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A smooth fault-tolerant control (FTC) of induction motor drives with sensor failures is presented in this paper. The drive uses concurrently active direct torque control (DTC), indirect field-oriented control (IFOC), and volts-per-hertz (V/f) controllers as replacements of each other in the case of sensor failure or recovery. Speed encoder, current, and voltage sensors are considered. The DTC and IFOC controllers are properly modified and integrated with the V/f controller in synchronous frame, which allows switching between dc-type voltage commands of different controllers. Therefore, difficult synchronization of different controllers is avoided, and a simple rate limiter is able to achieve smooth handoff transition of different controllers. Details of the DTC, IFOC, and V/f controllers, as well as their integration are presented. Simulation and experimental verification of the proposed FTC are given, where normal abc-frame switching and the proposed synchronous-frame switching of controllers are compared with different switching schemes and at different machine operation conditions. Simulation and experimental results show significantly smoother handoff transients. [ABSTRACT FROM AUTHOR]

Vector-controlled induction motor drives include several design and control variables that affect power losses. Flux may be weakened to reduce machine losses; switching and conduction losses in the inverter are affected by the flux ripple and current hysteresis bands. This paper combines the machine and inverter to investigate the effects of various control variables on the total system power loss. Both indirect field-oriented control and direct torque control are evaluated. Power losses considered include semiconductor switching and conduction losses and machine core and copper losses. Magnetic saturation is taken into account. A 1.5-hp system is simulated and experimentally tested to find minimum-loss operating points for various control variable combinations. Experimental results show that the operating point for minimum system-level power loss is slightly different from that for minimum machine power loss, but both can yield significant energy savings. The results presented here suggest that, for efficient system operation, control aspects should be utilized and integrated into motor drive designs. [ABSTRACT FROM PUBLISHER]