Continuous input currents and high step-up ratios are desired from the dc-dc converters that work with renewable energy sources such as photovoltaic panels and fuel cells. Most dc-dc converters use transformers to have high step-up ratios. There is another type of converters that use coupled inductors, but they need to operate at high duty cycles to increase the gain. These converters suffer from low efficiency values because of the leakage inductance values and long reverse recovery times of the diodes. A new dc-dc converter based on Z-source topology is proposed in this study. It uses coupled inductors to increase the step-up ratio. Its main features are high step-up ratios, continuous input currents, high efficiency and galvanic isolation between input and output. Simulation and experimental results are given for a prototype converter that converts 25-400 V dc at 300 W with over 91% efficiency.

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This study presents two-stage inverter topology for single-phase grid-connected photovoltaic (PV) applications and its control implementations. The two-stage systems are reliable and work well. Typically, the second stage inverts solar power into AC power, whereas the first stage which is used to increase low PV panel voltage can achieve maximum power point tracking. In this configuration, a boost or a flyback type DC/DC converter topology is usually employed. However, such converters have major drawbacks such as low efficiency and limited voltage gain due to power losses. In the proposed topology, a low-voltage PV panel can be connected to power grid through solar inverter by using high-gain DC/DC converter which has unique features such as galvanic isolation and continuous current for AC module applications. Conventional controller results in poor control performance due to the finite gain at desired frequencies. Hence, a plug-in repetitive controller is proposed to obtain low total harmonic distortions (THDs). The performance of the proposed system is provided for the system which injects the PV panel current in the maximum power point voltage to a grid of 220 V (rms) at a power range of 150-300 W with a unity power factor and a low input current THD.

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