Du/Dt; Efficiency - Danfoss VLT DriveMotor FCM 106 Design Manual

Specifications

6.11 dU/dt

Shaft output power
[kW]
0.55
0.75
1.1
1.5
2.2
3.0
4.0
5.5
7.5
Table 6.14 dU/dt, MH1-MH3
a) Data available upon future release

6.12 Efficiency

Efficiency of the frequency converter (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 , even if the motor supplies
M,N
100% of the rated 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 480V.
Frequency converter efficiency calculation
Calculate the efficiency of the frequency converter at
different loads based on Illustration 6.6. The factor in this
graph must be multiplied with the specific efficiency factor
listed in the specification tables:
1.01
1.0
0.99
0.98
0.97
0.96
0.95
0.94
0.93
0.92
0% 50%
% Speed
100% load 75% load
Illustration 6.6 Typical Efficiency Curves
®
VLT DriveMotor FCP 106 and FCM 106 Design Guide
Cable length AC line voltage
[m] [V]
0.5 400
0.5 400
0.5 400
0.5 400
<0.5 400
<0.5 400
<0.5 400
<0.5 400
<0.5 400
)
VLT
100% 150% 200%
50% load 25% load
MG03M102 - 08/2015
Rise time
[µs]
0.1
0.1
0.1
0.1
a)
a)
a)
a)
a)
Example: Assume a 22 kW, 380-480V AC frequency
converter runs at 25% load at 50% speed. The graph
shows 0.97, whereas rated efficiency for a 22 kW frequency
converter is 0.98. The actual efficiency is then:
0.97x0.98=0.95.
Efficiency of the motor (η
MOTOR
The efficiency of a motor connected to the frequency
converter depends on the magnetizing 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
SYSTEM
To calculate the system efficiency, the efficiency of the
frequency converter (η ) is multiplied by the efficiency of
VLT
the motor (η ):
MOTOR
η = η x η
SYSTEM VLT MOTOR
V dU/dt
peak
[kV] [kV/µs]
0.57 4.5
0.57 4.5
0.57 4.5
0.57 4.5
a) a)
a) a)
a) a)
a) a)
a) a)
)
)
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