Sensorless position control of induction motors - An emerging technology

Concepts for sensorless position control of induction motor drives rely on anisotropic properties of the machine rotor. Such anisotropies can be incor porated as periodic variations of magnetic saliencies in various ways, The built-in spatial anisotropy is detected by injecting a high-frequency flux wave into the stator. The resulting stator current harmonics contain freque ncy components that depend on the rotor position, Models of the rotor salie ncy serve to extract the rotor position signal using phase-locked loop tech niques. A different approach makes use of the parasitic effects that origin ate from the discrete winding structure of a cage rotor. It has the merit o f providing high spatial resolution for incremental positioning without sen sor. The practical implementation of sensorless position identification and of a high-accuracy position control system are reported.