Brushless motor control method and brushless motor control device and electric power steering device

A method of controlling a brushless motor that includes a stator, which includes an outer-side ring portion, a plurality of tooth portions protruding from the outer-side ring portion toward a radial-direction inner side, and armature windings of a plurality of phases that form a sinusoidal waveform as an induced voltage between lines via a slot formed between the tooth portions, and a rotor, in which a permanent magnet is embedded and which is disposed on an inner side of the stator in a rotatable manner, wherein the rotor is rotated by magnet torque that is caused by magnetic attraction force of the permanent magnet and by reluctance torque that is based on a difference in inductance between magnetic paths, the method characterized by comprising:

• calculating fundamental-wave current indicating a winding current value by which a maximum torque is output in the brushless motor, in accordance with a load condition of the brushless motor;
• calculating a first higher harmonic wave component that has the same amplitude and the same cycle as a torque ripple caused by the magnet torque and is opposite in phase to the torque ripple, based on a correction map that shows relation between phase current of the armature winding and parameters that are used to calculate the first higher harmonic wave component;
• calculating a second higher harmonic wave component that has the same amplitude and the same cycle as a torque ripple caused by the reluctance torque with the first higher harmonic wave component being superimposed thereon and is opposite in phase to the torque ripple, based on a correction map that shows relation between phase current of the armature winding and parameters that are used to calculate the second higher harmonic wave component;
• and
• correcting current that is supplied to the armature windings by superimposing the first and second higher harmonic wave components on the fundamental-wave current.

A control device of a brushless motor that includes a stator, which includes an outer-side ring portion, a plurality of tooth portions protruding from the outer-side ring portion toward a radial-direction inner side, and armature windings of a plurality of phases that form a sinusoidal waveform as an induced voltage between lines via a slot formed between the tooth portions, and a rotor, in which a permanent magnet is embedded and which is disposed on an inner side of the stator in a rotatable manner, wherein the rotor is rotated by magnet torque that is caused by magnetic attraction force of the permanent magnet and by reluctance torque that is based on a difference in inductance between magnetic paths, the control device characterized by comprising:

• a current sensor that detects phase current of the armature windings;
• a base current calculation section that calculates fundamental-wave current indicating a winding current value by which a maximum torque is output in the brushless motor, in accordance with a load condition of the brushless motor;
• a correction component calculation section that calculates, based on a phase current value detected by the current sensor, a first higher harmonic wave component that has the same amplitude and the same cycle as a torque ripple caused by the magnet torque and is opposite in phase to the torque ripple, and a second higher harmonic wave component that has the same amplitude and the same cycle as a torque ripple caused by the reluctance torque with the first higher harmonic wave component being superimposed thereon and is opposite in phase to the torque ripple;
• a correction map that shows relation between the phase current and parameters that are used to calculate the first and second higher harmonic wave components;
• and
• a current correction section that corrects current that is supplied to the armature windings by superimposing the first and second higher harmonic wave components calculated by the correction component calculation section on the fundamental-wave current.

An electric power steering device that uses, as a driving source, a brushless motor that includes a stator, which includes an outer-side ring portion, a plurality of tooth portions protruding from the outer-side ring portion toward a radial-direction inner side, and armature windings of a plurality of phases that form a sinusoidal waveform as an induced voltage between lines via a slot formed between the tooth portions, and a rotor, in which a permanent magnet is embedded and which is disposed on an inner side of the stator in a rotatable manner, wherein the rotor is rotated by magnet torque that is caused by magnetic attraction force of the permanent magnet and by reluctance torque that is based on a difference in inductance between magnetic paths, the electric power steering device characterized by:

• calculating fundamental-wave current indicating a winding current value by which a maximum torque is output in the brushless motor, in accordance with a load condition of the brushless motor;
• calculating a first higher harmonic wave component that has the same amplitude and the same cycle as a torque ripple caused by the magnet torque and is opposite in phase to the torque ripple, based on a correction map that shows relation between phase current of the armature winding and parameters that are used to calculate the first higher harmonic wave component;
• calculating a second higher harmonic wave component that has the same amplitude and the same cycle as a torque ripple caused by the reluctance torque with the first higher harmonic wave component being superimposed thereon and is opposite in phase to the torque ripple, based on a correction map that shows relation between phase current of the armature winding and parameters that are used to calculate the second higher harmonic wave component;
• and
• correcting current that is supplied to the armature windings by superimposing the first and second higher harmonic wave components on the fundamental-wave current.