DRIVE CONTROLLER OF MOTOR

PROBLEM TO BE SOLVED: To solve such a problem of prior art where the average value of neutral point voltage is detected via a low-pass filter lower than the PWM frequency, and abnormality such as ground fault is detected by comparing the average value with a predetermined threshold, that since harmonic components dependent on a modulation signal are superposed on the neutral point voltage, characteristics of a low-pass filter must be set to a time constant corresponding to the entire output frequency band of the inverter, and voltage variation due to the modulation signal must be separated from voltage variation due to the ground fault.SOLUTION: Abnormality such as output line ground fault or supply fault can be determined by determining abnormality of an output line on the basis of the actual neutral point voltage of a motor which changes stepwise on the basis of the PWM pulse pattern of an inverter, and a regular neutral point voltage determined on the basis of the PWM pattern of the inverter. Highly reliable abnormality detection according to the neutral point voltage waveform is possible, and stabilized abnormality detection is possible regardless of the inverter output frequency.