In this section, we describe the final artifact design (Basic Design Principles for the EMSA Model) and its definition (Development of the EMSA Model). Multiple iterations and feedback cycles were conducted, considering informal feedback from discussions with system engineering and domain experts, who applied the model and framework during the three-year ELECTRIFIC project for multiple systems.
Basic design principles for the EMSA model
From the analyzed systems architecture models, we extract principles for the design of our artifact. These constitute the guidelines for the development of the e-mobility systems architecture model. The first three design principles are directly extracted from the related work analysis. Design principles four and five are more generic and stem from the basic principles for the domain-specific SGAM.
Design principle 1: Scope and applicability The systems architecture model is intended to be comprehensive and cover the complete scope of the e-mobility sector. It should be applicable for standalone usage, considering use cases and systems, which are not related to any other sectors. At the same time, it should also be applicable for systems that affect multiple sectors (e.g. compatible with the GSCAM approach).
Design principle 2: Multi-dimensional structure The systems architecture model is intended to provide an appropriate number of useful sector-specific dimensions. For a model, which is based on the SGAM and compatible with the GSCAM, the ideal structure also consists of three dimensions: interoperability layers, domains and zones. Contiguity (either geographical, hierarchical or logical) of all dimensions along each axis is essential. Only limited aspects of the domain value chain should be changed, providing a clear domain abstraction (Uslar and Gottschalk 2015).
Design principle 3: Allocation, localization and consistency The fundamental idea of the systems architecture model is to provide an appropriate allocation of all e-mobility entities to its structure. Across all dimensions, the appropriate location for each entity should be identified and specified. By adhering to this principle, all entities and their relations can be represented in a clear systematic and comprehensive view. Further, a consistent mapping is essential in order to be able to identify gaps in specifications or inconsistencies in the system (CEN-CENELEC-ETSI Smart Grid Coordination Group 2012).
Design principle 4: Universality and flexibility The systems architecture model is intended to represent e-mobility architectures in a common and neutral view. It should be technology-agnostic and not give any preferences to existing architectures. Obtaining flexibility on all layers supports alternative use cases, system designs and implementations. It further supports future advancements and enables concepts like scalability and extensibility (CEN-CENELEC-ETSI Smart Grid Coordination Group 2012).
Design principle 5: Extensibility and scalability The systems architecture model can be extended with additional entities or even by adding new domains and zones, when the sector evolves (compatibility with the SGAM needs to be maintained). The systems architecture model can be scaled up to a top-level view of the whole e-mobility ecosystem or scaled down to a specific and very detailed subset of use cases, functions and systems (CEN-CENELEC-ETSI Smart Grid Coordination Group 2012).
The EMSA is developed considering the above mentioned five design principles. In order to apply some of the SGAM framework’s tools, it is recommended to only alter aspects of the domain dimension (Uslar and Trefke 2014). This principle is also in line with the GSCAM approach (Neureiter et al. 2014). Subsequently, the EMSA is defined in a way, that is compatible with the GSCAM but also usable as standalone architecture model. Cross-cutting issues, that cannot be allocated explicitly to one domain or one zone like telecommunication systems and security, need to be represented separately and are not considered in this work (CEN-CENELEC-ETSI Smart Grid Coordination Group 2012).
Development of the EMSA model
In the following, the structure of the EMSA Model including all relevant domains along the e-mobility process chain will be discussed. For the EMSA scope, e-mobility is not limited to battery electric vehicles, but also includes all kind of other vehicles with an electric drive train, for example electric tram or hydrogen trucks with fuel cells. The dimensions of the EMSA Model are visualized in Fig. 3. In order to obtain a maximum level of compatibility to GSCAM and SGAM, both the number of layers (five - business, function, information, communication, component) and zones (six - process, field, station, operation, enterprise, market) in the EMSA Model are kept the same as in SGAM. The definition of the zones is adapted to be more appropriate for the context of e-mobility.
Definition of domains
Similar to the energy supply chain in SGAM, the whole e-mobility process chain is represented on the domain axis and split into different domains. Inspired by Schuh et al. (2013), the proposed domains are also classified as immobile (Energy Conversion, Energy Transfer from/to EV) and mobile (Electric Vehicle, EV User Premises). Next, we provide a definition for each domain by giving specific examples:
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Energy Conversion includes energy sources and the energy conversion chain. This contains the electricity system with all levels including generation, transmission grid, distribution grid and local power generation like photo-voltaic systems. It can also represent energy from other sources that is later transformed into electrical energy, like hydrogen fuels that may be generated locally or transported via a piping system.
