Sensor fault tolerant direct torque and flux control of induction motors

In this paper we propose the use of a multisensor switching control strategy for fault tolerant direct torque and flux control (DTFC) of induction motors. The proposed strategy combines three current sensors and associated observers that estimate the rotor 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 error between the estimated rotor flux magnitude and a desired flux reference. The measurements provided by the selected pair are used by a DTFC controller to implement the control law. Pre-checkable conditions are derived that guarantee fault tolerance under an abrupt fault of a current sensor. These conditions are such that measurements from faulty sensors are automatically avoided by the switching mechanism, thus maintaining good performance levels even in the presence of a faulty sensor. Simulation results under realistic conditions illustrate the effectiveness of the scheme.