Application analysis of film capacitors in new energy vehicles

New energy vehicles refer to the use of unconventional vehicle fuels as power sources. New energy vehicles include hybrid vehicles, pure electric vehicles, fuel cell electric vehicles, hydrogen engine vehicles, and other new energy sources (such as high-efficiency energy storage, dimethyl ether). ) Various categories of products such as automobiles.

Motor, battery and motor control technology are the three cores of new energy vehicles. The core of motor control technology is inverter technology that requires high-efficiency motor control. Inverter technology for high-efficiency motor control requires a powerful IGBT module and a matching DC support capacitor.

Technical advantages of film capacitors:

Early DC support film capacitors used electrolytic capacitors. With the development of film capacitor technology, especially the development of base film technology and the emergence of metallization using segmentation technology, the volume of film capacitors has become smaller and smaller. , The product’s withstand voltage level is still maintained at a considerable level. Now more and more companies use high-temperature polypropylene film capacitors as DC support capacitors. A typical example is the improvement of Toyota’s RIUS models; while domestic car companies are typical Representatives are BYD F3DM and E6, both of which use film capacitors as DC support capacitors. The filter capacitor used in the first generation Toyota Prius was an electrolytic capacitor, and since the second generation, film filter capacitor banks have been used.

A. Good product safety and strong overvoltage resistance

Since the film capacitor has a self-healing phenomenon, and the design of the film capacitor is in accordance with the 1EC61071 standard, the capacitor's anti-surge voltage capability is greater than the rated voltage of 1.5, and the capacitor adopts the split film technology, the capacitor theoretically will not cause short circuit breakdown Phenomenon, which greatly improves the safety of this type of capacitor, the typical failure mode is open circuit. The anti-peak voltage capability of a capacitor in a specific application is also an important indicator of capacitance. In fact, for electrolytic capacitors, the maximum allowable surge voltage is 1.2 times. This situation forces users to consider the peak voltage instead of the nominal voltage.

B. Good temperature characteristics, the product temperature range is wide, ranging from -40C to 105C

The high temperature polypropylene film used in DC support film capacitors has temperature stability that polyester film and electrolytic capacitors do not. With the increase of temperature, the overall capacity of polypropylene film capacitors decreases, but the rate of decrease is very small, about 300PPM/C; while the polyester film capacity changes with temperature regardless of whether it is in the high temperature stage or the low temperature stage. It is much larger, +200~+600PPM/C.

C. Stable frequency characteristics, good high-frequency characteristics of the product

At present, the switching frequency of most controllers is about 10KHZ, which requires good high-frequency performance of the product. For electrolytic capacitors and polyester film capacitors, this requirement is a problem.

D. No polarity, can withstand reverse voltage

The electrode of the film capacitor is a nanometer metal vapor-deposited on the film. The product has no polarity, so it is very convenient for users, and there is no need to consider the issue of positive and negative electrodes; for electrolytic capacitors, if it exceeds 1.5 When a reverse voltage of times Un is applied to an electrolytic capacitor, it will cause a chemical reaction inside the capacitor. If this voltage lasts long enough, the capacitor will explode, or the electrolyte will flow out as the pressure inside the capacitor is released.

E. High rated voltage, no need for series and balance resistors

In order to increase the output power, the bus voltage of hybrid vehicles and fuel cell vehicles has a trend of increasing. The typical battery voltages currently available on the market for motors are 280V, 330V and 480V. The matching capacitors vary from manufacturer to manufacturer, but they generally choose 450V, 600V, 800V, and the capacity ranges from 0.32mF to 2mF. The rated voltage of the electrolytic capacitor is not higher than 500V, so when the bus voltage is higher than 500V, the system can only increase the withstand voltage level of the capacitor bank by connecting electrolytic capacitors in series. 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, strong ability to withstand ripple current

The film capacitor is greater than 200mAμF, and the electrolytic capacitor has a ripple current capacity of 20mAμF. This feature can greatly reduce the capacity of the capacitor required in the system. The main products of domestic manufacturers are currently 04-0.5m2, and the maximum ripple current value ranges from tens of amperes to hundreds of amperes.

G. Low ESL

The low-inductance design of the inverter requires extremely low inductance for its main component, the DC-Link capacitor. The high-performance DC-Link DC filter film capacitor minimizes its self-inductance (<30nH) by integrating the bus into the capacitor module, greatly reducing the oscillation effect at the necessary switching frequency. Therefore, the absorption capacitance connected in parallel to the DC-Link capacitor_ is often omitted, and the capacitor electrode is directly connected to the GBT.

H. Strong anti-surge current capability

Able to withstand instantaneous large currents, using wave slitting technology and capacitor coating thickening edge technology can improve the product's surge current temperature and mechanical shock ability

I. Long service life

The film’s resistance to aging determines the long life of the film capacitor, especially under the rated voltage and rated temperature, the service life is more than 15000 hours; if the average 30Km/H is used, the life can be 450,000Km, and the life of the capacitor The mileage of the car is sufficient.

Film sensor:

This kind of Film sensor has many functions in our daily communication. In our actual daily life, the role of electric power in our various industries is also very extensive. Now, the role of the transportation industry at this stage of ours is very broad, so this film capacitor is also involved in these fields. For example, our trains are more popular now.

The main reason for this is that the moving speed of the train is very fast. Moreover, the technology of the railway industry can also be developed rapidly in recent years, and it is an industry with very broad prospects. Therefore, the film sensor plays an important role in the electrification of railways. What's more, what makes us pay more attention is that some industries, such as the hybrid electric vehicle industry, are also more important for the development of these industries.

to sum up:

The high-performance DC-LINK film capacitor is a capacitor that uses a new manufacturing process and metal seven film technology. It increases the energy density of the traditional film capacitor, that is, the volume of the capacitor is also reduced. On the other hand, it meets customers' flexible size requirements by integrating capacitor cores and busbars, which not only makes the entire inverter module more compact, but also greatly reduces the stray inductance in the application circuit and improves the performance of the circuit. More superior. The circuits used in electric vehicles are designed with high voltage, high effective value current, overvoltage, reverse voltage, high peak current, and long life requirements. Film capacitors are undoubtedly the best DC support capacitors for electric vehicles. Best choice.