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Fast Charging

Fast-Charging Technology: The Key to Speeding Electric Vehicle Adoption

Mar 10, 2020
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The EV era has arrived. The next step is building a fast and ubiquitous charging infrastructure.

After many years of overly optimistic promises and dashed hopes, electric vehicle (EV) sales are now growing at a virtually exponential rate — up 81% from 2017 to 2018, according to the Edison Electric Institute, an association representing U.S. investor-owned electric companies. Now, as a new decade begins, all signs indicate that rapid EV sales growth will continue well into the foreseeable future.

The numbers tell the story. Assisted by support from vehicle manufacturers and global governments, up to 45% of global vehicle production will be electrified by 2025, reports market research firm IHS Markit. Approximately 46 million EVs are now sold annually, a number that IHS Markit estimates will climb by up to 57% by 2030 (some 62 million vehicles). By 2023, IHS Markit forecasts that 43 brands will offer at least one EV option, including nearly all existing brands as well as new brands entering the market.

Curing “range anxiety”

The biggest barrier preventing even greater EV adoption is the lack of a widely distributed charging infrastructure, particularly one that can charge vehicles rapidly, efficiently, and reliably. In fact, if anything could stifle future EV growth, it’s the lack of charging stations in many areas. A survey conducted for Volvo in 2018 by Harris Polling showed that for most people, the top obstacle to buying an electric vehicle is running out of power (58%), followed by the limited availability of charging stations (49%). The survey also found that “more charging stations” was the leading factor that would increase respondents’ likelihood of buying an EV.

The current lack of charging stations is fueling “range anxiety,” a fear created when EV drivers wonder how far they will be able to travel before requiring a charge and where to find a station before the vehicle’s battery is depleted. Help is on the way, however, with DC charging coverage expanding rapidly in China and accelerating in the U.S. and Europe.

The need for speed

Simply adding more charging stations won’t, by itself, cure range anxiety. Charging times also need to be reduced. A typical EV with a 60-kWh battery needs just under eight hours to charge from empty to full at a conventional 7-kW charging point. Most car owners, however, are looking for a charging experience that more closely mimics “filling up at the pump” — in other words, fewer than 15 minutes.

Tesla has already addressed the need for faster charging with its growing string of high-speed charging stations. The company’s Supercharger stations can supply up to 150 kW of power, distributed between two cars, at up to 150 kW per car, depending on the model. According to Tesla, it takes approximately 20 minutes to charge its original 85-kWh Model S to 50%, 40 minutes to charge it to 80%, and 75 minutes to 100%. As of January 2020, Tesla reported operating 1,804 Supercharger locations worldwide a good start but far short of the 8-10 million fast charger stations expected to be needed by 2023.

The solution is Silicon Carbide

EVs, in one form or another, have been around for more than a century, tantalizing the public with promises of clean journeys with quick, smooth, and silent acceleration. Thomas Edison himself began marketing an electric car in 1912. Unfortunately, the vehicle’s $300 cost (approximately double the price of a gasoline-powered car of the era), along with charging and range limitations, resulted in Edison’s EV mimicking the fate of the year’s leading news event — the sinking of the Titanic.

EVs have come a long way since Edison’s time. Improved battery technologies have played a major role in growing EV sales. Now, Silicon Carbide (SiC), a powerful new semiconductor technology, is taking the driver’s seat to lead EVs into a new era of performance, convenience, and affordability.

EV manufacturers have traditionally relied on conventional silicon power transistors to run the drivetrain motors, charge batteries, and supply necessary system management and infotainment. Various semiconductor materials possess unique properties that make them suitable for different types of EV systems. SiC now stands out as the technology of choice for high-power EV drivetrain electronics and battery charging on and off the car.

Silicon Carbide’s value as a power semiconductor material has been known since the beginning of the semiconductor revolution. The challenge has always been growing the high purity, performance-optimized Silicon Carbide crystals with low enough defectivity and cost to make devices built of SiC commercially viable. Since its beginning or establishment in 1986, Wolfspeed has been singularly focused on those challenges and has innovated every step from crystal growth to device design and processing to achieve the goal.

