A control device and a control method can improve a voltage utilization ratio of an inverter for a green car, in which an input DC voltage of the inverter is modulated by a maximum amount into an output AC voltage of the inverter by changing the output AC voltage incapable of being linearly output into a voltage capable of being linearly output. The control method includes steps of: generating a two-phase current command having two phases of a first current command and a second current command; generating a two-phase voltage command having two phases of a first voltage command and a second voltage command; generating a three-phase pole voltage command; modulating the three-phase pole voltage command into a linear output voltage capable of being linearly output; and calculating a voltage gain value, using the two-phase voltage command and an input DC voltage of the inverter.