Based On Power Feed-forward Single Stage Three-phase Grid-connected Photovoltaic Inverter

Single-stage photovoltaic grid-connected system uses only an energy conversion tocomplete these two functions: Maximum power point tracking (MPPT) and grid conne-cted, so it has a large advantage of cost and efficiency. But at the same time it has alsobrought some disadvantages, such as control is relatively complicated, DC bus voltage istoo high, etc. As a result in-depth research of single-stage photovoltaic inverter ismeaningful and useful for the future energy problems.In this paper, the research is about the single-stage three-phase grid-connectedinverter. Firstly, this paper analyzes the principle and characteristics of photovoltaic cellsand establish of a mathematical model. According to the characteristics of photovoltaiccells, it comparatives analysis three commonly used methods of maximum power pointtracking-constant voltage tracking method, perturbati-on and observation method,incremental conductance method and comparative analysis advantage and disadvantage ofthese three methods. Based on these, a “Pendulum” MPPT method is proposed. Then“Pendulum” MPPT algorithm is compared to perturbation and observation method. Theadvantages of “Pendulum” MPPT algorithm are highlighted.Secondly, this paper analyzes the single-stage three-phase photovoltaic inverter,establishes its mathematical model and analysis its control strategies. The focuse oftraditional double loop control has a slow response in the DC bus voltage, MPPT is notconducive to fast search, the power feed-forward is applied to the outer loop control ofthis system，and is compared to traditional PI control with simulation. In addition, thegrid-connected of PI regulator is unreasonable, parameters trial and error and other issues,the PI regulator design conducted in-depth research, through detailed theoreticalderivation proposed a new PI regulator design method.After completing the analysisMPPT algorithm and inverter control strategy, the “Pendulum” MPPT algorithm combinedwith power feed-forward control strategy has carried on the simulation research ofsingle-stage three-phase photovoltaic inverter.Finally, this paper designs the entire system of hardware and software in detail. A 3kVA single-stage three-phase photovoltaic inverter has been designed, through the digitalcontrol, to complete the entire system of the experiment. And the experiment resultsdemonstrate, which can prove the feasibility and effectiveness of “Pendulum” MPPTalgorithm with power feed-forward control strategy.