Research On High Voltage Gain Z-source Topologies Based On Active Switched Capacitor Network

Excessive consumption of traditional energy has brought about energy shortages and global environmental pollution problems,making the vigorous development and use of renewable energy has become the consensus of all countries in the world.Solar energy is a kind of clean,pollution-free and renewable energy that can be developed and utilized on a large scale,and it has attracted much attention in the field of new energy power generation.Therefore,the research on solar photovoltaic power generation system is a subject of practical significance.In the application of photovoltaic grid-connected system,the output of solar panel is usually in the form of a low dc voltage with wide variation and the dc-dc converter with high voltage gain and inverter are required before connecting to the power grid.The Z-source inverter utilizes a unique LC impedance network(Z-source network)structure,which can realize a single-stage boost inverter,which is very suitable for photovoltaic power generation systems with a wide voltage range.In addition,the Z-source inverter allows the upper and lower switch tubes of the inverter bridge to conduct simultaneously,which improves the reliability of the system.By analyzing the development trend of Z-source converters and combining the characteristics of quasi-Z-source boost network and active switched capacitor boost network,this thesis proposes a new single-phase high-gain switching Z-source boost inverter.This article mainly completed the following work:(1)The topology research of Z-source converters.The current research status of the Zsource converter topology is introduced,and three main directions of the research on the topology structure of the Z-source converter at present are summarized.(2)In order to reveal the inherent boost mechanism of the Z-source converters,the topology of the quasi-Z-source inverter and the improved quasi-switching boost inverter based on the Z-source inverter are studied.According to the working principles of Z-source inverter and quasi Z-source inverter,the structure characteristics of these boost networks are summarized and their features provide construction directions for the novel Z-source network with high voltage gain.(3)Combining the quasi-Z-source boost network and the active switched capacitor boost network,a new single-phase high-gain switching Z-source boost inverter is obtained.The working principle and circuit characteristics of this topology are analyzed in detail,and compared with other typical topologies to highlight its advantages.While achieving high voltage gain,this topology expands the value range of the modulation factor of the inverter bridge arm,thereby improving the quality of the output power.(4)Four common PWM control strategies currently applied to Z-source inverters are introduced,and simple boost control is selected as the control strategy of the proposed topology.Based on this,simulation and experimental verification are carried out,and the results show the feasibility of the proposed topology and the correctness of the theoretical analysis.