Patent ID: 8269439

Claim:
A drive controller for an electric motor, comprising: a first motor control unit for performing, when a first control mode in which a rectangular wave voltage is applied to an AC electric motor is selected, feedback control for adjusting phase of said rectangular wave voltage in accordance with torque deviation from a torque command value; and a second motor control unit for performing, when a second control mode in which a voltage applied to said AC electric motor is controlled in accordance with pulse width modulation control is selected, feedback control of a motor current, said second control mode including a sinusoidal pulse width modulation control mode in which, when the DC voltage is converted in accordance with a voltage command of the voltage applied to said AC electric motor, correlation waveform of said voltage command assumes sinusoidal waveform, and an overmodulated pulse width modulation control mode, having higher modulation factor than said sinusoidal pulse width modulation control mode, the driving controller further comprising: a mode switching determining unit for determining whether switching between said first and second control modes is necessary, based on a state of said AC electric motor, with operating at every prescribed period longer than a control period of said first motor control unit, wherein when said first control mode is selected, said mode switching determining unit determines, based on said state of said AC electric motor, whether switching from said first control mode to said overmodulated pulse width modulation control mode is necessary, and when switching from said first control mode to said overmodulated pulse width modulation control mode is determined to be necessary, said mode switching determining unit permits switching from said first control mode to said overmodulated pulse width modulation control mode at a next operation timing, and inhibits updating of a phase of said rectangular wave voltage by said first motor control unit until said next operation timing.