It is a widespread political will in many countries to reduce vehicles with combustion engines and to substitute them with electrical drives. At the same time, experts the share of electric vehicles sold on all vehicles to increase from 1% in 2015 to 54% in 2040.
High-efficiency traction motors without rare earth materials
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:
Induction motor with copper rotor
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.
Synchronous reluctance motors
Synchronous reluctance motors are being developed in recent years, in particular in industrial applications where they offer good performance and efficiency with a cost-effective rotor construction.
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.
When compared to PM motors, conventional SynRels are known for their lower specific (peak) power and specific (peak) torque, higher noise and lower power factor. Nevertheless, adequate performances can be achieved through an optimized rotor design, in particular at high speed. Within the ReFreedrive Project, new design technics and rotor geometries are evaluated and adopted to enhance as much as possible the motor performances. Different prototypes have been manufacturing to demonstrate the effectiveness of the proposed design.
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.
The power electronics have been integrated into the motor housing to enhance the power density.
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).
Aurubis supplies the rotor bars as an assembly in a squirrel cage for the 2 rated motors (75kW and 200kW); this involves the design and manufacture of extrusion and drawing tooling and the production of the rotor bars in the specified alloy.
Breuckmann eMobility is in charge of casting copper rotors made from pure copper and its alloy as well as finishing the casted rotors. The company also contributes to the design, simulation and production of the die casting tool of the squirrel cage for the SynRel machine.
CIDAUT is responsible for the coordination and management of the project, cooperates in the induction machine mechanical design, performs the testing of the e-drive assembly in a test bench and the LCA analysis.
CSM is involved in the characterization and selection of FeSi Materials for Induction Motors and SynREL motors. The materials selection are based on a global assessment of magnetic properties and the manufacturing process. The analyses include also the mechanical characterization of the materials and FEM stress analysis.
European Copper Institute
The ECI supports the industrial network and long-term involvement in the copper-rotor technology, ECI provides the required background and advice on the induction technology track as needed, both in terms of the value chain and industrialization perspectives.
IFP Energies Nouvelles
IFPEN supports the project research through 3 main axes: leading the SynRel design work package and designing PMaSynRel motor, designing the power electronics based on wide bandgap technology for the high power range application and is involved in motor and inverter characterization.
+33 6 16 53 83 71
Mavel's main role is the manufacturing of the PM-assisted SynRel motors as well as the integration of the power inverter in the motors.
Motor Design design an advanced Induction Motor that meets the project’s requirements. Additionally, MDL supports the cooling system design and thermal analysis of the Synchronous Reluctance machine and uses the bench test and full-vehicle validation data to improve the fidelity of the simulation models and of the Motor-CAD software, where necessary.
Jaguar Land Rover
JLR sets the vehicle specifications, providing the baseline for the high power electric motors. JLR also supported the machine designs, as well as the integration into a vehicle and the testing of the motors. JLR was also the leader of the project’s techno-economic evaluation.
Privé is the project system integrator and end-user, providing specifications and performing the in-vehicle integration and validation tests.
R13 is in charge of the Power Electronics Manufacturing. R13 supports also UNIAQ for motor control strategies and power electronic design.
Tecnomatic produces flat wire winding stator for the induction machines, collaborating actively in the design.
University of L'Aquila
University of L'Aquila supports the project research collaborating in the Motor Design of both technologies, conducting thermal analysis, developing the electric drive design with the support of modelling and simulation activities, implementing dynamic models and control strategies, and finally, supporting the manufacturing and testing activities.
Prof. Marco Villani
- Website ReFreeDrive: http://www.refreedrive.eu/
- Webinar #1 - Rare-earth free motor designs for e-mobility
- Webinar #2 - Control strategies and electric drive design of motors for e-mobility
- Webinar #3 - Induction motors for e-mobility. Advanced manufacturing features
- INEA - Next generation electric drivetrains for electric vehicles, focusing on high efficiency and low cost
- European Copper Institute - Motor Summit 2018 Interview Fernando Nuño
- LinkedIn ElectricDrivetrain Innovation Cluster (for videos and more)