Patent ID: 8796960

Claim:
A control device for a motor drive system for driving an AC motor having a magnet in a rotor, said motor drive system including a DC power supply configured to be chargeable, a first converter for stepping up a power supply voltage supplied from said DC power supply and an inverter for driving said AC motor by converting DC power from said first converter to AC power, said control device generating a step-up command value for said first converter based on a torque command value for said AC motor, determining whether to carry out field-weakening control for increasing a current in a direction weakening force of said magnet that is supplied from said inverter to said AC motor based on said step-up command value and a state of drive of said AC motor, and further increasing generated said step-up command value when said field-weakening control should be carried out and when an absolute value of said torque command value is smaller than a threshold value.