On-Site EMC Pre-Compliance and EMI Troubleshooting for Large Energy Storage & Inverter System

This case study describes an on-site EMC pre-compliance test and EMI troubleshooting engagement for a large energy storage system with a bi-directional inverter. The system delivers dynamic bursts of power for heavy industrial equipment, and its size and complexity made traditional compliance testing risky and costly. Mach One Design was brought in to perform bench-top and in-situ conducted and radiated emission measurements, identify emission failure mechanisms, and implement mitigation strategies on the prototype system before formal accredited testing.

Client Context

A UK-based engineering firm developed an innovative energy storage solution using flywheel technology to deliver large bursts of power to heavy equipment—such as cranes—on demand. The system features a bi-directional inverter, enabling dynamic energy flow in both directions.

Due to its size, high power levels, and complexity, full compliance testing in an accredited lab posed major logistical and financial challenges. The client sought assurance ahead of lab testing to avoid surprises that could derail their development timeline and impact cost.

We were engaged to perform on-site EMC pre-compliance testing, identify any emission issues, and help ensure first-time success in formal testing.

Scope of Work

• Conduct on-site EMC pre-compliance tests, focusing on conducted and radiated emissions.

• If failures occur, carry out in-situ EMI troubleshooting and mitigation.

• Document findings and recommend design adjustments for production readiness.

A three-phase LISN was used for measuring conducted emissions 

Technical Approach

For large or high-power systems, we bring calibrated test equipment directly to the client’s site. In this case, the test suite included:

• A 3-phase LISN for conducted emission measurement

• A calibrated EMI receiver

• Appropriate antennas for radiated emission scans

Testing was carried out according to CISPR principles for industrial equipment. Test data were captured, logged, and reviewed in real time.

Troubleshooting & Mitigation

During initial testing, conducted emissions exceeded acceptable limits. Using near-field probing and RF current diagnostics, we localised two distinct emission problems:

Sub-1 MHz Band

Root Cause: Insufficient filtering on the neutral line

Solution: Replaced the existing 3-phase 3-wire filter with a 3-phase 4-wire EMC filter, ensuring proper attenuation on the neutral conductor.

1–2 MHz Band

Root Cause: Grounding scheme between the filter housing and motor drive cabinet led to loop-induced noise

Solution: Revised the grounding layout, ensuring controlled grouping and bonding between filter case and the motor drive panel. This significantly reduced common-mode noise.

We used a special diagnostic tool to confirm assumptions and validate the effectiveness of each fix. All adjustments were implemented directly on the prototype system, allowing for iterative validation without the need for additional lab testing. 

Outcome

• Conducted emissions brought under control across all measured bands

• Radiated emissions verified to be within limits, with no signs of critical failure

• The client moved forward to accredited EMC testing with confidence of compliance

• Design lessons documented to support final production readiness and future system variants

Conclusion

This project highlights the value of on-site EMC diagnostics in large industrial systems. By combining measurement capability with real-world troubleshooting expertise, we helped the client minimize certification risk, reduce project delays, and ensure robust EMI performance.