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1.1 Definition and classification of film capacitorsCapacitors are electronic components that can store electrical energy and discharge it when necessary. Together with resistors and inductors, they are called three passive components. An insulator (dielectric) sandwiched between two parallel metal plates (electrodes) forms a simple capacitor. Capacitors directly affect the performance of various electronic devices and are widely used in smartphones, IoT devices, servers, networks, and wireless communication devices.According to the different materials and structures used, capacitors can be divided into ceramic capacitors, film capacitors, electrolytic capacitors and so on. Among them, the film capacitor is a capacitor with plastic film as the dielectric, with non-polarity, low high frequency loss (low ESR), good temperature characteristics, high capacity accuracy, long life and other characteristics, which makes its application system design more simplified, anti-ripple ability more prominent, and more reliable in harsh environments. Compared with ceramic capacitors and aluminum electrolytic capacitors, thin film capacitors with their advantages of high voltage resistance, low ESR, good temperature characteristics, long life, etc., are suitable for applications with higher requirements for stability and reliability.According to the different plastic film materials, film capacitors can be divided into polyethyl ester (PET), polypropylene (PP), polyphenylene sulfide (PPS) and polyethylene naphthalene dicarboxylate (PEN). Previously, miniaturized, inexpensive PET was usually used as a general material, and PP with excellent high frequency characteristics (low ESR) was used in high frequency and high current applications. PP has the characteristics of high safety and high moisture resistance. With the development of PP film capacitor miniaturization technology,PP has been more widely used. PPS and PEN have high heat resistance and are used in surface mount film capacitors. The electrical characteristics of PEN are close to PET, and PPS is close to PP.

1.2 Main application areas of film capacitorsThe application scenarios of thin film capacitors have expanded from traditional household appliances, lighting, industrial control, electric power, electrified railway fields to new energy vehicles, wind power, photovoltaic and other emerging industries. Here is a brief overview of some of the main application areas:New energy vehicles: New energy vehicles refer to the use of a new power system, part or all of the use of new energy as a power source, with energy-saving and environmental protection characteristics of the car. New energy vehicles include pure electric vehicles (BEV), plug-in hybrid electric vehicles (PHEV), and fuel cell vehicles (FCEV). The functions of film capacitors on new energy vehicles include DC support (DC-link), EMI filtering, power factor correction (Passive PFC), buffering/resonance(Snubber/Resonant). The single-vehicle value of film capacitors on new energy vehicles is about 450 yuan, which is the most important demand side of film capacitors.Wind power: Wind power refers to the use of wind power to drive wind turbine rotation, wind energy into electricity, a renewable energy. Wind turbine is mainly composed of wind turbine, generator, gearbox, tower barrel, control system and other parts. The functions of film capacitors in wind turbines include DC support (DC-link), input/output filtering, inverter system buffer circuit, etc. The single-unit value of thin film capacitors in wind turbines is about 27,000 yuan /MW, which is another important demand side of thin film capacitors.Photovoltaic: photovoltaic refers to the use of solar photovoltaic effect, the solar energy into electricity, a renewable energy. Photovoltaic power generation system is mainly composed of solar cell modules, photovoltaic inverters, support systems, control systems and other parts. The functions of film capacitors in photovoltaic inverters include DC support (DC-link), input/output filtering, inverter system buffer circuit, etc. The single-unit value of thin film capacitors in photovoltaic inverters is about 45,000 yuan /MW, which is also an important demand side of thin film capacitors.