Review of Film Capacitor Trends and Design Changes as a Result of Improved Technologies in Power Electronics

Abstract:
The SIC technology further fuels the trend towards more compact and efficient designs within power electronics. This allows higher switching frequencies leading to more efficiency in power systems as well as downsizing of the complete system and much higher power density. The design of capacitors used in power electronics such as DC-link and AC filtering components, will be challenged especially in terms of higher temperature and high frequency operation requirements. This nominal working temperature in capacitors based on metalized polypropylene technology which provides high current handling capabilities is 85 °C hot spot temperature (hottest point inside the capacitor) at full load and requires strong derating in voltage to achieve higher temperatures. This will not match the requirements for the future designs of IGBTs or SIC power electronics. This presentation will compare and summarize different film technologies and their strength and weakness in respect to thermal challenges. Furthermore; by moving the switching frequencies from 10 kHz - 30 kHz to more than 500 kHz, the internal resonances can appear leading to distribution of current flow inside the capacitors which is different then what will be measured outside at the terminals. The differences will be shown in presentation as well as possibilities how to tackle and overcome these issue.presentation will focus on two main points for capacitors: 1) Effects on raw material to withstand higher temperatures and tougher environmental conditions 2) Effects on construction and design of capacitors to ensure reliable, robust components. Capacitors as of today are mainly manufactured with film technologies based on Polypropylene and Polyesters which have restrictions to handle higher temperatures. Most used technology today is Polypropylene, due to the good self-healing capabilities and low dielectric losses. The need for increasing working temperatures pushes all passive component manufacturers to seek for new base film materials or new processes. The