Drive device of electric motor

A drive device for an electric motor including a field winding and having a field pole formed by a field current passing through said field winding, comprising:

• a power source;
• a converter for converting output voltage of said power source and outputting the voltage between first and second power lines;
• and
• an inverter receiving the voltage between the first and second power lines and converting the voltage into electric power for driving and controlling said electric motor, wherein
• said converter includes a voltage boosting switching element to be electrically connected between said field winding and said second power wire,
• said field winding is electrically connected onto an electric current channel between said power source and said first power line and formed so that voltage switched by said voltage boosting switching element is applied to both ends, and
• said drive device of the electric motor further comprises:
• a field switching element to be connected in parallel to said field winding;
• and
• a controller controlling said field current and adjusting density of magnetic flux between a rotor and a stator by performing switching control on said voltage boosting switching element and said field switching element, and also controlling a voltage boosting current outputted from said converter to said first power line and converting the output voltage of said power source into voltage in accordance with a voltage command value.