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7.4
Vector speed/torque control with/without an encoder
Description
Compared with V/f control, vector control offers the following benefits:
● Stability vis-à-vis load and setpoint changes
● Short rise times with setpoint changes (–> better command behavior)
● Short settling times with load changes (–> better disturbance characteristic)
● Acceleration and braking are possible with maximum adjustable torque
● Motor protection due to variable torque limitation in motor and regenerative mode
● Drive and braking torque controlled independently of the speed
● Maximum breakaway torque possible at speed 0
These benefits are available without speed feedback.
Vector control can be used with or without an encoder.
The following criteria indicate when an encoder is required:
● High speed accuracy is required
● High dynamic response requirements
– Better control behavior
– Better response to disturbances
● Torque control is required in a control range greater than 1:10
● A defined and/or variable torque should be maintained for speeds below approx. 10% of
the rated motor frequency (p0310)
● A speed controller is normally always required for applications in which an unknown
speed can represent a safety risk (where a load can drop, e.g. lifting gear, elevators, ...).
With regard to setpoint input, vector control is divided into:
● Speed control
● Torque/current control (in short: torque control)
Enclosed Drives
Operating Instructions, 12/2018, A5E36652151A
Setpoint channel and closed-loop control
7.4 Vector speed/torque control with/without an encoder
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