Speed Sensorless Field Oriented Control of Induction Machines using Flux Observer

The indirect field oriented control method is widely used for induction motor drives. This method needs a speed sensor such as a shaft encoder not only for the speed control but also for the torque control. The application of the speed sensor reduces the sturdiness of the system and make it expensive. Therefore, a drive system without speed sensors is required. Although the direct field oriented control method with a flux estimator which uses a pure integrator does not need the speed sensor for the torque control, this method is not practical. This is because the flux estimator does not work well in a low speed region. The pole of the flux estimator is on the origin of the s plane, and it is very sensitive to the off-set of the voltage sensor and the stator resistance variation. To solve this problem, it is effective to use observers to estimate rotor fluxes. This paper reviews speed sensorless induction motor drive methods using flux observers including Kalman filters.