This has triggered a surge in research and development to search for technical solutions for even better drive systems suitable for everyday use.

Highly efficient motors have required magnets, i.e. materials based on rare earth. For various reasons, this is not without problems. For example, more than half of the final price is formed by raw materials cost.

A consortium of 13 companies and organizations, including the University of Aquila, has joined forces in the ReFreeDrive project to develop the next generation of electric drivetrains, ensuring the industrial feasibility for mass production while focusing on the low cost of the manufacturing technologies.

Throughout the project duration between 2017 and 2020, ReFreeDrive chose the World Magnetic Conference at Coiltech to disseminate the findings.

These dissemination sessions are one prerequisite for the funding on behalf of the European Commission which funded the project (Horizon 2020, GV04 programme, grant no. 770143). 

The project partners have simultaneously researched and developed two solutions for the electric drive system of electric vehicles. Both solutions are brushless AC electric machines: induction machine with a fabricated and die-cast copper rotor (IM) and synchronous reluctance machine (SynRel).

The involvement of 13 companies - whose individual focus is on different levels in the development and production process - from the design stage ensures the feasibility of a minimization of the manufacturing cost. ReFreeDrive motor topologies have good room for cost reduction by off-setting permanent magnet use.

Publication of the results and project funding by the European Commission

Throughout the duration of the project, between 2017 and 2020, ReFreeDrive chose Coiltech's World Magnetic Conference to disseminate the results.

These dissemination sessions are a prerequisite for the project funding by the European Commission (Horizon 2020, programme GV04, grant no. 770143).

Prices for rare earth materials have been fluctuating greatly in some cases and there are only a few suppliers worldwide. This means a high procurement risk, especially if a product is highly competitive mass production, such as cars, depends on the availability of such material.

ReFreeDrive had developed the prototype of a 200kW e-power drivetrain that works without rare earth materials that is just as if not even slightly more performant as a conventional motor that is already in mass production. The performance and efficiency of the prototype are promising for mass production.

A successful design and prototyping of two types of motors ( Induction Motors - IM - and Synchronous Reluctance Motors - SyncRel - in two meaningful power ranges (75kW and 200kW) requires the development of innovations at different levels including electromagnetic design, materials investigation, power electronics, control algorithm and cooling.

The following companies and institutions have united their forces for the development of rare earth-free traction technologies beyond the current state-of-art, with a strong focus on industrial feasibility for mass production:

The induction motor is a promising technology for automotive applications with good performance in terms of torque capability, specific power and efficiency. The rotors are made by laminated electrical steel and aluminium or copper-based squirrel cage, making this motor technology highly recyclable.

The adoption of copper as rotor conductor material enhance the motor performance and efficiency but the manufacturing of the squirrel cage is quite challenging. Cooling aspects are also critical.

Induction Motor Die-cast Copper Cage

When die-casting technology is used, high temperatures and pressure are involved, and degradation of the rotor laminations is possible. Properly developed die-casting technology is capable to manage the whole process to obtain high-quality copper rotors.

The ReFreedrive IM is designed in cooperation with copper die-casting experts to exploit at the best the capabilities of this technology in EV traction motors.

Induction Motor with Fabricated Copper Cage

The fabricated copper rotor technology has been evaluated as an alternative copper rotor technology. This technique adopts properly designed copper bars to be mechanically installed in the rotor slots. The bar dimension and the alloy have been carefully designed in cooperation with copper bars manufacturers in order to sustain the centrifugal stress in the rotor at high speed without affecting conductivity.

Additional attention must be paid to the end-ring assembly, where the brazing process may alter the electrical and mechanical connection between the parts in contact, resulting in lower electromagnetic performance and poorer mechanical resistance.

Pure synchronous reluctance technology is based on a rotor made only by laminated electrical steel, where the particular rotor shape is the key for torque production. Synchronous Reluctance Motors are becoming of great interest in recent years, due to their potential cost-effectiveness, efficiency and performance.

The PM assisted synchronous reluctance motor enhances the characteristics of the synchronous reluctance motors through the introduction of Permanent Magnets. Low cost rare-earth free ferrite permanent magnets were implemented in the rotor in order to increase specific performances of this motor topology without any use of rare earth material. High performances were achieved with standard AC currents though rotor design optimisation technics taking the most of low-performance magnets such as ferrites.

Best in class electronics power modules featuring the Silicon Carbide Technology is adopted to reach very high-efficiency ratings, up to 99%. Custom laminated bus bar has been designed to allow a high-performance interconnection for the DC capacitors and power modules. Despite the today cost of the Silicon Carbide Power Modules it is estimated to be competitive for mass production in 2025 (about 3-5€/kW).