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Top 5 EMI Design Lessons for Battery Energy Storage Systems

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Battery Energy Storage Systems (BESS) are becoming the backbone of modern energy infrastructure. As utilities, industrial facilities, and residential installations demand more flexibility in storing and dispatching renewable power, the scale and complexity of BESS technology continue to grow.

But with this growth comes a major challenge: electromagnetic interference (EMI) compliance.

High-voltage, high-current switching architectures — especially those operating up to 1500 VDC or 1000 VAC — generate significant conducted and radiated noise. For manufacturers trying to meet both Class A industrial and Class B residential compliance limits, EMI can quickly become a costly roadblock.

At Astrodyne TDI, we’ve helped numerous clean energy OEMs design EMI solutions for battery storage applications. In a recent webinar, Anand Awasthi, Director of Product Marketing for our EMI Filters Business Unit, shared real-world insights on how to overcome these challenges.

Here are the top five EMI design lessons for BESS developers.

Solution The right filter + layout + shielding. (3)

1. Start EMI Testing Early: Don’t Wait for Final Prototypes

A common mistake in BESS design is treating EMI as a box to check at the end of development. Many teams build complete prototypes, send them to a compliance lab, and only then discover emissions 20–40 dB above the limit lines. At that point, the fixes require redesigns, retesting, and months of delay.

Best practice:

  • Integrate EMI testing into early design stages.

  • Use pre-compliance scans at subsystem levels (inverters, DC/DC converters, battery management units) to identify noise sources.

  • Build margin into the design by assuming real-world variance will increase emissions compared to ideal lab setups.

Takeaway: The earlier you identify the noise, the easier and less expensive it is to fix.

2. Understand Coupling Paths in High-Voltage Systems

In BESS, the sheer scale of voltage and current means that EMI problems extend beyond switching frequency harmonics. Common-mode noise coupling into long DC busbars, AC lines, and even the system enclosure can dominate the emissions profile.

Key issues include:

  • Stray capacitance between high-voltage conductors and chassis.

  • An imbalance in the current return paths causes common-mode leakage.

  • Grounding schemes that unintentionally create resonant loops.

Design strategies:

  • Use short, controlled conductor layouts to reduce parasitics.

  • Ensure balanced current return paths wherever possible.

  • Apply shielding and bonding to minimize radiated noise from enclosure seams.

Takeaway: Compliance failures often come from the way noise escapes the system, not just the noise generated inside it.

3. Don’t Oversize Your Filters: Target the Problem Frequencies

When facing compliance failures, many OEMs resort to brute-force filters: significant, multi-stage components with excessive attenuation. While these may solve the immediate problem, they often:

  • Increase footprint and reduce packaging flexibility.

  • Add thermal losses, lowering system efficiency.

  • Drive unnecessary cost into the bill of materials.

Astrodyne TDI has seen better results with iterative, frequency-targeted filter design. Instead of over-filtering the entire spectrum, focus on the frequencies that are failing. In one BESS project, a properly tuned custom filter achieved a 60 dB reduction at the problem frequency, while keeping size and cost within budget.

Takeaway: Smarter filtering beats oversized filtering every time.

4. Use Iterative Design and On-Site Support for Faster Compliance

EMI is notoriously sensitive to real-world variables. Cable routing, grounding points, and even test chamber setups can affect results. That’s why iterative testing and design adjustments are critical.

At Astrodyne TDI, we often work on-site during compliance testing with OEM partners. By making quick adjustments — swapping components, adding a damping element, or reconfiguring filter layout — teams can pass testing in a single cycle instead of scheduling multiple costly retests.

Key benefits:

  • Faster time-to-market.

  • Reduced rework costs.

  • Confidence that results reflect real-world installation conditions.

Takeaway: EMI design is not one-and-done — it’s an iterative process that works best with engineering support at the point of testing.

5. Design for Real-World Variance: Not Just Lab Results

Passing a compliance test in the lab doesn’t guarantee real-world success. BESS installations face:

  • Variability in cable lengths and routing.

  • Changes in grid conditions (harmonics, fault currents).

  • Environmental factors like temperature and humidity.

These can shift EMI performance by several dB — enough to push a borderline system back into failure.

Best practice:

  • Test using worst-case configurations (longest cables, maximum load conditions).

  • Validate across temperature ranges to account for component drift.

  • Incorporate a safety margin in filter attenuation to handle real-world variability.

Takeaway: Don’t design for the test lab, design for the field.

battery storage systems

Real-World Case Study: From EMI Failure to Class B Compliance

One BESS OEM came to Astrodyne TDI after multiple failed compliance attempts. Their system needed Class B certification to sell into residential markets, but emissions were exceeding limits by more than 40 dB.

Our approach included:

  • Characterizing the dominant EMI paths through busbars and enclosures.

  • Designing a custom high-current EMI filter rated for 3500 A at 1500 VDC.

  • Adjusting the physical layout to minimize parasitic coupling.

  • Providing on-site support during testing to fine-tune the solution.

Result: The system achieved Class B compliance, with up to 60 dB emission reduction, all while maintaining the OEM’s size and cost constraints. Most importantly, they avoided an additional 6–9 months of redesign and retesting delays.

Conclusion

Battery Energy Storage Systems are critical to the clean energy future, but EMI compliance can make or break a product launch. By applying these five lessons — early testing, understanding coupling paths, avoiding brute-force filters, embracing iterative design, and validating against real-world conditions — OEMs can move from failure to compliance faster, with lower cost and greater confidence.

At Astrodyne TDI, we provide both standard EMI filters up to 3500 A / 1500 VDC and custom solutions optimized for your system. More importantly, we bring engineering expertise and on-site support to ensure your design succeeds in the lab and the field.

Watch our on-demand webinar with Anand Awasthi to see the full technical deep dive, including real-world test data and frequency response plots.