EV Engineering December 2023

DECEMBER 2023

A DESIGN WORLD SUPPLEMENT

ALSO INSIDE: Rare earths and EVs — it’s not about batteries

Reducing range anxiety: PAGE 48

How automakers are increasing EV battery voltages PAGE 42

cover – ev engineering supplement dw dec 2023 v2 final.indd 51

12/14/23 8:23 AM

EV ENGINEERING

How silicon-carbide technology can address high-voltage EV challenges?

By Anthony Schiro, VP Quality & Sustainability • Stephen Oliver, VP Corporate Marketing & IR • avitas Semiconductor

S

ales of new electric vehicles (EVs) in the US exceeded five percent of the total market for the first time in 2022, joining 18 other countries worldwide that have surpassed the same milestone.

Although EVs are achieving market acceptance that bodes well for future success, adoption must continue and accelerate. Changing to tailpipe-free vehicles is a pillar of governments’ plans to meet climate pledges under the Paris Accord and improve air quality in major cities.

Standing in the way of progress, the usability of EVs is a key issue for many would-be buyers. Charging an EV at home can be impractical for those living in properties without offstreet parking or allocated spaces.

Moreover, while today’s EVs offer a decent driving range to handle average daily usage, longer trips still require stops to recharge.

There’s also concern about the location and availability of suitable charging stations and the stop duration. Whereas a liquid-fuel tank can be refilled in a couple of minutes, a typical discharged EV battery requires about 25 minutes to recharge to 80% of its full capacity.

Driving range and charging times still need better solutions to strengthen

42

December 2023

batteries – ev engineering supplement dw dec 2023 v5 final.indd 42

the case for EVs and drive faster market adoption to satisfy targets on emissions and sustainability.

Higher voltage, greater efficiency One way automakers are advancing electric-vehicle architecture is by increasing battery voltages. Some prestige and high-performance EV models have voltages as high as 800 V. Increasing the voltage provides greater power transfer, enabling faster battery charging.

Additionally, a higher operating voltage means thinner and lighter cables can handle the power delivered into the charging and traction systems and lower “I2R” losses, contributing to a longer driving range.

While greater passenger EVs use 400 or 800 V, a new 1,250 V charging specification promises to cut the charging times of long-haul trucks, including the high-capacity Class 7 and 8 vehicles. Productivity is a major concern in commercial haulage. The Megawatt Charging System (MCS) has been proposed to ensure the fastest possible charging times — standardized as SAE J3271.

Currently, SAE J3271 is under development and specifies charging

www.evengineeringonline.com

from 440 kW at 350 A and 1,250 VDC without cooling and up to 3.75 MW at 3000 A and 1,250 VDC with active cooling.

As a guide, charging at 1.6 MW for 30 minutes would deliver 400 miles of driving with a standard Class 8 tractor. The SAE J3271 specification standardizes aspects, such as the plug design, communications protocols, and safety requirements, providing interoperability between vehicles, charging stations, charging networks, and the electric grid.

Higher battery voltages could extend the driving range by about five to 10%.

Technology for the transition Raising EV battery voltages can lead to faster charging and greater driving range, but it also puts extra demands on the vehicle’s essential powerhandling functions. These include the traction inverter, onboard charger (OBC), and HVAC systems.

As battery voltages are increased to 800 and 1,250 V, silicon-carbide (SiC) technology is inherently better suited to these applications. SiC MOSFETs offer advantages, including

DESIGN WORLD

12/11/23 10:30 AM

What Does It Take To Keep Industrial Automation Alive?

LAPP networking technologies are the lifelines of automation systems, reliably transmitting the power and data that enable the seamless interaction of machines, devices and plants.

Using our in-depth expertise, we design powerful communication solutions that enable the most reliable connections on the market— meeting your toughest industrial requirements and keeping production lines running. lapp.com/us

lapp group – ev engineering december 2023.indd 5

12/11/23 10:31 AM

EV ENGINEERING

Table 1.

