Hanno Georg

Software-defined networking for Smart Grid communications: Applications, challenges and advantages

Future power systems are characterized by a high degree of complexity with a large number of intelligent devices, exchanging and processing both huge amounts of data and realtime critical information. Accordingly reliable, real-time capable and secure communication networks are required for enabling autonomous monitoring, management and control to guarantee stable power system operation. In this paper, we present and analyse a flexible and dynamic network control approach based on Software-Defined Networking (SDN) for meeting the specific communication requirements of both distribution and transmission power grid. Therefore a testbed is introduced, enabling the evaluation of multiple failure scenarios such as link disturbance and congestion by analysing corresponding fast recovery and prioritization solutions. The performance and robustness of the developed strategies is shown using highly-critical monitoring and control messages on basis of IEC 61850 and considering the mutual impact with low priority background traffic. Results indicate the advantages of SDN compared to traditional routing and Quality-of-Service mechanisms, providing a more reliable communication network, which is able to handle complex failure scenarios. In particular, SDN enables the integration of diverse network management functions and thus offers the power system new options for dealing with faults even in the case of overall outages. On the basis of these results, we demonstrate challenges and derive future benefits for a SDN-enabled Smart Grid communication network, holding the potential to evolve into a self-healing infrastructure.

Hybrid simulation of power systems and ICT for real-time applications

With the rise of smart grid technologies, the interdependencies of ICT and power systems become increasingly important in both transmission and distribution networks. For the design of time-critical applications, simulation tools for an integrated analysis of these domains are needed. In the case of electrical transmission systems, high-performance ICT solutions and fast controllable power equipment enable a new era of dynamic power system operation whereas applications for this purpose need to be investigated with a special focus on their real-time performance. This paper presents a novel, modular co-simulation environment for comprehensive analysis of mutual effects, taking into account communication networks, IT processing and power system response. This hybrid simulation environment has been developed with a focus on the evaluation of the real-time performance of wide-area monitoring, protection and control (WAMPAC) applications, nonetheless, it is applicable to a variety of smart grid applications in transmission and distribution networks. The simulator architecture takes into account various standards from different areas of research - such as IEEE 1516-2000 (High-Level Architecture), IEC 61850, OPC and CIM - in order to provide a highly flexible simulation environment and to enable development of applications close to industrial implementation.

Analyzing Cyber-Physical Energy Systems:The INSPIRE Cosimulation of Power and ICT Systems Using HLA

For simulating cyber-physical energy systems, distinct simulation domains need to be integrated for a comprehensive analysis of the interdependent subsystems. In particular, continuous time-based power system simulation and discrete event-based simulation of information and communication technology (ICT) networks are critical for investigating future smart grids. This paper presents the novel cosimulation environment INtegrated coSimulation of Power and ICT systems for Real-time Evaluation (INSPIRE) of power and ICT systems using the high-level architecture (HLA) (IEEE Std. 1516-2010). By applying the HLA standard, the environment is extendable to other simulation domains and a variety of functionalities and models, like thermal load models and additional third-party tools. Moreover, the HLA enables computational performance by distributed execution of each simulator on its own hardware and, thus, the applicability to realistic large-scale scenarios. INSPIRE has been designed under consideration of industrial standards [IEC 61850,object linking and embedding (OLE) for process control (OPC), and the common information model (CIM) (IEC 61968/61970)] in order to enhance interoperability, and to develop and validate solutions close to practice. The simulation results underline the interdependencies of power and ICT systems, and the necessity of an integrated analysis.

INSPIRE: Integrated co-simulation of power and ICT systems for real-time evaluation

Future power systems in terms of Cyber - Physical Energy Systems (CPES) apply the integration of IT and physical processes using local and wide area communication networks. The smart grid is a typical example of the application of CPES and poses additional challenges to the engineering as these networks consist of two components: the power system itself and an underlying communication network applied for transmitting monitoring and control information. Therefore, performance evaluations of CPES need to take into account both networks in detail in order to provide meaningful results. In this paper, we introduce our simulation environment INtegrated co-Simulation of Power and ICT systems for Real-time Evaluation (INSPIRE), which is based on the Hybrid Simulator Architecture [1] and capable of evaluating both power system and communication network within a co-simulation framework. Besides the simulator architecture, we detail our time synchronization approach, which is applied for interconnecting communication and power system simulation. Secondly, we present reference scenarios and configuration settings for the combined simulation system. Finally, we introduce the first performance evaluation carried out using INSPIRE, covering characteristics of the communication network and highlighting the retroactive effects on the power system using an exemplary control algorithm.

Performance evaluation of time-critical communication networks for Smart Grids based on IEC 61850

Driven by the increasing application of Smart Grid technologies in todays power systems, communication networks are becoming more and more important for exchanging monitoring, control and protection information on local and wide area level. For communication the IEC 61850 standard is a candidate for the Smart Grid and has been introduced for Substation Automation Systems (SAS) some years ago. IEC 61850 provides interoperability among various manufactures and enables systemwide communication between intelligent components of future power systems. However, as IEC 61850 addresses Ethernet (ISO/IEC 8802-3 family) as network technology, especially high performance aspects of Ethernet have become increasingly important for time-critical communication within substation automation systems. In this paper we introduce the generic architecture of IEC 61850 and present our modelling approach for evaluating high performance and real-time capability of communication technologies for future smart grid application. First, we give a short overview of the IEC 61850 protocol and present communication flows in substation automation systems according to the standard. Here we focus on substation automation at bay level, located inside an exemplary substation node taken from the IEEE 39-bus power system network. Afterwards we demonstrate our modeling approach for communication networks based on IEC 61850. For performance evaluation we developed a simulation model along with an analytical approach on basis of Network Calculus, enabling to identify worst case boundaries for intra-substation communication. Finally results for simulative and analytical modelling are provided and cross validated for two bay level scenarios, showing the applicability of Network Calculus for real-time constrained smart grid communication.

