Permanent magnet electrical machine

A permanent magnet electrical machine having:

• an axis;
• a rotor rotating about the axis and supporting a circumferential row of permanent magnets;
• a stator coaxial with the rotor and the axis, the stator having a circumferential row of stator teeth carrying respective coil windings, the teeth providing paths for magnetic flux produced by the magnets, thereby electromagnetically linking the magnets and the coils when the rotor rotates relative to the stator;
• wherein the teeth have respective core portions on which the coil windings are mounted, and respective tip portions located between the core portions and the rotor, the circumferential row of tip portions being controllably rotatable about the axis between a first position in which the tip portion and the core portion of each tooth are angularly aligned to enhance magnetic flux linkage between the magnets and the coils, and a second position in which the tip portion of each tooth is rotated out of angular alignment with its core portion to reduce magnetic flux linkage between the magnets and the coils.