Leakage current generation in view of circuit topology of non‐isolated full‐bridge neutral point clamped grid‐tied photovoltaic inverters

Abstract

Full-bridge neutral point clamped (NPC) non-isolated inverter topologies are used to mitigate leakage current at switching frequency due to non-ideal circuit parameters. Among these topologies, this current is the highest in optimised non-isolated inverter (oH5I) despite lowest switch count. This study analyses the limitations of oH5I in mitigating the leakage current by considering the junction capacitance of switches into account. This analysis elucidates the dependency of common-mode voltage (CMV) characteristics on circuit topology and dead time requirement. In order to ascertain this fact, a novel non-isolated full-bridge NPC inverter (NIFB-NPCI) is proposed. The CMV characteristics of this inverter are analysed during mode transitions and compared with that in oH5I. A 1 kVA unified prototype circuit of these inverters is designed and fabricated for experimental validation. The circuit topology and dead time requirement of oH5I cause a spike in CMV during each mode transition. However, these limitations are addressed in the proposed inverter, and CMV is maintained at a constant value. Hence, NIFB-NPCI evinces lower leakage current at switching frequency than oH5I. Therefore, the effect of topological limitation of full-bridge NPC non-isolated inverters on leakage current mitigation is validated.