Research On Dual Three-Phase Permanent Magnet Brushless AC Motors Accounting For Cross-coupling Magnetic Saturation

The permanent magnet (PM) motors are applied widely in the fields of aerospace, electric ship propulsion, electric vehicles and numerical control machines because of their high performance. Conventionally, the PM brushless motors are three-phase, but it has limit in high power applications. Therefore, multiphase motors become more and more popular because of their several attractive features. In this thesis, the dual three-phase PM brushless AC motor with fractional-slot and concentrated non-overlapping winding is studied. The electromagnetic performances, slot/pole combinations, alternate winding distributions and also the d-q models of the dual three-phase motor are analysed. In addition, the influence of cross-coupling magnetic saturation on torqur calculation is investigated.First four existing torque calculation methods including constant parameters method, partial-coupling method, flux-linkage method and direct finit element method are described and compared. Then an improved analytical method accounting for cross-coupling and skew is proposed. It is employed to predict the d-and q-axis inductances and torque-speed characteristic of a skewed interior PM BLAC motor in the flux-weakening mode of operation, and validated by measurements.Then the electromagnetic performances of dual three-phase PM BLAC motor are analyzed. A 12-slot 10-pole combination is selected, and two different winding connections are described. The open-circuit electromagnetic performances, armature reaction, phase winding inductances and static torque of a surface-mounted PM (SPM) BLAC motor are calculated and analyzed, and compared with those of conventional three-phase and six-phase motors.Then the slot/pole combinations and winding connections of the dual three-phase motor with all teeth and alternate teeth wound are investigated. Winding factors are derived and calculated. A formula for winding factor calculation of dual three-phase motor is developed. Then the electromagnetic performances of a 12-slot 10-pole SPM BLAC motor with alternate teeth wound are analyzed and compared to those of all teeth wound motor.Finally the d-q models for dual three-phase PM BLAC motors are analyzed. The transformation and the steady-state electromagnetic torque equation when one set d-and q-axis quantities are transformed from the whole dual three-phase windings are deduced. The d-and q-axis inductances in one set d-q model for dual three-phase motor and two sets d-q models for three-phase motor are calculated and compared, and their relations are derived. Then the d-and q-axis inductances and torque-speed characteristic accounting for cross-coupling of the 12-slot 10-pole dual three-phase SPM BLAC motor with two different winding connections are computed and compared.