Sensorless Control For Asynchronous Motors (Open Loop); Sensorless Control - Baumuller b maXX BM3000 Operating Manual

Description of the Software Modules and Parameters

4.8.11 Sensorless control for asynchronous motors (open loop)

4.8.11.1 Sensorless control

The drive controller b maXX
speed control without a rotary encoder (open loop control). However, a position controlled
operation (operating modes position control, synchronous operation, positioning, etc.) or
pure torque control is not possible.
The open loop control operation is based upon calculating the speed of an asynchronous
motor from its model. For this purpose, the motor data (as e. g. inductance and resis-
tance) must be exactly known.
The motor voltages are not measured, but the voltage set values, which were calculated
from the motor control, are used instead. The dead time compensation must also be ac-
tivated, so that the nonlinearity of the power unit can be compensated.
The reliability of open loop operation at low frequencies below 2 Hz is compromised by
the accuracy of motor model parameters and compensation of power unit nonlinearity.
Therefore, for applications requiring persistent operation in this region, it is recommended
to use the closed loop control with an encoder.
m Motoring operation at very low speeds (output frequency below 2 Hz) should be avoid-
m Generating operation at very low speeds (output frequency below motor rated slip)
m Change of speed direction without load is possible.
m Generating operation until standstill is possible.
m A longer lasting generator-based operation (1-2 sec) at very low speeds is not possi-
m The persistent operation at zero frequency is not possible.
m Operation with motors connected parallel is not possible.
Performance specifications
Frequency operation limits:
Performance of closed-loop speed control:
ed.
should be avoided.
ble.
m Minimum output operation frequency motoring mode f
m Minimum output operation frequency regenerating mode f
m Maximum output operation frequency f
m Control range = 1:100
m Static accuracy = 30% of motor rated slip
m Maximum speed regulation bandwidth = 15 Hz
®
3300 permits an operation of an asynchronous motor in
= 150 Hz
max
Parameter manual b maXX BM3000
Document no.: 5.12001.07
= 2.0 Hz
min_m
= motor rated slip
min_r
4
655
of 820