Planar, trench, and trenchassisted planar comparison.

smaller feature sizes, lower parasitic capacitances, and lower on-resistance in relation to their breakdown voltage rating (VBR) compared to silicon IGBTs or MOSFETs, the typical alternative.

The lower capacitances permit faster switching with lower losses, resulting in greater energy efficiency.

The lower on-resistance allows for fewer transistors in parallel, resulting in smaller module dimensions, lower weight, and a reduced bill of materials. SiC can also handle higher operating temperatures, and the devices have lower thermal impedance, which can help simplify the vehicle’s cooling systems while preserving reliability.

SiC in roadside chargers Roadside EV fast chargers must be upgraded to meet increased EV battery voltages, especially to ensure faster charge times. Accordingly, SiC’s device size and efficiency advantages make this technology an ideal fit for charging applications where high speed, reliability, flexibility, and space savings are critical.

Many chargers are becoming more intelligent to better manage

44

December 2023

batteries – ev engineering supplement dw dec 2023 v5 final.indd 44

smart infrastructures powered by renewable energy sources. In a world where grid-connected storage is essential to maintain stability, the value of a nation’s fleet of EVs connected to the grid is inestimable as a storage solution.

An EV with a 40-kW battery could satisfy the energy demand of an entire household. The vehicle could be recharged when necessary and ready for the owner’s next trip. Vehicle-to-grid (V2G) communication is a specification that enables smart charging systems to use an EV as a resource to help balance energy flow through the grid and keep pace with continuously changing supply and demand.

Trench-assisted planar-gate technology Although the performance advantages of SiC devices have been well documented, designing SiC MOSFETs for the real world involves compromises between performance, reliability, and manufacturability. Typically, the choices are between a planar or trench architecture.

Trench architectures can offer lower on-resistance per die area and faster switching performance. However, the

www.evengineeringonline.com

manufacturing yield can be low, and the gate oxide thickness is difficult to control, often leading to device failures in the field.

Planar devices benefit from superior gate ruggedness and shortcircuit capability, as well as simpler manufacturing processes. There’s also scope for future generations of the technology to deliver additional improvements in die size and cell performance.

The GeneSiC MOSFET platforms stretch from 650 to 6,500 V, addressing a range of high-voltage, fast-charging systems. Patented trench-assisted planar-gate designs combine the established strengths of planar technology with fast switching capability, extended operating lifetime, and high manufacturing yield. Table 1 compares the relative merits of the three architectures.

With low RDS(ON) at high temperatures and low energy losses at high speeds, trench-assisted planar devices outperform alternatives, including trench-gate structures. Their extremely low RDS(ON) temperature coefficient is significant.

In datasheets, RDS(ON) is typically stated at 25° C, but conventional

DESIGN WORLD

12/11/23 10:21 AM

te connectivity – dw december 2023.indd 5

12/11/23 10:31 AM

EV ENGINEERING

The electrification of heavy-goods vehicles is also significant to the transition to climateneutral mobility. The US has committed to ensuring all new trucks sold will be zero-emission vehicles by 2040.

Replacing 100,000 40ton trucks with electric Figure 1. Lower RDS(ON) temperature equivalents on long-haul coefficient of GeneSiC MOSFETs. routes is expected to save 10 million tons of the call to reduce emissions by CO2 annually. developing diesel-electric drivetrains, To support these efforts, certain electric pumps, and generators. long-haul routes could be targeted to Finally, hydrogen fuel-cell change first — prioritizing those that Future trends technology is expected to have a role let vehicles cover long distances at a The future must contain more fastin future e-mobility. It can leverage constant speed, with MCS chargers charging locations if EV adoption is the energy efficiency, ruggedness, placed in specific locations along to grow. However, installing more fast compactness, and reliability of SiC the route.

This approach, which chargers can demand a significant power semiconductors in hydrogen could establish a minimum viable financial commitment to upgrade the production by electrolysis and in the infrastructure as a platform for further supplying utility infrastructure and electric powertrains of hydrogen fuelprogress, would give fleet operators could slow the rate of progress. cell vehicles. and vehicle manufacturers confidence A fast and relatively low-cost to make investments in zero-emission approach involves upgrading Level Conclusion haulage.

