Danfoss VLT Midi Drive FC 280 Design Guide

2.5.6 Ziegler Nichols Tuning Method
To tune the PID controls of the frequency converter,
Danfoss recommends the Ziegler Nichols tuning method.
NOTICE
Do not use the Ziegler Nichols Tuning method in
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. Increase the proportional gain
until observing 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 and is the gain, at which the oscillation is obtained.
The period of the oscillation (P
u
) (called the ultimate
period) is determined as shown in Illustration 2.25 and
should be measured when the amplitude of oscillation is
small.
1. Select only proportional control, meaning that
the integral time is set to the maximum value,
while the dierentiation time is set to 0.
2. Increase the value of the proportional gain until
the point of instability is reached (sustained
oscillations) and the critical value of gain, K
u
, is
reached.
3. Measure the period of oscillation to obtain the
critical time constant, P
u
.
4. Use Table 2.11 to calculate the necessary PID
control parameters.
The process operator can do the nal tuning of the control
iteratively to yield satisfactory control.
130BA183.10
y(t)
t
P
u
Illustration 2.25 Marginally Stable System
Type of
control
Proportional
gain
Integral time Dierentiation
time
PI-control 0.45 x K
u
0.833 x P
u
–
PID tight
control
0.6 x K
u
0.5 x P
u
0.125 x P
u
PID some
overshoot
0.33 x K
u
0.5 x P
u
0.33 x P
u
Table 2.11 Ziegler Nichols Tuning for Regulator
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Danfoss VLT Midi Drive FC 280 Specifications

General

Brand	Danfoss
Model	VLT Midi Drive FC 280
Category	DC Drives
Language	English