The vehicle of the future will be electrically, battery or hybrid powered, due to governmental requirements to reduce CO2 and NOx emissions as well as scarce fossil fuel resources. This means reinventing the established vision of a car and brings a lot of challenges, developments and changes with it. Driving across entire Germany with one tank full in today´s combustion engine equipped cars puts the driver´s expectations for electric cars high. Easy and quick re-charging during a coffee break (below 15 minutes) with an infrastructure of charging points in place every few kilometers is also required.
In addition, lower investment cost, longer reach and higher energy efficiency are in the consumer´s mind.
Today’s trends and challenges in e-drive motors
Today´s electric cars have a high energy consumption which is not only caused by driving itself, but by invisible energy consumers in the on-board network, such as entertainment/infotainment systems, heating and air conditioning systems, battery thermal management, etc. Those represent the biggest challenge to the energy management of the vehicle.
Nowadays, only niche models such as Formula-e-cars or few outstanding high-performance models such as Porsche Taycan, Audi e-tron GT or Aston Martin Rapid E are already equipped with an 800 V system. Currently available electric cars are delivered with an on-board power supply of 400 V.
In order to achieve widespread social acceptance of electromobility, enormous efforts are being made, such as significant improving of the range and the fast-charging capability of electric vehicles.
Increasing the voltage level from 400V to 800V represents the most efficient way to optimize performance. By doubling the voltage level, considerably more power can be transmitted in the same time with the same current, which can lead to up to half of the charging time compared to a 400V system.
The question arises: Are we, and are all players along the automotive value chain aware of the implications of this high-voltage architecture on board the car of the future?
800 V as a standard to enable future large-scale production
Increasing the voltage level to 800 V offers a range of benefits to the consumer like faster charging, substantially lower weight and volume at highest efficiency, comfort and performance.
The advantages are evident in high-performance vehicles, which are very sensitive to the weight-to-performance ratio. But lower cost vehicles will also benefit from the 800-V systems, when cost-optimized versions will become available thanks to a larger number of cars produced. Consequently, the introduction of the 800-V technology will most likely follow a top-down strategy from the OEM over the Tier 1, Tier 2 to the molder down to the raw-material producer, also accompanied most probably by further governmental-driven measures.
When scaling up the electrical vehicles to 800 V, the requirements to all sub-components change, all parts in the e-drive motor´s construction must be adapted and entire mechanical sub-systems need to be electrificated. In short: a redesign of all under-the-bonnet components is necessary in order to make the entire circuit of power match. This is of course quite costly and only gets profitable in a large-scale production.
Which are the most convincing arguments to undertake these all-encompassing and significant financial investments?
The increase in voltage to 800 V can be one reply to the consumer´s expectations, looking for faster charging times and longer driving autonomy. Improving the battery efficiency for longer distance rides by increasing the number of battery cells, further weight savings and upscaling to mass-production can be further replies to the consumer´s demands. In a high voltage system, the battery charging time for a vehicle in the 400-km-range can indeed be reduced from 29 minutes in a 400-V system to this coffee-break-long charging time of 15 minutes or less, while the reach of a vehicle must be substantially increased. But it also means that automotive OEMs must invest additional development effort, time and cost in applying the 800-V system from niche products on to broader mass passenger vehicles.
Improving the energy efficiency across the entire vehicle means also limiting unnecessary power loss which occurs when being in a traffic jam, driving low speed in a city center with many traffic lights, but of course also when charging or discharging the car. Whether it be low or high power demands, these power losses waste a significant amount of energy and thus resources and money. At higher voltage levels, the power loss is significantly lowered. For example, a 400 V cable charges for 200 km at a power loss of 85 W. At 800 V, the power loss would be four times less, meaning 20 W only. In order to ensure that power losses are kept to a minimum, the charging voltage should match the battery voltage as well as the voltage of the entire propulsion system. Thus, to make it work, the 800- transformation must involve more than a charging system.
Likewise, in vehicles with an 800V voltage level, new electrical semiconductors made of e.g. silicon carbide and gallium nitride are used to control the electric motor. The use of these materials sustainably reduces power losses, which also leads to less heat dissipation. The advantage is that expensive cooling systems can be saved and the size and weight of the entire structure can be reduced. The use of these new generations of semiconductors sustainably increases the efficiency of the electric motor on the one hand, but on the other hand (due to very fast switching cycles/rising times) puts a strain on the motor’s insulation system (and thus its durability).
Here, Von Roll´s high-voltage know-how comes into play: thanks to its specific expertise, many Automotive OEMs have been contracting the Von Roll Institute in recent years for tests of 400V eDrive systems. Von Roll´s conclusion of many successful tests is that the industry is slowly preparing for this big step towards an 800-V onboard supply system as the future standard for high-performance electric vehicles, most probably in the next 10 years to come.
Increasing efficiency and profitability with 800 V
Assuming a constant power level, the required current can be reduced by 50% in a 800-V system compared to a 400-V system (Power=voltage*current). As a result, less copper is used, which benefits the overall system costs as well as the vehicle weight.
A welcome side effect is that the charging plug and the charging socket no longer need to be cooled, as an increase in the voltage in the cable does not increase the heat in the charging system, but the charging process itself is faster.
