Fuji Electric FRENIC-HVAC User Manual page 106

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Figure 3.2 Output Torque Characteristics (Base frequency: 60 Hz)
(1) Continuous allowable driving torque (Curve (a) in Figures 3.1 and 3.2)
Curve (a) shows the torque characteristic that can be obtained in the range of the inverter continuous
rated current, where the motor cooling characteristic is taken into consideration. When the motor runs
at the base frequency of 60 Hz, 100 % output torque can be obtained; at 50 Hz, the output torque is
somewhat lower than that in commercial power, and it further lowers at lower frequencies. The
reduction of the output torque at 50 Hz is due to increased loss by inverter driving, and that at lower
frequencies is mainly due to heat generation caused by the decreased ventilation performance of the
motor cooling fan.
(2) Maximum driving torque in a short time (Curves (b) and (c) in Figures 3.1 and 3.2)
Curve (b) shows the torque characteristic that can be obtained in the range of the inverter rated current
in a short time (the output torque is 110% for one minute) when dynamic torque-vector control (F42 =
1) is enabled. At that time, the motor cooling characteristics have little effect on the output torque.
Curve (c) shows an example of the torque characteristic when one class higher capacity inverter is
used to increase the short-time maximum torque. In this case, the short-time torque is 20 to 30%
greater than that when the standard capacity inverter is used.
(3) Starting torque (around the output frequency 0 Hz in Figures 3.1 and 3.2)
The maximum torque in a short time applies to the starting torque as it is.
(4) Braking torque (Curve (d) in Figures 3.1 and 3.2)
In braking of the motor, kinetic energy is converted to electrical energy and regenerated to the
reservoir capacitor on the DC link bus of the inverter. Only the motor and inverter consume this energy
as their internal losses, so the braking torque is as shown in curve (d).
Note that the torque value in % varies according to the inverter capacity.
(c)
(b)
(a)
5 0 6 0
(d)
3-2
Output
frequency
(Hz)