STARTING A BRUSHLESS DC MOTOR

摘要

A brushless dc motor is started by the following basic steps: (1) specify an arbitrary rotor position and apply such drive currents to the three motor phase inputs that the rotor moves to the arbitrary rotor position; (2) apply a current pulse to the appropriate winding such that the rotor moves in the desired direction of rotation; (3) after the motor has begun to turn, stop the current supply to the motor phase inputs; (4) allow the current in the motor to decay to a level where the I x R voltage drops in the windings are substantially less than the back EMFs at the speed the motor is turning at; (5) sample the (very small) back EMFs generated in the windings; (6) monitor the sampled back EMFs to detect whether the rotor has moved to a position requiring a change in commutation; (7) supply drive current to the three motor phase inputs in accordance with whether or not a need for a change in commutation was detected in step (5) and so that the rotor will continue to turn in the required direction; (8) repeat steps (4) to (7) a predetermined number of times at a rate greater than the commutation rate (i.e. more frequently as the motor speed increases) and at a rate directly proportional to the speed of the motor; (9) repeat steps (4) and (5); (10) determine the current position of the rotor from the sampled back EMFs; (11) supply such current to the three motor phase inputs that will cause the motor to turn in the required direction form the current position; (12) repeat steps (4) to (11) until the back EMF voltages are significantly greater than the IR losses in the windings; (13) when the back EMFs are significantly greater than the IR losses in the windings, supply current to the motor phase inputs (i.e. commutate) in dependence on the current position of the rotor as determined by continuous comparison of the back EMFs.