Fractional Horsepower Synchronous Electrostatic Machines for Direct Drive Industrial Applications

Synchronous Electrostatic Machines (SEMs) derive their torque from voltage, not current, thereby incurring low conduction loss, even at stall. Additionally, their construction requires far less semi-precious materials, e.g. zero rare earths, more than 90% less copper, etc. These attributes may provide a significant advantage in low speed industrial applications and this paper seeks to evaluate SEMs as candidates for fractional horsepower direct drive pumps, conveyors or fans. The low conduction loss benefits extend beyond stall and enable lightweight, torque dense machines with no cooling system required for low speed applications (less than 300 rpm). The design and validation of a 360 W (1/2 HP), 18 Nm, 200 rpm SEM constructed from aluminum, fiberglass and plastic is presented as a viable candidate for industrial use. Measured results for torque, efficiency and loss distribution are presented. The SEM meets IE4 criteria for 75% of operating speed range. The SEM is compared with interior permanent magnet (IPM) and squirrel cage induction machines (IM) paired with gearboxes in a hydraulic pump application. The SEM demonstrates substantially better thermal performance and 30% - 100% increased fluid flow per Watt [Lpm/W].