Parallel Resonances between Filter Capacitors and the Low Voltage Power Grid

• Main Author: Bienholz, Markus
• Format: Others
• Language: en
• Published: 2019
• Online Access: https://tuprints.ulb.tu-darmstadt.de/8773/1/2019-06-07_Bienholz_Markus.pdf; Bienholz, Markus <http://tuprints.ulb.tu-darmstadt.de/view/person/Bienholz=3AMarkus=3A=3A.html> (2019): Parallel Resonances between Filter Capacitors and the Low Voltage Power Grid.Darmstadt, Technische Universität, [Ph.D. Thesis]

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.