Wirkungen von Entladungen auf dielektrische Grenzflächen bei Gleichspannung und überlagerter mittelfrequenter Wechselspannung. - Ilmenau : Universitätsbibliothek, 2022. - 1 Online-Ressource (iv, 127 Seiten)
Technische Universität Ilmenau, Dissertation 2022
Mit der Energiewende und der damit verbundenen verstärkten Nutzung von regenerativen Energien und effizienten Energieversorgungssystemen nimmt die Anwendung der Gleichstromtechnik stark zu. Zur Anbindung erneuerbarer Energieanlagen und Kopplung zwischen Gleichspannungsnetzen werden leistungselektronische Stromrichter genutzt. Die Schaltfrequenzen leistungselektronischer Topologien reichen in der Regel bis zu 100 kHz (Mittelfrequenz). Dadurch können Spannungen auftreten, die einen unterlagerten Gleichspannungsanteil und einen überlagerten Wechselspannungsanteil aufweisen. Diese Spannungsform wird als Mischspannung bezeichnet. Für die wissenschaftlichen Untersuchungen wird eine sinusförmige mittelfrequente Wechselspannung einer Gleichspannung überlagert. Entladungen an dielektrischen Grenzflächen von Isoliersystemen bei dieser Mischspannungsform besitzen ein großes Zerstörungspotential. Sie sind Untersuchungsgegenstand dieser Arbeit. Es werden verschiedene Wirkungen von Entladungen an der dielektrischen Grenzfläche zwischen Luft und Polyethylen bei Mischspannung untersucht. Dabei wird die elektrische Durchschlagfestigkeit der dielektrischen Grenzfläche beim Auftreten von Teilentladungen (direkte Wirkung) und die Aufladung der dielektrischen Grenzfläche durch Teilentladungen (indirekte Wirkung), die zu einer erhöhten elektrischen Feldbeanspruchung führt, bei Mischspannung bestimmt. Es zeigt sich der wesentliche thermisch-erosive Einfluss von Teilentladungen bei mittelfrequenter Spannung auf den Durchschlagsprozess eines Isoliersystems. Anhand der Entladungseinsetzspannung und der Entladungsanzahl bei Mischspannung wird das Zerstörungspotential aufgezeigt. Außerdem wird die Aufladung der dielektrischen Grenzfläche durch die bei den Entladungsvorgängen gebildeten Raumladungen bei Mischspannung gemessen. Die Änderung der elektrischen Feldstärke durch den Aufbau der Raumladungen beeinflusst die Entstehung von Entladungsprozessen und die Aufladung der dielektrischen Grenzfläche erheblich. Die Erkenntnisse der Aufladungsmessung werden durch Plasma-Simulationen mittels Finite-Elemente-Methode unterstützt. Diese Dissertation liefert somit wichtige Erkenntnisse zu den relevanten Wirkungen von Entladungen auf dielektrische Grenzflächen bei mittelfrequenten Mischspannungen. Die Kenntnis dieser Wirkungen können als Basis für Alterungsuntersuchungen genutzt werden.
https://doi.org/10.22032/dbt.55251
Reinforcement learning-assisted controller parameterization based on improving oscillatory stability in converter-dominant power system. - In: 2022 IEEE PES Innovative Smart Grid Technologies Conference Europe (ISGT-Europe), (2022), insges. 5 S.
Due to the cascade control loop in the single converter and interactions among converters, the converter-based system is more likely to become unstable. The general controller parameterization methods for a converter are based on its parameters and states. Considering the possible oscillation effect from other converters nearby, a new procedure of controller parameterization with the help of reinforcement learning (RL) is then proposed. By setting an oscillatory stability indicator as a reward during the training of an RL-agent, a set of controller parameters are calculated and applied in the converter-dominant power system to improve the system oscillatory stability. To this end, an indicator that can represent the stability margin should be first selected. Afterwards, a mathematical relationship is constructed between the controller parameters, the stability indicator, and the current observed states. Experimental results are presented and compared with the standard analytical parameterization method.
https://doi.org/10.1109/ISGT-Europe54678.2022.9960583
Modellbildung und Regelung leistungselektronischer Systeme unter Verwendung nichtlinearer Entwurfsverfahren. - Düren : Shaker Verlag, 2022. - vi, 180 Seiten. - (Berichte aus der Elektrotechnik)
Technische Universität Dresden, Habilitationsschrift 2022
ISBN 978-3-8440-8858-8
Stability assessment and optimization of MMC energy balancing for drive applications at standstill using an averaging approach. - In: 2022 24th European Conference on Power Electronics and Applications (EPE'22 ECCE Europe), (2022), S. P.1-P.10
A new controller design framework for periodic systems is presented and applied to the Modular Multi-level Converter energy balancing. It provides a rigorous stability analysis for the state-of-art averaging control and the approach using constants as reference for the instantaneous energies. An optimized controller with improved performance is derived and verified by simulation and experiment.
