Drive Configuration
Controller Tuning
5.4.2 Tuning of the Current Controller
This section describes how the proportional gain
Kr
and the integral time constant
Tn
for the
current
controller
can be determined with
Bode
Tuning
. See section 5.2 on how to initially set up the other pa-
rameters in the current controller structure. The following steps are required to start the tuning:
1. Make sure, that the controller gain
Kr
is set to 0 (this step is not required if the current controller
is already configured with a stable setting).
2. Execute a bode measurement and save the measured data. See section 4.3 on how to do the
measurement.
3. Open the measured data with the
Bode Tuning
application. See section 4.4 on how to open the
measurement and how to use the application.
4. To setup the current controller, select the
Current
radio button in the
Select Controller
panel.
5. Initially, set the controller gain
Kr
to 1 (if
Kr
is zero, no transfer functions are plotted).
The controller parameters
Kr
and
Tn
can now be modified. After each change of a parameter the
Bode
or
Nyquist
plots are updated. The
Bode
plot shows the amplitude and the phase of the following com-
plex transfer functions:
H
r
(
f
)=
Kr
(
1
+
1
s Tn
)
;
H
o
(
f
)=
H
r
(
f
)
i
u
(
f
)
;
H
c
(
f
)=
H
o
(
f
)
1
+
H
o
(
f
)
;
s
=
j
2
π
f
with
f
: frequency
H
r
(f)
: current controller transfer function
H
o
(f)
: open loop transfer function
H
c
(f)
: closed loop transfer function
i/u(f)
: measured frequency response function between voltage and current.
The
Nyquist
plot shows the open loop transfer function
H
o
(f)
in the complex area.
The goal for the tuning is to get a stable controller with the following characteristics (see also Figure 46
and 47):
a) wide bandwidth of
H
c
(f)
b) high amplification in the pass-band of
H
o
(f)
c) sufficient attenuation in the stop-band of
H
o
(f)
Therefore,
Kr
should be increased while
Tn
is reduced as close to zero as possible by considering the fol-
lowing criteria. See Figure 57 on how the parameters influence the curve.
Tuning criteria in
Bode
plot view:
d) The phase-margin of
H
o
(f)
should be in range of 50° to 70°.
e) The amplitude of the
H
c
(f)
should not exceed 1dB over the whole frequency range.
9 The phase-margin is the difference between the phase-angle of a transfer function
G
o
(f
gc
)
at the frequency
f
gc
where the amplitude of
H
o
(f
gc
)
crosses 0dB and -180°. See d) in Figure 46.
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