Research On Control Strategy Of Three-Level DC/DC Converter In Photovoltaic Microgrid Power Generation System

In recent years,with the increasing demand for electricity in public life,in the form of Micro-grid has received more and more attention as a power supply model for correct use of renewable energy.The DC/DC converter in the photovoltaic Micro-grid generation system is the core device for achieving stable boosting and Maximum power point tracking(MPPT)technology.The two-level DC/DC converters have low withstand voltage and large switching losses,and cannot reach the high voltage and high power photovoltaic Micro-grid power generation system’s demand.Three-Level DC/DC converter can apply a switching device with a low withstand voltage to high-voltage and high-power situation,but the topology of the Three-Level DC/DC converter causes the fluctuation of the Midpoint voltage of the output voltage,which directly affects the quality and stability of the output voltage.Simultaneously,using the MPPT technology for Three-Level DC/DC converters has also became an important guarantee for efficient operation of photovoltaic Micro-grid power generation systems.According to Three-Level DC/DC converter topology used in this paper,Effective control strategies are presented for Midpoint voltage fluctuation and MPPT problem.In order to solve the Midpoint voltage fluctuation,through the comparison and analysis of several modulation strategy,a multi-carrier pulse-width modulation strategy is adopted,and a double closed-loop control method based on this modulation strategy is proposed to achieve suppression of Midpoint voltage fluctuation.It’s necessary for us to find the Applicable MPPT technology.After the analysis of the advantages and disadvantages of the three traditional MPPT techniques,an improved perturbation and observation method is put forword,which greatly increases the accuracy and stability of MPPT technology.Finally,MPPT technology is combined with the Midpoint voltage fluctuation control strategy to verify Effectiveness of the whole system.The parameters of the main circuit and control circuit components were calculated and designed according to photovoltaic array input power 12 kW and expected output voltage 1200 V.The model and simulation analysis were built by MATLAB software.Under the input of the photovoltaic array,It is proved that MPPT improves the tracking accuracy from 97.2% to 98.1%,and the Midpoint voltage control strategy restores the fluctuating voltage to stability within 0.2s.Expected goals is achieved.It shows that the research of this paper is reasonable,and has practical application value.