Many electric vehicle (EV) power electronics systems use silicon carbide (SiC) and gallium nitride (GaN) devices. These wide-bandgap (WBG) semiconductors enable significantly higher switching frequencies and power densities than silicon insulated-gate bipolar transistors (IGBTs).
SiC and GaN introduce broadband electromagnetic interference (EMI) challenges across conducted and radiated emissions testing, shielding, grounding, and high-frequency measurement. This article reviews how EMI testing is evolving to address those issues in EV power architectures.
Why wide-bandgap devices change the EMI problem
As shown in Figure 1, SiC and GaN outperform silicon across the key material properties that drive faster switching speeds and broader EMI spectra.
SiC and GaN transistors can switch with rise and fall times under 20 nanoseconds (ns) in EV traction designs. These steep edges push harmonic energy well above 10 MHz, extending EMI concerns into frequency ranges addressed by conducted, radiated, and immunity testing.
For example, an EV inverter operating at a 20 kHz switching frequency can become a significant EMI source from roughly 50 kHz to 50 MHz as large di/dt and dV/dt transients drive energy into higher harmonics.
These fast transitions can also increase common-mode noise relative to IGBT-based designs. Parasitic capacitances between switching nodes and chassis couple common-mode currents into the high-voltage (HV) bus and motor phase cables, turning them into potential radiating structures.
These coupling paths reduce the margin available for meeting formal EMI limits and electromagnetic compatibility (EMC) requirements, even when the standards themselves have not changed as much as the devices. As a result, simulations targeting parasitic coupling paths and filter effectiveness now enter the design flow before formal EMC testing begins.
Conducted emissions: test configurations and filter design
EV conducted emissions testing centers on CISPR 25 methods and OEM-specific requirements. Measurements typically extend from 150 kHz into the tens of megahertz and, depending on the method, up to 108 MHz.
WBG switching edges generate significant noise above 10 MHz, where resonances can subsequently contribute to radiated failures during validation. Pre-compliance workflows increasingly extend frequency sweeps beyond the required range before full antenna-based testing.
As shown in Figure 2, CISPR 25 defines two primary conducted emissions methods: line impedance stabilization network (LISN)-based voltage measurement and current-probe measurement on harnesses.
Both require probes, LISNs, and receivers with sufficient bandwidth to maintain accuracy with WBG transition speeds.
Test bench configuration is just as important as measurement equipment. Laboratory power supplies with internal Y-capacitors to earth can create unintended common-mode paths that distort measured EMI from onboard chargers and dc-dc converters. To avoid those artifacts, many test setups use isolated sources or dedicated line filtering. This configuration discipline is especially important during filter validation.
Filters must provide high-frequency common-mode and differential-mode attenuation while withstanding full HV bus conditions and peak traction currents without saturation. This creates a design constraint for Y-capacitors. Because IEC and OEM specifications limit HV-to-chassis leakage current, filter designers cannot simply increase capacitance to extend high-frequency attenuation.
High-inductance common-mode chokes and multi-stage LC networks tuned with realistic parasitic models help compensate for leakage-current limits on Y-capacitance. In WBG designs, parasitic capacitance, mutual inductance, and PCB layout coupling paths frequently dominate residual conducted EMI. Bench validation with spectrum analyzers and time-domain oscilloscopes is essential for identifying these effects.
Radiated emissions and near-field diagnostics
Radiated emissions testing under CISPR 25 spans 150 kHz to 2.5 GHz at the vehicle and component levels. WBG harmonics and enclosure resonances in the 30 MHz to 300 MHz range are common sources of compliance risk. Because chamber time is expensive and late-cycle remediation can add significant program cost, many pre-compliance workflows now rely on near-field scanning of boards, modules, and harnesses with electric-field and magnetic-field probes before far-field antenna measurements.
Near-field H-field and E-field probes help separate current-driven and voltage-driven emissions sources. H-field probes identify high di/dt loop-current hotspots, while E-field probes identify high dV/dt nodes. This distinction helps determine whether mitigation should focus on reducing loop area, modifying return paths, adding shielding, or reducing node capacitance.
Near-field scanning helps identify cable-related radiation paths. Traction inverter HV cables and motor phase conductors can carry common-mode currents excited by WBG switching transitions, producing substantial radiation even when differential-mode currents are well filtered.
