Efficient Networks Siemens Sinamics S120 - Manual (Page 89)

Servo control
3.11 Sensorless operation (without an encoder)
Drive Functions
Function Manual, (FH1), 07/2007 Edition, 6SL3097-2AB00-0BP4
89
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 technique. 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 Motor Module.
The default setting is 50% (synchronous motor) or 80% (induction motor) of the rated motor
current (p0305). When parameterizing the motor current (p1612), you must take into account
the thermal motor load.
Note
Sensorless operation (without an encoder) is not permitted for vertical axes or similar.
Sensorless operation 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).
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