Siemens SINAMICS S120 Function Manual page 144

Servo control
4.12 Encoderless operation
To accept a high load torque even in the open-loop controlled range, the motor current
(current setpoint) can be set using 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). For induction motors, the magnetizing current (r0331) must be additionally taken
into account in p1612. In the lower speed range, the required current cannot be measured
directly on the Motor 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, as the current entered in p1612
is impressed in I/f-controlled operation also without load.
Note
Encoderless operation is not permitted for vertical axes or similar. Encoderless operation is
not suitable for a higher-level closed-loop position control either.
The starting behavior of synchronous motors from standstill can be improved further by
parameterizing the pole position identification (p1982 = 1).
Behavior once pulses have been canceled
Once the pulses have been canceled in operation without an encoder, the current actual
speed value of the motor can no longer be calculated. Once the pulses are enabled again,
the system must search for the actual speed value.
p1400.11 can be used to parameterize whether the search is to begin with the speed
setpoint (p1400.11 = 1) or with speed = 0.0 (p1400.11 = 0). Under normal circumstances,
p1400.11 = 0 because the motor is usually started from standstill. If the motor is rotating
faster than the changeover speed p1755 when the pulses are enabled, p1400.11 = 1 must
be set.
If the motor is rotating and the start value for the search is as of the setpoint (p1400.11 = 1),
the speed setpoint must be in the same direction as the actual speed before the pulses can
be enabled. A large discrepancy between the actual and setpoint speed can cause a
malfunction.
Evaluating incorrect information about the motor speed
Once the pulses have been canceled, no information about the motor speed is available.
The drive sets its speed actual value = "0" Messages and signals derived from the actual
value no longer provide any information. Evaluating these messages and signals can result
in the risk of injury and material damage.
• Take this behavior into consideration when engineering your plant or system.
144
CAUTION
Function Manual, 11/2017, 6SL3097-4AB00-0BP5
Drive functions