The Research Of Distributed Single Phase Non-isolated PV Grid-connected Inverter

With the continuous use of fossil fuels,human survival is facing a huge threat,and the development and utilization of clean energy is imminent.Solar energy has a wide distribution area,can be used in many ways.It is one of the most promising clean energy in the future.Photovoltaic(PV)power generation is one of the main ways of solar energy utilization.It,clean and pollution-free,is an effective way to ease the electricity tension and improve the ecological environment in the future.The form of large-scale centralized PV power generation still has an absolute advantage in china.With the transmission difficulty of large-scale PV power plant and more and more serious problem of discarding light in western of china,large-scale PV power plants did not meet our expectations of the use of solar power.Development of distributed power generation using solar energy could be able to well avoid the problems,which China's PV power generation encountered in the current stage,and investment is smaller,generation cycle is shorter.It will inevitably replace the centralized PV power generation as the main form of PV power generation.At present,there are main problems of distributed PV grid-connected inverter:1.Circuit selection and miscarriage of justice in the front DC/DC converter.Increasing the front DC/DC in the inverter improves the system on-time and make sure the PV array output power to maximize;But as to the inverter itself,the increase of DC/DC converter in inverter increase the power consumption,and the misjudgment in the process of MPPT will lead to output power jitter.2.The problem of internal low-order harmonic in inverter.The fluctuation of the instantaneous output power in the single-phase inverter makes the DC bus voltage Secondary ripple,which will reduce the life of the inverter and increase the third harmonic of the output current.3.The problem of common-mode(CM)current to the grid.The parasitic capacitance between the PV cell and the grounded metal case forms a loop with the grid,the CM voltage of the high frequency generates current through the loop,which reduces the security of the system.In this paper,firstly,the ZVT-Boost circuit is used to reduce the loss of the front stage in the inverter,and the traditional INC method is optimized about the directionmisjudgment during the external environment change.The output power of the PV cell is estimated to avoid the misjudgment problem.Secondly,in order to reduce the output current harmonics to improve the inverter's life,it is proposed to add the source filter device on the DC bus to filter the secondary ripple.Thirdly,the inverter topologies which can keep the CM voltage constant is analyzed.Combined with the CM equivalent circuit,the reason of high frequency components in CM current are elaborated on.The novel double CM inner loops method was proposed to restrain the high-frequency components in CM current.Finally,the contents of this paper are analyzed and validated by the simulation and experiment,proving the validity of the research results in this paper.