At present, the efficiency of photovoltaic (PV) power generation is low, it is impossible to meet people’s demand for power, thus the combined power supply mode with both utility power and PV power is proposed. Considering the power supply mode of utility power and PV power is not the same, the principle of PV power generation and utility power are studied systematically, to determine the possibility of switching between utility power supply mode and PV power supply mode. PV power generation is greatly affected by solar light intensity, time and other factors, thus the automatic switching control system based on 51 single chip machine for grid-disconnected PN power generation system and utility power is proposed. In accordance with this design, the 2 kW grid-disconnected power generation and supply system in the new energy research center of Ningxia University is retrofitted, the system is operating with good effects;the correctness and feasibility of the design are verified.%针对目前光伏发电效率较低，无法完全满足人们对电力需求的现状，提出了市电和光伏发电共同为居民供电的供电方式。考虑到市电和光伏发电供电方式不尽相同，对光伏发电和市电原理进行了系统学习，确定了市电和光伏发电供电方式间切换的可能性。考虑到光伏发电受太阳光照强度、时间等因素影响较大，提出了基于51单片机控制系统的离网光伏发电系统和市电的自动切换控制方式。按照本设计对宁夏大学新能源研究中心2 kW离网发电供电系统进行改造，系统运行效果良好，验证了本设计的正确性及可行性。
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