Ultrasonically modulated drive system incorporating permanent magnet machine

The combination of a rare earth permanent magnet machine and an ultrasonically modulated inverter produces a drive system which is both efficient, economical and flexible. The machine can be designed with a high power to weight ratio and does not need to be derated when connected to the inverter supply. Audio acoustic noise generated by the inverter is eliminated and the system is, therefore, suited to many applications involving quiet drives, in particular fan drives and ventilation systems. Other applications involve systems where a precisely controlled speed is required. Because of the use of a modular approach in the inverter construction the drive rating can be easily expanded. From a single pole module design an entire range of drive ratings can be produced and manufactured cheaply in quantity. The use of digital control for the system leads to greater reliability whilst reducing the controller costs