The power electronics in the modern industry field has a higher requirement on the choice of components, whether it is the electrical characteristic or the operating condition of the environment. Capacitor is no exception, the reliability of the product is more and more important. In power electronics applications, thin film capacitors have more advantages than other capacitors.
Thin film capacitors are widely used in high voltage and high frequency power electronic devices, especially in DC-LINK. The thin film capacitors and electrolytic capacitors have excellent electrical properties, such as high ripple current, high pressure, low ESR and ESL, long life, no polarity and high frequency.
Advantages of thin film capacitors
? 1 to withstand the high effective current capacity, the highest up to 1Arms/ F.
? 2 anti surge ability, can withstand the surge voltage of 2UnV
3 to withstand the peak current capacity, dv/dt up to 100V/ s, ESL inductance is small, fast charge and discharge rate.
4 high voltage, can withstand 1.5 times the rated voltage.
5 no polarity, can withstand the reverse pulse voltage for a long time.
The 6 medium loss is small, ESR is small, the internal temperature of the product is low, the temperature characteristic is good.
7 small size, long life, no acid pollution.
8 can be long time storage.
The 9 alternative is not equal? Electrolysis capacity substitution, but replace the function, determine the capacity according to different requirements.
Development trend of thin film capacitors (for DC-LINK)
Since 1980, the use of metal based membranes and membrane metal segmentation technology of DC filter capacitor has been a considerable development. During the past years, the volume and weight of the capacitor has been reduced by 3 to 4 times. Thin film manufacturers have now developed a thinner film, which has improved the development of the technology of metal based segmentation. With dry design, the film capacitor can be more economical to cover the voltage range of 600VDC to 1200VDC than the electrolytic capacitor.
1, dry to replace oil immersed
Oil immersed capacitor because of the oil impregnated to film inside (more than 1200V capacitance more), when the capacitor leakage oil or aging due to direct contact with oil to film and metal coating electrode, will affect the performance of the capacitor, greatly reducing the life of the capacitor and dry type capacitor can solve the above problems, and the reduction of the production process, to ensure the consistency of the product.
2, electrical explosion-proof alternative pressure explosion-proof
Oil immersed capacitor commonly used pressure explosion-proof or the internal fuse in series of explosion-proof, and now foreign dry film capacitor is generally used more advanced electrical explosion-proof, namely the network safety film, and explosion-proof electrical pressure explosion-proof type and internal series fuse explosion-proof reliability higher, explosion-proof effect better.
Key materials for thin film capacitor
Medium - plastic film (such as: polypropylene (PP), polyester (PET), polycarbonate (PC), PPS, (PPS)), the performance of plastic film directly affects the life and performance of electrical capacitor films, PP films and the best manufacturers at home and abroad to do the high quality PP films (such as Germany take a spoon, Thai history, France and Japan) Dongli boluolai gap is still quite large, especially the effect of PP thin film capacitor life, the pressure and temperature characteristics of crystallinity, the domestic manufacturers can only achieve the crystallinity of 60~65%, while abroad can reach the crystallinity of 75~80%, and gradually improve, so if the process, film with the same thickness of the same product made abroad, the high quality membrane than the best domestic film products long life, high pressure of more than 30% 50%.
Common structures and classification of thin film capacitors
A. internal structure classification
1 double side metal film, internal series structure
2 single metal film, internal series structure
3 single side metal film, internal not string
4 single metal film, network security structure
B. by contour structure classification
1 Outsourcing: wire, tape, axial lead plate, screw
2 standard plastic housing package, wire / film extraction
3 standard metal shell, screw / lead screw
4 custom, shaped shell
C. by target classification
Snubber (absorption) (PSD, PSC, PSM)
DC-link (direct current filtering, DC link support) (PDP, PDF, PDE, PDB)
AC-filter (AC filter, LC,) (PAF, PAR)
Resonant (Xie Zhen) (PSC, PGH)
Switching (switch) (PWH)
A comparative analysis of the film capacitor and electrolytic capacitor
1, electrical properties (from product design and structure analysis)
Electrolytic capacitors are used in the form of an implicit foil type, and the film capacitor is made of metal film without winding structure, as shown in the following figure:
From the structure of the electrolytic capacitors and film capacitors can be seen: electrolytic capacitor is a winding, current flow path far (equal to the length of the electrolytic aluminum foil), resulting in the power of the capacitor ESL and ESR larger, so that the temperature is too high, while the film capacitor is no sense winding, the current flow direction of the film is short (equal to film width), thin film capacitors ESR and ESL, so it can withstand large ripple current and no fever.
2, life comparison
Electrolytic capacitors are generally only 2000~3000 hours, while the long life of 5000~6000 hours, but prone to leakage and the existence of shelf life; and the thin film electric capacity is generally more than 100000 hours, and is dry and no shelf life; the next is a thin film capacitor life curve:
Function and application of DC-LINK capacitor in power electronic equipment
Schematic diagram of thin film capacitor in power electronic equipment
C1: DC link