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Latest technological trends in aluminum electrolytic capacitors for automobiles and film capacitors for motor drives


1.	Latest technological trends in aluminum electrolytic capacitors for automobiles

Societal demand for energy efficiency in automobiles has been increasing in recent years as have concerns about the environment and electronic controls for running various onboard automotive devices have become an important part of meeting this demand. Consequently, the inclusion of electronic control units in automobiles, in other words the increased use of electronics, will continue to progress, so electronic components with the proper specifications for automotive use will increasingly be in demand.
  In this article, we would like to introduce examples of new technological trends in Nichicons aluminum electrolytic capacitors and conductive polymer aluminum solid electrolytic capacitors for automotive use.

Latest technological trends in aluminum electrolytic capacitors

Aluminum electrolytic capacitors have greater capacitance per unit volume than other capacitors typesb, and are comparatively lower in price because they are mostly made of aluminum. These attributes make them broadly applicable for use in electronic devices. Aluminum electrolytic capacitors are used in the automotive field in various types of controllers, such as engine control units (ECUs) or for driving or vehicle control, which are often mounted in or around the engine compartment. Nichicon offers the UCX-series lineup to meet the demand for capacitors that can withstand high temperatures in the engine compartment environment but can also be used in cold locations. The UCX series is the first in the industry to offer a 135 C with low equivalent series resistance (ESR). The UCX series employs an electrolyte with improved stability in high temperature environments as well as highly reliable seal, high-power anode foil, thinner electrolysis paper, and optimized construction to ensure a long life of 2000 hours at 135C. The lineup consists of a range of eight sizes from Φ6.310L - Φ1821.5L, with a rated voltage range of 10-50V, and rated capacitance range of 47 - 3300μF.

Latest technological trends in conductive polymer aluminum solid electrolytic capacitors

Conductive polymer aluminum solid electrolytic capacitors are widely used in PCs and telecommunications terminals, and because of their low ESR, stabletemperature characteristics, and long life they are becoming widely used in automotive electronics and industrial equipment. Developing products for automotive use requires increasing the ability to withstand high temperatures, and while Nichicon already offered the 125 deg C PCX lineup, we have added the PCR series which offershigher capacitance, and longer life with a 4000 hours at 125 deg C rating. Development of the PCR series was based on the existing PCX series, and aimed for higher capacitance and optimization of conductive polymer formation, part structure, and materials design with the goal of smaller size and higher capacitance. Automotive use also requires vibration resistance, so we offer an individual lineup of vibration-resistant products. Automotive applications are diversifying, so we are currently developing a product capable of handling 135 deg C to meet demands for higher temperature ratings.
  While the above represent the latest technology trends, Nichicon will not stand still and will continue to develop new aluminum electrolytic and conductive polymer aluminum solid electrolytic capacitor products that meet the future needs of auto manufacturers.

[Photo 1] UCX-series 135deg C low ESR regulated chip-type aluminum electrolytic capacitors

[Photo 1] UCX-series 135deg C low ESR regulated chip-type aluminum electrolytic capacitors

[Photo 2]PCR-series conductive polymer aluminum solid electrolytic capacitors

[Photo 2]PCR-series conductive polymer aluminum solid electrolytic capacitors

2.Latest technological trends in film capacitors for motor drives

In recent years, the following have come to be required of EV and HV components:

(1) Higher voltage for high output from motor drive systems and higher efficiency;
(2) More compact size for lighter weight for greater fuel efficiency.

The inverters in these motor drives in the past required smoothing capacitors to smooth out the direct current because of the use of inexpensive, high capacity aluminum electrolytic capacitors.
Now, thanks to a revolution in dielectric film technology and progress in making it thinner, we have now succeeded in improving film capacitor specifications for superior electronic properties such as higher voltage tolerance, reduced loss, high ripple current, and long life.
The key to the proliferation of EVs and HVs in future will be how low-cost and compact systems can be made, and in this respect film capacitors must become smaller and able to handle higher ripple currents and higher temperatures. Further development of film capacitors, therefore, must focus on:

  • Reducing size through use of thinner dielectric film
  • Higher withstand voltages and lower ESR through vapor-deposition technologies
  • Ability to handle higher ripple currents
  • Improved reliability throuth structural materials development
  • Improved heat dissipation optimization of the structure

[Photo 3] Film capacitor for HVs

[Photo 3] Film capacitor for HVs

Features of Film Capacitors

  Film capacitors use a plastic film that is only several microns thick as the dielectric material. In the power electronics field, the main type used is a vapor-deposited film (metalized film) in which metal is vapor-deposited on a polypropylene film to create an internal electrode, mainly for use in hybrid vehicles (HVs) and electric vehicles (EVs). Film capacitors have the following outstanding electrical, safety, and reliability features.

(1) Stable capacitance over a wide temperature range
(2) Superb withstand voltage, ideal for high-voltage applications
(3) Low loss for greater energy efficiency
(4) Exceptional high frequency characteristics and superior filtering
(5) High ripple current capability for greater current density per unit of volume
(6) Self-healing function for greater safety
(7) Maintenance free for at least 10 years under high-temperature conditions

  Conventional film capacitors using polypropylene film had superb electrical characteristics but were limited in how small they could be made and how much capacitance they could achieve per unit of volume. As a result, they were limited to certain applications. But todays film capacitors have thinner films and improved vapor-deposition technology, putting them in greater demand in power electronics applications.

Latest technological trends in film capacitors

  • Development of thinner dielectric film
      Film thickness determines the capacitance in film capacitors, so if the film thickness is 1/2, 4x the capacitance can be achieved in the same volume or only of the volume is needed to achieve the same capacitance. Thin polypropylene film is thinner, up to 2.5 microns, and even thinner film is in development.

[Figure 1] Vapor deposition pattern
[Figure 1] Vapor deposition pattern
  • Vapor deposition technology(vapor patterning)
      If the film is made thinner it must also have increased withstand voltage. Therefore, forming a metal pattern using vapor deposition provides a fuse function through a pattern of small segments. Improved vapor-deposited patterns are being developed to offer the properties required, such as higher withstand voltages and lifespan.

High ripple current

Polypropylene film is a low-loss material, but because the fuse created through the vapor deposition pattern is a resistive element, applying high ripple current will result in a temperature increase. Consequently, high ripple current capability can be attained through the development of a improvedvapor deposition pattern designs that can straddle high voltage and high ripple current, even whilelimiting the thickness of the metalized film.


From the Dempa Shinbun,Jul.1,2014

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