| At present,small and medium power single phase photovoltaic power generation systems use non isolated inverter to reduce volume and improve efficiency.A major technical difficulty of non isolated inverters is the suppression of common mode leakage current after isolating transformers.In this context,the single-phase non isolated photovoltaic grid connected inverter based on H6 topology is studied in this paper.First of all,taking the non isolated photovoltaic grid connected inverter as the research object,the mathematical modeling formula of the photovoltaic cell used in the practical engineering is introduced.The working principle of the H4 bridge and the H6 bridge is compared and analyzed,and the mathematical model is established.Then simulation analysis is carried out.The simulation tool is Matlab2014a/Simulink.In the aspect of grid current control strategy,the PI+QPR control strategy is put forward.In Matlab R2014 a,the Bode diagram of the three persons,which are combined control,PI control and QPR control,is analyzed.The composite control is based on the retention of QPR no static difference tracking ability.Compared with simple PI control,it has stronger ability to resist grid voltage fluctuation.At the same time,compound control has stronger ability to suppress signal in low frequency than pure QPR control.At last,based on the case of rooftop photovoltaic engineering in Anhui,the specific parameters of the traditional single-phase grid inverter used in the project are used as data,and the simulation models of single phase full bridge inverters and H6 bridge inverters are built respectively.Comparing and analyzing the ability to suppress the common mode leakage current,the superiority of the H6 bridge inverter in the small and medium power roof photovoltaic power generation system is verified,and the two stage roof photovoltaic inverter system is built with the H6 bridge inverter as the core.In this model,three control strategies are adopted,PI control,QPR control and PI+QPR control respectively.The performance of the system is compared and analyzed.The simulation results show that the performance of PI+QPR complex control strategy is more advantageous than traditional PI control in the performance of no static error tracking,DC component suppression and power grid voltage disturbance. |
