Brushless permanent magnet motor system

A control system for a multi-phase brushless permanent magnet motor having a stator with at least one phase winding per phase of the motor, a rotor mounted for rotation in the stator, said rotor carrying a plurality of permanent magnets so that rotation of the rotor with respect to the stator generates a back EMF in the phase windings of the stator, and motor terminals for each phase adapted to be connected to a power source, comprising:

• means connected to the motor terminals for sensing the back EMF of each phase and in response thereto periodically generating signals representing the relative position of the rotor with respect to the stator;
• means for detecting when the back EMF for each phase referenced to motor neutral crosses zero;
• means for decoding the periodically generated signals to determine the presence of the rotor at one of a plurality of predetermined rotary positions with respect to the stator;
• said decoding means including means for generating an interrupt signal in response to the presence of the rotor at one of the plurality of predetermined rotary positions with respect to the stator;
• electrically controllable switch means connected to the phase windings to control the flow of current therethrough;
• microprocessor control means responsive to the interrupt signal for controlling in a closed loop manner the switch means to commutate the phase windings of the motor a predetermined time after receipt of the interrupt signal, said microprocessor control means also being responsive to the speed of the motor to start the motor in an open loop mode and to shift commutation to the closed loop mode once the motor reaches a predetermined speed.

A method for controlling a multi-phase brushless permanent magnet motor having a stator with at least one phase winding per phase of the motor, a rotor mounted for rotation in the stator, said rotor carrying a plurality of permanent magnets so that rotation of the rotor with respect to the stator generates a back EMF in the phase windings of the stator, zero crossing detecting means for detecting when the back EMF crosses motor netural zero motor terminals for each phase, and electrically controllable switch means connected between a power source and the phase windings to control the flow of current therethrough, comprising the steps of:

• sensing the back EMF of each phase and in response thereto periodically generating signals representing the relative position of the rotor with respect to the stator;
• decoding the periodically generated signals to determine the presence of the rotor at one of a plurality of predetermined rotary positions with respect to the stator;
• generating an interrupt signal in response to the presence of the rotor at one of the plurality of predetermined rotary positions with respect to the stator;
• starting the motor in an open loop mode;
• once a predetermined motor speed has been reached, shifting from said open loop mode to a closed loop mode of operation;
• and
• controlling the switch means in a closed loop to commutate the phase windings of the motor a predetermined time after receipt of the interrupt signal once the predetermined motor speed has been reached.