Compared to silicon, Silicon Carbide offers numerous benefits, including more power delivered per die area, higher switching speeds, superior energy efficiency, and better thermal performance resulting in smaller, lighter, lower cost power conversion systems that make EVs better performing and more price-competitive.

Silicon Carbide’s higher efficiency and switching speed allow use of simpler circuit implementations that use fewer semiconductor devices and smaller passive components and heatsinks to produce more power in smaller, lighter, and less costly converters. That translates into faster charging (30 minutes or less), lower utility cost per charge, smaller batteries, and/or greater vehicle range, all at lower car and charger costs, greater ruggedness, and reliability.

Multiple applications

As the EV market continues to grow and expand, the demand for fast chargers will continue to soar, and the space, efficiency, and system cost gains provided by Silicon Carbide in various applications will become an increasingly important advantage.

When applied to fast charging, SiC MOSFETs and diodes offers the benefits of up to 30% lower losses, a 2× to 3× faster switching speed, and a 65% increase in power density. Other advantages include a 30% reduction in components and a lower overall system cost. Now available in a wide variety of voltage, current ratings and in many discrete and multi-chip power module configurations, Silicon Carbide power devices from Wolfspeed can be the backbone of charger systems from a few kilowatts on board the car to hundreds of kilowatts in Fast Charger stations. The newest and most powerful Silicon Carbide chips also are emerging in high efficiency powertrain drivers for vehicles’ motors.

Fast off-board charger systems

On-board chargers (OBCs) attached directly to EVs are currently widely used. However, they are limited in power and therefore charge time by size and weight requirements. Fast off-board chargers bypass the EV’s OBC to provide rapid direct battery charging. Off-board fast-charging stations enhanced by Silicon Carbide technology are rapidly gaining momentum. Off-board stations allow more modest OBCs, charge faster at higher power levels, and create opportunities to provide a variety of chargers optimized for best energy efficiency, smallest size and weight, or highest ruggedness and reliability, all benefitting from cost advantages.

The technology allows charging stations to fully refresh batteries in approximately 30 minutes, versus several hours when using an OBC. SiC-based off-board chargers are typically constructed from multiple 15-kW to 25-kW power-conversion blocks. The chargers are stacked and segmented to provide higher up-time. The scalable design also allows faster time to market and reduced R&D costs. Silicon Carbide based off-board chargers offer the highest possible efficiency, improved power density, very high ruggedness and reliability, and a bidirectional energy flow for smart grid enablement or to make vehicles a mobile power generator.

SiC AC/DC converters and SiC DC/DC converters

Wolfspeed offers Silicon Carbide based power semiconductor devices that can be used to build AC/DC and DC/DC converters required by fast chargers. When compared to their silicon-based counterparts, the sub-systems Wolfspeed has developed have proven capable of providing the entire power conversion block used in those chargers in demonstration hardware. Details are available through Wolfspeed’s web site. The initial hardware shows a unidirectional 20kW charger block (that can be stacked to provide chargers from 20-200kW) which, when compared to a 15kW block implemented in silicon, has proven a 33% increase in power from 25% smaller area, all at higher efficiency and lower component cost.

Currently under development by Wolfspeed is a new version Silicon Carbide fast charger (again, AC/DC and DC/DC) featuring higher output power and higher output voltage required by today’s latest 800V and bidirectional battery systems. — Stay tuned for upcoming details.

Into the future

It now appears inevitable that most, if not all, EV manufacturers will soon switch over to Silicon Carbide technology. The reason is simple: EVs incorporating Silicon Carbide will gain the lead in power efficiency, range, performance, and overall cost. While traditional silicon components will still find a home in digital and low-voltage subsystems, Silicon Carbide technology will be the predominant choice in EV charger and drivetrain power electronics.

Wolfspeed, with thousands of customers and millions of MOSFETs and diodes already in use, is now leading the way into a new era of EV production and support. Offering AEC-Q101–qualified factories and products, and more than 6 trillion field hours of Silicon Carbide power devices, Wolfspeed is uniquely positioned to help make EVs the top choice for drivers worldwide.

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