Real-time self-diagnosis method in operation of motor of electric power steering system

The invention discloses a real-time self-diagnosis method in operation of a motor of an electric power steering system. Two phase line relays are installed on phase lines of the motor of the electric power steering system, an estimation value of control voltage Vd of a direct shaft d, an estimation value of control voltage Vq of an alternating shaft q, an estimation value of current id of the direct shaft d and an estimation value of current iq of the alternating shaft q are respectively estimated based on a motor control model, each obtained estimation value is compared to a corresponding practical controlling value, and differential values serve as bases which are used for judging whether motor faults exist or not; and when the motor faults are confirmed to exist, the two phase lines installed on the phase lines of the motor are cut off, current between accesses of the phase lines of the motor is cut off, a motor return circuit is prevented from generating current, and the electric power steering system is