Vishay – How to implement a reliable, long-life DC link capacitor bank in high-voltage power circuits

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The functional requirement for an electric vehicle’s fixed battery charger is to charge the battery in the shortest possible time, while minimising battery ageing and maintaining safe operation.

This requires accurate control of high amounts of power: depending on battery capacity, an overnight recharge can require a charger capable of providing up to 30kW of power. A fast charge at a high-voltage charging station, replenishing the battery to 80% of its capacity, can use as much as 250kW, as shown in Figure 1.

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Fig. 1: Nissan LEAF charging at the Freedom Station in Houston, Texas. This is an eVgo Network station with both Level 2 and DC fast chargers. (Image credit: eVgo Network under Creative Commons licence)

Such an application calls for components which provide reliable performance during the high-power part of the battery’s charging cycle. A key function in the power circuit of the fixed battery charger is provided by the DC link capacitor bank. It provides a stable DC voltage for the switching power circuit that controls the rate of charge; at the same time, it is the low-impedance return path for the switching currents from that same circuit. Failure of the DC link capacitor bank renders the battery charger powerless.

To meet this need for robust, high-power capacitance, Vishay Intertechnology has introduced the new 299 PHL-4TSI series of 400V and 450V snap-in, four-terminal aluminium electrolytic capacitors in a large can, as shown in Figure 2. They offer improved ripple-current capability at an ambient temperature of 105°C, with a useful life of 5,000h. The characteristics of this series of capacitors make it well suited for use in fixed battery chargers as well as other high-power applications.

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Fig. 2: The 299 PHL-4TSI capacitor from Vishay

The high ripple-current rating, which ranges from 2.45A to 6.77A at 100Hz, can enable the designer to reduce component count when ripple current is the most important parameter in the specification of the capacitor bank. The use of a so-called extended-cathode construction ensures that even higher ripple currents can be handled when the parts are cooled with forced air or via a heat-sink.

The long useful life of 5,000h is equivalent to 24/7 operation over a period of more than 20 years, provided that the ambient temperature does not exceed 65°C. For cyclic operation, as in a fixed battery charger, the maximum ambient temperature can be higher while still achieving this 20-year lifetime.

Case size (D x L)35mm x 50mm to 45mm x 100mm
Capacitance Range470μF to 2,200μF
Capacitance Tolerance±20%
Ripple-current Range at 100Hz and 105°C2.45A to 6.77A
Rated Voltage Range400V to 450V
Operating-temperature Range-40°C to 105°C
Useful life at 105°C5,000h

The 299 PHL-4TSI series capacitors, available in can sizes ranging from 35mm x 60mm to 45mm x 100mm, have four-terminal snap-in pins suitable for soldering. This pin configuration not only provides keyed polarity, but also better mechanical stability than the two-terminal snap-in pin configuration used on capacitors with smaller can sizes.

The solderable pins provide an additional benefit: manufacturers may choose to build a DC link with screw-terminal capacitors that are hand-mounted on a bus bar. But worthwhile cost savings are gained when the same DC link is built with these large-can, four-terminal snap-in capacitors from Vishay, placed on a high-current PCB and mounted using a wave solder process.

With the new 299 PHL-4TSI series, Vishay Intertechnology provides designers with a new solution to tackle the challenges in demanding power electronics applications.

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