The NASA Glenn Research Center has developed and successfully demonstrated a self-levitated motor control technology for a 12-8 (12 poles in the stator and 8 poles in the rotor) switched-reluctance motor operating in liquid nitrogen (boiling point, 77 K (-196 °C, or -321 °F)). This year, Glenn’s Bearingless Motor Control Team pushed previous disciplinary limits of electromagnetic controller technique by extending the state-of-the-art bearingless motor (see the photograph) operating at liquid nitrogen for high-specific-power applications. The motor was levitated even in its nonlinear region of magnetic saturation, which is believed to be a world first for the motor type.
Glenn’s bearingless, cryogenic switched-reluctance motor.
Early in fiscal year 2006, the Bearingless Motor Team demonstrated self-levitation of the motor at room temperature by limiting the coil currents to the linear region to avoid magnetic saturation as the first step of the study. The present work demonstrated self-levitation well into the fully saturated magnetic region where a super-high-power-density motor operates. The team developed two innovative features in hardware and software. First, the motor does not have separate coils for motor action and magnetic bearing action, but only motor coils as in a conventional motor configuration. Second, because it does not use a mathematical plant model, this simple observation-based controller avoids mathematical complexity and can be implemented in real-time at much higher rotor speeds. The following figures show the rotor orbit within the backup bearing clearance circle at rotor speeds to 4000 rpm, with the maximum available current for the existing amplifier.
Rotor orbits within backup bearing clearance circle. Left: 20 A at 4000 rpm. Right: 22 A at 4000 rpm.
These unique features can significantly reduce controller design time and overall system weight by eliminating separate mechanical or magnetic bearing systems and the associated plumbing and electrical subsystems. Furthermore, they drastically improve overall system efficiency (increasing net power) and reliability because of the simple architecture that needs no additional magnetic bearing system. This noncontact rotor bearing system operating at extremely low temperature is an enabling technology for future NASA missions in space exploration. In addition, this pioneering research can help bring to reality an all-electric, quiet, pollution-free aircraft propulsion system. This work is in support of the Noncombustion Based Propulsion Project.
Glenn contacts:Last updated: November 15, 2007
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