Permanent magnet technology for electric motors in automotive applications

With significant advance of rare earth permanent magnets (REPM) and power electronic components in the last two decades REPM motor drives have gradually been integrated into various automotive applications. Those include electric traction and propulsion, various X-by-wire and other electromechanical systems. REPM traction motors for electric propulsion and REPM motor drives for electric power steering (EPS) applications, just to name a few, are successful commercial examples in today´s automotive marketplace for mass production. In spite of many perceived benefits, for instance reduction of weight and CO₂ emission, automotive REPM drive manufacturers have today to face high manufacturing costs, due primarily to a recent tremendous price increase of REPM. In this paper, permanent magnet design technology is reviewed, which covers the main PM categories with key features. The aim is to provide a fundamental guideline for material selection. Furthermore, synthesis, design and optimization of magnetic circuits of magnet rotors for different permanent magnet motor topologies are discussed. For electric motors in automotive applications it is of great importance to minimize the cost without compromising the motors´ performance, overall reliability and stability with respect to demagnetization. A number of innovative magnetic circuit design examples are revealled in this report, demonstrating how to handle different types of motor topologies and which kind of magnet should be used for.