Antriebe und Energiesysteme von morgen 2023

ZF is a leading company for electric drivelines. Advanced driveline technologies are being developed as a knowledge base for future electric drives. ZF has built a demo-vehicle to demonstrate a highly efficient driveline concept in an electric all-wheel drive architecture. The ultimate efficiency front axle has a highly efficient gearbox layout in combination with an efficient electric motor. The rear axle in combination with eConnect, an ultra-efficient, switchable second drive, delivers power on demand and is disconnected during standard driving situations to avoid drag losses. Both e-motors avoid heavy rare earth elements for sustainability reasons. A benchmark vehicle was rebuilt with ZF-advanced technology and is released to drive on public roads. It has shown a range extension by 7%, which can be measured by energy consumption compared with the original benchmark vehicle.

The path to a sustainable and climate neutral industrial society requires the use of defossilized regenerative energy carriers. The development of efficient storage technologies and the secured energy supply without the use of fossil energy sources are the major challenges of the energy transition. Without these, a sustainable and climate-neutral mobility is not possible.

There are three concepts for a CO₂-neutral and sustainable mobility: First, the direct use of electric energy for battery-electric vehicles (BEV). Secondly, hydrogen as energy carrier for fuel cell electric vehicles (FCEV) by the transition of regeneratively produced electricity into green hydrogen and lastly, by the transition of synthetic fuels out of green hydrogen. The technologies will complement each other in terms of vehicle weight, distance and required drive power.

As the lightest and at the same time most abundant element with its high energy density, hydrogen offers great potential for the future. Sustainable mobility requires “green” hydrogen, which is obtained from the electrolysis of water using renewable energies. Water is decomposed into its components hydrogen and oxygen.

Because electrical energy is required for electrolysis, this process is only climate-neutral if the electricity comes from renewable sources. Since the economic generation of renewable energy does not take place geographically where it is needed to meet energy demand, transport and storage technology is crucial. Here, hydrogen has clear advantages over electrical energy, so that the hydrogen energy chain is the basis for a defossilized, sustainable energy supply and mobility.

For a successful implementation, the economic production of electrochemical cells for electrolyzers and fuel cells in serial scale is the missing link. These mainly consist of bipolar plates. For the development and production of these, the competences in material technology, electrochemistry, the forming and joining technology as well as coating technology are successfully utilized. A more efficient serial production and the according progress in the specific production technologies leads to a successful technical implementation and distribution. Moreover, by using cost-efficient materials and a clear reduction of noble metals like platin due to great progress in material- and coating technologies, the costs and the product carbon footprint could be reduced significantly. By the development of an extremely thin, noble metal free and performant coating in nano- to micrometer range, it could be achieved to use cost-efficient and well processable steel as base material, instead of titanium or graphite. Compared to alternative, precious metal-based coatings, the coating has a CO₂ footprint reduced by approximately 99 percent. Therefore, the overall CO₂-balance of the bipolar plate is reduced by approximately 20% compared to conventional products. This pioneering development will make an important contribution to the successful hydrogen energy chain and -mobility and was awarded with the CLEPA Award 2022 in the category “Clean & Sustainable Mobility”.

Fuel cells are a promising but challenging technology for achieving zero-emission heavy-duty commercial vehicles. AVL has developed a modular 156 kW fuel cell system and based on it an optimized fuel cell powertrain for a long-haul semitrailer tractor that meets the industry requirements of lifetime, driving performance, fuel consumption, driving range as well as the costs for acquisition and operation.

Within this publication the project »BiFoilStack« is presented, aiming to develop novel stack concepts for heavy duty applications using graphite-polymer composite bipolar foil-based plates. The stack requirements are derived from current long-haul applications, considering the latest efforts in standardization of fuel cell systems, and considering the targets set by the European Clean Hydrogen Partnership as well as the US Department of Energy. Overall target is the increase of durability and power density of the stack. This will be realized through the careful formulation of the graphite-polymer compound foil, used as material for the BPP, and the design of the cells. A design approach is shown to define and pre-optimize the high-level specifications of the fuel cell—cell aspect ratio, port areas, flow field concept, and channel design. Furthermore, the design is targeted to enable high current density operation, facilitating water removal and cooling. Additionally, the production process of the bipolar foil is shown including a characterization of the fundamental mechanical properties. First reshaping investigations, with a within the project developed reference flow field, proved excellent formability of the used material for the target size of the involved structures. Next steps are the wholistic characterization of the material properties and continuous optimization of the material formulation. Furthermore, the design of the flow field will be computationally optimized, and the MEA specified. The project will be concluded with the electrochemical characterization of short stacks on dedicated test benches to confirm the achievement of the set targets.

