Patent ID: 7288911

Claim:
A method for adjusting a rotational speed of a rotor in a polyphase motor from a first speed towards a second, faster speed when the motor is commutating according to a commutation scheme at a first commutation phase angle, the method comprising: determining said first commutation angle utilizing a first back EMF voltage detected in said motor; commutating said motor when the first back EMF voltage is detected in said motor; selecting an advanced phase angle relative to the first commutation phase angle for commutating the motor; and adjusting the commutation scheme to be commutating at the advanced phase angle by calculating a rate of change of back EMF in the motor at the first speed using a back EMF constant of the motor; determining a second back EMF voltage according to the rate of change in respect of the advance phase angle; and adjusting the commutation scheme to commutate when the second back EMF voltage is observed, whereby the rotational speed of the rotor increases from the first speed towards the second speed as the motor is commutating at the advanced phase angle.