Design Of Micro Power Photovoltaic Grid-connected Inverter Based On Bidirectional Flyback Converter

Photovoltaic grid-connected power generation and utilization of clean, renewable solar energy, is an important choice to solve the global energy crisis. Traditional centralized grid-connected PV system problems become more andmore evident, and micro-power inverters for distributed grid system has anti- partial shading capability, high reliability, scalability,easy configuration and other advantages.Photovoltaic cells have the characteristics of low output voltage and wide voltage range. The inverter should have the boost conversion function, and should have a high frequency transformer to achieve electrical isolation which is based on the needs of security and reliability. Single stage high frequency link inverter made up for the inadequacy of two-stage type, has obviously improve on the efficiency and the function.Flyback topology can simultaneously achieve boost and isolation function, and the structure is simple and easy to control. So it is a good choice for the topology of grid-connected inverter. Therefore, we use bidirectional flyback converter as micro-power PV grid-connected inverter topology.This paper introduces the operation principle of bi-directional flyback inverter and compares the differential control and unilateral control modes. It gets the conclusion that the bidirectional flyback inverter using unilateral control is more suitable for the micro-power grid-connected PV system. Then this paper accomplishes modeling,simulation of grid connected current loop and studies the control strategy of flyback converter under DCM and CCM two operating modes in order to achieve unity power factor. At the same time, it studies the distortion problem of grid current when the current is around zero. In addition, This paper studies the maximum power tracking(MPPT).Different from two stages grid-connected inverter system, The MPPT is designed as the outer loop, and the output of the MPPT loop is as the given reference of the grid-connected current inner loop in the single stage grid inverter system. This paper establishes a photovoltaic cell model in the MATLAB simulation environment, and writes the S function of the MPPT algorithm Based on the perturbation observation method to achieve the maximum power point tracking. Finally, the paper designs the parameters of hardware circuit and software processes.