Smooth Fault-Tolerant Control of Induction Motor Drives With Sensor Failures

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.