Advanced Motor Designs to Mitigate MnBi Permanent Magnet Demagnetization

University of Pittsburgh researchers have developed an innovative design methodology to mitigate the risk of temperature-dependent irreversible demagnetization in rare earth (RE) free/lean permanent magnet synchronous motors (PMSMs). This method is particularly useful for Manganese Bismuth (MnBi) permanent magnets, which have high energy density at high temperatures but are susceptible to demagnetization at low temperatures. The design optimizes the permeance of flux paths in PMSMs, ensuring reliable performance and competitive power densities.

Description

The invention employs an iterative multi-objective optimization (MOO) design procedure to control the risk of demagnetization by tuning the permeance of flux paths in PMSMs. The method involves optimizing the shape of stator teeth/slots to minimize air gap flux density dips, which can cause demagnetization. Key parameters include magnet arc ratio, magnet reduction, magnet radial thickness, slot opening ratio, slot depth ratio, tooth width ratio, airgap length, and tooth tip angle. This approach is demonstrated in a 1 kW MnBi surface permanent magnet synchronous motor (SPMSM) prototype, showing that thicker stator teeth with larger tooth tips and smaller slot openings effectively mitigate demagnetization risk.

Applications

• Electric vehicles (EVs) and electrified transportation systems
• High-frequency power electronics
• Renewable energy systems
• Industrial motor applications

Advantages

This technology offers a novel approach to mitigating demagnetization in RE-free/lean PMSMs, particularly for MnBi permanent magnets. The design methodology considers a wide range of geometric parameters, ensuring comprehensive optimization. The method can be adapted to various motor topologies, including interior permanent magnet synchronous motors (IPMSMs) and PM assisted synchronous reluctance motors (PMASynRM). The optimized designs provide reliable performance, competitive power densities, and enhanced durability.

Invention Readiness

The invention is currently at the design stage, with a 1 kW MnBi SPMSM prototype demonstrating the effectiveness of the methodology. Further development includes optimizing the design for higher power levels and different motor topologies. The project is supported by a US DOE STTR grant, with industry partners Powdermet and Dimagnetica involved in scaling the MnBi manufacturing process and motor manufacturing, respectively.