Efficiency - Danfoss VLT AutomationDrive FC 300 Design Manual

FC 300 Design Guide

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 FC 300 Series (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
shaft torque or only 75%, i.e. in case of part loads.
This also means that the efficiency of the frequency converter does not change even
if other U/f characteristics are chosen.
However, the U/f characteristics influence the efficiency of the motor.
The efficiency declines a little when the switching frequency is set to a value of above 5 kHz. The efficiency
will also be slightly reduced if the mains voltage is 500 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 magnetising level. 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.
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 FC 300 Series (η
by the efficiency of the motor (η
η ) = η x η
SYSTEM VLT MOTOR
Calculate the efficiency of the system at different loads based on the graph above.
How to Select Your VLT
)
VLT
, even if the motor supplies 100% of the rated
M,N
)
MOTOR
)
SYSTEM
):
MOTOR
MG.33.B4.02 - VLT is a registered Danfoss trademark
) is multiplied
VLT
61