Nowadays, a swift growth of global electricity consumption and the destructive consequences of traditional power generation such as greenhouse effects and air pollution especially in crowded cities, have forced human beings to search for new energy sources. Moreover, due to the fact that traditional energy sources are finite, major research has been carried out to find new clean methods of power generation which are renewable and less pollutant. Among the renewable energy technologies, Photovoltaic energy (PV), is being known as the leading technology in recent years. The solar energy is clean, renewable, abundant and free source of energy that all countries have great access to it. There are many circuit topologies to gain energy by means of PV-modules; however, AC-modules which consist of a PV panel integrated with a grid-connected inverter have become more attractive recently. The ease of use called “Plug and Play” and the ability of non-limited expansion help them to become an optimum option especially forhouseholds and residential complexes. Although AC-modules have several advantages, they suffer from some drawbacks such as low output voltage, low lifetime, ground leakage current and low efficiency. One of the most important problems associated with ac modules is originated from the use of electrolytic capacitors needed for power decoupling in these systems. This effectively reduces the ac modules’ life span to one third. In recent years, major research has been carried out on Ac-modules in order to improve their weak points and to enhance their efficiency. In this thesis, after a short survey on grid-connected photovoltaic systems particularly in the application of AC-modules, their improvement methods are investigated. Then a new electrolyte-free microinverter topology based on an isolated SEPIC topology with its control circuit is introduced.The proposed converter is analyzed and the presented simulation and experimental results confirm the theoretical analysis. Finally, an improved, high step-up ratio, soft switched topology of this microinverter is proposed. It uses coupled inductors for stepping up the output voltage and soft switching technique for diminishing the switching loss in semiconductor elements. Keywords AC-Modules, PowerDecouplingCapacitor,Grid-ConnectedInverter, Soft Switching Techniques,Electrolyte-Free Microinverters