Patent ID: 8716964

Claim:
A motor drive device for driving a brushless DC motor including a rotor and a stator having three-phase windings, the device comprising: an inverter for converting DC electric power to AC electric power and supplying the electric power to the brushless DC motor; a current phase detection unit for detecting a phase of a current flowing through the brushless DC motor; a speed command unit for indicating a command speed of the brushless DC motor; a position detection unit for detecting a relative position of the rotor of the brushless DC motor; a phase correction unit for outputting a commutation signal for switching a winding to be energized in the brushless DC motor based on: a detection result of the current phase detection unit; the command speed indicated by the speed command unit; and the relative position detected by the position detection unit, so that a phase of a current flowing in a predetermined winding of the brushless DC motor and a phase of a voltage hold a predetermined relation; and a drive unit for outputting a drive signal to the inverter based on the commutation signal output from the phase correction unit, wherein the drive signal indicates a supplying timing of the electric power supplied to the brushless DC motor by the inverter, and wherein the phase correction unit outputs the commutation signal so that: the motor drive device performs a feedback control when the brushless DC motor is under low-load conditions; and the motor drive device performs a synchronous drive when the brushless DC motor is under high-load conditions, and wherein the phase correction unit comprises; a first commutation unit that outputs a first commutation signal for switching a winding to be energized in the brushless DC motor based on a signal of the position detection unit and the command speed; and a second commutation unit that: obtains the phase of a current detected by the current phase detection unit, the command speed, and a time from a reference current phase to a commutation; calculates a finite difference by comparing the time with an average of the time of the past; calculates a corrected amount of the communication cycle based on the finite difference decides a corrected commutation cycle of a second commutation signal by adding the corrected amount to the commutation cycle; and outputs the second commutation signal for switching a winding to be energized in the brushless DC motor.