| 摘要 |
A method of controlling a brushless permanent-magnet motor comprises dividing each half of an electrical cycle of the motor into a conduction period followed by a primary freewheel period. The conduction period is then divided into a first excitation period, a secondary freewheel period, and a second excitation period. The method then comprises exciting a winding of the motor during each excitation period and freewheeling the winding during each freewheel period. The secondary freewheel period has a position and length within the conduction period that acts to reduce the harmonic content of current in the winding relative to back EMF in the winding. As a result, the efficiency of the motor is improved. The secondary freewheel period may occur at a time when back EMF in the winding is rising, and the primary freewheel period when back EMF is principally falling. The method may be used within a specified speed range only. |
