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In the last decades, fault diagnosis of voltage source inverters has received a lot attention since their application to variable speed drives has become an industrial standard. Recently, some methods have been suggested for open-circuit faults in the switching devices of voltage source inverters. However, most of these methods might not work properly for different working conditions of the motor drive. In this paper, the evaluation of a robust model-based fault detection and isolation scheme for actuator faults in induction motor drives is presented. Residuals are synthesized by applying a differential geometry approach, and they are generated by using a bank of proportional-integral observers. Departing from previous results (Espinoza-Trejo and Campos-Delgado, 2008), the diagnosability and decoupling conditions for actuator faults are satisfied in the induction motor model. In this way, residuals are decoupled from the load torque and operating conditions, and simultaneous faults can be addressed. Finally, a variable voltage and frequency evaluation of this new model-based diagnosis scheme is presented. The variable speed evaluation is verified experimentally in a test-bench of 1 HP under single and simultaneous faults, and by considering three reference frequencies.