Patent ID: 8310181

Claim:
A motor drive system for a multiphase AC motor that rotates a rotor with respect to a stator, the AC motor including multiphase windings whose one ends are connected, at a neutral point, to each other in star configuration, the rotor of the multiphase AC motor having a d-axis and a q-axis electromagnetically orthogonal to each other, the motor drive system comprising: a DC power source connected with the neutral point of the multiphase windings and designed to output a voltage; a multiphase inverter having first and second DC input terminals and multiphase alternating-current output terminals, one of the first and second DC input terminals being connected with the DC power source, the multiphase alternating-current output terminals being respectively connected with the other ends of the multiphase windings; a power charge unit connected between the first and second DC input terminals of the multiphase inverter in parallel thereto; and a controller that, according to a current flowing through each of the multiphase windings, a rotational angle of the rotor, the outputted voltage from the DC power source, and a voltage charged in the power charge unit, carries out: generation of a voltage command value for each of the d-axis and q-axis; conversion of the voltage command value for each of the d-axis and q-axis into a voltage command value for each of the multiphase windings; and control of the multiphase inverter based on the voltage command value for each of the multiphase windings to thereby cause the multiphase inverter to generate a multiphase AC voltage to be applied to the multiphase windings, the controller being configured to: add, to the voltage command value for the q-axis, a first compensation voltage value for compensating torque ripples to thereby output a compensated voltage command value for the q-axis, the first compensation voltage value containing m-th harmonic components in the AC motor and varying depending on the rotational angle of the rotor, the m corresponding to the number of phase of the multiphase windings; and use, as the voltage command value for the q-axis, the compensated voltage command value for the q-axis.