Permanent-magnet synchronous machine having skewed magnets for reduced torque ripple

1. A permanent-magnet synchronous machine for three-phase operation, comprising:

a stator having plural teeth, each tooth surrounded by a winding, said stator having a number of holes q=½ which is defined as q=N1/(3×2p), wherein N1 is the number of stator slots; 3 is the number of phases; and 2p is the number of poles of the rotor; and

a rotor defining an axis and having permanent magnets arranged in a circumferential direction with a pole gap in a range from 20% to 42.9% in relation to a pole pitch, the rotor having a skew with a skew angle on an axial projection in the circumferential direction of 40% to 57.2%, in relation to the pole pitch,

wherein a ratio of the skew angle/pole pitch to a ratio of the pole gap/pole pitch is schdpt=−0.75×pldpt+72.2%, with schdpt being the ratio of the skew angle/pole pitch, and pldpt being the ratio of the pole gap/pole pitch, and

wherein the pole gap and the skew are designed such that oscillating torques caused by the fifth and seventh harmonics of a stator field and of a rotor field are mutually reduced.

2. The synchronous machine of claim 1 , wherein the oscillating torques caused by the fifth and seventh harmonics of the stator field and of the rotor field substantially compensate one another.

3. The synchronous machine of claim 1 , wherein the permanent magnets are staggered in the circumferential direction for providing the skew.

4. The synchronous machine of claim 1 , wherein the permanent magnets are arranged in a circumferential direction with a uniform pole pitch and a uniform pole gap irrespective of a position of the permanent magnets on the rotor along the rotor axis.

5. The synchronous machine of claim 1 , wherein the stator has 9 pole teeth and the rotor has 3 pole pairs (2p=6).

6. A permanent-magnet synchronous machine for three-phase operation, comprising:

a stator having plural teeth, each tooth surrounded by a winding, said stator having a number of holes q=½ which is defined as q=N1/(3×2p), wherein N1 is the number of stator slots; 3 is the number of phases; and 2p is the number of poles of the rotor; and

a rotor defining an axis and having permanent magnets arranged in a circumferential direction with a pole gap in a range from 20% to 42.9% in relation to a pole pitch, the rotor having a skew with a skew angle on an axial projection in the circumferential direction of 40% to 57.2%, in relation to the pole pitch,

wherein a ratio of the skew angle/pole pitch to a ratio of the pole gap/pole pitch is −0.75×pldpt+72.2% to −0.75×pldpt+72%-10%, with schdpt being the ratio of the skew angle/pole pitch, and pldpt being the ratio of the pole gap/pole pitch, and

wherein the pole gap and the skew are designed such that oscillating torques caused by the fifth and seventh harmonics of a stator field and of a rotor field are mutually reduced.

7. The synchronous machine of claim 6 , wherein the oscillating torques caused by the fifth and seventh harmonics of the stator field and of the rotor field substantially compensate one another.

8. The synchronous machine of claim 6 , wherein the permanent magnets are staggered in the circumferential direction for providing the skew.

9. The synchronous machine of claim 6 , wherein the permanent magnets are arranged in a circumferential direction with a uniform pole pitch and a uniform pole gap irrespective of a position of the permanent magnets on the rotor along the rotor axis.

10. The synchronous machine of claim 6 , wherein the stator has 9 pole teeth and the rotor has 3 pole pairs (2p=6).