Research On A Modified Cockcroft-Walton Quasi-Z-Source Inverte

As the development of the chemical industry has increased the pollution of the land,the problem of non-renewability of traditional energy has become increasingly prominent.The photovoltaic power generation industry has emerged in response to the changes of the times,and has gradually transformed into the main core of emerging clean energy,which has been favored by the international community and experts from various countries.With the continuous advancement of technology,how to use energy more effectively,reduce losses,and improve efficiency in the conversion process of electric energy has become a major problem for photovoltaic grid connection,which puts forward more stringent requirements for the development and progress of modern power electronic technology.As a single-stage structure,the(quasi)Z-source inverter(qZSI)can complete the two conversion processes of boost and inverter with a simple structure.In response to the limitations of traditional voltage-type inverters that affect the safety performance of the system after shoot-through state occurs,this new type of inverter not only enhances the reliability and safety of the system,but also participates in the normal operating state.It makes fuller use of energy,and also combines its own simple structure to improve the performance and efficiency of the system in the practical application of photovoltaic grid-connected.This thesis presents a new type of qZSI that can achieve high voltage gain and is composed of coupled inductors.It is obtained by embedding a new boost module into the qZSI by recombining the Cockcroft-Walton voltage doubler cell.The novel topology inherits all the advantages of the qZSI,such as continuous input current,common ground for input and output,simple and reliable structure,etc.At the same time,due to the existence of the coupled inductor,the circuit can achieve the purpose of adjusting the voltage gain from the two types of variables(ie,double degrees of freedom)of turn ratio and duty ratio,and achieve high boost ability under a small duty ratio,which has higher modulation index and high-quality output sine wave.This thesis first derives the evolution process of the new topology and analyzes the steady state.It studies its own boosting capability,the stress on the device and the power consumption of each part,and compares them with the qZSI and its related improvement single-stage boost inverter.In addition,in order for the system to operate stably and reliably,a small signal model analysis is established,and the system is compensated and corrected to realize closed-loop control.Finally,after using Saber simulation software to simulate according to the actual experimental parameters,an experimental prototype with an output power of up to 1k W was made in the laboratory and the experiment was performed after the normal function test.The experimental waveforms and data finally obtained are consistent with the theoretical research and simulation results in the previous article,effectively confirming the engineering practical significance and reliability of this new topology.