Drive Configuration
Controller Tuning
ω
d
=
2
π
fd
=
2
π
EdgeFrequencyDenominator
D
d
=
Dd
=
DampingDenominator
ω
n
=
2
π
fn
=
2
π
EdgeFrequencyNumerator
D
n
=
Dn
=
DampingNumerator
.
The Notch2 filter can be considered as the product of a
Lowpass2
defined by
fd
and
Dd
and a
Highpass2
filter defined by fn and
Dn
(Figure 58). The
Highpass2
parameters
fn
and
Dn
define the location and the
sharpness of the notch. The
Lowpass2
is used to compensate the strong amplification with higher fre-
quencies caused by the
Highpass2
. As a simple approach, set the parameters as follows:
fn
=
Frequency to compensate
Dn
=
0.01..0.05
fd
=
fn
Dd
=
10 Dn
.
When
Advanced
mode is not checked in the
Filter Parameters
panel,
fd
and
Dd
are automatically calcu-
lated according the equations above.
Consider the phase drop in the phase plot of Figure 58 below the notch frequency. This phase drop may
reduce the phase margin and could reduce the stability of the controller. Therefore, the stability of the
controller has to be checked after a filter is added or modified.
Figure 59 shows a resonance which causes an instability at 2000Hz. In the Nyquist plot, resonances ap-
pear as circles. Figure 60 shows the same transfer function now with a Notch2 filter applied at 2000Hz.
The controller loop is now stable.
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Figure 58: The Notch2 filter as product of a Highpass2 with fd=1and Dd= 0.2
and a Lowpass2 with fn=1 and Dd=0.01.
