Analysis of the properties of damped LCL filters including measurement-based assessment

Voltage-source converters need grid-side filters to connect to the grid. These grid-side filters on the one hand couple the converter-generated grid-side voltages to the grid voltages and on the other hand mitigate the influence of the switching of the power-electronic devices of the converter on the grid. While uncontrolled diode bridges usually couple via inductances (due to their low switching frequency defined by the grid frequency) self-commutated converters need more sophisticated filter structures, usually of LCL-type, to damp the effects generated by the switching of the power-electronic devices such, that EMC requirements imposed by grid codes are met. Such filters rely on resonance - and various types of resonances may lead to interactions between multiple converters connected to a grid, e.g. in case of solar farms. Resonance effects may lead to additional stress on components, additional losses in e.g. transformers, interruption of service and even damage to components. Consequently, damping of the filter is one option to improve the interoperability of a filter - but it needs additional components and causes cost and losses. This paper researches the effect of filter damping based on a demonstrative example.