![background image](http://html.mh-extra.com/html/danfoss/fc-300/fc-300_design-manual_507599038.webp)
NOTE!
If necessary, start/stop can be activated a number of times in order to provoke a variation of the feedback signal.
3.4.5 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.
NOTE!
The method described must not be used on applications that could be damaged by the oscillations created by marginally stable control
settings.
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 observe continuous oscillations (as
measured on the feedback), that is, until the system becomes marginally
stable. The corresponding gain
(K
u
)
is called the ultimate gain. The period
of the oscillation
(P
u
)
(called the ultimate period) is determined as shown
in Figure 1.
Figure 3.4: Figure 1: Marginally stable system
P
u
should be measured when the amplitude of oscillation is quite small. Then we “back off” from this gain again, as shown in Table 1.
K
u
is the gain at which the oscillation is obtained.
Type of Control
Proportional Gain
Integral Time
Differentiation Time
PI-control
0.45 *
K
u
0.833 *
P
u
-
PID tight control
0.6 *
K
u
0.5 *
P
u
0.125 *
P
u
PID some overshoot
0.33 *
K
u
0.5 *
P
u
0.33 *
P
u
Table 1: Ziegler Nichols tuning for regulator, based on a stability boundary.
Experience has shown that the control setting according to the Ziegler Nichols rule provides a good closed-loop response for many systems. The process
operator can perform final tuning of the control iteratively to yield satisfactory control.
Step-by-step Description:
Step 1:
Select only Proportional Control, meaning that the Integral time is selected to the maximum value, while the differentiation time is selected to
zero.
3 Introduction to AutomationDrive FC 300
FC 300 Design Guide
3-22
MG.33.BC.22 - VLT
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