The electrification of the powertrain – at all levels — is a bonanza for semiconductor companies. From micro hybrids, where 48 V systems are accommodating the need for more on-board power, to all-electric vehicles with batteries capable of delivering many hundreds of volts, semiconductors play a vital role.
On average, cars with conventional internal combustion engines today contain semiconductors worth some $350. In electric and hybrid vehicles, the semiconductor content easily doubles — not only because of additional electronic controls for the drive motors but also for battery management and lighting. Lighting? Yes, because electric vehicles need to maximize efficiency anywhere they can, they are typically equipped with LED exterior and interior lighting, which, in turn, requires electronic LED drivers based on power electronic devices.
And, because vehicle characteristics increasingly depend on the performance of the semiconductor components, relationships along the supply chain are changing: “A decade ago, from the perspective of the automotive industry, semiconductors used to be nothing else but a component that had to be bought at the best possible price. Today, the awareness is growing within engineering departments of the automotive industry that semiconductors lay the foundation for achieving the strategically important properties of the vehicles,” says Gerd Teepe, marketing director of semiconductor manufacturer Globalfoundries. This realization has led to innovation partnerships between carmakers and semiconductor vendors. For instance, Daimler is cooperating with Qualcomm in the development of the wireless charging technology for electric vehicles. Volkswagen recently entered an innovation partnership with Infineon. Audi’s “Progressive Semiconductor Program” (PSCP) addresses semiconductors across all disciplines of automotive electronics. Members of the program are, among others, Renesas and STMicroelectronics.
While electromobility is not the sole focus of these partnerships, it is inconceivable without them; – OEMs, tier-one suppliers, and semiconductor manufacturers are collaborating closely on motors, electromechanical components, energy storage and control systems that together make up an electric car. Robert Bosch for instance, itself a large semiconductor manufacturer albeit only for its captive demand, has launched a business unit exclusively dedicated to electromobility. Currently, Bosch’s engineers are busy readying the electric powertrain for the mass market. “We increase the efficiency of the drive system, for example by integrating gearbox, power electronics and motor in an electrical axis,” explains Bosch spokesman Florian Flaig. “Currently, a drive train for electric or hybrid vehicles consists of individual components. In the future, the Bosch electric drive system will combine transmission, electric machine and power electronics in a compact housing.” The goal is reducing the complexity of the electric drive and making the drivetrain considerably cheaper, more compact and more efficient.
Nevertheless, as yet there is no such thing as one standard drive concept for electric vehicles. From a centrally located single-motor drive to separate motors driving the front and the rear axle to wheel hub drives, each approach is currently designed into the next generation of vehicles. Bosch competitor Schaeffler Technologies, for example, developed a wheel hub drive along with R&D partner Ford Motor Company – one motor for each wheel. “There are several benefits benefit of this approach”, a Schaeffler spokesperson explains. “The entire technological content of the drive – including power electronics – is integrated into one compact design. This gives car designers the freedom to rethink the entire vehicle. Since no more space is wasted for the engine compartment, such a car would be very compact yet spacious”.
What gives the car designer the freedom to rethink the vehicle may create headaches for the electronic design engineer. Wheel hub drives are rather challenging in terms of cooling – after all, they inherently have a particularly high energy density and at the same time fewer options to remove the heat. Schaeffler claims to have solved the problem – a solution made possible only by the latest generation of power semiconductors.
Currently, semiconductors to drive such motors mostly are high-voltage IGBTs (insulated gate bipolar transistor) or MOSFETs. Voltages of motor designs today typically range from 600 VDC to 800 VDC. “But we see a trend towards higher DC link voltages, therefore our latest automotive IGBT generation is designed for 750 V and 1200 V”, says Stephan Zizala, Vice President and General Manager of Infineon’s automotive division. To enable higher power densities, the company’s power modules come in a special package that enables double-sided cooling. According to Zizala, this allows designers to reduce the inverter volume by up to 20%.
For even higher power densities, the industry is betting on new materials such as Silicon Carbide (SiC) or, farther down the line, Gallium Nitride (GaN). Infineon’s Zizala believes that for the next five to ten years, conventional IGBTs and MOSFETs will continue to be the dominant semiconductor for electric drive trains. Starting around 2021, SiC will be used for high-end battery vehicles at a larger scale. SiC is expected to bring significant improvements in power density, resulting in up to 80% reduction of the inverter size – mostly driven by higher efficiency and thus less waste heat. This efficiency gain also has an impact on the battery: It will allow a battery downsizing of 5%, Zizala said.
For the time being, Infineon’s focus in SiC development aims at achieving the same reliability level as today’s IGBTs and MOSFETs. The broader introduction of GaN is expected to follow significantly later “because of known and unknown reliability issues,” as Zizala puts it.
Much like Infineon, other semiconductor vendors are currently exploring the potential of SiC and GaN devices. ON Semiconductor, for example, will be ready to offer SiC MOSFETs already in 2017. Competitor Rohm is already introducing its third generation of SiC devices. The company integrates real-world experiences to further advance this technology through cooperation with the Formula E racing team Venturi. “The insights we are gaining today in Formula E will be applied in the production of electric series cars tomorrow,” says Alessandro Maggioni, technical marketing manager at Rohm. The use of gallium nitride is currently under investigation, but the Rohm expert does not yet regard this material as suitable for car applications.