Reluctance Assisted External Rotor PMSM
A reluctance assisted external rotor permanent magnet machine provided with fewer magnets without scarifying performance is described herein. Torque ripple and cogging torque reductions are discussed.
1 . An external rotor electric machine comprising:
an internal stator; and
an external rotor coaxial to the internal stator; the external rotor including an inner surface facing the internal stator; the external rotor including permanent magnets arranged in a circumferential direction on the internal surface of the rotor, and magnetically susceptible protrusions respectively arranged between adjacent permanent magnets; the magnetically susceptible protrusions being so configured and sized as to position the magnets so as to reduce cogging torque and torque ripple.
2 . The external rotor electric machine as recited in claim 1 , wherein the protrusions consist of stacks of laminations made of soft magnetic material.
3 . The external rotor electric machine as recited in claim 2 , wherein the stacks of laminations are individual ring segments including a central protrusion, two lateral protrusions and two permanent magnet receiving portions located on either side of the central protrusion.
4 . The external rotor electric machine as recited in claim 3 , wherein the individual ring segments are so configured and sized as to be applied to the internal surface of the rotor.
5 . The external rotor electric machine as recited in claim 4 , wherein the sizes of the central and lateral protrusions are such that adjacent magnets are angularly shifted.
6 . The external rotor electric machine as recited in claim 5 , wherein adjacent magnets are angularly shifted of an angle of 15 degrees.
7 . The external rotor electric machine as recited in claim 5 , wherein adjacent magnets are angularly shifted of an angle of 30 degrees.
8 . The external rotor electric machine as recited in claim 1 , wherein the protrusions consist of blocks of SMC (Soft Magnetic Composite).
9 . The external rotor electric machine as recited in claim 8 , wherein the SMC blocks are so configured and sized as to be applied to the internal surface of the rotor.
10 . The external rotor electric machine as recited in claim 9 , wherein the sizes of SMC blocks are such that adjacent magnets are angularly shifted.
11 . The external rotor electric machine as recited in claim 10 , wherein adjacent magnets are angularly shifted of an angle of 15 degrees.
12 . The external rotor electric machine as recited in claim 10 , wherein adjacent magnets are angularly shifted of an angle of 30 degrees.