Harmonic Mitigation in a Coreless Double-Wound Flywheel Machine: Experimental Verification

This paper aims at analyzing harmonics and interharmonics present in a flywheel-based driveline developed at Uppsala University. The flywheel machine is a permanent magnet synchronous machine with two sets of windings in the stator, with a Wye–Wye connection as standard. Different sources of harmonic distortion have been evaluated. Flywheel machine simulations are performed in finite element method (FEM) (Comsol) and experimental verifications are presented. Several methods for harmonic mitigation have been evaluated. The driveline suffers almost exclusively from second-order harmonics but the THD (total harmonic distortion) seldom exceeds 5%. Very little interharmonics are present. A Delta–Wye connection of the flywheel eliminates most of the harmonics but at the expense of a high-phase current through the Delta connection. Grounding the neutral conductor in Wye connections increases the distortion.