| 摘要 |
<p>As the permanent-magnet rotor of an electric machine accelerates, it induces an increasing back-emf in a winding of the machine. It therefore becomes increasingly difficult to drive power into the electric machine. The invention is a method of controlling an electric machine in which a winding of the electric machine is excited in advance of zero-crossings of back emf in the winding by a fixed advanced time T_ADV over a range of speeds of the electric machine. Therefore the advance angle increases with the speed of the rotor. The fixed advance time T_ADV may vary with excitation voltage. A battery may supply the excitation voltage and as the battery pack discharges the excitation voltage and hence the advance time varies so that power output of the electric machine remains constant. The electric machine may be a motor and is suitable for use in a vacuum cleaner.</p> |
