Abstract
Due to the limited fossil energy and greenhouse effect, more and more countries are devoting to development and promotion of renewable energy sources. Among the various renewable energy sources, solar energy has the advantages of being inexhaustible and noiseless. Hence, installation of photovoltaic (PV) energy harvesting system keeps a rather high growing rate in recent years. For most PV systems, a switching power converter is required as a regulator for harvesting the maximum output power. However, the inherent current ripple of switching power converter may cause significant impact on the output of PV system. In this dissertation, the first objective is focused on the study of the quantitative ripple-affected power reduction of PV energy harvesting systems as well as proposing a passive ripple cancelling technique to solve the above dilemma. A passive continuous ripple cancelling circuit (PCRCC) and a passive pulsating ripple cancelling circuit (PPRCC) are proposed for eliminating the continuous and pulsating current ripple of power converters, respectively. Special features of the proposed passive ripple cancelling circuits (PRCCs) include simple, modular structure, and high degree of design flexibility. A zero input current ripple Ćuk-type converter is adopted and analyzed as an example for the proposed PCRCC because of its step up/down capability and non-pulsating input/output current feature. On the other hand, for the proposed PPRCC, a zero input current ripple flyback-type converter is proposed and analyzed as an example because of its comprehensive utilization in small power rating commercial products. The corresponding steady-state analysis, zero ripple design criteria, and the topologies of several conventional power converters integrated with the proposed PCRCC/PPRCC are provided. In addition, a novel high voltage gain single-stage DC/AC converter is proposed for low-voltage and high-current output PV module applications. A flyback-type auxiliary circuit is integrated with an isolated Ćuk-derived voltage source DC/AC converter to achieve a much higher voltage gain so that the conversion efficiency can be enhanced. Steady-state characteristics, performance analysis, simulation and experimental results are given to show the merits of the proposed high voltage gain single-stage DC/AC converter. Based on the same integration concept, a family of different topologies is also presented for reference. Moreover, the proposed PRCC is also integrated into the proposed high voltage gain DC/AC converter as an example for further increasing the output power. Finally, three converter prototypes are constructed for verifying the effectiveness of the proposed PCRCC, PPRCC, and high voltage gain DC/AC converter, respectively. First, the experimental results of the 90W rating zero input current ripple Ćuk-type converter prototype show that the resulting peak-to-peak input current ripple is reduced by 98% of the original Ćuk converter input current ripple, and the harvested average PV power of the proposed converter can be increased by 7% as compared with that of the converter without the proposed PCRCC. Second, the experimental results of the 100W rating zero input current ripple flyback-type converter prototype show that the resulting peak-to-peak input current ripple is reduced by 98% of the original flyback converter input current ripple, and nearly 2.83% and 10.23% improvement in efficiency can be achieved by the proposed PPRCC, at 70W and 100W load conditions, respectively. Third, the experimental results of the 200W rating high voltage gain DC/AC converter show that the highest efficiency of 92.3% can be achieved. There is approximately 10% improvement in efficiency at 40W light load as compared with the conventional isolated Ćuk-derived DC/AC converter. Also, it indicates that nearly 3% and 1.4% improvement in efficiency can be achieved by the proposed DC/AC converter, under 120W and 200W load conditions, respectively.