Meanwhile, the converter 530 may a bidirectional converter that converts DC power, input from a DC source, into a half sine wave voltage.

Meanwhile, the inverter 540 may be an unfolding inverter that allows a half sine wave voltage to pass therethrough by a plurality of switching elements during one half cycle of a grid voltage while reversing the half sine wave voltage during the other half cycle of the grid voltage so that the half sine wave voltage is converted into AC power.

For the purposes of reactive power control and power factor control, the converter 550 controls the converter 530 rather than the unfolding inverter 540.

Accordingly, the controller 550 may include a power factor correction unit that controls a power factor by controlling a grid power and phase of output AC power of the unfolding inverter 540. Alternatively, the controller 550 may be referred to as a power factor correction unit.

In particular, the controller 550 may perform current correction so as to enable the converter 530 to operate as a bidirectional converter to control reactive power and a power factor.

Specifically, the controller 550 or the power factor correction unit may perform current correction so as to make a half sine wave voltage have the opposite polarity in a period in which output power of the bidirectional converter 530 is smaller than 0 or negative in polarity.

The controller 550 or the power factor correction unit may control a half sine wave voltage to have a negative polarity current only in a section where current correction is performed, and to have a positive polarity current in other sections.