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5.8 Parameter Group 7-** Controllers
5.8.1 Speed PID Droop
This feature implements precise torque sharing between multiple motors on a common mechanical shaft. Speed PID droop is useful
for marine and mining applications where redundancy and higher dynamics are required. Speed PID droop allows to reduce inertia
by utilizing multiple small motors instead of 1 large motor.
e3
0b
e1
97
.1
1
Set-point
Calculation
External Set-point
Ramp
Droop
Speed
PID
Torque
PID
M2
M3
Drive 2
Drive 3
Set-point
Calculation
Ramp
Droop
Speed
PID
-
Set-point
Calculation
Ramp
Droop
Speed
PID
Torque
PID
M1
Drive 1
-
-
Torque
PID
Illustration 72: Concept of Speed PID Droop
The value in
parameter 7-01 Speed PID Droop
ensures that the load is shared equally between the motors. If the torque on the motor
is 100% of nominal motor torque, the drive reduces its output to this motor by 100% of the value in
parameter 7-01 Speed PID Droop
.
If the torque is 50% of nominal motor torque, the drive reduces its output to this motor by 50% of the value in
parameter 7-01 Speed
PID Droop
. This ensures that the motors share the load evenly. A side effect of using speed PID droop is that the actual shaft speed
does not match the reference exactly. Speed PID droop is not efficient in low-speed applications because the adjustment range may
be insufficient.
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 drive 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 drive 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 drives in the torque sharing system use the same speed reference and start and stop signal.
AU275636650261en-000101 / 130R0334 | 253
Danfoss A/S © 2022.12
Parameter Descriptions
VLT AutomationDrive FC 301/302
Programming Guide