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Setpoint channel and closed-loop control
7.4 Vector speed/torque control with/without an encoder
Closed-loop operation up to approx. 0 Hz (settable via parameter p1755) and the ability to
start or reverse at 0 Hz directly in closed-loop operation (settable via parameter p1750)
result in the following benefits:
● No switchover operation required within closed-loop control (bumpless behavior, no
frequency dips, no discontinuities in the torque).
● Closed-loop speed control without encoder down to and including 0 Hz
● Passive loads down to a frequency of 0 Hz
● Steady-state closed-loop speed control down to approx. 0 Hz possible
● Higher dynamic performance when compared to open-loop controlled operation
Note
Automatic changeover
If, in the closed-loop controlled mode, start from 0 Hz or reversing takes longer than 2 s, or
the time set in p1758 - then the system automatically changes over from closed-loop
controlled into open-loop controlled operation.
Note
Operation in sensorless torque control
Operation in sensor less torque control only makes sense if, in the speed range below the
changeover speed of the motor model (p1755), the setpoint torque is greater than the load
torque. The drive must be able to follow the setpoint and the associated setpoint speed
(p1499).
Closed-loop operation down to standstill for passive loads
By restricting to a passive load at the starting point, it is possible to maintain stationary
closed-loop operation down to zero frequency (standstill) without having to change over to
open-loop operation.
Parameter p1750.2 = 1 must be set.
The closed-loop control without switchover is restricted to applications involving passive
loads:
These include applications in which the load cannot produce a regenerative torque when
starting and the motor comes to a standstill when pulses are inhibited; for example, loads
with high moments of inertia, brakes, pumps, fans, centrifuges, extruders, ....
Standstill of any duration is possible without holding current, only the motor magnetization
current is impressed.
Steady-state regenerative operation at a frequency close to 0 Hz is not possible.
It is also possible to select sensorless control for passive loads during commissioning by
setting p0500 = 2 (technology application = passive loads (for sensorless control down to
f = 0)).
This function is activated automatically if quick commissioning is exited with p3900 > 0, or if
automatic calculation is called (p0340 = 1, 3, 5 or p0578 = 1).
460
Operating Instructions, 12/2018, A5E36652151A
Enclosed Drives
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