Sensorless brushless dc motor starting system and method

Abstract

A method for starting a sensorless brushless DC motor. The present invention uses the physical equations of motion of the motor to calculate commutation advancement rates during the motor's start-up period. An algorithm initially calculates the commutation advancement rates for the motor's maximum theoretical accelleration. The commutation applied to the motor is advanced through a predetermined number of commutation states using these maximum rates. After the predetermined number of commutation states have been applied, the speed of the motor is checked to determine whether the motor is spinning at a high enough speed to permit use of the motor's normal commutation state advancement system. If the motor is not up to speed, the rate at which the commutation states are advanced is incrementally decreased until satisfactory operation of the motor is obtained or until motor failure is diagnosed and starting is aborted. By starting at a high commutation state advancement rate and incrementally reducing the commutation advancement rate until proper accelleration of the motor is attained, the present invention continuously adapts the rate of advancement of the applied commutation states to the condition of the motor, thereby automatically compensating for changes in the motor's performance over time.