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Energy Transfer from/to EV includes the necessary infrastructure for transferring the energy to the EV and vice versa. As example, CSs, catenary wires for trains or hydrogen fuel stations can be listed. In addition, the CS management system and all kind of entities required for the process of getting energy to/from the EV, like vehicle-to-vehicle, vehicle-to-grid, grid-to-vehicle, vehicle-to-home or home-to-vehicle, are included.
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Electric Vehicle includes the entities to perform the electric driving process. This includes e-bikes, e-scooters, e-cars, e-buses and e-railway. In addition, all components and systems, that are part of the moving EV, like the battery, Battery Management System (BMS) or monitoring systems as well as EV (fleet) management systems are part of this domain.
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EV User Premises includes interfaces for the end users like mobile devices, personal computers or (RFID) charging cards. This could be an interface for the purpose of managing the EV (e.g. smartphone app for EV preconditioning) or searching/booking/reserving CSs or vehicles, e.g. train and car-sharing. In addition, intelligent route planning, navigation and all kind of e-mobility services for end users are located in this domain.
Definition of zones
The zones represent the hierarchical levels of e-mobility management and use the concept of aggregation and functional separation. Concerning the aggregation, one can distinguish between data aggregation (e.g. data concentrated from field to station zone) and spatial aggregation (from distinct location at field and station to wider area at operation, enterprise and market). Functional separation is given, inter alia, by the spatial aggregation, as local functions, like in-car communication or protection equipment in the CS or in the grid, are mainly implemented in the field and station zones. The same applies for more global functions like monitoring or billing, which are located in the zones operation, enterprise and market. We therefore define the zones of the EMSA Model similar to the well-defined zones in SGAM in order to also ensure compatibility with the GSCAM framework. However, the definition has been adjusted to better fit the e-mobility sector:
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Process includes the physical or chemical transformation of energy (electricity, hydrogen fuel, etc.), the information flow in all domains, and all directly involved physical equipment. This can be entities of the power grid, CSs, EVs, end user devices or any kind of sensors and actuators which are directly associated with the e-mobility process.
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Field includes equipment to protect, control, monitor and support the process of e-mobility such as (1) protection relays at a CS, power grid or in the EV, (2) metering devices and any kind of intelligent electronic devices which acquire, process and use related data like the RFID authentication method.
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Station represents the areal aggregation for the field zone, e.g. for data concentration, functional aggregation or local sensor systems. An aggregation level could be a charging spot with multiple CSs or the internal communication and control system of an EV (e.g. in-car Ethernet, FlexRay or CAN bus).
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Operation hosts management entities in the respective domain for the processing of aggregated data, e.g. Local or Grid Energy Management System, EV Management System, CS Management System, Human Machine Interface Devices for input from the user or data provision services.
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Enterprise includes commercial and organizational processes, services and infrastructures for enterprises (utilities, service providers, energy traders, etc.), such as asset management, logistics, work force management, staff training, customer relation management, billing and procurement.
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Market reflects the market operations possible along the e-mobility chain, e.g. charging service networks, e-mobility provider services, EV sharing, energy trading, as well as (user) data trading platforms.
EMSA interoperability layers
One methodology for complexity handling is the separation of concerns, which can be realized by considering different architecture viewpoints such as business, functional or communication architecture, here implemented as layers. On each layer, various standardization and harmonization means are implemented to ensure interoperability and enhance re-usability. Further, all relevant entities are appropriately allocated to the EMSA dimensions (layers, domains, zones).
EMSA business layer On the business layer, different economic and legal aspects of the business architecture can be modelled, e.g. business cases, business services, business processes, business models and regulatory constraints. Harmonization and abstraction are the major constituents to handle complexity on this layer. Besides standardized notation languages such as UML, a harmonized business actor role model is essential. The most important business actor roles in the domain of e-mobility, compiled from different standards (Open Charge Alliance 2018; Nationaal Kennisplatform Laadinfrastructuur et al. 2019; ISO Central Secretary 2016), are shown and allocated to the EMSA domains (not considering zones) in Fig. 4.
The EV user can be differentiated into private EV Owner and EV Fleet User (e.g. a taxi driver). The latter one is using an EV that is owned by the EV Fleet Operator. The Equipment Provider sells or leases equipment (e.g. EV or battery) to EV Owner and EV Fleet Operator (e.g. public bus transport). In the energy conversion and transfer domains, three major roles exist. The Power Grid Operator (typically the Distribution System Operator (DSO) or Transmission System Operator (TSO)) provides the grid infrastructure either directly to the EV fleet operator (e.g. catenary for trains) or to the CS operator. Both actors are provided with electricity from the Energy Supplier. The CS operator provides charging infrastructure to the EV user and enters into a bilateral agreement with the E-Mobility Service Provider. The E-Mobility Service Provider offers services to the EV user and also handles the billing process. Payment transaction settlement is done via roaming by a Clearing House.
