Sai Priya Munagala

More electric propulsion across automotive and aerospace has led to a demand for significant improvement in the power density of electrical machines. This has, in turn, triggered research into advanced manufacturing methods for higher-performance magnet systems in machines. The application of laser powder bed fusion (LPBF), a form of additive manufacture (AM), to the current carrying coils of the electromagnetic circuit of a machine has allowed several significant improvements to the design of these parts. One benefit which can be realized in this way is the tailoring of conductor form to the operating field and the alteration of conductor topology to reduce the ac loss. Another advantage of these manufacturing techniques is the ability to introduce methods of direct cooling to the coil, including highly efficient heat exchangers derived from generative design techniques. It is significant that the electrical conductivity achieved is now equivalent to that of conventional drawn Cu wire. This article hypothesizes that the lessons learned in developing production methods for next-generation, high-performance components for electric machines might also find utility in the very demanding electromagnetic circuits found in magnetic confinement fusion. Potential benefits for the production of cable-in-conduit conductor (CICC) superconducting (SC) bus-bar joints, or even larger elements of conductors are discussed. This is used to motivate future experimental studies of the mechanical and electrical performance of AM Cu at cryogenic temperatures as well as the further development of the manufacturing state of the art.

To lower the ac losses in electrical machines, additive manufacturing (AM) has been adopted to exploit the geometrical freedom in winding design. However, AM brings about new challenges such as surface roughness and porosity which can create difficulties for post processing of the windings such as applying insulation coatings. The article investigates the influence of surface roughness (profile) of AM-processed CuCrZr as a potential candidate for electrical windings in terms of geometry, surface roughness, porosity, and oxidation on their insulation. The feasibility and characteristics of insulations applied via three processing techniques namely powder, spray, and dip coating are compared. The entire process is quantified via techniques such as computed tomography, surface profilometry, optical microscopy, X-ray photon spectroscopy, and breakdown voltage (BV) at different stages of the coating process. The study also includes coating on a commercial rectangular copper wire as a reference. The initial assessment of coatings concludes that surface roughness and the coating process are both vital determinants for the success of insulating AM components. Basic surface smoothening is needed to get rid of burs and the spray coating technique was the best among others for its capability to produce conformal coating.

The reliability of the SiC MOSFET has always been a factor hindering the device application, especially under high voltage and high current conditions, such as in the short circuit events. This paper experimentally reviews the failure mechanisms caused by destructive short circuit impulses, and investigates the degradation patterns of key electrical parameters under repetitive short circuit events. The impact of test parameters on the short circuit reliability of SiC MOSFET has been analyzed. Approaches to characterize the electrical-thermal-mechanical stress during the short circuit period and advanced test methods are highlighted. Finally, the constraints from the standpoint of both manufacturers and users have been presented, including comparison of current SiC MOSFET devices, reliability evaluation of parallel SiC MOSFET devices, reliability improvement of the chip, performance improvement of protection circuits, and reliability assessment of SiC MOSFET devices under application-representative stress.

Efficient and power-dense electrical machines are critical in driving the next generation of green energy technologies for many industries including automotive, aerospace and energy. However, one of the primary requirements to enable this is the fabrication of compact custom windings with optimised materials and geometries. Electrical machine windings rely on highly electrically conductive materials, and therefore, the Additive Manufacturing (AM) of custom copper (Cu) and silver (Ag) windings offers opportunities to simultaneously improve efficiency through optimised materials, custom geometries and topology and thermal management through integrated cooling strategies. Laser Powder Bed Fusion (L-PBF) is the most mature AM technology for metals, however, laser processing highly reflective and conductive metals such as Cu and Ag is highly challenging due to insufficient energy absorption. In this regard, this study details the 400 W L-PBF processing of high-purity Cu, Ag and Cu–Ag alloys and the resultant electrical conductivity performance. Six Cu and Ag material variants are investigated in four comparative studies characterising the influence of material composition, powder recoating, laser exposure and electropolishing. The highest density and electrical conductivity achieved was 88% and 73% IACS, respectively. To aid in the application of electrical insulation coatings, electropolishing parameters are established to improve surface roughness. Finally, proof-of-concept electrical machine coils are fabricated, highlighting the potential for 400 W L-PBF processing of Cu and Ag, extending the current state of the art.