A motor drive device includes: a converter that converts AC power supplied from an AC power source into DC power and outputs the DC power to a DC link; a capacitor installed in the DC link; an inverter that converts the DC power at the DC link into AC power for driving a motor and outputs the AC power; a charging circuit that has a charging resistor for preventing inrush current during the period of pre-charging of the capacitor; a charging control unit that controls the pre-charging of the capacitor executed by the charging circuit; and an abnormality determination unit that determines, during the period of pre-charging of the capacitor, whether an abnormality has occurred, on the basis of a measurement value of the voltage of the capacitor and/or a measurement value of the current flowing through the DC link.

A method to identify rotor slot harmonics (RSH) in a motor current spectrum of an AC induction motor includes receiving current data from the motor operated at two different load values, obtaining a motor current frequency spectrum comprising a first motor current spectrum corresponding to a first load value and a second motor current spectrum corresponding to a second load value, detecting a number of peak current values for a frequency range of the motor current frequency spectrum, and comparing the detected number of peak current values for the frequency range from the first motor current spectrum to the second motor current spectrum. Pairs of consecutive peaks are determined from the detected number of peak current values for each of first load value and second load value and compared. When the comparison is above a threshold value, the pair of consecutive peak current values are identified as RSH.