Introduction

Road transport plays a crucial role in actual society, however pollution (including noise) generated by circulation has become a serious impediment to the quality of life and even the health of urban populations. Moreover, energy consumption by urban transportation has dramatically increased the dependency on petroleum. Progressive vehicle electrification is considered one of the main ways to promote efficiency and to meet broad environmental concerns; yet its greener version, i.e., pure electric vehicle (EV), has not been extended so far due to the insufficient energy density of batteries to provide the desirable autonomy and power. In recent years a technological breakthrough has occurred on this issue: largely driven by the explosion in consumer electronic demand (laptops, digital cameras, etc.) lithium-ion battery technology is reaching energy densities approaching 200Wh/kg and even more due to ongoing research (including current EU funded projects HELIOS, AMELIE and EUROLIION), which makes EVs with practical ranges of >130 km become physically possible while respecting reasonable vehicle size/mass/cost limits.

Now the strong growth potential of the technology's consumption faces a challenge in that it is reliant on some material (lithium) that has been in short use to date. Even though there is some controversy on whether lithium carbonate suppliers will be able or not to accommodate the growing demand occasioned by a growing electric car market in the future, the truth is that the countries with extensive, relatively low-cost, lithium brine deposits are Argentina, Bolivia, Chile, China, and the United States, with the only presence of Portugal among European countries in the list of significant producers.

However the raw material dependence problem of the EU is even more worrying when it comes to the electric motors themselves rather than their batteries. Currently, the most powerful and efficient electric machines use permanent magnets composed by rare-earth materials such as neodymium and dysprosium. The problem is that 95% of the global supply of these materials is provided by China only which puts at risk a mass introduction of EVs in Europe if the current motor technology is exclusively embraced. In order to establish a successful large scale EV manufacturing industry in Europe a new necessity arises: finding an efficient and power dense alternative to permanent-magnet machines.

In this context, two different approaches can be followed:

1. Development of materials for permanent magnets without rare-earth content, with magnetic properties comparable to them.
2. Design electric machines with less permanent-magnet material, with materials different from rare-earths or even completely magnet free.

The VENUS project follows this second approach as it poses some advantages over the first method on the basis of three key criteria for the automotive industry:

• Cost. Permanent magnets are expensive and their avoidance allows European manufacturers to use only well-known and (relatively) cheap engineering materials (e.g. steel, copper), reducing the total cost of the motor.
• Reliability. Permanent magnets have risk of demagnetization which can generate performance variations at elevated temperatures. Magnet-free designs can offer steady behaviour, practically unaffected by exposure to environment conditions and/or external magnetic fields, thus more reliable for their integration in EVs.
• Manufacturability. The electrical machine's assembly process must deal with magnetic fields in the presence of permanent magnets. This may lead to increased failure in assembled motors. Magnet-free designs could simplify this process as there are no magnetic fields and assembly process could be significantly simplified.

In order to come up with a valid solution the main goal of the VENUS project is to address and overcome the following challenges:

• Efficiency. Permanent-magnet motor efficiency is around 92-95%, whereas other alternative technologies integrated in pure EVs (e.g. induction motor in Tesla Roadster) only reach efficiencies around 85%.
• Power density. Permanent-magnet motors characterize for a large power to weight/size ratio. Current magnet-free motor technologies implemented in EVs (induction) are large in size and have low power density.
• Manufacturability. New motor designs focused to improve power density (e.g. axial-flux configurations) have been shelved prior to large volume marketing due to their manufacturing complexity, or poor/simple winding arrangements have been used to overcome such manufacturing difficulties with the associated performance loss.

Analogous to the Earth's twin planet Venus which has no magnetic field (to be exact its intensity is 0.000015 times that of the Earth's magnetic field), the VENUS motors aim to replace their "twin" motors that are currently mounted in most EV-s without making use of permanent magnets.