Quiet, Compact High Frequency Brushless DC Motor and Controller

Torpedo and unmanned underwater vehicles (UUV) need 8-20 HP electric motors with variable speed to 800 RPM. The magnetic iron core used in motors for carrying the magnetic flux, generates audible noise if the operating frequency and its harmonics are in the audible range. Thus a low speed motor generally has audible noise associated with its magnetic circuit. We propose a permanent magnet (PM) brushless motor that operates at a high fundamental frequency level in the electromagnetic circuits, but has low operating speeds because of the unique magnetic circuit configuration. This configuration allows use of a large number of magnetic poles resulting in the required low speed of operation. This together with the ability to have a small concentric air gap between the stator and the rotor, helps to reduce the overall size of the motor. A zero voltage switching resonant type converter is planned for the motor controller to minimize the radiated noise. During Phase I, complete electromagentic design of the motor will be accomplished based on specific needs for a UUV application. Controller topology and sizing will be also addressed. Critical items such as power density, audible noise, EMI, and reliability will be analyzed during Phase I. During Phase II, a complete prototype system including the motor and the controller will be fabricated and tested. Test measurements will include full load operation, efficiency measurements, and noise and EMI measurements.