Design Of Non-isolated And Two-stage Series Photovoltaic Grid-connected Inverter

As the core of the current small and medium-sized photovoltaic power station system,the series inverter can convert the direct current generated by solar cells into alternating current with the same frequency and phase as the power grid and integrate it into the power grid.Therefore,it is particularly important to improve the quality and efficiency of power output to ensure the stability of the public power grid.In this paper,the interleaved Boost converter was selected as the frontstage circuit,and it can reduce the amplitude of the input current ripple and is more reliable.Its topology,working mode and output current ripple were studied and simulated.The mathematical model of solar cell was established to explain the principle of maximum power point tracking.At the same time,the incremental method of variable step length conductance was designed to realize the tracking of maximum power point and the simulation was completed.The dynamic response speed is faster and the stability is better,and the contradiction between the dynamic velocity and the steady-state accuracy is resolved.The H6 inverter bridge was selected as the backstage circuit,and it can effectively inhibit the common mode leakage current.Its topology,working mode and common mode leakage current were studied and simulated.The principle of current control technology was explained.At the same time,the quasi-proportional resonance control was designed to realize the non-static tracking of the grid current and the simulation was completed.It can better adapt to the change of grid frequency,and the output power quality is good.Finally,the non-isolated and two-stage series photovoltaic grid-connected inverter with TMS320F28335 digital signal processor as control chip was designed.The main circuit and peripheral circuit of the system were designed,and the parameters and models of the main components of the hardware circuit were calculated and selected.The control algorithm anddigital PLL were realized by software.The experimental platform was set up and the grid connection experiment was carried out.The output current of the prototype inverter is verified to be in the same frequency and phase with the grid voltage by the upper computer data and oscilloscope waveforms.The total harmonic current meets the requirements of grid-connection,and the power and conversion efficiency are also ideal.