Method of determining a position of a rotor of a brushless permanent magnet motor

A brushless permanent magnet motor, comprising a controller configured to:

• measure instantaneous phase current flowing through a phase winding of the motor during excitation of the phase winding;
• measure voltage applied to the phase winding of the motor during excitation of the phase winding;
• calculate a phase of back EMF induced in the phase winding using the measured instantaneous phase current and the measured voltage;
• determine, using the calculated phase of back EMF induced in the phase winding, a zero-crossing point of the back EMF induced in the phase winding of the motor;
• and
• determine, based on when the back EMF induced in the phase winding is at the zero-crossing point, an aligned position of the rotor of the brushless permanent magnet motor.

A data carrier comprising machine readable instructions for the operation of a controller of a brushless permanent magnet motor to:

• measure instantaneous phase current flowing through a phase winding of the motor during excitation of the phase winding;
• measure voltage applied to the phase winding of the motor during excitation of the phase winding;
• calculate a phase of back EMF induced in the phase winding using the measured instantaneous phase current and the measured voltage;
• determine, using the calculated phase of back EMF induced in the phase winding, a zero-crossing point of the back EMF induced in the phase winding of the motor;
• and
• determine, based on when the back EMF induced in the phase winding is at the zero-crossing point, an aligned position of the rotor of the brushless permanent magnet motor.