A substance from outer space combined with new inverter technology can bring a major boost in EV efficiency, says Ian Foley, managing director of Equipmake.
It might only naturally occur beyond our solar system, but stardust – otherwise known as silicon carbide – is about to have an enormous impact on electric vehicles.
Bringing a step change in performance, without any cost burden, silicon carbide really is a wonder material. So, it’s just as well, that while it might only be found naturally on carbon-rich stars (or on Earth in meteorites), human beings have found a way to mass-produce a synthetic version, mixing silica sand and carbon at extremely high temperatures.
Offering higher power levels, lower power losses and improved overall efficiency, silicon carbide has a huge role to play in EV development when used in a key powertrain component: the inverter.
Converting DC charge from the battery to AC to drive the motor, an inverter also times the switching changes to adjust the frequency of the AC charge to control the motor’s speed too. In many ways it is like the fuel injection system on an ICE car, allowing the petrol in
the tank (i.e. the battery) to drive the engine (the electric motor). The faster and more efficient the inverter is, the more efficient the whole vehicle is.
Traditional inverters use insulated-gate bipolar transistors (IGBTs), which switch current at up to 20kHz, but the very latest SiC-mosfet (metal-oxide-semiconductor field-effect transistor) versions can do 80kHz, and a much higher switching speed is important for the types of motors used in EVs.
SiC-mosfet inverters are also smaller and lighter, allowing car makers to package them better, while reducing the amount of cooling needed, too. With a power-to-weight ratio of 100kW/kg – versus 40kW/kg
for IGBTs – it’s easy to see the advantages of its supreme efficiency, especially when you consider the positive effects on EV range.
Take a typical EV saloon, for instance. A SiC inverter can reduce battery size by a whopping 10% – or up to 50kg. Given the battery is the most expensive component, this has huge benefits, enabling car makers to pass the saving on to customers (or spend that money on another component), offering a vehicle that has the same or likely better range than before.
Or they can keep the battery the same size and offer even more range.
Are there any challengers to SiC? Depending on the application requirements gallium nitride can perform even better but is currently more competitive in lower voltage inverter applications (e.g. up to 400V). At Equipmake, we aim to achieve the highest power density and performance, which means a higher voltage range (around 800V), where SiC has a clear advantage and is currently the best fit.
The industry is waking up to the benefits: passenger EVs equipped with SiC inverters are predicted to overtake those with IGBT units by 2024 and, by 2030, 95% of all EVs will use silicon carbide. It’s not hard to see why SiC tech will outpace demand for IGBT inverters very soon: how often does an innovation arrive that gives you something for nothing? You can even say it comes from the stars too.
