An Integrated LLCL Filter with Accelerated Balancing and Harmonic Attenuation for Single-Phase Converter

Single-phase symmetrical converter with five-level switching and a high-order filter offers remarkably low switching harmonics. It however experiences noticeable DC neutral-point imbalance, worsened by second-order power ripples associated with all single-phase systems. Although the imbalance will naturally rectify, its progress is very slow. It is therefore common to add an active or a passive balancing booster to accelerate the process. An active booster however requires sensitive sensors and control modifications, which usually will deteriorate reliability and high-frequency spectral performance of the converter. A passive booster may therefore be appealing, but it is presently included as a separate entity from the filter. The outcome is more LC components than necessary. This paper therefore proposes to coordinately design a LLCL filter integrated with both accelerated balancing and harmonic mitigation, while using much lesser LC components. A reconfigured LLCL filter has promptly been developed and tested experimentally with a single-phase symmetrical T-type converter.