Research On Novel Grid-Connected Photovoltaic Flyback Inverter

As global economic is quickly increasing, a number of traditional fossil fuel is being consumed, so that the world is facing energy crisis. Many countries of the world are engaged in developing and using new energy. Solar energy is abundant, distributed widely, regenerative, and non-pollution. These advantages make scholars pay attention to solar energy. Photovoltaic inverter could transform energy between solar panel and power system. Its security, reliability, conversion efficiency and cost strongly influence the characteristics and investment of power system. So the inverter is the core of the photovoltaic system. This paper proposed a novel flyback inverter for photovoltaic applications, and analyzed it in very great detail. This paper also proposed a new method for maximum power point tracking. Based on the TMS320F2812 chip, a 500W prototype is designed at the end.Based on the research on the topology and control method of PV inverter during recent years, this paper proposed a novel flyback PV inverter topology, and analyzed its operating principle in great detail. The equivalent electric circuits of different working states are set up to be analyzed. The proposed circuit topology is derived from traditional Sepic converter and flyback inverter. Its structure is very simple and it could achieve both soft-switching and enhanced power decoupling, without the need for additional circuitry. Thus the switch loss is decreased and the efficiency is enhanced. Peak current mode control method is used in the control schemes to ensure pure sinusoidal current flow into AC grid.The output characteristic of solar panel is non-linear. As the external environment and internal parameter is changing, the output power is also changing. But under some specific conditions, the output power could achieve a maximum point. So the PV inverter needs to track the maximum power point of solar panel at any moment. This paper analyzed and compared several MPPT schemes, and proposed a new control method to track the maximum power point of solar panel. Simulation results based on Matlab/Simulink verify the novel is fit for the proposed PV inverter, and it could remarkably enhance the efficiency of the solar panel. Finally a 500W inverter prototype based on DSP digital control is designed, including the hardware design and program design. Experimental results show that all the performance index of the proposed PV inverter have reach the goals. The results also verify the validity of the circuit topology and control scheme of the proposed inverter, as well as feasibility of theoretical analysis, and establish the basic of its practicalization and commercialization.