Research On The Control Method For Single-phase Cascaded Pv Grid-connected Inverter

Due to the increasingly serious environmental pollution problems and the increasing demand for energy,the development and utilization of new energy sources is imminent.Because of its clean,environmentally friendly and inexhaustible advantages,solar energy stands out from many energy sources.Grid-connected inverters are the core equipment of photovoltaic power generation.Their structural composition and performance control can directly affect the quality of grid-connected power.Therefore,the control strategy of grid-connected inverters has become the focus of research.First of all,this article briefly introduces the current world energy demand and background of photovoltaic power generation,the development status of photovoltaic grid-connected inverters at home and abroad.As well as the control links in the control strategy of the cascade H-bridge inverter,a variety of grid-connected current control methods are listed and the advantages and disadvantages are summarized.Then,taking the cascaded H-bridge inverter as the research object,and its topology and working principle,MPPT control technology and modulation method are analyzed.This paper mainly studies the current control and power balance control technology of grid-connected inverters.Compared with the traditional double closed-loop control,the basic principle of current predictive control is analyzed,and an improved predictive control method for photovoltaic grid-connected inverter is proposed on a single H-bridge unit.It not only suppresses the DC voltage fluctuation,accelerates the current dynamic adjustment speed,reduces the harmonic distortion rate,and improves the output waveform quality.The stability of the control method is analyzed with MATLAB / Simulink,and a simulation model of a unit photovoltaic inverter is built.The results of the comparison of the output waveforms verify the effectiveness and superiority of the improved control method proposed in this paper.Then,based on the research results of the above-mentioned single H-bridge inverter,the proposed improved predictive control method is extended to a multi-level photovoltaic unit cascade structure.Take three-unit cascade as an example,each power unit independently completes MPPT control.However,affected by factors such as light intensity and temperature,the power imbalance between the photovoltaic units appears,resulting in DC voltage fluctuations and so on.Aiming at this problem,the power weighting improvement strategy is studied.Compared with traditional power balance control,the DC voltage ripple of this method is significantly reduced,the quality of the grid-connected waveform is significantly improved,and the system dynamic response speed is faster.A three-unit photovoltaic grid-connected inverter simulation model was built in MATLAB,and the quality of the output waveform was analyzed to verify the correctness of the method.Finally,a photovoltaic inverter experimental platform for a single photovoltaic unit and three photovoltaic units is built in this paper.The experimental results verify the feasibility and practicability of the proposed improved predictive control method and power balance control strategy.