The high innovation value of this work is based on the overall system optimization enabling the development of a high-performance e-drive system for automotive application that sets a torque-to-weight benchmark. Beside of the system optimization advance innovation approaches are combined in this e-drive to further improve ZF’s current technology portfolio.

Powertrains commonly used in Battery Electric Vehicles (BEV) are mostly based on electric axles with either permanently excited synchronous machines (PSM) or externally excited synchronous machines (EESM). These are usually designed as radial flux machines. The torque is transmitted to the wheels via a single-stage spur gear reducer with differential and output shafts on both sides. With high demands for drivability, efficiency, and feature integration for better packaging, new drive architectures, and novel components are being developed. This paper determines specifications for the driveline and electric machines based on longitudinal dynamic drivability requirements for a B-segment vehicle. The research was conducted with an example of axial-flux machines. The methods however can be applied to various other electric machine (EM) types. The drivetrain consists of an EM and a planetary gear reducer. An existing map of an axial flux machine was scaled along with the gear ratio to ensure the driving requirements and, drivetrain efficiency over the “Worldwide harmonized Light vehicles Test Cycle” (WLTC). To accomplish this a multi-criteria optimization approach is used. The efficiency analysis also considers corresponding gearbox maps for different gear ratios and designs. Based on the results, different performance and design variants for EMs were created. A parameter study and local optimization using an inverse vehicle model determined the drivetrains with the highest efficiencies. The results of this work provide a key decision factor which powertrain architecture and EM will be developed further with a higher level of detail.

The electrification sharp progress in the automotive domain, as a solution for the environmental impact reduction of the transportation, brings up a new challenge on materials used in the electric powertrains and their availability.

Current challenges in the development of new electric traction drives are focusing on increasing efficiency and power while minimizing installation space and system costs. On one hand the use of new SiC power modules has led to an increase of efficiency. On the other hand, higher component costs must be amortized by an increased utilization of the inverter which is challenging for the lifetime and reliability of the inverter. The increasing spread of electric powertrains in commercial vehicles and rising safety requirements due to future automated driving functions place increasing demands on the reliability of the drive system which have to be considered during component design. Potential for a system optimization of SiC traction inverters and a reconciliation of efficiency, costs and reliability arise from optimized control strategies and a connection of IAV’s technology-oriented powertrain synthesis method with thermal and lifetime simulations of the inverter.

The latest study of the EVBox Mobility Monitor shows once again fast charging is one of the key features of an electric car that needs to be improved for more customer acceptance [1]. Over the last couple of years battery cells reached higher and higher energy densities. This leads to higher driving ranges. But there is a natural conflict between optimizing for energy or power density. High power charging capability suffers significantly when high-energy cells are used. This means longer charging times or battery systems that suffer extremely during fast charging and age prematurely.

APL sheds light on the bottlenecks during fast charging. Charging infrastructure, cables and plugs, and the battery itself all play a role. In the battery, the cell is the limiting factor. Temperature, kinetics and prevention of aging must be taken care of. With new analysis methods, optimized fast charging profiles are determined at cell level, tailored to the individual cell chemistry. For this purpose, APL builds special laboratory cells under an argon atmosphere and records anode potential-controlled charging curves. This prevents lithium-plating and takes the issue of aging into account. Another issue is the dissipation of the released thermal energy. For this reason, the right cooling strategy is an essential building block for successfully combining fast charging with high-energy cells. Through APL’s use of new test and development methods, the subject of immersed battery cooling is gaining momentum.

Fast charging of battery electric vehicles (BEVs) is an essential purchase criterion. In the case of heavy-duty vehicles, it influences the commercial usage and in the case of passenger cars represents added value for the driver in real-life driving. Even if the necessary charging infrastructure is either still being developed or is at least not yet sufficiently available. This publication looks at possible energy system architectures at vehicle level and component solutions to achieve very high charging power and associated fast charging speed in km/min, where the state of the art lies and which challenges still need to be overcome. In this context, the derived requirements for the charging stations will be discussed. Furthermore, the fundamental question of whether fast charging can be efficient will be discussed and an outlook on the possible roll-out of the technology will be given.

