太陽能微換流器之電流解耦合策略

Abstract

本篇論文提出一個新的具有電流解耦合策略之太陽能微換流器，來達成不使用電解電容便能實現最大功率追蹤(Maximum Power Point Tracking, MPPT)功能之目的。傳統上，併網型太陽能微換流器因為注入交流市電功率，會在太陽能板端產生兩倍頻電壓漣波，所以在太陽能板端需要並聯一個大電解電容，來抑制兩倍頻電壓漣波，以達到最大功率追蹤效能。但是，短壽命之電解電容將會大幅減少太陽能微換流器之可靠度。因此，已有文獻提出不同種類之主動式解耦合槽(Active Decoupling Tank, ADT)，減少輸入電容容值，以達到使用高壽命之薄膜電容來取代電解電容的目的。但和傳統以功率解耦合為基礎的ADT不同，本論文中提出一個基於電流解耦合策略，來簡化微換流器之控制機制。而且，為了實現所提出之電流解耦合策略，本論文也提出一個新型的微換流器電路架構。本論文所提出之微換流器，其中的ADT能作為太陽能板定電流及市電整流弦波電流之間的緩衝。因此，太陽能板端輸入容值能大幅降低，而且能使用長壽命的薄膜電容來取代電解電容。太陽能微換流器之可靠度及MPPT精準度都能提升。本論文中，首先針對不同ADT類型之現有微換流器進行分類介紹。接著說明所提出具有電流解耦合控制之微換流器的操作原理及控制方塊圖。再提供元件設計及基於小訊號模型推導之補償器設計。最後，藉由一個240瓦太陽能微換流器原型電路之模擬及實驗結果，來驗證所提出電流解耦合策略之效能。

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.