Why ROHM matters

Current-E-Formula-E-Punta-Del-Este-2015-Dan Bathie-ROHM logo on Venturi car

Just ahead of the 2016 Paris Formula E race, the Venturi team issued a press release informing us of a new partnership with ROHM, a Japanese electronics and semi-conductor maker. In all the hubbub surrounding the debut of the all-electric racing series in the French capital, the news almost passed us by.

That would have been quite some oversight – ROHM’s involvement signals not only the intention and technical development direction of Venturi’s S3 powertrain but also underlines how important Formula E is becoming to suppliers involved in (or who want to be involved in) the design and manufacture of electric vehicles.

The news first. “The Venturi Formula E team has been boosted by an exclusive technical partnership with the renowned Japanese semi-conductor and electronics company, ROHM Semiconductor,” read the release. “The technical partnership will see Venturi Automobiles using cutting-edge silicon carbide (SiC) technology in the Venturi Formula E cars to take advantage of the development permitted within the technical regulations in the field of electronics from the start of season three.”

Technical bulletins such as these are often stuffed with phrases like “cutting-edge” but in this case the claim is justified. SiC is seen as something of a wonder material and has been made commercially available only relatively recently. To get a handle on what it is and the implications of the material’s use, we’d recommend reading this excellent 2011 article published by the IEEE (Institute of Electrical and Electronics Engineers).

The article notes: “Silicon has long been the semi-conductor of choice for power electronics. But soon this ubiquitous substance will have to share the spotlight. Devices made from silicon carbide (SiC) – a faster, tougher, and more efficient alternative to straight silicon – are beginning to take off. Simple SiC diodes have already started to supplant silicon devices in some applications. And over the last few years, they’ve been joined by the first commercially available SiC transistors, enabling a new range of SiC-based power electronics… Within five years, we should see this market balloon as SiC devices find their way into power electronics for hybrid and all-electric vehicles, creating simpler and more efficient power systems.”

(This article puts it another way: “Compared to silicon-based devices… SiC power chips operate at higher voltages, frequencies and temperatures, helping to eliminate up to 90% of the power losses in electricity conversion.”)

What would the benefits of SiC hold for electric vehicles? The IEEE article goes on: “Of all the electronics in an electric vehicle, the traction drive draws the most power. The drive has two main parts: a boost converter that increases the DC voltage from the battery and an inverter that converts this electricity into the three-phase AC needed by the motor. The three-phase inverter in turn consists of six diodes and six transistors. In computer and laboratory simulations, we’ve shown that simply swapping silicon diodes with SiC Schottky diodes cuts the inverter’s energy loss by 33%, consistent with other estimates. The reduction doubles if you also replace the silicon transistors with SiC transistors.”

Formula E is an efficiency game, with drivers only able to use a specified amount of battery energy in the race. Therefore, extracting greater efficiency from the powertrain will result in cars able to go faster and longer, improving the chances of winning. A 33% efficiency boost in the inverter would be a great start to Venturi’s S3 title hopes.

There’s more, though: “In hybrid and all-electric vehicles, SiC’s operating temperature is high enough to obviate the need for one of the bulkiest engine components: the liquid cooling system. Liquid cooling adds significantly to the overall size of the engine and, if the liquid leaks out, it can destroy the electronics. Our simulations suggest that SiC inverters, because they can operate at higher temperatures, could reduce the size of the cooling system by 60%. If we combine these inverters with other high-temperature components like high-temperature capacitors, we might be able to eliminate the second loop altogether and simply cool the electronics with air.”

So utilising SiC devices could lead to considerable simplification, weight loss and better packaging for the S3 powertrain along with a more efficient inverter. (On the subject of weight loss, the article also notes: “A SiC-based device can have the same dimensions as a silicon device but withstand 10 times the voltage. What’s more, a SiC device can be less than a tenth the thickness of a silicon device but carry the same voltage rating.”) Those are the sorts of things that engineers get very excited about when designing racing cars.

Current-E-Formula-E-Punta-Del-Este-2015- Dan Bathie-ROHM logo on Stephane Sarrazin's Venturi helmet

“SiC enables us to improve our thermal efficiencies and the electronic performance of our inverters which will allow us to run higher motor speeds,” Venturi owner Gildo Pallanca Pastor said in the team’s press release. Venturi is working with McLaren again to develop the inverter, echoing the team’s season two partnership. That suggests that the McLaren motor in service presently will return for season three in the black cars.

ROHM is a multi-billion dollar enterprise and one of a handful of global suppliers of this technology. The company’s partnership with Venturi is not just designed to capture a few pretty trophies and Formula E bragging rights.

“The ROHM partnership is the strongest indication yet that the Formula E platform is now being taken very seriously by companies that wish to demonstrate their technology competences to the EV industry,” one team source told us. “In ROHM’s case, their SiC technology gives their customers an advantage in the inverter component of the powertrain by improving thermal efficiency and switching frequency. ROHM plans to use its partnership with Venturi to position ROHM at the forefront of EV inverter development. The decision to enter FE with Venturi was a main board decision from Japan. It is further evidence that the appeal of FE is now reaching beyond the marketing allure that has driven the car manufacturers to sign up to the tier one suppliers, who want to show the OEMs that they should be buying their technology for their EV products.”

It’s inconceivable that McLaren isn’t taking some learning from all of this too. The motor in use with Venturi began life in the P1 hybrid hypercar. Advancements made with both Venturi and Mahindra Racing in Formula E will be giving the automotive company a head start on tech for its next generation of hybrid sports cars (and perhaps even its other racing endeavours).

Sometimes it’s the smallest components that can make the biggest impact. We’ll have to wait for season three to see what Venturi, ROHM and McLaren have cooked up. In the meantime, the news highlights how Formula E is becoming a genuine technological testbed for the automotive industry.

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