switched reluctance motor-technical-report

The switched reluctance motor drive is the most rugged of all motor types and is fault tolerant since the phases (pole-pairs) are energized by separate circuits. With proper design, one or more phases can be lost without totally disabling the motor, thus giving “limp home” capability. Other advantages include high power/torque density, low rotor losses, low cost, simple power electronics, and low switching speed and associated losses. The historical problems associated with switched reluctance motors – audible noise and torque ripple – have already been largely solved for other applications and are not a factor in the LCAC environment.

The type of lead screw proposed for LCAC service is a variant called a “roller screw”. The roller approach makes dramatic improvements in speed, thrust, maintenance, wear, lifetime and reliability when compared to the better known “power screw” and “ball screw” configurations. When coupled with advanced coatings, a roller screw should not need any lubrication and will be virtually maintenance free. The housing of the overall actuator mechanism will likely use lightweight, energy-dampening composite materials.

The new linear actuator could be completely self-contained with the lead screw, motor, power electronics and sensors integrated into a single package, but in the LCAC application it is more prudent to put the power electronics unit on the inside of the robust metal support for the nacelle which surrounds the propulsion propellers. This location provides protection from damage and direct sun, and will minimize the weight of the components subject to vibration. While the approach has pushed state-of-the-art of linear actuators ahead with respect to the constituent technologies – switched reluctance motor drives, lead screws and advanced materials and coatings – it also offers a near-term solution to ongoing maintenance issues for the LCAC. In addition, the new linear actuator can be used in many other applications in Navy vessels and thus contributes to the Navy’s long-term all-electric ship efforts where hydraulic systems will be replaced with power electronics and advanced motors.

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