Photovoltaic Micro-inverter With Power Decoupling

ABSTRACT:With large-scale mining and utilization of fossil fuels, global environmental pollution and energy crisis have become increasingly prominent. The solar energy is inexhaustible and clean, which leads to a rising utilization of photovoltaic (PV) generation. At this historic moment, the grid-tied photovoltaic inverter turns into a hotspot. In recent years, in order to improve its efficiency, reduce its cost and achieve the modularity, the concept of micro-inverter has been proposed. With the advantages of its simple structure, acceptable volume, plug and play and easy extention, the research on PV micro-inverters becomes a trend. But in single-phase grid-tied PV inverter, the difference between input and output instantaneous power results in the parallel connection of large electrolytic capacitors. And the lifetime of electrolytic capacitors is relatively short, which severely limits the life span of the inverter. To solve this problem, power decoupling unit is added in the inverter, which means electrolytic capacitors are replaced by small-value film capacitors. Thus the life span of the inverter can be extended.This thesis studies the PV micro-inverter with power decoupling from the perspective of three-port, including PV port, AC port and power decoupling port. It introduces the basic units of each port, analyzes the combination principle of each port and the common topologies. This thesis starts with a simplified PV micro-inverter with power decoupling, and then introduces its working principle, verifies the theoretical analysis by simulation and experiment at last. However, due to the adoption of power decoupling unit, it has an impact on the steady-state characteristics of the inverter. Therefore, in order to study the performance of this type of topology further, another modified PV micro-inverter with power decoupling has been discussed, which decoupling loop current is halved. Based on this topology, the main circuit design and loss analysis have been made. In addition, its feasibility by PSIM simulation has been done, and a100W experimental platform has also been built to complete the experimental verification.This paper also uses three methods to optimize the efficiency of the modified topology, which can make the efficiency as high as89.24%. Finally, the thesis summarizes the advantages of the topology according to the theoretical analysis and experimental results. It can be summarized that the decoupling circuit’s operation is changed by improving the circuit structure, which greatly improves the steady-state characteristics of the PV micro-inverter.