Emerson Powerdrive F300 User Manual page 158

Safety Product Mechanical
information information installation
Speed Loop Gains (Pr 00.007 {03.010}, Pr 00.008 {03.011}, Pr 00.009 {03.012})
The speed loop gains control the response of the speed controller to a change in speed demand. The speed controller includes proportional (Kp)
and integral (Ki) feed forward terms, and a differential (Kd) feedback term. The drive holds two sets of these gains and either set may be selected for
use by the speed controller with Pr 03.016. If Pr 03.016 = 0, gains Kp1, Ki1 and Kd1 (Pr 00.007 to Pr 00.009) are used, and if Pr 03.016 = 1, gains
Kp2, Ki2 and Kd2 (Pr 03.013 to Pr 03.015) are used. Pr 03.016 may be changed when the drive is enabled or disabled. If the load is predominantly
a constant inertia and constant torque, the drive can calculate the required Kp and Ki gains to give a required compliance angle or bandwidth
dependant on the setting of Pr 03.017.
NOTE: In sensorless mode, the speed controller bandwidth may need to be limited to 10 Hz or less for stable operation.
Speed Controller Proportional Gain (Kp), Pr 00.007 {03.010} and Pr 03.013
If the proportional gain has a value and the integral gain is set to zero the controller will only have a proportional term, and there must be a speed
error to produce a torque reference. Therefore as the motor load increases there will be a difference between the reference and actual speeds. This
effect, called regulation, depends on the level of the proportional gain, the higher the gain the smaller the speed error for a given load. If the
proportional gain is too high either the acoustic noise produced by speed feedback quantization becomes unacceptable, or the stability limit is
reached.
Speed Controller Integral Gain (Ki), Pr 00.008 {03.011} and Pr 03.014
The integral gain is provided to prevent speed regulation. The error is accumulated over a period of time and used to produce the necessary torque
demand without any speed error. Increasing the integral gain reduces the time taken for the speed to reach the correct level and increases the
stiffness of the system, i.e. it reduces the positional displacement produced by applying a load torque to the motor. Unfortunately increasing the
integral gain also reduces the system damping giving overshoot after a transient. For a given integral gain the damping can be improved by
increasing the proportional gain. A compromise must be reached where the system response, stiffness and damping are all adequate for the
application. For RFC-A Sensorless mode, it is unlikely that the integral gain can be increased much above 0.50.
Differential Gain (Kd), Pr 00.009 {0 3.012} and Pr 03.015
The differential gain is provided in the feedback of the speed controller to give additional damping. The differential term is implemented in a way that
does not introduce excessive noise normally associated with this type of function. Increasing the differential term reduces the overshoot produced
by under-damping, however, for most applications the proportional and integral gains alone are sufficient.
There are six methods of tuning the speed loop gains dependant on the
setting of Pr 03.017:
1. Pr 03.017 = 0, User set-up.
This involves the connecting of an oscilloscope to analog output 1 to
monitor the speed feedback.
Give the drive a step change in speed reference and monitor the
response of the drive on the oscilloscope.
The proportional gain (Kp) should be set up initially. The value should
be increased up to the point where the speed overshoots and
then reduced slightly. The integral gain (Ki) should then be increased
up to the point where the speed becomes unstable and then reduced
slightly.
It may now be possible to increase the proportional gain to a higher
value and the process should be repeated until the system response
matches the ideal response as shown.
The diagram shows the effect of incorrect P and I gain settings as
well as the ideal response.
2. Pr 03.017 = 1, Bandwidth set-up
If bandwidth based set-up is required, the drive can calculate Kp and
Ki if the following parameters are set up correctly:
Pr 03.020 - Required bandwidth,
Pr 03.021 - Required damping factor,
Pr 03.018 - Motor and load inertia.
The drive can be made to measure the motor and load inertia by
performing an inertia measurement autotune (see Autotune
Pr 00.040, earlier in this table).
3. Pr 03.017 = 2, Compliance angle set-up
If compliance angle based set-up is required, the drive can calculate
Kp and Ki if the following parameters are set up correctly:
Pr 03.019 - Required compliance angle,
Pr 03.021 - Required damping factor,
Pr 03.018 - Motor and load inertia The drive can be made to
measure the motor and load inertia by performing an inertia
measurement autotune (see Autotune Pr 00.040, earlier in this
table).
4. Pr 03.017 = 3, Kp gains times 16
If Speed Controller Set-up Method (03.017) = 3 the selected proportional
gain used by the drive is multiplied by 16.
158
Electrical Getting Basic
installation started parameters the motor
Running NV Media Card
Optimization
Operation
Speed demand
Insufficient proportional
gain [
Excessive proportional
gain [00.007]
Excessive integral gain
[00.008]
Ideal response
5. Pr 03.017 = 4 - 6
If Speed Controller Set-up Method (03.017) is set to a value from 4 to 6
the Speed Controller Proportional Gain Kp1 (03.010) and Speed
Controller Integral Gain Ki1 (03.011) are automatically set up to give the
bandwidths given in the table below and a damping factor of unity. These
settings give low, standard or high performance.
Pr 03.017
4
5
6
6. Pr 03.017 = 7
If Speed Controller Set-up Method (03.017) = 7 then Speed Controller
Proportional Gain Kp1 (03.010), Speed Controller Integral Gain Ki1
(03.011) and Speed Controller Differential Feedback Gain Kd1 (03.012)
are set up to give a closed-loop speed controller response that
approximates to a first order system with a transfer function of 1 / (s
τ
1), where = 1/
damping factor is meaningless, and Damping Factor (03.021) and
Compliance Angle (03.019) have no effect.
Onboard Advanced Technical
PLC parameters data
00.007 ]
Performance
Low
Standard
High
ω ω
bw and bw = Bandwidth (03.020). In this case the
Powerdrive F300 User Guide
UL listing
Diagnostics
information
Bandwidth
5 Hz
25 Hz
100 Hz
τ
+
Issue Number: 2