Nidec Unidrive M200 User Manual page 53

Safety Product Mechanical
information information installation
Frequency Loop Gains
(Pr 65 {03.010}, Pr 66 {03.011}
The frequency loop gains control the response of the frequency controller to a change in frequency demand. The frequency 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 frequency controller with Pr 03.016. If Pr 03.016 = 0, gains Kp1, Ki1 and Kd1 (Pr 03.010 to Pr 03.012) 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.
Frequency Controller Proportional Gain (Kp), Pr 65 {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
frequency error to produce a torque reference. Therefore as the motor load increases there will be a difference between the reference and actual
frequencies. This effect, called regulation, depends on the level of the proportional gain, the higher the gain the smaller the frequency error for a
given load. If the proportional gain is too high either the acoustic noise produced by numerical quantization becomes unacceptable, or the stability
limit is reached.
Frequency Controller Integral Gain (Ki), Pr 66 {03.011} and Pr 03.014
The integral gain is provided to prevent frequency regulation. The error is accumulated over a period of time and used to produce the necessary
torque demand without any frequency error. Increasing the integral gain reduces the time taken for the frequency 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 03.012 and Pr 03.015
The differential gain is provided in the feedback of the frequency 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.
Gain Change Threshold, Pr 03.017
If the Frequency Controller Gain Select (03.016) = 2, gains Kp1, Ki1 and Kd1 (Pr 03.010 to Pr 03.012) are used while the modulus of the frequency
demand is less than the value held by Gain Change Threshold (03.017), else gains Kp2, Ki2 and Kd2 (Pr 03.013 to Pr 03.015) will be used.
Tuning the frequency loop gains:
This involves the connecting of an oscilloscope to analog output 1 to
monitor the frequency feedback.
Give the drive a step change in frequency 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 frequency overshoots
and then reduced slightly.
The integral gain (Ki) should then be increased up to the point where
the frequency 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
approaches the ideal response as shown.
The diagram shows the effect of incorrect P and I gain settings as
well as the ideal response.
Unidrive M200 / M201 Control User Guide
Issue Number: 2
Electrical Getting Basic
installation started parameters
Running the NV Media
Optimization
motor Card
Frequency demand
Insufficient proportional
gain [Pr 65 ]
Excessive proportional
gain [Pr 65]
Excessive integral gain
[Pr 66 ]
Ideal response
Onboard Advanced
Diagnostics
PLC parameters
UL Listing
53