The Design Of Grid-connected Photovoltaic Micro-inverter System

With the development of the industrial society, the human’s demand for energy is further increased. Conventional energy, which includes coal, oil and natural gas, occupies the large proportion. Otherwise, the storage capacity of fossil energy is so limited that it can’t satisfy the needs of economic development. On the one hand, the outbreak of local conflicts for energy is constant. Even the national war for resources occurs occasionally. On the other hand, with a large amount of consumption of fossil fuels, the trend of environmental pollution becomes worse. It finally destroys global environment. Therefore, human must develop sustainable energy strategy to ease the current energy crisis.Solar energy, as one of the world’s most clean energy, has drawn the attention of the governments around the world. The governments have developed all kinds of policies for solar energy. They encourage the development and utilization of photovoltaic power generation. Micro-inverter as the core component of photovoltaic power generation system, significantly improves the efficiency of the whole PV system. It effectively solves the shadow problem and hot spot problem which always puzzle the traditional centralized inverter. So Micro-inverter has great commercial value and practical value in the photovoltaic grid-connected power system.This paper first introduces the world’s photovoltaic development policy and the development trend of the current solar panel technology. Three kinds of popular solutions for photovoltaic grid-connected power system are specially analyzed. This article adopts efficient structure of interleaving flyback topology. It gives the related hardware designs which belong to the core module of grid-connected photovoltaic micro-inverter. From the perspective of safety isolation, grid-connected photovoltaic micro-inverter can be divided into the original system and the secondary system. It also gives analysis of principle and hardware design which includes the main power topology, control circuit and auxiliary power supply. According to two portion of hardware design, software design of micro-inverter can be divided into the original system design and the secondary system design.As far as the original system is concerned, it gives current open-loop DCM algorithm of micro-inverter in detail and puts forward the algorithm of adaptive BCM. This algorithm can make micro-inverter realize efficient current modulation and significantly reduce the current harmonics. On the analysis of the PV characteristic and P&Q algorithm, modified MPPT algorithm based on bang- bang control ideas is put forward. It can achieve good dynamic response and steady-state accuracy without the need of testing the DC current. Moreover, by analyzing advantages and disadvantages of Sandia active islanding algorithm, it proposes modified Sandia active islanding algorithm which based on frequency hopping. This method can efficiently improve detection sensitivity when the islanding fault occurs.For the secondary system design, after analyzing the principle of d-q synchronous phase locking algorithm, it proposes d-q software phase lock algorithm based on bang- bang control. The modified algorithm can realize accurate and fast synchronization with the utility grid. Furthermore, according to the characteristics of the Electricity LAN, it proposes adaptive network model based on power line carrier communication. The secondary MCU of micro-inverter is responsible for network address allocation. The method realizes the distributed network communication and component-level monitoring. Using software and hardware design of this paper, the sample of 250 W micro-inverter is designed. It gives testing waveform of main algorithms. Finally, some personal advices on current problems and the future development direction of micro-inverter are given.