Specifications

6
Current Control Loop Model
The motor amplifier has a current control loop. As configured in the Motorlab apparatus this loop has a
bandwidth of approximately 400 Hz. Using data acquired from step and sinusoidal responses the following two
closed loop transfer functions have been identified as approximate models for the closed-loop current control
dynamics.
)2(
)(
2
2
2
nn
n
i
ssz
zs
T
ωςω
ω
++
+
=
and
st
nn
n
idelay
d
e
ssz
zs
T
−
++
+
=
)2(
)(
2
2
2
ωςω
ω
where
)sec(t
)sec(rad
)sec(radz
d
n
0002.0
8.0
/ 2230
/ 2170
=
=
⋅=
⋅
=
ς
πω
π
One of the models above contains a time delay while the other does not. In the following two figures the responses
of these two models are compared with actual data acquired from one of the Motorlab systems. Both the step
response and the frequency response models are shown.
0 0.001 0.002 0.003 0.004 0.005
0
0.2
0.4
0.6
0.8
1
1.2
Time (sec)
Current (Amp)
Step Response of Current Control Loop
Command
Experimental Data
Model w/o Time Delay
Model with Time Delay
-10
-8
-6
-4
-2
0
2
Magnitude (dB)
10
0
10
1
10
2
10
3
-180
-135
-90
-45
0
Phase (deg)
Experimental Data
Model w/o Time Delay
Model with Time Delay
Frequency Response of Current Control Loop
Frequency (Hz)