November 2010

Power capacitor chips for e-mobility

Space-saving DC link solution

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Jointly with Infineon Technologies, EPCOS has developed two new reference designs for inverters in HEVs and EVs. They use space-saving PCC™ solutions from EPCOS as DC link capacitors.

Infineon Technologies has developed two reference designs for IGBT inverters for use in hybrid and fully electric drives in automotive electronics: HybridPACK™1 for mild hybrid drives and HybridPACK™2 for full-electric and full-hybrid drives.

The HybridPACK1 with an output of up to 20 kW is used to support the internal combustion engine. As a rule, a combined starter generator is located between the engine and transmission system and is connected directly to the crankshaft. It supports the internal combustion engine and increases its torque, especially when accelerating. Some concepts enable exclusive use of the electric drive for short distances.

Infineon Technologies offers the HybridPACK2 for high powers, including use for purely electric traction. It has an output of up to 90 kW (Figure 1).

Figure 1: HybridPACK2 evaluation kit with a PCC
The HybridPACK evaluation kit from Infineon Technologies can be used to develop EV drives of up to 90 kW. In addition to controllers and software, it also contains the PCC DC link capacitor from EPCOS.

For both concepts, Infineon supplies evaluation kits inclusive of controllers, software and DC link capacitors. They are based on the proven PCC technology. The table below shows the key technical data of the PCCs.

EPCOS has been successfully developing PCC technology for several years, especially for use in hybrid technology or as compact DC link capacitors for frequency converters. A particular advantage of this technology is the compact dimensions of the capacitors. Conventional winding technologies produce regular or flattened round windings. This is not the case for PCCs: they use stacked winding technology. Polygon winding machines create a completely flat, rectangular and creaseless capacitor winding, so that the volume fill factor of the implemented capacitor is nearly 1. Another advantage of this technology is its adaptability: its dimensions can be varied over very broad ranges and thus adapted optimally to the design of the frequency converter. The electrical and mechanical terminals – the busbars – can also be matched ideally to the requirements of the system. This allows PCCs to be mounted directly onto the IGBT modules. On the one hand, this considerably reduces assembly costs and, on the other, no separate boards are required as for other DC link solutions.

Figure 2: PCC from EPCOS for hybrid drives
In addition to their compact case size and volume fill factor of nearly 1, PCCs also feature busbars that are matched precisely to the IGBT modules. This results in very low ESL values and minimum assembly costs.

Specifically for hybrid drives, EPCOS has also developed a PCC which is arranged in a ring configuration in the bell housing around the starter generator (Figure 3).

Figure 3: Ring-shaped PCC
In this configuration, the PCC is arranged in a ring directly around the starter generator.

The short terminal connections and internal structure of the capacitors produce a very low-inductance design. Depending on the capacitor design, values of only a few nH are attained. This is particularly important with the steep switching edges of converters in order to avoid excess voltages. As a rule, therefore, additional protective circuitry for the IGBT with snubber capacitors can be dispensed with.

The high peak current capability of the capacitors is also important. Especially with start-stop cycles of the kind occurring in urban traffic, peak currents can reach a multiple of the rated current. A DC link capacitor must supply these currents over its entire operating life without sustaining damage. Figure 4 shows a typical driving cycle of 1800 seconds. The mean current critical for the operating life is somewhat above 100 A.

Figure 4: Load diagram for the DC link

The short-term peak currents are around 325 A. The new PCC generations can withstand peak currents from 1200 to 2000 A without sustaining damage.

With an expected operating life of 15,000 hours and an upper continuous operating temperature of 110 °C (up to 125 °C for brief periods), PCC technology is especially suited for automotive electronics.

This concept also offers outstanding safety and reliability: the capacitors are self-healing, meaning that breakdowns of the film at overload do not produce short circuits or lead to the destruction of the capacitor. The fact that the capacitors are not filled with flammable or acidic fluids is a crucial factor in the event of accidents.

All these factors make the PCC an advanced and optimal DC link solution for inverters in e-mobility applications as well as for compact frequency converters in industrial electronics.

Table: Technical data of the PCCs for HybridPACK

Parameter / TypeB25655J4307K001B25655J4507K005
Suitable forHybridPACK1HybridPACK2
Rated voltage [V DC]450450
Capacitance [μF] ±10 %300500
Rated energy [Ws]3050
Max. continuous current [A]80120
Operating temperature [°C]-40 to +110-40 to +110
ESR max. [mΩ]810
ESL max. [nH]2515
Dimensions [mm] 140 x 72 x 50237 x 72 x 50
Operating life [h]15,00015,000



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