This paper proposes an algorithm for fault tolerance of three-phase inverter fed speed
sensorless control of three- phase induction motor drive system. The fault tolerance of inverter
when one switch is open or one leg of six-switch inverter is lost is considered. The control of the
drive system is based on indirect rotor field oriented control theory. Also, the speed estimator is
based on model reference adaptive system (using stator current and rotor flux as state variables for
estimating the speed). The fault tolerant algorithm is able to adaptively change-over from six
switch inverter to four switch inverter topologies when the fault is occurred; also, it makes a
smooth transition of the motor speed, torque and current when changing over from faulty condition
to new healthy status which is (Four-Switch Three-Phase Inverter (FSTPI) topology), thus, the Six
Switch Three-Phase Inverter (SSTPI) topology (pre-fault status) almostly retained. The proposed
algorithm is simulated by using the MATLAB/SIMULINK package. The obtained results from
the simulation model demonstrate the performance enhancement and good validity of the fault‌tolerance control for speed sensorless induction motor drive system