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1. A motor drive device comprising:
a converter unit having a rectifier circuit configured to rectify AC voltage supplied from an AC power supply via a first switch into DC voltage; a power supply unit configured to smooth the DC voltage rectified by the rectifier circuit through a capacitor; a plurality of inverter units configured to convert the DC voltage from the power supply unit to AC voltage to drive multiple motors, respectively, by switching operation of semiconductor switching elements in an upper arm, connected between a positive-side terminal of the capacitor and a motor coil as well as semiconductor switching elements in a lower arm, connected between a negative-side terminal of the capacitor and the motor coil; a second switch configured to connect one terminal of the capacitor to the earth; a current detector configured to measure current flowing between the one terminal of the capacitor and the earth; a voltage detector configured to measure voltage between both ends of the capacitor; and, an insulation resistance detector configured to detect insulation resistance which is resistance between a motor coil of a motor selected as a target for measurement and the earth, based on current and voltage measured in a condition that operation of the motors is stopped, the first switch is turned off, the second switch is turned on, semiconductor switching elements connected between the other terminal of the capacitor and the motor coil, among the semiconductor switching elements in the upper or lower arm to which the motor coil of the motor to be measured is connected are turned on, and the semiconductor switching elements connected between the one terminal of the capacitor and the motor coil, among the semiconductor switching elements in the upper or lower arm to which a motor coil of a motor other than the motor to be measured is connected are turned on. |
