Nils Dorsch

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.

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.

Empirical comparison of virtualized and bare-metal switching for SDN-based 5G communication in critical infrastructures

Advancements in the field of Critical Infrastructures (CI), such as the advent of Smart Grids or automated transportation systems, offer new services and functionalities. However these novel Cyber Physical Systems (CPS) necessitate increasingly complex monitoring and control schemes, which are commonly orchestrated by industrial Supervisory Control and Data Acquisition (SCADA) systems. As thousands of distributed field devices are involved in the operation of Critical Infrastructures, the enabling communication technologies need to fulfil exacting performance requirements as well as provide high levels of robustness, Quality of Service, flexibility and scalability. The ongoing evolution of cellular LTE (Long Term Evolution) towards 5G networks promises to meet all these specifications. In this context Software-Defined Networking (SDN) is set to play a crucial part within the mobile networks wired backhaul as well as core infrastructures and is thus included in many proposed 5G architectures. However, basic performance characteristics allowing a comparison of the two prevalent approaches to SDN, fully virtualised and hardware based Bare-Metal switching, are currently not widely available. Therefore this paper proposes a test-platform for the benchmarking of SDN as well as a prototypical architecture. The latter serves to facilitate the evolutionary development of LTE towards 5G for use in Critical Infrastructure communication in general and Smart Grids in particular. A comparative evaluation of switching performance, realized via the described testbed, is presented and an assessment is given. Based on the introduced architecture and testbed, future work will develop new mechanisms for end-to-end slicing as well as application aware scheduling.

Intertwined: Software-defined communication networks for multi-agent system-based Smart Grid control

Facing current and future developments of the energy system, including the integration of large numbers of renewable energy sources and electric vehicles, live monitoring and control becomes essential for stable operation of the power grid. This transition to a Smart Grid requires coupling the power system with a reliable and real-time capable communication infrastructure. In response to this demand, we propose a combined approach for the control of power and communication systems, exploiting the opportunities of Software-Defined Networking (SDN). Due to its real-time capability, a Multi Agent System (MAS) is applied for controlling power flows, handling overloads and guaranteeing voltage stability in a decentralized manner. The MAS is supported by an Information and Communication Technologies (ICT) infrastructure, which follows the paradigms of SDN by applying a programmable controller platform with global network view to orchestrate traffic flows. To meet specific requirements of the MAS, we implement an SDN Northbound Interface, enabling control agents to communicate with the SDN controller directly. Thus, agents can advertise their demands to the controller, which translates them into corresponding forwarding rules and establishes them in the network. By applying fine grained prioritisation and integrating MAS and SDN controller, we showcase reliable and timely transmission of critical command messages, thereby ensuring power grid stability.

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.

Holistic modelling approach for techno-economic evaluation of ICT infrastructures for smart grids

Current alterations of energy systems bring about increased communication requirements, making the selection of suitable Information and Communication Technology (ICT) solutions a major issue of Smart Grid implementation. With this paper we set out to present a comprehensive, extendable modelling approach for the communication network of future Smart Grids, which enables estimating the Total Cost of Ownership (TCO), associated with installing and operating such an ICT infrastructure. Our framework integrates the following three fundamental components: First off, a traffic model is developed, combining number and distribution of intelligent devices for each Smart Grid use case with their respective traffic requirements. This model serves as a basis for statistical network dimensioning, carried out for different technologies e.g. LTE, Fibre, PLC, which are considered candidates for Smart Grid communication, as well as for mixed deployments of these. Building on these results, TCO are determined for each network configuration. We demonstrate the application of our modelling approach on a typical Smart Grid use case, including urban to rural environments. Our analysis results indicate that finding an appropriate ICT solution for Smart Grid communication heavily depends on given scenario parameters such as traffic requirements and device penetration. Finally, a variety of suitable business models for investing into and operating such communication networks are discussed.

Enhanced Fast Failover for Software-Defined Smart Grid Communication Networks

Future energy systems depend on a corresponding Information and Communication Technology (ICT) overlay, allowing timely transmission of critical grid information in particular in case of failures or other unanticipated events. Therefore, to maintain grid stability, Smart Grid communication networks are required to be highly reliable and real-time capable. Within this paper, we propose and evaluate techniques for improved fault tolerance with regard to link failures within the ICT infrastructure, utilizing the concepts of Software-Defined Networking (SDN). centralized and decentralized approaches for both failure detection and traffic recovery are compared. While decentralized approaches, employing Bidirectional Forwarding Detection and OpenFlows fast failover groups, allow for shorter traffic disruptions by saving the delay of controller-switch communication, they result in sub-optimal configurations and possibly overloaded links. Vice versa, controller-driven approaches, using a custom heartbeat detection mechanism, may offer better alternative configurations due to fast re-calculation of routes, yet incur higher delays. Combining the advantages of both approaches, a hybrid concept is proposed, which enables nearly instant local recovery, succeeded by immediate optimal route updates, issued by the SDN controller. Thus, failover times are reduced to 4.5 ms mean delay, fulfilling IEC 61850 Smart Grid requirements, while providing optimal routes almost continuously and maintaining defined Quality-of-Service (QoS) levels.

Validation of ICT-based protection and control applications in electric power systems

The use of Information and Communication Technology (ICT)-based power system applications increases continually which poses new engineering challenges regarding the development, validation and management of both - the applications and the intertwined infrastructures. In this paper the need for a joint analysis of power and ICT systems for evaluating smart grid applications is discussed and a systematic validation approach is proposed. After reviewing state of the art validation techniques, a newly developed Wide-Area Monitoring, Protection and Control (WAMPAC) system is introduced. Its extensive use of wide-area communication and the combination of centralized and decentralized decision making stress the complexity of such a cyber-physical system, where the interdependency between the power system and the ICT domains are challenging to validate. Deduced from these requirements, a validation concept is proposed that comprises (i) the usage of a comprehensive smart grid reference model, (ii) a systematic and objectively verifiable generation of scenarios, and (iii) a single and multi-domain validation process using analytical, simulative and experimental techniques. For the latter, a composition of analyses using co-simulation, Hardware-in-the-Loop (HiL) simulations and an empirical test bed is outlined.

Analysing the real-time-capability of wide area communication in smart grids

Current developments towards Cyber-Physical Energy Systems (CPES) [1] requires the close integration of traditional power grids and appropriate Information and Communication Technology (ICT) infrastructures. Driven by additional requirements of future monitoring and control, increasing amounts of data have to be handled to ensure safe operation of the power grid and to maintain frequency stability. Therefore an appropriate ICT infrastructure becomes crucial for enabling fast and reliable transmission of time critical messages such as switching commands. This paper provides an evaluation on the real-time capability of the communication network in three scenarios analysing different levels of the power grid infrastructure: within the substation, between neighbouring substations and between a substation and the control centre. Communication is modelled according to the standard IEC 61850 using both simulation and the analytical approach of Network Calculus. Thus, we determine mean values as well as worst-case bounds on the delay of messages, evaluating the impact of varying network and traffic conditions. The results highlight the applicability of IEC 61850-based communication as a holistic solution for the power grid, supporting advanced tele protection and remote control applications.