Importance

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Abstract

In a positioning control performed in an event of starting a low-speed sensorless control, a positioning energization mode of energizing two phases among three phases of a brushless motor and maintaining this energization is implemented. When a predetermined time has elapsed from the implementation of the positioning energization mode, a variation α of a non-energized phase voltage in the positioning energization mode is computed so as to estimate an operation direction of a rotor, and a switching flag Fmod of an energization mode is set based on whether this variation a is positive or negative. Then, in response to a value of the switching flag Fmod, the energization mode is temporarily switched to other energization mode so as to generate torque for the rotor in a direction reverse to the operation direction thereof, and a “brake” is applied, resulting in a shortened time required to position the rotor.

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First Claim