Von Roll is working intensively on the introduction of new materials to meet the requirements of an 800 V vehicle electrical system. This includes, for example, new types of impregnating resins and insulation systems for electric motors, which have improved thermal conductivity and thus lead to higher efficiency in the engine. Due to faster processability and shorter curing times, which are possible at ambient temperature, such an electrical insulation system is much more user-friendly. This means that electric motors can be manufactured quicker, which in the long-term, leads to massive time and energy savings as well as lower manufacturing costs.
Problem: today, all necessary under-the-bonnet components are not yet available in their high voltage version
But, the investments quickly become profitable: let´s take an e-drive motor at a cost of 1500 EUR – the Von Roll insulation system can procure 10 % more performance which results either in using less material or using a smaller e-drive motor. The cost per piece would be reduced down to 1350 EUR, at one million cars produced p.a., this saves 150 million EUR straight into the pocket, thanks to the high-performance insulation system, without changing anything at the e-drive motors themselves yet.
Mastering high-voltage – mastering upcoming challenges of e-Drives
Increased stress on the drive fed motor, like fast rise time pulses of up to 50kV/µs cause encumbrances with power peaks challenge the insulation system´s and e-drive motor´s performance. Let´s have a look at the phenomenon of partial discharges and how to cope with it in order to extend the motor´s and car´s lifetime massively starting with a 400 V system and particularly in an 800 V – system.
Partial discharges (PDs) are small electrical arcs (also called “corona”) in voids inside or on the surface of the insulation ignited by high electrical fields. During the impregnation process, the air between the copper wires is supposed to be filled entirely with resin. However, some of the air bubbles do remain in the resin as well as between the wires. Depending on the geometry, the air pressure and temperature inside these voids – conditions for corona presence – may be leading to insulation degradation, to harmful corona effects and finally motor failure.
Applying pulses (in the car: meaning “voltage shape”) by using a pulse-width modulated inverter with a high voltage level (800 V and higher) increases the possibility of PD creation and power of PD, leading to pre-mature insulation failure. In short, without improvement of the e-drive-motor design and application of the appropriate insulation systems, partial discharge may cause significant damage during the lifetime of the machine.
Therefore, car manufacturers of tomorrow´s vehicles test and drive already at higher voltage levels since it will bring many advantages with it.
Over 100 years of experience in the high-voltage business with lab tests even up to 100,000 V for various market segments like wind power, hydro or even, in the past, power (like coal / nuclear / gas), make Von Roll an unmatched specialist in this field. Most important criteria and learnings from these industries are achieving 100% security, durability and absolute robustness in a 0 failure environment. Evaluating the thermal and electrical stresses on insulation systems, selecting proper insulation materials, assessing the compatibility of the materials and finally testing and analyzing them under real-world conditions are essential.
The electrical stresses on e-Drive insulation systems are approaching similar levels now. It has to be proved that such motors survive these kinds of conditions. At the Von Roll Institute, industrials are constantly trained on the use of specific insulation materials and physics of PD effects, tests for 400 V and 800 V insulation systems are undertaken for eCar manufacturers. The testing capacities include material tests under extreme stresses, like high thermal (up to 350 °C), high voltage (up to 7 kV) and high frequency (up to 30 kHz). Last, but not least, even lightning impulses can be simulated in the Institute.
Combining the experience of large-series production in the 400-V range with the experience in the high-voltage business, Von Roll transfers this knowledge now in order to meet the high demands of the 800-V automotive market, while taking into account two major challenges: there is only little space in the construction room for the motor and, compared to big high voltage generators for example, the number of produced pieces is significantly higher. However, the automotive industry is very cost-conscious, needs high-cycle rates and the motors have to be robust against harsh environments.
In order to significantly extend the lifetime of the vehicle and in particular the electric motor, Von Roll’s expertise, such as thermal protection, electrical insulation and successfully lowering all the way down to completely preventing from partial discharge takes effect and finds for the first time application in the in the optimization of the car manufacturing.
Will 800V become the future standard in e-mobility? Conclusion and outlook
The aim for the car of the future is to drive reliable lightweight electrical cars with low CO2 emissions at affordable prices with higher performance and shorter charging times.
About 80 % of today´s 400 V electric, battery or hybrid powered cars which are matriculated in Europe are already equipped with Von Roll´s proven insulation technology systems for e-drive motors, comprising impregnation resins to avoid short-circuits, coated wires and flexible laminates. Worldwide, and especially with regards to the Chinese local market with cars in a different configuration and range, about 30 to 40 % of today´s cars drive on the Von Roll system.
Although most Automotive OEMs are active in the field of electric mobility, the technology, even of 400 V electrical cars is not yet finalized, due to their very high entry-prices or still a series of missing standards. The infrastructure of charging points still needs to be built up on a commercial scale and many other questions are not clarified yet, like the grid load, the electricity taxation, the parking spaces or loading facilities.
While Tesla for example delivers the car and the charging point, other car makers don´t yet invest too much effort in the compatibility of charging stations and docking points.
Driven a lot by governmental requirements regarding the regulation of CO2 emissions or percentage of car parts which need to contain lightweight material, electrical cars are today still a nice-to-have and need to receive more acceptance throughout the European population.
Both systems, 400 V and 800 V play key roles in today´s automotive developments. We are now only in the first generation of electric vehicles and the developments require some more time. E-mobility and its advantages must get through to the width mass. Von Roll happily supports the Automotive industry with solutions for less power loss, thermal protection and electrical insulation and more energy savings and invests in the next generation of car manufacturing.
