Transformerless switched-capacitor-based fault-tolerant multilevel inverters for PV systems: a comprehensive review

Abstract

A transformerless switched-capacitor-based multilevel inverter (TLSCMLI) has emerged as an optimistic substitute for traditional inverters due to reduced component counts, self-voltage balancing, inherent voltage-boosting capability, removal of bulky magnetic components, and the compact size of the photovoltaic (PV) inverter system. Conventional SCMLI topologies inherently generate multiple voltage levels at the output and statically boost voltage with switched-capacitor (SC) cells; galvanic isolation between the AC output and the DC input is typically performed with line-frequency transformers. Whereas, TLSCMLI suppresses leakage current by adopting the advanced switching strategies for SC charging/discharging, and common-ground (CG) structures, without the requirement of line frequency bulky isolation transformers. However, the transformerless inverter poses challenges in terms of the ground capacitive circulating current present in the PV inverter system. The CG transformerless MLI has been recognized as a favorable method to minimize the concern of common mode current from the PV system. Furthermore, modern PV applications pose significant challenges in terms of fault tolerance and reliability. In view of the above, this article provides a critical review of latest developments in single-phase TLSCMLI topologies for PV applications. It classifies grid-connected PV inverters and provides a comparative analysis of two-level and multilevel single-phase inverter topologies. It emphasizes the role of CG MLI structures in mitigating leakage current from TLSCMLI. Moreover, fault-tolerant SCMLI topologies are analyzed under open switch fault conditions, enhancing PV system reliability. Further, to provide proof of concept, simulation and hardware results of the selected MLI have been performed.