A novel modulation method which decreases leakage current and increases dynamic performance of z source inverters used in solar systems

Today's developing technology and welfare level causes an increase in energy demand and utilization of electrical appliances. Several energy sources are used to meet these demands, and one of them is solar power. Photovoltaic panels that are used for converting solar energy to electrical energy are utilized increasingly in recent years. It has been estimated that photovoltaic utilization will be increased due to changes in legislation which gives supports in renewable energy. One of the most important parts of photovoltaic system is power conditioning unit which is a power electronics circuit between source and load. Design of this circuit affects primarily of the whole system's efficiency, cost and volume. In recent years transformerless inverters have become a popular research topic, in order to increase efficiency and decrease cost and volume. The newest transformerless inverter topology is Z source inverter. ZSI' s buck-boost ability makes it advantageous against other topologies. That's because researches about ZSI are increasing rapidly in recent years. The output of a power conditioning unit shall be in tolerances specified by international standards. It shall meet both safety and performance requirements. ZSI has two main problems. There is a leakage current due to absence of a galvanic insulation between source and load. This causes EMI, safety and loss problems. Moreover, changes in ZSI boosting ratio causes oscillation in ZSI output voltage. Therefore, dynamic performance of ZSI is poor, and it does not give a stable output voltage. There are some researches in literature which try to solve these problems and new researches are continuing to be published. In this thesis work, a novel modulation technique which decreases leakage current and a novel control method which improves dynamic performance have been proposed. Leakage current has been decreased up to %50 (efficiency of the method depends on switching frequency and load power factor). Moreover, ZSI dynamic performance has been increased. A stable output voltage has been sustained during sudden changes in input voltage or load level. Theoretical analysis of proposed methods have been given and these are simulated with residential load parameters. Results are verified theoretical analysis. Moreover, effectiveness of the proposed method in order to decrease leakage current has been verified by experiments with various voltage levels and power factors.