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Setpoint channel and closed-loop control
7.4 Vector speed/torque control with/without an encoder
Figure 7-12
Zero crossing in open-loop controlled operation at low speeds
Extended method: closed-loop controlled operation to zero speed
By superimposing high-frequency pulses on the driving fundamental voltage and evaluating
the resulting offset pulse in the machine current, it is possible to determine the continuous
rotor position up to frequency zero (standstill).
1FW4 and 1PH8 series Siemens torque motors can be started from standstill with any load
up to the rated torque or even hold the load at standstill.
The procedure is suitable for motors with internal magnets.
Note
Use of a sine-wave filter
If a sine-wave filter is used, the open-loop controlled procedure should be used.
The following advantages are obtained by maintaining closed-loop controlled operation:
● No switchover required within closed-loop control (smooth switching, no discontinuities in
the torque).
● Sensorless closed-loop speed and torque control down to and including 0 Hz
● Higher dynamic performance when compared to open-loop controlled operation.
● Encoderless operation of drive line-ups (e.g. in the paper industry, master-slave
operation).
● Active (including hanging/suspended) loads down to zero frequency.
462
Operating Instructions, 12/2018, A5E36652151A
Enclosed Drives
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