motor
Proportional Gain
Set par. 7-33 (
begins to vary continuously. Then, reduce the value until the feedback signal has stabi-
lized. Now lower the proportional gain by 40-60%.
Set par. 7-34 (Integral Time) to 20 sec. and reduce the value until the feedback signal
again begins to vary continuously. Increase the integration time until the feedback signal
stabilizes, followed by an increase of 15-50%.
Only use par. 7-35 for very fast-acting systems (differentiation time). The typical value
is four times the set integral time. The differentiator should only be used when the setting
of the proportional gain and the integral time has been fully optimized. Make sure that
oscillations in the feedback signal are sufficiently damped by the low-pass filter on the
feedback signal.
NOTE
If necessary, start/stop can be activated a number of times in order to provoke a
variation of the feedback signal.
NOTE
The method described must not be used on applications that could be damaged by
the oscillations created by marginally stable control settings.
(K )
is called the ultimate gain. The peri-
u
(P )
(called the ultimate
u
MG.33.B9.22 - VLT
) to 0.3 and increase it until the feedback signal again
3.2: Figure 1: Marginally stable system
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FC 300 Design Guide