Johanna Myrzik

The growth of renewable energy generators in public energy networks demands suitable approaches to simulate future power grids, e.g. low voltage networks. One main distributed energy generator are small power photovoltaic systems interconnected by single-phase inverters. The increasing penetration of such inverters requires models that are suitable for large-scale studies. This study analyses the aggregation characteristics based on time domain simulations. The results suggest that under specific circumstances the aggregation of multiple inverters connected at the same point having similar output power can be approximated by multiplying the individual inverter characteristics. In case the inverters have different output powers a simple aggregation is not possible.

Power electronic (PE) penetration in energy networks has been increasing rapidly in recent years due to the campaign to rely on distributed generation as a clean, sustainable energy source. This increase leads to new challenges and stability problems occurring because of the increase in the harmonic current injected into the power network. To study and address such issues, accurate and computationally efficient models are required. In this article, a Hammerstein–Wiener-based approach is proposed to develop black-box models for PE devices capable of capturing the devices’ harmonic characteristics. A novel method based on magnitude square coherence is also proposed to compare the results of different models in the frequency domain. The method is implemented in a simulation environment and was further tested and validated through laboratory measurements.

The large number of distributed generators, storages, and other devices which might be connected to the distribution grid pose significant modelling and control questions. It is computationally unattractive and sometimes infeasible to model and control all these devices individually; some method of aggregating them both for modelling and for control is appealing so that they can be represented collectively. It would also be preferable to limit the complexity of the controlled devices' dynamic behavior for easy integration with higher‐level (i.e., higher‐authority) controllers in the cascade. This paper describes a method combining these control goals based on geometric flexibility regions, constrained optimization, and transfer function considerations to enforce approximated first‐order transfer function behaviour at the bus. Time‐domain simulations are used for validation and demonstration.

The integration of efficient supply technologies like electric heat pumps and combined-heat-and-power (CHP) plants into multi-energy-systems is of growing interest. However, typical off-the-shelf systems like CHP units and industrial heat pumps are characterized as single-degree-of-freedom systems, which means the interaction between electric and thermal power input/output is well-defined and cannot be altered. In this work, the technically feasible working points of individual plants are translated into a mathematical set representation, which can then be visualized in Portfolio Flexibility Plots (PFP). The proposed PFPs reveal a new degree-of-freedom of partially uncoupled thermal and electric supply. This flexibility can be exploited to derive efficient supply portfolios under consideration of exact technical constraints and arbitrary time-varying supply tasks.

This paper shows a technical solution to locate and to identify an electrical load and to allocate it with controllers for interchanging clearing and control information e.g. in smart grid applications. It is a solution where the controller can be easily integrated in smart meters, substations and in external control devices. The appliance uses its integrated switching power supply for establishing a communication link. Therefore the control of the integrated power factor correction (PFC) is modified. Thus plugging to a normal socket-outlet is sufficient for allocating the device with controllers in a way like a Plug'n'Play system. The technique does not need new lines and can be installed in existing electrical installations with minimal effort. The allocating technique uses two different communication channels. The first one is a unidirectional channel with a very low frequency which uses the electrical current as a carrier, and the second one is a bidirectional channel. The management system detects, if an appliance is connected to the pathway behind the controller and it establishes an individual communication link. The controller can check its responsibility because grid's impedance for low frequencies is much lower than the impedance of the connected loads so that the current flows only on the pathway to the transformer station. The method has some more features such as setting up a hierarchized system with several management units for different tasks such as power management, clearing services or congestion management.

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.

Due to the increasing share of distributed energy resources, which will be integrated into the electrical grid within the next decades, innovative grid structures and management concepts are required to ensure a reliable supply of electrical energy in the future. The integration of energy storage devices will become more and more important in this context to ensure the stability of the electrical system. Within this paper, an energy storage management system will be presented, which uses the multi agent system approach to coordinate distributed energy storage devices in future distributions grids. Thereby, the storage devices operate in a virtual energy storage. The agent based realization of the virtual energy storage, as well as its application will be presented in this paper. Thereby, a case study is used to demonstrate the suitability of the agent based management of several energy storage devices in future distribution grids.

Due to much larger numbers of small generators it will be more complex to control the balance between supply and demand in future power systems. To deal with this complexity, autonomous power networks could be effective. Autonomous power networks are aggregations of producers and consumers on both physical and economical level and have the capability to control complex systems with simple rules. To demonstrate economic dispatch within an autonomous power network, this paper describes the setup of a model for matching supply and demand within control zones. Next, a method for distributed economic dispatch is incorporated in the model to show how allocation of generators can be executed in a decentralised way.

Nowadays the number of dispersed generators (DG) is growing rapidly. This change will greatly influence the power system dynamics. A distribution network, where DG are connected to the grid, cannot be considered as passive anymore. So in future it will not be possible to use simple equivalents of distribution networks for power system dynamic modeling as it was done before. In dynamic studies whole power system cannot be represented in detailed manner because of huge system dimension. Therefore special techniques have to be applied for aggregation and order-reduction of distribution networks with DG. In this paper brief review of existing techniques has been done, and afterwards dynamic reduction using balanced truncations has been performed for a small distribution network consisting of DG of different type