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DC links circuits are everywhere. Any time two AC (alternating current) systems with differing voltages and frequencies are connected, an intermediate DC (direct current) stage can be found.
This AC/AC converter requires capacitors to store the energy that has been converted from AC into DC before it is then converted back into the new AC voltage. These capacitors must exhibit a number of key characteristics:
- High voltage rating
- Low dissipation
- Low inductance
Traditionally this function has been fulfilled by electrolytic capacitors as a result of their high power density. However, more recently polypropylene film capacitors have found their way into DC-link applications in a number of industries including railroad, renewable energy and robotics.
Polypropylene film capacitors offer a number of advantages over electrolytic types:
- High voltage capabilities
- Low inductance
- Low ESR and flat response up to 50 KHz
- Wide operating temperature range
- Improved reliability due to inherent self-healing properties
- Long life expectancy and excellent mechanical stability
KEMET have introduced the C4AE polypropylene film series, a range of radial capacitors with 2 or 4 leads. This series features a metallised film within a rectangular plastic box which is filled with resin. They are ideal for an array of applications including DC filtering and energy storage.