Model of Double-Star IPM Machines with General Mutual Inductance Relationships between the Two Three-Phase Winding Sets

This paper proposes a decoupled d–q model of double-star interiorpermanent magnet (IPM) machines, whose stator consists of two three-phase winding sets displaced by an arbitrary angle. The model is based on the elaboration of the inductance parameters and is obtained by deriving a transformation that diagonalizes the original 6 × 6 stator inductance matrix of the machine. In the derivation of the transformation, the common assumption of the regularity of the mutual inductances between the two three-phase sets is omitted. Thus, the transformation diagonalizes the stator inductance matrix even if the mutual inductances do not have specific symmetry. It is demonstrated that in order to obtain decoupled reference frames in such a case, the transformation depends on the machine parameters. The validity of the machine model is verified by experimental tests with a double-star IPM machine, in which the two three-phase winding sets are displaced by 30 electrical degrees.