Speed-based open-loop start-up method for brushless DC motor

摘要

A method of starting a brushless DC motor 12 at any initial speed (A) establishes a initial stator-field speed and setting a counter of synchronisation, (B) measures a speed of a rotor of the motor, (C) compares the speed of the rotor with the stator-field speed to determine if the rotor is synchronised with the stator-field. If the rotor is not synchronised with the stator-field, the method includes (a) re-setting the counter of synchronisation, (b) increasing an acceleration portion of motor current (Iacc) to enhance torque, (c) setting the stator-field speed higher than the rotor speed, (d) calculating a period of an open-loop timer, (e) calculating a value for a load portion of the motor current (Ild), where total motor current I = Iacc + Ild, (f) performing commutation based on the open-loop timer and returning to step (B) until the rotor is synchronised with the stator-field. If synchronisation of the rotor and stator-field is determined, the method includes incrementing the counter of synchronisation, determining if the counter is greater than a certain value, and if the counter is greater than the certain value, switching from open-loop commutation to closed-loop commutation. If the counter is not greater than the certain value, the method includes proceeding to step (c).