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Silicon carbide (SiC) devices for the next-generation of electric vehicles
18 Mar 2021
Before electric cars become a familiar sight on Europe’s roads, the technology behind them needs to evolve to improve the size and efficiency of their drivetrains, the speed that they can be charged and the range that they can drive. The silicon carbide inverter could be crucial to helping to overcome these issues
Sales of battery-electric vehicles (BEVs) are increasing as consumers and automakers alike benefit from European government subsidies for electric vehicles. Momentum is gathering pace as automakers including Ford, Jaguar Land Rover and Volvo have all announced plans to phase out internal combustion engines in their vehicles.
Despite the small steps being taken so far by the technology, the move towards an electrified fleet in Europe is unstoppable and the days of petrol and diesel engines are already numbered. It is a question of when, not if, we will all be driving electric cars in the future.
But before we reach this point, the technology behind BEVs needs to evolve to overcome a number of challenges, which include the size and efficiency of their drivetrains, the speed at which they can be charged and the range that they can cover.
A crucial element in all this is the inverter. This component controls the input of electricity from the battery or batteries to the motor. Aside from converting incoming direct current to alternating current, the inverter controls the variability of power supplied to the motor when the driver demands it. As motors develop and migrate from 400-volt electrical systems to the far more versatile 800-volt units, the inverter is playing a crucial role.
Increasingly, the industry is moving away from silicon to the use of silicon carbide inverters (SiCs), which have a number of significant advantages when twinned with high-voltage systems.
Thomas Steffen, Senior Lecturer in Control Engineering at Loughborough University in the UK, explains: “A conventional inverter is about 97% to 98% efficient in moving energy from the battery to the motor, and a SiC-based inverter can push this to an amazing 99%. Although this is only a modest increase of 1% to 2%, the benefits for the whole vehicle can be more significant.”
The two materials are very different in that they have varied physical parameters. Silicon carbide has the advantage that it is well suited to higher thermal conductivity, which is important in high-revving, high-voltage motors.
“Compared with other silicon conductors, silicon carbide has a higher maximum operation temperature, which means you can squeeze more power out of it,” says Roland Bittner, a senior engineer at Semikron Elektronik, which is a partner of Drivemode, an EU research project. Its goal is to produce small adaptable electric modules consisting of power electronics including an SiC-inverter, a gearbox, and the motor itself. These modules are capable of being scaled up from one unit to four according to the power requirements of different vehicle segments.
SiC inverters are ideal in such a modular approach because they allow a reduction in the size of all the crucial components. Bittner says: “If you go to higher battery voltage [such as 800V] and require less current, you also need smaller cables and smaller cables means less cost, less weight in the vehicle. It is also easier to assemble [the modules] in the vehicle.”
Steffen adds: “Through reduced weight and increased regenerative braking, the range and the efficiency of the vehicle can increase by about 3%. For a typical vehicle, this translates into about 10 miles (16 km) more range.”
Driver anxiety in relation to the distance a BEV can drive between charges is one of the biggest hurdles in their acceptance among consumers and key to next-generation models. A small 800-volt enabled module, as used by Drivemode, frees up additional space that not only benefits internal passenger and storage possibilities, but also enables the placement of additional batteries in order to extend range in BEVs.
Hyundai Motor Group is among the first automakers to commercialise 800-volt systems with their new Electric-Global Modular Platform (E-GMP). The company unveiled its IONIQ 5 on the platform last month, and the automaker says the crossover model can reach 80% of its full power within 18 minutes on a fast charger. This is roughly a fifth of the time a conventional 400-volt car needs to reach the same charge, and the added efficiency of the SiC inverter means more of this power survives to drive the vehicle.
“We want to offer best efficiency and this starts [with less lost power] from charging, up to driving and recuperation. With 800-volt charging, the current can go directly to the battery without any transformation (possible losses),” a spokesman said. The automaker is expecting to launch 23 new Hyundai and Kia BEV models by 2025 in a bid to hit 1 million cars by mid-decade.
Like the Drivemode project, the company has packaged its electric powertrain system into a compact module that includes a SiC inverter, something that Thomas Steffen expects to see more and more automakers adopting in the move to next-generation BEVs.
