Reseach On Long-lifetime Single Phase PV Grid-connected Micro-inverter

At present, the development of PV power generation industry is mainlyconcentrated in the high-power centralized inverters and micro-inverters.Compared with the former, the latter uses power unit controlling, and effectivelysolves the problem of partial occlusion. It is more conducive to the needs offamilies and small or medium size power generation. As the interface equipmentof PV array and the gird, inverter is the key part in the whole PV system.Compared with25years lifetime of PV array, most inverters only can be usedlasting five to ten years, thus inverter becomes the weak point to improve theworking lifetime of PV system. This paper researches on the topology andcontrol method of PV grid-connected micro-inverter and tries to extent theinverter’s service lifetime.According to the requirements of grid-connected regulations and PV array,this paper proposed a three stages topology structure with a high-frequencytransformer for the micro-inverter. The proposed structure has a smaller value ofDC-bus capacitor, which makes it possible to use small film capacitor or ceramiccapacitor to replace the traditional aluminum electrolytic capacitor, thus theservice lifetime can be prolonged. The proposed structure can be divided intothree stages. The first stage is voltage amplifier stage, which is designed to boostthe voltage and track the maximum power point of PV array. The second stage iscurrent shaping stage, which is designed to change the voltage source to currentsource and output a rectified sine-wave current. This part is controlled by voltageouter-loop which uses a PI controller and current inner-loop which useshysteresis current control strategy. The third stage is an unfolding bridge stage,which transforms the100Hz rectified sine-wave to50Hz sine wave. All the drivesignals of the four MOSFETs are synchronized with grid voltage.Simulation results prove that this system can work stable. Each of the threestages in the proposed structure is tested respectively with resistance loads andthe whole system is also tested with grid-connected experiment. The structure isproved to be stable and the current of inverter matches the grid-connectedregulation. The lifetime of proposed system is longer than20years withtheoretical analysis.