Speed Trim - Danfoss VLT AutomationDrive FC 302 Programming Manual

Parameter Descriptions
Use speed trim if the application requires the following
features:
•
Accurate speed (the actual shaft speed matches
the reference speed).
•
Precise speed adjustment down to 0 RPM.
Enabling PID droop
To enable speed PID droop:
•
Run the frequency converter in 1 of the following
modes:
•
Flux closed loop (parameter 1-01 Motor
Control Principle, [3] Flux w/ motor feedb).
•
Flux sensorless (parameter 1-01 Motor
Control Principle, [2] Flux sensorless).
•
Run the frequency converter in speed mode
(parameter 1-00 Configuration Mode, option [0]
Speed open loop or [1] Speed closed loop).
•
Ensure that parameter 1-62 Slip Compensation
contains the default value (0%).
•
Ensure that all frequency converters in the torque
sharing system use the same speed reference and
start and stop signal.
•
Ensure that all frequency converters in the torque
sharing system use the same parameter settings.
•
Adjust the value in parameter 7-01 Speed PID
Droop.
NOTICE
Do not use overvoltage control when using the PID
droop function (select [0] Disabled in
parameter 2-17 Over-voltage Control).
NOTICE
If the speed reference is lower than the value in
parameter 7-01 Speed PID Droop, the frequency converter
makes the PID droop factor equal to the speed reference.
Example for a PM motor
In a set-up with the following configuration:
MG33MP02
Programming Guide
•
•
The frequency converter provides the following output:
Load on the motor
0%
100%
100% regenerative load
Table 3.24 Output with Speed PID Droop
This is why droop is sometimes referred to as negative slip
compensation (the frequency converter reduces the output
instead of increasing it).

3.8.3 Speed Trim

The speed trim function is an add-on to the speed PID
droop. The speed trim provides torque sharing with precise
speed down to 0 RPM. The function requires wiring of
analog signals.
In speed trim, the master frequency converter runs normal
speed PID without droop. The follower frequency
converters use the speed PID droop, but instead of
reacting on their own load they compare their own load to
the load of other frequency converters in the system and
then use that data as input for the speed PID droop.
A set-up with a single source, where the master frequency
converter sends information about torque to all followers,
is limited by the number of available analog outputs on
the master frequency converter. It is possible to use a
cascade principle, which overcomes this limitation but
makes the control less fast and less accurate.
The master frequency converter operates in speed mode.
The follower frequency converters operate in speed mode
with the speed trim. The trim function uses torque data
from all frequency converters in the system.
Danfoss A/S © 10/2018 All rights reserved.
Reference speed = 1500 RPM.
Parameter 7-01 Speed PID Droop = 50 RPM.
Output
3
1500 RPM
1450 RPM
1550 RPM
145
3