Speed-sensorless control of induction motors with improved fault tolerance against current sensor failure

In this paper we propose the use of a multisensor switching strategy for fault tolerant speed-sensorless vector control of induction motors. The proposed strategy combines three current sensors and associated observers that estimate rotor speed and flux. The estimates provided by the observers are compared at each sampling time by a switching mechanism which selects the sensors-observer pair with the smallest value of an appropriately chosen switching cost. The switching selection is such that measurements from faulty current sensors are automatically avoided by the switching mechanism, thus maintaining good performance levels even in the presence of a faulty sensor. The measurements provided by the selected pair are used by a vector controller (DTFC or FOC) to implement the control law. Simulation results under realistic conditions illustrate the effectiveness of the scheme.