Patent ID: 8896252

Claim:
An electric motor driving device that drives an electric motor that includes a field winding, a rotor and a stator, wherein the rotor and the stator each form a field pole by passing a field current through the field winding, the electric motor driving device comprising: a power supply device; a converter that includes a reactor that at least partially serves as the field winding to share the field winding with the electric motor, and that is configured to receive a voltage from the power supply device to carry out voltage conversion between a first power line and a second power line and to pass the field current through the field winding during operation of the voltage conversion; an inverter that is configured to receive a direct-current power from the converter and to convert the direct-current power to an alternating-current power for driving the electric motor; and a controller that controls the converter so that a current flows through the field winding in the same direction both during power running of the electric motor and during regeneration of the electric motor, wherein the converter includes a switching unit that switches between a first current path along which a current flows during power running of the electric motor and a second current path along which a current flows during regeneration of the electric motor, and the controller controls the switching unit so that a current flows through the field winding in the same direction both when a current flows along the first current path and when a current flows along the second current path, wherein the switching unit is connected between a first end that is one end of the field winding and a negative electrode of the power supply device so that a direction from the field winding toward the negative electrode of the power supply device is set as a forward direction, the switching unit includes a step-up switching element that is used to step up the voltage from the power supply device and a field switching element that controls a current flowing through the field winding, a second end that is the other end of the field winding is electrically connected to the first power line, and the controller carries out switching control of the step-up switching element and the field switching element to control the field current to thereby regulate a magnetic flux density between the rotor and the stator and to control a step-up current output from the converter to the second power line to thereby convert the voltage from the power supply device to a voltage according to a target value of a step-up voltage.