Novel Modulation Technology Based Quasi-Z Source PV Inverter

This study based on a novel Hybrid modulation controlled single-phase Quasi-Z source cascade multilevel inverter. Cascade inverter system is composed of single-phase Quasi-Z source inverter module and combines the advantages of Quasi-Z source inverter and cascade H-Bridge. In photovoltaic power generation systems, the Quasi-Z source inverter realizes buck/boost with the structure of the single stage by using LC network instead of the traditional DC/DC conversion circuit. It is suitable for wide range of PV voltage changes, and be able to overcome the problem of conventional inverter direct damage. Cascade H-bridge structure can take advantage of low-voltage switching devices to achieve high-voltage output and it greatly reduced the harmonics of the output voltage with the lower switching frequency. As a basic component unit of the cascade inverter system, Quasi-Z source inverter module is very important.The new hybrid modulation controlled single-phase Quasi-Z source inverter has many advantages:1) reducing the Quasi-Z source capacitance and inductance parameters, reduce the switching frequency of system, thus to reduce the loss of the system and improve efficiency. Because, huge capacitance and inductance of Quasi-Z network is uaually used when SPWM is used to ensure the quality of output. In addition, there are at least two switch device have through vector in the zero vector, which will lead to switching frequency increases, But, hybrid modulation allows2ω ripple of dc bus voltage, and in the PAM stage, there are always two switches no switching action.2) Less CMV than SPWM.3) Better output votage than SPWM in cascade system. Therefore, the novel hybrid modulation technology do not only solved the problems when the traditional SPWM method is used mostly, but also have many advantages.This paper introduces the Quasi-Z source inverter and cascaded Quasi-Z source system of SPWM modulation. Traditional modulation for Quasi-Z source cascade inverter is introduced and a novel hybrid modulation is put forward in detail. The structure and control strategy of this system also has been analyzed and the simulation results improved its validity. At last, prototype of one Quasi-Z source inverter module is build. Experiment results verify the validity of the theoretical analysis.