Due to the transition of the energy sector, power generation is becoming more and more decentralized, increasing the need for control of the electricity system and requiring more digitization and networking of the individual components. Interoperability is becoming increasingly important to ensure that components interact smoothly. The Institute of Electrical and Electronics Engineers – IEEE defines interoperability as “the ability of two or more systems or components to exchange information and to use the information exchanged” . The International Organization for Standardization/International Electrotechnical Commission (ISO/IEC) further requires that functionality must be ensured even with little or no knowledge of the unique characteristics of each entity . In addition to the exchange of data and the interpretation of these, the interacting components must pursue the same economic goals and also interact within the same economic and regulatory framework.
According to , three overarching levels of interoperability can be defined, which are shown in Figure 1. The technical level covers the basic capability for exchanging data and the compatibility of the data structure. The information level describes the ability to recognize and correctly classify/interpret the information contained in the data. The organizational level ensures that the business, economic and regulatory framework conditions are met.
Depending on the use case, the levels can be further subdivided. For example, in the Smart Grid Architecture Model (SGAM) , the technical level is divided into a component and communication level and the organizational level into a functional and business level.
Methods for assessing and ensuring interoperability
For each level, interoperability between individual systems and actors must be analyzed, assessed, and existing or possibly missing standards identified.  defines three different ways of interoperability assessment:
- Compatibility analysis of two systems
Verification if two systems are interoperable
- Potential analysis
Interoperability with regard to the environment e.g. can wallbox communicate with all electrical vehicles
- Performance analysis
Evaluation of the interaction between systems during operation with regard to the time required
Several methods for interoperability assessment can be found in the literature. A comprehensive overview is provided by Gabriel et al . The SGAM is suitable for investigating smart grid use cases. SGAM takes into account the entire supply chain, from electricity generation and transport to the end consumer. A more detailed analysis for pure electric mobility applications allows the E-Mobility System Architecture Model (EMSA model) based on the SGAM . Like the SGAM, the EMSA also contains a coordinate system consisting of the dimensions domain, zone and layer. This is visualized in Figure 2.
The interoperability layers and zones are identical to the SGAM. The individual zones are defined as follows:
- Process includes the physical or chemical conversion of energy
- Field covers devices to protect, control, monitor, and support the process of e-mobility
- Station represents spatial aggregation for the Field zone, e.g., data concentration, functional aggregation, or local sensor systems.
- Operations comprises management units in the respective domain for processing aggregated data, e.g., energy management system
- Enterprise includes commercial and organizational processes, services and infrastructures for companies
- Market reflects the possible market activities along the e-mobility chain
For a more detailed analysis for electric mobility applications, the EMSA model has four relevant domains, which can be divided into immobile (energy conversion and energy transmission) and mobile (electric vehicle, EV User Premises ). These can also be expanded as needed.
- Energy conversion covers the energy conversion chain from generation to the supply at the grid connection point.
- Energy transmission from/to the electric vehicle refers to the infrastructure required to transmit the energy to the electric vehicle, for example a wallbox and associated management systems.
- Electric vehicle includes the units that perform the electric driving process. This does not have to be e-cars, but can also refer to e-bikes or e-buses.
- EV User Premises considers all interfaces to the end user. This can be e.g. apps or car sharing.
For the analysis, all components relevant to the use case, such as hardware and software, people, but also states, are placed in the EMSA coordinate system. The relationships and effects between the individual components are considered for each interoperability level and analysed with regard to obstacles, conflicts and, for example, missing standards. In  the application of the model is demonstrated for the generation of a travel plan for the EV user based on his goals.
Interoperability in the project unIT-e²
In the unIT-e² project funded by the BMWK, the integration of electric vehicles in energy grids, markets and process chains is being advanced by developing and testing smart-charging concepts. The solutions developed in four different clusters are intended to be internationally interoperable and contribute to goal-oriented standardization in order to ensure a successful market ramp-up of electromobility. To achieve this, all stakeholders of the electromobility are involved in the project. This includes companies from the automotive industry, development of smart meter gateways (SMGW), grid operators, energy suppliers, development of charging equipment, aggregators, software development, operators of charging equipment and research. In the course of the project, the solutions developed will be evaluated and tested with regard to their interoperability.
This research was conducted as part of the activities of FfE in the project “unIT-e² – Living Lab for Integrated E-Mobility”. The project is funded by the Federal Ministry for Economic Affairs and Climate Action (BMWK) (funding code: 01MV21UN11).
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 ISO/IEC. International Technology for Learning, Education, and Training. International Standard, Geneva: ISO, 2003.
 GridWise Architecure Council, GridWise Interoperability Context-Setting Framework., 2008 https://gridwiseac.org/pdfs/GridWise_Interoperability_Context_Setting_Framework.pdf
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 INTEROP NoE, Deliverable DI.3: Enterprise Interoperability Framework and Knowledge Corpus, (2007) . http://interop-vlab.eu/interop/.
 Gabriel et al.: Interoperability assessment: A systematic literature review, Computers in Industry, Volume 106, 2019, Pages 111-132, https://doi.org/10.1016/j.compind.2019.01.002.
 Kirpes et al.: E-Mobility Systems Architecture: a model-based framework for managing complexity and interoperability. Energy Inform 2, 15 (2019). https://doi.org/10.1186/s42162-019-0072-4