“Now with SiC inverters, it makes sense to connect the inverter and motor into one unit with a common case and cooling circuit,” he says. “What is interesting about the Drivemode project is that they aim for a drive unit that is both integrated and modular. So the inverter is integrated into a common case with the motor,” he adds.
Such technology is leading industry observers to forecast that BEVs will likely reach cost parity with internal combustion engine vehicles by mid-decade, which means they could soon be a more common sight on Europe’s roads.
By David Jolley
Why reducing drivetrain size can make electric cars even greener
10 Mar 2021
Battery electric vehicles (BEVs) already go some way to reducing air pollution in Europe. The latest developments in electric drivetrain technology, however, are helping to take that one step further
Battery electric vehicles (BEVs) are starting to win market share in Europe, as consumers opt for cleaner technology and lawmakers strengthen emissions rules for automakers in a bid to bring down pollution levels.
BEVs already go a long way to improving the environment, particularly in cities, by helping to cut CO2 and particulate pollution. But the latest developments in electric drivetrain technology are helping to take that one step further.
Making motors smaller and encapsulating them in modular systems with other key components could not only be the next step to cutting the costs of electric motoring, but it will help make it even greener too, in a variety of ways.
Automakers are under intense pressure to move beyond the initial euphoria of introducing zero-emissions vehicles to the market and start using these models to help make serious inroads into reducing CO2 pollution.
The European Union’s target this year aims to reduce average fleet emissions of new cars sold in the bloc to 95 grams per kilometre. Automakers that fail to hit this target will face fines of 95 euros for every excess gram of CO2 they emit. Understandably, they are keen to comply and avoid penalties that can quickly mount up to many millions of euros.
“The incentive is rather big. The reaction of most automakers – complaining and at the same time saying ‘yes, we will do more’ – speaks for itself,” says Juergen Pieper, an auto analyst and director of research at Bankhaus Metzler in Frankfurt.
The emissions targets are one of the reasons Pieper believes the shift towards an electric future is now fully underway, despite the fact that technology needed for the next generation of BEVs is still in its infancy, technology such as higher-voltage electrical systems.
While most manufacturers have traditionally used 400-volt layouts, automakers such as Porsche and Hyundai have started to introduce larger 800-volt units with big environmental benefits. Professor Damijan Miljavec of the University of Ljubljana’s Faculty of Electrical Engineering was instrumental in developing a high-voltage unit for the European Union research project Drivemode, which is seeking to develop a highly efficient and compact modular electric drivetrain consisting of power electronics, a gearbox, and the motor. These modules are designed to be scalable according to the power requirements of different vehicle segments.
Professor Miljavec’s initial task was to choose a smaller, greener motor for the module as he explains: “We increased the speed [of the motor] by a factor of two, from 10,000 [revs per minute] to 20,000, which means, to maintain the same power output, we can halve the size of the motor, which reduces the amount of copper and the amount of magnets.”
This is significant because permanent magnet motors use rare-earth materials that are very environmentally unfriendlyto mine. The ores that rare earths are extracted from are often separated using large amounts of toxic compounds such as sulphate, ammonia and hydrochloric acid. Processing one ton of rare earths can result in many more tons of toxic waste.
In addition to halving the use of these materials in their motors, Drivemode also claims the modules are fully recyclable: “You can take out the copper and reuse the parts by melting them down and producing new parts. You can also quite easily remove the magnets and reuse them, so it is 100% recyclable,” Miljavec says.
From a practical view, these smaller, lighter motors also offer energy savings for consumers. Reducing the weight of the vehicle means it can travel further on a single charge. This leads to an increased vehicle efficiency of about 3% or 10 miles (16 km) more range for an average BEV, industry observers say.
The silicon carbide inverter used by the EU project also reduces power leakage between the battery and the motor by up to 2%, which represents a significant saving for BEV drivers.