2 charging points by integrating an Automotive OEMs have demonstrated Off-highway applications, such as energy storage system to boost the that passenger and commercial EVs charger output. The storage is charged agricultural and construction vehicles, can be practical, reliable, convenient, are expected to transition to electric continuously from the same lowand cost-effective. However, further powertrains more slowly. Arguably, voltage infrastructure used to supply improvements in charging times are such vehicles cover less distance than the Level 2 charger and discharged critical to reduce range anxiety and passenger cars and long-haul trucks. quickly into the EV battery when However, leading brands are answering accelerate adoption. The latest 800 connected. and 1,250 V systems require 1,700 V or 3,300 V SiC FETs and diodes, which IN-CIRCUIT, HIGH-SPEED TEST must be efficient and reliable to meet critical needs for the migration to faster charging. EV devices can suffer from a significant increase in resistance at elevated temperatures. GeneSiC MOSFETs have been shown to operate with up to 15% lower RDS(ON) over the rated temperature range (Figure 1).

This reduces energy losses, leading to increased system efficiency. Also, reducing device self-heating can lower the case temperature by as much as 25° C compared to equivalent alternative SiC devices operated with the same gate drive and ambient conditions (Figure 2). The 25° C cooler operation translates into a device lifetime that’s three times longer.

Figure 2. Operating temperature reduced by 25° C.

46

December 2023

batteries – ev engineering supplement dw dec 2023 v5 final.indd 46

www.evengineeringonline.com

References • freewiretech.com • reuters.com/business/cop/us-aimszero-emissions-heavy-duty-vehiclesby-2040-2022-11-17 • man.eu/corporate/en/experience/ megawatt-charging-revolutioniseslong-haul-truck-transport-120000.html • mckinsey.com/industries/travellogistics-and-infrastructure/our-insights/ powering-the-transition-to-zeroemission-trucks-through-infrastructure • deere.com/en/engines-and-drivetrain/ diesel-electric

DESIGN WORLD

12/11/23 10:21 AM

Custom Prototypes and Production Parts for Electric Vehicles Machining Molding Casting 3D Printing Laser Cutting Assembly And More Work with our experienced automotive team to bring your biggest projects to life.

xometry – ev engineering december 2023.indd 5

12/11/23 10:32 AM

EV ENGINEERING

Figure 2. Researchers are developing alternatives to rare earth minerals, which would negate concerns over supply chain security, environmental damage, and sustainability.

Rare earths and EVs — it’s not about batteries

By Jeff Shepard

R

are earths are important in the manufacture of electric vehicles (EVs). Although there are sustainability challenges related to EV batteries, rare earths are not used in lithium-ion batteries. They’re necessary for the magnets that form the main propulsion motors. The batteries mostly rely on lithium and cobalt (not rare earths).

At the same time, the magnets in the motors need neodymium or samarium and can require terbium

48

December 2023

minerals – ev engineering supplement dw dec 2023 v3 final.indd 48

and dysprosium -- all are rare earth elements. The most common rare-earth magnets are the neodymium-iron-boron (NdFeB) and samarium cobalt (SmCo).

Let's review what constitutes a rare earth element, consider where NdFeB and SmCo magnetic materials fit into the landscape of available magnetic materials, and briefly examine the applications beyond EVs for rare earth magnetic materials. We'll also present examples of the efforts underway worldwide to minimize or eliminate www.evengineeringonline.com

the need for rare earths in highperformance magnets.

What’s rare about rare earths?

Contrary to their name, rare earths are neither rare nor earths. The 17 rare earths consist of 15 lanthanides, including cerium, dysprosium, erbium, europium, holmium, gadolinium, lanthanum, lutecium, neodymium, praseodymium, promethium, samarium, terbium, thulium, ytterbium, and the metals scandium and yttrium.

