Designing Dual-Output MMC for EV Aux Power

During my internship at Jaguar Land Rover TBSI we explored ways to avoid a dedicated DC-DC converter for auxiliary loads. The idea: run the traction MMC and pull a stable 12 V output from the same hardware.

Architecture

• Modular multilevel converter supplying 400 V AC to the motor inverter.
• Tapped auxiliary output with additional modulation to regulate 12 V DC.
• Common control layer to coordinate arm capacitor balancing and auxiliary regulation.

Simulation Notes

• Tools: PSIM models for MMC and harmonic analysis of the auxiliary branch.
• Strategy: phase-shifted PWM for traction plus low-frequency injection to shape the DC bus seen by the aux filter.
• Outcome: clean 12 V rail with ripple under 2% while traction THD stayed within spec.

What Worked

Keeping the aux control slow (bandwidth below arm balancing) prevented interference. A simple PI loop on the aux branch plus notch filtering on the traction side kept interactions contained.

Next Steps

• Thermal check on arm capacitors under combined load.
• Hardware validation with DC-link perturbations and step loads on the aux branch.
• Exploring interleaved aux branches for redundancy.