Drive device and method for three-phase brushless motor

A drive device for a three-phase brushless motor, the drive device comprising:

• a drive circuit for driving the three-phase brushless motor;
• and
• a controller for outputting a control signal to the drive circuit so as to perform sensorless control by sequentially switching between six energization modes each for selecting two phases to be energized from three phases of the three-phase brushless motor, wherein
• before performing the sensorless control,
• the controller outputs, to the drive circuit, the control signal for momentarily energizing, as first energization, the three-phase brushless motor according to each of the six energization modes, and detects six first induced voltages each generated in a non-energized phase by the first energization, and calculates three induced voltage differences corresponding respectively to three non-energized phases, each induced voltage difference being a difference between two of the six first induced voltages that are detected during the first energization according to two energization modes that share a non-energized phase,
• the controller outputs, to the drive circuit, the control signal for energizing, as second energization, the three-phase brushless motor according a predetermined energization mode set based on size comparison between the three induced voltage differences, and detects a second induced voltage generated in a non-energized phase along with a rotation of a rotor caused by the second energization performed subsequently to the first energization, and
• the controller estimates an initial position of the rotor based on a change in the second induced voltage generated by the second energization.