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Parallel Resonances between Filter Capacitors and the Low Voltage Power Grid

Bienholz, Markus (2019):
Parallel Resonances between Filter Capacitors and the Low Voltage Power Grid.
Darmstadt, Technische Universität, [Online-Edition: https://tuprints.ulb.tu-darmstadt.de/8773],
[Ph.D. Thesis]

Abstract

This work studies the resonances which appear between the capacitors of power electronics grid interfaces and the inductance of the power grid. For this purpose it firstly introduces a frequency domain simulation method that is able to model asymmetrical components as well as symmetrical components.

Models of typical power electronic components are derived from measurement for a frequency range of 2kHz to 150kHz . The asymmetrical cable model shows much better results than publications using a symmetrical model. A measurement procedure to measure impedances while connected to the power grid using coupling circuits is described and used for the measurement of the grid impedance up to 150kHz.

A set of simulations of two power electronic converters at a point of common coupling is carried out, showing that a resonance between EMI filter capacitors and the grid inductance appears. The frequency of this resonance is determined by the value of the grid inductance and the total capacitance connected to the grid. The damping of the resonance and the resulting resonant currents are found to depend predominantly on the resistivity of the grid impedance. Long cables can shift and dampen the resonance, however connecting a load to the filter versus leaving it idle has no influence on the resonance. Measurements are provided that prove all findings of the simulation and additionally demonstrate a thermal threat to the filter capacitors as well as a significant negative impact on the voltage quality at the point of common coupling.

Finally an integration of the EMI filter into an LCL filter is proposed. A first analysis shows equivalent behavior in terms of control while the total filter component size is decreased over the traditional approach. A decrease in filter damping is accompanied by decreased likeliness of exciting or suffering from a resonance with the power grid. Further improvements of this filter design are proposed for coming research.

Item Type: Ph.D. Thesis
Erschienen: 2019
Creators: Bienholz, Markus
Title: Parallel Resonances between Filter Capacitors and the Low Voltage Power Grid
Language: English
Abstract:

This work studies the resonances which appear between the capacitors of power electronics grid interfaces and the inductance of the power grid. For this purpose it firstly introduces a frequency domain simulation method that is able to model asymmetrical components as well as symmetrical components.

Models of typical power electronic components are derived from measurement for a frequency range of 2kHz to 150kHz . The asymmetrical cable model shows much better results than publications using a symmetrical model. A measurement procedure to measure impedances while connected to the power grid using coupling circuits is described and used for the measurement of the grid impedance up to 150kHz.

A set of simulations of two power electronic converters at a point of common coupling is carried out, showing that a resonance between EMI filter capacitors and the grid inductance appears. The frequency of this resonance is determined by the value of the grid inductance and the total capacitance connected to the grid. The damping of the resonance and the resulting resonant currents are found to depend predominantly on the resistivity of the grid impedance. Long cables can shift and dampen the resonance, however connecting a load to the filter versus leaving it idle has no influence on the resonance. Measurements are provided that prove all findings of the simulation and additionally demonstrate a thermal threat to the filter capacitors as well as a significant negative impact on the voltage quality at the point of common coupling.

Finally an integration of the EMI filter into an LCL filter is proposed. A first analysis shows equivalent behavior in terms of control while the total filter component size is decreased over the traditional approach. A decrease in filter damping is accompanied by decreased likeliness of exciting or suffering from a resonance with the power grid. Further improvements of this filter design are proposed for coming research.

Place of Publication: Darmstadt
Divisions: 18 Department of Electrical Engineering and Information Technology
18 Department of Electrical Engineering and Information Technology > Institute for Power Electronics and Control of Drives
Date Deposited: 14 Jul 2019 19:55
Official URL: https://tuprints.ulb.tu-darmstadt.de/8773
URN: urn:nbn:de:tuda-tuprints-87736
Referees: Griepentrog, Prof. Dr. Gerd and Myrzik, Prof. Dr. Johanna
Refereed / Verteidigung / mdl. Prüfung: 3 June 2019
Alternative Abstract:
Alternative abstract Language
Die vorliegende Arbeit befasst sich mit Resonanzen zwischen netzseitigen Kondensatoren leistungselektronischer Schaltungen und der Netzinduktivität. Hierzu wird zuerst eine Simulationsmethode im Frequenzbereich vorgestellt, die in der Lage ist sowohl symmetrische als auch asymmetrische Komponenten zu modellieren. Modelle aller typischen leistungselektronischen Bauteile werden durch Messungen für einen Frequenzbereich von 2kHz bis 150kHz bestimmt. Insbesondere das asymmetrische Kabelmodell zeigt deutliche Verbesserungen gegenüber in Veröffentlicheungen üblichen symmetrischen Modellen. Ein Messverfahren zur Vermessung von Impedanzen unter anliegender Netzspannung wird beschrieben und für die Bestimmung der Netzimpedanz bis 150kHz verwendet. Verschiedene Simulationen zweier Wechselrichter an einem gemeinsamen Anschlusspunkt werden durchgeführt um Resonanzen zwischen den Kondensatoren eines EMV-Filters und der Netzinduktivität nachzuweisen. Die Frequenz der Resonanz wird durch den Wert der Netzinduktivität und die gesamte Kapazität am Anschlusspunkt bestimmt. Die Dämpfung und die sich ergebenden Ströme hängen nachweislich hauptsächlich vom resistiven Anteil der Netzimpedanz ab. Die dargestellten Messungen bestätigen die Erkenntnisse der Simulationen und zeigen darüber hinaus eine thermische Gefährdung der Filterkondensatoren sowie einen erheblichen negativen Einfluss auf die Spannungsqualität am Netzanschlusspunkt auf. Abschließend wird die Integration des EMV-Filters in ein LCL-Filter vorgeschlagen. Eine erste Analyse dieses Vorgehens bestätigt ein gleichbleibendes regelungstechnisches Verhalten, während die benötigten Bauteilwerte reduziert werden. Eine Reduktion der Filterdämpfung steht einer Reduktion der Anregung sowie Anfälligkeit für Resonanzen mit dem Netz gegenüber. Optimierungsmöglichkeiten am vorgeschlagenen Filterdesign werden für künftige Untersuchungen aufgezeigt.German
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