Control Method Of Harmonic Current Of An Improved Grid-connected PV Power Generation System

As the crisis of energy source and the environmental problems are increasingly apparent,the renewable energy as a green energy is paid more attention.The proportion of electric energy produced by the grid-connected photovoltaic(PV)power generation system is increasing in the whole power system,the safe and stable influence on power quality of utility grid is also growing.Although GB/T14549 standard has strict requirements on the single harmonic current and the total harmonic current under the condition of rated power for the gird-connected PV power generation system,when output power of the PV array is small,the problem of the large grid-connected harmonic current still exists.In this paper,three existing solutions are combined and an improved grid-connected PV power generation system is proposed to make the grid-connected current THD<5%in full power ranges.The system includes a master inverter with an LCL filter and a slave inverter with an L filter.Two inverters are connected in parallel at the output side,and then they are connected with the utility grid via an isolated line-frequency transformer.Meanwhile,two additional DC contactors are used to realize the function of harmonic compensation.To achieve the improved system proposed in this paper,firstly,system structure and working methods of the improved system are described.Secondly,a design method of the slave inverter is analyzed.Thirdly,a design method of the main inverter is analyzed.Fourthly,the simulation model is designed,and the system simulation is carried out.Finally,the experimental platform is built,the experiments are done.Simulation results and experimental results verify that the system design and its control strategies are feasible.