Update Rates; Hard Speed Reference Update Rate - Control Techniques unidrive sp Advanced User's Manual

Parameter Keypad and
Parameter x.00
structure display
3. When a destination is changes the old destination is written to zero,
unless the destination change is the result of loading defaults or
transferring parameters from a SMARTCARD. When defaults are
loaded the old destination is set to its default value. When
parameters are loaded from a SMARTCARD the old destination
retains its old value unless a SMARTCARD value is written to it.
4.3

Update rates

Update rates are given for every parameter in the hearder table as
shown below.
3.03 Speed error
Drive modes Closed-loop vector, Servo
Bit SP
Coding
Range Closed-loop vector, Servo
Update rate 4ms write
Some parameters have an increased update in special circumstances.
4.3.1 Speed reference update rate
The normal update rate for the speed references (via menu 1) is 4ms,
however it is possible to reduce the sample time to 250µs by selecting
the reference from particular sources. The fast update rate is only
possible provided the conditions given below are met. (Note: high speed
updating is not provided for frequency references - i.e. Open-loop
mode.)
Analog input references (not including I/O expansion Solutions
Module)
1. The reference must be derived via Pr 1.36 or Pr 1.37
2. The analog inputs must be in voltage mode with zero offset
3. Bipolar mode must be used or unipolar mode with the minimum
speed (Pr 1.07) set to zero
4. No skip bands are enabled, i.e. Pr 1.29, Pr 1.31 and Pr 1.33 must be
zero.
5. The jog and velocity feed-forward references must not be enabled.
Applications and fieldbus Solutions Modules
Pr 91.02 must be used to define the speed reference (this parameter is
only visible from the Solutions Modules). Any value written to Pr 91.02
should be automatically mapped into preset Pr 1.21 by the Solutions
Module.
In fast update mode the references are sampled every 250µs. A sliding
window filter may be applied to analog input 1 (see Pr 7.26) in normal or
high speed updating modes. The default value for this filter is 4ms,
therefore Pr 7.26 must be set to zero to obtain the fastest possible
update rate.
When fast updating is used the scaling is performed by a simple
multiplication. This minimises software execution time, but also ensures
that there is no loss of resolution from the v to f converter used to
implement analog input 1. Therefore the speed of the motor may be
controlled with infinite resolution from analog input 1 except for
deadband effects around zero reference. The scale factor used for the
multiplication cannot exactly duplicate the scaling for the two stage
conversion (i.e. conversion in menu 7 to a percentage of full scale, and
conversion to 0.1rpm units) used when high speed updating is not in
operation. Therefore the absolute scaling of the analog inputs varies
slightly between normal and high speed updating. The amount of
difference depends on the maximum speed, user scaling in menu 7, and
the analog input 1 the filter time. The worst case difference for analog
input 1 is 0.12% of full scale, and for analog inputs 2 and 3 the difference
is less than 0.12% with a maximum speed of 50rpm or more. Typical
differences (1500rpm maximum speed, menu 7 scaling of 1.000, analog
input 1 filter of 4ms) are 0.015% for analog input 1 and 0.004% for
analog inputs 2 and 3.
Unidrive SP Advanced User Guide
Issue Number: 7
Parameter Advanced parameter
description format
FI DE Txt VM DP ND RA NC NV
1 1 1 1
±SPEED_MAX rpm
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http://nicontrols.com
Serial comms
Macros
descriptions
PT US RW BU
1 1
4.3.2

Hard speed reference update rate

The normal update rate for the hard speed reference is 4ms, however it
is possible to reduce the sample time to 250µs by selecting the
reference from particular sources. The fast update rate is only possible
provided the conditions given below are met.
Analog inputs (not including I/O expansion Solutions Module)
The analog inputs must be in voltage mode with zero offset
Limitations are the same as for the references via menu 1 described
above.
Applications and fieldbus Solutions Modules
For faster update rate Pr 91.03 must be used (this parameter is only
visible from the Solutions Modules). Any value written to Pr 91.03 is
automatically mapped into the hard speed reference Pr 3.22.
Encoder reference
It is possible to use the drive encoder as the source for the hard speed
reference. To do this the drive encoder reference destination (Pr 3.46)
should be routed to the hard speed reference parameter. If, and only if,
the maximum drive encoder reference (Pr 3.43) is set to the same value
as the maximum reference value (SPEED_FREQ_MAX), and the
scaling (Pr 3.44) is 1.000, the drive takes the encoder pulses directly.
This gives a form of reference slaving where the integral term in the
speed controller accumulates all pulses from the reference and tries to
match them to the feedback from the motor encoder. Pulses are lost if
the reference reaches a minimum or maximum limit including zero speed
in unipolar mode. The reference is sampled every 250µs. When a
position feedback Solutions Module writes to the hard speed reference,
although the module can write every 250µs, the data is only acted on
every 4ms. When the reference comes from a Solutions Module there is
no guarantee that all pulses are counted. The encoder reference can be
scaled in high speed update mode by modifying the number of encoder
lines per revolution.
4.3.3 Torque reference update rate
The normal update rate for the torque reference (Pr 4.08) is 4ms,
however it is possible to reduce the sample time to 250µs by selecting
the reference from particular sources, but only in closed-loop vector or
servo modes. The fast update rate is only possible provided the
conditions given below are met.
Analog inputs 2 or 3 on the drive
The analog inputs must be in voltage mode with zero offset.
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Feature look-
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21