Overview
For a large-scale introduction of Electric Vehicles (EV) in Europe, adequate volume supply of current PM based motors could be at risk, as the rare earth metals they contain can only be found under single source monopolies. In this context, the development of high efficiency motors using a limited amount of permanent magnets or completely new magnet-free motor designs is crucial. A promising option for this new generation of electric motors could be reluctance technology, which has been left out of the first line up to now due to its lower power density when compared to PM motors. On the other hand, the use of axial-flux configurations has proved recently in PM motors that power density can be increased in a relatively cost-effective way. The combination of both approaches, reluctance motors in axial-flux configuration, could lead to power densities comparable to those of PM motors in current EV-s while minimizing (PM assisted synchronous reluctance motors, PMSynRM) or avoiding (switched reluctance motors, SRM) the usage of scarce magnet materials.
The aim of this project is to develop both axial-flux SRMs and PMSynRMs in parallel (meeting EV power density requirements), exploiting their commonalities and synergies in the design and prototyping phases, to further opt for the most suitable solution to be integrated in commercial EV-s. Being the combination of reluctance technology and axial-flux configuration a completely novel approach for EV applications (SRMs) and for any kind of application in general (PMSynRMs), one of the main challenges of the project will be to get a cost-effective and high efficiency motor design, considering a potential large scale manufacturing and industrialisation of this new generation of motors.
Funding
Results
High-efficiency and high-power density electrical motors without reliance on rare earth materials
The wide-scale introduction of electric vehicles (EVs) is highly dependent on permanent magnets composed of rare earth materials in limited supply and with prohibitive costs. An EU initiative introduced motors without such elements.
Global supply of these materials mainly rests on China, and they cannot be supplied in adequate volumes at a competitive cost. What is more, the future availability and price of rare earth magnets remains grim. Many experts foresee a supply deficit of some rare earth metals, as demand is expected to exceed the industry’s ability to produce these rare earth elements.
The EU-funded http://www.venusmotorproject.eu/ (VENUS) (Switched/synchronous reluctance magnet-free motors for electric vehicles) project set out to develop an electric drive system for EVs that does not contain scarce magnet materials, meets EV efficiency and power density performance, and is feasible for mass production.
Work began by designing a prototype motor with an original electromagnetic configuration. The mechanical design differs from conventional radial-flux machines. To this end, project partners developed specific electromagnetic design and calculation tools, and advanced thermal models. They also developed power electronics. These include a new inverter consisting of a control board, interface board, driver board, semiconductor device, cooling system, DC-Link capacitor and aluminium housing. For the control system, a switched reluctant machine model was implemented with non-linear flux linkage.
With the design in place, the VENUS team manufactured the components. The full motor assembly was then tested and integrated into an electric van.
The power density achieved by researchers is 10 % better than benchmark motors without permanent magnets in low-powered vehicles and two-, three- and four-wheel vehicles. They also calculate that the inverter can provide the highest power per litre in the market: 19 kW/l (320 kW in 16.8 l).
To exploit the motor, a comprehensive industrialisation analysis was carried out, including cost evaluation, manufacturing processes and required investments.
VENUS developed a motor that can provide similar performance at a competitive price and reduced size. The absence of rare earth magnets in the motor means that no supply shortage will ever occur in key components during mass production.