8
MOTOR CONTROL
scheme of Figure 8.20 on page 8-27. In this control strategy, losses, efficiency, rated slip and power factor of the
motor are considered in order to improve the control performance.
The main advantage compared to the V/f control is the best frequency regulation with greater torque capacity
at low speeds (frequencies below 5 Hz), allowing a relevant improvement in the drive performance in permanent
duty. Besides, the VVW control has a quick and simple setting and it is suitable for most medium-performance
applications in the control of three-phase induction motor.
By just measuring the output current, the VVW control instantly obtains the motor torque and slip. Thus, the VVW
actuates in the output voltage compensation and slip compensation. Therefore, the VVW controller action replaces
the classical V/f functions in P137 and P138, but with a calculation model much more sophisticated and accurate,
meeting several load conditions or operation points of the application.
In order to achieve a good frequency regulation in permanent duty with a good operation of the VVW control, the
parameter setting in the range P399 to P407, and the stator resistance in P409 are essential for the good operation
of the VVW control. These parameters can be easily obtained on the motor nameplate.
8-26 | Micro Mini Drives
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