Patent ID: 9742341
Date: 2017-08-22
CPC Classifications: H02J,H02P

Claim:
1. An AC motor drive system comprising: a converter that supplies DC power; an inverter that converts the DC power into AC power; a DC bus that connects the converter and the inverter; an AC motor that is driven by the AC power; a DC voltage value detector that detects a DC voltage value on an output side of the converter; a power storage device that stores the DC power from the DC bus and releases the stored DC power to the DC bus; a charging and discharging circuit that is connected to the DC bus and is in parallel with the inverter, and charges and discharges the power storage device; a charging and discharging current value detector that detects a charging and discharging current value of the power storage device; and a charge and discharge controller that outputs a control signal to control the charging and discharging circuit on a basis of the DC voltage value and the charging and discharging current value, wherein when regenerative power from the AC motor via the inverter exceeds a predetermined power threshold, the charge and discharge controller causes the power storage device to be charged such that the DC voltage value becomes a voltage threshold corresponding to the power threshold, when the regenerative power is lower than or equal to the power threshold, the converter performs a regeneration operation when the DC voltage value rises to reach a predetermined regeneration start voltage threshold and ends the regeneration operation when the DC voltage value drops to reach a predetermined regeneration end voltage threshold, a time average value of the DC voltage value during the regeneration operation in the converter is lower than the DC voltage value at no-load time when the converter does not perform power supply and regeneration, and the charge and discharge controller maintains constant current with which the power storage device is charged only during a period based on a cycle in which the DC bus voltage value reaches a voltage threshold based on a DC bus voltage value at which the converter starts the regeneration operation.