Research On Active-Clamp Flyback Type Photovoltaic Grid-Connected Inverter

With increasing energy crisis and environment pollution problems around the world, the developments and utilizations of renewable energy are gaining more and more visibility. Solar energy becomes one of the world's most promising green energy for its clean, environmental friendly, renewable and large reserves. Photovoltaic power generation is one of the main forms of solar energy utilization. As the interface between the PV array and the grid, Inverters determine the general performance of the PV system.This research mainly focuses on the PV grid inverter. First of all, several typical topologies of PV grid-connected inverter are analyzed and compared. Among this, flyback converter with unfolding DC-AC inverter can reach a high efficiency, which becomes the research emphasis.Flyback converters show the characteristics of current source when operating in DCM and BCM, so a current reference can be applied to make the flyback output current half wave sinusoid. Then the inverter switching at line frequency unfolds the rectified current to a sinusoidal one and injects it into the grid. In order to maximize the energy generated by PV array fed into the grid, the peak current control strategy, the MPPT control method and the main circuit topology will be deeply analyzed and optimized.A snubber is necessary to deal with the leakage energy for the two reasons below: a. the leakage energy dissipation accounted for a large proportion in the system; b. the voltage spikes due to the parasitic resonance between the leakage inductor and the parasitic capacitors increase the voltage stress of the primary main power switch. So a digitally controlled active clamp technique applying to the flyback converter with unfolding DC-AC inverter is proposed in this thesis, which can recycle the leakage energy, eliminate the parasitic ring and achieve the soft switching for the main switch. Power rating of the inverter can be increased by interleaved technology. Digitally controlled active clamp interleaved flyback converters are introduced to the PV grid-connected inverter in this thesis.On the basis of theoretical analysis, an 175W experimental prototype of PV grid-connected inverter based on FPGA was constructed. The experimental results demonstrate the performance of the active clamp flyback-type PV grid-connected inverter.