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DC Filters
Design Guide
3 Product Overview
3.1 DC Filter for DC/DC Converter
The DC filter is used as an energy storage and damping element between the DC source and the DC/DC converter.
The filter inductor stores energy and reduces the di/dt slope of the load current. The stored energy is released back to the system
with decreasing current.
The DC filter reduces the harmonic content of the load current and keeps it at an acceptable level. The amount of ripple current
allowed in the system depends on the type of energy storage.
Sometimes the DC filter consists only of an inductor. In some applications, capacitors are needed, and an LC filter is used.
DC/DC Converter
DC+
C
DC
DC-
Illustration 1: Example DC/DC Converter Application with a DC Filter
3.2 Voltage and Current Range
The DC filter is designed for 380–690 V AC voltage systems. The voltage span across the DC filter is typically high. The difference
between input and output voltage can be as high as 1100 V, that is 1150 V D input and 50 V DC output. Due to the high voltage
difference, a high inductance value is required to guarantee proper functionality in all operation points. The DC filters are designed
according to a 5 kHz switching frequency.
The current range of the DC filters is 10–1150 A.
3.3 Cooling
The cooling methods used for DC filters:
•
Natural convection (AN)
•
Forced air cooling (AF)
•
Liquid cooling
For the cooling method used for each filter type, see
3.4 DC Filter Types
An L-type inductor is used as default and the same inductor can be used as the inductor part for an LC filter. A typical filter solution
consists of three 1-phase inductors which are installed at the outputs of the individual phases of the DC/DC converter.
Note: The type codes are for filter assemblies, which include three 1-phase inductors. For example, LDC-0092-5-0-APt consist of 3 x
92 A, 750 V DC inductors.
Example
The type code can have this format, for example:
LDC-0092-5-0-APtX
Table 2: Type Code Description
Code
Description
LDC
Filter type
Danfoss A/S © 2023.01
DC Filter
L
1
7.4 Technical
Data.
Product Overview
+
Battery
-
AJ377845348678en-000101 / 172F4785 | 7
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