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) power generation systems keeps a rather high growing rate in recent years. However, the output voltage of the solar cells changes rapidly with the insolation. Hence, a switching power converter is required as a regulator for achieving the maximum output power of the PV power generation system. In this thesis, Cuk converter is adopted because of its step up/down capability and nonpulsating input/output current feature. However, the inherent current ripple of switching power converter indeed may cause significant impact on the output power. Hence, the major objective of this thesis is focused on the further study of the quantitative output power reduction effect of the input current ripple of PV systems as well as proposing ripple cancelling techniques to solve the above dilemmas. Basically, the contributions of this thesis can be summarized as follows. First, the power reduction caused by the current ripple of solar cells is analyzed through an accurate mathematical model. Second, an active ripple cancelling technique is proposed to eliminate the current ripple of the conventional Cuk converter effectively. By proper design of an auxiliary circuit, zero input and output current ripples can be achieved. The proposed method does not require an extra control and feedback circuit. Furthermore, based on the ripple cancelling concept, a simple passive ripple cancel technique is proposed. It turns out that the maximum output power of the PV system can now be fully extracted. Third, both DC and AC models of the proposed zero input current ripple Cuk converter are derived for convenient closed-loop controller design. Also, simulation results are made to verify the accuracy of the models. Finally, a 90W, 24V~34V input, 19V output laboratory prototype is constructed to verify the effectiveness of the proposed converter. It is seen that the resulting peak to peak input current ripple is about 2% of the current ripple due to the conventional Cuk converter. Furthermore, at 0.8 kW/m^2 insolation, 50℃ test condition, it is seen that the average output power of the PV array can reach 75W by using the proposed technique. In other words, this amounts to an increase of 7% averaged output power as compared with the conventional Cuk converter.