Ground Potentials in Transformerless Grid-Connected Multi-Level Power Electronic Converters

This paper aims to develop models for the ground potentials in transformerless grid-connected multi-level power electronic converters (PECs). These PECs are widely used in photovoltaic systems, motor drives, and solid-state power transformers, where they offer reduced input and output harmonic distortions. The desired models for ground potentials are constructed based on common-mode voltages across each leg of the multi-level PECs. The constructed models for ground potentials are to be used for creating local grounding, along with designing adequate grounding circuits for transformerless grid-connected multi-level PECs. An adequate local grounding (for transformerless grid connected PEC) ensures blocking ground currents from flowing through the host grid grounding, and guarantees eliminating ground potentials. The developed models and grounding circuits are evaluated for transformerless grid-connected diode-clamped, flying-capacitor, and cascaded H-bridge multi-level PECs under different operating conditions. Test results demonstrate the significant advantages of the adequate grounding of transformerless grid-connected PECs, in terms of reduced input and output harmonic distortion, minimized ground potentials, and improved efficiency.