Renewable energy plays an important role toreplace traditional natural resources such as fuel and coal as the energydemand is increasing due to the rapid increase of the human population andfast-growing industries. Photovoltaic (PV) energy has recently become a commoninterest of research because it is free, green, and inexhaustible. Meanwhile thetransformer-less grid connected PV inverters are manifested to offer thebenefits of lower cost, higher efficiency, smaller size, and weight. However, agalvanic connection is formed between the power grid and the PV module when thetransformer is omitted. Therefore, a varying CM voltage is generated; as aresult, leakage current flows through the loop consisting of the parasiticcapacitors, the filter inductors, the bridge, and the utility grid. Thisleakage current can compromise their higher efficiency. So the low leakagecurrent and high efficiency are two crucial points in transformer-less PVsystems. In recent years some efforts have been made toimprove the efficiency of these PV inverters by reducing switching losses viaZVT and ZCT techniques considering leakage current limitations. This researchwork engages in single phase transformer-less PV inverters which are facing twocrucial as well as intrinsic challenges of efficiency and leakage current. Themain focus of this dissertation is to find the novel solutions for improving theperformance of these inverters by taking into account the limitations and ofcourse with minimum effects on leakage current characteristics. Following thesegoals, this work presents quasi-resonant DC-Link transformer-less PV inverters,utilizing dc-decoupling topologies. The proposed quasi-resonant auxiliary circuits areapplied to H6 and H5 structures and the expectations are met according to calculationsand simulation reports. Finally a 20 kHz 1-kWuniversal prototype is built and operation characteristics, soft switchingconditions and efficiency improvement of proposed QRDCL transformer-less PVinverters are verified.