DESIGN WORLD

12/12/23 10:57 AM

chroma – ev engineering december 2023.indd 5

12/12/23 10:59 AM

EV ENGINEERING

Permanent Magnet

Ba Ferrite

Ferrite

Sr Ferrite Alnico

Metal

Rare Earth

Bonded They’re all relatively abundant in the earth’s crust but are “rare” because they occur in relatively low concentrations compared with the ores for other metals. Metals like iron, gold, silver, copper, and others can be found in high concentrations in ores. While rare earths don’t occur in ores like other metals, their overall availability is three times that of copper, two times that of zinc, and 200 times more abundant than platinum or gold.

However, their low concentrations make rare earths much more challenging to acquire than other metals. They’re also relatively difficult to separate from one another and the ores in which they occur. The difficulty in mining and refining rare earths presents problems related to environmental damage and sustainability.

Where do rare earth magnets fit in?

Rare earth magnets are the strongest permanent magnets. They produce much stronger fields than other options like ferrite or alnico permanent magnets. For example, rare earth magnets can produce magnetic fields of 1.6 Teslas (T) or more.

At the same time, other materials are limited to 0.5 to 1.0 T. Metals, ferrites, and bonded structures are used to fabricate permanent magnets. Rare earth magnets are a

50

December 2023

minerals – ev engineering supplement dw dec 2023 v3 final.indd 50

Figure 1. Rare earth permanent magnets are a branch of metal permanent magnets. (Image source: Shin-Etsu Chemical Co.)

SmCo Nd2Fe14B

subset of metal magnets (Figure 1).

One challenge with rare earth magnets can be corrosion, especially for NdFeB magnets.

NdFeB and SmCo both make powerful magnets. The primary difference is their operating temperature range. Other than high opposing magnetic fields, high temperatures commonly demagnetize permanent magnets. NdFeB and SmCo magnets have different operating temperature capabilities and temperature coefficients.

NdFeB, the strongest available magnets, are typically room temperature up to about 180 °C. Above that temperature, SmCo magnets are superior. One reason for the excellent performance of SmCo magnets at high temperatures is their lower temperature coefficient. SmCo’s temperature coefficient is about 0.200.30 %/° C, while the corresponding specification for NdFeB is 0.45-0.60 %/° C. The temperature performance of these materials has a major impact on their use.

Not just for EVs There’s some overlap, but because of their different operating temperature capabilities and corrosion resistances, NdFeB and SmCo magnets are generally used in other applications.

NdFeB magnets are suited for use at up to about 180° C, where corrosion resistance is not a significant concern.

www.evengineeringonline.com

SmCo5 Sm2Co17

Applications include: • Drive motors in EVs • Accessory motors in general automotive systems • Motors in industrial and commercial robots • Sensors • Portable electronics • Speakers and other electroacoustic devices SmCo magnets are better suited for applications with heavy loads or that operate at elevated temperatures like: • Locomotive traction motors • Marine and large industrial motors and generators • Motors in military and aerospace systems • Oil and gas production and exploration downhole equipment Stepping away from rare earths EV motors require high coercivity and the ability to maintain magnetization, even at elevated temperatures. In many instances, about 30% of the materials used in the magnets in EV motors are rare earths.

To improve the high-temperature operation of Nd magnets, terbium (Tb) and dysprosium (Dy) are added.

Unfortunately, Tb and Dy are highly costly and subject to severe supply chain risks. To address these concerns and performance needs, Toyota has developed a new Nd magnetic material that uses no Tb or Dy. In the new material, part of the Nd is

DESIGN WORLD

12/12/23 10:57 AM

Maximize Vehicle Range and Cabin Comfort with Quiet and Efficient Thermal Management Systems Allegro provides holistic solutions that enable more flexible and scalable EV TMS with low noise and precise control, improving energy efficiency.

