Current ripple
The velocity feedback signal in standard SC900 Drives operating
with the standard 20 arcmin resolver can have up to 3% p-p
ripple. The resulting motor torque current ripple, with no
ARF0/ARF1
filtering, can be calculated using the following
formula:
Current ripple (amps p-p) =
3
100
2
60
*
*
Speed (RPM)*
π
KVP
» .
*
0 003 Speed (RPM)*
KVP
There can be cause for concern when this p-p number exceeds
40% of the drive’s or motor’s current rating. The motor current
should be monitored using Dac Monitors on J4-3 to insure actual
ripple current, with
ARF0/ARF1
filtering, is not excessive.
Motor current ripple can often be reduced by lowering the
ARF0
,
ARF1
low-pass filter break frequencies. This benefit is limited
by velocity loop bandwidth and stability constraints. Velocity
feedback ripple, and hence motor current ripple, can also be
reduced by specifying a higher accuracy resolver.
KVI
The parameter
KVI
sets the so called “lag-break” frequency of
the velocity loop.
KVI
is equal to the frequency in Hz where the
velocity loop compensation transitions from predominantly
integral characteristics to predominantly proportional
characteristics. Drive rejection of torque disturbances increase as
KVI
increases. Default values for
KVI
are shown below:
Gentle
Medium
Stiff
KVI (Velocity Loop
Lag-Break Freq. (Hz))
1.7
5.0
13.3
MA950
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