Development of film capacitors for electric vehicles

Development of film capacitors for electric vehicles

With the intensification of automobile electrification, the voltage and output power of automobile circuit systems have been greatly improved, and key components have stricter requirements on the voltage and impact resistance of electronic components. The change of working conditions puts forward new requirements on the performance of capacitor components in electronic systems, thereby driving the demand for film capacitors in the automotive industry. For example, the second-generation Toyota Prius replaced the original aluminum electrolytic capacitors with film capacitors. On the one hand, because of the voltage and impact resistance of the film capacitor, it is very suitable for use in the electrical environment of new energy vehicles. On the other hand, in the past years of development, the system and weight of film capacitors have been reduced by 3 to 4 times, while the metallization segmentation technology has been improved, which has greatly helped the development of film capacitors. At present, film capacitors can cover the voltage range between 600VDC and 1200VDC more economically than electrolytic capacitors. ...

Generally speaking, a film capacitor is a capacitor in which a metal foil is used as an electrode, which is overlapped with different plastic films from both ends, and then wound into a cylindrical structure. Due to the difference in film materials, film capacitors exhibit different performance. Among them, the film capacitors made of polypropylene have good pressure and impact resistance and strong self-healing properties, which are particularly suitable for high frequency, high voltage, high stability, high pulse and AC applications. In new energy vehicles, film capacitors are commonly found in motor drive circuits, DC/DC conversion circuits, DC/AC conversion circuits, and battery management systems. For example, in the motor drive circuit, due to the reverse pulse voltage when the IGBT is turned off, three 800VDC film capacitors are generally connected in parallel as DC filter capacitors. In the power filter circuit of the battery management system, there are generally two film capacitors for high-frequency filtering, and so on. The film used in the film capacitor has a direct impact on the performance of the product. There is still a very large gap between the best domestic manufacturers of polypropylene film and foreign high-quality polypropylene films (such as Steiner, Chuangsipu in Germany, Bolloré in France and Toray in Japan). The crystallinity of PP film with capacitor life, pressure resistance and high temperature characteristics can only be achieved by domestic manufacturers at 60% to 65%, while foreign manufacturers can reach 75% to 80%, and are gradually increasing. In this case, if you use the same thickness of film and the same technical process to make products, foreign high-quality films will evade the best domestic film products by 50%, and withstand voltage higher than 30%. In addition to the need to provide high-quality products, the ability to respond quickly to customer needs and good cost control capabilities is an important barrier to competition in the film capacitor industry.