A power transmission apparatus may comprise: a motor/generator unit configured to drive a motor with three-phase alternating current (AC) power converted from a supplied AC power or generating electrical power to supply AC power; a battery unit configured to charge electrical energy with direct current (DC) power and supplying the DC power by using the charged electrical energy; and/or a converter configured to convert the DC power supplied from the battery unit to the AC power to supply the AC power to the motor/generator unit or an external electrical grid based on control signals, or configured to convert the AC power supplied from the external electrical grid or the motor/generator unit to the DC power to charge the battery unit with the DC power based on the control signals.