Advantages of film capacitor products
Early DC support film capacitors all used electrolytic capacitors. With the development of film capacitor technology, especially the development of base film technology and the emergence of metallization segmentation technology, not only the volume of film capacitors has become smaller and smaller, but the product's withstand voltage level has also remained 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 model; and typical representatives of domestic car companies are BYD F3DM and E6, both of which use film capacitors as DC support capacitors. The filter capacitors used in the first generation of Toyota Prius are electrolytic capacitors. Starting from the second generation, film filter capacitors DC-LINK capacitors have been used instead.
A. Good product safety and strong overvoltage resistance
Since film capacitors have self-healing properties and are designed in accordance with the 1EC61071 standard, the capacitor's surge voltage resistance is greater than 1.5 of the rated voltage. In addition, the capacitor uses split film technology, so the capacitor will not produce short circuit breakdown in theory, which greatly improves the safety of this type of capacitor. The typical failure mode is open circuit. In specific applications, the capacitor's peak voltage resistance is also an important indicator for evaluating capacitors. In fact, for electrolytic capacitors, the maximum surge voltage allowed is 1.2 times, which forces users to consider peak voltage rather than nominal voltage.
B. Good temperature characteristics, the product temperature range is wide, from -40C-105C
The high-temperature polypropylene film used in the DC support film capacitor has temperature stability that polyester film and electrolytic capacitors do not have. As the temperature rises, the capacity of the polypropylene film capacitor decreases overall, but the decrease ratio is very small, about 300PPM/C; while the polyester film capacity changes much more with temperature, whether in the high temperature stage or in the low temperature stage, which is +200~+600PPM/C.
C. Stable frequency characteristics, good high-frequency characteristics of the product
Currently, most controller switching frequencies are about 10K HZ, which requires the product to have good high-frequency performance. For electrolytic capacitors and polyester film capacitors, this requirement is a problem.
D. No polarity, can withstand reverse voltage
The electrodes of film capacitors are nano-scale metals deposited on thin films. The product has no polarity, so it is very convenient for users, and there is no need to consider the positive and negative poles. For electrolytic capacitors, if a reverse voltage exceeding 1.5 times Un is applied to the 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 internal pressure of the capacitor is released.
E. High rated voltage, no series and balancing resistors are required
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 provided to motors on the market are 280V, 330V and 480V. The capacitors that match them are different from different manufacturers, but generally they are 450V, 600V, 800V, and the capacity ranges from 0.32mF to 2mF. The rated voltage of electrolytic capacitors is not higher than 500V, so when the bus voltage is higher than 500V, the system can only improve the withstand voltage level of the capacitor bank by connecting electrolytic capacitors in series. In this way, not only the volume and cost of the capacitor bank are increased, but also the inductance and ESR in the circuit are increased.
F. Low ESR, strong ripple current resistance
The film capacitor is greater than 200mA/μF, and the electrolytic capacitor has a ripple current capacity of 20mA/μF. This feature can greatly reduce the capacity of the capacitor required in the system.
G. Low ESL
The low inductance design of the inverter requires that its main component, the DC-Link capacitor, has extremely low inductance. High-performance DC-Link DC filter film capacitors integrate the busbar into the capacitor module to minimize its self-inductance (<30nH), greatly reducing the oscillation effect at the necessary switching frequency. Therefore, the absorption capacitor connected in parallel to the DC-Link capacitor is often omitted, and the capacitor electrode is directly connected to the IGBT.
H. Strong surge current resistance
It can withstand instantaneous large currents. The wave cutting technology and capacitor coating thickening technology can improve the product's surge current temperature and mechanical shock capabilities.
J. Long service life
The film's non-aging characteristics determine that the film capacitor has a very long life, especially at rated voltage and rated operating temperature, the service life is greater than 15000-20000 hours; if the average is 30Km/H, it can have 450000Km in the service life, and the capacitor life is sufficient for the car's mileage.
High-performance DC-LINK film capacitors are capacitors that use new manufacturing processes and metallized film technology. They increase the energy density of traditional film capacitors, which means that the size of the capacitors is also reduced. On the other hand, it integrates the capacitor core and the busbar to meet customers' flexible size requirements, which not only makes the entire inverter module more compact, but also greatly reduces the stray inductance in the application circuit, making the circuit performance more stable. The circuit design used in electric vehicles has high voltage, high effective current, overvoltage, reverse voltage, high peak current, and long life requirements. Film capacitors are undoubtedly the choice of electric vehicles as DC support capacitors.
CRE provides professional capacitor solutions for electric cars and hybrid electric cars. Our DKMJ-AP series and DMJ-PC series offer important DC-Link filtering function in EV and HEV motor controllers. They have large energy capacitance in small physical size and wide bandgap (WGB) to fulfill your production criteria.
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