| 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 according to the speed of the machine. Over a first speed range a winding of the electric machine is excited in synchrony with zero-crossings of back emf in the winding. Over a second speed range the winding is excited in advance of the zero-crossings by a fixed period of time T_ADV. Over a third speed range the winding is excited in advance of the zero-crossings by a period of time T_ADV that varies with speed. The electric machine may be a motor and is suitable for use in a vacuum cleaner.</p> |
