ELECTRICITY CONVERSION DEVICE

There is provided a power conversion apparatus including a power converter being so configured that an alternating-current switch constituted of a series connection of two valve devices each constituted of a semiconductor element and a diode connected in inverse parallel with the semiconductor element is connected between a connection point of the valve devices and a connection point of the direct-current power supplies in each arm, and each of the alternating-current switches is turned on or off, thereby enabling the power converter to perform three-level operation or two-level operation. The power conversion apparatus includes a comparison circuit (9) which compares a determination element related to a loss in the power converter with a switching reference value and outputs a determination instruction when a difference has occurred between the determination element and the switching reference value, a determination circuit (11) which determines whether the determination element is greater or less than the switching reference value when having received a determination instruction from the comparison circuit (9), and outputs a two-level operation switching instruction when the determination element is greater than or equal to the switching reference value, and a switching circuit (12) which, when having received a two-level operation switching instruction from the determination circuit (11), turns off the alternating-current switch and turns on the valve devices in the arm sequentially, thereby bringing the power converter into a two-level operation state.