Operating instructions

Setpoint channel and closed-loop control
7.4 Vector speed/torque control with/without encoder
Drive converter cabinet units
Operating Instructions, 10/2008, A5E00288214A
271
7.4 Vector speed/torque control with/without 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
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:
● Maximum speed accuracy requirements
● Maximum dynamic response requirements
– Better command behavior
– Shortest settling times when disturbances occur
● Torque control is required in a control range greater than 1:10
● Allows a defined and/or variable torque for speeds below approx. 10% of the rated motor
frequency (p0310) to be maintained.
● A speed controller is normally always required for applications in which an unknown
speed can represent a safety risk (where a load can be dropped, e.g. lifting gear,
elevators, etc).
With regard to setpoint input, vector control is divided into:
● Speed control
● Torque/current control (in short: torque control)