5.4 Details of Function Codes
5-106
Torque boost
y Manual torque boost (F09)
- Data setting range: 0.0 to 20.0 (%), (100%/Rated voltage at base frequency)
In torque boost using F09, constant voltage is added to the basic V/f pattern, regardless of the load. To
secure a sufficient starting torque, manually adjust the output voltage to optimally match the motor and its
load by using F09. Specify an appropriate level that guarantees smooth start-up and yet does not cause
over-excitation at no or light load.
Torque boost using F09 ensures high driving stability since the output voltage remains constant regardless
of the load fluctuation.
Specify the F09 data in percentage to the rated voltage at base frequency. At factory shipment, F09 is preset
to a level that assures approx. 100% of starting torque.
y Specifying a high torque boost level will generate a high torque, but may cause overcurrent
due to over-excitation at no load. If you continue to drive the motor, it may overheat. To avoid
such a situation, adjust torque boost to an appropriate level.
y When the non-linear V/f pattern and the torque boost are used together, the torque boost
takes effect below the frequency on the non-linear V/f pattern’s point.
Figure 5.4-38
y Auto torque boost
This function automatically optimizes the output voltage to fit the motor with its load. Under light load, auto
torque boost decreases the output voltage to prevent the motor from over-excitation. Under heavy load, it
increases the output voltage to guarantee the output torque of the motor.
y This function is controlled in accordance with the motor characteristics. Since this function
relies also on the characteristics of the motor, set the base frequency 1 (F04), the rated
voltage at base frequency 1 (F05), and other pertinent motor parameters (P01 through P03
and P06 through P99) in line with the motor capacity and characteristics, or else perform
auto-tuning (P04).
y When a special motor is driven or the load does not have sufficient rigidity, the maximum
torque might decrease or the motor operation might become unstable. In such cases, do not
use auto torque boost but choose manual torque boost using F09 (F37 = 0 or 1).
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