EMSA function layer The function layer describes the functional architecture and elements of the system. It connects business cases with their physical implementation by an abstraction of interconnected functions. The interactions of the functions indicates required information exchange between them. Depending on the level of abstraction, the functions can be described, grouped and clustered differently. In Fig. 5, the most relevant high-level function groups of e-mobility sector (extracted from CEN-CENELEC (2015)) are allocated to the EMSA function layer. The functional architecture can be detailed, e.g. by utilizing UML activity or sequence diagrams.
EMSA component layer The component layer is the basis for the upper four layers. In Fig. 6, the component layer of the EMSA Model and the most relevant systems and hardware/software components for battery-electric mobility are shown. The components for non-battery e-mobility are excluded for reasons of clarity and comprehensibility. To comply with the case study in the validation section, here the focus is limited to battery-electric mobility.
EMSA information layer The information layer is closely linked to the communication layer. The focus of the information layer is on the three aspects of data management, integration concepts and the required information exchange interfaces. Standardized information flow and data models between services are important for homogeneous connected sub-systems, ultimately leading to interoperability of the whole complex system-of-systems. In Fig. 7, the most relevant standards and protocols for the e-mobility sector, in specific for battery-electric mobility, are categorized. The protocols are extracted from ElaadNL (2017); Rodríguez et al. (2015); Schmutzler et al. (2013). This allocation helps in identifying gaps in standardization.
Various standards from IEC, ISO, ETSI, ITU, IEEE and SAE can be mapped to the different zones and domains. In the area of grid management, the IEEE 2030.5 (Adoption of Smart Energy Profile), the IEC 61850 family and OpenADR (IEC 62746-10-1) can be mentioned. For the information exchange between the Grid Operator and the CS operator, OSCP (Portela et al. 2015) or the Flexibility Reward Scheme (Danner et al. 2018) deliver solution to adjust the EV charging processes to the needs of the power grid. Information exchange protocols related to energy markets are for example OASIS EMIX, IEC 62325, EN 62325-301/351 (Entso-e MADES). The information exchange between car and CS could be handled with IEC 15118 or IEC 61851-1. The information exchange and control from the CS management system or an Energy Management System to the CS is usually done with OCPP. To handle information exchange between the CS operator and the E-Mobility Service Provider, OCPI or OCHPdirect could be used within a direct communication or OCHP, OICP or eMIP using an E-Mobility Clearing House as mediator.
EMSA communication layer The main objective of the communication layer is to visualize the communication infrastructure (protocols, technology) and identify gaps in the existing communication standardization, or to show lack of standards implementation in the respective system. Therefore, we allocated existing and commonly used protocols, extracted from CEN-CENELEC (2015); ElaadNL (2017); Rodríguez et al. (2015), to the corresponding domains and zones. The result is shown in Fig. 8 and indicates no major gap for communication standards. In high level zones (operation, enterprise and market, as well as, for the communication with end user devices), usually Web Services, HTTP over SSL and TCP/IP are used. For energy markets the IEC 61968-100 and for general market places EN82325-450/451 can be mentioned. Communication in the field of metering and grid management usually uses domain-specific protocols, e.g. the IEC 62056 xDLMS/COSEM for smart meter communication in general and CLC/prTS 50568-5 for smart meter data exchange communication are relevant, for their communication with higher zones usually ISO 9506 (MMS) from the IEC61850 standard family comes into play. Concerning communication from EV to CS either Pulse Width Modulation (PWM) signals according to IEC61851-1 (SAE J1772) or the newer communication standard ISO/IEC 15118-2 XML (EXI) TCP/IP can be utilized. CHAdeMO uses two CAN buses for communication to the EV. Charging spots can use ETSI TS 101 556 ASN.1 and future standards for OCPP/OCHP. For in-car communication, typically the ISO 11898 CAN bus or more recently the former industry standard FlexRay (now ISO 17458-1 to 17458-5) or Ethernet (ISO/DIS 8802/3) are used for sending information between the different components.
MDA approach for the EMSA model
In the smart grid domain, MDA as a sub-discipline of Model-Driven Engineering is a suitable approach for handling systems complexity in combination with the SGAM (Uslar et al. 2019; Dänekas et al. 2014). We apply this methodology and re-use this mapping to propose a similar approach for our EMSA Model (represented in Fig. 9). The MDA concept is intended to foster separation of concerns by separating the business and functional architecture from a specific technological implementation (Object Management Group 2014). Mapped to the EMSA Model, the Computational Independent Model is defined in the System Analysis Phase on business and function layer. The Platform Independent Model is specified during the System Architecture Phase on component, information and communication layer. In the last phase, the Design and Implementation Phase, the Platform Independent Model is transformed into a Platform Specific Model and implemented as Platform Specific Implementation.