New Dielectric Polymer Film Capacitors for Pulse Power Applications

Abstract

High voltage pulse power technologies utilized by the Department of Defense applications such as armor/anti-armor, electromagnetic/electrothermal guns, lasers, high power microwave weapons, etc. are usually satisfied today by film capacitor technologies. Commercial applications extend to a.c. motors, lighting, and automotive and implantable and portable defibrillators, among others. Film capacitors based on polypropylene (PP) and polyester (PET) have the ability to operate at very high voltages and with good reliability. They also offer high breakdown voltages, inherent low losses, excellent frequency response, low dissipation factor (DF), and good self-healing abilities. Unlike most other circuit components, existing capacitor technologies now present a barrier to achieving significant packaging (size and weight) reductions and struggling to meet market-driven performance requirements. The energy density of commercial film capacitors is less than 1 J/cc. Polyvinylidene fluoride (PVDF) has a much higher dielectric constant (12) than commercial films such as polypropylene (PP) (2.5) and a practical energy density of about 2.4 J/cc. However, it has a number of drawbacks including non-linearity of the dielectric constant with voltage, very poor insulation resistance, poor clearing or self-healing ability, poor dissipation factor (DF), higher leakage currents, relatively lower breakdown voltages and is very costly. In recent SBIR Programs, Lithium Power Technologies demonstrated that by combining PP with PVDF in a polymer blend, one could obtain a material with a very high dielectric constant as well as other excellent electrical properties. Electrical data on biaxial oriented thin films and capacitors demonstrated very high breakdown voltages of 700 V/μm to over 1050 V/μm. In contrast, PP films and capacitors resulted in breakdown voltages of 220 to 560 V/±m. Preliminary energy density for the new dielectric capacitor was about 12 J/cc compared to less than 0.5 J/cc for PP. The frequency response data with respect to the DF demonstrated an almost negligible loss in dielectric activity at high frequencies. The new polymer dielectric offers a number of key advantages, including improved performance and lower cost per unit of energy. The technology is a promising candidate for the development of a higher energy density, high voltage metallized film capacitor for a large number of applications including, defense, aerospace, defibrillator, automotive, and electric power generation. This paper will discuss the development of this new technology and commercial potential.