Patent ID: 8044620

Claim:
A driving apparatus for a multi-phase AC synchronous motor having a stator coil, which is star-connected to a neutral point to generate a rotating magnetic field to rotate a rotor, the driving apparatus comprising: an inverter circuit having a plurality of pairs of switching elements in correspondence to the number of phases of the motor, each pair of switching elements including a positive-side switching element connected to a positive bus line and a negative-side switching element connected to a negative bus line and connected to each other in series, and the plurality of pairs of switching elements being connected in parallel one another between the positive bus line and the negative bus line; a capacitor having a positive electrode and a negative electrode, the positive electrode being connected to the positive bus line, and the negative electrode being connected to either one of the negative bus line and the neutral point; and an inverter control circuit configured to turn on the positive-side switching element and turn off the negative-side switching element in each pair when a first command wave of each phase is greater than a carrier wave, and turn on the negative-side switching element and turn off the positive-side switching element in each pair when the first command wave of each phase is less than the carrier wave, the first command wave having a magnitude periodically changing from a first reference level to a positive side and a negative side, and the carrier wave having a magnitude periodically changing from a second reference level to the positive side and the negative side, the inverter control circuit being configured to output, by turning on and off the pair of switching elements, an AC current to the stator coil to generate the rotating magnetic field from the stator coil based on an output voltage of the DC power source and an output voltage of the capacitor, the inverter control circuit being configured to turn on the negative-side switching element to store energy in the stator coil by a current flowing from the DC power source to the stator coil, and turn off the negative-side switching element to charge the capacitor by the energy of the stator coil, which flows as a current flowing from the stator coil to the positive electrode of the capacitor bypassing the positive-side switching element, and the inverter control circuit being configured to offset the first reference level of the first command wave of each phase to be closer to a maximum value of the carrier wave than the second reference level is, so that a turn-on period of the negative-side switching element becomes shorter than a turn-on period of the positive-side switching element.