Research On 1kW Photovoltaic Grid-connected Inverter

Under the double restrict between the shortage of global energy and the stringent requirements of environmental protection,distributed generation systems based on renewable energy has been getting more and more attention.Photovoltaic power technology is an indispensable part of distributed generation systems.Its development and utilization are a hot topic currently.Inverter is the major aspect and key factor of Photovoltaic power generation,because it determines the system efficiency,cost and reliability.According to the singleness of working mode in photovoltaic inverter,a stand-alone/grid-connected low-power single-phase photovoltaic inverter has been studied and designed in this paper.Firstly,by looking up massive literature material and synthesizing the domestic and foreign scholar's research,this part introduced the research profile of distributed generation technology,discussed the background and basic components of Photovoltaic power generation technology,and illustrated the importance of the inverter in the whole system.Secondly,starting from the introduction of PV inverter's common circuit topology and control scheme,according to design requirements and specific technical indicators,DC/DC/AC double-stage structure is selected as the system's main circuit topology,and ATMEGA64A is used as the system's control chip.The former stage adopts isolation full-bridge DC/DC converter with high-frequency transformer.Aiming at the problems of traditional full-bridge DC/DC converter,a novel phase-shift ZVS full-bridge DC/DC converter is designed.By using chip UC3875 and blocking capacitor,the expected boost effect is achieved.Moreover,this circuit can resolve hard-switching loss problem and one-way saturation of transformer magnet cores problem caused by inconsistency switching characterist.The latter stage adopts full-bridge inverter,and controlled by the unipolar double frequency multiplication SPWM.Voltage feedback and feedforward method is used as the control strategy of inverter under stand-alone mode.Current feedback and grid voltage feedforward method is used as the control strategy of inverter under grid-connected mode.A circuit selecting method based on chip UTC4053 is proposed to control the operating mode.The main circuit is simulated by MATLAB/SIMULINK at last.Thirdly,according to phase-locked and islanding detection,which are two key technical requirements of photovoltaic grid-connected system,a novel reference sinusoid circuit is deeply analyzed and proposed.In combination with over-voltage protection/under-voltage protection,over-frequency protection/under-frequency protection and phase-shift method,this circuit's output sinusoidal voltage is synchronous with grid voltage,and it also can achieve islanding detection function.Finally,a 1kW prototype is built.The stand-alone and grid-connected experiments have achieved good results.