Abstract
In view of the problems of global climate change, environmental impact and shortage of fossil fuels, exploring the use of renewable energy has drawn a lot of attention internationally. Among a variety of renewable energy technologies, photovoltaic technology has more environmental and economic benefits than the others. However, existing DC converters still face the partial shading effects bottleneck problem. Recently, module-integrated converters (MIC) have become a hot research topic as a means for overcoming the partial shading effects of photovoltaic systems and achieving high safety. Hence, in this thesis, to further improve the energy yield, emphasis is placed on the development of a novel ZVS isolated module-integrated converter for photovoltaic systems. Major contributions of this thesis can be summarized as follows. First, a novel MIC with pseudo dc-link and galvanic isolation is proposed. It consists of an isolated SEPIC converter cascaded with a full-bridge inverter operating under line frequency to achieve high efficiency. Furthermore, active-clamped circuits are added to the isolated SEPIC converter to achieve zero voltage switching and alleviate the reverse-recovery current of the output diodes. Secondly, a simple control strategy is proposed to generate a rectified sine waveform voltage at the dc-link capacitors. Also, to reduce input current ripple, an interleaved control strategy is adopted. It has been found that the duty ratio of the active switches can be operated in full range to achieve wider output voltage control range. Finally, a prototype with 25 V input, 110 Vrms output and 150 W rating has been constructed for verifying the feasibility of the proposed MIC. Experimental results have shown that the overall efficiency of the MIC can be maintained above 86.7% as the load varies from 40 W to 150 W, and the highest efficiency of 92.4% has been achieved at 40W.