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Film Capacitors for Automotive and Industrial Applications

The demand for energy savings and for alternative energy sources has called for an accelerated introduction of products such as Hybrid Electric Vehicles, Solar Converters, and Wind Generators. A DC to AC inverter is a key system for the operation of these devices. The inverters require Filter and DC-Link Capacitors with higher operating voltages and ripple currents in order to support the need of increasing power. Other important parameters are low inductance to limit the switching transient voltages, high frequency capability , large range of working temperature, long expected life time, low dissipation factor and low ESR, high stability vs. time of the Capacitance value, withstanding of high peak voltage, mechanical strength, low weight, maximum flexibility of adaptation to the shape of the available space, customized termination technology (through hole wires, tabs, bus-bars, lead frames, and SMD), and low total cost. The Film capacitor is the type of capacitor that comes closest to satisfying these requirements. Several choices of film capacitor manufacturing technologies are available: Wound, Soft-Winding, and Stacked. There have been recent advances in these technologies. The Wound and Soft-Winding capacitors have seen significant advances in capacitance, voltage and current capabilities, and expected life time (100kh continuous use). The Soft-winding capacitors have benefited from very thin and high temperature Polypropylene film in combination with a new process of winding and thermal treatment. The Stacked capacitors can now use two base plastic films (Polypropylene and Polyester) and new techniques of metallization and insulation during the cutting process. This paper will discuss the technical basis for advances in each of these technologies and give some guidance on the optimum areas (capacitance, size, voltage and current) for the application of each technology.