"Social Device" Special Interview

The contents were published from August 2017 to February 2018 on "Nikkei Technology Online",
the engineering information website run by Nikkei Business Publications, Inc.,
and reprinted with the author's permission.

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What’s Next in Cars After Electrics? Key Evolutionary Developments Drive Technology

Electric vehicles may well transform mobility, and thereby the society mobility supports. Professor Yoichi Hori of the University of Tokyo Graduate School talked with Satoshi Sawamura, President of automotive semiconductor leader ROHM Corp., about technical trends in EVs and concepts about the future of mobility.

Next-Gen Technology Driving Vehicle Evolution

Pushing the Merits of Key Technologies

Sawamura

 The development of Electric Vehicles (EV) created new demand for automotive semiconductor devices, and continues to be a key growth vector for ROHM. The company was born in 1954 as a manufacturer of resistors, and we began our shift into the semiconductor business in the 1960s. Semiconductor devices were originally primarily for the consumer electronics sector, but from about a decade ago we have been concentrating on growth in automotive and industrial equipment sectors. Today, these two sectors account for about 43% of sales revenue. EVs represent only a fairly small portion of the total automotive market at present, but they are expected to achieve significant growth in the near future.

Hori

 If fundamental, significant evolution in EVs can be achieved, they will spread extremely rapidly, I think.

 EVs today are still constrained by the concepts of traditional automobiles, basically just replacing the conventional automobile engine with an electric motor. EVs have a number of characteristics that are not found in engine automobiles, however, specifically torque response is much faster, the power train can be distributed, and generated torque can be measured accurately. I believe that an EV that effectively leverages these characteristics will offer unique added value. For example, the precise control afforded by motor drive minimizes tire slip, which means that tires can be made narrower without losing any mobility, improving mileage.

 Each time EVs demonstrate significant evolution, I think the EV market will experience a major spurt of growth.

Sawamura

 Electrification is progressing must faster than the industry expected, but even so I don’t expect the automotive market to suddenly switch over to EVs. I think conventional automobiles will remain on the market for some time. That’s why our automotive semiconductor business is based on a gradual shift from engine designs to EVs, and then to autonomous driving.

Fig.1 The ROHM Solution for Electric Vehicles
Fig.1 The ROHM Solution for Electric Vehicles
Hori

 The development of new automotive technologies is accelerating, and the media is covering the industry more frequently as a result. There seems to be a lot more interest in when EVs will replace engine designs, and when autonomous driving will finally enter widespread use. I agree that it’s unlikely to change rapidly, though: there will probably be a long period when the technologies coexist. I think it’s a good idea to grow your business in line with market reality.

Sawamura

 Our automotive semiconductor business is designed to address three major themes: safety, automation and Advanced Driver Assistance Systems (ADAS), and electrification and energy efficiency. As part of our approach to safety we strive to deliver zero defects, delivering the highest possible quality in our entire range of automotive products from high-performance large-scale integration (LSI) chips down to the general-purpose components such as resistors and discretes that we command such a large market share in.

 We are also working on developing new products offering improved functional safety. For example, the instrument clusters and side mirrors in cars are beginning to transition to electronic designs, and faults in their electronic systems can lead to major accidents. ROHM was the first in the industry to offer a liquid crystal display (LCD) chipset for cluster panels with onboard functions to detect chip errors and faults, helping prevent accidents from happening. We implemented the technology in this product first because we recognized the high degree of functional safety required in automotive electronics.

Hori

 As automotive electronics becomes increasingly pervasive, electronics will become even more critical in assuring safety. The role of semiconductor manufacturers will become even more important. What about the other two themes you mentioned?

Sawamura

 We are supporting development in automation and ADAS primarily through the communications integrated circuits (IC) that empower sensing devices, and safe power supply.We are supporting development in automation and ADAS primarily through the communications integrated circuits (IC) that empower sensing devices, and safe power supply.

 Our activity in automobile electrification and energy efficiency covers a wide range of vehicle types, not only EVs. The 48V mild hybrids gaining popularity in Europe, for example, use a state-of-the-art power supply IC featuring ROHM’s proprietary “nano-pulse control” high-efficiency supply technology. For inverters in plug-in hybrids and EVs we provide silicon carbide (SiC) power devices, gate drivers, and other chips.

Hori

 As a university researcher I’ve been studying the evolution of automobiles over a long span. I’m specifically interested in applications such as EV control, wireless power transmission systems, and electric double-layer capacitors, or supercapacitors, capable of rapid charge and discharge. The underlying premise to my work is that the vehicles of a century from now will run on motors, capacitors, and wireless technology.

