The Research On Photovoltaic Gird-connected Inverter Based On The New Z Source Topology

With the more pollution of the atmosphere and the continuous deterioration of thenatural environment, the natural environment is very harsh. The extreme weather and climateevents happened frequently, such as haze, dust and freezing rain. People have realized that itis very importance for us to develop the green GDP. Photovoltaic power generation usingsolar energy as the main technology increasingly has drawn worldwide attention, its maincomponent; the inverter is one of the investigative hotspots in photovoltaic systems in theworld. There are still many problems for the inverter used in photovoltaic systems to resolve,such as: How to improve the work efficiency of the inverter, how to reduce its volume andhow to reduce the cost of the system. The Z source inverter has some advantages in circuittopology. Because it increases shoot-through time, it can boost/buck the input voltage insingle stage structure. In this way, this topology improves the efficiency of the inverter. Thisthesis is for the new Z source inverter grid-connected photovoltaic systems. The main contentof the whole thesis are as following:(1) Carrying on theoretical analysis of the working principle of the photovoltaic cell, themathematical model of the photovoltaic cell is obtained by Engineering Mathematics. Themathematical expressions reflect the variation between the various parameters. Using thepatterns of mathematical expressions, the simulation model of the PV array is put up inMatlab/Simulink environment. The analysis is verified by simulation results.(2) To introduce maximum power point tracking principles, it gives a brief introductionof the basic theory of the MPPT algorithms and explain the advantages and disadvantages ofeach. Using the Perturbation And Observation and Incremental Conductance to set up modelsused the M functions, simulation experiments combined with the dynamic simulation modelof the PV array are performed in Simulink environment. The analysis is verified bysimulation results which analysis effectiveness and characteristics of the two algorithms.(3) Studying traditional Z source inverter and Quasi-Z source inverter circuit structure, itshows that the Z source circuit network element is characteristic of the Z source invertercircuit. Analysis of circuit structure and basic working principle, the new Z source invertertopology which is of three-type is proposed. The improved Quasi-Z source inverter and theQuasi-Z Source Inverter have the same boost capacity. It shows that the improved Quasi-ZSource inverter effectively reduce the capacitor voltage. Thus, in the case of using the samecapacitance and inductance, improved Quasi-Z source inverter topology can withstand highermodulation factor, to improve the output voltage of the quality and stability of the system.(4) The control method which is used in the Z source inverter is introduced. The controlmethod chooses simple boost control. Through the simulation results, this article designed improved Quasi-Z inverter topologies have advantages. It shows that they have a theoreticalvalue and practical significance.The innovation of thesis: based on the study of Z source inverter and Quasi-Z sourceinverter, three improved Quasi-Z inverters topology is proposed. While maintaining acapacity similar to the boost capacity, it reduces the stress levels of the capacitors andimproves the circuit response time.