Patent ID: 8736215

Claim:
A motor drive device including a converter unit for converting AC power of an AC power supply to DC power and an inverter unit for converting the DC power converted by the converter unit to variable-frequency AC power, wherein the converter unit comprises: a power supply voltage monitoring unit for monitoring voltages of respective phases of the AC power supply to detect a power failure; DC link voltage detecting means which detects low voltage by monitoring DC link voltage; capacitor total capacity calculating means which calculates total capacity of DC link smoothing capacitors provided for the converter unit and the inverter unit; DC link low-voltage alarm detection level setting means which varies a DC link low-voltage alarm detection level for an instantaneous power failure as necessary; and alarm generating means which monitors the DC link voltage and, in the case where the DC link voltage kills below the DC link low-voltage alarm detection level, generates an alarm to protect the converter unit, and wherein when the power supply voltage monitoring unit of the AC power supply detects the power failure, the DC link low-voltage alarm detection level is increased in accordance with the total capacity of the DC link smoothing capacitors.