Vector Control Without Encoder - Siemens SINAMICS G150 Operating Instructions Manual

Setpoint channel and closed-loop control
7.4 Vector speed/torque control with/without encoder
7.4.1

Vector control without encoder

Description
For sensorless vector control only (SLVC: Sensorless Vector Control), the position of the flux
and actual speed must be determined via the electric motor model. The model is buffered by
the incoming currents and voltages. At low frequencies (approx. 1 Hz), the model cannot
determine the speed.
For this reason and due to uncertainties in the model parameters or inaccurate
measurements, the system is switched from closed-loop to open-loop operation in this
range.
The changeover between closed-loop/open-loop operation is controlled on the basis of time
and frequency conditions (p1755, p1756, p1758 - only for induction motors). The system
does not wait for the time condition to elapse if the setpoint frequency at the ramp-function
generator input and the actual frequency are below p1755 x (1 - (p1756 / 100%))
simultaneously.
Transition from open-loop to closed-loop operation always takes place when the changeover
speed in p1755 (characteristic "1" in the figure below). If the speed increase is set very slow
and a changeover delay time > 0 is set in p1759, transition takes place after the changeover
delay time (characteristic "2" in the figure below).
Figure 7-11
Setting the torque setpoint
In open-loop operation, the calculated actual speed value is the same as the setpoint value.
For vertical loads and when accelerating, parameters p1610 (static torque setpoint) and
p1611 (additional acceleration torque) must be adjusted to the necessary maximum torque in
order to generate the static or dynamic load torque of the drive. If, on induction motors,
p1610 is set to 0%, only the magnetizing current r0331 is injected; at a value of 100%, the
rated motor current p0305 is injected.
For permanent-magnet synchronous motors, at p1610 = 0%, a pre-control absolute value
derived from the supplementary torque r1515 remains instead of the magnetizing current for
induction motors.
438
Changeover conditions
Converter cabinet units
Operating Instructions, 07/2016, A5E03347396A