Research On Improved High-gain Z-source Photovoltaic Grid-connected Inverter

With the growing depletion of traditional fossil energy and environmental pollution,the new type of renewable clean energy represented by solar energy has received more and more attention from people.As a connection link between new-type power supplies and large power grids,the research of grid-connected inverters has become one of the key technologies for the integration of new energy sources.The traditional two-stage(DC/DC+DC/AC)inverter is slightly insufficient in energy transfer efficiency ? wide-range voltage input adaptability and inverter reliability.While a new type of Z-source inverter with the characteristics of single-stage structure?better boosting characteristics and allowing the bridge arm to pass through,it can make up for the shortcomings of traditional inverters.Therefore,the improved high-gain Z-source inverter is studied in this paper and applied to the photovoltaic grid-connected system.This paper first introduces the traditional Z-source inverter.Through the analysis of its limitation,an improved high-gain Z-source inverter is proposed.The working principle of the new Z-source inverter is analyzed and its mathematical model is established by signal flow diagram method and state space average method,which laid a physical foundation for the study of control strategies.Secondly,on the basis of the physical model,the control objectives of the Z-source grid-connected inverter are clarified.Two kinds of inverter control methods,direct and indirect control,are studied.The methods of Z-source inverter direct implementation and grid-connected control are analyzed in this paper,a PQ grid-connected control strategy based on SVPWAM is proposed,which can reduce the switching frequency of the system while achieving the unity power factor grid connection.The simulation results are verified by MATLAB software.Then,the maximum power point tracking(MPPT)technology ofphotovoltaic power generation is studied.Through the modeling of photovoltaic cells,the output characteristics of photovoltaic cells are analyzed.Through the study of the working principle of MPPT and various MPPT methods,a kind of MPPT optimization algorithm based on compound control is proposed.It combines fuzzy perturbation and observation method and scanning voltage threshold method.It can well adapt to the conventional gradient environment and partial shadow conditions.The verification analysis is performed by MATLAB software.Finally,the simulation model for photovoltaic grid-connected system with an improved high-gain Z-source inverter is established by MATLAB software,which verifies the effectiveness and feasibility of the proposed new Z-source inverter structure,grid-connected control strategy and MPPT method for photovoltaic power generation.