Patent ID: 8653783

Claim:
An AC motor drive device comprising: a DC bus connected to a DC power supply; an inverter that converts DC power supplied from the DC bus to AC power required for driving an AC motor; and a power storage system that is connected to the DC bus in parallel with the inverter for controlling DC power of the DC bus, wherein the power storage system comprises: a power storage element that can store DC power; a step-up/step-down bidirectional chopper circuit that includes two switching elements in series and a choke coil whose one end is connected to a serially connected terminal of the two switching elements, and is arranged between the DC bus and the power storage element to perform a charge operation from the DC bus to the power storage element and a discharge operation from the power storage element to the DC bus; and a control circuit that executes control so that an operation of the step-up/step-down bidirectional chopper circuit is switched to a first operation as a first chopper circuit in which a positive terminal of one of the switching elements is connected to a positive side of the DC bus and the other end of the choke coil is connected to a positive terminal of the power storage element, or to a second operation as a second chopper circuit in which the other end of the choke coil is connected to the positive terminal of the DC bus and the positive terminal of the one switching element is connected to the positive terminal of the power storage element, wherein the control circuit compares a voltage of the DC bus with a voltage of the power storage element, and before and after a timing at which a result of the comparison is changed, switches and executes the first operation and the second operation in a predetermined order, thereby realizing the charge operation and the discharge operation, respectively.