Research On Single-phase Photovoltaic Grid-connected Flyback Micro-Inverter

The Energy is material basis that promotes economic and social progress and improves people’s living level. As a branch of solar photovoltaic power generation, PV micro inverter power system is convenient and fast, very suitable for family, city and other small power electric field. This paper will deeply research on single phase photovoltaic grid flyback micro inverter.First of all, the structure of the topological network according to the division of the different forms of micro inverter are introduced, the final selection of the two type high-frequency isolation type micro inverter as the main circuit topology of grid connected PV system.On this basis, each module commonly used circuits of the main circuit were analyzed and compared, integrated system cost, volume and efficiency factors into consideration, this paper puts forward interleaved flyback micro inverter topology, which consists of a new switch inductance Boost boost circuit, high frequency converter, switch inductance Boost full bridge inverter circuit and LC filter circuit, this paper discusses the working principle and the waveform of the circuit.Secondly, by comparing several common grid inverter current digital control strategy analysis, design the control strategy of grid connected inverter current that based on fractional PI, and track control grid-connected inverter output current. Through the flexible adjustment of the integral order, this method can make the system have good dynamic performance, steady state performance, anti disturbance and robustness, and can realize the grid connected operationThen, the hardware circuit and software flow chart of single phase photovoltaic grid connected inverter system are designed.Basis on the overall system control block diagram and the technical indexes and select system involves power devices reasonably and the flyback transformer, LC filter, control circuit, voltage and current sampling circuit, drive circuit, auxiliary circuit, the main program and interrupt program flow charts were designed.Thirdly, it summarizes the several common active and passive islanding detection method, initial chopping factor, positive feedback coefficient and positive feedback quantity of the positive feedback active frequency drift method (AFDPF) detection algorithm is improved, a method that combine of active and passive to improve islanding detection method is proposed.This method can meet our standards,compared with the traditional AFDPF method, which can be more rapid and accurate.Finally, the system experiment platform is used to carry out the hardware and software debugging.From the experimental results, we can know that the drive signal of each module circuit, the circuit working waveform is consistent with the theoretical value;Grid current waveform smooth, and with the same frequency and phase grid voltage, total harmonic distortion is less than 5%, to meet our single-phase grid-connected PV power systems requirements.