Rotor Reinforcement in High-Speed Motors by Polymer Composites

Reducing motor cost and increasing efficiency are key targets in the pursuit of longer range and lower cost electric propulsion systems. In this paper, a study is presented to increase the operational speed, power, torque, and efficiency of electric motors by reinforcing the rotor with non-conductive, non-magnetic polymer composites. The proposed rotor reinforcement approach is applied to a 16,000 rpm synchronous reluctance motor that does not contain any permanent magnets and therefore utilizes only reluctance torque. Two methods of polymeric reinforcement are studied. In both methods, the polymer composite is inserted into the air-filled slots in the rotor and structurally binds to the electrical steel. In the first method, the structural binding is achieved by mechanical interlocks whereas in the second method it is accomplished through chemical adhesion. Size reduction or complete elimination of electrical steel webs that structurally reinforce the rotor against the centrifugal forces is pursued. These webs are responsible for reduced torque, power, and efficiency in traditional motor designs. In the case of permanent magnet machines, the structural webs also reduce the power factor and the utilization of magnet material, increasing the system cost. In this study, the two polymeric reinforcement methods are compared in terms of structural and electromagnetic performance of the rotor using Finite Element Analysis. Results show that chemical adhesion provides better structural and electromagnetic performance of the rotor than joining by mechanical interlock. Elimination of the webs is predicted to significantly increase torque, power, and efficiency of the motor. Experimental testing is conducted to evaluate the bonding between electrical steel and polymer composites, demonstrating that sufficient bonding strength is achievable between these materials.