Research And Design Of Low Power Photovoltaic Grid-connected Inverter System

Social progress depends heavily on a solid material foundation,a rich spiritual civilization and advanced science and technology.But it is inseparable from the consumption of energy.The limited fossil energy and sustainable development of soeiety have become a new form contradiction in today.The clean energy generation method represented by photovoltaic power generation is of great significance to the national energy structure adjustment.Low-power photovoltaic power generation system is widely used in rooftop photovoltaic distributed generation and in remote areas where public grids can not cover.Because of that,it has the advantages of convenient installation,strong flexibility,small influence by geographical environment,and high portability.In this paper,the topological structure and grid-connected control strategy of low-power photovoltaic grid-con[ected inverter system are studied in depth.Firstly,the topology and working principle of various low-power inverters are analyzed.The power imbalance between the DC side and the grid-connected side is studied based on the main circuit topology of the two-stage self-isolated staggered flyback inverter.According to the output voltage waveform of the staggered flyback circuit,with considering the factors such as system design cost,volume and efficiency,a software-compensated control staggered flyback inverter topology is proposed.The different working state of circuits are analyzed according to the sequence diagram,and the working principle and control process of the circuits are explained in detail.It is verified by simulation that the compensation control has the effect of suppressing the output voltage fluctuation of the interleaved flyback,and the smoother output voltage waveform.Secondly,based on the analysis and comparison of the advantages and disadvantages of the digital grid-connected control strategy commonly used in low-power inverters,the reactive power compensation for single-phase photovoltaic grid-connected inverter systems under non-ideal grid conditions is studied and a vector grid-connected control method based on Second Order Generalized Integral(SOGI)is designed.A virtual stationary coordinate system is established by using SOGI.The AC component in phase with the same frequency of the power grid is separated from the output power of the system as its reactive power compensation.Combined with the voltage and current double closed-loop grid-connected control strategy,the problem of grid-connected reactive power compensation under grid voltage interference is solved.The simulation results verify that the system can achieve single-phase grid-connected operation with good stability and robustness.Finally,the system design is based on the technical requirements of the low-power single-phase photovoltaic grid-connected inverter system.Acoording to the hardware,the design of the hardware circuit of the main circuit,drive circuit,microprocessor control circuit and auxiliary circuit of the interleaved flyback inverter is completed.In terms of software,the design of system control main program,interleaved flyback compensation control interrupt program and grid connection control interrupt program are completed.Simulation and experimental verification has been carried out on PSIM and power electronic test.The experimental results show that the output current waveform of grid-connected inverters is smooth.Its frequency and phase are same with the grid voltage.The total current distortion rate(THD)is less than 5%,which satisfies the grid-connected requirements of Chinese single-phase photovoltaic grid-connected system.