Averaged models and control of modular multilevel converters
Final Report Abstract
Modular multilevel converters are used in high-voltage direct current transmission systems and in applications for medium voltage. This is because the series connection of cells offers a good scalability of the desired voltage level. However, the control task is significantly more difficult compared to other converter topologies. This is because the mathematical model derived from the network equations leads to an internal dynamics when the load current is choosen as an output. In particular, this difficulty concerns the control of the energies stored in the branches. This problem can be avoided by using models describing the long-term behavior and which are derived by averaging. This approach has been shown useful in practical applications but a methodological justification has been missing. This gap was closed by the project by applying methods from perturbation theory which allow to derive a dynamical model of the topology which only considers the behavior of the system on a slower timescale. In order to test the approach, several use cases have been investigated. Furthermore, results have been obtained in order to assess the domain of validity of the modeling approach. As a result, the obtained models can be used for control design and for the identification of stationary operating regimes. In both cases, it could be shown that there is some freedom in the particular design tasks that can be exploited, e.g. in order to increase the efficiency of the converter system. A large portion of the results have been verified experimentally using a low-voltage test-bench. Finally, it is emphasized that the modeling framework can be used for other topologies with quasi-periodic operating regimes, in particular other cell-based converters.
Publications
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matlab scripts for MMC Pareto optimization. Technische Universität Dresden.
Lopez, Mario & Fehr, Hendrik
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Energy-Balancing of a Modular Multilevel Converter with Pulsed DC Load Using an Online Trajectory Planning Algorithm. 2021 23rd European Conference on Power Electronics and Applications (EPE'21 ECCE Europe), P.1-P.10. IEEE.
Gui, Qiuye; Fehr, Hendrik & Gensior, Albrecht
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matlab scripts: mmc periodic signal model. Open Access. Juli 2021.
Fehr, H.
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Modeling and Energy Balancing Control of Modular Multilevel Converters Using Perturbation Theory for Quasi-Periodic Systems. IEEE Transactions on Power Electronics, 36(2), 2201-2217.
Gensior, Albrecht & Fehr, Hendrik
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Pareto Frontier of the Arm Energy Ripple and the Conduction Losses of a Modular Multilevel Converter. Energies, 14(2), 392.
Lopez, Mario; Fehr, Hendrik; Perez, Marcelo A. & Gensior, Albrecht
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MMC Stationary Operating Regimes in Case of Periodic Power Demand on the DC Side. IEEE Transactions on Power Electronics, 37(7), 7640-7651.
Fehr, Hendrik & Gensior, Albrecht
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Modellbildung und Regelung leistungselektronischer Systeme unter Verwendung nichtlinearer Entwurfsverfahren. Habilitationsschrift. Shaker, 2022
Gensior, A.
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„Stability Assessment and Optimization of MMC Energy Balancing for Drive Applications at Standstill Using an Averaging Approach“. In: 24th European Conference on Power Electronics and Applications (EPE’22 ECCE Europe). 2022.
Gui, Q., H. Fehr & A. Gensior
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Optimized Stationary Operating Regime and Common-Mode Voltage Design for Modular Multilevel Converters in Drive Applications at High Frequency. 2023 25th European Conference on Power Electronics and Applications (EPE'23 ECCE Europe), 1-10. IEEE.
Gui, Qiuye; Fehr, Hendrik & Gensior, Albrecht
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Energy Control of Modular Multilevel Converters for Drive Applications at Low Frequency Using General Averaging. IEEE Transactions on Power Electronics, 39(5), 5239-5256.
Gui, Qiuye; Fehr, Hendrik & Gensior, Albrecht
