EVs drive power capacitor designs

Vehicle electrification is the biggest growth driver for capacitors used in power converters, according to a recent report from Yole Intelligence, part of Yole Group. The power capacitor market share for hybrid and fully electric vehicle (xEV) applications is expected to reach 44% by 2028, up from 29% in 2022.

The overall power capacitor market is forecast to reach $7 billion by 2028, up from $4.9 billion in 2022, growing at a compound annual growth rate (CAGR) of 5.9%, according to Yole. The largest markets by revenue include EV, industrial systems and photovoltaic applications. The CAGR for the EV segment is pegged at 13%.

Yole reports that capacitors represent about 10% of the total power converter costs in 2022. Film capacitors, which are the most expensive, are primarily used for high power levels. This translates into higher capacitor costs as the system’s power level increases, requiring more of these passive components.

The report, Capacitors for Power Converters 2023, finds that the three main applications are DC link, snubber and I/O filters. Film capacitors are the mainstream for DC link, though some OEMs will use electrolytic capacitors in markets where there is severe cost pressure, according to Yole analysts. In addition, film capacitors along with multilayer ceramic capacitors (MLCCs) are typically used in snubber applications, while film and ceramic capacitors are typically used in I/O filters.

In general, MLCCs target low- to medium-voltage ranges, such as home appliances and mild hybrid electric vehicles, and film capacitors are used for medium- to high-voltage ranges such as fully electric vehicles, rail and wind.

In the xEV market, automotive OEMs are driving the need for several improvements in power capacitor technologies due to challenging requirements for high power density, high integration and high voltages. In addition, components also need to withstand high temperature (including junctions) and high vibration environments as well as operate reliably under frequent thermal cycling.

Another trend is miniaturization. There is a growing need for compact capacitors in xEV applications, said Yole. The roadmap (below) shows polypropylene film capacitors for power inverters shrinking to 10 × 37.5 mm.

Capacitor technology roadmap for power converters (Source: Yole Développement, 2022)

One of the biggest areas of innovation is DC-link film capacitors, including for EV DC chargers, a big growth segment for power capacitors with a CAGR of about 20% from 2022 to 2028, reaching $155 million by 2028.

CDE Series 944L Low Inductance Film Capacitors

One example is the new 944L series of high-current DC-link film capacitors from Cornell Dubilier Electronics, Inc. These capacitors can be used in Level 3 EV chargers as well as green energy inverter systems. These applications call for power converters that deliver more power in a smaller footprint.

The 944L series leverages large diameter, non-inductive windings with low-inductance internal buss connections, which delivers equivalent series inductance (ESL) values ranging from 10 to 15 nH. In addition, thanks to low-loss polypropylene dielectric with metalized electrodes optimized for applications in fast-switching power inverters, the capacitors offer ripple current ratings of up to 90 A at an ambient temperature of 55°C.

The film capacitors are available in capacitance values from 33 to 220 µF, with voltage ratings of 800, 1000, 1200 and 1400 VDC. They meet a 5,000-hour life test @ 85°C with rated voltage applied, translating into an expected lifetime of 100,000 hours or greater with ripple current or ambient temperature derating.

They are housed in a vibration-resistant UL94V-0-rated plastic case with integral mounting flanges and standard termination options include M8 threaded studs or M5 threaded inserts made of tin-plated brass. All case sizes offer an 84.5 mm diameter with heights of 40, 51 and 64 mm, depending on the rating.

Vishay’s MKP1848Se DC-Link capacitor (Source: Vishay Intertechnology)

Vishay Intertechnology, Inc. extended its film capacitor family with a low-profile, AEC-Q200 qualified DC-Link metallized polypropylene film capacitor for high-humidity automotive applications. The radial capacitor is suited for space-constrained automotive applications, including HVAC systems, on-board and inductive battery charging systems, air conditioning compressors, and motor drives for EVs and plug-in hybrid electric vehicles.

The Vishay Roederstein MKP1848Se DC-Link is touted as the first such device to withstand temperature humidity bias (THB) testing of 60°C/93% relative humidity for 56 days at rated voltage. The automotive-grade capacitor is available in four heights — 12 mm, 15 mm, 18 mm, and 24 mm — and 12 standard dimension options.

The capacitor offers a capacitance range from 1 µF to 75 µF and low equivalent series resistance (ESR) down to 3 mΩ. The RoHS-compliant device provides high ripple current capabilities up to 27 A and rated voltages of 500 VDC, 700 VDC, 900 VDC and 1200 VDC at 85 °C.

TDK’s EPCOS B43652 series of snap-in aluminum electrolytic capacitors (Source: TDK Corp.)

In some cases, as noted by Yole’s report, aluminum electrolytic capacitors can be used in the DC link. One recent example is the EPCOS B43652 series of snap-in aluminum electrolytic capacitors from TDK Corp., which can be used in the DC-link circuitry of onboard chargers in xEVs.

The compact snap-in capacitors offer 85% increased ripple current capability, up to 11.28 A at 100 Hz and 85°C. This is thanks to a new design, said TDK, with a reinforced bucket bottom for improved active cooling. “In conventional capacitors, the valve is located at the bottom of the bucket, but in the new design, it is on the side,” said the company.

 The capacitors are designed for a maximum rated voltage of 450 VDC with a capacitance range from 270 µF to 820 µF with seven types. The capacitance values from 270 µF to 560 µF are offered in different dimensions, which increases design flexibility, said TDK. Dimensions range from 25 × 40 mm to 35 × 55 mm (D × H), depending on the capacitance value. The AEC-Q200 qualified devices are RoHS compliant.

Kemet’s AAR80 series of aluminum electrolytic capacitors (Source: Yageo)

Another aluminum electrolytic capacitor aimed at the DC link is Kemet Corp.’s AAR80 series. The company’s snap-in aluminum electrolytic caps have been “widely used” as a DC-link capacitor for stabilizing the output PFC DC voltage in onboard chargers and the new AAR80 caps offer the same performance with space savings, said the company.

The AEC-Q200 qualified capacitor for automotive applications delivers high capacitance, good ripple current capability and robust vibration resistance. The AAR80 series offers a capacitance range of 150 µF to 270 µF with a rated voltage of 450 VDC. The operating temperature range is -40°C to 105°C and life is rated at 2,000 hours at 105°C [(VR) and (IR) applied]. The series also can withstand high vibration up to 20 g.

In terms of design, the rectangular caps offer a shape that lends itself to modular stacking, said Kemet, and the large surface area of the case with a stainless-steel shell allows them to be easily used with heat sinks.