Additionally, smaller, high-voltage systems such as Drivemode’s are much faster to charge: Hyundai, which launched its Ioniq 5 last month using an 800-volt setup, says the BEV can reach 80% of its full power within 18 minutes on a fast charger, which is about a fifth of the time needed by a conventional 400-volt car. This could remove the need to pack cars with additional batteries in a bid to extend range and avoid lengthy charging stops. Since batteries contain materials such as lithium and cobalt that are mined using high levels of energy and water, any reduction in battery demand has a positive effect on the environment.
As automakers move away from fitting electric drivetrains to existing combustion-engine vehicles and more towards developing brand new BEVs, modular systems can offer obvious environmental benefits in standardising, simplifying and ultimately speeding up the manufacturing process.
“In principle, standardised modular designs could offer pre-set capacities, voltages, and form factors in much the way that AA or AAA batteries do for many small electrical products today,” says Professor Peter Wells, of Cardiff University’s Centre for Automotive Industry Research. Wells also sees the benefits of an industry-wide move to pool next-generation BEV technology that could help smaller, less cash-rich automakers build their own electric vehicles.
This will lead to a larger market for BEVs that will not only help automakers, but also the environment around us.
By David Jolley
Electric cars – Making the move from niche to mainstream
23 Feb 2021
Battery electric cars are slowly gaining in popularity among consumers in Europe as mainstream automakers respond to an industry-wide shift away from petrol and diesel vehicles. But despite pledges from regional governments to abolish sales of new combustion-engine vehicles in the next two decades, and pressure from the European Union to reduce carbon emissions, consumers are still not opting for battery-driven models in the numbers that are needed to turn them from a niche segment to mainstream one.
Data released this month from Europe’s ACEA industry association shows that despite a 10.5% rise in electrified vehicles last year, driven by a 117% jump in BEVs, petrol and diesel models still commanded an overall 75.5% share of European sales.
Volkswagen Group, the world’s second biggest automaker by volume after Toyota, is currently investing 73 million euros up to 2025 to prepare its German plants in Hanover, Emden and Zwickau for the production of BEVs.
Despite this, just 231,600 cars sold by the automaker last year were full-electric models, from overall global sales of 9.3 million vehicles.
One of the biggest problems BEVs face is their price. As an example, Opel’s entry-level full-electric e-Corsa currently costs 29,900 euros in Germany, whereas its petrol-driven sibling starts at 14,415 euros, less than half the price.
Part of the reason for the high pricing is a lack of uniformity in production. Automakers are only now beginning to produce universal electric platforms that can be scaled up or down for different-sized vehicles segments. Electric drivetrains, however, are still largely built in a bespoke fashion for different BEVs.
There are other big hurdles that impact the cost of BEVs, and they include the cost of batteries and high raw material costs.
One European Union research project addressing all these issues is Drivemode. It seeks to develop a highly efficient and compact modular drivetrain for BEVs that uses the vehicle’s stored energy more efficiently through a higher-voltage 800-volt electric system. Currently, most automakers are using 400-volt systems.
“With Drivemode we have a very integrated unit. That way it makes [everything including] the assembly process, the sourcing, the storing and the assembly, to putting it in the vehicle, very optimal, so you have a reduced production cost,” explains Deepak Singh, an engineer from National Electric Vehicle Sweden (NEVS), one of the project’s partners.
In Singh’s opinion, automakers are still taking a complicated approach by implementing varying electrical setups for each vehicle segment they design a BEV for, whether that is a passenger car or a light commercial vehicle, such as a van. “It makes it very difficult to do a quick product placement in the market,” Singh says. The project’s modular system on the other hand brings together the electronics, a gearbox, and the motor in a unit that can be scaled up according to the power requirements of a given vehicle. Put simply, that means that one of the modules could be used to drive a small city car, while a sports-car might require four modules. This approach would have an obvious effect in reducing the cost of building mass-market BEVs.
Drivemode’s use of an 800-volt electrical system also helps address other cost hurdles. In general, motor size is defined by torque capability. The higher-voltage systems, which run at speeds of 20,000 rpm, need less torque to achieve efficiency, meaning that they can be smaller in size and weight.
The use of smaller motors means that cars will be lighter than those with larger units and consequently can travel further on less battery power.
