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Broken rotor bar/end-ring and eccentricity are common faults in squirrel-cage induction motors and have been thoroughly investigated in the case of ac grid supply. In this paper, these types of faults are studied in the case of inverter-driven motors. More specifically, a novel investigation in inverter input current spectrum is made in order to reliably detect the fault-indicative frequency components. These harmonics give the ability for fault detection and classification, even under low load and low motor severity fault condition in steady-state or transient operation. The proposed diagnostic method has been particularly designed for open-loop controlled variable frequency induction motor drives, which is a usual case in low-cost industrial drives where precise speed control of the motor is not required. Moreover, an alternative technique is also presented in case the stator current is measured.