The grid connected inverters of solar systems are divided into two groups, with transformer and without transformer that transformerless converters have received more attention due to advantages such as high efficiency, lower cost and weight, and low complexity. One of the main problems of these converters is Leakage Current (LC) and Parasitic Capacitor between the panels and the ground, which causes a decrease in efficiency and creates safety issues. For this purpose, extensive research has been done in this regard and various methods and structures have been created to keep the common mode voltage constant and eliminate the leakage current in transformerless grid-connected inverters. Also, due to the fact that the output voltage of solar panels is lower than the grid voltage and in order to inject current into the grid, a voltage higher than the grid voltage must be produced, voltage boosting converters are used, which cause increasing the complexity of control in solar systems. As a result, the aim of this thesis is eva‎luating a structure to reduce the complexity of control in solar inverters along with removing the leakage current from the system. In this regard, firstly the different structures of single-phase transformerless inverters in eliminating the leakage current have been investigated and the advantages and disadvantages of each structure have been discussed. The simplest structure in eliminating the leakage current is the H5 structure. For this purpose, in order to reduce the complications of control caused by voltage converters, a structure based on H5 has been presented with the integration of the convertor in the inverter to reduce the complications of the inverter. Also according to the presented structure, in the second proposed scheme, in order to reduce the tension and stress of the switches, a structural change has been made in the inverter. Due to the reduction of the switch stress in proposed structure, the leakage current will not be removed. For this reason, an EMI filter is considered at the input of the inverter and by coupling the filter inductors with the suggested convertor inductor, the problem of removing the leakage current is also solved. Finally, with the aim of creating soft switching, a snubber circuit is considered in the inverter. The efficiency method of each of the proposed designs in eliminating the leakage current and other purposes has been theoretically investigated and the functional modes of the circuit have been eva‎luated. Also, in order to observe the correctness of the performance and results, the simulation of the structures is done in the PSIM software. The first proposed design based on integration of converter and inverter is built and the results are verified based on practical implementation.

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حسين فرزانه فرد

احمدرضا تابش، نسرين رضايي