Film capacitor dc support the technical advantages of early film capacitor is used electrolytic capacitor, along with the development of the plastic film technology, especially the basal membrane technology development and metallization using integral technology, not only makes the volume of a thin film capacitor in the do at the same time, the smaller the pressure level remains at the level of the products, now more and more companies using high temperature of polypropylene film capacitor as support dc capacitance, a typical example is the Toyota PRIUS models improvement; The typical representatives of domestic car companies are byd F3DM and E6, which use thin-film capacitors as dc support capacitors. The filter capacitor used by the first Toyota Prius is an electrolytic capacitor; From the second generation, the thin-film filter capacitor bank was used.
Currently, thin-film capacitors are used for dc support, mostly using high temperature polypropylene film as the medium, and polypropylene film capacitor has the following advantages:
A. product has good security, overpressure resistant capability is strong because the film capacitor has self-healing phenomenon, and the design of thin film capacitor is in accordance with the standards of IEC61071, electric capacitive reactance surge voltage ability is greater than 1.5 rated voltage, and capacitance using membrane technology, as shown in figure 4, won't produce the phenomenon of short circuit breakdown capacitance theory, which greatly improved the security of this kind of capacitor, the typical failure mode is open. The ability to peak voltage in a particular application is also an important indicator of capacitance. In fact, for electrolytic capacitors, the allowable surge voltage is 1.2 times, forcing users to consider peak voltages instead of nominal voltages.
B. good temperature characteristic, the product temperature range is wide, can from 105 ℃ to 40 ℃ - dc support film capacitor using the high temperature of polypropylene film, polyester film and electrolytic capacitors no temperature stability, specific as follows in figure 5, figure 6.
C. frequency stability, good frequency characteristic product at present most of the controller switch frequency in about 10 KHZ, which requires the products of high frequency performance is good, for polyester film capacitors and electrolytic capacitor, this requirement is a difficult problem.
D. no polarity, can withstand the reverse voltage film capacitor electrode is nanoscale metal deposition on the membrane, the product has no polarity, so is very convenient for users, do not need to consider the question is negative; For electrolytic capacitors, if the reverse voltage of more than 1.5 times Un is added to the electrolytic capacitor, the internal chemical reaction of the capacitor will occur. If the voltage lasts long enough, the capacitor will explode, or the electrolyte will leak as the internal pressure of the capacitor is released.
E. The rated voltage is high and there is no need for series and balance resistance in order to improve the output power. The bus voltage of hybrid and fuel cell vehicles has a tendency to improve continuously. Now in the market for motor typical values provided by the battery voltage 280 v, 330 v and 480 v, different matching capacitor manufacturer is different, but generally is can choose such as 450 v, 600 v, 800 v, mF capacity from 0.32 to 2 mF, and electrolytic capacitor is not higher than the rated voltage 500 v, so when the bus voltage is higher than 500 v, the system only by electrolytic capacitor in series to improve the withstand voltage of capacitor Banks. This not only increases the volume and cost of the capacitor bank, but also increases the inductance and ESR in the circuit.
F low ESR, through strong resistance to ripple current film capacitor is larger than 200 ma/u f, electrolytic capacitors by ripple current capacity to 20 ma/u f, this feature can greatly reduces the size of the need of capacitor in the system. Domestic manufacturer main products such as xiamen ferrari is 0.4 0.5 m Ω, ripple current value varies from dozens to hundreds of ampere ampere.
G. Low ESL inverter's low inductance design requires that its main components, DC - Link capacitors, have extremely low inductance. The high performance DC - Link DC filter film capacitor reduces the oscillation effect of the necessary switching frequency by integrating the bus into the capacitor module and reducing its self-inductance (< 30nh). Therefore, the absorber capacitance of parallel in the dc - link capacitor is often omitted, and the capacitor electrode is directly connected to igbt. < >
H. anti surge current ability to withstand instantaneous large current, the wave of cutting technology and capacitance coated thicken edge technology, can improve products surge current temperature and mechanical shocks. I. The non-aging properties of long-lived films determine the long life of the thin-film capacitor, especially at the rated voltage and the rated temperature, which is greater than 100,000 hours. If the average 30Km/H is averaged, the life span can be 450000Km, and the lifetime of the capacitor is sufficient for the mileage of the car.