Low Cost, Power Dense, Axial Gap, Rare-Earth-Free PM Motor for Electric Drive Vehicles

Cost and size reductions are needed in the electric traction drive system currently used for electric drive vehicles (EDV) to make them cost and performance competitive with fossil fuel vehicles. Such cost parity is critical to achieving public acceptance and expanded market share of EDV products. To achieve cost and size parity, the DoE’s Electrical and Electronics Technical Team has established 2025 technical targets, which include $3.3/kW and 50kW/L for the electric traction motor. Interior permanent magnet (IPM) synchronous motors have proven a popular choice for the traction motor in current EDVs due to their high torque and power density, high efficiency, simple construction, easy control, and field weakening ability for constant power operation.However, the rare-earth magnets used in these motors are costly, accounting for 20% to 30% of the total motor cost.Furthermore, as China is the primary supplier of the rare-earth materials used in these magnets, they are susceptible to supply constraints and cost volatility.Therefore, the DoE is seeking a motor solution that can meet stringent 2025 cost and power density targets without the use of rare-earth materials. Proposed for this application is a novel, axial gap, IPM motor design that uses low cost Alnico magnets. This design possesses a number of attractive features that make it a promising candidate for meeting 2025 targets. First, it uses a single stator, dual-rotor topology that makes efficient use of active materials (i.e. magnetic core and windings) while minimizing non-active components for lower cost and higher power- density. Second, it uses a unique wave winding that provides low copper losses, excellent cooling, and a large magnetic air gap for further power-density enhancement. Third, it employs an advanced rotor design expected to provide high air-gap flux densities while avoiding demagnetization of the Alnico magnets. This structure should also enable efficient constant power operation over a wide speed range, desirable for an economical power converter. The Phase I effort will explore several design variations and choose the most promising to optimize. This design will be optimized and evaluated relative to its ability to meet 2025 cost and power density targets. Assuming feasibility is confirmed, Phase II will construct and test a working prototype system and validate performance expectations. Commercialization of the technology will be pursued following successful validation.