Use Off-the-Shelf EMI Filters to Simplify EV Powertrain Compliance

Modern electric vehicles (EVs) use 25 or more processors to control various aspects of their operation, from critical advanced driver assistance systems (ADAS) to less vital in-vehicle networking and entertainment systems. With such a large array of electronic systems in tight spaces, designers must address electromagnetic compatibility (EMC) certification and the risk of electromagnetic interference (EMI). A major source of EMI is the vehicle’s power system, which converts DC power from the vehicle’s batteries into high voltages and currents used to drive the EV’s motors.

The heart of the vehicle’s power system is the power inverter, which uses switching semiconductors to convert DC into motor drive waveforms. Due to the inverter’s fast switching speeds, it can generate EMI, either conducted through the power lines or radiated. Consequently, EMC certification is among the more stubborn barriers in the design of EV drive trains.

Standard off-the-shelf EMC filters

To help facilitate EMC certification, TDK has introduced the CarXield Power EMI filters for EVs. These filters offer a fully validated, cost-effective, off-the-shelf design, reducing the need for in-house development and subsequent qualification.

In practice, the CarXield filter fits between the shielded inverter and the battery (Figure 1, bottom). The motor is isolated from the inverter using a common-mode ring core (Figure 1, top and bottom). Within the inverter shield case, the positive and negative buses are bypassed to the shield via a capacitor in series with a damping resistor.

Figure 1 : The CarXield filter is placed between the shielded inverter and the battery, and a common-mode ring core is inserted between the inverter and the motor. (Image source: TDK Electronics)

The CarXield filters effectively suppress inverter interference with the battery, improving the EMI performance of the vehicle's powertrain and simplifying the regulatory compliance and certification for mid-range EVs.

CarXield filter design

The CarXield is a three-stage filter comprising common-mode chokes and X and Y capacitors (Figure 2). The common-mode chokes (also called current-compensated chokes) suppress common-mode interference. X capacitors are connected between the power buses to reduce differential-mode interference, while Y capacitors are connected between each bus and ground to suppress common-mode noise.

Figure 2: The CarXield three-stage filter comprises common-mode inductors and Y capacitors to reduce common-mode interference and noise, and X capacitors to minimize differential interference. (Image source: TDK Electronics)

The chokes use nanocrystalline core technology, ensuring superior magnetic performance and low power losses. The design includes a passive discharge circuit to safely reduce stored voltage when powered off.

The CarXield filters, designed for chassis mounting, are housed in a compact metal case with a plastic cover and measure 5.5 × 2.3 × 1.97 inches (in.) (140 × 59 × 50.0 millimeters (mm)). They are available with integral busbars (Figure 3, left) or without (Figure 3, right).

Figure 3: The CarXield filters are housed in a metal case with a plastic cover with (left) or without (right) integral busbars. (Image source: TDK Electronics)

Busbars are secured from the top using four screws. Multiple ground lugs support exceptional grounding.

The filters are suitable for 500 and 1000 volt systems. For example, the B84252A0200A000 line filter is a 500 volt, 200 ampere (A) DC steady-state device at 85°C. It will handle peak currents of 350 A for up to 60 seconds (s) and 600 A for 10 s.

The B84252B0400A000 is rated for 1000 volts and a steady-state current of 400 A at 85°C. It can handle peak currents of 650 A for 60 s or 1000 A for up to 10 s.

Both filters have bus bars and are rated for an ambient temperature range of -40 to 85°C. Resistive self-heating under load is minimized by a typical DC resistance (DCR) of only 0.1 milliohm (mΩ).

Filter performance

The effectiveness of the filter is measured by its insertion loss versus frequency, which is plotted as attenuation in decibels versus frequency (Figure 4).

Figure 4 : Shown is a comparison of the insertion loss versus frequency for the B84252A0200A000 and B84252B0400A000 filters. (Image source: TDK Electronics)

Both the B84252A0200A000 and B84252B0400A000 filters exhibit similar insertion-loss characteristics, with low attenuation between 10 and 100 kilohertz (kHz). The attenuation increases significantly at frequencies above 1 megahertz (MHz).

The CarXield filter series complies with automotive reliability and endurance standards. The filters are certified to AEC-Q200 and are validated against MBN LV 124 profiles. These certifications decrease development time and reduce design risks compared to in-house designs.

Conclusion

EMI is a barrier to EMC certification in EV design. The TDK CarXield filter series suppresses EMI. Their high-performance, standardized design and packaging meet the needs of mid-sized EVs. Additionally, these filters offer packaging flexibility, with an option for busbars.