High-speed single-phase, permanent-magnet, electric machine

摘要

An electric system 5 comprises a single-phase permanent-magnet electric machine 8 and a control system 9 for driving the electric machine. The control system sequentially excites and freewheels a winding (19, fig. 3) of the electric machine. The control system then varies the times at which the winding is excited and freewheeled in response to changes in excitation voltage such that the electric machine is driven at speeds in excess of 60 krpm over a range of excitation voltages extending between a minimum voltage and a maximum voltage, the minimum voltage being less than 80% of the maximum voltage. The machine may be a motor suitable for use in a vacuum cleaner. The power supply may be a removable battery pack. The control system may vary the time at which the winding is excited and the time over which the winding is freewheeled such that the vacuum cleaner maintains substantially constant suction in response to changes in the voltage of the power supply.