This book is essential and valuable reference for graduate students and academics majored in power electronics, engineers engaged in developing distributed grid-connected inverters, and senior undergraduate students majored in electrical engineering and automation engineering. Soft-switching (SS) technique is an important way to achieve high conversion efficiency and high switching frequency for power converters, which is beneficial to improve power density and reduce volume and cost of power electronics equipment. This book mainly discusses SS technique for transformerless grid-connected inverters (TLIs), and a SS configuration named as "Freewheeling-Resonance-Tank Inverters" is proposed for TLIs fulfilling requirements of switching loss-free, full power factor range, and constant common-mode voltage performance. The detailed theoretical analysis and experimental validations are presented from ZCT and ZVT type topologies, respectively.