New techniques for the assessment of harmonic stability in public low voltage networks with very high share of distributed power electronic devices

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The general objective of the study is the analysis of harmonic instabilities in the public low voltage grid caused by high penetration of power electronic devices interacting with the harmonics of the grid voltage and current and the harmonic impedance of the grid itself. A comprehensive analysis is necessary in order to assess the loss of damping by nonlinear devices, the risk of harmonic instabilities and shift and/or generation of harmonic resonances due to the increasing number of devices. Different to classical steady state harmonic studies the harmonic behavior concerning immunity and emission of the converter systems and its controls are in the focus of the investigation. In order to investigate this specific behavior, detailed white-box models are needed. Due to the lack of information from manufacturers, especially regarding the controller design and the high complexity of model development, sufficant detailed harmonic models for converter systems are not available yet. So, these models will be developed in this project.However, the simulation with a high amount of parallel operating detailed models is quickly limited by available computing power and needs excessive simulation times. Because of the complexity of the white-box models, the nonlinearity of the components, the different time-scales and the often uncomplete knowledge about the control strategy a method of generic modelling will be used to generate the reduced and simplified harmonic black-box models which are capable of the parallel execution of a huge number of models. These models are necessary to investigate the harmonic instabilities, reduced damping effect and resonance phenomena of a mass implementation of power electronic devices in the low voltage grid in a sufficient manner.In order to evaluate the developed harmonic models, methods for validation and parametrization of these models are needed. Each white- and black-box model will be validated based on laboratory measurements. Therefore, a laboratory test set up with appropriate test signals will be implemented. A simple case study will be executed with several models operating in parallel for testing the functionality and suitability of the harmonic black-box models for harmonic load flow simulation. The simulation results of this case study will be validated in the laboratory as well. Additionally, the achieved results can be used to develop grid and device specific indices. They can be used to approximate and classify future harmonic instabilities and to give recommendation to DNOs and manufactures for grid planning and device designing issues, respectively. The evaluated models and different sets of parameters for converters available on the market will be collected in a model library.