Electric braking in BLDC motors with windings partially and electronically shunted

The paper describes principle of operation of drive using BLDC motor with PM excitation, electronic commutation and two-zone speed control. Smooth transition from constant torque zone to constant power zone is achieved by gradual disconnection (shunting) of parts of motor windings with help of electronic elements (IGBT transistors). This type of control is particularly suited to those PM motors, where it is difficult to use magnets inset into iron (e.g. disc motors, motors with rotating external excitation) and using magnets glued onto rotor surface leads to rapid decrease in motor torque when field is weakened. Basic transistor control systems used during recuperative braking in BLDC motors with electronic shunting of part of armature winding are shown. Different algorithms for braking in 1st and 2nd speed control zone are presented and discussed. The text is illustrated with waveforms obtained on the basis of elaborated mathematical model of the system.