https://ieeexplore.ieee.org/document/9907170
A simplified braking method for direct matrix converter-fed PMSM drives with consideration of avoiding regenerative energy. - In: 2022 24th European Conference on Power Electronics and Applications (EPE'22 ECCE Europe), (2022), S. P.1-P.8
This paper presents a simplified braking method for direct matrix converter (DMC) - fed permanent magnet synchronous motor (PMSM) drives with special consideration of avoiding the regenerative energy from feeding back to the grid. As a four-quadrant converter, the DMC has the bidirectional energy-flow capability, which is seen as a great benefit. However, the regenerative energy feeding back to the grid is not always needed, in some cases might be not allowed or not possible. These could happen due to the grid load status, strict quality specifications of the grid current or grid failure, where the DMC needs to be decoupled from the grid. In order to avoid the regenerative energy temporarily or completely, a three-phase diode bridge (B6) with chopper resistance on the motor side is employed together with the traditional B12-clamp circuit, which is used for overvoltage protection. Furthermore, the motor torque during braking could be controlled without large fluctuation and within the required limitation. The principle of the proposed strategy is described in detail. Simulation results are used to verify the feasibility of the proposed strategy.
https://ieeexplore.ieee.org/document/9907709
Feasibility assessment of variable-speed generator set concepts with focus on rating of power electronic equipment. - In: 2022 24th European Conference on Power Electronics and Applications (EPE'22 ECCE Europe), (2022), S. P.1-P.10
Mobile generator sets are mainly used for the supply of electrical power in off-grid applications, e.g. at construction sites, as well as for grid support parallel to weak grid access points. Furthermore, they are used for emergency power supply.
https://ieeexplore.ieee.org/document/9907088
An optimized compensation strategy of direct matrix converter-fed PMSM drives with field weakening under unbalanced supply conditions. - In: 2022 24th European Conference on Power Electronics and Applications (EPE'22 ECCE Europe), (2022), S. P.1-P.10
This paper presents an optimized compensation strategy for direct matrix converter (DMC) - fed permanent magnet synchronous motor (PMSM) drives with special consideration of the modification in field weakening control under unbalanced supply conditions. The imbalance of input voltage conditions in a three wire system are analysed and considered to be composed of positive and negative sequence components. To determine unbalance factor of the grid and decompose the positive and negative sequence components, the dual second order generalized integrator (DSOGI) and positive sequence calculator (PSC) algorithm are introduced. In order to achieve balanced output while optimizing the input current to be sinusoidal, the modulation index based on direct modulation method and the field weakening regulator are then adjusted according to unbalance factor of the input voltage conditions. The principle of the proposed compensation strategy is explained in detail. Simulation results are used to verify this proposed strategy. A low voltage laboratory platform consisting of DMC and servo motor is implemented and controlled using hybrid hardware concept based on field-programmable gate array (FPGA) and digital signal processor (DSP). Experimental studies on the laboratory prototype confirm the feasibility and effectiveness of the proposed method.
https://ieeexplore.ieee.org/document/9907529
Model reduction using singular perturbation methods for a microgrid application. - In: 2022 24th European Conference on Power Electronics and Applications (EPE'22 ECCE Europe), (2022), S. P.1-P.10
The paper deals with the modeling of an island grid for the purpose of simulation. Since the behavior of the system is affected by phenomena taking influence in different time-scales, a model reduction scheme is proposed that leads to simpler models which reduce the computational burden in simulations. Compromises in the modeling procedure are addressed by investigating simulation studies.
https://ieeexplore.ieee.org/document/9907517
Design of LCL filter for DC converter by using analytical equations. - In: PESS 2021 - Power and Energy Student Summit, (2022), S. 46-51
This paper proposes a design method of the DC inverter LCL filter based on the buck circuit to improve the power quality. The LCL filter reduces output ripple current and ripple voltage and improves the power quality. Two design methods are given in the article. The first method is to design an LCL filter without feedback. Another way is to design an LCL filter with feedback through transfer function and Fourier transform. Finally, the influence of the LCL filter developed using two different methods on the circuit is compared and analyzed through modelling and simulation results.
Performance evaluation of a GaN flying capacitor multilevel inverter for industrial applications. - In: CIPS 2022, (2022), S. 508-516
Standard industrial grid connected inverters including their corresponding EMI filter have power densities of only one liter per kilowatt. This application, known as active front end, is typically based on a two-level topology using Si-IGBTs and Si-Diodes and therefore has a limited switching frequency below 10 kHz. It is possible to decrease the filter effort by reducing the voltage-time related area of the switching events. Recent investigations in this area are mainly focused on two-level SiC or three-level Si topologies. With these methods the voltage-time related area is typically reduced by a maximum factor of ten. The volume of the resulting inverters is reduced but is still dominated by the EMI filter. In contrast there are some investigations focused on the flying capacitor multilevel topology in combination with GaN switches. The major part of these publications is focused on motor applications and the presented inverters reach power densities of more than ten kilowatts per liter. In contrast this project is focused on such a multilevel GaN approach for a grid connected 16 kW industrial application. Based on a theoretical optimization an 800 kHz inverter with nine voltage levels is a good compromise between efficiency and power density. This target design reduces the voltage-time related area by a factor of 800 and therefore shrinks the filter effort tremendously. The prototype for this design is presented in this paper and compared to a grid connected standard two-level silicon based inverter.