# Generic Digital Twin Architecture for Industrial Energy Systems
## 1 Introduction
### Related Work  
In general, a DT can be defined as \"a formal digital representation of some asset, process or system that captures attributes and behaviors of that entity suitable for communication, storage, interpretation or processing within a certain context\" [7]. A very basic concept for structuring a DT defines three different aspects: the physical space, the virtual space, and the connection between them to exchange data and information [8]. A similar concept is known from the industrial domain as Cyber-Physical System (CPS) or more specifically as Cyber-Physical Production System (CPPS). In [9], CPSs are described as autonomous and cooperative elements and sub-systems across all levels of production, able to communicate with each other in situation-dependent ways. The goal of CPSs is to have elements that can acquire and process data, allowing them to self-control certain tasks and interact with humans. To reach that goal, a certain kind of virtual representation of the production system has to be available. Therefore, a CPS can be characterized by a physical asset and its cyber counterpart, which means that a DT can be seen as only the digital model inside a CPS [5]. Conversely, this also implies that a DT is the prerequisite for a CPS [10]. For CPSs, a five layer architecture (5C architecture) was proposed in [11], defining a \"Smart Connection Level\", \"Data-to-Information Conversion Level\", \"Cyber Level\", \"Cognition Level\", and \"Configuration Level\". These layers should help to develop and implement CPSs at a certain layer of this 5C architecture. In this context, the Smart Connection Level has to deal with acquiring accurate and reliable data from the physical entity and is the first step to create a CPS. Afterward, meaningful information is inferred from the data at the Data-to-Information Conversion Level. This level brings self-awareness to the machines. The Cyber Level acts as an information hub inside the 5C architecture, which also introduces the possibility of self-comparison of the performance of machines. In-depth knowledge of the monitored system is created at the Cognition Level. Expert users will be supported by this information to make the correct decision. At the Configuration Level, feedback is given from the cyber-space to the physical space. Here, the supervisory control resides and makes machines self-configurable and self-adaptive. This functional view of a CPS can also be beneficial for designing and implementing a DT for certain applications. Typical applications have been identified by a literature review in [12] and can be clustered in the following categories: simulation and optimization, monitoring, diagnosis, and prediction. Another important concept for describing DTs is the so-called Five-Dimensional Digital Twin (5D-DT) [13]. It is an evolution of the previously mentioned DT concept, which extends the three dimensions (\"Physical Entity\", \"Virtual Entity\", \"Connection\") by the data aspect as well as the service aspect. These five dimensions and their relations are shown in Figure 1. The \"Physical Entity\" consists of various subsystems that perform specific tasks, facilitated with different sensors that collect the states and working parameters. The \"Virtual Entity\" aims to model the physical entity with high precision by the integration of multiple different types of models such as geometry models, physical models, behavior models, and rule models. The \"Service Model\" includes services for the \"Physical Entity\" and the \"Virtual Entity\". It optimizes the operations of the \"Physical Entity\" and ensures the high fidelity of the \"Virtual Entity\" through calibration of the \"Virtual Entity\" parameters during run-time. The \"Data Model\" consists of five parts: data from the physical entity, data from the virtual entity, data from the services, domain knowledge, and the fusion of those data. The \"Connection Model\" describes each connection between the components of the DT. The ideas of the 5D-DT concept are the foundation for our proposed GDTA.