 It’s pretty clear that vehicle drive power is changing from engines and motors, but I don’t think the EVs of today will achieve widespread market penetration. One of the reasons is problems with energy distribution. EVs today store energy in onboard Li-ion rechargeable batteries, and the vehicle can’t be used for long periods of time while charging. Worse, the batteries can only store relatively small amounts of energy… in fact, the amount of energy stored in the batteries of an EV is a factor of ten less than the energy of a single tank of gasoline. As a result, EV drivers have to always be careful of how far they can get on their remaining charge

 It would be best, in my opinion, to have an infrastructure like that of electric trains, supplying EVs directly with power. Even long-haul drives would be quite possible if you have quick-charge systems operating while waiting at red lights or toll gates, combined with slow-charging technology to gradually charge vehicles via roadway charging systems. There would be no need for a single vehicle to store so much energy. If that sort of infrastructure could be implemented it would revolutionize mobility and society. Any system supplying power from infrastructure, however, will depend on capacitors capable of rapid charge and discharge, and wireless power supply technology to connect vehicles to the electric power grid.

Sawamura

 A number of advanced technologies will need to be developed as a base to get that kind of futuristic system kickstarted: we call them “seed technologies.” These seed technologies can “bloom” in the form of new ideas and systems, and the technologies to implement them. By rapidly providing semiconductor devices with outstanding characteristics and function, we can contribute to the continuing evolution of the automobile.

Hori

 Yes, semiconductor devices are unquestionably seed technologies. In fact, I believe that the practical wireless power supply system, offering non-contact electric power transmission, was first achieved using high-efficiency SiC power devices.

 The team led by Associate Professor Hiroshi Fujimoto of the University of Tokyo Graduate School of Frontier Sciences, for example, prototyped an EV using in-wheel motors powered by wireless transmission in May 2015, in collaboration with two Japanese firms, Toyo Denki Seizo KK and NSK Ltd. The drive motors are mounted inside each of the four wheels. In the past motor power was supplied through cables, but the cables were constantly subject to load as the vehicle bounced up and down. The prototype supplies wireless power through electromagnetic resonant coupling, eliminating the need for cables.

 That wireless power supply system attained a high transmission efficiency (ratio of transmitted to received power) of 94.3%, thanks to SiC power devices. The system converts the direct current (DC) power required by the drive motors into high-frequency alternating current (AC) for wireless transmission, and a key point in achieving the high transmission efficiency is reducing losses generated in the power conversion circuit. The in-wheel motors also use high-efficiency SiC power devices to further minimize conversion losses. As a whole, the system improves power transmission efficiency to the level of practical utilization.

 In March 2017, the same research group announced another prototype vehicle using a wireless power supply system, but the power was supplied to the in-wheel motors by transmitters located in the roadway itself (Fig. 2). This second-generation design also achieved a power transmission efficiency of over 90% through the use of SiC power devices in the wireless transmission system, the step-up chopper, the motor control inverter, and other electronics.

Second-Generation In-Wheel Motor EV Developed by Professor Fujimoto of the University of Tokyo Graduate School
Fig.2 Second-Generation In-Wheel Motor EV Developed by Professor Fujimoto of the University of Tokyo Graduate School
Sawamura

 SiC power devices are one of the products we are prioritizing. Compared to the silicon (Si) that has been the most common semiconductor material, SiC is a next-gen material offering superior electrical properties. SiC power devices can contribute significantly to reducing energy consumption and power levels in a range of relatively high-power circuits. The potential advantages of SiC power devices, however, are not as widely known as they could be. As part of our effort to improve the situation, in 2016 we began serving as an official technology partner to the Venturi Formula E racing team. Formula E racing is the most important race for the electric vehicle class.

 It is a sort of test bed for advanced technology relating to EVs. For Season 3 (2016/2017) ROHM provided the SiC Schottky barrier diodes for the drive system inverters, and in Season 4 (2017/2018) and the following Season 5 we are also providing SiC MOSFETs to complete the transition to a completely SiC configuration for the inverters. Compared to the partial-SiC inverters used in Season 2, these new full-SiC designs are 43% smaller by volume, with weight reduced by 6 kg (Fig. 3). The weight and size reductions should improve vehicle performance. We’re really looking forward to the races!

Fig.3 The Venturi Formula E Team Vehicle and Inverter Comparisons (SiC power device wafer in inset)
Fig.3 The Venturi Formula E Team Vehicle and Inverter Comparisons (SiC power device wafer in inset)
Hori

 I also think it is important to demonstrate superior technology where it can be appreciated by many people, because it may stimulate new and exciting ideas from universities, or other organizations. Inverters and their component semiconductor devices have a crucial role to play in vehicle electrification, as is evident in the wireless power supply application I mentioned earlier. As systems evolve, however, sub-systems such as these can get overlooked. The industry is moving toward tighter integration of electronics and machinery when it comes to motors, but that trend will also mean that people will have fewer opportunities to appreciate the importance of semiconductor devices. I hope that you will continue to display the advantages of new semiconductor device technology in a diverse range of situations.

Sawamura

 Changes in society and technological progress are dramatically changing the concept of mobility, and ROHM believes that this period of transition offers us an abundance of opportunities to contribute through technology and products. We’re committed to continuing our technical leadership in the automotive sector.

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