Functions
8.24 Open-loop and closed-loop control
Control Units CU240S
8-172 Operating Instructions, 11/2006, A5E00766042B AA
8.24.2.1 Vector control without speed encoder
Data
P1400 … P1780
P1610, P1611
P1750
Parameter range:
P1755, P1756, P1758
Warnings: -
Faults: -
Function chart number: FP7000
Description
When Vector control is used without a speed encoder (SLVC) then the position of the flux
and the actual speed must be determined using the motor model. In this case, the model is
supported by the accessible currents and voltages. At low frequencies (≈ 0 Hz), the model is
not able to determine the speed. Inability of the model to determine the speed at ≈ 0 Hz,
uncertainty in model parameters and measurement inaccuracy are the reasons why there is
a changeover from closed-loop to open-loop controlled operation in this range.
The changeover between closed-loop controlled and open-loop controlled operation is
controlled using the time and frequency conditions (P1755, P1756, P1758) (see figure
below). The system does not wait for the time condition if the setpoint frequency at the ramp-
function generator input and the actual frequency simultaneously lie below P1756.
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Figure 8-89 Changeover condition for SLVC
In the open-loop controlled mode, the speed actual value is the same as the setpoint. For
suspended loads or when accelerating, parameter P1610 (constant torque boost) and P1611
(torque boost when accelerating) must be modified in order to allow the motor to provide the
steady-state and/or dynamic load torque. If P1610 is set to 0 %, then only the magnetizing
current r0331 is impressed for a value of 100 % of the rated motor current P0305. In order
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