Research On A Single-phase Single-stage Boost Photovoltaic Inverter

Due to the decrease of primary energy reserve of petroleum or coal and the improvement of awareness to protecting our environment,technologies for the utilization of green energy like geothermal energy,wind energy,solar energy have brought worldwide attention.Meanwhile,solar energy has attracted more attention because it is environmentally friendly and abundant reserves.Nowadays,the grid-connected photovoltaic power generation technology is the dominating form of solar energy utilization.And the photovoltaic inverter is a very important intermediate equipment in solar power generation system.Therefore,based on the traditional inverter,a single-phase single-stage step-up inverter is studied.Because the output voltage of a single photovoltaic cell is low and the range of variation is wide,photovoltaic power generation system usually uses the way of connecting multiple photovoltaic cells in series and then connecting to the traditional full bridge inverter to generate grid connection or directly supply AC load.Traditional full bridge inverter is a step-down converter,and there will be leakage current problems in different degrees when adopting unipolar or bipolar modulation,so it will be limited in photovoltaic grid connected system.In view of the above problems,a single-phase single-stage boost photovoltaic inverter without leakage current is proposed.The topological structure realizes the ability of boosting and inverting by combining a boost unit with a traditional full bridge inverter organically.At the same time,the application of input-output common ground structure can inhibit the generation of leakage current and improve the reliability of system.In this paper,the working principle and steady-state performance of the proposed single-phase single-stage step up photovoltaic inverter are introduced in detail.Through the analysis and comparison of two PWM modulation methods,a unified half cycle modulation strategy is designed.In this modulation method only two power switches operate at very high frequency per switching cycle,which reduces the loss of system.In addition,the grid connected control methods and MPPT algorithm suitable for the proposed photovoltaic inverter in this paper are studied.The corresponding control system model of the grid connected PV inverter is established by using the MATLAB/Simulink simulation tool,which have proven the effectiveness of the studied grid connection control strategy and conductance incremental MPPT control algorithm.Finally,the experimental platform based on TMS320F2812 core controller is established,which verifies the correctness of the proposed inverter topology and theoretical analysis.