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Operation
8.5 Functions
Vector control without an encoder
Vector control without an encoder is used with induction motors.
In vector control without an encoder, 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. 0 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 switchover is governed by time and frequency conditions (p1755, p1756, and p1758). If the
setpoint frequency at the ramp-function generator input and the actual frequency are below
p1755 x p1756 simultaneously, the system does not wait for the time condition.
Figure 8-3
In open-loop operation, the actual speed value is the same as the setpoint value.
To provide the resulting static or dynamic load torque for suspended loads or acceleration
tasks, modify the following parameters:
● p1610 (constant torque increase)
● p1611 (torque increase)
Vector control without encoder has the following features in the low frequency range:
● Closed-loop operation up to approx. 1 Hz output frequency
● Start-up in closed-loop operation (directly after drive is energized)
● Passes through low frequency range (0 Hz) in closed-loop operation
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Switchover conditions
If p1610 is set to 0%, only the magnetizing current r0331 is impressed. For a value of 100%,
the rated motor current p0305 is impressed.
To ensure that the drive does not stall during acceleration, p1611 can be increased or
acceleration pre-control for the speed controller used. The p1611 increase is also advisable
to ensure that the motor is not subject to thermal overload at low speeds.
Note
In this case, the speed setpoint upstream of the ramp-function generator must be greater
than p1755.
SINAMICS SM150 6SL3815-7NP41-0AA1
Operating Instructions Rev.201910281301 EXAMPLE
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