Efficient Networks S120 manual Vector control, Sensorless vector control Slvc

Vector control 4

Compared with vector V/f control, vector control offers the following benefits:

●Stability vis-à-vis load and setpoint changes

●Short rise times with setpoint changes (–> better command behavior)

●Short settling times with load changes (–> better disturbance characteristic)

●Acceleration and braking are possible with maximum available torque

●Motor protection due to variable torque limitation in motor and regenerative mode

●Drive and braking torque controlled independently of the speed

●Maximum breakaway torque possible at speed 0

Vector control can be used with or without an encoder.

The following criteria indicate when an encoder is required:

●High speed accuracy is required

●High dynamic response requirements

–Better command behavior

–Better disturbance characteristic

●Torque control is required in a control range greater than 1:10

●Allows a defined and/or variable torque for speeds below approx. 10% of the rated motor frequency (p0310) to be maintained.

With regard to setpoint input, vector control is divided into:

●Speed control

●Torque/current control (in short: torque control)

4.1Sensorless vector control (SLVC)

In sensorless vector control (SLVC), 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 changeover between closed-loop/open-loop controlled operation is controlled using time and frequency conditions (p1755, p1756, p1758 - only for induction motors). The system does not wait for the time condition to elapse when the setpoint frequency at the ramp- function generator input and the actual frequency are below p1755 * (1 - (p1756/100%)) simultaneously.

Drive Functions	115
Function Manual, (FH1), 07/2007 Edition, 6SL3097-2AB00-0BP4