High Speed Water-Cooled Permanent Magnet Motor for Pulse Alternator-Based Pulse Power Systems

Pulse alternator-based pulse power systems for electromagnetic rail guns store the required energy for powering the rail gun as stored mechanical inertial energy in the rotating member. The pulse alternator (PA) converts the stored inertial energy into electrical energy that is supplied to the rail gun terminals. The losses in the system and energy delivered to the rail gun projectile reduce the stored inertial energy of the pulse alternator by reducing the operating speed. Pulse alternators require a charging mechanism to accelerate the rotor of the alternator to the desired speed, providing the mechanical stored energy. This is generally accomplished by a motor attached to the alternator shaft. This paper describes the design, manufacture and initial testing of a high speed, water- cooled permanent-magnet (PM) synchronous motor specially designed to accelerate a high speed pulse alternator. The charging motor has been designed to accelerate the pulse alternator from zero speed to full rated alternator speed and to accelerate the alternator back to rated speed after the pulse discharge. Two PM motors are also used to synchronize two separate paralleled pulse alternators prior to discharge into a rail gun load. The PM motor is directly attached to the PA shaft and designed to minimize the axial footprint of the assembly. The motor is operated in a continuous duty cycle which requires water cooling of the stator assembly and air cooling of the rotor. The PM synchronous motor is powered by a variable-frequency, variable voltage electronic drive and operated in a constant torque mode.