Application And Research Of Soft Switching Technology In Photovoltaic System

With the prominence of environmental pollution and energy shortages,the world hope to find new energy which can replace traditional energy.Owing to the advantages of cleanliness,pollution-free,renewable,large storage capacity,etc.,solar photovoltaic technology becomes the most promising energy internationally,which leads the development direction of new energy sources.Since the output voltage of photovoltaic panels is low,the connection to the public network or load is accomplished with the help of two-stage energy conversion of the DC-DC boost converter and the DC-AC inverter.The DC-DC and DC-AC of conventional photovoltaic systems work under the hard-switching conditions.However,with the increasing of switching frequency,the effect of switching losses cannot be ignored.Soft-switching technology provides a satisfactory solution to solve this problem.In the ideal cases,soft-switching technology achieves zero switching losses,which improves the efficiency of photovoltaic systems.Considering the two-stage photovoltaic system as application object,this paper is aimed at studying soft-switching technology.Firstly,the principle and application of soft-switching technology are introduced.Meanwhile,the topology and classification of soft-switching are discussed in detail.By analyzing and comparing the topology of typical soft-switching circuit,a technical scheme of the parallel resonant high step-up ratio photovoltaic grid-connected system is given.In addition,the circuit principle and the parameter are designed.The pre-stage of the parallel resonant high step-up ratio photovoltaic grid-connected system can achieves boost as well as soft switching,and the post-stage realizes contravariance as well as grid connection.Secondly,the resonant DC-link inverter technology is studied to achieve soft-switching of the DC-AC inverter.A technical scheme of a simple topology of the resonant DC-link inverter is presented.Moreover,the circuit principle and parameters of the inverter are designed.By using the serial resonance technology,the soft-switching of DC-AC inverter is achieved.In addition,based on the research of SVPWM modulation algorithm,a simplified SVPWM modulation algorithm is proposed,which is then successfully applied to the resonant DC-link soft-switching inverter.The model of parallel resonant high step-up ratio photovoltaic grid-connected system,resonant DC-Link inverter,traditional SVPWM modulation algorithm,and SVPWM simplified modulation algorithm are built by MATLAB/Simulink tools.And the simulation experiments of various typical operating conditions are given respectively.The simulation results show that the two proposed topologies are correct as well as feasible,and the soft-switching operates stably.Simultaneously,the simplified SVPWM algorithm can achieve the performance as the traditional algorithm and the expected design target.