Current Control for Dual Three-Phase Permanent Magnet Synchronous Motors Accounting for Current Unbalance and Harmonics

This paper proposes an improved vector space decomposition current control scheme for dual three-phase permanent magnet (PM) synchronous motors having two sets of three-phase windings spatially shifted by 30° electrical degrees. A proportional-integral (PI) and resonant (second) controller is developed for eliminating the current unbalance in αβ subplane, which is effective irrespective of the degree of current unbalance, while PI plus multifrequency resonant (second and sixth) control is employed to eliminate the current unbalance, fifth and seventh current harmonics in z₁z₂ subplane. Compared with existing methods only accounting for current unbalance in z₁z₂ subplane, the proposed method has considered the current unbalances in both z₁z₂ and αβ subplanes and can eliminate them simultaneously at the steady-state of operation. Consequently, the full compensation of current unbalance can be achieved, by which both the current unbalance between two sets and current unbalance between phase windings in each set are eliminated. Meanwhile, the fifth and seventh current harmonics caused by nonsinusoidal back electromotive force and inverter nonlinearity can also be fully compensated. The effectiveness of proposed method is verified by a set of comparative experiments on a prototype dual three-phase PM machine system. It shows that fully balanced currents without the fifth and seventh current harmonics at the steady state of operation can be achieved.