Batteries are currently the most expensive single item in EVs, and although their cost is falling fast, they are seen as currently making up about a quarter of the overall price.
This is an opinion echoed by many industry observers including JATO Dynamics auto analyst Felipe Muñoz: “Big range might be the trendy topic in the BEV world right now, but I’m sure in the near future, many consumers will prefer a more affordable BEV than a very long range one with a higher price tag.”
Higher-voltage systems such as Drivemode’s can cut charging times by up to 75 percent in vehicles using high-speed chargers. In the real world this means that a car such as the Porsche Taycan, currently the only commercial 800-volt vehicle on the market, can be charged to 80 percent of its battery capacity in just over 20 minutes.
This helps make a smaller battery range more acceptable to consumers by bringing down the time they need to charge. “It’s better to have less battery power and faster charging systems than spending one hour every time you need to fully charge your big battery,” Muñoz says.
Another cost-saving advantage of smaller high-voltage motors is a reduction in the use of precious materials such as copper, which is achieved through a decrease in electrical current to the motor.
A small electric car (using a 400-volt electrical system) currently contains about 40 kilograms of copper, roughly four times its combustion-engine equivalent. But despite the slow take up of electrification in Europe currently, industry observers are optimistic that BEVs will reach price parity with internal combustion models this decade.
Matthias Schmidt at Schmidt Automotive Research in Berlin expects this to happen in around four years, but believes it will be down to the costs of meeting new emissions standards, rather than any dramatic fall in BEV prices, because such technology “will increase the cost per unit for ICE (internal combustion engine) technology to meet the new Euro 7 technology level.”
And while Munoz thinks parity could arrive in 2023, he expects that this will likely only be in premium segments, with parity in mass-market segments arriving later in the decade.
By David Jolley
*image credit: NEVS
Shifting to 800-volt systems: Why boosting motor power could be the key to better electric cars
13 Feb 2021
The latest results from research on 800-volt battery-driven vehicles show that this could lead to smaller, lighter, and more environmentally friendly motors. Cars using these powertrains could also be charged faster and travel further on a single charge
Sales of electric vehicles are slowly beginning to gain traction in Europe as mainstream brands including Volkswagen, BMW, Fiat, Opel and Hyundai start to roll out battery-powered models.
But, despite a push by many governments to ban sales of new petrol and diesel cars in the next two decades in favour of full-electric vehicles, the existing technology in battery vehicles restricts their ranges and makes them more time-consuming to refuel than their combustion-engine rivals. This and their higher price continue to hamper their chances of becoming mainstream any time soon.
For many industry observers though, developments to boost the electrical systems of battery-driven vehicles to 800-volts from the current industry standard of 400 volts could be the breakthrough that finally allows electric vehicles to move to the next level and better compete, and eventually replace, combustion vehicles. A necessary transition as Europe strives to lower vehicle emissions and tackle climate change.
Professor Peter Wells, of Cardiff University’s Centre for Automotive Industry Research, says: “As is usually the case with ‘premium’ technology options in the automotive industry, we can expect a rapid transfer to the mass market arising from competitive pressures. In some cases, manufacturers have designed-in the ability to migrate from 400 volt to 800 volts as costs fall and as competitiveness comes to require such systems.”
Among those companies who have already embraced this technology is Volkswagen Group’s sports car brand Porsche, who have fitted an 800-volt system in their full-electric Taycan sports car, which was launched last year. For Otmar Bitsche, director of e-mobility in the automaker’s research and development unit, the reasons for opting for the higher-powered unit are clear: “Lower weight, higher efficiency and faster charging” are the major benefits to 800-volt systems, he believes.
Charging time can be greatly reduced when using fast chargers capable of working at up to 270 kilowatts. “If the charger provides 800 volts and a minimum of 300A, the Taycan can charge from 5% to 80% in 22.5 minutes. 400V chargers typically provide 50kW only. The same charging capacity would need 90 minutes,” Bitsche explains. The automaker, which was the first to introduce an 800-volt electrical system commercially, claims a 420-kilometre range between charges for its four-door coupe-styled saloon.
