A self-commutating PM machine with implicit rotor position sensing using search coils

The detection of rotor position required for a self-commutating machine can be performed using search coils embedded in the stator, and without reference to any external encoder. The closed-loop speed control system is able to drive the motor accurately and at maximum efficiency for a wide range of speeds and loads, using the same search coil sensor technique for speed control as for the inverter switching. A complete self-contained drive system can therefore be built using this technique