A HLA based simulator architecture for co-simulating ICT based power system control and protection systems

Power systems and especially Smart Grids increasingly apply Information and Communication Technologies (ICT) for exchanging information over wide area networks. Here, the performance of the ICT has become crucial for the development of new Wide Area Monitoring, Protection And Control (WAMPAC) [1] systems. In this context, simulations are a common way for evaluation, but power systems and communication networks are usually analysed with dedicated simulators. Therefore a combined simulation for analysing the dynamics and mutual impacts of both domains is needed. In this paper we present a generic hybrid simulation architecture based on the IEEE standard 1516 - High Level Architecture [2] to enable a combined simulation of power systems and communication networks in an integrated simulation environment. First, we introduce our hybrid simulator architecture, along with the communication and synchronization process between sub-simulators. Secondly, we present our communication networks architecture for modelling the network traffic caused by the information transmitted by control and protection algorithms within the electrical transmission system. Finally, we introduce our modelling approach for mapping entities between the power systems and the communication networks. For this purpose, we introduce our concept of a Substation Data Processing Unit, which represents entities on substation level by providing an IEC 61850 [3] based model for mapping logical functions for local process control, implementing decentralized protection and control algorithms and providing additional components for the power systems (e.g Phasor Measurement Units (PMUs) [4]).

Interfacing Power System and ICT Simulators: Challenges, State-of-the-Art, and Case Studies

With the transition toward a smart grid, the power system has become strongly intertwined with the information and communication technology (ICT) infrastructure. The interdependency of both domains requires a combined analysis of physical and ICT processes, but simulating these together is a major challenge due to the fundamentally different modeling and simulation concepts. After outlining these challenges, such as time synchronization and event handling, this paper presents an overview of state-of-the-art solutions to interface power system and ICT simulators. Due to their prominence in recent research, a special focus is set on co-simulation approaches and their challenges and potentials. Further, two case studies analyzing the impact of ICT on applications in power system operation illustrate the necessity of a holistic approach and show the capabilities of state-of-the-art co-simulation platforms.

Performance analysis of radio propagation models for Smart Grid applications

Realizing future Smart Grid applications highly depend on the communication technologies being used. For this purpose, an ubiquitous communication infrastructure is essential, providing real time communication and reliable connectivity to Smart Grid components. Especially nowadays wireless radio networks offer a cost-efficient, reliable and well-engineered solution. In this paper we present a performance analysis based on a comparison of analytic channel models and Ray Tracing simulations for wireless digital cellular networks with respect to actual Smart Grid deployment scenarios. Both methods are applied especially under consideration of a typical outdoor-to-indoor transition models. Based upon these results a coverage analysis for wireless digital cellular networks (e.g. GSM or UMTS) is shown considering different Smart Metering and energy management application scenarios including position-based radio characteristics, like basement, indoor and outdoor installations. The network topology is described using a simulation environment including various analytic models in order to analyze the capacity of the transmission technology in real-world scenarios. Our analysis shows the impact on the path loss, caused by frequencies, geographical position and indoor deployment, which leads to an additional deviation up to 25 dB.

Einbindung von intelligenten Entscheidungsverfahren in die dynamische Simulation von elektrischen Energiesystemen

ZusammenfassungDie Betriebsführung elektrischer Transport- und Verteilnetze wird zunehmend dynamischer. Gründe hierfür sind einerseits die Herausforderungen durch hoch ausgelastete Netze sowie volatile Einspeisung, auf die die Netzbetreiber rechtzeitig reagieren müssen, andererseits der zunehmende Einsatz schnell regelbarer Betriebsmittel und leistungsstarker Kommunikations- und Informationstechnik. Um intelligente Entscheidungsverfahren für dynamische Systemeingriffe zu entwickeln, müssen solche Applikationen zunächst in eine dynamische Simulation des elektrischen Energiesystems eingebunden werden. In diesem Beitrag werden zwei Realisierungsmöglichkeiten zur Einbindung externer Softwaretools in die elektromechanische Simulation des verbreiteten kommerziellen Energiesystemsimulators DIgSILENT PowerFactory vorgestellt. Hierbei wird exemplarisch die Einbindung eines Multiagentensystems zur Koordination von Leistungsflussreglern gezeigt. Neben der Implementierung werden vergleichende Simulationsergebnisse bei Nutzung der beiden Schnittstellen und ermittelte Leistungswerte präsentiert.

Analysis of communication networks for smart substations using a virtualized execution platform

The current development of the power grid towards a Smart Grid advances the complexity of the system, involving active control, new software components and large amounts of data. This, in turn, requires new approaches for the ICT infrastructure to guarantee real-time capability and reliability. In this work, we present our design of a novel infrastructure for smart substations in the transmission grid, applying the concept of virtualization to substation devices. Since virtualization has already been successfully applied for fault-tolerant and dependable computer systems, it promises to be a valuable concept for substation automation. However, virtualization poses additional challenges to the real-time capability of the substation infrastructure in terms of additional traffic and resource allocation. For analysing the impact on substation communication, we apply simulations and the analytical technique Network Calculus to provide guarantees on the performance of the proposed communication infrastructure. In addition, the performance of the execution platform is studied empirically, measuring occurring delays in a test-bed set-up. Finally, we combine the results from both evaluations to derive an end-to-end delay bound for a power grid related example. Our results show that, other than Fast Ethernet, Gigabit Ethernet networks can guarantee the secure operation of virtualized, fault-tolerant substation infrastructures.