Anti-cogging apparatus for permanent magnet electrical machines

A permanent magnet electrical machine with reduced cogging torque, said machine comprising:

• a rotor with permanent magnets;
• a stator concentrically mounted to said rotor, for relative rotation of said rotor to said stator thereby generating a cogging torque;
• a first component mechanically coupled to one of said rotor and said stator and having a first set of elements of magnetic material disposed along a first circle;
• and
• a second component mechanically coupled to the other one of said rotor and said stator and having a second set of at least one element of magnetic material disposed along a second circle coaxial with said first circle, said second set facing said first set for passive magnetic interaction, with an air gap between said first and said second set;
• wherein at least one of said first set and said second set has permanent magnets for generating an anti-cogging torque as a result of the passive magnetic interaction between said first set and said second set, said anti-cogging torque having a magnitude substantially matching the magnitude of said cogging torque and a direction opposite to the direction of said cogging torque, thereby substantially canceling out said cogging torque.

A method for reducing the cogging torque of a permanent magnet machine, said method comprising:

• providing a permanent magnet machine having a rotor and a stator;
• determining the cogging torque of said machine;
• providing a first component having a first set of elements of magnetic material disposed along a first circle, and a second component having a second set of at least one element of magnetic material disposed along a second circle, wherein at least one of said first set and said second set has permanent magnets for generating an anti-cogging torque as a result of passive magnetic interaction between said first set and said second set, said anti-cogging torque having an magnitude substantially matching the magnitude of said cogging torque and a direction opposite to the direction of said cogging torque, thereby substantially canceling out said cogging torque;
• and
• mechanically coupling one of said first and said second component to said rotor and mechanically coupling the other component to said stator such that said first circle is coaxial to said second circle and that said first set faces said second set with an air gap for magnetic interaction.