October 2020

US SCIENTISTS HAVE created a composite material that, they say, can boost the current- carrying capacity of copper wires by 14%, while improving their mechanical properties – such as strength and weight – by up to 20% compared to pure copper. The researchers, from the US government’s Oak Ridge National Laboratory (ORNL), add that the material could be used in any component that uses copper, resulting, for example, in more efficient busbars, smaller connectors and ultra-efficient, high-power-density motors. The work is part of a programme aimed at reducing barriers to the wider adoption of electric vehicles, including cutting the costs of ownership and improving the performance and life of components such as motors and power electronics. “Electric motors are basically a combination of metals – steel laminations and copper windings,”points out Burak Ozpineci, manager of ORNL’s Electric Drive Technologies programme and leader of its Power Electronics and Electric Machinery group.“To meet Department of Energy’s Vehicle Technologies Office 2025 electric vehicle targets and goals, we need to increase power density of the electric drive and reduce the volume of motors by eight times, and that means improving material properties.” To produce their conductive material, the ORNL researchers deposited and aligned carbon nanotubes (CNTs) on flat copper substrates. This resulted in a metal-matrix composite material with a higher current- handling capacity and better mechanical properties than copper by itself. CNTs are lightweight, strong and electrically conductive. Previous attempts use them in composites have been limited to samples that are only micrometres or millimetres long – or to longer lengths that performed poorly. The ORNL team decided to experiment with depositing single-wall CNTs using a technique that creates fibres by passing a jet of liquid through an electric field. It allows the structure and orientation of the deposited materials to be controlled. The process allowed the researchers to orient the CNTs in one general direction to enhance the flow of electricity. The team then used a vacuum-coating technique to add thin layers of copper filmon top of the CNT-coated copper tapes. The coated samples were then annealed in a vacuum furnace to produce a highly conductive copper- CNT network by allowing the copper to diffuse into the CNTmatrix. The scientists created a copper-carbon nanotube composite that is 10cm long and 4cmwide and offers“exceptional properties”. “By embedding all the great properties of carbon nanotubes into a copper matrix, we are aiming for better mechanical strength, lighter weight and higher current capacity,” says the project’s lead investigator, Tolga Aytug.“Then you get a better conductor with less power loss which, in turn, increases the efficiency and performance of the device. Improved performance, for instance, means we can reduce volume and increase the power density in advanced motor systems.” As well as enhancing the performance and properties of electric motors, the composite could also could have benefits in other applications where efficiency, mass and size are key factors.. The improved performance can be achieved using commercially viable techniques, opening up new possibilities for advanced conductors in a wide range of electrical and industrial applications. Nanotubes raise current-carrying capacity of copper by 14% to boost motor performance MITSUBISHI ELECTRIC has announced a second generation of silicon carbide (SiC) power modules, based on a newly developed SiC chip, that, it predicts, will lead to the development of smaller, lighter, more efficient power electronic equipment in various industrial fields. The family of 12 SiC modules, due to be launched in January 2021, will include devices capable of controlling up to 1.2kA at 1.2kV. SiC power semiconductors are attracting growing interest for their potential to cut power losses and boost the energy efficiency of power conversion equipment. Mitsubishi says that the low power loss characteristics and high carrier frequency operation of the SiC-Mosfet (metal oxide semiconductor field-effect transistor) and SiC-SBD (Schottky barrier diode) chips in the new modules will help to cut power losses by around 70% compared to those of conventional silicon-based IGBT modules. The reduced power losses and high carrier frequencies will also allow the use of smaller, lighter external components, such as reactors and coolers. In addition, the junction field-effect transistor (JFET) doping technology in the modules will reduce their on-resistance by about 15% compared to previous SiC modules. Reducing mirror capacitance will enable fast switching and cut losses. SiC powermodules will cut losses by 70%compared to silicon IGBTs n TECHNOLOGY October 2020 www.drivesncontrols.com 26 The US-developed composite material uses nanotubes the improve the electrical and physical properties of copper and could boost the performance of motors and many other electrical components Photo: Andy Sproles/ORNL, US Department of Energy