Lenze MCH Series - Manual (Page 57)

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18 BASE FREQ
The BASE FREQUENCY determines the V/Hz ratio by setting the frequency at which
the drive will output full voltage to the motor. For most applications the base frequency
should be set to match the motor’s rated frequency.
For example, if the drive is rated for 460 Vac output, and the BASE FREQUENCY is
set to 60 Hz, the drive will maintain a constant ratio of 7.66 V/Hz (except when FIXED
BOOST is active, (refer to Parameter 19) from 0 Hz to 60 Hz. This range is the region
of constant torque. If the motor speed is increased past 60 Hz, the output voltage
remains constant while the frequency increases, resulting in a reduced V/Hz ratio. This
range, from 60 Hz to about 90 Hz, is the region of constant horsepower. Above 90
Hz, horsepower begins to decrease as frequency increases. Refer to Section 6.1 -
DESCRIPTION OF AC MOTOR OPERATION.
19
FIXED BOOST
This parameter is used in applications that require high starting torque. FIXED BOOST
increases the output voltage at lower output frequencies (below 30 Hz for 60 Hz base
frequency), in order to boost the torque capability of the motor. Refer to the diagram
that follows this paragraph. The factory default for FIXED BOOST depends on the
horsepower rating of the drive as listed in the table below.
FX BOOST FACTORY DEFAULT SETTINGS
HP
FACTORY
DEFAULT
HP
FACTORY
DEFAULT
0.25 - 1 5.30 % 20 2.00 %
1.5 - 2 4.40 % 25 1.80 %
3 3.60 % 30 1.60 %
5 3.00 % 40 1.20 %
7.5 2.70 % 50 - 75 0.80 %
10 2.40 % 100 - 125 0.60 %
15 2.20 % 150 - 250 0.40 %
The diagram below illustrates how FIXED BOOST alters the V/Hz ratio to increase
motor torque.
The FIXED BOOST setting represents the amount of boost at 0 Hz (approximately
15% in the example below), and as the output frequency approaches 30 Hz, the boost
decreases to zero. Therefore, at 30 Hz and above, the V/Hz ratio returns to its “normal”
state.