Johanna Myrzik

Overview of short-circuit contribution of various Distributed Generators on the distribution network

Apart from the positive technical consequences like reducing losses, the increasing penetration of distributed generation (DG) units connected to the distribution network, has lead to the increase of the short-circuit (sc) currents and the fault level. Therefore it is important to know the contribution of each unit. This paper presents the available analytical equations to calculate the short-circuit current, and makes a comparison between the IEC 60909 and the results obtained by the simulations in a test network that incorporates these units.

Harmonics and resonances in the low voltage grid caused by compact fluorescent lamps

The effects of a widespread use of Compact Fluorescent Lamps (CFLs) on harmonics in the low voltage grid are analyzed. Therefore, measurements of the harmonic characteristics of nine different brands of CFLs are done. Based on these measurement results, a simulation model is developed, which enables to study the interaction of multiple CFLs. Thereby, the harmonic content of both currents and voltages are considered. Additionally, the impact of the capacitive behavior of CFLs on resonances phenomena is investigated and its consequences for the harmonic spectrum are represented.

Harmonic current interaction at a low voltage customer's installation

The increased use of power electronics and switching devices in the electricity network have changed the operational environment of the power system. These devices have non-linear voltage-current characteristics and produce harmonic currents, and consequently distort the voltage waveform. A low voltage domestic customer can have mixed loads that consist of linear and non-linear loads such as home appliances and lighting devices. In the PQ laboratory of TU/Eindhoven, the harmonic fingerprints of various household devices are measured. A LV household customers installation, consisting of various home appliances, is simulated in the network analysis tool ‘Power Factory’. The measured harmonic fingerprints of the connected devices are fed in to this software to perform harmonic simulations. The simulation results give the total harmonic current distortion level at the installation and the combined harmonic current interaction effects of different household devices. Furthermore, a case study is done to evaluate the total current harmonic distortion level at a customers installation when the grid voltage is polluted with a specific order of harmonic (such as the 5th harmonic). This is expected to be a typical futuristic scenario when many non-linear devices would be connected in the network and would distort the supply voltage.

Investigations in low voltage distribution grids with a high penetration of distributed generation and heat pumps

This paper reviews regulations and issues in grids with high penetrations of distributed generation. The characteristics of the voltage profile with PV, HP and CHP systems are shown by simulations. Furthermore the influence on the voltage profile with combinations of those appliances is examined.

Practical implementation of the coupled norton approach for nonlinear harmonic models

Because of an expected increasing use of harmonic producing devices, the harmonic content in electrical distribution networks attracts more and more attention. Primarily, harmonics are caused by modern loads, which are connected to the electrical grid by power electronic interfaces. In order to analyze the effects of a widespread use of such nonlinear appliances, suitable nonlinear models have to be developed. This paper focusses on the practical implementation of an advanced mathematical approach, which is described theoretically in literature as the coupled Norton model. In order to consider the voltage dependency of current distortions, this approach describes the nonlinearity in time domain as a linear set of equations in frequency domain. This theoretical idea is analyzed and verified by suitable measurements. The model parameters are evaluated and validated for different groups of nonlinear devices. Because of a significant dependency of the model parameters on the underlying measurement set, special requirements are outlined. Furthermore, in order to apply the resulting nonlinear models in harmonic studies, an iterative harmonic load flow is proposed.

Harmonic measurement and modeling for mass implementation of nonlinear appliances

In order to analyze the effects of a widespread use of nonlinear appliances harmonic measurements are done on specific examples like compact fluorescent lamps (CFL) and photovoltaic (PV) inverters. The results of the investigation determine requirements on nonlinear models, which are necessary to consider the impact of mass implementation. Particularly, the voltage and operating point dependency of the harmonic currents are taken into account. Furthermore, this paper provides an overview of existing nonlinear models and emphasizes their advantages and disadvantages. Thereby, the main focus is on models, which uses a measurement based approach.

On the problem formulation of model predictive control for demand response of a power-to-heat home microgrid

In this paper, MPC problem formulations for demand response of a power-to-heat residential microgrid are investigated. Two demand response operation strategies using MPC are proposed and thoroughly evaluated. The simulation results indicate that the problem formulation always poses a trade-off between comfort of the inhabitants, peak power reduction at point of common coupling and CPU time for the optimizer. These aspects have to be taken into consideration for a roll-out of demand response technology for residential buildings. While for the case presented in this paper, a quadratic objective function is the most promising one, the necessity of further investigations is derived from the results.

Agent based coordination of distributed energy storage devices in future distribution grids

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.

Probabilistic determination of the operational flexibility of active distribution networks with high penetration of full-converter interfaced renewable distributed generation units

In this paper a method to estimate the flexibility of an active distribution network (ADN) with full-power converter interfaced distributed generation (DG) units based on intermittent renewable energy sources (RES) is presented. The proposed method can be used to assess the capability of an ADN to reliably provide ancillary services from a given moment for a short period of time considering the probabilistic availability of intermittent RES and the operating limits of DG units, converter interfaces and the distribution grid.

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.