| Summary: | 博士 === 國立臺灣大學 === 電機工程學研究所 === 105 === The objective of this dissertation is to propose a current-decoupling strategy for the PV micro-inverter to achieve maximum power point tracking (MPPT) performance without using large electrolytic capacitors. Conventionally, the grid-connected PV micro-inverter needs a large PV-side electrolytic capacitor to suppress the double-line-frequency voltage ripple, which is caused by the injected AC grid power, to achieve the desired MPPT performance. However, the short-lifetime electrolytic capacitor would reduce the PV micro-inverter’s reliability dramatically. Therefore, different active decoupling tanks (ADTs) have been proposed in published papers to reduce the required input capacitance so that the long-lifetime thin-film capacitor can be used to replace the electrolytic capacitor. Unlike the conventional ADTs with charging and discharging modes operation, a novel current decoupling strategy, which is based on the concept of current decoupling instead of power decoupling, is proposed to simplify the control mechanism of the PV micro-inverter. Furthermore, to accomplish the proposed current decoupling concept, a novel circuit topology for the micro-inverter is also proposed. With the proposed current decoupling strategy, the ADT inside the proposed micro-inverter can buffer the current difference between the constant current from the PV panel and the rectified sinusoidal current of the AC grid current. Therefore, the input capacitance on the PV-side can be reduced dramatically and the long-lifetime thin-film capacitor can be used to replace the electrolytic capacitor. The reliability and the MPPT performance of the PV micro-inverter can be increased. In this dissertation, the classification of published micro-inverters with different types of ADTs is introduced. The operation principle and control block diagram of the proposed micro-inverter with current decoupling strategy are presented. Then, the component design and the compensator design based on the derived small-signal model are provided. Simulation results and experimental results of a prototype 240 W PV micro-inverter are shown to verify the performance of the micro-inverter with current decoupling strategy.
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