Patent ID: 7535188

Claim:
A motor driving apparatus which includes a rotor and a stator having motor coils of a plurality of phases, the motor driving apparatus comprising: a virtual neutral point unit that has a virtual neutral point, and provides a voltage obtained by averaging motor terminal voltages at the virtual neutral point; an inverter comprising a plurality of switching elements; a back electromotive voltage detecting unit operable to detect a back electromotive voltage of the motor; a neutral point difference voltage detecting unit operable to detect a neutral point difference voltage which is a difference voltage between the virtual neutral point and an actual neutral point which is a common connection point of the motor coils; a rotor position detecting unit operable to detect a position of the rotor on the basis of the neutral point difference voltage; and a controller operable to control commutation of the inverter, wherein the controller has, as operational modes, a searching start mode for determining conduction phases at the start of the motor on the basis of the detection result by the rotor position detecting unit and energizes the coils of the determined conduction phases; and a back electromotive voltage feedback mode for controlling commutation on the basis of the back electromotive voltage detected by the back electromotive voltage detecting unit, the controller alternately performs a rotor position searching process and a rotation start torque applying process in the searching start mode, the rotor position searching process applies a search pulse for detecting the rotor position in forward and backward directions of at least a pair of conduction phases to detect neutral point difference voltages, and adds up the neutral point difference voltage obtained in the forward direction and the neutral point difference voltage obtained in the backward direction, to determine the rotor position on the basis of a polarity of the added neutral point difference voltage; and the rotation start torque applying process applies a predetermined rotation torque to the rotor on the basis of the rotor position determined by the rotor position searching process.