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The shape of the average temperature is constant regardless of the stator frequency. The peak temperature, however, follows the
shape of the output power for small stator frequencies and goes towards the average temperature for increasing stator frequency.
This results in higher temperature variations for small stator frequencies. This means that the expected lifetime of the component
decreases for small stator frequencies if no compensation is used. Therefore, for low values of the stator frequency where the tem-
perature variations are large, the switching frequency can be reduced to lower the peak temperature and thereby the temperature
variations.
For VT applications, the load current is relatively small for small stator frequencies and the temperature variations are thus not as
large as for the CT applications. For this reason, also the load current is considered.
e
3
0
b
b
9
8
0
.1
0
f
sw
[kHz]
SFAVM only
f
sw,fm1
f
sw,fm2
f
sw,fm3
f
sw,fm4
I
s
< K
Is1
x I
nom,ho
K
Is1
x I
nom,ho
< I
s
< K
Is2
x I
nom,ho
I
s
> K
Is2
x I
nom,ho
f
m1
f
m2
f
m3
f
m4
f
m5
(f
m,switch 1
)
f
m
[Hz]
Illustration 29: Switching Frequency (f
sw
) Variation for Different Stator Frequencies (fm)
The points that limit the derating are individual for each frame size and are coded in the EEPROM.
N O T I C E
The VLT AQUA DriveFC 202 never derates the current automatically. Automatic derating refers to adaptation of the switching fre-
quency and pattern.
For VT applications, the load current is considered before derating the switching frequency at low motor speed.
6.1.9.7 High Internal Temperature
The switching frequency is derated based on both control card- and heat sink temperature. This function may sometimes be refer-
red to as the temperature-adaptive switching frequency function (TAS).
N O T I C E
In the example, 1 temperature affects the derating. In fact there are 2 limiting temperatures: control card temperature and heat
sink temperature. Both have their own set of control temperatures.
See
.
Δt
e3
0b
b9
81
.1
1
Δt
Δt
T [°C]
Tas T
RefHigh
Tas T
RefNormal
Tas T
Hys
f
sw
[kHz]
f
swMax
f
swMin
Illustration 30: Switching Frequency Derating due to High Temperature
N O T I C E
dt is 10 s when the control card is too hot but 0 s when the heat sink is too hot (more critical).
The high warning can only be violated for a certain time before the drive trips.
AJ300847815559en-000101 / 130R0337 | 43
Danfoss A/S © 2020.09
Product Features
VLT® AQUA Drive FC 202
Design Guide