Rapid and transformative advances in power electronic systems are currently taking place following technological breakthroughs in wide-bandgap (WBG) power semiconductor devices. The enhancements in switching speed and operating temperature, and reduction in losses offered by these devices will impact all sectors of low-carbon industry, leading to a new generation of robust, compact, highly efficient and intelligent power conversion solutions. WBG devices are becoming the device of choice in a growing number of power electronic converters used to interface with and control electrical machines in a range of applications including transportation systems (aerospace, automotive, railway and marine propulsion) and renewable energy (e.g. wind power generators). However, the use of WBG devices produces fast-fronted voltage transients with voltage rise-time (dv/dt) in excess of 10~30kV/us which are at least an order of magnitude greater than those seen in conventional Silicon based converters. These voltage transients are expected to significantly reduce the lifetime of the insulation of the connected machines, and hence their reliability or availability. This, in turn, will have serious economic and safety impacts on WBG converter-fed electrical drives in all applications, including safety critical transportation systems. The project aims to advance our scientific understanding of the impact of WBG devices on machine insulation systems and to make recommendations that will support the design and test of machines with an optimised power density and lifetime when used with a WBG converter. This will be achieved by quantifying the negative impact of fast voltage transients when applied to machine insulation systems, by identifying mitigating strategies that are assessed at the device and systems level and by demonstrating solutions that can support the insulation health monitoring of the WBG converter-fed machine, with support from a range of industrial partners in automotive, aerospace, renewable energy and industrial drives sectors.

The ReFreeDrive project is focused on contributing to avoid the use of rare earth magnets through the development of a next generation of electric drivetrains, ensuring the industrial feasibility for mass production while focusing on the low cost of the manufacturing technologies. This proposal intends to study and develop simultaneously two solutions for the power traction system of electrical vehicles. Both solutions are brushless AC electrical machines: induction machine with fabricated and copper die-cast rotor (IM) and synchronous reluctance (SynRel) machine. Through their configurations these machines not only are rare-earth magnet free, but also share common features that can be exploited during the design step, as well in the manufacturing process. These common features lead to a complex synergy between the two technologies, which justify the development of different topologies of electric machines in just one project. The design of the ReFreeDrive motors will take as a premise the reduction of use of materials, as more than half of the final price is formed by raw materials cost. Also, a minimization of manufacturing costs will be ensured by an early involvement of manufacturers, from the design stage. ReFreeDrive motor topologies have good room for cost reduction by off-setting permanent magnet use. However, it is not feasible to change the commodity prices for copper and steel. Therefore, one of the key avenues for cost reduction is the reduction of size through different techniques (outer rotor, higher rotational speed, compact winding…). An optimized use of copper on the project provides technical design with a higher efficiency due to lower losses regards other alternatives, and more efficient heat management. Beyond the motor design, ReFreeDrive also consider an integrated design of the power train that allows the optimization of the electric connections, the cooling systems and the housing.

Performance improvement of electrical machines in terms of power-density and efficiency is central to the success of hybrid- and electric- vehicles and more- or all- electric aircraft, as indicated by the UK Advanced Propulsion Centre and the Aerospace Technology Institute. Efficiency and packaging volume of conventional electrical machines are limited by the method used to manufacture electrical windings, i.e. using pre-insulated conductors of uniform cross-section wound around the teeth of the stator. Here, we propose the use of metal additive manufacturing (3d printing), in which feedstock or powdered material is selectively bonded in a succession of 2D layers to incrementally form a compact 3D winding. The geometric freedom offered by additive manufacturing allows the simultaneous minimisation of end-winding volume and individual shaping of conductor profiles to optimise efficiency all while acting as a substrate for high performance inorganic electrical insulation materials. The technology could address the increasing drive to low batch size, flexibility and customisation in design for high integrity and high value electrical machines for the aerospace, energy and high value automotive sectors while enabling CO2 reductions demanded by legislation and market sentiment. Specifically, I will lead this multidisciplinary project exploring the potential benefits of Additive Manufacturing of High Performance Shaped Profile Electrical Machine windings leveraging expertise from industrial and academic partners Renishaw, 3TAM, Motor Design Ltd and Teesside University. The partners represent leading electrical machine design (Motor Design Ltd, University of Bristol), electrical insulation materials (Teesside University), UK additive manufacturing supply chain (Renishaw) and end-use additive manufacturing part production (3TAM). This range of partners cover the necessary skills and capability to go from theoretical winding design to manufactured, insulated prototype windings. As such, the project will result in a significant growth in the UK's knowledge and skills base in this area and develop a technology demonstrator to illustrate the quantitative benefit of such windings to industry and academia. This will allow new cross-sector relationships and collaborations to be cultivated with a view to perpetuate the research beyond the project period, ultimately leading to industrial adoption and further poising the UK as a centre for excellence in high value electrical machine technologies.