System Manual – MOVIDRIVE® compact Drive Inverters
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Overload capacity of the inverter
Project Planning
4.7
Overload capacity of the inverter
MOVIDRIVE
®
drive inverters calculate the load on the inverter output stage permanently
(unit utilization). Consequently, they enable the maximum possible power to be pro-
duced in each operating status. The heat sink constant T of the inverter is used as the
time unit. The heat sink time constant T is different for every size (
→
Sec. "Heat sink
time constant")
Determining the
overload capacity
Three steps are required to determine the overload capacity:
1. Determine the continuous output current I
out
depending on the output frequency (es-
pecially < 2 Hz) and the PWM frequency.
2. Characterize the duration of the overload:
– Minutes:
t
overload
≥
0.25 T (e.g. fans)
– Seconds:
t
overload
< 0.25 T (e.g. roller conveyor)
– Fraction of a second:
t
overload
≤
1 s (e.g. dynamic servo applications)
3. Determine the overload capacity in the characterized time range (
→
following figure):
– Minutes: Overload diagrams (A)
→
– Seconds: Tables and formulas (B)
→
– Fraction of a second: Overload diagrams (C)
→
Heat sink time
constant T
Load cycle
The required load cycle is the basis for determining the overload capacity of the inverter.
The following conditions must be fulfilled for periodic repetition of a load cycle:
•
At the end of the overload time t
1
, the value is just below the critical heat sink
temperature.
•
During the following low-load time t
2
, the heat sink temperature drops to such a
degree that another overload is possible for the duration t
1
.
Figure 62 shows an example of such a load cycle. The temperature profiles of the heat
sink for the overload time t
1
and the low-load time t
2
are shown under the load cycle. If
you arrange the temperature profiles as shown in Figure 62 , you can check whether the
overload limit is exceeded.
56450AXX
A
B
C
Heat sink time constant T for inverter size
1
2
3
4
5
3.5 min = 210 s
5 min = 300 s
4 min = 240 s
9 min = 540 s
5 min = 300 s
Summary of Contents for MOVIDRIVE compact MCH41A
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