A power regeneration converter that is placed between an AC power supply and an inverter device for controlling a motor is known as a conventional power regeneration device. The power regeneration converter converts power supplied from the motor via the inverter device into AC power by using a switching element and supplies the AC power to the AC power supply in order to perform power regeneration when the motor is decelerated.
The power regeneration by the power regeneration converter is performed in synchronization with the phase of the AC power supply. In other words, the power regeneration converter detects an AC voltage from the AC power supply and detects the phase of the AC power supply on the basis of the detection result. Then, the power regeneration converter controls the switching element in accordance with the detected phase of the AC power supply to perform the power regeneration. The power regeneration converter has been known as disclosed in, for example, Japanese Laid-open Patent Publication No. 2011-101473.
In this case, it is preferable that the power regeneration device is, when a continuous operation is performed even during a power outage, for example, in a state where the device is operated in synchronization with the phase of the AC power supply at the time when power is recovered from the power outage.