While this is not hugely higher than figures achieved by rivals using 400-volt systems such as the I-Pace from Jaguar, which can cover the 354 kilometres on a single charge, the use of an 800-volt system considerably increases the possibilities to boost the range of their electric vehicles.
One such advantage is that 800-volt electrical systems allow a greater retention of power, which is normally lost through heat generated during the charging process. A higher voltage system allows a lower current to be used when charging the battery, which reduces overheating and allows better power retention in the system. This power can be used towards a longer driving range.
Higher voltage systems also offer a number of key weight- and mass-saving advantages. The reduction of copper is one of these. Electric motors are much simpler than combustion engines in construction and at their core they have a rotor, which turns in response to a rotating magnetic field created by electricity from the battery. To achieve this, electrical systems often use up to four times the amount of copper found in combustion engines. Using higher-voltage systems can lead to the amount of copper used in motors being significantly cut.
Michael Burghardt, senior project manager at AVL, a German company developing and testing powertrain technology for cars and trucks, says: “Higher voltages mean less current and less current means less copper in the car. Less copper means less weight, and this is the goal we are reaching for.”
Burghardt is collaborating with the European Union research project Drivemode, which is seeking to develop a highly efficient and compact modular drivetrain for full-electric cars that uses the vehicle’s stored energy more efficiently through a higher-voltage electric system.
Besides reducing the weight of motors, an 800-volt system has the added advantage of reducing their mass too. Since the higher voltage allows the motors to run at speeds of 20,000 rpm, well over double that of their 400-volt siblings, they have better power density. This means that they convert electrical power to mechanical power with this speed and not high torque. “In general, motor size is defined by torque capability,” Bitsche says, which means removing torque from the equation allows motors to be much smaller. So much, in fact, that smaller high-speed motors can weigh as little as 25 kilograms, with the result that they reduce the overall weight of a vehicle, enabling it to travel much further on a single charge.
Smaller motors also mean the vehicle has additional space for batteries as Professor Wells notes: “The reduced weight of 800-volt systems will further help with increased range and acceleration performance or allow for larger battery packs with even greater range.”
Reducing the size of the motors along with optimising the efficiency of the drivetrain is central to Drivemode’s goal of producing small adaptable electric modules that consist of power electronics, a gearbox, and the motor itself. Modules that can be scaled up according to the power requirements of a given vehicle.
“The intention of the Drivemode project was to have one motor which can fit in different modular systems having one to four motors in one car,” Burghardt says.
That goal is one of many technical challenges that the project has met and overcome since it was launched. Technology derived from Drivemode is now expected to make its way into production vehicles in the next few years as the auto industry makes the move to the next generation of electric vehicles.
According to Professor Wells, the 800-volt technology will take a couple of model generations to really filter through to becoming the de facto standard, but by 2026 it can be expected to be the dominant application.
By David Jolley
PCIM digital days
6 Jul 2020
This year, PCIM Europe event will take place as digital event on 7th-8th July 2020.
Our partner SEMIKRON will participate to the Dialogue Sessions with the Poster Presenters Automotive II on Wednesday 08 July 2020, 15:00 – 16:30 and present the DRIVEMODE SiC-Inverter.
For further information, visit the event website: https://pcim.mesago.com/nuernberg/en/conference/program-speakers/program.detail.html/736/522.html
Download here the Conference Program
Oil flows and churning torque prediction in DRIVEMODE transmission
8 Oct 2018
DRIVEMODE aims to develop a smaller and lighter drivetrain module for the automotive industry by significantly increasing the speed of the electrical motor. This brings the challenge for the transmission system to operate with a high input speed and a high gear ratio.
One critical question for design is proper lubrication. For the development of the transmission of the demonstrator unit in the DRIVEMODE project a particle based CFD software was used. The tool helps to rapidly and accurately predict oil flows and churning torque in the transmission.
Traditionally, the lubrication system of a gearbox is optimized through physical testing, using a plastic housing. This is a time consuming and expensive method which does not allow multiple iterations of the design. Through the use of this tool, multiple modifications of the housing can be virtually tested. This does not eliminate the need for physical testing of the system, but helps to find the optimal solution.