Efficiency - Danfoss VLT 7000 Series Manual

Efficiency

To reduce energy consumption it is very important
to optimize the efficiency of a system. The
efficiency of each single element in the system
should be as high as possible.
Efficiency of VLT 7000 Booster ( η
The load on the frequency converter has little effect on
its efficiency. In general, the efficiency is the same at
the rated motor frequency f
the motor supplies 100% of the rated shaft torque
or only 75%, i.e. in case of part loads.
The efficiency declines a little when the switching
frequency is set to a value of above 4 kHz (parameter
407 Switching frequency). The rate of efficiency will
also be slightly reduced if the mains voltage is 460
V, or if the motor cable is longer than 30 m.
Efficiency of the motor (η
The efficiency of a motor connected to the frequency
converter depends on the sine shape of the
current. In general, the efficiency is just as good
as with mains operation. The efficiency of the
motor depends on the type of motor.
In the range of 75-100% of the rated torque, the
efficiency of the motor is practically constant, both
when it is controlled by the frequency converter
and when it runs directly on mains.
124
)
VLT
, regardless of whether
M,N
)
MOTOR
VLT® 7000 Booster
In small motors, the influence from the U/f characteristic
on efficiency is marginal; however, in motors from 11
kW and up, the advantages are significant.
In general, the switching frequency does not affect
the efficiency of small motors. Motors from 11 kW
and up have their efficiency improved (1-2%). This
is because the sine shape of the motor current is
almost perfect at high switching frequency.
Efficiency of the system (η
To calculate the system efficiency, the efficiency
of VLT 7000 Booster (VLT) is multiplied by the
efficiency of the motor (MOTOR):
η = η x η
SYSTEM VLT MOTOR
Based on the graph outlined above, it is possible to
calculate the system efficiency at different speeds.
MG.70.A1.02 - VLT is a registered Danfoss trademark
)
SYSTEM