Technical data

Drive functions
7.1 Servo control
Function Manual
Function Manual, 06/2012, 6SL3097-4AB10-0BP4
149
Description
This allows operation without an encoder and mixed operation (with/without encoder).
Encoderless operation with the motor model allows a higher dynamic response and greater
stability than a standard drive with V/f control. Compared with a drive with an encoder,
however, speed accuracy is lower and the dynamic response and smooth running features
deteriorate.
Since the dynamic response in operation without an encoder is lower than in operation with
an encoder, accelerating torque pre-control is implemented to improve the control dynamic
performance. It controls, knowing the drive torque, and taking into account the existing
torque and current limits as well as the load moment of inertia (motor moment of inertia:
p0341*p0342 + load torque: p1498) the required torque for a demanded speed dynamic
performance optimized from a time perspective.
Note
If the motor is operated with and without an encoder (e.g. p0491 not 0 or p1404 < p1082),
the maximum current during operation without an encoder can be reduced via p0642
(reference value is p0640) in order to minimize interfering, saturation-related motor data
changes during operation without an encoder.
A torque smoothing time can be parameterized via p1517 for the torque pre-control. The
speed controller needs to be optimized for operation without an encoder due to the lower
dynamic response. This can be carried out via p1470 (P gain) and p1472 (integral time).
In the low-speed range, the actual speed value, the orientation, and the actual flux can no
longer be calculated during operation without an encoder due to the accuracy of the
measured values and the parameter sensitivity of the process. For this reason, an open-loop
current/frequency control is selected. The switchover threshold is parameterized via p1755
and the hysteresis via p1756.
To accept a high load torque even in the open-loop controlled range, the motor current can
be increased via p1612. To do so, the drive torque (e.g. friction torque) must be known or
estimated. An additional reserve of approx. 20% should also be added. In synchronous
motors, the torque is converted to the current via the motor torque constant (p0316). In the
lower speed range, the required current cannot be measured directly on the Power Module.
The default setting is 50% (synchronous motor) or 80% (induction motor) of the motor rated
current (p0305). When parameterizing the motor current (p1612), you must take into account
the thermal motor load.
Note
Operation without an encoder is not permitted for vertical axes or similar. Operation without
an encoder is not suitable for a higher-level closed-loop position control either.
The start behavior of synchronous motors from standstill can be improved further by
parameterizing the pole position identification (p1982 = 1).