Research On Circuit Topology Ang Control Strategy Of Grid-connected Photovoltaic Inverter

Fully absorbing solar energy for power generation is one of the most ideal ways to generate electricity in the future as solar energy is one of the cleanest and most environmentally friendly sources of energy.Because of the disadvantages of high voltage stress,high switching loss and high output current harmonic content,the traditional two-level grid-connected inverter can only be used in small power systems,Three-level inverter can effectively solve these problems and is suitable for medium and large power systems.Based on the study of two NPC-type three-level photovoltaic grid-connected inverters,a simplified topology three-level inverter is introduced in this thesis,And the space voltage vector modulation(SVPWM)technology and grid-connected control strategy of the system are analyzed and studied.The details are as follows:Firstly,the world energy situation is introduced,and the research status of photovoltaic power generation and photovoltaic inverter is analyzed.The space voltage vector modulation technology and grid-connected control strategy adopted in this thesis are given,and the work of this thesis is introduced.Then,the whole photovoltaic power generation system is introduced,the photovoltaic array and maximum power point tracing technology are briefly analyzed,and the three-level and two-level passive inverter circuits are modulated by a simple SPWM modulation method.The advantages of three-level inverter are illustrated by simulation.Based on the analysis of two NPC three-level inverters,a three-level circuit topology which is more simplified than NPC three-level inverter is introduced,and compared with two NPC inverters through the simulation,the output effect of them is highly consistentFinally,the SVPWM modulation technology of simplified three-level inverter is modeled according to the steps of coordinate transformation,sector judgment,calculation of vector action time and state assignment,and several methods of dividing large sector and small sector are analyzed.And choose the most appropriate division method.The grid-connected control strategy is designed according to the order of current inner loop and voltage outer loop.The whole system is simulated and analyzed by builting the simulation model of PV grid-connected system.