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Film Capacitors for Power Electronics: Latest Technology Trends



With an expanding social infrastructure comes an increasing dependence on electrical energy. Against this backdrop many technologies now considered “indispensable” have emerged. Devices like converters for electrical power, and power electronics that convert and control electricity. In addition to their use in the field of electrical power, these technologies span a range of fields, including industrial equipment (machine tools, fans, etc.), automotive and rolling stock (traffic, rail transport, etc.), and electronic equipment (consumer electronics, office equipment, etc.).
What all these fields have in common is the use of power electronics to provide increased energy savings. Key to these energy savings in recent years has been the growing trend of power electronics equipment to use film capacitors, which are known for their high withstanding voltage, low loss, and high reliability.

2.Features of Film Capacitors

Film capacitors use a plastic film (such as polypropylene or polyethylene terephthalate), which are several microns thick, as their dielectric material. In the power electronics field, the main type used is a vapor-deposited film (metalized film) capacitor in which metal is vapor-deposited on a film surface. Film capacitors offer the following benefits.

(1) Outstanding electrical characteristics
  • Superb withstanding voltage; a single capacitor can withstand voltage of more than 1,000V
  • Low loss for handling high ripple current conditions
(2) High reliability
  • Self-healing function for greater safety
  • Maintenance free for at least 10 years under high-temperature conditions

3.Film Capacitors: Range of Applications and Development Trends

Currently, the dielectric material of film capacitors for power electronics is, for the most part, made of polypropylene due to this material’s high withstanding voltage and reliability. In recent years, film capacitors have started using thinner films and improved vapor-deposition technology, leading to rapidly shrinking capacitor sizes and opening up a wider range of applications.
The following are some of the more prevalent application fields benefitting from these rapid advances in capacitor products and capacitor technologies.

  • General-purpose inverters and machine tools in the field of industrial equipment
  • Traffic and transport (electric vehicles [EVs], hybrid electric vehicles [HVs], and plug-in hybrid electric vehicles [PHEVs]) in the automotive and rolling stock fields
  • Solar power and wind power in the renewable energy field

The trends in film capacitors as they relate to these application fields.

(1) Capacitors for Industrial Machinery and Rolling Stock

Capacitors for these fields must possess the seemingly contradictory characteristics of being able to withstand high voltage and high ripple current while also being compact. There has also been high demand in recent years for dry-type capacitors having no oil inside due to needs for safety and light weight.
Nichicon has developed the EJ Series, compact, high-ripple-current, and highly reliable DC dry film capacitors for use in the fields of rolling stock, industrial equipment, and environmental equipment.

Product Features
By making the film of the dielectric material even thinner and improving the component storage efficiency, we have made the EJ Series 40% more compact than its predecessor, the EU Series. The use of a resin-molded, case-less construction makes this capacitor capable of performing in both extremely low-temperature (-40°C) and high-temperature/high-humidity (85°C, 85% RH, 1,000h) environments. The product also utilizes environmentally friendly materials.


1.Compact (40% smaller than Nichicon’s previous product series)
2.Performs in both low-temperature (-40°C) and high-temperature/high-humidity (85°C, 85% RH, 1,000h) environments
3.Resin-mold type with safety mechanism
4.Maintenance free (long life, high reliability)
5.Environmentally friendly (complies with RoHS Directive, contains no oil)

Main specifications of EJ Series capacitors

Photo 1: EJ Series of DC dry film capacitors

[Photo 1] EJ Series of DC dry film capacitors

(2) Film Capacitors for Electric Vehicles (including hybrid electric vehicles [HVs] and plug-in hybrid electric vehicles [PHEVs])

Snubber and other film capacitors are widely used for applications including smoothing in EV, HV and PHEV products. With increasingly higher withstanding voltages to accommodate higher output and higher efficiency in motor drive systems, and demands for performance under higher ambient temperatures, capacitor manufacturers need an integrated process of film capacitor development—one covering everything from initial material development all the way to optimal structural design—so that, capacitors can be achieve lower loss and made smaller through the use of thinner film for the dielectric material.

Photo 2: Film capacitor for HVs

[Photo 2] Film capacitor for HVs

(3) Film Capacitors for Solar and Wind Power Applications

There is high demand for long-life, highly reliable direct current filter capacitors for renewable energy applications such as solar and wind power. These needs have been met by film capacitors that use cylinder-shaped aluminum for the exterior casing. These cylindrical film capacitors have come into use in recent years as general-purpose parts. Cylindrical film capacitors offer a grounding function thanks to their stud-bolt mounting; they also have improved heat dissipation, and can handle higher ripple current, and as a result are able to achieve greater reliability. Also, because they are constructed of a single, large element, cylindrical film capacitors are more efficient to manufacture and more cost-effective than conventional capacitors of the same rating.

Photo 3: Cylindrical film capacitor

[Photo 3] Cylindrical film capacitor


From the Dempa Shinbun, Jan.13, 2015

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