To understand the effects of geometry on finished capacitor functions it is first important to understand the section geometry (basic winding unencapsulated). In general, the shorter the section is the better it will function. The ideal capacitor would generally have the apparent diameter to length ratio of a hockey puck. The more end area there is, the more peak current the unit can handle.
Metallized film capacitors utilizing polypropylene dielectric have become the component of choice in critical applications because of their low dielectric loss and superior breakdown voltage strength. There are some concerns that in certain applications metallized polypropylene capacitors can fail in a manner such that the failure poses a hazard to the equipment and personnel. FuseacTM is a thermal fuse technology designed to protect against common capacitor failure modes in high power AC and DC applications.
For a battery-powered traction motor drive, the inverter dc bus presents high-frequency pulsating current due to device switching. Conventional inverter design sizing dc-bus capacitor based on voltage ripple is no-longer effective. In order to handle high current in high temperature environment, a lowinductance high-current film capacitor is proposed to replace the conventional electrolytic bulk capacitors for a 75-kW traction motor drive inverter.
Capacitor specifications vary between manufacturers and it can be difficult for a design engineering selecting a capacitor to interpret the information presented in literature for use in the actual application. This application note discusses how to manipulate published capacitor ratings to the actual system requirements and determine if the capacitor will function reliably for that application.
For years design engineers have chosen electrolytic capacitor technology for use as the bus link capacitor on inverter designs. The main attraction has always been the low cost per farad associated with electrolytic capacitors. This paper presents a practical mathematical approach on how to properly size a bus link capacitor for a high performance hard switched DC to AC inverter using film capacitors and will show how film capacitors are advantageous over electrolytic capacitors in terms of size, weight, lifetime, inverter efficiency and cost.