Design Of Grid And Off-grid Control System Of Single-phase Photovoltaic Inverter

With the rapid development of society,energy and environment crisis become very serious problems,which cann’t be ignored and result in an close attention to photovoltaic(PV) as a Clean pollution- free new energy.distributed PV system has been developed quickly in recent years,that the grid-connected inverter as an interface between the grid and PV system has been widely used.because of dynamic switching between grid-connected mode and off-grid mode that the grid-connected inverter can act,continuity and reliability of power supply locally have been challenging problems.So,this thesis study and design a off grid and grid control system of single phase PV inverter.main content include:(1)discussing the growing trend of single phase PV system in the domestic and overseas,and studying the concept of seamless switching for PV system and its difficulty.(2)Aim at the topological structure of single phase inverter,proposing mathmatical model and control strategy for grid connected and off-grid inverter,and designing an improved DPR controller which can ensure zero-error performance of signal tracking.(3)proposing software closed loop PLL method and island detection method for single phase PV system.(4)according to various problems caused by inverter mode switching,designing a dynamic switching method from grid-connected mode to off-grid mode.(5)proposing a control strategy for two level PV inverter system by analysing a variety of MPPT algorithm used in PV system.In the end,Through experiment testing,the results show that the control system designed by this thesis can perform smooth dynamic switching between grid-connected and off-grid modes,ensure the continuity and reliability of power supply locally and meet design requirements.