Lena Robitzky

Exchangeability of power flow simulators in smart grid co-simulations with mosaik

Power flow simulators are indispensible when simulating and assessing future energy system scenarios potentially comprising vast numbers of actors, devices, markets, environmental phenomena etc. While open source power flow simulators are an appealing choice - as they come free of charge - commercially available power flow simulation and optimization suites have the clear benefit of being well established and trusted by the industry. Open source implementations often lack validation against these “trusted” outputs. In this paper we will demonstrate and discuss the integration and exchange of different (commercial as well as open source) power flow simulators with the co-simulation framework mosaik for the sake of comparing and possibly benchmarking the output of open source simulators.

Agent-based redispatch for real-time overload relief in electrical transmission systems

Increasing uncertainties in power system operation require novel approaches for utilizing operational flexibility to enable a both secure and efficient power supply. This paper presents a real-time coordination approach for adaptive redispatch of generation and load in case of overloads in the electrical transmission network. For this, a previously developed multi-agent system for coordinating power flow controlling devices is extended by novel agent behaviors enabling a distributed decision making on adequate redispatch. Main features of the approach are its real-time adaptivity to unforeseen network conditions (e.g., (N-k)-cases) and its automated deployment of the controllability of future smart grids. By this, storages, demand side management and distributed generation in the distribution grid can support operational security of the transmission network in alert or emergency network conditions. Provision of such remedial actions is also of economic value as it enables a less constrained system operation due to the ability to meet uncertainties by flexibility. The applicability of the approach is demonstrated in a co-simulation of the MAS and a dynamic power system simulation.

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.

Agent-based prevention of voltage collapse in electrical transmission systems

Changing dynamics of power systems caused by the large-scale penetration of renewable energy sources and a different behaviour of future distribution networks increase the risk of large-scale blackouts due to voltage collapse, especially in case of unforeseen network conditions (e.g., (N-k)-cases). To enable a both secure and efficient power supply, novel emergency control systems are required that react reliably in due time and adaptively in case of changing network situations. This paper presents a distributed control approach for the prevention of voltage collapse by a coordinated activation of available countermeasures, in particular acting on distribution transformers, curtailing load as well as deploying the flexibilities of HVDC-converters and underlying active distribution networks. As the proposed scheme is based on limited system observability and only relies on local measurements, complete system information is not required. The applicability of the approach is demonstrated in a co-simulation with a dynamic power system simulation.

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.

Evaluating the performance of decentralized analyses of voltage stability and power flows

Increasing complexity and uncertainty of power system operation have led to a rising interest in decentralized control concepts as a complement or alternative to centralized control. For decision-making on appropriate control actions, such approaches need to perform analyses of the system state and the estimated impact of control actions basing on limited system information. Thus, it has to be ensured that the decentralized analyses yield sufficiently accurate results and enable reliable control. The choice of valid indicators and estimates of control responses depends particularly on the required level of accuracy and the size of the observed area. This paper presents a methodology for evaluating the performance of decentralized analyses of voltage stability and power flows depending on the observability area. The results shall provide developers of decentralized concepts with insights on the suitability of different indicators, the trade-off between accuracy and the size of the observed area, as well as awareness of potential threats due to the use of incomplete data, possibly causing unstable and adverse control effects.

Selective and decentralized underfrequency protection schemes in the distribution grid

The increasing feed-in of renewable energy sources leads to fundamental changes in the European energy system. Due to the integration of converter technologies the electrical frequency experiences a higher sensitivity towards severe disturbances leading to new challenges for underfrequency protection. Hence, if an imbalance in a power system threatens its stability, automatic load shedding is the ultimate countermeasure to prevent large-scale blackouts. In conventional under frequency load shedding schemes relays are located in primary substations and trip when a critical frequency is detected. The tripping process disconnects a part of the grid from the system to reduce the overall load. In future scenarios the risk of isolating renewable energy sources due to conventional load shedding schemes rises because of a high penetration of photovoltaic and wind farms in the medium and low voltage level. Therefore, it is necessary to develop new load shedding strategies to ensure a selective underfrequency protection process differentiating power consumers and producers. In this paper, the localization of underfrequency relays in lower voltage levels is investigated making use of already existing information and communication infrastructures of smart grids. In addition, novel parametrization algorithms are presented that allow for an optimal allocation of loads that needs to be shed in every step based on real-time measurements or forecasts, therewith increasing the accuracy of the load shedding scheme.