MOTOR DRIVE SYSTEM, MOTOR DRIVE SYSTEM CONTROL METHOD AND TRAVELLING DEVICE

To make it possible to avoid an unstable state with a simple configuration even one of the phases of the motor fails A motor drive system in accordance with the present invention includes a motor to which a plurality of phase coils of five phases or more are connected in a star connection, an inverter connected to one end of each of the phase coils, the inverter being configured to convert a DC power into an AC power and supply the AC power to each phase of the motor, a power relay disposed at another end of each of the phase coils, the power relay being configured so as to be able to cut off a supply power to at least one phase coil among the plurality of phase coils of the motor by using a plurality of contact points interposed between the star-connected coils, and a control unit that generates a control signal for the inverter and thereby controls driving of the motor. When one or more phase of the motor fails, the control unit opens a contact point of the power relay corresponding to the failed phase and drives three or more phases that are disposed at roughly equal phase-intervals among a plurality of remaining phases.