Photovoltaic Grid-Connection Based On Interleaved Flyback Topology Research On Micro-Inverter

Although the traditional energy sources,such as coal,oil and natural gas,are driving global economic development,they also lead to global environmental pollution and energy depletion.Solar power generation attracts lots of concern by the virtue of abundant resources and clean process.The micro-inverters,which play a role of boosting and inverting the voltage in solar power generation process,are analyzed in theory,and verified by simulation and experiments in this paper.Taking into account the wide range of photovoltaic cell output voltage range and the difficulty of system control design;a two-stage topology is selected: the first stage aims to achieve DC-DC boosting and the second stage aims to achieve DC-AC inverter.The topologies of the pre-class flyback circuits in the first stage and the full-bridge polarity inversion circuits are selected,after comparing of the existing DC-DC topology.In order to suppress the voltage spikes generated by the leakage inductance of the flyback transformer,an active clamp circuit with no energy loss is used.In order to increase the system power level and reduce the system input current ripple,an interleaved parallel connection is added to the topology.Then,based on the analysis of the working mode and working flow of the single-ended active-clamped flyback converter,the working mode of Continuous Current Mode(CCM)is selected.Based on the analysis of the equivalent physical model of the solar panel,the mathematical model is established which is simulated in Simulink.The maximum power point tracking(MPPT)based on the perturbation-and-observation(P&O)method is designed to ensure that the solar panels always work at the maximum power point,because the output characteristics of the solar panels change with temperature and light intensity.In order to ensure the stability of the system,and synchronize the frequency and phase of the output current to the grid,a double loop control strategy is designed.The inner loop controls the output current with PI compensation,and the outer loop controls the MPPT PV voltage.The feasibility of the double loop control strategy is verified by Simulink simulation.Finally,the voltage and current of the main circuits and control circuits are calculated and analyzed,which provides the theoretical basis for selecting the appropriate components.The software is also programmed.Based on these works,a single-phase PV grid-connected micro-inverter with 220 V and 200 W is designed and verified by the experimental.