Three-Dimensional Printed Fluid-Filled Electrostatic Rotating Machine Designed with Conformal Mapping Methods

Abstract

Recently, fluid-filled electrostatic machines demonstrated specific and volumetric torque densities that hold promise to be competitive with electromagnetic machines in niche applications, e.g., air-cooled, low-speed, and direct-drive machines. These demonstrations of variable capacitance (or elastance, which is the dual of reluctance) machines were nonoptimized from an electrostatics perspective as their geometry was heavily constrained by manufacturability issues. This paper proposes a semi-analytical design method that combines conformal mapping techniques with finite element analysis, leading to more optimal electrostatic machine geometries. Parametric sweeps of key relative dimensions establish best practices/guidelines for design. A fractional horsepower proof of concept machine was designed using the new approach and was built using stereolithographic three-dimensional printing to circumvent manufacturing constraints. The machine is mostly plastic, plated with conductor, and is, therefore, lightweight. This manufacturing approach suggests that a machine can be injected molded or cast in a single step. Measurements of the prototype demonstrate a torque density of 0.31 Nm/L and specific torque density of 0.22 Nm/kg, comparable with similar size NEMA frame fractional horsepower induction motors. Also the Nm/kV2 of the prototype machine is two orders of magnitude greater than prior nonliquid-filled work.