Magnetic Sensor ICs Switches & Latches Position Sensors Current Sensors Speed Sensors

Power ICs Motor Drivers Isolated Gate Drivers Non-Isolated Gate Drivers DC-DC Regulators LED Drivers

To learn more about the Allegro family of products and to explore available design resources, visit allegromicro.com

allegro – ev engineering december 2023.indd 5

12/11/23 10:33 AM

EV ENGINEERING

replaced by lanthanum (La) and cerium (Ce), relatively low-cost and more widely available rare earths.

Toyota significantly reduced the use of Tb and Dy in the fourthgeneration Prius motor. The recent development eliminates the use of Tb and Dy, reduces the amount of Nb needed, and replaces the Nb with La and Ce. The new material is more sustainable and is expected to be used across a similar range of applications as the Nb material it replaces.

Cosmic magnets Researchers at the University of Cambridge are taking a different approach to eliminate rare earths.

They're developing an industrialscale process to make tetrataenite, an iron-nickel alloy with magnetic properties approaching those of rare-earth magnets (Figure 2).

Natural tetrataenite forms in outer space in a meteorite as it slowly cools over millions of years. The long cooling time gives the iron and nickel atoms time to order themselves into a specific stacking sequence that supports the fabrication of highperformance permanent magnets without rare earths.

The long cooling time nor the stacking sequence makes it impractical to produce tetrataenite on a large scale. The recently proposed fabrication method

52

December 2023

minerals – ev engineering supplement dw dec 2023 v3 final.indd 52

involves the addition of phosphorous in the right proportions to the iron and nickel matrix. The new formulation speeds the formation of tetrataenite by up to 15 orders of magnitude, enabling it to be produced in a matter of seconds instead of millions of years. The material is now being characterized to determine how its performance compares with NdFeB and SmCo rare earth magnets and to refine the fabrication process further to make it suitable for industrialscale operations.

MnBi-based permanent magnets Another proposed alternative to rare earth magnets is manganese-bismuth (MnBi) based permanent magnets.

Researchers from the Department of Energy’s Critical Materials Institute and Ames National Laboratory are developing a new method of fabricating MnBi magnets based on microstructure engineering. MnBi is a potential material for high-temperature magnets because of its increasing coercivity (H) with increasing temperatures up to 255° C. In general, the H of a permanent magnet is always lower than that of the material used to make the magnet due to defects introduced during sintering or other powder consolidation processes.

For most materials, the reduction in H is insignificant, but for MnBi, up to 70% of H is lost during powder consolidation.

The structure of the magnetization domains controls the H of a MnBi bulk magnet, and the significant H

www.evengineeringonline.com

loss experienced during the powder consolidation process can be attributed to the inter-grain magnetic coupling. The grains in the MnBi bulk magnet must be separated with a nonmagnetic grain boundary phase (GBP) to achieve a high H. The research team engineered precise nanostructures by controlling the grain size, tailoring the GBP, and improving grain alignment.

Those enhancements greatly improved magnetic properties, including H for MnBi magnets.

Further development work is being undertaken with PowderMet, Inc. to design a commercially viable and large-scale process for fabricating high-performance MnBi permanent magnets.

Summary NdFeB and SSmCo-based rare earth magnets are important components in EVs and various industrial, commercial, and military-aerospace systems. They are significantly higher in performance compared to alternatives without rare earth content. The use of rare earths is fraught with concerns about supply chain security, environmental damage, and sustainability. As a result, numerous efforts are underway to develop alternatives to rare earth magnets with similar performance levels. EV References • sneci.com/blog/are-rare-earths-anissue-in-the-production-of-ev-batteries • ameslab.gov/news/improvingrare-earth-free-magnets-throughmicrostructure-engineering • cam.ac.uk/research/news/newapproach-to-cosmic-magnetmanufacturing-could-reduce-relianceon-rare-earths-in-low-carbon • global.toyota/en/newsroom/ corporate/21139684.html • en.wikipedia.org/wiki/Rare-earth_ magnet • shinetsu-rare-earth-magnet.jp/e/design/ index.html • idealmagnetsolutions.com/knowledgebase/samarium-cobalt-vs-neodymiummagnets

DESIGN WORLD

12/12/23 10:57 AM