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Rotational sensorless scalar control of three-phase induction motors and its application to automotive electric power assist steering

Abstract A rotational position/velocity sensorless scalar control method for three-phase induction motors is described. Although voltage/frequency (V/f) scalar control requiring such a sensor appears quite frequently in the literature, a general scheme without rotational sensors using a scalar method is not common. The method described in this work is simple in terms of algorithm and computationally less demanding, and hence can be implemented with inexpensive microprocessors. To illustrate an application, the electric actuator assisted power steering for automobiles is considered where torque is the object of control. For this particular application with near-zero or zero speed operation in general, the scalar method described in this work is considered to be a competitive alternative to the rotational sensorless field-oriented control (FOC) method for induction motors. This is particularly due to the fact that the algorithm for position sensorless FOC is computationally quite intensive for such low-speed torque tracking operations when compared with the scalar method, and in general requires expensive digital signal processors. Although this work was undertaken with automotive steering applications in mind, the methodology can also be applied to other automotive and non-automotive applications where actuators are used.