As the adoption of EVs continues to grow, the challenges associated with managing and processing the increasing volumes of charging data and data resulting from associated services will become more significant. EV charging operators will need to invest in the necessary infrastructure, apply the right design principles and establish a transparent and scalable governance to ensure that they can handle this data growth effectively and efficiently.

Sector coupling is understood as a main measure within the energy transition and decarbonization of the energy system. Bidirectional charging is a very impressive example for an interconnected energy system in the sense of sector coupling. Beside of the electrotechnical solution concepts one main challenge is to get all demands for data and customer requirements fulfilled in one common system architecture. So, it is necessary to include all stakeholders and their requirements into one common system to get the various functions running. This was achieved successfully by the team of the funded research project “Bidirectional charging management” (BDL). Data handling in the dimension of connecting an electric vehicle, PV-systems, other controllable loads in a customer’s home with grid operator demands and the energy market as well is challenging: Customers want to have a wide overview not only on their electric vehicles charging process but on the general energy flow in their household as well, information on the current cost situation with savings and potential earnings included. So, a lot of personal and private date are mandatory and lead us directly to all the legal requirements in terms of data privacy. In future service products, terms & conditions in the contract between customer and service provider have to respect data privacy. To get all required data, several measurement devices have to be installed not only in the electric vehicle and the wallbox, but also in the home installation. To enable interoperable and cost-efficient solutions, standardized equipment and interfaces are mandatory. A promising step into this direction will become the German smart metering system (intelligentes Messsystem—iMSys). This system will not only help to save the installation of additional meters and the related cost but also contribute to stabilizing the energy grid. The final question is: “How to bring all the resulting information to the customer by which means?” For this, app-solutions are already state of the art for single devices as electric vehicles or PV inverters. What’s missing today, are overall solutions integrating all these various domains.

The Bidirectional Charging project, which began in May 2019, aimed to develop an intelligent bidirectional charging management system and associated EV components to optimize the EV flexibility and storage capacity of the energy system. This paper focuses on the two main demonstrated use cases in the private customer field trial: PV self-consumption optimization and intraday arbitrage. In the PV self-consumption optimization use case, EVs were used as home storage systems to store PV energy that is charged into the traction battery during the day and then used to cover household loads after sunset. Results from the field trial showed that the customers who participated in the PV-Use Case saved an average of 7.5% of their electricity costs through feed-in from the EV after about one year of operation. The intraday arbitrage use case aimed to generate revenue through arbitrage trading of price differences in the intraday market. On a daily average, an EV charged 16 kWh and discharged 9 kWh in the intraday use case. Despite the challenges in implementation, the intraday arbitrage use case was successful in generating revenue through arbitrage trading. With the help of system optimizations such as improved flexibility forecasting based on a larger fleet and optimized trading, revenues would increase.

High user acceptance is an important prerequisite for the successful integration of the bidirectional charging technology in the energy system. A field trial within the research project “Bidirectional Charging Management—BCM” offered the unique opportunity to investigate real user perceptions and behavior in two use cases: 20 participants were equipped with the overall bidirectional charging system and integrated it into their daily lives to test the technology for a year. Using a multi-method research program including in-depth interviews, questionnaire-based online surveys, and diary studies allowed us to better understand user motivations and barriers; further, it helped us to evaluate participants’ satisfaction with different aspects of the system, its components, and the overall organization of the field trial. In this article, we present results from different studies and provide insights as well as implications for a user-friendly future development of the bidirectional charging technology.

Refueling of a fuel cell electric vehicle (FCEV) usually takes place at public refueling stations. These aim to be comparable to today’s petrol stations and should be able to refuel many cars throughout the day. These stations require high CAPEX (Capital Expenditure) and high OPEX (Operational Expenditure) per refueling process since they are not yet close to high utilization. Home refueling based on green hydrogen could supplement and support the refueling infrastructure rollout by lowering operating and capital costs [1]. Another advantage is, that it could enable the usage of the seasonal energy surplus of photovoltaics energy from summer during the rest of the year by storing unused energy as produced hydrogen.

Therefore, a concept for a family home with average parameters for a family household in Germany was developed. A detailed energy analysis for this model household was carried out to prove whether a year-round refueling using only roof-top photovoltaic energy is possible. For the compression of hydrogen, an electrochemical hydrogen compressor (EHC) was used. This device works noiseless and requires only small space, it is therefore perfectly suitable for the usage in residential buildings.

