Ansys EMC Plus helps EV Project Mitigate EMC Risk

A Colorado company is saving time and money by using Ansys EMC Plus (formerly EMA3D® Cable) for electromagnetic compatibility (EMC) analysis early in the design process. Lightning eMotors was founded in 2008 and is based in Loveland, Colorado. The company provides specialized and sustainable driving options, including complete zero-emission all-electric medium- and heavy-duty vehicles. This includes delivery trucks, shuttle buses, passenger vans, and repowered transit buses. In 2019, Lightning eMotors added a line of charging stations to its portfolio, making it easier for fleets to transition toward electric. Now the company is working on developing a mobile battery vehicle charger (MBVC). The MBVC has the capability to relocate to almost any area and bring enough on-board battery storage to charge up to five electric vehicles.

Design Process

During the early stages of the process, designers had some concerns, which drove the desire for early EMC testing.
Concerns included:

1. The DC/DC converter selection was ideal in terms of cost and performance but came with potential concerns about electromagnetic noise based on CISPR 25 testing.
2. Knowledge that high voltage/ high power systems of this kind have been known to cause self-compatibility issues on other EVs, with interference to CAN lines sometimes rendering a system inoperable.
3. The need to avoid impact to schedules if an EMC problem was discovered on a physical prototype, requiring extensive on-site troubleshooting, and potentially costly re-designs.

Lightning eMotors contacted EMA about using Ansys EMC Plus to analyze the MBVC system and determine potential threats and mitigations. A design of the MBVC can be seen in Figure 1.

Figure 1. Trailer shown with enclosure skeleton, minus enclosure covers.

Testing

To get started, EMA first created a simplified model of the MBVC using CAD provided by Lightning eMotors. This model was used for simulation in Ansys EMC Plus.

Cable harness parameters were set to capture the potential noise level of the threat and immunity concerns of the victim. The threat was a shielded HV cable carrying high frequency noise from the DC/DC converter. The victim was co-routed or nearby low voltage CAN lines. The stimulus on the threat cable was chosen to replicate the levels found in component level CISPR 25 testing. These steps took approximately 48 hours of work to develop.

Using realistic threat and victim parameters and close co-routing of the cables, EMA confirmed that there was a real threat to the CAN network of the MBVC if HV and LV cables are routed carelessly. The results showed voltages up to 22 dB above the interference threshold in the 100 kHz- 100 MHz range appearing on the twisted CAN lines.

Knowing that a threat existed, EMA tested several possible solutions to find the best design. These included:
• Separating the threat and victim cables by routing HV near the floor and CAN near the ceiling. This reduced the noise but not to acceptable levels.
• Routing the CAN along the ceiling with a well-bonded metal cable tray for support, offering potential shielding between CAN and HV. This also reduced the noise but not sufficiently.
• Routing the HV cable through and under an aluminum floor panel. This actually made the noise worse due to antenna effects where the cable passed through the hole in the floor.
• Routing HV cable under an aluminum floor panel using a through-bulkhead connector. This method did eliminate the noise, but the HV connector was not a cost-effective solution.
• Limiting the distance of parallel routing between the HV and CAN lines. This reduced noise, but not in the case where HV and CAN lines terminated on the same electronics box.

After several failures, there was a successful solution. This time, the HV cables were routed through a metal tunnel on the aluminum floor of the MBVC, a diagram is shown in Figure 2. In this configuration CAN lines could be routed as close to the HV cables as needed. The results showed that as long as the cables remained outside of the HV tunnel the high frequency noise remained below the interference threshold.

Figure 2. Successful layout of victim cables and HV line.

Conclusion

Using CAD and less than two months of calendar time, EMA was able to use Ansys EMC Plus to determine that there was a real threat to the MBVC development project. EMA was able to quickly test multiple design solution options to find one that was low-cost and relatively easy to implement. This process happened in parallel with the normal design and production schedule. Completing EMC testing early avoided a potentially severe cost and schedule impact during the prototype phase. It also allowed the project to proceed with using the original DC/DC converter choice, even if that unit presented some EMC challenges.

The White Paper on this project is available here: Lightning eMotors WP.

To learn more about Ansys EMC Plus and how it can help with your projects, click here.