Radiated emissions can also originate from enclosure apertures and poorly bonded seams that behave as slot antennas. Practical design rules limit the longest dimension of any opening to well below one-twentieth of a wavelength at the highest relevant frequency, leaving very small permissible gap dimensions for WBG harmonic spectra. For cable-related emissions, lossy ferrite common-mode chokes placed at cable ends, where antenna impedance is lowest, help reduce radiation in the 10 MHz to 300 MHz band.
Shielding effectiveness and grounding strategies
Many HV harnesses near EMI-sensitive low-voltage electronics use 360-degree shield terminations at connector backshells. Single-ended, one-point shield terminations become ineffective above a few hundred kilohertz, where WBG inverter harmonics are strongest.
Shields must connect as part of the enclosure structure rather than function as high-frequency current return paths. Routing return currents through the shield causes it to behave as a radiating element.
Thin, highly conductive shields provide high-frequency E-field containment when bonded to chassis with low-inductance connections around the full perimeter. EMC test programs increasingly verify shield bonds around the perimeter rather than relying on assumed performance from spot contacts.
Some EV architectures place WBG power stages near sensitive low-voltage electronic control units (ECUs). This proximity requires formal analysis of common-mode coupling paths from the HV bus through device and cable parasitics to chassis and into low-voltage systems. OEMs define bonding points between HV returns, low-voltage grounds, and chassis to control loop areas and transient voltage differences.
The same return-path discipline applies at the PCB level. Solid, continuous ground planes minimize loop inductance and H-field radiation in WBG converter designs. Split planes remain appropriate only where galvanic isolation requirements force a separation. When splits are necessary, a single well-defined connection point helps prevent large ground loops that increase conducted and radiated emissions.
High-frequency measurement and design correlation
Capturing the fast, high-energy switching events of WBG devices requires higher probe bandwidth and common-mode rejection than IGBT-era test equipment typically provides.
Standard probes and current clamps can underestimate high-frequency content, producing inaccurate EMI data that leads to under-designed filters and grounding strategies. As shown in Figure 3, double-pulse testing of WBG devices, combined with high-bandwidth pulse-isolated probes, characterizes voltage overshoot, ringing, and layout-induced common-mode currents that translate into EMI compliance risk.
These measurements are especially useful when correlated with frequency-domain emissions data. Correlation allows engineers to link gate-drive parameters, snubber values, and PCB layout decisions to specific emissions signatures. An integrated debug workflow identifies which design variables affect compliance margins before formal CISPR and ISO test submissions.
Even with frequency-domain correlation, accurately predicting absolute emissions levels remains challenging because small parasitic variations and environmental coupling can dominate results.
To address this limitation, engineers use electromagnetic and circuit co-simulation to evaluate trends and filter options rather than predict exact emissions levels. Emerging machine learning frameworks may further reduce full compliance test iterations by monitoring and predicting EMC behavior from inverter operating data.
Summary
EMI testing for EV power electronics with SiC and GaN devices emphasizes wider frequency coverage, earlier pre-compliance workflows, and tighter time/frequency-domain correlation.
Conducted testing extends beyond formal CISPR ranges to identify WBG resonances before they contribute to radiated failures. Near-field scanning isolates high di/dt loops and high dV/dt nodes before chamber testing. Shielding and grounding strategies prioritize 360-degree terminations, perimeter-verified bonds, and common-mode path analysis.
This evolution reflects the core WBG challenge: broadband, nanosecond-transient EMI requires design-phase characterization rather than end-of-cycle compliance testing.
References
- Optimizing Wide-Bandgap Semiconductor Switches for EMI Compliance, Rohde & Schwarz
- EV EMC design: shielding, grounding, and CISPR 25, PatSnap
- EMC Tips and Tricks for WBG Devices, Wurth Elektronic
- Power Modules: One Shortcut to EMI Compliance, Wolfspeed
- Addressing EMI Conducted Emissions Challenges in EVs with GaN-Based OBCs, TI
- Silicon Carbide and Gallium Nitride Bring New Challenges for Semiconductor Test, Teradyne
- How to Test Wide-Bandgap Semiconductors, Keysight
- Wide-Bandgap Semiconductors: Performance and Benefits of GaN Versus SiC, TI
- Effective PCB Layout Techniques to Minimize EMI from ESD Events, AllPCB
- Mastering EMI Control in PCB Design: Crosstalk Prevention for Better EMI, Altium
