A method for detecting a magnetic field location in an electric motor, which comprises:
- a rotor having a permanent magnetic field;
- and a stator having three-phase coils, and which is initiated by 120°-energization of a constant-voltage DC electric source,
- the electric motor further comprising:
- output means for two-way-energizing the coils through a half-bridge type inverter circuit;
- measurement means for A/D-converting coil voltage and sending the converted voltage to control means;
- and
- the control means for PWM-controlling coil output on the basis of a command of a superordinate controller, storing energization angle information and energization pattern information, for continuous rotation, in units of 60°-energization sections, switching-controlling the output means so as to switch an energization state on the basis of the stored information, inputting a measurement value of the measurement means, and determining an end point of the 60°-energization section,
- wherein an energization section of electric angle of 30°-90° is named as a section 1, an energization section of electric angle of 90°-150° is named as a section 2, an energization section of electric angle of 150°-210° is named as a section 3, an energization section of electric angle of 210°-270° is named as a section 4, an energization section of electric angle of 270°-330° is named as a section 5, and an energization section of electric angle of 330°-30° is named as a section 6, and a positive-side threshold value and a negative-side threshold value, each of which has prescribed potential difference, within a range not exceeding peak voltage or bottom voltage of non-energization-phase voltage, with respect to a neutral point potential which is a half of inter-energization-phase voltage, are previously set in the control means,
- said method comprising the steps of:
- performing PWM-energization, which periodically includes off-cycles, in an energization pattern in which a location of self-excitation-stopping caused by two-phase locked energization performed by the output means corresponds to a start point of the 60°-energization section, when present locations and rotational directions of the rotor have been decided;
- measuring energization-phase voltage and non-energization-phase voltage in on-cycles of the PWM-energization;
- obtaining, through calculation, a neutral point potential from the energization-phase voltage measured by the measurement means;
- determining the start point of the 60°-energization section when the non-energization-phase voltage intersects the neutral point;
- obtaining a difference between the neutral point potential and the non-energization-phase voltage;
- performing magnitude comparison between the difference and the negative-side threshold value in the case where the present location is an odd-numbered section or between the difference and the positive-side threshold value in the case where the present location is an even-numbered section;
- and determining an end point of the 60°-energization section when the difference exceeds the threshold value in a direction away from the neutral point potential.