Rockwell Automation Allen-Bradley 20-750-TLINK-FOC-10, Руководство пользователя, Страница: 25 / 28

Rockwell Automation Publication 750COM-UM100A-EN-P - June 2021 23
Appendix
C
Load Sharing Applications
Droop
Droop is the simplest form of load sharing to set up and, therefore, the least
precise and less flexible. The precision of this control is dependent on three
factors, the drives control algorithm, the motor characteristics, and the type of
load being controlled.
Flux vector modes must be used to get data when using TLink option modules
in droop applications. The leader drive must provide data on the fiber
connection to use the send speed reference with TLink option module.
When two motors are coupled to the same load each slips according to its
portion of load, forcing the load to be picked up by the other motor. In this
regard, a high slip motor is better for load sharing applications. However in a
general sense, the slip of a motor is representative of its efficiency rating. High
slip motors tend to have high starting torque but have low efficiency. Though
high efficiency motors will slip when loaded, they may not have enough slip at
full load to achieve a reasonable degree of load sharing. For this reason, many
drives offer a feature that is called “Droop”.
The Droop feature enhances the natural slip of the motor by reducing the
output frequency in proportion to load current. Ideally it is only the torque-
producing component of the load current that determines the droop. The
amount of droop can usually be programmed in the drive in hertz or % speed.
Torque Follower
This type of load sharing requires a drive that can operate in “torque mode”,
such as the 1336 IMPACT™ drive. If speed regulation is required, one of the
drives may be in “speed mode” (called the “leader”). The drive in speed mode
still calculates torque reference value to achieve given speed (that is, velocity).
While in speed mode the speed regulator provides a torque command output.
This torque command output can be distributed to the other drives on the
system (called the “followers” or “Torque Followers”). This torque signal may be
scaled at the leader output or the follower input to divide the load sharing in
any ratio desired. As the leader’s torque decreases, the followers torque must
increase to equalize the torque reference.
In this case, it is possible to have drive and motor sets of varying horsepower
sizes each pulling load to the extent of their capability. For example, a 100
horsepower and a 75 horsepower drive and motor set each running at 86% of
its power rating could power a system requiring 150 horsepower. The ratio of
load sharing can be adjusted such that each motor and drive set pulls a
proportional amount of load under all conditions.