The demand for green hydrogen will grow exponentially in the future, without it being clear how the demand will be met. Of course, this also applies to the supply of hydrogen for mobile applications. There are essentially four candidates for industrial hydrogen production: alkaline electrolysis, SOEC electrolysis, AEM and PEM electrolysis. These technologies have specific advantages and disadvantages that further limit the universal industrial use for the production of green hydrogen. The situation is examined against the background of decentralized supply units, which are of particular importance for mobile applications. The focus is on the stack—the stacked electrolysis cells—as the heart of the electrolyzers, which ultimately determines the performance of the electrolyzer. Dimensioning, manufacturability and availability of the required materials are discussed, as well as their consequences are shown.

Cross-industry collaboration is needed to meet the challenge of integrating electric vehicles into the electricity grid. The unIT-e² project meets this requirement with a consortium of partners covering the entire value chain—from electric vehicles to charging, IT and metering infrastructure to grid operators. At the same time, this special feature brings with it a number of challenges, such as the different backgrounds of the partners in terms of technical know-how. In order to meet these challenges, the project is set up by a consistent and uniform project structure. This includes on the one hand the division into subprojects and practice clusters and on the other hand the uniform approach applied across them. Another special feature of the collaboration between the energy and automotive industries is the different “markets” that they serve. While the energy industry is predominantly based on the German market and regulation, the automotive and component manufacturers aim to develop globally marketable products. unIT-e² addresses this issue by integrating a European perspective in the synthesis and a subsequent analysis regarding the applicability of the developed approaches to other European countries.

This paper describes a methodology and scenario-based software toolbox for the analysis, design and optimization of electric bus operations. The software toolbox contains all relevant alternative propulsion concepts and enables the identification of a cost-optimal solution for planning the necessary charging and refueling infrastructure. The toolbox has a modular structure and enables an investigation adapted to the boundary conditions of the bus network. The current procedure for identifying new locations for charging infrastructure is very manual. In a complex system, manual analyses hardly lead to a cost-optimized solution. During the optimization with the developed toolbox, a heuristic and rule-based greedy optimization algorithm is used to determine f.e. the minimum number of electrified stations and the number of required charging points. Furthermore, the infrastructure planning includes the analysis of the required grid connection to supply the infrastructure with energy. Two case studies present selected results from the application of the software toolbox. For a rural bus operation in Germany, the operation of electric buses was investigated and compared. Depending on the ambient temperature (−20°C to +40°C), different energy consumptions in bus operation could be determined. In this study, the energy consumption of a 12m solo battery bus is between approx. 1.4 kWh/100km and 4.3 kWh/100km. The optimization of electrified stations is presented in the second case study. In a system with hundreds of rotations and almost 100 end stations, in the base setup 77 stations were identified that enable electrified operation. Through the optimization based on the software toolbox, the number of required stations could be reduced by approx. 35% to 50 stations compared to the manual variant.

The communication between electric vehicle and charging infrastructure is standardized in the several documents of ISO 15118. One of the recently published parts is ISO 15118-20. In combination with part ISO15118-8 further charging options such as inductive and automated charging can now be implemented in professional solutions. Furthermore for wired charging solutions extended functions are available. Especially for bi-directional charging with AC or DC current and intelligent load management (dynamic or scheduled charging) valuable and future proof solutions supporting energy transition are provided. In this document the extended potential using ISO 15118-20 will be presented and a prospect will be given for further developments of the standard, i.e. support of megawatt charging systems.

Experts and politicians agree that combustion engines must be replaced by electric motors for the decarbonization of private transport and that 100% of the energy for this must be generated from renewable sources in the future. Electric mobility is locally emission-free, efficient in energy use, quiet and offers an attractive driving experience. If this consensus continues to translate into concrete action, there will be an exponential growth of electric vehicles. In the future, up to 40 million new customers will join the German power grid. Customers who, on the one hand, want to charge conveniently—i.e., with high performance and in sufficiently large quantities at all times. On the other hand, however, with 11 or 22 kW, these customers have by far the largest power requirement that we see in private households. Due to the latest funding programs, we are currently observing a sharp increase in requests for the grid connection of private charging points. In order to test the challenges for our power grid in real life, Netze BW has set up several NETZlabore (grid labs). The findings of these real life labs help us to assess which capacities our power grid provides in extreme cases and how we can use them optimally to guarantee our customers the fastest connection possible. In addition, Netze BW has defined relevant, holistic and future-oriented action points for the implementation in practice. These include the provision of a customer-centric grid connection, early detection of grid bottlenecks through transparency in the power grid, intelligent optimization of the existing power grid, and forward-looking and future-proof grid development.