On the Capability of Cascaded H-Bridge Converter-Based Energy Systems to Tolerate Intraphase Active Power Imbalance

The cascaded H-bridge (CHB) converter is an attractive topology to interface energy sources, such as battery energy storage or photovoltaic systems, with the medium-voltage grid. The submodules in CHB converter-based energy systems unavoidably process different active power during operation. However, there exist inherent limits that prohibit an arbitrarily imbalanced intraphase active power distribution. Failing to consider such limits can result in output current distortion and capacitor voltage deviation, which can jeopardize the CHB converter. Crucially, these limits vary depending on the modulation method utilized, whose selection is, thus, of utmost relevance. Accordingly, this article derives and compares the feasible intraphase active power imbalance range of existing modulation methods. The analysis is experimentally corroborated in a 1-kVA single-phase CHB converter with six submodules per phase. Based on the comparison, suggestions on which modulation methods are preferred for different CHB applications are provided.